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NNTP                                                          C. Feather
Internet-Draft                                                  Thus plc
Expires: August 30, 2003                                   March 1, 2003


                    Network News Transport Protocol
                       draft-ietf-nntpext-base-17

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 at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on August 30, 2003.

Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

   The Network News Transport Protocol has been in use in the Internet
   for a decade and remains one of the most popular protocols (by
   volume) in use today.  This document is a replacement for RFC 977 and
   officially updates the protocol specification.  It clarifies some
   vagueness in RFC 977, includes some new base functionality and
   provides a specific mechanism to add standardized extensions to NNTP.

Administration

   This document is a product of the NNTP Working Group, chaired by Russ
   Allbery.




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   This is draft 17 pre-publication version 2.

Outstanding issues

   Outstanding substantive (as opposed to editorial) issues in the text
   are shown as in the following case.

   OUTSTANDING ISSUE

      Reference consistency: should every RFC that is mentioned be
      included in the references? Where the same document is referred to
      in more than one place, should every occasion have a reference
      number (that is, "RFC 977 [3]" or similar), or only the first one,
      or only the first one in each section?


Author's Note

   This draft is the first produced using a new formatting process.  It
   therefore may contain unintentional layout or formatting changes
   compared with previous drafts.  The author would appreciate being
   informed of any problems this has caused.

   This draft is written in XML using an NNTP-specific DTD.  Custom
   software is used to convert this to RFC 2629 [12] format, and then
   the public "xml2rfc" package to further reduce this to text, nroff
   source, and HTML.

   No perl was used in producing this draft.

Rights

   UNIX is a registered trademark of the X/Open Company Ltd.


















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Table of Contents

   1.       Introduction . . . . . . . . . . . . . . . . . . . . . .   7
   2.       Notation . . . . . . . . . . . . . . . . . . . . . . . .   8
   3.       Basic Operation  . . . . . . . . . . . . . . . . . . . .   9
   3.1      Response Codes . . . . . . . . . . . . . . . . . . . . .  11
   3.1.1    Generic Response Codes . . . . . . . . . . . . . . . . .  13
   3.1.1.1  Examples . . . . . . . . . . . . . . . . . . . . . . . .  15
   3.2      Pipelining . . . . . . . . . . . . . . . . . . . . . . .  16
   3.2.1    Examples . . . . . . . . . . . . . . . . . . . . . . . .  17
   4.       The WILDMAT format . . . . . . . . . . . . . . . . . . .  18
   4.1      Wildmat syntax . . . . . . . . . . . . . . . . . . . . .  18
   4.2      Wildmat semantics  . . . . . . . . . . . . . . . . . . .  18
   4.3      Extensions . . . . . . . . . . . . . . . . . . . . . . .  19
   4.4      Examples . . . . . . . . . . . . . . . . . . . . . . . .  20
   5.       The GREETING Step  . . . . . . . . . . . . . . . . . . .  21
   5.1      Initial Connection . . . . . . . . . . . . . . . . . . .  21
   5.1.1    Usage  . . . . . . . . . . . . . . . . . . . . . . . . .  21
   5.1.2    Description  . . . . . . . . . . . . . . . . . . . . . .  21
   5.1.3    Examples . . . . . . . . . . . . . . . . . . . . . . . .  21
   5.2      MODE READER  . . . . . . . . . . . . . . . . . . . . . .  22
   5.2.1    Usage  . . . . . . . . . . . . . . . . . . . . . . . . .  22
   5.2.2    Description  . . . . . . . . . . . . . . . . . . . . . .  22
   5.2.3    Examples . . . . . . . . . . . . . . . . . . . . . . . .  23
   6.       The CAPABILITIES DISCOVERY step  . . . . . . . . . . . .  25
   6.1      LIST EXTENSIONS  . . . . . . . . . . . . . . . . . . . .  25
   6.1.1    Usage  . . . . . . . . . . . . . . . . . . . . . . . . .  25
   6.1.2    Description  . . . . . . . . . . . . . . . . . . . . . .  25
   6.1.3    Examples . . . . . . . . . . . . . . . . . . . . . . . .  26
   7.       Article posting and retrieval  . . . . . . . . . . . . .  27
   7.1      Group and article selection  . . . . . . . . . . . . . .  27
   7.1.1    GROUP  . . . . . . . . . . . . . . . . . . . . . . . . .  27
   7.1.1.1  Usage  . . . . . . . . . . . . . . . . . . . . . . . . .  28
   7.1.1.2  Description  . . . . . . . . . . . . . . . . . . . . . .  28
   7.1.1.3  Examples . . . . . . . . . . . . . . . . . . . . . . . .  29
   7.1.2    LAST . . . . . . . . . . . . . . . . . . . . . . . . . .  30
   7.1.2.1  Usage  . . . . . . . . . . . . . . . . . . . . . . . . .  30
   7.1.2.2  Description  . . . . . . . . . . . . . . . . . . . . . .  30
   7.1.2.3  Examples . . . . . . . . . . . . . . . . . . . . . . . .  31
   7.1.3    NEXT . . . . . . . . . . . . . . . . . . . . . . . . . .  32
   7.1.3.1  Usage  . . . . . . . . . . . . . . . . . . . . . . . . .  32
   7.1.3.2  Description  . . . . . . . . . . . . . . . . . . . . . .  32
   7.1.3.3  Examples . . . . . . . . . . . . . . . . . . . . . . . .  32
   7.2      Retrieval of articles and article sections . . . . . . .  33
   7.2.1    ARTICLE  . . . . . . . . . . . . . . . . . . . . . . . .  33
   7.2.1.1  Usage  . . . . . . . . . . . . . . . . . . . . . . . . .  33
   7.2.1.2  Description  . . . . . . . . . . . . . . . . . . . . . .  34
   7.2.1.3  Examples . . . . . . . . . . . . . . . . . . . . . . . .  35



