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draft-ietf-ipp-implementers-guide-v11-01.txt
                                                             T. Hastings
                                                       Xerox Corporation
                                                               C. Manros
                                                       Xerox Corporation
                                                               C. Kugler
                                                 IBM Printing Systems Co
                                                                H. Holst
                                                 i-data Printing Systems
                                                               P. Zehler
                                                       Xerox Corporation
                                                            May 30, 2000


          Internet Printing Protocol/1.1: Implementer's Guide

    Copyright (C) The Internet Society (2000). All Rights Reserved.

Status of this Memo

This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of [RFC2026].  Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas, and
its working groups.  Note that other groups may also distribute working
documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time.  It is inappropriate to use Internet-Drafts as reference material
or to cite them other than as "work in progress".

The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt

The list of Internet-Draft Shadow Directories can be accessed as
http://www.ietf.org/shadow.html.



Abstract

This document is one of a set of documents, which together describe all
aspects of a new Internet Printing Protocol (IPP).  IPP is an
application level protocol that can be used for distributed printing
using Internet tools and technologies.  This document contains
information that supplements the IPP Model and Semantics [IPP-MOD] and
the IPP Transport and Encoding [IPP-PRO] documents.  It is intended to

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help implementers understand IPP/1.1, as well as IPP/1.0, and some of
the considerations that may assist them in the design of their client
and/or IPP object implementations.  For example, a typical order of
processing requests is given, including error checking.  Motivation for
some of the specification decisions is also included.












































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The full set of IPP documents includes:
  Design Goals for an Internet Printing Protocol [RFC2567]
  Rationale for the Structure and Model and Protocol for the Internet
     Printing Protocol [RFC2568]
  Internet Printing Protocol/1.1: Model and Semantics [IPP-MOD]
  Internet Printing Protocol/1.1: Encoding and Transport [IPP-PRO]
  Mapping between LPD and IPP Protocols [RFC2569]

The document, "Design Goals for an Internet Printing Protocol", takes a
broad look at distributed printing functionality, and it enumerates
real-life scenarios that help to clarify the features that need to be
included in a printing protocol for the Internet.  It identifies
requirements for three types of users: end users, operators, and
administrators.  The design goal document calls out a subset of end user
requirements that are satisfied in IPP/1.1.  Operator and administrator
requirements are out of scope for version 1.1.

The document, "Rationale for the Structure and Model and Protocol for
the Internet Printing Protocol", describes IPP from a high level view,
defines a roadmap for the various documents that form the suite of IPP
specifications, and gives background and rationale for the IETF working
group's major decisions.

The document, "Internet Printing Protocol/1.1: Model and Semantics",
describes a simplified model with abstract objects, their attributes,
and their operations.  The model introduces a Printer and a Job.  The
Job supports multiple documents per Job.  The model document also
addresses how security, internationalization, and directory issues are
addressed.

The document, "Internet Printing Protocol/1.1: Encoding and Transport",
is a formal mapping of the abstract operations and attributes defined in
the model document onto HTTP/1.1.  It also defines the encoding rules
for a new Internet media type called "application/ipp".

The document, "Mapping between LPD and IPP Protocols", gives some advice
to implementers of gateways between IPP and LPD (Line Printer Daemon)
implementations.












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                           TABLE OF CONTENTS

1  INTRODUCTION.......................................................8

 1.1 Conformance language.............................................8
 1.2 Other terminology................................................9
 1.3 Issues Raised from Interoperability Bake Offs....................9

2  IPP OBJECTS........................................................9

3  IPP OPERATIONS....................................................10

 3.1 Common Semantics................................................10
   3.1.1 Summary of Operation Attributes.............................10
   3.1.2 Suggested Operation Processing Steps for IPP Objects........16
     3.1.2.1 Suggested Operation Processing Steps for all Operations.17
      3.1.2.1.1   Validate version number............................17
      3.1.2.1.2   Validate operation identifier......................19
      3.1.2.1.3   Validate the request identifier....................19
      3.1.2.1.4   Validate attribute group and attribute presence and
      order       19
        3.1.2.1.4.1 Validate the presence and order of attribute
        groups      19
        3.1.2.1.4.2 Ignore unknown attribute groups in the expected
        position    20
        3.1.2.1.4.3 Validate the presence of a single occurrence of
        required Operation attributes................................20
      3.1.2.1.5   Validate the values of the REQUIRED Operation
      attributes  27
      3.1.2.1.6   Validate the values of the OPTIONAL Operation
      attributes  31
     3.1.2.2 Suggested Additional Processing Steps for Operations that
     Create/Validate Jobs and Add Documents..........................35
      3.1.2.2.1   Default "ipp-attribute-fidelity" if not supplied...35
      3.1.2.2.2   Check that the Printer object is accepting jobs....35
      3.1.2.2.3   Validate the values of the Job Template attributes.36
     3.1.2.3 Algorithm for job validation............................37
      3.1.2.3.1   Check for conflicting Job Template attributes values42
      3.1.2.3.2   Decide whether to REJECT the request...............43
      3.1.2.3.3   For the Validate-Job operation, RETURN one of the
      success status codes...........................................44
      3.1.2.3.4   Create the Job object with attributes to support...45
      3.1.2.3.5   Return one of the success status codes.............46
      3.1.2.3.6   Accept appended Document Content...................47
      3.1.2.3.7   Scheduling and Starting to Process the Job.........47
      3.1.2.3.8   Completing the Job.................................47
      3.1.2.3.9   Destroying the Job after completion................47
      3.1.2.3.10  Interaction with "ipp-attribute-fidelity"..........48
      3.1.2.3.11  Character set code conversion support..............48


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      3.1.2.3.12  What charset to return when an unsupported charset is
      requested (Issue 1.19)?........................................49
      3.1.2.3.13  Natural Language Override (NLO)....................50
   3.1.3 Status codes returned by operation..........................52
     3.1.3.1 Printer Operations......................................52
      3.1.3.1.1   Print-Job..........................................52
      3.1.3.1.2   Print-URI..........................................54
      3.1.3.1.3   Validate-Job.......................................54
      3.1.3.1.4   Create-Job.........................................55
      3.1.3.1.5   Get-Printer-Attributes.............................55
      3.1.3.1.6   Get-Jobs...........................................56
      3.1.3.1.7   Pause-Printer......................................57
      3.1.3.1.8   Resume-Printer.....................................57
        3.1.3.1.8.1 What about Printers unable to change state due to
        an error condition?..........................................58
        3.1.3.1.8.2 How is 'printer-state' handled on Resume-Printer?58
      3.1.3.1.9   Purge-Printer......................................59
     3.1.3.2 Job Operations..........................................59
      3.1.3.2.1   Send-Document......................................59
      3.1.3.2.2   Send-URI...........................................60
      3.1.3.2.3   Cancel-Job.........................................60
      3.1.3.2.4   Get-Job-Attributes.................................61
      3.1.3.2.5   Hold-Job...........................................62
      3.1.3.2.6   Release-Job........................................63
      3.1.3.2.7   Restart-Job........................................63
        3.1.3.2.7.1 Can documents be added to a restarted job?.......63
   3.1.4 Returning unsupported attributes in Get-Xxxx responses (Issue
   1.18) 63
   3.1.5 Sending empty attribute groups..............................64
 3.2 Printer Operations..............................................64
   3.2.1 Print-Job operation.........................................64
     3.2.1.1 Flow controlling the data portion of a Print-Job request
     (Issue 1.22)....................................................64
     3.2.1.2 Returning job-state in Print-Job response (Issue 1.30)..65
   3.2.2 Get-Printer-Attributes operation............................66
   3.2.3 Get-Jobs operation..........................................66
     3.2.3.1 Get-Jobs, my-jobs='true', and 'requesting-user-name'
     (Issue 1.39)?...................................................66
     3.2.3.2 Why is there a "limit" attribute in the Get-Jobs
     operation?......................................................66
   3.2.4 Create-Job operation........................................67
 3.3 Job Operations..................................................67
   3.3.1 Validate-Job................................................67
   3.3.2 Restart-Job.................................................67

4  OBJECT ATTRIBUTES.................................................68

 4.1 Attribute Syntax's..............................................68
   4.1.1 The 'none' value for empty sets (Issue 1.37)................68

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   4.1.2 Multi-valued attributes (Issue 1.31)........................68
   4.1.3 Case Sensitivity in URIs (issue 1.6)........................69
   4.1.4 Maximum length for xxxWithLanguage and xxxWithoutLanguage...69
 4.2 Job Template Attributes.........................................70
   4.2.1 multiple-document-handling(type2 keyword)...................70
     4.2.1.1 Support of multiple document jobs.......................70
 4.3 Job Description Attributes......................................70
 4.4 Printer Description Attributes..................................71
   4.4.1 queued-job-count............................................71
     4.4.1.1 Why is "queued-job-count" RECOMMENDED (Issue 1.14)?.....71
     4.4.1.2 Is "queued-job-count" a good measure of how busy a printer
     is (Issue 1.15)?................................................71
   4.4.2 printer-current-time (dateTime).............................71
   4.4.3 'Printer-uri................................................72
 4.5 Empty Jobs......................................................72

5  DIRECTORY CONSIDERATIONS..........................................73

 5.1 General Directory Schema Considerations.........................73
 5.2 IPP Printer with a DNS name.....................................73

6  SECURITY CONSIDERATIONS...........................................73

 6.1 Querying jobs with IPP that were submitted using other job
 submission protocols (Issue 1.32)...................................73

7  ENCODING AND TRANSPORT............................................74

 7.1 General Headers.................................................76
 7.2 Request  Headers................................................77
 7.3 Response Headers................................................78
 7.4 Entity  Headers.................................................79
 7.5 Optional support for HTTP/1.0...................................80
 7.6 HTTP/1.1 Chunking...............................................80
   7.6.1 Disabling IPP Server Response Chunking......................80
   7.6.2 Warning About the Support of Chunked Requests...............80

8  REFERENCES........................................................81

9  AUTHORS' ADDRESS..................................................82

10  NOTICES..........................................................83


                                 TABLES


Table 1 - Summary of Printer operation attributes that sender MUST
   supply............................................................10

Table 2 - Summary of Printer operation attributes that sender MAY supply
    .................................................................11


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Table 3 - Summary of Job operation attributes that sender MUST supply13

Table 4 - Summary of Job operation attributes that sender MAY supply.14

Table 5 - Printer operation response attributes......................15

Table 6 - Examples of validating IPP version.........................18

Table 7 - Rules for validating single values X against Z.............37








































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1  Introduction

The IPP Implementer's Guide (IIG) (this document) contains information
that supplements the IPP Model and Semantics [IPP-MOD] and the IPP
Transport and Encoding [IPP-PRO] documents.  As such this information is
not part of the formal specifications.  Instead information is presented
to help implementers understand the specification, including some of the
motivation for decisions taken by the committee in developing the
specification.  Some of the implementation considerations are intended
to help implementers design their client and/or IPP object
implementations.  If there are any contradictions between this document
and [IPP-MOD] or [IPP-PRO], those documents take precedence over this
document.

Platform-specific implementation considerations will be included in this
guide as they become known.

In order to help the reader of the IIG and the IPP Model and Semantics
document, the sections in this document parallel the corresponding
sections in the Model document and are numbered the same for ease of
cross reference.  The sections that correspond to the IPP Transport and
Encoding are correspondingly offset.


1.1 Conformance language


Usually, this document does not contain the terminology MUST, MUST NOT,
MAY, NEED NOT, SHOULD, SHOULD NOT, REQUIRED, and OPTIONAL.  However,
when those terms do appear in this document, their intent is to repeat
what the [IPP-MOD] and [IPP-PRO] documents require and allow, rather
than specifying additional conformance requirements.  These terms are
defined in section 13 on conformance terminology in [IPP-MOD], most of
which is taken from RFC 2119 [RFC2119].

Implementers should read section 13 (APPENDIX A) in [IPP-MOD] in order
to understand these capitalized words.  The words MUST, MUST NOT, and
REQUIRED indicate what implementations are required to support in a
client or IPP object in order to be conformant to [IPP-MOD] and [IPP-
PRO].  MAY, NEED NOT, and OPTIONAL indicate was is merely allowed as an
implementer option.  The verbs SHOULD and SHOULD NOT indicate suggested
behavior, but which is not required or disallowed, respectively, in
order to conform to the specification.




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1.2 Other terminology


The term "sender" refers to the client that sends a request or an IPP
object that returns a response.  The term "receiver" refers to the IPP
object that receives a request and to a client that receives a response.


1.3 Issues Raised from Interoperability Bake Offs


The IPP WG has conducted two open interoperability "Bake Offs".  The
first bake off was held in September 1998 and Bake Off2 was held in
March 1999.  See the summary reports in:

ftp://ftp.pwg.org/pub/pwg/ipp/new_TES/

The issues raised from the first bake off are numbered 1.n in this
document and are described in:

ftp://ftp.pwg.org/pub/pwg/ipp/approved-clarifications/ipp-agreed-fixes-
981030.pdf

These issue resolutions have been incorporated into the November 16,
"IPP/1.0 Model and Semantics" [ipp-mod] and the "IPP/1.0 Encoding and
Transport" [IPP-PRO] documents.  However, some of the discussion is left
here in the Implementer's Guide to help understanding.

The issues raised from Bake Off2 are numbered 2.n in this document and
are described in:

ftp://ftp.pwg.org/pub/pwg/ipp/issues/issues-raised-at-bake-off2.pdf


2  IPP Objects

The term "client" in IPP is intended to mean any client that issues IPP
operation requests and accepts IPP operation responses, whether it be a
desktop or a server.  In other words, the term "client" does not just
mean end-user clients, such as those associated with desktops.

The term "IPP Printer" in IPP is intended to mean an object that accepts
IPP operation requests and returns IPP operation responses, whether
implemented in a server or a device.  An IPP Printer object MAY, if
implemented in a server, turn around and forward received jobs (and
other requests) to other devices and print servers/services, either
using IPP or some other protocol.





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3  IPP Operations

This section  corresponds to Section 3 "IPP Operations" in the IPP/1.1
Model and Semantics document [IPP-MOD].


3.1 Common Semantics


This section discusses semantics common to all operations.


3.1.1 Summary of Operation Attributes

Legend for the following table:

R indicates a REQUIRED operation that MUST be supported by the IPP
object (Printer or Job).  For attributes, R indicates that the attribute
MUST be supported by the IPP object supports the associated operation.

O indicates an OPTIONAL operation or attribute that MAY be supported by
the IPP object (Printer or Job).

+ indicates that this is not an IPP/1.0 feature, but is only a part of
IPP/1.1 and future versions of IPP.

   Table 1 - Summary of Printer operation attributes that sender MUST
                                 supply

                     Printer Operations
                     Requests                                 Respo
                                                              nses
 Operation           Print-   Pri  Crea Get-     Get Pause-   All
 Attributes          Job,     nt-  te-  Printer- -   Printer  Opera
                     Validate URI  Job  Attribut Job ,        tions
                     -Job (R) (O)  (O)  es (R)   s   Resume-
                                                 (R) Printer
                                                     ,
                                                     Purge-
                                                     Printer
                                                     (O+)
 Operation parameters--REQUIRED to be supplied by the sender:
 operation-id           R      R    R      R      R      R
 status-code                                                    R
 request-id             R      R    R      R      R      R      R
 version-number         R      R    R      R      R      R      R
 Operation attributes--REQUIRED to be supplied by the sender:
 attributes-charset     R      R    R      R      R      R      R
 attributes-            R      R    R      R      R      R      R
 natural-language


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                     Printer Operations
                     Requests                                 Respo
                                                              nses
 Operation           Print-   Pri  Crea Get-     Get Pause-   All
 Attributes          Job,     nt-  te-  Printer- -   Printer  Opera
                     Validate URI  Job  Attribut Job ,        tions
                     -Job (R) (O)  (O)  es (R)   s   Resume-
                                                 (R) Printer
                                                     ,
                                                     Purge-
                                                     Printer
                                                     (O+)
 document-uri                  R
 job-id*
 job-uri*
 last-document
 printer-uri            R      R    R      R      R      R
 Operation attributes--RECOMMENDED to be supplied by the sender:
 job-name               R      R    R
 requesting-user-       R      R    R      R      R      R
 name



Table 2 - Summary of Printer operation attributes that sender MAY supply

                      Printer Operations
                      Requests                                Respo
                                                              nses
Operation Attributes  Print- Prin  Crea  Get-    Get  Pause-  All
                      Job,   t-    te-   Printer -    Printer Opera
                      Valida URI   Job   -       Job  ,       tions
                      te-Job (O)   (O)   Attribu s    Resume-
                      (R)                tes (R) (R)  Printer
                                                      ,
                                                      Purge-
                                                      Printer
                                                      (O+)
Operation attributes--OPTIONAL to be supplied by the sender:
status-message                                                  O
detailed-status-                                                O
message
document-access-                                                O**
error
compression             O     O
document-format         R     R            R
document-name           O     O
document-natural-       O     O
language

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                      Printer Operations
                      Requests                                Respo
                                                              nses
Operation Attributes  Print- Prin  Crea  Get-    Get  Pause-  All
                      Job,   t-    te-   Printer -    Printer Opera
                      Valida URI   Job   -       Job  ,       tions
                      te-Job (O)   (O)   Attribu s    Resume-
                      (R)                tes (R) (R)  Printer
                                                      ,
                                                      Purge-
                                                      Printer
                                                      (O+)
ipp-attribute-          R     R     R
fidelity
job-impressions         O     O     O
job-k-octets            O     O     O
job-media-sheets        O     O     O
limit                                             R
message
my-jobs                                           R
requested-attributes                        R     R
which-jobs                                        R

*  "job-id" is REQUIRED only if used together with "printer-uri" to
identify the target job; otherwise, "job-uri" is REQUIRED.
**  "document-access-error" applies to the Print-URI response only.
























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 Table 3 - Summary of Job operation attributes that sender MUST supply

                         Job Operations
                         Requests                            Respons
                                                             es
Operation Attributes     Send-  Send  Cance Get-    Hold-    All
                         Docume -URI  l-Job Job-    Job,     Operati
                         nt     (O)   (R)   Attrib  Release  ons
                         (O)                utes    -Job,
                                            (R)     Restart
                                                    -Job
                                                    (O+)
Operation parameters--REQUIRED to be supplied by the sender:
operation-id               R     R     R      R       R
status-code                                                    R
request-id                 R     R     R      R       R        R
version-number             R     R     R      R       R        R
Operation attributes--REQUIRED to be supplied by the sender:
attributes-charset         R     R     R      R       R        R
attributes-natural-        R     R     R      R       R        R
language
document-uri                     R
job-id*                    R     R     R      R       R
job-uri*                   R     R     R      R       R
last-document              R     R
printer-uri                R     R     R      R       R
Operation attributes--RECOMMENDED to be supplied by the sender:
job-name
requesting-user-name       R     R     R      R       R



















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  Table 4 - Summary of Job operation attributes that sender MAY supply

                       Job Operations
                       Requests                                   Respo
                                                                  nses
Operation Attributes   Send-   Sen  Cance Get-   Hold-  Relea     All
                       Documen d-   l-Job Job-   Job,   se-       Opera
                       t       URI  (R)   Attrib Restar Job       tions
                       (O)     (O)        utes   t-Job  (O+)
                                           (R)    (O+)
Operation attributes--OPTIONAL to be supplied by the sender:
status-message                                                     O
detailed-status-                                                   O
message
document-access-error                                             O**
compression              O     O
document-format          R     R
document-name            O     O
document-natural-        O     O
language
ipp-attribute-
fidelity
job-impressions
job-k-octets
job-media-sheets
limit
message                               O             O      O
job-hold-until                                      R
my-jobs
requested-attributes                         R
which-jobs
*  "job-id" is REQUIRED only if used together with "printer-uri" to
identify the target job; otherwise, "job-uri" is REQUIRED.
**  "document-access-error" applies to the Send-URI operation only.














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            Table 5 - Printer operation response attributes

                  Printer Operations
                  Response
 Operation        Print-    Validat Prin  Create Get-   Get- Pause-
 Attributes       Job       e-Job   t-    -Job   Printe Jobs Printer
                  (R),Send  (R)     URI   (O)    r-     (R)  ,
                  -                 (O),         Attrib      Resume-
                  Document          Send         utes        Printer
                  (O)               -URI         (R)         ,
                                     (O)                     Purge-
                                                             Printer
                                                             (O+)
 job-uri          R                 R     R
 job-id           R                 R     R
 job-state        R                 R     R
 job-state-       R+                R+    R+
 reasons
 number-of-       O                 O     O
 intervening-
 jobs
 document-                          O
 access-error+

























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3.1.2 Suggested Operation Processing Steps for IPP Objects

This section suggests the steps and error checks that an IPP object MAY
perform when processing requests and returning responses.  An IPP object
MAY perform some or all of the error checks.  However, some
implementations MAY choose to be more forgiving than the error checks
shown here, in order to be able to accept requests from non-conforming
clients.  Not performing all of these error checks is a so-called
"forgiving" implementation.  On the other hand, clients that
successfully submit requests to IPP objects that do perform all the
error checks will be more likely to be able to interoperate with other
IPP object implementations.  Thus an implementer of an IPP object needs
to decide whether to be a "forgiving" or a "strict" implementation.
Therefore, the error status codes returned may differ between
implementations.   Consequentially, client SHOULD NOT expect exactly the
error code processing described in this section.

When an IPP object receives a request, the IPP object either accepts or
rejects the request. In order to determine whether or not to accept or
reject the request, the IPP object SHOULD execute the following steps.
The order of the steps may be rearranged and/or combined, including
making one or multiple passes over the request.

A client MUST supply requests that would pass all of the error checks
indicated here in order to be a conforming client.  Therefore, a client
SHOULD supply requests that are conforming, in order to avoid being
rejected by some IPP object implementations and/or risking different
semantics by different implementations of forgiving implementations.
For example, a forgiving implementation that accepts multiple
occurrences of the same attribute, rather than rejecting the request
might use the first occurrences, while another might use the last
occurrence.  Thus such a non-conforming client would get different
results from the two forgiving implementations.

In the following, processing continues step by step until a "RETURNS the
xxx status code ..." statement is encountered.  Error returns are
indicated by the verb: "REJECTS".  Since clients have difficulty getting
the status code before sending all of the document data in a Print-Job
request, clients SHOULD use the Validate-Job operation before sending
large documents to be printed, in order to validate whether the IPP
Printer will accept the job or not.

It is assumed that security authentication and authorization has already
taken place at a lower layer.



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3.1.2.1   Suggested Operation Processing Steps for all Operations

This section is intended to apply to all operations.  The next section
contains the additional steps for the Print-Job, Validate-Job, Print-
URI, Create-Job, Send-Document, and Send-URI operations that create
jobs, adds documents, and validates jobs.

IIG Sect #         Flow                 IPP error status codes
----------         ----                 ----------------------
                     |
                     v          err
3.1.2.1.1   <Validate version>  --> server-error-version-not-supported
                   ok|
                     v          err
3.1.2.1.2  <Validate operation> --> server-error-operation-not-supported
                   ok|
                     v          err
3.1.2.1.4.1- <Validate presence> --> client-error-bad-request
3.1.2.1.4.2    <of attributes>
                   ok|
                     v          err
3.1.2.1.4.3 <Validate presence> --> client-error-bad-request
            <of operation attr>
                   ok|
                     v          err
3.1.2.1.5  <Valied values of>   --> client-error-bad-request
            <operation attrs>       client-error-request-value-too-long
          <(length, tag, range,>
              <multi-value)>
                   ok|
                     v          err
3.1.2.1.5    <Validate values>  --> client-error-bad-request
          <with supported values>   client-error-charset-not-supported
                   ok|              client-error-attributes-or-values-
                     |                           not-supported
                     v          err
3.1.2.1.6 <Validate optionally> --> client-error-bad-request
             <operation attr>       client-error-natural-language-not-
                   ok|                           supported
                     |              client-error-request-value-too-long
                     |              client-error-attributes-or-values-
                     v                           not-supported


3.1.2.1.1 Validate version number

Every request and every response contains the "version-number"
attribute.  The value of this attribute is the major and minor version


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number of the syntax and semantics that the client and IPP object is
using, respectively.  The "version-number" attribute remains in a fixed
position across all future versions so that all clients and IPP object
that support future versions can determine which version is being used.
The IPP object checks to see if the major version number supplied in the
request is supported.  If not, the Printer object REJECTS the request
and RETURNS the 'server-error-version-not-supported' status code in the
response.  The IPP object returns in the "version-number" response
attribute the major and minor version for the error response.  Thus the
client can learn at least one major and minor version that the IPP
object supports.  The IPP object is encouraged to return the closest
version number to the one supplied by the client.

The checking of the minor version number is implementation dependent,
however if the client supplied minor version is explicitly supported,
the IPP object MUST respond using that identical minor version number.
If the major version number matches, but the minor version number does
not, the Printer SHOULD  accept and attempt to process the request, or
MAY reject the request and return the 'server-error-version-not-
supported' status code.  In all cases, the Printer MUST return the
nearest version number that it supports.   For example, suppose that an
IPP/1.2 Printer supports versions '1.1' and '1.2'.  The following
responses are conforming:


Table 6 - Examples of validating IPP version

        Client          Printer Accept Request? Printer returns
        supplies

        1.0             yes (SHOULD)            1.1

                        no (SHOULD NOT)         1.1

        1.1             yes (MUST)              1.1

        1.2             yes (MUST)              1.2

        1.3             yes (SHOULD)            1.2

                        no (SHOULD NOT)         1.2



It is advantageous for Printers to support both IPP/1.1 and IPP/1.0, so
that they can interoperate with either client implementations.  Some
implementations may allow an Administrator to explicitly disable support
for one or the other by setting the "ipp-versions-supported" Printer
description attribute.

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Likewise, it is advantageous for clients to support both versions to
allow interoperability with new and legacy Printers.


3.1.2.1.2 Validate operation identifier

The Printer object checks to see if the "operation-id" attribute
supplied by the client is supported as indicated in the Printer object's
"operations-supported" attribute.  If not, the Printer REJECTS the
request and returns the 'server-error-operation-not-supported' status
code in the response.


3.1.2.1.3 Validate the request identifier

The Printer object SHOULD NOT check to see if the "request-id" attribute
supplied by the client is in range: between 1 and 2**31 - 1 (inclusive),
but copies all 32 bits.

Note: The "version-number",  "operation-id", and the "request-id"
parameters are in fixed octet positions in the IPP/1.1 encoding.  The
"version-number" parameter will be the same fixed octet position in all
versions of the protocol.  These fields are validated before proceeding
with the rest of the validation.


3.1.2.1.4 Validate attribute group and attribute presence and order

The order of the following validation steps depends on implementation.


3.1.2.1.4.1 Validate the presence and order of attribute groups

Client requests and IPP object responses contain attribute groups that
Section 3 requires to be present and in a specified order.  An IPP
object verifies that the attribute groups are present and in the correct
order in requests supplied by clients (attribute groups without an * in
the following tables).

If an IPP object receives a request with (1) required attribute groups
missing, or (2) the attributes groups are out of order, or (3) the
groups are repeated, the IPP object REJECTS the request and RETURNS the
'client-error-bad-request' status code.  For example, it is an error for
the Job Template Attributes group to occur before the Operation
Attributes group, for the Operation Attributes group to be omitted, or
for an attribute group to occur more than once, except in the Get-Jobs
response.



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Since this kind of attribute group error is most likely to be an error
detected by a client developer rather than by a customer, the IPP object
NEED NOT return an indication of which attribute group was in error in
either the Unsupported Attributes group or the Status Message.  Also,
the IPP object NEED NOT find all attribute group errors before returning
this error.


3.1.2.1.4.2 Ignore unknown attribute groups in the expected position

Future attribute groups may be added to the specification at the end of
requests just before the Document Content and at the end of response,
except for the Get-Jobs response, where it maybe there or before the
first job attributes returned.  If an IPP object receives an unknown
attribute group in these positions, it ignores the entire group, rather
than returning an error, since that group may be a new group in a later
minor version of the protocol that can be ignored.  (If the new
attribute group cannot be ignored without confusing the client, the
major version number would have been increased in the protocol document
and in the request).  If the unknown group occurs in a different
position, the IPP object REJECTS the request and RETURNS the 'client-
error-bad-request' status code.

Clients also ignore unknown attribute groups returned in a response.

Note:  By validating that requests are in the proper form, IPP objects
force clients to use the proper form which, in turn, increases the
chances that customers will be able to use such clients from multiple
vendors with IPP objects from other vendors.


3.1.2.1.4.3 Validate the presence of a single occurrence of required
        Operation attributes

Client requests and IPP object responses contain Operation attributes
that [IPP-MOD] Section 3 requires to be present.  Attributes within a
group may be in any order, except for the ordering of target, charset,
and natural languages attributes.  These attributes MUST be first, and
MUST be supplied in the following order: charset, natural language, and
then target. An IPP object verifies that the attributes that Section 4
requires to be supplied by the client have been supplied in the request
(attributes without an * in the following tables).  An asterisk (*)
indicates groups and Operation attributes that the client may omit in a
request or an IPP object may omit in a response.

If an IPP object receives a request with required attributes missing or
repeated from a group or in the wrong position, the behavior of the IPP
object is IMPLEMENTATION DEPENDENT.  Some of the possible
implementations are:


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  1. REJECTS the request and RETURNS the 'client-error-bad-request'
  status code

  2. accepts the request and uses the first occurrence of the attribute
  no matter where it is

  3. accepts the request and uses the last occurrence of the attribute
  no matter where it is

  4. accept the request and assume some default value for the missing
  attribute

Therefore, client MUST send conforming requests, if they want to receive
the same behavior from all IPP object implementations.  For example, it
is an error for the "attributes-charset" or "attributes-natural-
language" attribute to be omitted in any operation request, or for an
Operation attribute to be supplied in a Job Template group or a Job
Template attribute to be supplied in an Operation Attribute group in a
create request.  It is also an error to supply the "attributes-charset"
attribute twice.

Since these kinds of attribute errors are most likely to be detected by
a client developer rather than by a customer, the IPP object NEED NOT
return an indication of which attribute was in error in either the
Unsupported Attributes group or the Status Message.  Also, the IPP
object NEED NOT find all attribute errors before returning this error.

The following tables list all the attributes for all the operations by
attribute group in each request and each response.  The order of the
groups is the order that the client supplies the groups as specified in
[IPP-MOD] Section 3.  The order of the attributes within a group is
arbitrary, except as noted for some of the special operation attributes
(charset, natural language, and target).  The tables below use the
following notation:

  R indicates a REQUIRED attribute or operation that an IPP object MUST
               support
  O indicates an OPTIONAL attribute or operation that an IPP object
               NEED NOT support
  * indicates that a client MAY omit the attribute in a request and
               that an IPP object MAY omit the attribute in a response.
               The absence of an * means that a client MUST supply the
               attribute in a request and an IPP object MUST supply the
               attribute in a response.
  + indicates that this is not a IPP/1.0 operation, but is only a part
               of IPP/1.1 and future versions of IPP.

                           Operation Requests

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The tables below show the attributes in their proper attribute groups
for operation requests:


Note: All operation requests contain "version-number", "operation-id",
and "request-id" parameters.



Print-Job Request (R):
     Group 1: Operation Attributes (R)
          attributes-charset (R)
          attributes-natural-language (R)
          printer-uri (R)
          requesting-user-name (R*)
          job-name (R*)
          ipp-attribute-fidelity (R*)
          document-name (R*)
          document-format (R*)
          document-natural-language (O*)
          compression (O*)
          job-k-octets (O*)
          job-impressions (O*)
          job-media-sheets (O*)
     Group 2: Job Template Attributes (R*)
          <Job Template attributes> (O*)
               (see [IPP-MOD] Section 4.2)
     Group 3: Document Content (R)
          <document content>

Validate-Job Request (R):
     Group 1: Operation Attributes (R)
          attributes-charset (R)
          attributes-natural-language (R)
          printer-uri (R)
          requesting-user-name (R*)
          job-name (R*)
          ipp-attribute-fidelity (R*)
          document-name (R*)
          document-format (R*)
          document-natural-language (O*)
          compression (O*)
          job-k-octets (O*)
          job-impressions (O*)
          job-media-sheets (O*)
     Group 2: Job Template Attributes (R*)
          <Job Template attributes> (O*)
               (see [IPP-MOD] Section 4.2)


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Print-URI Request (O):
     Group 1: Operation Attributes (R)
          attributes-charset (R)
          attributes-natural-language (R)
          printer-uri (R)
          document-uri (R)
          requesting-user-name (R*)
          job-name (R*)
          ipp-attribute-fidelity (R*)
          document-name (R*)
          document-format (R*)
          document-natural-language (O*)
          compression (O*)
          job-k-octets (O*)
          job-impressions (O*)
          job-media-sheets (O*)
     Group 2: Job Template Attributes (R*)
          <Job Template attributes> (O*) (see
               (see [IPP-MOD] Section 4.2)

Create-Job Request (O):
     Group 1: Operation Attributes (R)
          attributes-charset (R)
          attributes-natural-language (R)
          printer-uri (R)
          requesting-user-name (R*)
          job-name (R*)
          ipp-attribute-fidelity (R*)
          job-k-octets (O*)
          job-impressions (O*)
          job-media-sheets (O*)
     Group 2: Job Template Attributes (R*)
          <Job Template attributes> (O*) (see
               (see [IPP-MOD] Section 4.2)

Get-Printer-Attributes Request (R):
     Group 1: Operation Attributes (R)
          attributes-charset (R)
          attributes-natural-language (R)
          printer-uri (R)
          requesting-user-name (R*)
          requested-attributes (R*)
          document-format (R*)

Get-Jobs Request (R):
     Group 1: Operation Attributes (R)
          attributes-charset (R)
          attributes-natural-language (R)

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          printer-uri (R)
          requesting-user-name (R*)
          limit (R*)
          requested-attributes (R*)
          which-jobs (R*)
          my-jobs (R*)

Send-Document Request (O):
     Group 1: Operation Attributes (R)
          attributes-charset (R)
          attributes-natural-language (R)
          (printer-uri & job-id) | job-uri (R)
          last-document (R)
          requesting-user-name (R*)
          document-name (R*)
          document-format (R*)
          document-natural-language (O*)
          compression (O*)
     Group 2: Document Content (R*)
          <document content>

Send-URI Request (O):
     Group 1: Operation Attributes (R)
          attributes-charset (R)
          attributes-natural-language (R)
          (printer-uri & job-id) | job-uri (R)
          last-document (R)
          document-uri (R)
          requesting-user-name (R*)
          document-name (R*)
          document-format (R*)
          document-natural-language (O*)
          compression (O*)

Cancel-Job Request (R):
Release-Job Request (O+):
     Group 1: Operation Attributes (R)
          attributes-charset (R)
          attributes-natural-language (R)
          (printer-uri & job-id) | job-uri (R)
          requesting-user-name (R*)
          message (O*)

Get-Job-Attributes Request (R):
     Group 1: Operation Attributes (R)
          attributes-charset (R)
          attributes-natural-language (R)
          (printer-uri & job-id) | job-uri (R)

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          requesting-user-name (R*)
          requested-attributes (R*)

Pause-Printer Request (O+):
Resume-Printer Request (O+):
Purge-Printer Request (O+):
     Group 1: Operation Attributes (R)
          attributes-charset (R)
          attributes-natural-language (R)
          printer-uri (R)
          requesting-user-name (R*)

Hold-Job Request (O+):
Restart-Job Request (O+):
     Group 1: Operation Attributes (R)
          attributes-charset (R)
          attributes-natural-language (R)
          (printer-uri & job-id) | job-uri (R)
          requesting-user-name (R*)
          job-hold-until (R*)
          message (O*)


                          Operation Responses

The tables below show the response attributes in their proper attribute
groups for responses.