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   7.2.2    HEAD . . . . . . . . . . . . . . . . . . . . . . . . . .  36
   7.2.2.1  Usage  . . . . . . . . . . . . . . . . . . . . . . . . .  36
   7.2.2.2  Description  . . . . . . . . . . . . . . . . . . . . . .  37
   7.2.2.3  Examples . . . . . . . . . . . . . . . . . . . . . . . .  37
   7.2.3    BODY . . . . . . . . . . . . . . . . . . . . . . . . . .  39
   7.2.3.1  Usage  . . . . . . . . . . . . . . . . . . . . . . . . .  39
   7.2.3.2  Description  . . . . . . . . . . . . . . . . . . . . . .  39
   7.2.3.3  Examples . . . . . . . . . . . . . . . . . . . . . . . .  39
   7.2.4    STAT . . . . . . . . . . . . . . . . . . . . . . . . . .  40
   7.2.4.1  Usage  . . . . . . . . . . . . . . . . . . . . . . . . .  40
   7.2.4.2  Description  . . . . . . . . . . . . . . . . . . . . . .  41
   7.2.4.3  Examples . . . . . . . . . . . . . . . . . . . . . . . .  41
   7.3      Article posting  . . . . . . . . . . . . . . . . . . . .  42
   7.3.1    POST . . . . . . . . . . . . . . . . . . . . . . . . . .  42
   7.3.1.1  Usage  . . . . . . . . . . . . . . . . . . . . . . . . .  42
   7.3.1.2  Description  . . . . . . . . . . . . . . . . . . . . . .  43
   7.3.1.3  Examples . . . . . . . . . . . . . . . . . . . . . . . .  44
   7.3.2    IHAVE  . . . . . . . . . . . . . . . . . . . . . . . . .  44
   7.3.2.1  Usage  . . . . . . . . . . . . . . . . . . . . . . . . .  44
   7.3.2.2  Description  . . . . . . . . . . . . . . . . . . . . . .  45
   7.3.2.3  Examples . . . . . . . . . . . . . . . . . . . . . . . .  46
   8.       Information commands . . . . . . . . . . . . . . . . . .  48
   8.1      DATE . . . . . . . . . . . . . . . . . . . . . . . . . .  48
   8.1.1    Usage  . . . . . . . . . . . . . . . . . . . . . . . . .  48
   8.1.2    Description  . . . . . . . . . . . . . . . . . . . . . .  48
   8.1.3    Examples . . . . . . . . . . . . . . . . . . . . . . . .  48
   8.2      HELP . . . . . . . . . . . . . . . . . . . . . . . . . .  48
   8.2.1    Usage  . . . . . . . . . . . . . . . . . . . . . . . . .  48
   8.2.2    Description  . . . . . . . . . . . . . . . . . . . . . .  49
   8.2.3    Examples . . . . . . . . . . . . . . . . . . . . . . . .  49
   8.3      NEWGROUPS  . . . . . . . . . . . . . . . . . . . . . . .  49
   8.3.1    Usage  . . . . . . . . . . . . . . . . . . . . . . . . .  49
   8.3.2    Description  . . . . . . . . . . . . . . . . . . . . . .  49
   8.3.3    Examples . . . . . . . . . . . . . . . . . . . . . . . .  50
   8.4      NEWNEWS  . . . . . . . . . . . . . . . . . . . . . . . .  50
   8.4.1    Usage  . . . . . . . . . . . . . . . . . . . . . . . . .  51
   8.4.2    Description  . . . . . . . . . . . . . . . . . . . . . .  51
   8.4.3    Examples . . . . . . . . . . . . . . . . . . . . . . . .  51
   8.5      Time . . . . . . . . . . . . . . . . . . . . . . . . . .  52
   8.5.1    Examples . . . . . . . . . . . . . . . . . . . . . . . .  52
   8.6      The LIST commands  . . . . . . . . . . . . . . . . . . .  53
   8.6.1    LIST ACTIVE  . . . . . . . . . . . . . . . . . . . . . .  53
   8.6.1.1  Usage  . . . . . . . . . . . . . . . . . . . . . . . . .  53
   8.6.1.2  Description  . . . . . . . . . . . . . . . . . . . . . .  53
   8.6.1.3  Examples . . . . . . . . . . . . . . . . . . . . . . . .  54
   8.6.2    LIST ACTIVE.TIMES  . . . . . . . . . . . . . . . . . . .  55
   8.6.2.1  Usage  . . . . . . . . . . . . . . . . . . . . . . . . .  55
   8.6.2.2  Description  . . . . . . . . . . . . . . . . . . . . . .  55



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   8.6.2.3  Examples . . . . . . . . . . . . . . . . . . . . . . . .  55
   8.6.3    LIST DISTRIBUTIONS . . . . . . . . . . . . . . . . . . .  56
   8.6.3.1  Usage  . . . . . . . . . . . . . . . . . . . . . . . . .  56
   8.6.3.2  Description  . . . . . . . . . . . . . . . . . . . . . .  56
   8.6.3.3  Examples . . . . . . . . . . . . . . . . . . . . . . . .  57
   8.6.4    LIST DISTRIB.PATS  . . . . . . . . . . . . . . . . . . .  57
   8.6.4.1  Usage  . . . . . . . . . . . . . . . . . . . . . . . . .  57
   8.6.4.2  Description  . . . . . . . . . . . . . . . . . . . . . .  57
   8.6.4.3  Examples . . . . . . . . . . . . . . . . . . . . . . . .  58
   8.6.5    LIST NEWSGROUPS  . . . . . . . . . . . . . . . . . . . .  58
   8.6.5.1  Usage  . . . . . . . . . . . . . . . . . . . . . . . . .  58
   8.6.5.2  Description  . . . . . . . . . . . . . . . . . . . . . .  59
   8.6.5.3  Examples . . . . . . . . . . . . . . . . . . . . . . . .  59
   9.       The CONCLUSION step  . . . . . . . . . . . . . . . . . .  60
   9.1      QUIT . . . . . . . . . . . . . . . . . . . . . . . . . .  60
   9.1.1    Usage  . . . . . . . . . . . . . . . . . . . . . . . . .  60
   9.1.2    Description  . . . . . . . . . . . . . . . . . . . . . .  60
   9.1.3    Examples . . . . . . . . . . . . . . . . . . . . . . . .  60
   10.      Framework for NNTP extensions  . . . . . . . . . . . . .  61
   10.1     Initial IANA registry  . . . . . . . . . . . . . . . . .  63
   10.2     Standard extensions  . . . . . . . . . . . . . . . . . .  63
   10.3     The LISTGROUP extension  . . . . . . . . . . . . . . . .  63
   10.3.1   LISTGROUP  . . . . . . . . . . . . . . . . . . . . . . .  63
   10.3.1.1 Usage  . . . . . . . . . . . . . . . . . . . . . . . . .  63
   10.3.1.2 Description  . . . . . . . . . . . . . . . . . . . . . .  64
   10.3.1.3 Examples . . . . . . . . . . . . . . . . . . . . . . . .  64
   10.4     Article metadata . . . . . . . . . . . . . . . . . . . .  65
   10.4.1   The :bytes metadata item . . . . . . . . . . . . . . . .  65
   10.4.2   The :lines metadata item . . . . . . . . . . . . . . . .  66
   10.5     The OVER extension . . . . . . . . . . . . . . . . . . .  66
   10.5.1   OVER . . . . . . . . . . . . . . . . . . . . . . . . . .  66
   10.5.1.1 Usage  . . . . . . . . . . . . . . . . . . . . . . . . .  66
   10.5.1.2 Description  . . . . . . . . . . . . . . . . . . . . . .  67
   10.5.1.3 Examples . . . . . . . . . . . . . . . . . . . . . . . .  68
   10.5.2   LIST OVERVIEW.FMT  . . . . . . . . . . . . . . . . . . .  69
   10.5.2.1 Usage  . . . . . . . . . . . . . . . . . . . . . . . . .  69
   10.5.2.2 Description  . . . . . . . . . . . . . . . . . . . . . .  70
   10.5.2.3 Examples . . . . . . . . . . . . . . . . . . . . . . . .  71
   10.6     The HDR extension  . . . . . . . . . . . . . . . . . . .  72
   10.6.1   HDR  . . . . . . . . . . . . . . . . . . . . . . . . . .  72
   10.6.1.1 Usage  . . . . . . . . . . . . . . . . . . . . . . . . .  72
   10.6.1.2 Description  . . . . . . . . . . . . . . . . . . . . . .  72
   10.6.1.3 Examples . . . . . . . . . . . . . . . . . . . . . . . .  74
   11.      Augmented BNF Syntax for NNTP Commands . . . . . . . . .  76
   12.      Security Considerations  . . . . . . . . . . . . . . . .  79
   12.1     Personal and Proprietary Information . . . . . . . . . .  79
   12.2     Abuse of Server Log Information  . . . . . . . . . . . .  79
   12.3     Weak Authentication and Access Control . . . . . . . . .  79



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   12.4     DNS Spoofing . . . . . . . . . . . . . . . . . . . . . .  80
   12.5     UTF-8 issues . . . . . . . . . . . . . . . . . . . . . .  80
   13.      Acknowledgments  . . . . . . . . . . . . . . . . . . . .  82
            Normative References . . . . . . . . . . . . . . . . . .  84
            Informative References . . . . . . . . . . . . . . . . .  85
            Author's Address . . . . . . . . . . . . . . . . . . . .  85
            Intellectual Property and Copyright Statements . . . . .  86












































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1. Introduction

   This document specifies the Network News Transport Protocol (NNTP),
   which is used for the distribution, inquiry, retrieval, and posting
   of net news articles using a reliable stream-based mechanism.  For
   news reading clients, NNTP enables retrieval of news articles that
   are stored in a central database, giving subscribers the ability to
   select only those articles they wish to read.

   The net news model provides for indexing, cross-referencing, and
   expiration of aged messages.  For server-to-server interaction, NNTP
   is designed for efficient transmission of net news articles over a
   reliable full duplex communication channel.

   Every attempt is made to ensure that the protocol specification in
   this document is compatible with the version specified in RFC 977
   [1].  However, this version does not support the ill-defined SLAVE
   command and permits four digit years to be specified in the NEWNEWS
   and NEWGROUPS commands.  It changes the default character set to
   UTF-8 [2] instead of US-ASCII [3].  It also extends the newsgroup
   name matching capabilities already documented in RFC 977.

   Generally, new functionality is made available using new commands.
   Part of that new functionality involves a mechanism to discover what
   new functionality is available to clients from a server.

   This mechanism can also be used to add more functionality as needs
   merit such additions.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [4].

   An implementation is not compliant if it fails to satisfy one or more
   of the MUST requirements for this protocol.  An implementation that
   satisfies all the MUST and all the SHOULD requirements for its
   protocols is said to be "unconditionally compliant"; one that
   satisfies all the MUST requirements but not all the SHOULD
   requirements for NNTP is said to be "conditionally compliant".

   For the remainder of this document, the term "client host" refers to
   a host making use of the NNTP service, while the term "server host"
   refers to a host that offers the NNTP service.








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2. Notation

   The following notational conventions are used in this document.

     UPPERCASE     indicates literal text to be included in the
                   command;
     lowercase     indicates a token described elsewhere;
     [brackets]    indicate that the parameter is optional;
     ellipsis...   indicates that the parameter may be repeated any
                   number of times (it must occur at least once);
     vertical|bar  indicates a choice of two mutually exclusive
                   parameters (exactly one must be provided).

   The name "message-id" for a command or response parameter indicates
   that it is the message-id of an article as described in Section 7.
   The actual parameter MUST include the angle brackets.

   The name "wildmat" for a parameter indicates that it is a wildmat as
   defined in Section 4.  If the parameter does not meet the
   requirements of that section (for example, if it does not fit the
   grammar of Section 4.1) the NNTP server MAY place some interpretation
   on it (not specified by this document) or otherwise MUST treat it as
   a syntax error.

   Responses for each command will be described in tables listing the
   required format of a response followed by the meaning that should be
   ascribed to that response.

   Examples in this document are not normative but serve to illustrate
   usages, arguments, and responses.  In the examples, a "[C]" will be
   used to represent the client host and a "[S]" will be used to
   represent the server host.  Most of the examples do not rely on a
   particular server state.  In some cases, however, they do assume that
   the current selected newsgroup (see the GROUP command (Section
   7.1.1)) is invalid; when so, this is indicated at the start of the
   example.















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3. Basic Operation

   Every NNTP session MUST involve the following in this order:

      CONNECTION
      GREETING
      DISCONNECTION

   Other steps may occur between the GREETING and DISCONNECTION step.
   They are:

      CAPABILITIES DISCOVERY
      NEWS EXCHANGE
      CONCLUSION

   NNTP operates over any reliable data stream 8-bit-wide channel.  When
   running over TCP/IP, the official port for the NNTP service is 119.
   Initially, the server host starts the NNTP service by listening on a
   TCP port.  When a client host wishes to make use of the service, it
   MUST establish a TCP connection with the server host by connecting to
   that host on the same port on which the server is listening.  This is
   the CONNECTION step.  When the connection is established, the NNTP
   server host MUST send a greeting.  This is the GREETING step.  The
   client host and server host SHOULD then exchange commands and
   responses (respectively) until the connection is closed or aborted.
   This final step is called the DISCONNECTION step.

   If there is a CONCLUSION step, it MUST immediately precede the
   DISCONNECTION step.  There MUST be only one CONNECTION, CONCLUSION
   and DISCONNECTION step for each NNTP session.  All other steps MAY be
   repeated as needed.  For example, the GREETING step may be repeated
   if the client makes use of the MODE READER command (see Section 5.2
   for more on the MODE READER command).

   OUTSTANDING ISSUE

      Do we actually need this GREETING / NEWS EXCHANGE / DISCONNECTION
      type stuff? I don't see that it buys us anything compared with
      simply saying that there's the initial greeting and a set of
      commands.