Note: All operation responses contain "version-number", "status-code",
and "request-id" parameters.


Print-Job Response (R):
Create-Job Response (O):
Send-Document Response (O):
     Group 1: Operation Attributes (R)
          attributes-charset (R)
          attributes-natural-language (R)
          status-message (O*)
          detailed-status-message (O*)
     Group 2: Unsupported Attributes (R*) (see Note 3)
          <unsupported attributes> (R*)
     Group 3: Job Object Attributes(R*) (see Note 2)
          job-uri (R)
          job-id (R)
          job-state (R)
          job-state-reasons (O* | R+)
          job-state-message (O*)
          number-of-intervening-jobs (O*)

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Validate-Job Response (R):
Cancel-Job Response (R):
Hold-Job Response (O+):
Release-Job Response (O+):
Restart-Job Response (O+):
     Group 1: Operation Attributes (R)
          attributes-charset (R)
          attributes-natural-language (R)
          status-message (O*)
          detailed-status-message (O*)
     Group 2: Unsupported Attributes (R*) (see Note 3)
          <unsupported attributes> (R*)

Print-URI Response (O):
Send-URI Response (O):
     Group 1: Operation Attributes (R)
          attributes-charset (R)
          attributes-natural-language (R)
          status-message (O*)
          detailed-status-message (O*)
          document-access-error (O*)
     Group 2: Unsupported Attributes (R*) (see Note 3)
          <unsupported attributes> (R*)
     Group 3: Job Object Attributes(R*) (see Note 2)
          job-uri (R)
          job-id (R)
          job-state (R)
          job-state-reasons (O* | R+)
          job-state-message (O*)
          number-of-intervening-jobs (O*)

Get-Printer-Attributes Response (R):
     Group 1: Operation Attributes (R)
          attributes-charset (R)
          attributes-natural-language (R)
          status-message (O*)
          detailed-status-message (O*)
     Group 2: Unsupported Attributes (R*) (see Note 4)
          <unsupported attributes> (R*)
     Group 3: Printer Object Attributes(R*) (see Note 2)
          <requested attributes> (R*)

Get-Jobs Response (R):
     Group 1: Operation Attributes (R)
          attributes-charset (R)
          attributes-natural-language (R)
          status-message (O*)

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          detailed-status-message (O*)
     Group 2: Unsupported Attributes (R*) (see Note 4)
          <unsupported attributes> (R*)
     Group 3: Job Object Attributes(R*) (see Note 2, 5)
          <requested attributes> (R*)

Get-Job-Attributes Response (R):
     Group 1: Operation Attributes (R)
          attributes-charset (R)
          attributes-natural-language (R)
          status-message (O*)
          detailed-status-message (O*)
     Group 2: Unsupported Attributes (R*) (see Note 4)
          <unsupported attributes> (R*)
     Group 3: Job Object Attributes(R*) (see Note 2)
          <requested attributes> (R*)

Pause-Printer Response (O+):
Resume-Printer Response (O+):
Purge-Printer Response (O+):
     Group 1: Operation Attributes (R)
          attributes-charset (R)
          attributes-natural-language (R)
          status-message (O*)
          detailed-status-message (O*)
     Group 2: Unsupported Attributes (R*) (see Note 4)
          <unsupported attributes> (R*)


Note 2 - the Job Object Attributes and Printer Object Attributes are
returned only if the IPP object returns one of the success status codes.

Note 3 - the Unsupported Attributes Group is present only if the client
included some Operation and/or Job Template attributes or values that
the Printer doesn't support whether a success or an error return.

Note 4 - the Unsupported Attributes Group is present only if the client
included some Operation attributes that the Printer doesn't support
whether a success or an error return.

Note 5:  for the Get-Jobs operation the response contains a separate Job
Object Attributes group 3 to N containing requested-attributes for each
job object in the response.


3.1.2.1.5 Validate the values of the REQUIRED Operation attributes

An IPP object validates the values supplied by the client of the
REQUIRED Operation attribute that the IPP object MUST support.  The next

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section specifies the validation of the values of the OPTIONAL Operation
attributes that IPP objects MAY support.


The IPP object performs the following syntactic validation checks of
each Operation attribute value:

a)     that the length of each Operation attribute value is correct for
  the attribute syntax tag supplied by the client according to [IPP-
  MOD] Section 4.1,

b)     that the attribute syntax tag is correct for that Operation
attribute according to [IPP-MOD] Section 3,

c)     that the value is in the range specified for that Operation
attribute according to [IPP-MOD] Section 3,

d)     that multiple values are supplied by the client only for
operation attributes that are multi-valued, i.e., that are 1setOf  X
according to [IPP-MOD] Section 3.



If any of these checks fail, the IPP object REJECTS the request and
RETURNS the 'client-error-bad-request' or the 'client-error-request-
value-too-long' status code.  Since such an error is most likely to be
an error detected by a client developer, rather than by an end-user, the
IPP object NEED NOT return an indication of which attribute had the
error in either the Unsupported Attributes Group or the Status Message.
The description for each of these syntactic checks is explicitly
expressed in the first IF statement in the following table.

In addition, the IPP object checks each Operation attribute value
against some Printer object attribute or some hard-coded value if there
is no "xxx-supported" Printer object attribute defined. If its value is
not among those supported or is not in the range supported, then the IPP
object REJECTS the request and RETURNS the error status code indicated
in the table by the second IF statement.  If the value of the Printer
object's "xxx-supported" attribute is 'no-value' (because the system
administrator hasn't configured a value), the check always fails.


-----------------------------------------------

attributes-charset (charset)

     IF NOT a single non-empty 'charset' value, REJECT/RETURN 'client-
          error-bad-request'.
     IF the value length is greater than 63 octets, REJECT/RETURN
          'client-error-request-value-too-long'.

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     IF NOT in the Printer object's "charset-supported" attribute,
          REJECT/RETURN "client-error-charset-not-supported".


attributes-natural-language(naturalLanguage)

     IF NOT a single non-empty 'naturalLanguage' value, REJECT/RETURN
          'client-error-bad-request'.
     IF the value length is greater than 63 octets, REJECT/RETURN
          'client-error-request-value-too-long'.
     ACCEPT the request even if not a member of the set in the Printer
          object's "generated-natural-language-supported" attribute.  If
          the supplied value is not a member of the Printer object's
          "generated-natural-language-supported" attribute, use the
          Printer object's "natural-language-configured" value.


requesting-user-name

     IF NOT a single 'name' value, REJECT/RETURN 'client-error-bad-
          request'.
     IF the value length is greater than 255 octets, REJECT/RETURN
          'client-error-request-value-too-long'.
     IF the IPP object can obtain a better-authenticated name, use it
          instead.


job-name(name)

     IF NOT a single 'name' value, REJECT/RETURN 'client-error-bad-
          request'.
     IF the value length is greater than 255 octets, REJECT/RETURN
          'client-error-request-value-too-long'.
     IF NOT supplied by the client, the Printer object creates a name
          from the document-name or document-uri.


document-name (name)

     IF NOT a single 'name' value, REJECT/RETURN 'client-error-bad-
          request'.
     IF the value length is greater than 255 octets, REJECT/RETURN
          'client-error-request-value-too-long'.


ipp-attribute-fidelity (boolean)

     IF NEITHER a single 'true' NOR a single 'false' 'boolean' value,
          REJECT/RETURN 'client-error-bad-request'.
     IF the value length is NOT equal to 1 octet, REJECT/RETURN 'client-
          error-request-value-too-long'
     IF NOT supplied by the client, the IPP object assumes the value
          'false'.

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document-format (mimeMediaType)

     IF NOT a single non-empty 'mimeMediaType' value, REJECT/RETURN
          'client-error-bad-request'.
     IF the value length is greater than 255 octets, REJECT/RETURN
          'client-error-request-value-too-long'.
     IF NOT in the Printer object's "document-format-supported"
          attribute, REJECT/RETURN 'client-error-document-format-not-
          supported'
     IF NOT supplied by the client, the IPP object assumes the value of
          the Printer object's "document-format-default" attribute.


document-uri (uri)

     IF NOT a single non-empty 'uri' value, REJECT/RETURN 'client-error-
          bad-request'.
     IF the value length is greater than 1023 octets, REJECT/RETURN
          'client-error-request-value-too-long'.
     IF the URI syntax is not valid, REJECT/RETURN 'client-error-bad-
          request'.
     If the client-supplied URI scheme is not supported, i.e. the value
          is not in the Printer object's referenced-uri-scheme-
          supported" attribute, the Printer object MUST reject the
          request and return the 'client-error-uri-scheme-not-supported'
          status code. The Printer object MAY check to see if the
          document exists and is accessible.  If the document is not
          found or is not accessible, REJECT/RETURN 'client-error-not
          found'.
     last-document (boolean)
     IF NEITHER a single 'true' NOR a single 'false' 'boolean' value,
          REJECT/RETURN 'client-error-bad-request'.
     IF the value length is NOT equal to 1 octet, REJECT/RETURN 'client-
          error-request-value-too-long'


job-id (integer(1:MAX))

     IF NOT an single 'integer' value equal to 4 octets AND in the range
          1 to MAX, REJECT/RETURN 'client-error-bad-request'.
     IF NOT a job-id of an existing Job object, REJECT/RETURN 'client-
          error-not-found' or 'client-error-gone' status code, if keep
          track of recently deleted jobs.


requested-attributes (1setOf keyword)

     IF NOT one or more 'keyword' values, REJECT/RETURN 'client-error-
          bad-request'.


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     IF the value length is greater than 255 octets, REJECT/RETURN
          'client-error-request-value-too-long'.
     Ignore unsupported values, which are the keyword names of
          unsupported attributes.  Don't bother to copy such requested
          (unsupported) attributes to the Unsupported Attribute response
          group since the response will not return them.


which-jobs (type2 keyword)

     IF NOT a single 'keyword' value, REJECT/RETURN 'client-error-bad-
          request'.
     IF the value length is greater than 255 octets, REJECT/RETURN
          'client-error-request-value-too-long'.
     IF NEITHER 'completed' NOR 'not-completed', copy the attribute and
          the unsupported value to the Unsupported Attributes response
          group and REJECT/RETURN 'client-error-attributes-or-values-
          not-supported'.
     Note: a Printer still supports the 'completed' value even if it
          keeps no completed/canceled/aborted jobs:  by returning no
          jobs when so queried.
     IF NOT supplied by the client, the IPP object assumes the 'not-
          completed' value.


my-jobs (boolean)

     IF NEITHER a single 'true' NOR a single 'false' 'boolean' value,
          REJECT/RETURN 'client-error-bad-request'.
     IF the value length is NOT equal to 1 octet, REJECT/RETURN 'client-
          error-request-value-too-long'
     IF NOT supplied by the client, the IPP object assumes the 'false'
          value.


limit (integer(1:MAX))

     IF NOT a single 'integer' value equal to 4 octets AND in the range
          1 to MAX, REJECT/RETURN 'client-error-bad-request'.
     IF NOT supplied by the client, the IPP object returns all jobs, no
          matter how many.


-----------------------------------------------



3.1.2.1.6 Validate the values of the OPTIONAL Operation attributes

OPTIONAL Operation attributes are those that an IPP object MAY or MAY
NOT support.  An IPP object validates the values of the OPTIONAL
attributes supplied by the client.  The IPP object performs the same

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syntactic validation checks for each OPTIONAL attribute value as in
Section 3.1.2.1.5.  As in Section 3.1.2.1.5, if any fail, the IPP object
REJECTS the request and RETURNS the 'client-error-bad-request' or the
'client-error-request-value-too-long' status code.

In addition, the IPP object checks each Operation attribute value
against some Printer attribute or some hard-coded value if there is no
"xxx-supported" Printer attribute defined. If its value is not among
those supported or is not in the range supported, then the IPP object
REJECTS the request and RETURNS the error status code indicated in the
table.  If the value of the Printer object's "xxx-supported" attribute
is 'no-value' (because the system administrator hasn't configured a
value), the check always fails.

If the IPP object doesn't recognize/support an attribute, the IPP object
treats the attribute as an unknown or unsupported attribute (see the
last row in the table below).


-----------------------------------------------

document-natural-language (naturalLanguage)

     IF NOT a single non-empty 'naturalLanguage' value, REJECT/RETURN
          'client-error-bad-request'.
     IF the value length is greater than 63 octets, REJECT/RETURN
          'client-error-request-value-too-long'.
     IF NOT a value that the Printer object supports in document
          formats, (no corresponding "xxx-supported" Printer attribute),
          REJECT/RETURN 'client-error-natural-language-not-supported'.


compression (type3 keyword)

     IF NOT a single 'keyword' value, REJECT/RETURN 'client-error-bad-
          request'.
     IF the value length is greater than 255 octets, REJECT/RETURN
          'client-error-request-value-too-long'.
     IF NOT in the Printer object's "compression-supported" attribute,
          copy the attribute and the unsupported value to the
          Unsupported Attributes response group and REJECT/RETURN
          'client-error-attributes-or-values-not-supported'.
     Note to IPP/1.0 implementers:  Support for the "compression"
          attribute was optional in IPP/1.0 and was changed to REQUIRED
          in IPP/1.1.  However, an IPP/1.0 object SHOULD at least check
          for the "compression" attribute being present and reject the
          create request, if they don't support "compression".  Not
          checking is a bug, since the data will be unintelligible.

job-k-octets (integer(0:MAX))
     IF NOT a single 'integer' value equal to 4 octets,

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     REJECT/RETURN 'client-error-bad-request'.
     IF NOT in the range of the Printer object's "job-k-octets-
          supported" attribute, copy the attribute and the unsupported
          value to the Unsupported Attributes response group and
          REJECT/RETURN 'client-error-attributes-or-values-not-
          supported'.


job-impressions (integer(0:MAX))

     IF NOT a single 'integer' value equal to 4 octets,
     REJECT/RETURN 'client-error-bad-request'.
     IF NOT in the range of the Printer object's "job-impressions-
          supported" attribute, copy the attribute and the unsupported
          value to the Unsupported Attributes response group and
          REJECT/RETURN 'client-error-attributes-or-values-not-
          supported'.


job-media-sheets (integer(0:MAX))

     IF NOT a single 'integer' value equal to 4 octets,
     REJECT/RETURN 'client-error-bad-request'.
     IF NOT in the range of the Printer object's "job-media-sheets-
          supported" attribute, copy the attribute and the unsupported
          value to the Unsupported Attributes response group and
          REJECT/RETURN 'client-error-attributes-or-values-not-
          supported'.


message (text(127))

     IF NOT a single 'text' value, REJECT/RETURN 'client-error-bad-
          request'.
     IF the value length is greater than 127 octets,
     REJECT/RETURN 'client-error-request-value-too-long'.


unknown or unsupported attribute

     IF the attribute syntax supplied by the client is supported but the
          length is not legal for that attribute syntax, REJECT/RETURN
          'client-error-request-value-too-long'.
     ELSE copy the attribute and value to the Unsupported Attributes
          response group and change the attribute value to the "out-of-
          band" 'unsupported' value, but otherwise ignore the attribute.

Note: Future Operation attributes may be added to the protocol
specification that may occur anywhere in the specified group.  When the
operation is otherwise successful, the IPP object returns the
'successful-ok-ignored-or-substituted-attributes' status code.  Ignoring
unsupported Operation attributes in all operations is analogous to the

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handling of unsupported Job Template attributes in the create and
Validate-Job operations when the client supplies the "ipp-attribute-
fidelity" Operation attribute with the 'false' value. This last rule is
so that we can add OPTIONAL Operation attributes to future versions of
IPP so that older clients can inter-work with new IPP objects and newer
clients can inter-work with older IPP objects.  (If the new attribute
cannot be ignored without performing unexpectedly, the major version
number would have been increased in the protocol document and in the
request).  This rule for Operation attributes is independent of the
value of the "ipp-attribute-fidelity" attribute.   For example, if an
IPP object doesn't support the OPTIONAL "job-k-octets" attribute', the
IPP object treats "job-k-octets" as an unknown attribute and only checks
the length for the 'integer' attribute syntax supplied by the client.
If it is not four octets, the IPP object REJECTS the request and RETURNS
the 'client-error-bad-request' status code, else the IPP object copies
the attribute to the Unsupported Attribute response group, setting the
value to the "out-of-band" 'unsupported' value, but otherwise ignores
the attribute.