   The character set for all NNTP commands is UTF-8.  Commands in the
   NNTP MUST consist of a keyword, which MAY be followed by one or more
   arguments.  An US-ASCII CRLF pair MUST terminate all commands.
   Multiple commands MUST NOT be on the same line.  Keywords MUST
   consist of printable US-ASCII characters.  Unless otherwise noted
   elsewhere in this document, arguments SHOULD consist of printable
   US-ASCII characters.  Keywords and arguments MUST be each separated



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   by one or more US-ASCII SPACE or US-ASCII TAB characters.  Keywords
   MUST be at least three US-ASCII characters and MUST NOT exceed 12
   US-ASCII characters.  Command lines MUST NOT exceed 512 octets, which
   includes the terminating US-ASCII CRLF pair.  The arguments MUST NOT
   exceed 497 octets.

   Commands may have variants, using a second keyword immediately after
   the first to indicate which variant is required.  The only such
   commands in this specification are LIST and MODE.

   Keywords are case-insensitive; the case of keywords for commands MUST
   be ignored by the server.  Command and response parameters are case
   or language specific only when specified (either in this document or
   in RFC 1036 [6]).

   An NNTP server MUST implement all the commands in this specification
   except for those marked as optional and those in extensions.

   Each response MUST start with a three-digit response code that is
   sufficient to distinguish all responses.  Certain valid responses are
   defined to be multi-line; for all others, the response is contained
   in a single line.

   OUTSTANDING ISSUE

      Should the initial response line be limited to 512 octets as well?
      Possible text:

      The first or only line of the response MUST NOT exceed 512 octets,
      which includes the response code and the terminating US-ASCII CRLF
      pair.

      The text further down about "does not place any limit on the
      length" would need equivalent edits.

   All multi-line responses MUST adhere to the following format:

   1.  The response consists of a sequence of one or more "lines", each
       being a stream of octets ending with 0x0D 0x0A (US-ASCII CRLF).
       Apart from those line endings, the stream MUST NOT include the
       octets 0x00, 0x0A, or 0x0D (US-ASCII NUL, LF, and CR).

   2.  The first such line contains the response code as with a single
       line response.

   3.  If any subsequent line begins with the "termination octet" (0x2E
       or US_ASCII "."), that line MUST be "byte-stuffed" by pre-pending
       an additional termination octet (0x2E) to that line of the



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       response.

   4.  The lines of the response MUST be followed by a terminating line
       consisting of a single termination octet (0x2E or US_ASCII ".")
       followed by CRLF in the normal way.  Thus a multi-line response
       is always terminated with the five octets CRLF "." CRLF (in
       US-ASCII).

   5.  When interpreting a multi-line response, the "byte stuffing" MUST
       be undone; i.e.  the client MUST ensure that, in any line
       beginning with the termination octet followed by octets other
       than US-ASCII CRLF, that initial termination octet is
       disregarded.

   6.  Likewise, the terminating line "." CRLF (in US-ASCII) MUST NOT be
       considered part of the multi-line response; i.e.  the client MUST
       ensure that any line beginning with the termination octet
       followed immediately by US-ASCII CRLF is disregarded; (the first
       CRLF of the terminating CRLF "." CRLF is, of course, part of the
       last line of the response).

   Note that texts using an encoding (such as UTF-16 or UTF-32) that may
   contain the NUL octet or the CR or LF octets in contexts other than
   the CRLF line ending cannot be reliably conveyed in the above format.

   This document does not place any limit on the length of a line.
   However, the standards that define the format of articles may do so.

   An NNTP server MAY have an inactivity autologout timer.  Such a timer
   SHOULD be of at least three minutes duration, with the exception that
   there MAY be a shorter limit on how long the server is willing to
   wait for the first command from the client.  The receipt of any
   command from the client during the timer interval SHOULD suffice to
   reset the autologout timer.  Similarly, the receipt of any
   significant amount of data from the client while in the midst of
   sending a multi-line message to the server (such as during a POST or
   IHAVE command) SHOULD suffice to reset the autologout timer.  When
   the timer expires, the server SHOULD close the TCP connection without
   sending any response to the client, including when the client is in
   the middle of sending a multi-line message to the server.

3.1 Response Codes

   Each response MUST begin with a three-digit status indicator.  These
   are status reports from the server and indicate the response to the
   last command received from the client.

   The first digit of the response broadly indicates the success,



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   failure, or progress of the previous command.

      1xx - Informative message.
      2xx - Command completed OK.
      3xx - Command OK so far; send the rest of it.
      4xx - Command was correct, but couldn't be performed for some
      reason.
      5xx - Command unimplemented, or incorrect, or a serious program
      error occurred.

   The next digit in the code indicates the function response category.

      x0x - Connection, setup, and miscellaneous messages
      x1x - Newsgroup selection
      x2x - Article selection
      x3x - Distribution functions
      x4x - Posting
      x8x - Reserved for authentication and authorization extensions
      x9x - Reserved for private use (non-standard extensions)

   Certain responses contain parameters such as numbers and names in
   addition to the status indicator.  In those cases, to simplify
   interpretation by the client the number and type of such parameters
   is fixed for each response code, as is whether or not the code
   introduces a multi-line response.  Any extension MUST follow this
   principle as well, but note that, for historical reasons, the 211
   response code is an exception to this.  In all other cases, the
   client MUST only use the status indicator itself to determine the
   nature of the response.  The exact response codes that can be
   returned by any given command are detailed in the description of that
   command.

   Parameters MUST be separated from the numeric status indicator and
   from each other by a single US-ASCII space.  All numeric parameters
   MUST be in base 10 (decimal) format, and MAY have leading zeros.
   String parameters MUST contain at least one character and MUST NOT
   contain US-ASCII spaces, CR, LF, or tab.  The server MAY add any text
   after the response code or last parameter as appropriate, and the
   client MUST NOT make decisions based on this text.  Such text MUST be
   separated from the numeric status indicator or the last parameter by
   at least one US-ASCII space.

   The server MUST respond to any command with the appropriate generic
   response (given in Section 3.1.1) if it represents the situation.
   Otherwise, each recognized command MUST return one of the response
   codes specifically listed in its description or in an extension.  A
   server MAY provide extensions to this specification, including new
   commands, new variants or features of existing commands, and other



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   ways of changing the internal state of the server.  However, the
   server MUST NOT produce any other responses to a client that does not
   invoke any of the additional features.  (Therefore a client that
   restricts itself to this specification will only receive the
   responses that are listed.)

   If a client receives an unexpected response, it SHOULD use the first
   digit of the response to determine the result.  For example, an
   unexpected 2xx should be taken as success and an unexpected 4xx or
   5xx as failure.

   Response codes not specified in this document MAY be used for any
   installation-specific additional commands also not specified.  These
   SHOULD be chosen to fit the pattern of x9x specified above.