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3.1.2.2   Suggested Additional Processing Steps for Operations that
      Create/Validate Jobs and Add Documents

This section in combination with the previous section recommends the
processing steps for the Print-Job, Validate-Job, Print-URI, Create-Job,
Send-Document, and Send-URI operations that IPP objects SHOULD use.
These are the operations that create jobs, validate a Print-Job request,
and add documents to a job.

IIG Sect #         Flow                 IPP error status codes
----------         ----                 ----------------------
                     |
                     v             No
3.1.2.2.1 <ipp-attribute-fidelity> ------------------+
               <supplied?>                           |
                  Yes|                               |
                     |  ipp-attribute-fidelity = no  |
                     |<------------------------------+
                     v          No
3.1.2.2.2       <Printer is>    --> server-error-not-accepting-jobs
             <accepting jobs?>
                  Yes|
                     v          err
3.1.2.3    <Validate values of> --> client-error-bad-request
        <Job template attributes>   client-error-request-value-too-long
         <(length, tag, range,>
              <multi-value)>
                   ok|
                     v          err
3.1.2.3  <Validate values with> --> client-error-bad-request
          <supported values>        client-error-attributes-or-values-
                   ok|                           not-supported
                     v          err
3.1.2.3.1   <Any conflicting>   --> client-error-conflicting-attributes
       <Job Template attr values>   client-error-attributes-or-values-
                   ok|                           not-supported
                     v

3.1.2.2.1 Default "ipp-attribute-fidelity" if not supplied

The Printer object checks to see if the client supplied an "ipp-
attribute-fidelity" Operation attribute.  If the attribute is not
supplied by the client, the IPP object assumes that the value is
'false'.


3.1.2.2.2 Check that the Printer object is accepting jobs



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If the value of the Printer objects "printer-is-accepting-jobs" is
'false', the Printer object REJECTS the request and RETURNS the 'server-
error-not-accepting-jobs' status code.


3.1.2.2.3 Validate the values of the Job Template attributes

An IPP object validates the values of all Job Template attribute
supplied by the client.  The IPP object performs the analogous syntactic
validation checks of each Job Template attribute value that it performs
for Operation attributes (see Section 3.1.2.1.5.):


  a)     that the length of each value is correct for the attribute
  syntax tag supplied by the client according to [IPP-MOD] Section 4.1.

  b)     that the attribute syntax tag is correct for that attribute
  according to [IPP-MOD] Sections 4.2 to 4.4.

  c)     that multiple values are supplied only for multi-valued
  attributes, i.e., that are 1setOf  X according to [IPP-MOD] Sections
  4.2 to 4.4.

As in Section 3.1.2.1.5, if any of these syntactic checks fail, the IPP
object REJECTS the request and RETURNS the 'client-error-bad-request' or
'client-error-request-value-too-long' status code as appropriate,
independent of the value of the "ipp-attribute-fidelity".  Since such an
error is most likely to be an error detected by a client developer,
rather than by an end-user, the IPP object NEED NOT return an indication
of which attribute had the error in either the Unsupported Attributes
Group or the Status Message.  The description for each of these
syntactic checks is explicitly expressed in the first IF statement in
the following table.


Each Job Template attribute MUST occur no more than once.  If an IPP
Printer receives a create request with multiple occurrences of a Job
Template attribute, it MAY:

    1.  reject the operation and return the 'client-error-bad-request'
        error status code

    2.  accept the operation and use the first occurrence of the
        attribute

    3.  accept the operation and use the last occurrence of the
        attribute




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depending on implementation.  Therefore, clients MUST NOT supply
multiple occurrences of the same Job Template attribute in the Job
Attributes group in the request.


3.1.2.3   Algorithm for job validation

The process of validating a Job-Template attribute "xxx" against a
Printer attribute "xxx-supported" can use the following validation
algorithm (see section 3.2.1.2 in [ipp-mod]).

To validate the value U of Job-Template attribute "xxx" against the
value V of Printer "xxx-supported", perform the following algorithm:

1.If U is multi-valued, validate each value X of U by performing the
  algorithm in Table 7 with each value X. Each validation is separate
  from the standpoint of returning unsupported values. Example:  If U
  is "finishings" that the client supplies with 'staple', 'bind'
  values, then X takes on the successive values: 'staple', then 'bind'

2.If V is multi-valued, validate X against each Z of V by performing
  the algorithm in Table 7 with each value Z.  If a value Z validates,
  the validation for the attribute value X succeeds. If it fails, the
  algorithm is applied to the next value Z of V. If there are no more
  values Z of V, validation fails. Example"  If V is "sides-supported"
  with values: 'one-sided', 'two-sided-long', and 'two-sided-short',
  then Z takes on the successive values:  'one-sided', 'two-sided-
  long', and 'two-sided-short'.  If the client supplies "sides" with
  'two-sided-long', the first comparison fails ('one-sided' is not
  equal to 'two-sided-long'), the second comparison succeeds ('two-
  sided-long' is equal to 'two-sided-long"), and the third comparison
  ('two-sided-short' with 'two-sided-long') is not even performed.

3.If both U and V are single-valued, let X be U and Z be V and use the
  validation rules in Table 7.

Table 7 - Rules for validating single values X against Z

  Attribute      attribute       validated if:
  syntax of X    syntax of Z

  integer        rangeOfInteger  X is within the range of Z
  uri            uriScheme       the uri scheme in X is equal to Z
  any            boolean         the value of Z is TRUE
  any            any             X and Z are of the same type and are
                                  equal.




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If the value of the Printer object's "xxx-supported" attribute is 'no-
value' (because the system administrator hasn't configured a value), the
check always fails.  If the check fails, the IPP object copies the
attribute to the Unsupported Attributes response group with its
unsupported value.  If the attribute contains more than one value, each
value is checked and each unsupported value is separately copied, while
supported values are not copied.  If an IPP object doesn't
recognize/support a Job Template attribute, i.e., there is no
corresponding Printer object "xxx-supported" attribute, the IPP object
treats the attribute as an unknown or unsupported attribute (see the
last row in the table below).

If some Job Template attributes are supported for some document formats
and not for others or the values are different for different document
formats, the IPP object SHOULD take that into account in this validation
using the value of the "document-format" supplied by the client (or
defaulted to the value of the Printer's "document-format-default"
attribute, if not supplied by the client).  For example, if "number-up"
is supported for the 'text/plain' document format, but not for the
'application/postscript' document format, the check SHOULD (though it
NEED NOT) depend on the value of the "document-format" operation
attribute.  See "document-format" in [IPP-MOD] section 3.2.1.1 and
3.2.5.1.

Note: whether the request is accepted or rejected is determined by the
value of the "ipp-attribute-fidelity" attribute in a subsequent step, so
that all Job Template attribute supplied are examined and all
unsupported attributes and/or values are copied to the Unsupported
Attributes response group.


-----------------------------------------------

job-priority (integer(1:100))

     IF NOT a single 'integer' value with a length equal to 4 octets,
          REJECT/RETURN 'client-error-bad-request'.
     IF NOT supplied by the client, use the value of the Printer
          object's "job-priority-default" attribute at job submission
          time.
     IF NOT in the range 1 to 100, inclusive, copy the attribute and the
          unsupported value to the Unsupported Attributes response
          group.
     Map the value to the nearest supported value in the range 1:100 as
          specified by the number of discrete values indicated by the
          value of the Printer's "job-priority-supported" attribute.
          See the formula in [IPP-MOD] Section 4.2.1.



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job-hold-until (type3 keyword | name)

     IF NOT a single 'keyword' or 'name' value, REJECT/RETURN 'client-
          error-bad-request'.
     IF the value length is greater than 255 octets, REJECT/RETURN
          'client-error-request-value-too-long'.
     IF NOT supplied by the client, use the value of the Printer
          object's "job-hold-until" attribute at job submission time.
     IF NOT in the Printer object's "job-hold-until-supported"
          attribute, copy the attribute and the unsupported value to the
          Unsupported Attributes response group.


job-sheets (type3 keyword | name)

     IF NOT a single 'keyword' or 'name' value, REJECT/RETURN 'client-
          error-bad-request'.
     IF the value length is greater than 255 octets, REJECT/RETURN
          'client-error-request-value-too-long'.
     IF NOT in the Printer object's "job-sheets-supported" attribute,
          copy the attribute and the unsupported value to the
          Unsupported Attributes response group.


multiple-document-handling (type2 keyword)

     IF NOT a single 'keyword' value, REJECT/RETURN 'client-error-bad-
          request'.
     IF the value length is greater than 255 octets, REJECT/RETURN
          'client-error-request-value-too-long'.
     IF NOT in the Printer object's "multiple-document-handling-
          supported" attribute, copy the attribute and the unsupported
          value to the Unsupported Attributes response group.


copies (integer(1:MAX))

     IF NOT a single 'integer' value with a length equal to 4 octets,
     REJECT/RETURN 'client-error-bad-request'.
     IF NOT in range of the Printer object's "copies-supported"
          attribute
     copy the attribute and the unsupported value to the Unsupported
          Attributes response group.


finishings (1setOf type2 enum)

     IF NOT an 'enum' value(s) each with a length equal to 4 octets,
          REJECT/RETURN 'client-error-bad-request'.
     IF NOT in the Printer object's "finishings-supported" attribute,
          copy the attribute and the unsupported value(s), but not any



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          supported values, to the Unsupported Attributes response
          group.


page-ranges (1setOf  rangeOfInteger(1:MAX))

     IF NOT a 'rangeOfInteger' value(s) each with a length equal to 8
          octets, REJECT/RETURN 'client-error-bad-request'.
     IF first value is greater than second value in any range, the
          ranges are not in ascending order, or ranges overlap,
          REJECT/RETURN 'client-error-bad-request'.
     IF the value of the Printer object's "page-ranges-supported"
          attribute is 'false', copy the attribute to the Unsupported
          Attributes response group and set the value to the "out-of-
          band" 'unsupported' value.


sides (type2 keyword)

     IF NOT a single 'keyword' value, REJECT/RETURN 'client-error-bad-
          request'.
     IF the value length is greater than 255 octets, REJECT/RETURN
          'client-error-request-value-too-long'.
     IF NOT in the Printer object's "sides-supported" attribute, copy
          the attribute and the unsupported value to the Unsupported
          Attributes response group.


number-up (integer(1:MAX))

     IF NOT a single 'integer' value with a length equal to 4 octets,
     REJECT/RETURN 'client-error-bad-request'.
     IF NOT a value or in the range of one of the values of the Printer
          object's "number-up-supported" attribute, copy the attribute
          and value to the Unsupported Attribute response group.


orientation-requested (type2 enum)

     IF NOT a single 'enum' value with a length equal to 4 octets,
     REJECT/RETURN 'client-error-bad-request'.
     IF NOT in the Printer object's "orientation-requested-supported"
          attribute, copy the attribute and the unsupported value to the
          Unsupported Attributes response group.


media (type3 keyword | name)

     IF NOT a single 'keyword' or 'name' value, REJECT/RETURN 'client-
          error-bad-request'.
     IF the value length is greater than 255 octets, REJECT/RETURN
          'client-error-request-value-too-long'.


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     IF NOT in the Printer object's "media-supported" attribute, copy
          the attribute and the unsupported value to the Unsupported
          Attributes response group.


printer-resolution (resolution)

     IF NOT a single 'resolution' value with a length equal to 9 octets,
     REJECT/RETURN 'client-error-bad-request'.
     IF NOT in the Printer object's "printer-resolution-supported"
          attribute, copy the attribute and the unsupported value to the
          Unsupported Attributes response group.


print-quality (type2 enum)

     IF NOT a single 'enum' value with a length equal to 4 octets,
     REJECT/RETURN 'client-error-bad-request'.
     IF NOT in the Printer object's "print-quality-supported" attribute,
          copy the attribute and the unsupported value to the
          Unsupported Attributes response group.


unknown or unsupported attribute (i.e., there is no corresponding
Printer object "xxx-supported" attribute)

     IF the attribute syntax supplied by the client is supported but the
          length is not legal for that attribute syntax,
     REJECT/RETURN 'client-error-bad-request' if the length of the
          attribute syntax is fixed or 'client-error-request-value-too-
          long' if the length of the attribute syntax is variable.
     ELSE copy the attribute and value to the Unsupported Attributes
          response group and change the attribute value to the "out-of-
          band" 'unsupported' value.  Any remaining Job Template
          Attributes are either unknown or unsupported Job Template
          attributes and are validated algorithmically according to
          their attribute syntax for proper length (see below).

-----------------------------------------------

If the attribute syntax is supported AND the length check fails, the IPP
object REJECTS the request and RETURNS the 'client-error-bad-request' if
the length of the attribute syntax is fixed or the 'client-error-
request-value-too-long' status code if the length of the attribute
syntax is variable. Otherwise, the IPP object copies the unsupported Job
Template attribute to the Unsupported Attributes response group and
changes the attribute value to the "out-of-band" 'unsupported' value.
The following table shows the length checks for all attribute syntaxes.
In the following table:  "<=" means less than or equal, "=" means equal
to:

Name              Octet length check for read-write attributes

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-----------       --------------------------------------------
'textWithLanguage     <= 1023 AND 'naturalLanguage'  <= 63
'textWithoutLanguage' <= 1023
'nameWithLanguage'    <= 255 AND 'naturalLanguage'  <= 63
'nameWithoutLanguage' <= 255
'keyword'             <= 255
'enum'                = 4
'uri'                 <= 1023
'uriScheme'           <= 63
'charset'             <= 63
'naturalLanguage'     <= 63
'mimeMediaType'       <= 255
'octetString'         <= 1023
'boolean'             = 1
'integer'             = 4
'rangeOfInteger'      = 8
'dateTime'            = 11
'resolution'          = 9
'1setOf  X'


Note:  It's possible for a Printer to receive a zero length keyword in a
request.  Since this is a keyword, its value needs to be compared with
the supported values.  Assuming that the printer doesn't have any values
in its corresponding "xxx-supported" attribute that are keywords of zero
length, the comparison will fail.  Then the request will be accepted or
rejected depending on the value of "ipp-attributes-fidelity" being
'false' or 'true', respectively.  No special handling is required for


3.1.2.3.1 Check for conflicting Job Template attributes values

Once all the Operation and Job Template attributes have been checked
individually, the Printer object SHOULD check for any conflicting values
among all the supported values supplied by the client.  For example, a
Printer object might be able to staple and to print on transparencies,
however due to physical stapling constraints, the Printer object might
not be able to staple transparencies. The IPP object copies the
supported attributes and their conflicting attribute values to the
Unsupported Attributes response group.  The Printer object only copies
over those attributes that the Printer object either ignores or
substitutes in order to resolve the conflict, and it returns the
original values which were supplied by the client.  For example suppose
the client supplies "finishings" equals 'staple' and "media" equals
'transparency', but the Printer object does not support stapling
transparencies.  If the Printer chooses to ignore the stapling request
in order to resolve the conflict, the Printer objects returns
"finishings" equal to 'staple' in the Unsupported Attributes response


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group.  If any attributes are multi-valued, only the conflicting values
of the attributes are copied.

Note: The decisions made to resolve the conflict (if there is a choice)
is implementation dependent.


3.1.2.3.2 Decide whether to REJECT the request

If there were any unsupported Job Template attributes or
unsupported/conflicting Job Template attribute values and the client
supplied the "ipp-attribute-fidelity" attribute with the 'true' value,
the Printer object REJECTS the request and return the status code:

  1. 'client-error-conflicting-attributes' status code, if there were
     any conflicts between attributes supplied by the client.
  2. 'client-error-attributes-or-values-not-supported' status code,
     otherwise.

Note:  Unsupported Operation attributes or values that are returned do
not affect the status returned in this step.  If the unsupported
Operation attribute was a serious error, the above already rejected the
request in a previous step.  If control gets to this step with
unsupported Operation attributes being returned, they are not serious
errors.

In general, the final results of Job processing are unknown at Job
submission time.  The client has to rely on notifications or polling to
find out what happens at Job processing time.  However, there are cases
in which some Printers can determine at Job submission time that Job
processing is going to fail.  As an optimization, we'd like to have the
Printer reject the Job in these cases.

There are three types of "processing" errors that might be detectable at
Job submission time:

1.  'client-error-document-format-not-supported' :  For the Print-Job,
Send-Document, Print-URI, and Send-URI operations, if  all these
conditions are true:

     - the Printer supports auto-sensing,
     - the request "document-format"  operation attribute is
     'application/octet-stream',
     - the Printer receives document data before responding,
     - the Printer auto-senses the document format before responding,
     - the sensed document format is not supported by the Printer
then the  Printer should respond with 'client-error-document-format-not-
supported' status.

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2.  'client-error-compression-error':  For the Print-Job, Send-Document,
Print-URI, and Send-URI operations, if  all these conditions are true:

     - the client supplies a supported value for the "compression"
          operation attribute in the request
     - the Printer receives document data before responding,
     - the Printer attempts to decompress the document data before
          responding,
     - the document data cannot be decompressed using the algorithm
       specified by the "compression" operation attribute
then the Printer should respond with 'client-error-compression-error'
status.

3.  'client-error-document-access-error':  For the Print-URI, and Send-
URI operations, if the Printer attempts and fails to pull the referenced
document data before responding, it should respond with 'client-error-
document-access-error' status.

Some Printers are not able to detect these errors until Job processing
time.  In that case, the errors are recorded in the corresponding job-
state and job-state reason attributes.  (There is no standard way for a
client to determine whether a Printer can detect these errors at Job
submission time.)  For example, if auto-sensing happens AFTER the job is
accepted (as opposed to auto-sensing at submit time before returning the
response), the implementation aborts the job, puts the job in the
'aborted' state and sets the 'unsupported-document-format' value in the
job's "job-state-reasons".