   Neither this document nor any extension registered with IANA (see
   Section 10) will specify any response codes of the x9x pattern.
   (Implementers of extensions are accordingly cautioned not to use such
   responses for extensions that may subsequently be submitted for
   registration.)

3.1.1 Generic Response Codes

   The server MUST respond to any command with the appropriate one of
   the following generic responses if it represents the situation.

   If the command is not recognized, or it is an optional command or
   extension that is not implemented by the server, the response code
   500 MUST be returned.

   If there is a syntax error in the arguments of a recognized command,
   including the case where more arguments are provided than the command
   specifies, the response code 501 MUST be returned.  Note that where a
   command has variants depending on a second keyword (e.g.  LIST ACTIVE
   and LIST NEWSGROUPS), then 501 MUST be used when the requested
   variant is not implemented but the base command is.

   If the client is not authorized to use the specified facility when
   the server is in its current state, the response code 502 MUST be
   returned.  A different command might change the server state and
   permit the command if it is retried.

   If the server does not provide an optional feature, then the response
   code 403 MUST be returned if the omission is temporary (e.g.  because
   a necessary facility is unavailable) and the code 503 if it is
   permanent (e.g.  because the server does not store the required
   information).




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   OUTSTANDING ISSUE

      Is anyone aware of a server that implements 403, or is it an
      invention of our own? If the latter, do we want to keep it? INN
      apparently uses 503 for temporary errors; someone suggested adding
      the text:

         If the server encounters an unexpected internal error that
         prevents it from completing a command, the response code 503
         MAY be returned.

      Some servers return 503 for things like "can't contact a posting
      server" or "can't execute external authenticator".

   OUTSTANDING ISSUE

      The 503 response seems to have three separate meanings:

      1.  LIST ACTIVE.TIMES etc.  use it for "this data isn't stored".
          HDR uses it for "this header can't be requested", which is
          consistent.  Are there other commands that can reasonably
          return such a thing? If not, is this kind of 503 really a
          generic response?

      2.  Temporary errors, the kind that 403 is supposed to represent.

      3.  It's apparently returned by LIST EXTENSIONS, but what does it
          mean in this case? Not "there are no extensions", because
          that's 402.  Is this also an invention of our own? Again,
          would a different code be better?

   If the server has to terminate the connection for some reason, it
   MUST give a 400 response code to the next command and then
   immediately close the TCP connection.  It MAY give a 401 response
   code to any command to indicate that termination is imminent
   (following a 401 response, it MUST NOT close the TCP connection
   immediately).

   OUTSTANDING ISSUE

      Since the 401 doesn't terminate the session, what about commands
      that change the status? For example, if GROUP returns 401 what
      happens to the current selected newsgroup.

   With the exception of mandatory commands and the 500 response, the
   client MUST be prepared to receive any of these responses for any
   command.




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3.1.1.1 Examples

   Example of an unknown command:

      [C] MAIL
      [S] 500 Unknown command

   Example of an unsupported extension:

      [C] LIST EXTENSIONS
      [S] 202 Extensions supported:
      [S] LISTGROUP
      [S] .
      [C] OVER
      [S] 500 Unknown command

   Example of an unsupported variant:

      [C] MODE POSTER
      [S] 501 Unknown MODE option

   Example of a syntax error:

      [C] ARTICLE a.message.id@no.angle.brackets
      [S] 501 Syntax error

   Example of an overlong command line:

      [C] HEAD 53 54 55
      [S] 501 Too many arguments

   Example of a bad wildmat:

      [C] LIST ACTIVE u[ks].*
      [S] 501 Syntax error

   Example of an attempt to access a restricted facility:

      [C] GROUP secret.group
      [S] 502 Permission denied

   followed by a successful attempt following authentication:

      [C] XSECRET fred flintstone
      [S] 290 Password for fred accepted.
      [C] GROUP secret.group
      [S] 211 5 1 20 secret.group selected




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   Example of a temporary failure:

      [C] GROUP archive.local
      [S] 403 Archive server temporarily offline

   Example of the server needing to close down immediately:

      [C] ARTICLE 123
      [S] 400 Power supply failed, running on UPS
      [Server closes connection.]

   Example of imminent termination of the server:

      [C] STAT 123
      [S] 401 Pre-payment expired, you have 10 seconds
      [C] STAT 123
      [S] 423 No such article number in this group
      [C] NEXT
      [S] 400 Time expired
      [Server closes connection.]


3.2 Pipelining

   NNTP is designed to operate over a reliable bi-directional connection
   such as TCP.  Therefore, if a command does not depend on the response
   to the previous one, it should not matter if it is sent before that
   response is received.  Doing this is called "pipelining".  However,
   certain server implementations throw away all text received from the
   client following certain commands before sending their response.  If
   this happens, pipelining will be affected because one or more
   commands will have been ignored or misinterpreted, and the client
   will be matching the wrong responses to each command.  Since there
   are significant benefits to pipelining, but also circumstances where
   it is reasonable or common for servers to behave in the above manner,
   this document puts certain requirements on both clients and servers.

   Except where stated otherwise, a client MAY use pipelining.  That is,
   it may send a command before receiving the response for the previous
   command.  The server MUST allow pipelining and MUST NOT throw away
   any text received after a command.  Irrespective of whether or not
   pipelining is used, the server MUST process commands in the order
   they are sent.

   If the specific description of a command say it "MUST NOT be
   pipelined", that command MUST end any pipeline of commands.  That is,
   the client MUST NOT send any following command until receiving the
   CRLF at the end of the response from the command.  The server MAY



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   ignore any data received after the command and before the CRLF at the
   end of the response is sent to the client.

   The initial connection must not be part of a pipeline; that is, the
   client MUST NOT send any command until receiving the CRLF at the end
   of the greeting.

   If the client uses blocking system calls to send commands, it MUST
   ensure that the amount of text sent in pipelining does not cause a
   deadlock between transmission and reception.  The amount of text
   involved will depend on window sizes in the transmission layer, and
   is typically 4k octets for TCP.

3.2.1 Examples

   Example of correct use of pipelining:

      [C] GROUP misc.test
      [C] STAT
      [C] NEXT
      [S] 211 1234 3000234 3002322 misc.test
      [S] 223 3000234 <45223423@example.com> retrieved
      [S] 223 3000237 <668929@example.org> retrieved

   Example of incorrect use of pipelining (the LIST EXTENSIONS command
   may not be pipelined):

      [C] GROUP misc.test
      [C] LIST EXTENSIONS
      [C] DATE
      [C] NEXT
      [S] 211 1234 3000234 3002322 misc.test
      [S] 402 server has no extensions
      [S] 223 3000237 <668929@example.org> retrieved

   The DATE command has been thrown away by the server and so there is
   no 111 response to match it.