A client should always provide a valid "document-format" operation
attribute whenever practical.  In the absence of other information, a
client itself may sniff the document data to determine document format.

Auto sensing at Job submission time may be more difficult for the
Printer when combined with compression.  For auto-sensed Jobs, a client
may be better off  deferring compression to the transfer protocol layer,
e.g.; by using the HTTP Content-Encoding header.


3.1.2.3.3 For the Validate-Job operation, RETURN one of the success
       status codes

If the requested operation is the Validate-Job operation, the Printer
object returns:

  1. the "successful-ok" status code, if there are no unsupported or
     conflicting Job Template attributes or values.
  2. the "successful-ok-conflicting-attributes, if there are any
     conflicting Job Template attribute or values.

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  3. the "successful-ok-ignored-or-substituted-attributes, if there are
     only unsupported Job Template attributes or values.


Note:  Unsupported Operation attributes or values that are returned do
not affect the status returned in this step.  If the unsupported
Operation attribute was a serious error, the above already rejected the
request in a previous step.  If control gets to this step with
unsupported Operation attributes being returned, they are not serious
errors.


3.1.2.3.4 Create the Job object with attributes to support

If "ipp-attribute-fidelity" is set to 'false' (or it was not supplied by
the client), the Printer object:

  1. creates a Job object, assigns a unique value to the job's "job-
     uri" and "job-id" attributes, and initializes all of the job's
     other supported Job Description attributes.
  2. removes all unsupported attributes from the Job object.
  3. for each unsupported value, removes either the unsupported value
     or substitutes the unsupported attribute value with some supported
     value.  If an attribute has no values after removing unsupported
     values from it, the attribute is removed from the Job object (so
     that the normal default behavior at job processing time will take
     place for that attribute).
  4. for each conflicting value, removes either the conflicting value
     or substitutes the conflicting attribute value with some other
     supported value.  If an attribute has no values after removing
     conflicting values from it, the attribute is removed from the Job
     object (so that the normal default behavior at job processing time
     will take place for that attribute).

If there were no attributes or values flagged as unsupported, or the
value of 'ipp-attribute-fidelity" was 'false', the Printer object is
able to accept the create request and create a new Job object.  If the
"ipp-attribute-fidelity" attribute is set to 'true', the Job Template
attributes that populate the new Job object are necessarily all the Job
Template attributes supplied in the create request.  If the "ipp-
attribute-fidelity" attribute is set to 'false', the Job Template
attributes that populate the new Job object are all the client supplied
Job Template attributes that are supported or that have value
substitution.  Thus, some of the requested Job Template attributes may
not appear in the Job object because the Printer object did not support
those attributes.  The attributes that populate the Job object are
persistently stored with the Job object for that Job.  A Get-Job-


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Attributes operation on that Job object will return only those
attributes that are persistently stored with the Job object.

Note: All Job Template attributes that are persistently stored with the
Job object are intended to be "override values"; that is, they that take
precedence over whatever other embedded instructions might be in the
document data itself.  However, it is not possible for all Printer
objects to realize the semantics of "override".  End users may query the
Printer's "pdl-override-supported" attribute to determine if the Printer
either attempts or does not attempt to override document data
instructions with IPP attributes.

There are some cases, where a Printer supports a Job Template attribute
and has an associated default value set for that attribute.  In the case
where a client does not supply the corresponding attribute, the Printer
does not use its default values to populate Job attributes when creating
the new Job object; only Job Template attributes actually in the create
request are used to populate the Job object. The Printer's default
values are only used later at Job processing time if no other IPP
attribute or instruction embedded in the document data is present.

Note: If the default values associated with Job Template attributes that
the client did not supply were to be used to populate the Job object,
then these values would become "override values" rather than defaults.
If the Printer supports the 'attempted' value of the "pdl-override-
supported" attribute, then these override values could replace values
specified within the document data.  This is not the intent of the
default value mechanism. A default value for an attribute is used only
if the create request did not specify that attribute (or it was ignored
when allowed by "ipp-attribute-fidelity" being 'false') and no value was
provided within the content of the document data.

If the client does not supply a value for some Job Template attribute,
and the Printer does not support that attribute, as far as IPP is
concerned, the result of processing that Job (with respect to the
missing attribute) is undefined.


3.1.2.3.5 Return one of the success status codes

Once the Job object has been created, the Printer object accepts the
request and returns to the client:

  1. the 'successful-ok' status code, if there are no unsupported or
     conflicting Job Template attributes or values.
  2. the 'successful-ok-conflicting-attributes' status code, if there
     are any conflicting Job Template attribute or values.


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  3. the 'successful-ok-ignored-or-substituted-attributes' status code,
     if there are only unsupported Job Template attributes or values.

Note:  Unsupported Operation attributes or values that are returned do
not affect the status returned in this step.  If the unsupported
Operation attribute was a serious error, the above already rejected the
request in a previous step.  If control gets to this step with
unsupported Operation attributes being returned, they are not serious
errors.

The Printer object also returns Job status attributes that indicate the
initial state of the Job ('pending', 'pending-held', 'processing',
etc.), etc.  See Print-Job Response, [IPP-MOD] section 3.2.1.2.


3.1.2.3.6 Accept appended Document Content

The Printer object accepts the appended Document Content data and either
starts it printing, or spools it for later processing.


3.1.2.3.7 Scheduling and Starting to Process the Job

The Printer object uses its own configuration and implementation
specific algorithms for scheduling the Job in the correct processing
order.  Once the Printer object begins processing the Job, the Printer
changes the Job's state to 'processing'. If the Printer object supports
PDL override (the "pdl-override-supported" attribute set to
'attempted'), the implementation does its best to see that IPP
attributes take precedence over embedded instructions in the document
data.


3.1.2.3.8 Completing the Job

The Printer object continues to process the Job until it can move the
Job into the 'completed' state.  If an Cancel-Job operation is received,
the implementation eventually moves the Job into the 'canceled' state.
If the system encounters errors during processing that do not allow it
to progress the Job into a completed state, the implementation halts all
processing, cleans up any resources, and moves the Job into the
'aborted' state.


3.1.2.3.9 Destroying the Job after completion

Once the Job moves to the 'completed', 'aborted', or 'canceled' state,
it is an implementation decision as to when to destroy the Job object

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and release all associated resources.  Once the Job has been destroyed,
the Printer would return either the "client-error-not-found" or "client-
error-gone" status codes for operations directed at that Job.

Note:  the Printer object SHOULD NOT re-use a "job-uri" or "job-id"
value for a sufficiently long time after a job has been destroyed, so
that stale references kept by clients are less likely to access the
wrong (newer) job.


3.1.2.3.10     Interaction with "ipp-attribute-fidelity"


Some Printer object implementations may support "ipp-attribute-fidelity"
set to 'true' and "pdl-override-supported" set to 'attempted' and yet
still not be able to realize exactly what the client specifies in the
create request.  This is due to legacy decisions and assumptions that
have been made about the role of job instructions embedded within the
document data and external job instructions that accompany the document
data and how to handle conflicts between such instructions.  The
inability to be 100% precise about how a given implementation will
behave is also compounded by the fact that the two special attributes,
"ipp-attribute-fidelity" and "pdl-"override-supported", apply to the
whole job rather than specific values for each attribute. For example,
some implementations may be able to override almost all Job Template
attributes except for "number-up". Character Sets, natural languages,
and internationalization

This section discusses character set support, natural language support
and internationalization.


3.1.2.3.11     Character set code conversion support

IPP clients and IPP objects are REQUIRED to support UTF-8.  They MAY
support additional charsets.  It is RECOMMENDED that an IPP object also
support US-ASCII, since many clients support US-ASCII, and indicate that
UTF-8 and US-ASCII are supported by populating the Printer's "charset-
supported" with 'utf-8' and 'us-ascii' values.  An IPP object is
required to code covert with as little loss as possible between the
charsets that it supports, as indicated in the Printer's "charsets-
supported" attribute.


How should the server handle the situation where the "attributes-
charset" of the response itself is "us-ascii", but one or more
attributes in that response is in the "utf-8" format?




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Example:  Consider a case where a client sends a Print-Job request with
"utf-8" as the value of "attributes-charset" and with the "job-name"
attribute supplied.  Later another client submits a Get-Job-Attribute or
Get-Jobs request.  This second request contains the "attributes-charset"
with value "us-ascii" and "requested-attributes" attribute with exactly
one value "job-name".

According to the IPP-Mod document (section 3.1.4.2), the value of the
"attributes-charset" for the response of the second request must be "us-
ascii" since that is the charset specified in the request.  The "job-
name" value, however, is in "utf-8" format.  Should the request be
rejected even though both "utf-8" and "us-ascii" charsets are supported
by the server? or should the "job-name" value be converted to "us-ascii"
and return "successful-ok-conflicting-attributes"  (0x0002) as the
status code?

Answer:  An IPP object that supports both utf-8 (REQUIRED) and us-ascii,
the second paragraph of section 3.1.4.2 applies so that the IPP object
MUST accept the request, perform code set conversion between these two
charsets with "the highest fidelity possible" and return 'successful-
ok', rather than a warning 'successful-ok-conflicting-attributes, or an
error.  The printer will do the best it can to convert between each of
the character sets that it supports--even if that means providing a
string of question marks because none of the characters are
representable in US ASCII.  If it can't perform such conversion, it MUST
NOT advertise us-ascii as a value of its "attributes-charset-supported"
and MUST reject any request that requests 'us-ascii'.

One IPP object implementation strategy is to convert all request text
and name values to a Unicode internal representation.  This is 16-bit
and virtually universal.  Then convert to the specified operation
attributes-charset on output.

Also it would be smarter for a client to ask for 'utf-8', rather than
'us-ascii' and throw away characters that it doesn't understand, rather
than depending on the code conversion of the IPP object.


3.1.2.3.12     What charset to return when an unsupported charset is
       requested (Issue 1.19)?

Section 3.1.4.1 Request Operation attributes was clarified in November
1998 as follows:

All clients and IPP objects MUST support the 'utf-8' charset [RFC2044]
and MAY support additional charsets provided that they are registered
with IANA [IANA-CS].  If the Printer object does not support the client
supplied charset value, the Printer object MUST reject the request, set


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the "attributes-charset" to 'utf-8' in the response, and return the
'client-error-charset-not-supported' status code and any 'text' or
'name' attributes using the 'utf-8' charset.

Since the client and IPP object MUST support UTF-8, returning any text
or name attributes in UTF-8 when the client requests a charset that is
not supported should allow the client to display the text or name.

Since such an error is a client error, rather than a user error, the
client should check the status code first so that it can avoid
displaying any other returned 'text' and 'name' attributes that are not
in the charset requested.

Furthermore, [ipp-mod] section 14.1.4.14 client-error-charset-not-
supported (0x040D) was clarified in November 1998 as follows:

For any operation, if the IPP Printer does not support the charset
supplied by the client in the "attributes-charset" operation attribute,
the Printer MUST reject the operation and return this status and any
'text' or 'name' attributes using the 'utf-8' charset (see Section
3.1.4.1).


3.1.2.3.13     Natural Language Override (NLO)


The 'text' and 'name' attributes each have two forms.  One has an
implicit natural language, and the other has an explicit natural
language.  The 'textWithoutLanguage' and 'textWithLanguage' are the two
'text' forms.  The 'nameWithoutLanguage" and 'nameWithLanguage are the
two 'name' forms.  If a receiver (IPP object or IPP client) supports an
attribute with attribute syntax 'text', it MUST support both forms in a
request and a response.  A sender (IPP client or IPP object) MAY send
either form for any such attribute.  When a sender sends a
WithoutLanguage form, the implicit natural language is specified in the
"attributes-natural-language" operation attribute, which all senders
MUST include in every request and response.

When a sender sends a WithLanguage form, it MAY be different from the
implicit natural language supplied by the sender or it MAY be the same.
The receiver MUST treat either form equivalently.

There is an implementation decision for senders, whether to always send
the WithLanguage forms or use the WithoutLanguage form when the
attribute's natural language is the same as the request or response.
The former approach makes the sender implementation simpler.  The latter
approach is more efficient on the wire and allows inter-working with
non-conforming receivers that fail to support the WithLanguage forms.


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As each approach have advantages, the choice is completely up to the
implementer of the sender.

Furthermore, when a client receives a 'text' or 'name' job attribute
that it had previously supplied, that client MUST NOT expect to see the
attribute in the same form, i.e., in the same WithoutLanguage or
WithLanguage form as the client supplied when it created the job.  The
IPP object is free to transform the attribute from the WithLanguage form
to the WithoutLanguage form and vice versa, as long as the natural
language is preserved.  However, in order to meet this latter
requirement, it is usually simpler for the IPP object implementation to
store the natural language explicitly with the attribute value, i.e., to
store using an internal representation that resembles the WithLanguage
form.

The IPP Printer MUST copy the natural language of a job, i.e., the value
of the "attributes-natural-language" operation attribute supplied by the
client in the create operation, to the Job object as a Job Description
attribute, so that a client is able to query it.  In returning a Get-
Job-Attributes response, the IPP object MAY return one of three natural
language values in the response's "attributes-natural-language"
operation attribute: (1) that requested by the requester, (2) the
natural language of the job, or (3) the configured natural language of
the IPP Printer, if the requested language is not supported by the IPP
Printer.

This "attributes-natural-language" Job Description attribute is useful
for an IPP object implementation that prints start sheets in the
language of the user who submitted the job.  This same Job Description
attribute is useful to a multi-lingual operator who has to communicate
with different job submitters in different natural languages.  This same
Job Description attribute is expected to be used in the future to
generate notification messages in the natural language of the job
submitter.

Early drafts of [IPP-MOD] contained a job-level natural language
override (NLO) for the Get-Jobs response.  A job-level (NLO) is an
(unrequested) Job Attribute which then specified the implicit natural
language for any other WithoutLanguage job attributes returned in the
response for that job.  Interoperability testing of early
implementations showed that no one was implementing the job-level NLO in
Get-Job responses.  So the job-level NLO was eliminated from the Get-
Jobs response.  This simplification makes all requests and responses
consistent in that the implicit natural language for any WithoutLanguage
'text' or 'name' form is always supplied in the request's or response's
"attributes-natural-language" operation attribute.



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3.1.3 Status codes returned by operation

This section corresponds to [IPP-MOD] section 3.1.6 "Operation Response
Status Codes and Status Messages".  This section lists all status codes
once in the first operation (Print-Job).  Then it lists the status codes
that are different or specialized for subsequent operations under each
operation.


3.1.3.1   Printer Operations


3.1.3.1.1 Print-Job


The Printer object MUST return one of the following "status-code" values
for the indicated reason.  Whether all of the document data has been
accepted or not before returning the success or error response depends
on implementation.  See Section 13 in [IPP-MOD] for a more complete
description of each status code.

For the following success status codes, the Job object has been created
and the "job-id", and "job-uri" assigned and returned in the response:

  successful-ok:  no request attributes were substituted or ignored.
  successful-ok-ignored-or-substituted-attributes:  some supplied (1)
     attributes were ignored or (2) unsupported attribute syntaxes or
     values were substituted with supported values or were ignored.
     Unsupported attributes, attribute syntax's, or values MUST be
     returned in the Unsupported Attributes group of the response.
  successful-ok-conflicting-attributes:  some supplied attribute values
     conflicted with the values of other supplied attributes and were
     either substituted or ignored.  Attributes or values which conflict
     with other attributes and have been substituted or ignored MUST be
     returned in the Unsupported Attributes group of the response as
     supplied by the client.


[ipp-mod] section 3.1.6 Operation Status Codes and Messages states:

If the Printer object supports the "status-message" operation attribute,
it SHOULD use the REQUIRED 'utf-8' charset to return a status message
for the following error status codes (see section 13 in [IPP-MOD]):
'client-error-bad-request', 'client-error-charset-not-supported',
'server-error-internal-error', 'server-error-operation-not-supported',
and 'server-error-version-not-supported'.  In this case, it MUST set the
value of the "attributes-charset" operation attribute to 'utf-8' in the
error response.




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For the following error status codes, no job is created and no "job-id"
or "job-uri" is returned:

  client-error-bad-request:  The request syntax does not conform to the
     specification.
  client-error-forbidden:  The request is being refused for
     authorization or authentication reasons.  The implementation
     security policy is to not reveal whether the failure is one of
     authentication or authorization.
  client-error-not-authenticated:  Either the request requires
     authentication information to be supplied or the authentication
     information is not sufficient for authorization.
  client-error-not-authorized:  The requester is not authorized to
     perform the request on the target object.
  client-error-not-possible:  The request cannot be carried out because
     of the state of the system.  See also 'server-error-not-accepting-
     jobs' status code, which MUST take precedence if the Printer
     object's "printer-accepting-jobs" attribute is 'false'.
  client-error-timeout:  not applicable.
  client-error-not-found:  the target object does not exist.
  client-error-gone:  the target object no longer exists and no
     forwarding address is known.
  client-error-request-entity-too-large:  the size of the request
     and/or print data exceeds the capacity of the IPP Printer to
     process it.
  client-error-request-value-too-long:  the size of request variable
     length attribute values, such as 'text' and 'name' attribute
     syntax's, exceed the maximum length specified in [IPP-MOD] for the
     attribute and MUST be returned in the Unsupported Attributes Group.
  client-error-document-format-not-supported:  the document format
     supplied is not supported.  The "document-format" attribute with
     the unsupported value MUST be returned in the Unsupported
     Attributes Group.  This error SHOULD take precedence over any other
     'xxx-not-supported' error, except 'client-error-charset-not-
     supported'.
  client-error-attributes-or-values-not-supported:  one or more
     supplied attributes, attribute syntax's, or values are not
     supported and the client supplied the "ipp-attributes-fidelity"
     operation attribute with a 'true' value.  They MUST be returned in
     the Unsupported Attributes Group as explained below.
  client-error-uri-scheme-not-supported:  not applicable.
  client-error-charset-not-supported:  the charset supplied in the
     "attributes-charset" operation attribute is not supported.  The
     Printer's "configured-charset" MUST be returned in the response as
     the value of the "attributes-charset" operation attribute and used
     for any 'text' and 'name' attributes returned in the error
     response.  This error SHOULD take precedence over any other error,



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     unless the request syntax is so bad that the client's supplied
     "attributes-charset" cannot be determined.
  client-error-conflicting-attributes:  one or more supplied attribute
     values conflicted with each other and the client supplied the "ipp-
     attributes-fidelity" operation attribute with a 'true' value.  They
     MUST be returned in the Unsupported Attributes Group as explained
     below.
  server-error-internal-error:  an unexpected condition prevents the
     request from being fulfilled.
  server-error-operation-not-supported:  not applicable (since Print-
     Job is REQUIRED).
  server-error-service-unavailable:  the service is temporarily
     overloaded.
  server-error-version-not-supported:  the version in the request is
     not supported.  The "closest" version number supported MUST be
     returned in the response.
  server-error-device-error:  a device error occurred while receiving
     or spooling the request or document data or the IPP Printer object
     can only accept one job at a time.
  server-error-temporary-error:  a temporary error such as a buffer
     full write error, a memory overflow, or a disk full condition
     occurred while receiving the request and/or the document data.
  server-error-not-accepting-jobs:  the Printer object's "printer-is-
     not-accepting-jobs" attribute is 'false'.
  server-error-busy:  the Printer is too busy processing jobs to accept
     another job at this time.
  server-error-job-canceled:  the job has been canceled by an operator
     or the system while the client was transmitting the document data.

3.1.3.1.2 Print-URI


All of the Print-Job status codes described in Section 3.1.3.1.1 Print-
Job Response are applicable to Print-URI with the following
specializations and differences.  See Section 14 for a more complete
description of each status code.

  client-error-uri-scheme-not-supported:  the URI scheme supplied in
     the "document-uri" operation attribute is not supported and is
     returned in the Unsupported Attributes group.
  server-error-operation-not-supported: the Print-URI operation is not
     supported.


3.1.3.1.3 Validate-Job





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All of the Print-Job status codes described in Section 3.1.3.1.1 Print-
Job Response are applicable to Validate-Job.  See Section 13 in [IPP-
MOD] for a more complete description of each status code.


3.1.3.1.4 Create-Job


All of the Print-Job status codes described in Section 3.1.3.1.1 Print-
Job Response are applicable to Create-Job with the following
specializations and differences.  See Section 13 in [IPP-MOD] for a more
complete description of each status code.

  server-error-operation-not-supported:  the Create-Job operation is
     not supported.
  client-error-multiple-document-jobs-not-supported: while the Create-
     Job and Send-Document operations are supported, this implementation
     doesn't support more than one document with data.

3.1.3.1.5 Get-Printer-Attributes


All of the Print-Job status codes described in Section 3.1.3.1.1 Print-
Job Response are applicable to the Get-Printer-Attributes operation with
the following specialization's and differences.   See Section 13 in
[IPP-MOD] for a more complete description of each status code.

For the following success status codes, the requested attributes are
returned in Group 3 in the response:

  successful-ok:  no request attributes were substituted or ignored
     (same as Print-Job) and no requested attributes were unsupported.
  successful-ok-ignored-or-substituted-attributes:   same as Print-Job,
     except the "requested-attributes" operation attribute MAY, but NEED
     NOT, be returned with the unsupported values.
  successful-ok-conflicting-attributes:  same as Print-Job.

For the error status codes, Group 3 is returned containing no attributes
or is not returned at all:

  client-error-not-possible:  Same as Print-Job, in addition the
     Printer object is not accepting any requests.
  client-error-request-entity-too-large:  same as Print-job, except
     that no print data is involved.
  client-error-attributes-or-values-not-supported:  not applicable,
     since unsupported operation attributes MUST be ignored and
     'successful-ok-ignored-or-substituted-attributes' returned.
  client-error-conflicting-attributes:  same as Print-Job, except that
     "ipp-attribute-fidelity" is not involved.
  server-error-operation-not-supported:  not applicable (since Get-
     Printer-Attributes is REQUIRED).


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  server-error-device-error:  same as Print-Job, except that no
     document data is involved.
  server-error-temporary-error:  same as Print-Job, except that no
     document data is involved.
  server-error-not-accepting-jobs:  not applicable..
  server-error-busy:  same as Print-Job, except the IPP object is too
     busy to accept even query requests.
  server-error-job-canceled:  not applicable..

3.1.3.1.6 Get-Jobs


All of the Print-Job status codes described in Section 3.1.3.1.1 Print-
Job Response are applicable to the Get-Jobs operation with the following
specialization's and differences.   See Section 13 in [IPP-MOD] for a
more complete description of each status code.

For the following success status codes, the requested attributes are
returned in Group 3 in the response:

  successful-ok:  no request attributes were substituted or ignored
     (same as Print-Job) and no requested attributes were unsupported.
  successful-ok-ignored-or-substituted-attributes:   same as Print-Job,
     except the "requested-attributes" operation attribute MAY, but NEED
     NOT, be returned with the unsupported values.
  successful-ok-conflicting-attributes:  same as Print-Job.

For any error status codes, Group 3 is returned containing no attributes
or is not returned at all.  The following brief error status code
descriptions contain unique information for use with Get-Jobs operation.
See section 14 for the other error status codes that apply uniformly to
all operations:

  client-error-not-possible:  Same as Print-Job, in addition the
     Printer object is not accepting any requests.
  client-error-request-entity-too-large:  same as Print-job, except
     that no print data is involved.
  client-error-document-format-not-supported:  not applicable.
  client-error-attributes-or-values-not-supported:  not applicable,
     since unsupported operation attributes MUST be ignored and
     'successful-ok-ignored-or-substituted-attributes' returned.
  client-error-conflicting-attributes:  same as Print-Job, except that
     "ipp-attribute-fidelity" is not involved.
  server-error-operation-not-supported:  not applicable (since Get-Jobs
     is REQUIRED).
  server-error-device-error:  same as Print-Job, except that no
     document data is involved.
  server-error-temporary-error:  same as Print-Job, except that no
     document data is involved.
  server-error-not-accepting-jobs:  not applicable.

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  server-error-job-canceled:  not applicable.

3.1.3.1.7 Pause-Printer


All of the Print-Job status codes described in Section 3.1.3.1.1 Print-
Job Response are applicable to Pause-Printer with the following
specializations and differences.  See Section 13 in [IPP-MOD] for a more
complete description of each status code.

For the following success status codes, the Printer object is being
stopped from scheduling jobs on all its devices.

  successful-ok:  no request attributes were substituted or ignored
     (same as Print-Job).
  successful-ok-ignored-or-substituted-attributes:   same as Print-Job.
  successful-ok-conflicting-attributes:  same as Print-Job.


For any of the error status codes, the Printer object has not been
stopped from scheduling jobs on all its devices.

  client-error-not-possible: not applicable.
  client-error-not-found:  the target Printer object does not exist.
  client-error-gone:  the target Printer object no longer exists and no
     forwarding address is known.
  client-error-request-entity-too-large:  same as Print-Job, except no
     document data is involved.
  client-error-document-format-not-supported:  not applicable.
  client-error-conflicting-attributes:  same as Print-Job, except that
     the Printer's "printer-is-accepting-jobs" attribute is not
     involved.
  server-error-operation-not-supported: the Pause-Printer operation is
     not supported.
  server-error-device-error: not applicable.
  server-error-temporary-error:  same as Print-Job, except no document
     data is involved.
  server-error-not-accepting-jobs:  not applicable.
  server-error-job-canceled:  not applicable.

3.1.3.1.8 Resume-Printer


All of the Print-Job status code descriptions in Section 3.1.3.1.1
Print-Job Response with the specialization's described for Pause-Printer
are applicable to Resume-Printer.  See Section 13 in [IPP-MOD] for a
more complete description of each status code.

For the following success status codes, the Printer object resumes
scheduling jobs on all its devices.


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  successful-ok:  no request attributes were substituted or ignored
     (same as Print-Job).
  successful-ok-ignored-or-substituted-attributes:   same as Print-Job.
  successful-ok-conflicting-attributes:  same as Print-Job.

For any of the error status codes, the Printer object does not resume
scheduling jobs.

  server-error-operation-not-supported: the Resume-Printer operation is
     not supported.


3.1.3.1.8.1 What about Printers unable to change state due to an error
        condition?

If, in case, the IPP printer is unable to change its state due to some
problem with the actual printer device (say, it is shut down or there is
a media-jam as indicated in [ipp-mod]), what should be the result of the
"Resume-printer" operation?  Should it still change the 'printer-state-
reasons' and return success or should it fail ?

The 'resume-printer' operation must clear the 'paused' or 'moving-to-
paused' 'printer-state-message'.  The operation must return a
'successful-ok' status code.


3.1.3.1.8.2 How is 'printer-state' handled on Resume-Printer?



If "Resume-Printer" succeeds, what should be the value of 'Printer-
state' and  who should take care of the 'Printer-state' later on ?

The "Resume-Printer" operation may change the "printer-state-reasons"
value.

The "printer-state" will change to one of three states:

  1. 'idle' - no additional jobs and no error conditions present

  2. 'processing' - job available and no error conditions present

  3. current state (i.e. no change) an error condition is present  (e.g.
     media jam)

 In the third case the 'printer-state-reason' will be cleared by
automata when it detects the error condition no longer exists.  The
'printer-state' will move to 'idle' or 'processing' when conditions
permit. (i.e. no more error conditions)


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3.1.3.1.9 Purge-Printer


All of the Print-Job status code descriptions in Section 3.1.3.1.1
Print-Job Response with the specialization's described for Pause-Printer
are applicable to Purge-Printer.  See Section 13 in [IPP-MOD] for a more
complete description of each status code.

For the following success status codes, the Printer object purges all
it's jobs.

  successful-ok:  no request attributes were substituted or ignored
     (same as Print-Job).
  successful-ok-ignored-or-substituted-attributes:   same as Print-Job.
  successful-ok-conflicting-attributes:  same as Print-Job.

For any of the error status codes, the Printer object does not purge any
jobs.

  server-error-operation-not-supported: the Purge-Printer operation is
     not supported.

3.1.3.2   Job Operations


3.1.3.2.1 Send-Document


All of the Print-Job status codes described in Section 3.1.3.1.1 Print-
Job Response are applicable to the Get-Printer-Attributes operation with
the following specialization's and differences.   See Section 13 in
[IPP-MOD] for a more complete description of each status code.

For the following success status codes, the document has been added to
the specified Job object and the job's "number-of-documents" attribute
has been incremented:

  successful-ok:  no request attributes were substituted or ignored
     (same as Print-Job).
  successful-ok-ignored-or-substituted-attributes:  same as Print-Job.
  successful-ok-conflicting-attributes:  same as Print-Job.

For the error status codes, no document has been added to the Job object
and the job's "number-of-documents" attribute has not been incremented:

  client-error-not-possible: Same as Print-Job, except that the
     Printer's "printer-is-accepting-jobs" attribute is not involved, so
     that the client is able to finish submitting a job that was created
     with a Create-Job operation after this attribute has been set to
     'true'.  Another condition is that the state of the job precludes
     Send-Document, i.e., the job has already been closed out by the
     client.  However, if the IPP Printer closed out the job due to


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     timeout, the 'client-error-timeout' error status SHOULD  be
     returned instead.
  client-error-timeout:  This request was sent after the Printer closed
     the job, because it has not received a Send-Document or Send-URI
     operation within the Printer's "multiple-operation-time-out" period
     .
  client-error-request-entity-too-large:  same as Print-Job.
  client-error-conflicting-attributes:  same as Print-Job, except that
     "ipp-attributes-fidelity" operation attribute is not involved..
  server-error-operation-not-supported:  the Send-Document request is
     not supported.
  server-error-not-accepting-jobs:  not applicable.
  server-error-job-canceled:  the job has been canceled by an operator
     or the system while the client was transmitting the data.

3.1.3.2.2 Send-URI


All of the Print-Job status code descriptions in Section 3.1.3.1.1
Print-Job Response with the specialization's described for Send-Document
are applicable to Send-URI.  See Section 13 in [IPP-MOD] for a more
complete description of each status code.

  client-error-uri-scheme-not-supported:  the URI scheme supplied in
     the "document-uri" operation attribute is not supported and the
     "document-uri" attribute MUST be returned in the Unsupported
     Attributes group.
  server-error-operation-not-supported: the Send-URI operation is not
     supported.


3.1.3.2.3 Cancel-Job


All of the Print-Job status codes described in Section 3.1.3.1.1 Print-
Job Response are applicable to Cancel-Job with the following
specializations and differences.  See Section 13 in [IPP-MOD] for a more
complete description of each status code.

For the following success status codes, the Job object is being canceled
or has been canceled:

  successful-ok:  no request attributes were substituted or ignored
     (same as Print-Job).
  successful-ok-ignored-or-substituted-attributes:   same as Print-Job.
  successful-ok-conflicting-attributes:  same as Print-Job.


For any of the error status codes, the Job object has not been canceled
or was previously canceled.


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  client-error-not-possible:  The request cannot be carried out because
     of the state of the Job object ('completed', 'canceled', or
     'aborted') or the state of the system.
  client-error-not-found:  the target Printer and/or Job object does
     not exist.
  client-error-gone:  the target Printer and/or Job object no longer
     exists and no forwarding address is known.
  client-error-request-entity-too-large:  same as Print-Job, except no
     document data is involved.
  client-error-document-format-not-supported:  not applicable.
  client-error-attributes-or-values-not-supported:  not applicable,
     since unsupported operation attributes and values MUST be ignored.
  client-error-conflicting-attributes:  same as Print-Job, except that
     the Printer's "printer-is-accepting-jobs" attribute is not
     involved.
  server-error-operation-not-supported:  not applicable (Cancel-Job is
     REQUIRED).
  server-error-device-error:  same as Print-Job, except no document
     data is involved.
  server-error-temporary-error:  same as Print-Job, except no document
     data is involved.
  server-error-not-accepting-jobs:  not applicable..
  server-error-job-canceled:  not applicable.

3.1.3.2.4 Get-Job-Attributes


All of the Print-Job status codes described in Section 3.1.3.1.1 Print-
Job Response are applicable to Get-Job-Attributes with the following
specializations and differences.  See Section 13 in [IPP-MOD] for a more
complete description of each status code.

For the following success status codes, the requested attributes are
returned in Group 3 in the response:

  successful-ok:  no request attributes were substituted or ignored
     (same as Print-Job) and no requested attributes were unsupported.
  successful-ok-ignored-or-substituted-attributes:   same as Print-Job,
     except the "requested-attributes" operation attribute MAY, but NEED
     NOT, be returned with the unsupported values.
  successful-ok-conflicting-attributes:  same as Print-Job.

For the error status codes, Group 3 is returned containing no attributes
or is not returned at all.

  client-error-not-possible:  Same as Print-Job, in addition the
     Printer object is not accepting any requests.
  client-error-document-format-not-supported:  not applicable.
  client-error-attributes-or-values-not-supported:  not applicable.
  client-error-uri-scheme-not-supported:  not applicable.

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  client-error-conflicting-attributes:  not applicable
  server-error-operation-not-supported:  not applicable (since Get-Job-
     Attributes is REQUIRED).
  server-error-device-error:  same as Print-Job, except no document
     data is involved.
  server-error-temporary-error:  sane as Print-Job, except no document
     data is involved..
  server-error-not-accepting-jobs:  not applicable.
  server-error-job-canceled:  not applicable.

3.1.3.2.5 Hold-Job


All of the Print-Job status codes described in Section 3.1.3.1.1 Print-
Job Response are applicable to Hold-Job with the following
specializations and differences.  See Section 13 in [IPP-MOD] for a more
complete description of each status code.

For the following success status codes, the Job object is being held or
has been held:

  successful-ok:  no request attributes were substituted or ignored
     (same as Print-Job).
  successful-ok-ignored-or-substituted-attributes:   same as Print-Job.
  successful-ok-conflicting-attributes:  same as Print-Job.


For any of the error status codes, the Job object has not been held or
was previously held.

  client-error-not-possible:  The request cannot be carried out because
     of the state of the Job object ('completed', 'canceled', or
     'aborted') or the state of the system.
  client-error-not-found:  the target Printer and/or Job object does
     not exist.
  client-error-gone:  the target Printer and/or Job object no longer
     exists and no forwarding address is known.
  client-error-request-entity-too-large:  same as Print-Job, except no
     document data is involved.
  client-error-document-format-not-supported:  not applicable.
  client-error-conflicting-attributes:  same as Print-Job, except that
     the Printer's "printer-is-accepting-jobs" attribute is not
     involved.
  server-error-operation-not-supported: the Hold-Job operation is not
     supported.
  server-error-device-error: not applicable.
  server-error-temporary-error:  same as Print-Job, except no document
     data is involved.
  server-error-not-accepting-jobs:  not applicable.
  server-error-job-canceled:  not applicable.