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4. The WILDMAT format

   The WILDMAT format described here is based on the version first
   developed by Rich Salz [11], which in turn was derived from the
   format used in the UNIX "find" command to articulate file names.  It
   was developed to provide a uniform mechanism for matching patterns in
   the same manner that the UNIX shell matches filenames.

4.1 Wildmat syntax

   A wildmat is described by the following augmented BNF [5] syntax
   (note that this syntax contains ambiguities and special cases
   described at the end):

      wildmat = wildmat-pattern *("," ["!"] wildmat-pattern)

      wildmat-pattern = 1*wildmat-item

      wildmat-item = wildmat-exact / wildmat-wild

      wildmat-exact = %x21-29 / %x2B / %x2D-3E / %x40-5A / %x5E-7E /
         UTF-8-non-ascii ; exclude * , ? [ \ ]

      wildmat-wild = "*" / "?"

   UTF-8-non-ascii is defined in Section 11

   This syntax must be interpreted subject to the following rule:

   Where a wildmat-pattern is not immediately preceded by "!", it shall
   not begin with a "!".

   Note: the characters \ , [ and ] are not allowed in wildmats, while *
   and ? are always wildcards.  This should not be a problem since these
   characters cannot occur in newsgroup names, which is the only current
   use of wildmats.  Backslash is commonly used to supress the special
   meaning of characters and brackets to introduce sets, but there is no
   existing standard practice for these in wildmats and so they were
   omitted from this specification.  A future extension to this
   specification may provide semantics for these characters.

4.2 Wildmat semantics

   A wildmat is tested against a string, and either matches or does not
   match.  To do this, each constituent wildmat-pattern is matched
   against the string and the rightmost pattern that matches is
   identified.  If that wildmat-pattern is not preceded with "!", the
   whole wildmat matches.  If it is preceded by "!", or if no



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   wildmat-pattern matches, the whole wildmat does not match.

   For example, consider the wildmat "a*,!*b,*c*":

      the string "aaa" matches because the rightmost match is with "a*"

      the string "abb" does not match because the rightmost match is
      with "*b"

      the string "ccb" matches because the rightmost match is with "*c*"

      the string "xxx" does not match because no wildmat-pattern matches

   A wildmat-pattern matches a string if the string can be broken into
   components, each of which matches the corresponding wildmat-item in
   the pattern; the matches must be in the same order, and the whole
   string must be used in the match.  The pattern is "anchored"; that
   is, the first and last characters in the string must match the first
   and last item respectively (unless that item is an asterisk matching
   zero characters).

   A wildmat-exact matches the same character (which may be more than
   one octet in UTF-8).

   "?" matches exactly one character (which may be more than one octet).

   "*" matches zero or more characters.  It can match an empty string,
   but it cannot match a subsequence of a UTF-8 sequence that is not
   aligned to the character boundaries.

4.3 Extensions

   An NNTP server or extension MAY extend the syntax or semantics of
   wildmats provided that all wildmats that meet the requirements of
   Section 4.1 have the meaning ascribed to them by Section 4.2.  Future
   editions of this document may also extend wildmats.















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4.4 Examples

    In these examples, $ and @ are used to represent the two octets 0xC2
   and 0xA3 respectively; $@ is thus the UTF-8 encoding for the pound
   sterling symbol, shown as # in the descriptions.

     Wildmat    Description of strings that match
       abc      the one string "abc"
       abc,def  the two strings "abc" and "def"
       $@       the one character string "#"
       a*       any string that begins with "a"
       a*b      any string that begins with "a" and ends with "b"
       a*,*b    any string that begins with "a" or ends with "b"
       a*,!*b   any string that begins with "a" and does not end with
                "b"
     a*,!*b,c*  any string that begins with "a" and does not end with
                "b", and any string that begins with "c" no matter
                what it ends with
     a*,c*,!*b  any string that begins with "a" or "c" and does not
                end with "b"
       ?a*      any string with "a" as its second character
       ??a*     any string with "a" as its third character
       *a?      any string with "a" as its penultimate character
       *a??     any string with "a" as its antepenultimate character



























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5. The GREETING Step

5.1 Initial Connection

5.1.1 Usage

   Responses
      200   Service available, posting allowed
      201   Service available, posting prohibited
      400   Service temporarily unavailable [1]
      502   Service permanently unavailable [1]

      These are the only valid response codes for the initial greeting;
      the server MUST not return any other generic response code.

   [1] Following a 400 or 502 response the server MUST immediately close
      the connection.


5.1.2 Description

   There is no command presented by the client upon initial connection
   to the server.  The server MUST present an appropriate response code
   as a greeting to the client.  This response informs the client about
   what steps the client should take to reach the news exchange step.

   If the server will accept further commands from the client including
   POST, the server MUST present a 200 greeting code.  If the server
   will accept further commands from the client, but it is not
   authorized to post articles using the POST command, the server MUST
   present a 201 greeting code.

   Otherwise the server MUST present a 400 or 502 greeting code and then
   immediately close the connection.  502 MUST be used if the client is
   not permitted under any circumstances to interact with the server and
   400 otherwise.

5.1.3 Examples

   Example of a normal connection from an authorized client which then
   jumps directly to the conclusion step (see Section 9):

      [Initial TCP connection setup completed.]
      [S] 200 NNTP Service Ready, posting permitted
      [C] QUIT
      [S] 205 NNTP Service exits normally
      [Server closes connection.]




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   Example of a normal connection from an authorized client that is not
   permitted to post; it also jumps directly to the conclusion step:

      [Initial TCP connection setup completed.]
      [S] 201 NNTP Service Ready, posting prohibited
      [C] QUIT
      [S] 205 NNTP Service exits normally
      [Server closes connection.]

   Example of a normal connection from an unauthorized client:

      [Initial TCP connection setup completed.]
      [S] 502 NNTP Service permanently unavailable
      [Server closes connection.]

   Example of a connection from a client where the server is unable to
   provide service:

      [Initial TCP connection setup completed.]
      [S] 400 NNTP Service temporarily unavailable
      [Server closes connection.]


5.2 MODE READER

5.2.1 Usage

   This command MUST NOT be pipelined.

   Syntax
      MODE READER

   Responses
      200   Posting allowed
      201   Posting prohibited
      400   Service temporarily unavailable [1]
      502   Service permanently unavailable [1]

   [1] Following a 400 or 502 response the server MUST immediately close
      the connection.


5.2.2 Description

   MODE READER SHOULD be sent by any client that intends to use any
   command other than IHAVE, HEAD, STAT, LIST ACTIVE, LIST EXTENSIONS,
   or commands advertised by the server as available via LIST
   EXTENSIONS.



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   Servers MAY require that this command be issued before any other
   commands are sent and MAY reject any other commands until after a
   MODE READER command has been sent.

   The server MUST return a response using the same codes as the initial
   greeting (as described in Section 5.1.1) to indicate its ability to
   provide reading service to the client.  Note that the response need
   not be the same as the one presented during the initial greeting.

   Once MODE READER is sent, IHAVE (and any extensions intended for
   peer-to-peer article transfer) MAY no longer be permitted, even if it
   were permitted before the MODE READER command.  The results of LIST
   EXTENSIONS MAY be different following a MODE READER command than
   prior to the issuing of that command.

   Servers are encouraged to not require this command even though
   clients SHOULD send it when appropriate.  It is present to support
   some news architectures that switch between modes based on whether a
   given connection is a peer-to-peer connection with another server or
   a news reading client.

5.2.3 Examples

   Example of use of the MODE READER command by an authorized client
   which then jumps directly to the conclusion step (see Section 9):

      [C] MODE READER
      [S] 200 NNTP Service Ready, posting permitted
      [C] QUIT
      [S] 205 NNTP Service exits normally
      [Server closes connection.]

   Example of use of the MODE READER command by an authorized client
   that is not permitted to post; it also jumps directly to the
   conclusion step:

      [C] MODE READER
      [S] 201 NNTP Service Ready, posting prohibited
      [C] QUIT
      [S] 205 NNTP Service exits normally
      [Server closes connection.]

   Example of use of MODE READER by a client not authorized to receive
   service from the server as a news reader:

      [C] MODE READER
      [S] 502 NNTP Service permanently unavailable
      [Server closes connection.]



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   Example of a connection from any client where the server is unable to
   provide news reader service:

      [C] QUIT
      [S] 400 NNTP Service temporarily unavailable
      [Server closes connection.]













































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6. The CAPABILITIES DISCOVERY step

   To discover what extensions are available, an NNTP client can query
   the server with the LIST EXTENSIONS command.  If a particular
   extension is unavailable, the client can attempt to work around it or
   it may wish to terminate the session.

   See Section 10 for further discussion of extensions.

6.1 LIST EXTENSIONS

6.1.1 Usage

   This command is optional.

   This command MUST NOT be pipelined.

   Syntax
      LIST EXTENSIONS

   Responses
      202   Extension list follows (multiline)
      402   Server has no extensions
      503   Extension information not available


6.1.2 Description

   The LIST EXTENSIONS command allows a client to determine which
   extensions are supported by the server.  This command MUST be
   implemented by any server that implements any extensions defined in
   this document.

   To discover what extensions are available, an NNTP client SHOULD
   query the server early in the session for extensions information by
   issuing the LIST EXTENSIONS command.  This command MAY be issued at
   anytime during a session.  It is not required that the client issues
   this command before attempting to make use of any extension.  The
   response generated by this command MAY change during a session
   because of other state information.  However, an NNTP client MUST NOT
   cache (for use in another session) any information returned if the
   LIST EXTENSIONS command succeeds.  That is, an NNTP client is only
   able to get the current and correct information concerning available
   extensions during a session by issuing a LIST EXTENSIONS command
   during that session and processing that response.

   The list of extensions is returned as a multi-line response following
   the 202 response code.  Each extension is listed on a separate line;



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   the line MUST begin with an extension-label and optionally one or
   more parameters (separated by single spaces).  The extension-label
   and the meaning of the parameters are specified as part of the
   definition of the extension.  The extension-label MUST be in
   uppercase.

   The server MUST NOT list the same extension twice in the response,
   and MUST list all supported extensions.  The order in which the
   extensions are listed is not significant.  The server need not even
   consistently return the same order.  If the server does not support
   any extensions, a 402 response SHOULD be returned, but it MAY instead
   return an empty list.

   Following a 503 response an extension might still be available, and
   the client MAY attempt to use it.

6.1.3 Examples

   Example of a successful response:

      [C] LIST EXTENSIONS
      [S] 202 Extensions supported:
      [S] OVER
      [S] HDR
      [S] LISTGROUP
      [S] .

   The particular extensions shown here are simply examples of what
   might be defined in other places, and no particular meaning should be
   attributed to them.

   Example where no extensions are available, using preferred format:

      [C] LIST EXTENSIONS
      [S] 402 Server has no extensions

   Example where no extensions are available, using an empty list:

      [C] LIST EXTENSIONS
      [S] 202 Extensions supported:
      [S] .










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7. Article posting and retrieval

   News reading clients have available a variety of mechanisms to
   retrieve articles via NNTP.  The news articles are stored and indexed
   using three types of keys.  One key is the message-id of an article.
   According to RFC 1036, this identifier should be globally unique.
   Another key is composed of the newsgroup name and the article number
   within that newsgroup.  That key MUST be unique to a particular
   server (there will be only one article with that number within a
   particular newsgroup), but is not required to be globally unique.
   Additionally, because the same article can be cross-posted to
   multiple newsgroups, there may be multiple keys that point to the
   same article on the same server.  The final key is the arrival
   timestamp, giving the time that the article arrived at the server.

   The server MUST ensure that article numbers are issued in order of
   arrival timestamp; that is, articles arriving later MUST have higher
   numbers than those that arrive earlier.  The server SHOULD allocate
   the next sequential unused number to each new article.

   Article numbers MUST lie between 1 and 4,294,967,295 inclusive.  The
   client and server SHOULD NOT use leading zeroes in specifying article
   numbers, and MUST NOT use more than 16 digits.  In some situations,
   the value zero replaces an article number to show some special
   situation.

   Message-ids are as defined in RFC 2822 [7] with the following
   modifications:

   o  A message-id MUST NOT contain a US-ASCII space within any
      quoted-pair.

   o  A message-id MUST NOT be longer than 250 octets.

   o  RFC 2822 obsolete syntax for message-ids is not supported by the
      protocol specified in this document.


7.1 Group and article selection

   The following commands are used to set the "current selected
   newsgroup" and the "current article number", which are used by
   various commands.  At the start of an NNTP session, both of these
   values are set to the special value "invalid".

7.1.1 GROUP





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7.1.1.1 Usage

   Syntax
      GROUP ggg

   Responses
      211 n l h ggg   Group successfully selected
      411             No such newsgroup

   Parameters
      ggg = name of newsgroup
      n   = estimated number of articles in the group
      l   = reported low water mark
      h   = reported high water mark


7.1.1.2 Description

   The required parameter ggg is the name of the newsgroup to be
   selected (e.g.  "news.software.b").  A list of valid newsgroups may
   be obtained by using the LIST ACTIVE command (see Section 8.6.1).

   The successful selection response will return the article numbers of
   the first and last articles in the group at the moment of selection
   (these numbers are referred to as the "reported low water mark" and
   the "reported high water mark"), and an estimate of the number of
   articles on file in the group.