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3.1.3.2.6 Release-Job


All of the Print-Job status code descriptions in Section 3.1.3.1.1
Print-Job Response with the specialization's described for Hold-Job are
applicable to Release-Job.  See Section 13 in [IPP-MOD] for a more
complete description of each status code.

  server-error-operation-not-supported: the Release-Job operation is
     not supported.

3.1.3.2.7 Restart-Job


All of the Print-Job status code descriptions in Section 3.1.3.1.1
Print-Job Response with the specialization's described for Hold-Job are
applicable to Restart-Job.  See Section 13 in [IPP-MOD] for a more
complete description of each status code.

  server-error-operation-not-supported: the Restart-Job operation is
     not supported.


3.1.3.2.7.1 Can documents be added to a restarted job?

Assume I give a Create-Job request along with a set of 5 documents . All
the documents get printed and the job state is moved to completed . I
issue a Restart-Job request on the job. Now the issue is that, if  I try
to  add new documents to the restarted job, will the IPP Server permit
me to do so or  return "client-error-not-possible " and again print
those 5 jobs?

A job can not move to the 'completed' state until all the documents have
been processed.  The 'last-document' flag indicates when the last
document for a job is being sent from the client.  This is the semantic
equivalent of closing a job.  No documents may be added once a job is
closed. Section 3.3.7 of the IPP/1.1 model states "The job is moved to
the 'pending' job state and restarts the beginning on the same IPP
Printer object with the same attribute values." 'number-of-documents' is
a job attribute.




3.1.4 Returning unsupported attributes in Get-Xxxx responses (Issue
      1.18)

In the Get-Printer-Attributes, Get-Jobs, or Get-Job-Attributes
responses, the client cannot depend on getting unsupported attributes
returned in the Unsupported Attributes group that the client requested,


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but are not supported by the IPP object.  However, such unsupported
requested attributes will not be returned in the Job Attributes or
Printer Attributes group (since they are unsupported).  Furthermore, the
IPP object is REQUIRED to return the 'successful-ok-ignored-or-
substituted-attributes' status code, so that the client knows that not
all that was requested has been returned.


3.1.5 Sending empty attribute groups

The [IPP-MOD] and [IPP-PRO] specifications RECOMMEND that a sender not
send an empty attribute group in a request or a response.  However, they
REQUIRE a receiver to accept an empty attribute group as equivalent to
the omission of that group.  So a client SHOULD omit the Job Template
Attributes group entirely in a create operation that is not supplying
any Job Template attributes.  Similarly, an IPP object SHOULD omit an
empty Unsupported Attributes group if there are no unsupported
attributes to be returned in a response.

The [IPP-PRO] specification REQUIRES a receiver to be able to receive
either an empty attribute group or an omitted attribute group and treat
them equivalently.  The term "receiver" means an IPP object for a
request and a client for a response.  The term "sender' means a client
for a request and an IPP object for a response.

There is an exception to the rule for Get-Jobs when there are no
attributes to be returned.  [IPP-PRO] contains the following paragraph:

The syntax allows an xxx-attributes-tag to be present when the xxx-
attribute-sequence that follows is empty. The syntax is defined this way
to allow for the response of Get-Jobs where no attributes are returned
for some job-objects.  Although it is RECOMMENDED that the sender not
send an xxx-attributes-tag if there are no attributes (except in the
Get-Jobs response just mentioned), the receiver MUST be able to decode
such syntax.


3.2 Printer Operations


3.2.1 Print-Job operation


3.2.1.1   Flow controlling the data portion of a Print-Job request
      (Issue 1.22)

A paused printer, or one that is stopped due to paper out or jam or
spool space full or buffer space full, may flow control the data of a
Print-Job operation (at the TCP/IP layer), so that the client is not


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able to send all the document data.  Consequently, the Printer will not
return a response until the condition is changed.

The Printer should not return a Print-Job response with an error code in
any of these conditions, since either the printer will be resumed and/or
the condition will be freed either by human intervention or as jobs
print.

In writing test scripts to test IPP Printers, the script must also be
written not to expect a response, if the printer has been paused, until
the printer is resumed, in order to work with all possible
implementations.


3.2.1.2   Returning job-state in Print-Job response (Issue 1.30)

An IPP client submits a small job via Print-Job.  By the time the IPP
printer/print server is putting together a response to the operation,
the job has finished printing and been removed as an object from the
print system.  What should the job-state be in the response?

The Model suggests that the Printer return a response before it even
accepts the document content.  The Job Object Attributes are returned
only if the IPP object returns one of the success status codes. Then the
job-state would always be "pending" or "pending-held".

This issue comes up for the implementation of an IPP Printer object as a
server that forwards jobs to devices that do not provide job status back
to the server.  If the server is reasonably certain that the job
completed successfully, then it should return the job-state as
'completed'.  Also the server can keep the job in its "job history" long
after the job is no longer in the device.  Then a user could query the
server and see that the job was in the 'completed' state and completed
as specified by the jobs "time-at-completed" time, which would be the
same as the server submitted the job to the device.

An alternative is for the server to respond to the client before or
while sending the job to the device, instead of waiting until the server
has finished sending the job to the device.  In this case, the server
can return the job's state as 'pending' with the 'job-outgoing' value in
the job's "job-state-reasons" attribute.

If the server doesn't know for sure whether the job completed
successfully (or at all), it could return the (out-of-band) 'unknown'
value.

On the other hand, if the server is able to query the device and/or
setup some sort of event notification that the device initiates when the
job makes state transitions, then the server can return the current job

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state in the Print-Job response and in subsequent queries because the
server knows what the job state is in the device (or can query the
device).

All of these alternatives depend on implementation of the server and the
device.


3.2.2 Get-Printer-Attributes operation

If a Printer supports the "printer-make-and-model" attribute and returns
the .INF file model name of the printer in that attribute, the Microsoft
client will automatically install the correct driver (if available).

Clients which poll periodically for printer status or queued-job-count
should use the "requested-attributes" operation attribute  to limit the
scope of the query in order to save Printer and network resources.


3.2.3 Get-Jobs operation


3.2.3.1   Get-Jobs, my-jobs='true', and 'requesting-user-name' (Issue
      1.39)?

In [IPP-MOD] section 3.2.6.1 'Get-Jobs Request', if the attribute 'my-
jobs' is present and set to TRUE, MUST the 'requesting-user-name'
attribute be there too, and if it's not present what should the IPP
printer do?

[IPP-MOD] Section 8.3 describes the various cases of "requesting-user-
name" being present or not for any operation.  If the client does not
supply a value for "requesting-user-name", the printer MUST assume that
the client is supplying some anonymous name, such as "anonymous".


3.2.3.2   Why is there a "limit" attribute in the Get-Jobs operation?

When using the Get-Jobs operation a client implementer might choose to
limit the number of jobs that the client shows on the first screenful.
For example, if its UI can only display 50 jobs, it can defend itself
against a printer that would otherwise return 500 jobs, perhaps taking a
long time on a slow dial-up line. The client can then go and ask for a
larger number of jobs in the background, while showing the user the
first 50 jobs. Since the job history is returned in reverse order,
namely the most recently completed jobs are returned first, the user is
most likely interested in the first jobs that are returned. Limiting the
number of jobs may be especially useful for a client that is requesting
'completed' jobs from a printer that keeps a long job history. Clients


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that don't mind sometimes getting very large responses, can omit the
"limit" attribute in their Get-Jobs requests.


3.2.4 Create-Job operation

A Printer may respond to a Create-Job operation with "job-state"
'pending' or 'pending-held' and " job-state-reason" 'job-data-
insufficient' to indicate that operation has been accepted by the
Printer, but the Printer is expecting additional document data before it
can move the job into the 'processing' state.  Alternatively, it may
respond with "job-state" 'processing' and "job-state-reason" 'job-
incoming'  to indicate that the Create-Job operation has been accepted
by the Printer, but the Printer is expecting additional Send-Document
and/or Send-URI operations and/or is accessing/accepting document data.
The second alternative is for non-spooling Printers that don't implement
the 'pending' state.


Should the server wait for the "last-document" operation attribute set
to 'true' before starting to "process" the job?

It depends on implementation. Some servers spool the entire job,
including all document data, before starting to process, so such an
implementation would wait for the "last-document" before starting to
process the job. If the time-out occurs without the "last-document",
then the server takes one of the indicated actions in section 3.3.1 in
the [IPP-MOD] document. Other servers will start to process document
data as soon as they have some. These are the so-called "non-spooling"
printers. Currently, there isn't a way for a client to determine whether
the Printer will spool all the data or will start to process (and print)
as soon as it has some data.


3.3 Job Operations


3.3.1 Validate-Job

The Validate-Job operation has been designed so that its implementation
may be a part of the Print-Job operation.  Therefore, requiring
Validate-Job is not a burden on implementers.  Also it is useful for
client's to be able to count on its presence in all conformance
implementations, so that the client can determine before sending a long
document, whether the job will be accepted by the IPP Printer or not.


3.3.2  Restart-Job




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The Restart-Job operation allows the reprocessing of a completed job.
Some jobs store the document data on the printer.  Jobs created using
the Print-Job operation are an example.  It is required that the printer
retains the job data after the job has moved to a 'completed state' in
order for the Restart-Job operation to succeed.

Some jobs contain only a reference to the job data.  A job created using
the Print-URI is an example of such a job.  When the Restart-Job
operation is issued the job is reprocessed. The job data MUST be
retrieved again to print the job.

It is possible that a job fails while attempting to access the print
data.  When such a job is the target of a Restart-Job  the Printer SHALL
attempt to retrieve the job data again.


4  Object Attributes


4.1 Attribute Syntax's


4.1.1 The 'none' value for empty sets (Issue 1.37)

[IPP-MOD] states that the 'none' value should be used as the value of a
1setOf when the set is empty. In most cases, sets that are potentially
empty contain keywords so the keyword 'none' is used, but for the 3
finishings attributes, the values are enums and thus the empty set is
represented by the enum 3.  Currently there are no other attributes with
1setOf values, which can be empty and can contain values that are not
keywords.  This exception requires special code and is a potential place
for bugs.  It would have been better if we had chosen an out-of-band
value, either "no-value" or some new value, such as 'none'.  Since we
didn't, implementations have to deal with the different representations
of 'none', depending on the attribute syntax.


4.1.2 Multi-valued attributes (Issue 1.31)

What is the attribute syntax for a multi-valued attribute?  Since some
attributes support values in more than one data type, such as "media",
"job-hold-until", and "job-sheets", IPP semantics associate the
attribute syntax with each value, not with the attribute as a whole.
The protocol associates the attribute syntax tag with each value.  Don't
be fooled, just because the attribute syntax tag comes before the
attribute keyword.  All attribute values after the first have a zero
length attribute keyword as the indication of a subsequent value of the
same attribute.



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4.1.3 Case Sensitivity in URIs (issue 1.6)

IPP client and server implementations must be aware of the diverse
uppercase/lowercase nature of URIs.  RFC 2396 defines URL schemes and
Host names as case insensitive but reminds us that the rest of the URL
may well demonstrate case sensitivity.  When creating URL's for fields
where the choice is completely arbitrary, it is probably best to select
lower case.  However, this cannot be guaranteed and implementations MUST
NOT rely on any fields being case-sensitive or case-insensitive in the
URL beyond the URL scheme and host name fields.

The reason that the IPP specification does not make any restrictions on
URIs, is so that implementations of IPP may use off-the-shelf components
that conform to the standards that define URIs, such as RFC 2396 and the
HTTP/1.1 specifications [RFC2616].  See these specifications for rules
of matching, comparison, and case-sensitivity.

It is also recommended that System Administrators and implementations
avoid creating URLs for different printers that differ only in their
case.  For example, don't have Printer1 and printer1 as two different
IPP Printers.

Example of equivalent URI's

     http://abc.com:80/~smith/home.html

     http://ABC.com/%7Esmith/home.html

     http:/ABC.com:/%7esmith/home.html

Example of equivalent URI's using the IPP scheme

     ipp://abc.com:631/~smith/home.html

     ipp://ABC.com/%7Esmith/home.html

     http:/ABC.com:631/%7esmith/home.html

The HTTP/1.1 specification [RFC2616] contains more details on comparing
URLs.


4.1.4 Maximum length for xxxWithLanguage and xxxWithoutLanguage

The 'textWithLanguage' and 'nameWithLanguage' are compound syntaxes that
have two components.  The first component is the 'language' component
that can contain up to 63 octets.  The second component is the 'text' or
'name' component.  The maximum length of these are 1023 octets and 255


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octets respectively.  The definition of attributes with either syntax
may further restrict the length.  (e.g. printer-name (name(127)))

The length of the 'language' component has no effect on the allowable
length of 'text' in 'textWithLanguage' or the length of 'name' in
'nameWithLanguage'


4.2 Job Template Attributes


4.2.1 multiple-document-handling(type2 keyword)


4.2.1.1   Support of multiple document jobs

IPP/1.0 is silent on which of the four effects an implementation would
perform if it supports Create-Job, but does not support "multiple-
document-handling" or multiple documents per job.  IPP/1.1 was changed
so that a Printer could support Create-Job without having to support
multiple document jobs.  The "multiple-document-jobs-supported"
(boolean) Printer description attribute was added to IPP/1.1 along with
the 'server-error-multiple-document-jobs-not-supported' status code for
a Printer to indicate whether or not it supports multiple document jobs,
when it supports the Create-Job operation.  Also IPP/1.1 was clarified
that the Printer MUST support the "multiple-document-handling" (type2
keyword) Job Template attribute with at least one value if the Printer
supports multiple documents per job.


4.3 Job Description Attributes

The time-at-creation,  time-at-processing, and time-at-completed
attributes may be returned  in integer time ticks or absolute dateTime
syntax.    There are various ways for a Printer to get the time of day.
Some suggestions:

     1.   A Printer can get time from an NTP timeserver if there's one
     reachable on the network .  See RFC 1305.  Also DHCP option 32 in
     RFC 2132 returns the IP address of the NTP server.

     2.   Get the date and time at startup from a human operator

     3.   Have an operator set the date and time using a web
     administrative interface

     4.   Get the date and time from incoming HTTP requests, though the
     problems of spoofing need to be considered.  Perhaps comparing
     several HTTP requests could reduce the chances of spoofing.


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     5.   Internal date time clock battery driven.

     6.   Query "http://tycho.usno.navy.mil/cgi-bin/timer.pl"


4.4 Printer Description Attributes


4.4.1 queued-job-count


4.4.1.1   Why is "queued-job-count" RECOMMENDED (Issue 1.14)?

The reason that "queued-job-count" is RECOMMENDED, is that some clients
look at that attribute alone when summarizing the status of a list of
printers, instead of doing a Get-Jobs to determine the number of jobs in
the queue.  Implementations that fail to support the "queued-job-count"
will cause that client to display 0 jobs when there are actually queued
jobs.

We would have made it a REQUIRED Printer attribute, but some
implementations had already been completed before the issue was raised,
so making it a SHOULD was a compromise.


4.4.1.2   Is "queued-job-count" a good measure of how busy a printer is
      (Issue 1.15)?

The "queued-job-count" is not a good measure of how busy the printer is
when there are held jobs.  A future registration could be to add a
"held-job-count" (or an "active-job-count") Printer Description
attribute if experience shows that such an attribute (combination) is
needed to quickly indicate how busy a printer really is.


4.4.2 printer-current-time (dateTime)

A Printer implementation MAY support this attribute by obtaining the
date and time by any number of implementation-dependent means at startup
or subsequently.  Examples include:

  1. an internal date time clock,

  2. from the operator at startup using the console,

  3. from an operator using an administrative web page,

  4. from HTTP headers supplied in client requests,



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  5. use HTTP to query "http://tycho.usno.navy.mil/cgi-bin/timer.pl"

  6. from the network, using NTP [RFC1305] or DHCP option 32 [RFC2132]
     that returns the IP address of the NTP server.

If an implementation supports this attribute by obtaining the current
time from the network (at startup or later), but the time is not
available, then the implementation MUST return the value of this
attribute using the out-of-band 'no-value' meaning not configured.  See
the beginning of section 4.1.

Since the new "date-and-time-at-xxx" Job Description attributes refer to
the "printer-current-time", they will be covered also.


4.4.3 'Printer-uri

Must the operational attribute for printer-uri match one of the values
in printer-uri-supported?

A forgiving printer implementation would not reject the operation. But
the implementation has its rights to reject a printer or job operation
if the operational attribute printer-uri is not a value of the printer-
uri-supported. The printer may not be improperly configured. The request
obviously reached the printer. The printer could treat the printer-uri
as the logical equivalent of a value in the printer-uri-supported. It
would be implementation dependent for which value, and associated
security policy, would apply. This does also apply to a job object
specified with a printer-uri and job-id, or with a job-uri. See section
4.1.3 for how to compare URI's.


4.5 Empty Jobs


The IPP object model does not prohibit a job that contains no documents.
Such a job may be created in a number of ways including a 'create-job'
followed by an 'add-document' that contains no data and has the 'last-
document' flag set.

An empty job is processed just as any other job.  The operation that
"closes" an empty job is not rejected because the job is empty.  If no
other conditions exist, other than the job is empty, the response to the
operation will indicate success.  After the job is scheduled and
processed, the job state SHALL be 'completed'

There will be some variation in the value(s) of the 'job-state-reasons'
attribute.  It is required that if no conditions, other than the job
being empty, exist the 'job-state-reasons' SHALL include the 'completed-


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successfully'.  If other conditions existed, the 'completed-with-
warnings' or 'completed-with-errors' values may be used."


5  Directory Considerations


5.1 General Directory Schema Considerations


The [ipp-mod] document lists RECOMMENDED and OPTIONAL Printer object
attributes for directory schemas.  See [ipp-mod] APPENDIX E: Generic
Directory Schema.

The SLP printer template is defined in the "Definition of the Printer
Abstract Service Type v2.0" document [svrloc-printer].  The LDAP printer
template is defined in the "Internet Printing Protocol (IPP): LDAP
Schema for Printer Services" document [ldap-printer].  Both documents
systematically add "printer-" to any attribute that doesn't already
start with "printer-" in order to keep the printer directory attributes
distinct from other directory attributes.  Also, instead of using
"printer-uri-supported", "uri-authentication-supported", and "uri-
security-supported", they use a "printer-xri-supported" attribute with
special syntax to contain all of the same information in a single
attribute.


5.2 IPP Printer with a DNS name


If the IPP printer has a DNS name should there be at least two values
for the printer-uri-supported attribute. One URL with the fully
qualified DNS name the other with the IP address in the URL?

The printer may contain one or the other or both. It's up to the
administrator to configure this attribute.


6  Security Considerations

This section corresponds to the IPP-MOD Section 8 "Security
Considerations.


6.1 Querying jobs with IPP that were submitted using other job
    submission protocols (Issue 1.32)


The following clarification was added to [IPP-MOD] section 8.5:

     8.5 Queries on jobs submitted using non-IPP protocols



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If the device that an IPP Printer is representing is able to accept jobs
using other job submission protocols in addition to IPP, it is RECOMMEND
that such an implementation at least allow such "foreign" jobs to be
queried using Get-Jobs returning "job-id" and "job-uri" as 'unknown'.
Such an implementation NEED NOT support all of the same IPP job
attributes as for IPP jobs.  The IPP object returns the 'unknown' out-
of-band value for any requested attribute of a foreign job that is
supported for IPP jobs, but not for foreign jobs.

It is further RECOMMENDED, that the IPP Printer generate "job-id" and
"job-uri" values for such "foreign jobs", if possible, so that they may
be targets of other IPP operations, such as Get-Job-Attributes and
Cancel-Job.  Such an implementation also needs to deal with the problem
of authentication of such foreign jobs.  One approach would be to treat
all such foreign jobs as belonging to users other than the user of the
IPP client.  Another approach would be for the foreign job to belong to
'anonymous'.  Only if the IPP client has been authenticated as an
operator or administrator of the IPP Printer object, could the foreign
jobs be queried by an IPP request.  Alternatively, if the security
policy were to allow users to query other users' jobs, then the foreign
jobs would also be visible to an end-user IPP client using Get-Jobs and
Get-Job-Attributes.

Thus IPP MAY be implemented as a "universal" protocol that provides
access to jobs submitted with any job submission protocol.  As IPP
becomes widely implemented, providing a more universal access makes
sense.


7  Encoding and Transport

This section discusses various aspects of IPP/1.1 Encoding and Transport
[IPP-PRO].

A server is not required to send a response until after it has received
the client's entire request.  Hence, a client must not expect a response
until after it has sent the entire request.  However, we recommend that
the server return a response as soon as possible if an error is detected
while the client is still sending the data, rather than waiting until
all of the data is received.  Therefore, we also recommend that a client
listen for an error response that an IPP server MAY send before it
receives all the data.  In this case a client, if chunking the data, can
send a premature zero-length chunk to end the request before sending all
the data (and so the client can keep the connection open for other
requests, rather than closing it). If the request is blocked for some
reason, a client MAY determine the reason by opening another connection
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IPP, by design, uses TCP's built-in flow control mechanisms [RFC 793] to
throttle clients when Printers are busy.  Therefore, it is perfectly
normal for an IPP client transmitting a Job to be blocked for a really
long time.  Accordingly, socket timeouts must be avoided.  Some socket
implementations have a timeout option, which specifies how long a write
operation on a socket can be blocked before it times out and the
blocking ends.  A client should set this option for infinite timeout
when transmitting Job submissions.

Some IPP client applications might be able to perform other useful work
while a Job transmission is blocked.  For example, the client may have
other jobs that it could transmit to other Printers simultaneously.  A
client may have a GUI, which must remain responsive to the user while
the Job transmission is blocked.  These clients should be designed to
spawn a thread to handle the Job transmission at its own pace, leaving
the main application free to do other work.  Alternatively, single-
threaded applications could use non-blocking I/O.

Some Printer conditions, such as jam or lack of paper, could cause a
client to be blocked indefinitely.  Clients may open additional
connections to the Printer to Get-Printer-Attributes, determine the
state of the device, alert a user if the printer is stopped, and let a
user decide whether to abort the job transmission or not.

In the following sections, there are tables of all HTTP headers, which
describe their use in an IPP client or server.  The following is an
explanation of each column in these tables.

  -    the "header" column contains the name of a header
  -    the "request/client" column indicates whether a client sends the
  header.
  -    the "request/ server" column indicates whether a server supports
  the header when received.
  -    the "response/ server" column indicates whether a server sends
  the header.
  -    the "response /client" column indicates whether a client
  supports the header when received.
  -    the "values and conditions" column specifies the allowed header
  values and the conditions for the header to be present in a
  request/response.

The table for "request headers" does not have columns for responses, and
the table for "response headers" does not have columns for requests.
The following is an explanation of the values in the "request/client"
and "response/ server" columns.

  -    must: the client or server MUST send the header,


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  -    must-if: the client or server MUST send the header when the
  condition described in the "values and conditions" column is met,
  -    may: the client or server MAY send the header
  -    not: the client or server SHOULD NOT send the header. It is not
  relevant to an IPP implementation.

The following is an explanation of the values in the "response/client"
and "request/ server" columns.
  -    must: the client or server MUST support the header,
  -    may: the client or server MAY support the header
  -    not: the client or server SHOULD NOT support the header. It is
       not relevant to an IPP implementation.

7.1 General Headers

The following is a table for the general headers.


General-     Request         Response        Values and Conditions
Header

             Client  Server  Server  Client

Cache-       must    not     must    not     "no-cache" only
Control

Connection   must-if must    must-   must    "close" only. Both
                             if              client and server
                                             SHOULD keep a
                                             connection for the
                                             duration of a sequence
                                             of operations. The
                                             client and server MUST
                                             include this header
                                             for the last operation
                                             in such a sequence.

Date         may     may     must    may     per RFC 1123 [RFC1123]
                                             from RFC 2616
                                             [RFC2616]

Pragma       must    not     must    not     "no-cache" only

Transfer-    must-if must    must-   must    "chunked" only .
Encoding                     if              Header MUST be present
                                             if Content-Length is
                                             absent.

Upgrade      not     not     not     not



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General-     Request         Response       V alues and Conditions
Header

             Client  Server  Server  Client

Via          not     not     not     not


7.2 Request  Headers

The following is a table for the request headers.


Request-Header   Client    Server  Request Values and Conditions

Accept           may       must    "application/ipp" only.  This
                                   value is the default if the
                                   client omits it

Accept-Charset   not       not     Charset information is within
                                   the application/ipp entity

Accept-Encoding  may       must    empty and per RFC 2616 [RFC2616]
                                   and IANA registry for content-
                                   codings

Accept-Language  not       not     language information is within
                                   the application/ipp entity

Authorization    must-if   must    per RFC 2616. A client MUST send
                                   this header when it receives a
                                   401 "Unauthorized" response and
                                   does not receive a  "Proxy-
                                   Authenticate" header.

>From             not       not     per RFC 2616. Because RFC
                                   recommends sending this header
                                   only with the user's approval, it
                                   is not very useful

Host             must      must    per RFC 2616

If-Match         not       not

If-Modified-     not       not
Since

If-None-Match    not       not




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Request-Header   Client    Server  Request Values and Conditions

If-Range         not       not

If-Unmodified-   not       not
Since

Max-Forwards     not       not

Proxy-           must-if   not     per RFC 2616. A client MUST send
Authorization                      this header when it receives a
                                   401 "Unauthorized" response and a
                                   "Proxy-Authenticate" header.

Range            not       not

Referrer         not       not

User-Agent       not       not


7.3 Response Headers

The following is a table for the request headers.


Response-      Server  Client  Response      Values and Conditions
Header

Accept-Ranges  not     not

Age            not     not

Location       must-if may     per RFC 2616. When URI needs
                               redirection.

Proxy-         not     must    per RFC 2616
Authenticate

Public         may     may     per RFC 2616

Retry-After    may     may     per RFC 2616

Server         not     not

Vary           not     not

Warning        may     may     per RFC 2616




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Response-      Server  Client  Response        Values and Conditions
Header

WWW-           must-if must    per RFC 2616.   When a server needs to
Authenticate                                   authenticate a client.


7.4 Entity  Headers

The following is a table for the entity headers.


Entity-Header  Request         Response        Values and Conditions

               Client  Server  Server   Client

Allow          not     not     not      not

Content-Base   not     not     not      not

Content-       may     must    must     must   per RFC 2616 and IANA
Encoding                                       registry for content
                                               codings.

Content-       not     not     not      not    Application/ipp
Language                                       handles language

Content-       must-if must    must-if  must   the length of the
Length                                         message-body per RFC
                                               2616. Header MUST be
                                               present if Transfer-
                                               Encoding is absent..

Content-       not     not     not      not
Location

Content-MD5    may     may     may      may    per RFC 2616

Content-Range  not     not     not      not

Content-Type   must    must    must     must   "application/ipp"
                                               only

ETag           not     not     not      not

Expires        not     not     not      not

Last-Modified  not     not     not      not




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7.5 Optional support for HTTP/1.0


IPP implementations consist of an HTTP layer and an IPP layer.  In the
following discussion, the term "client" refers to the HTTP client layer
and the term "server" refers to the HTTP server layer.  The Encoding and
Transport document [IPP-PRO] requires that HTTP 1.1 MUST be supported by
all clients and all servers.  However, a client and/or a server
implementation may choose to also support HTTP 1.0.

- This option means that a server may choose to communicate with a
(non-conforming) client that only supports HTTP 1.0.  In such cases the
server should not use any HTTP 1.1 specific parameters or features and
should respond using HTTP version number 1.0.

- This option also means that a client may choose to communicate with a
(non-conforming) server that only supports HTTP 1.0.  In such cases, if
the server responds with an HTTP 'unsupported version number' to an HTTP
1.1 request, the client should retry using HTTP version number 1.0.


7.6 HTTP/1.1 Chunking


7.6.1 Disabling IPP Server Response Chunking

Clients MUST anticipate that the HTTP/1.1 server may chunk responses and
MUST accept them in responses.  However, a (non-conforming) HTTP client
that is unable to accept chunked responses may attempt to request an
HTTP 1.1 server not to use chunking in its response to an operation by
using the following HTTP header:

     TE: identity

This mechanism should not be used by a server to disable a client from
chunking a request, since chunking of document data is an important
feature for clients to send long documents.


7.6.2 Warning About the Support of Chunked Requests

This section describes some problems with the use of chunked requests
and HTTP/1.1 servers.

The HTTP/1.1 standard [RFC2616] requires that conforming servers support
chunked requests for any method.  However, in spite of this requirement,
some HTTP/1.1 implementations support chunked responses in the GET
method, but do not support chunked POST method requests.  Some HTTP/1.1
implementations that support CGI scripts [CGI] and/or servlets [Servlet]


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require that the client supply a Content-Length.  These implementations
might reject a chunked POST method and return a 411 status code (Length
Required), might attempt to buffer the request and run out of room
returning a 413 status code (Request Entity Too Large), or might
successfully accept the chunked request.

Because of this lack of conformance of HTTP servers to the HTTP/1.1
standard, the IPP standard [IPP-PRO] REQUIRES that a conforming IPP
Printer object implementation support chunked requests and that
conforming clients accept chunked responses.  Therefore, IPP object
implementers are warned to seek HTTP server implementations that support
chunked POST requests in order to conform to the IPP standard and/or use
implementation techniques that support chunked POST requests.


8  References

[CGI]
     CGI/1.1 (http://www.ietf.org/internet-drafts/draft-coar-cgi-v11-
     00.txt).

[IPP-MOD]
     R. deBry, T. Hastings, R. Herriot, S. Isaacson, P. Powell,
     "Internet Printing Protocol/1.0: Model and Semantics", draft-ietf-
     ipp-model-v11-06.txt, March 1, 2000.

[IPP-PRO]
     Herriot, R., Butler, S., Moore, P., Tuner, R., "Internet Printing
     Protocol/1.0: Encoding and Transport", draft-ietf-ipp-protocol-v11-
     05.txt, March 1, 2000.

[ldap-printer]
     Fleming, P., Jones, K., Lewis, H., McDonald, I., "Internet Printing
     Protocol (IPP): LDAP Schema for Printer Services", <draft-ietf-ipp-
     ldap-printer-schema-01.txt>, work in progress, April 27, 2000.

[RFC793]
     J. Postel, "Transmission Control Protocol", RFC 793.

[RFC1123]
     Braden, S., "Requirements for Internet Hosts - Application and
     Support", RFC 1123, October, 1989.

[RFC2026]
     S. Bradner, "The Internet Standards Process -- Revision 3", RFC
     2026, October 1996.

[RFC2119]



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       S. Bradner, "Key words for use in RFCs to Indicate Requirement
       Levels", RFC 2119 , March 1997.

[RFC2396]
      Berners-Lee, T., Fielding, R., Masinter, L., "Uniform Resource
      Identifiers (URI): Generic Syntax", RFC 2396, August 1998.

[RFC2565]
     R. deBry, T. Hastings, R. Herriot, S. Isaacson, P. Powell,
     "Internet Printing Protocol/1.0: Model and Semantics", RFC 2566,
     April 1999.

[RFC2566]
     Herriot, R., Butler, S., Moore, P., Tuner, R., "Internet Printing
     Protocol/1.0: Encoding and Transport", RFC 2565, April 1999.

[RFC2567]
     Wright, D., "Design Goals for an Internet Printing Protocol",
     draft-ietf-ipp-req-03.txt, November, 1998.

[RFC2568
     Zilles, S., "Rationale for the Structure and Model and Protocol for
     the Internet Printing Protocol", RFC 2568, April 1999.

[RFC2569]
     Herriot, R., Hastings, T., Jacobs, N., Martin, J., "Mapping between
     LPD and IPP Protocols", RFC 2569, April 1999.

[RFC2616]
     R. Fielding, J. Gettys, J. Mogul, H. Frystyk, L. Masinter, P.
     Leach, T. Berners-Lee, "Hypertext Transfer Protocol - HTTP/1.1",
     RFC 2616, June 1999.

[Servlet]
     Servlet Specification Version 2.1
     (http://java.sun.com/products/servlet/2.1/index.html).

[svrloc-printer]
     St. Pierre, P., Isaacson, S., McDonald, I., "Definition of the
     Printer Abstract Service Type v2.0", <draft-ietf-svrloc-printer-
     scheme-06.txt>, work in progress, March 8, 2000.

[SSL]
     Netscape, The SSL Protocol, Version 3, (Text version 3.02),
     November 1996.


9  Authors' Address

Hastings, Manros, Kugler, Holst, Zehler                       [page 82]
                      Expires November 30, 2000



INTERNET-DRAFT       IPP/1.1: Implementer's Guide           May 30, 2000


Thomas N. Hastings
Xerox Corporation
701 Aviation Blvd.
El Segundo, CA 90245
hastings@cp10.es.xerox.com

Carl-Uno Manros
Xerox Corporation
701 Aviation Blvd.
El Segundo, CA 90245
manros@cp10.es.xerox.com

Carl Kugler
Mail Stop 003G
IBM Printing Systems Co
6300 Diagonal Hwy
Boulder CO 80301
Kugler@us.ibm.com

Henrik Holst
i-data Printing Systems
Vadstrupvej 35-43
2880 Bagsvaerd, Denmark
hh@I-data.com

Peter Zehler
Xerox Corporation
800 Philips Road
Webster, NY 14580

Phone: 716 265-8755
peter.zehler@usa.xerox.com

10 Notices

The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to  pertain
to the implementation or use of the technology described in this
document or the extent to which any license under such rights might or
might not be available; neither does it represent that it has made any
effort to identify any such rights.  Information on the IETF's
procedures with respect to rights in standards-track and standards-
related documentation can be found in BCP-11[BCP-11].  Copies of claims
of rights made available for publication and any assurances of licenses
to be made available, or the result of an attempt made to obtain a
general license or permission for the use of such proprietary rights by
implementers or users of this specification can be obtained from the
IETF Secretariat.


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INTERNET-DRAFT       IPP/1.1: Implementer's Guide           May 30, 2000


The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary rights,
which may cover technology that may be required to practice this
standard.  Please address the information to the IETF Executive
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Copyright (C) The Internet Society (1999). All Rights Reserved

This document and translations of it may be copied and furnished to
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distributed, in whole or in part, without restriction of any kind,
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may not be modified in any way, such as by removing the copyright notice
or references to the Internet Society or other Internet organizations,
except as needed for the  purpose of developing Internet standards in
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The limited permissions granted above are perpetual and will not be
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This document and the information contained herein is provided on an "AS
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FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT
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FITNESS FOR A PARTICULAR PURPOSE.



















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