   If the group is not empty, the estimate MUST be at least the actual
   number of articles available, and MUST be no greater than one more
   than the difference between the reported low and high water marks.
   (Some implementations will actually count the number of articles on
   file.  Others will just subtract the low water mark from the high
   water mark and add one to get an estimate.)

   If the group is empty, one of the following three situations will
   occur.  Clients MUST accept all three cases; servers MUST NOT
   represent an empty group in any other way.

   o  The high water mark will be one less than the low water mark, and
      the estimated article count will be zero.  Servers SHOULD use this
      method to show an empty group.  This is the only time that the
      high water mark can be less than the low water mark.

   o  All three numbers will be zero.

   o  The high water mark is greater than or equal to the low water
      mark.  The estimated article count might be zero or non-zero; if



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      non-zero, the same requirements apply as for a non-empty group.

   The set of articles in a group may change after the GROUP command is
   carried out.  That is:

   o  articles may be removed from the group

   o  articles may be reinstated in the group with the same article
      number, but those articles MUST have numbers no less than the
      reported low water mark (note that this is a reinstatement of the
      previous article, not a new article reusing the number)

   o  new articles may be added with article numbers greater than the
      reported high water mark (if an article that was the one with the
      highest number has been removed, the next new article will not
      have the number one greater than the reported high water mark)

   Except when the group is empty and all three numbers are zero,
   whenever a subsequent GROUP command for the same newsgroup is issued,
   either by the same client or a different client, the reported low
   water mark in the response MUST be no less than that in any previous
   response for that newsgroup sent to any client.  The client may make
   use of the low water mark to remove all remembered information about
   articles with lower numbers, as these will never recur.  This
   includes the situation when the high water mark is one less than the
   low water mark.

   No similar assumption can be made about the high water mark, as this
   can decrease if an article is removed, and then increase again if it
   is reinstated or if new articles arrive.  When a valid group is
   selected by means of this command, the current selected newsgroup
   MUST be set to that group and the current article number MUST be set
   to the first article in the group.  If an empty newsgroup is
   selected, the current article pointer is made invalid.  If an invalid
   group is specified, the current selected newsgroup and current
   article number MUST NOT be changed.

   The GROUP command (or the LISTGROUP command, if implemented) MUST be
   used by a client and a successful response received before the any
   other command is used that depends on the value of the current
   selected newsgroup or current article number.

   If the group specified is not available on the server, a 411 response
   MUST be returned.

7.1.1.3 Examples

   Example for a group known to the server:



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      [C] GROUP misc.test
      [S] 211 1234 3000234 3002322 misc.test

   Example for a group unknown to the server:

      [C] GROUP example.is.sob.bradner.or.barber
      [S] 411 example.is.sob.bradner.or.barber is unknown

   Example of an empty group using the preferred response:

      [C] GROUP example.currently.empty.newsgroup
      [S] 211 0 4000 3999 example.currently.empty.newsgroup

   Example of an empty group using an alternative response:

      [C] GROUP example.currently.empty.newsgroup
      [S] 211 0 0 0 example.currently.empty.newsgroup

   Example of an empty group using a different alternative response:

      [C] GROUP example.currently.empty.newsgroup
      [S] 211 0 4000 4321 example.currently.empty.newsgroup


7.1.2 LAST

7.1.2.1 Usage

   Syntax
      LAST

   Responses
      223 n message-id   Article found
      412                No newsgroup selected
      420                Current article number is invalid
      422                No previous article in this group

   Parameters
      n          = article number
      message-id = article message-id


7.1.2.2 Description

   If the current selected newsgroup is valid, the current article
   number MUST be set to the previous article in that newsgroup (that
   is, the highest existing article number less than the current article
   number).  If successful, a response indicating the new current



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   article number and the message-id of that article MUST be returned.
   No article text is sent in response to this command.

   There MAY be no previous article in the group, although the current
   article number is not the reported low water mark.  There MUST NOT be
   a previous article when the current article number is the reported
   low water mark.

   Because articles can be removed and added, the results of multiple
   LAST and NEXT commands MAY not be consistent over the life of a
   particular NNTP session.

   If the current article number is already the first article of the
   newsgroup, a 422 response MUST be returned.  If the current article
   number is invalid, a 420 response MUST be returned.  If the current
   selected newsgroup is invalid, a 412 response MUST be returned.  In
   all three cases the current selected newsgroup and current article
   number MUST NOT be altered.

7.1.2.3 Examples

   Example of a successful article retrieval using LAST:

      [C] GROUP misc.test
      [S] 211 1234 3000234 3002322 misc.test
      [C] NEXT
      [S] 223 3000237 <668929@example.org> retrieved
      [C] LAST
      [S] 223 3000234 <45223423@example.com> retrieved

   Example of an attempt to retrieve an article without having selected
   a group (via the GROUP command) first:

      [Assumes current selected newsgroup is invalid.]
      [C] LAST
      [S] 412 no newsgroup selected

   Example of an attempt to retrieve an article using the LAST command
   when the current article number is that of the first article in the
   group:

      [C] GROUP misc.test
      [S] 211 1234 3000234 3002322 misc.test
      [C] LAST
      [S] 422 No previous article to retrieve

   Example of an attempt to retrieve an article using the LAST command
   when the current selected newsgroup is empty:



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      [C] GROUP example.empty.newsgroup
      [S] 211 0 0 0 example.empty.newsgroup
      [C] LAST
      [S] 420 No current article selected


7.1.3 NEXT

7.1.3.1 Usage

   Syntax
      NEXT

   Responses
      223 n message-id   Article found
      412                No newsgroup selected
      420                Current article number is invalid
      421                No next article in this group

   Parameters
      n          = article number
      message-id = article message-id


7.1.3.2 Description

   If the current selected newsgroup is valid, the current article
   number MUST be set to the next article in that newsgroup (that is,
   the lowest existing article number greater than the current article
   number).  If successful, a response indicating the new current
   article number and the message-id of that article MUST be returned.
   No article text is sent in response to this command.

   If the current article number is already the last article of the
   newsgroup, a 421 response MUST be returned.  In all other aspects
   (apart, of course, from the lack of 422 response) this command is
   identical to the LAST command (Section 7.1.2).

7.1.3.3 Examples

   Example of a successful article retrieval using NEXT:

      [C] GROUP misc.test
      [S] 211 1234 3000234 3002322 misc.test
      [C] NEXT
      [S] 223 3000237 <668929@example.org> retrieved

   Example of an attempt to retrieve an article without having selected



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   a group (via the GROUP command) first:

      [Assumes current selected newsgroup is invalid.]
      [C] NEXT
      [S] 412 no newsgroup selected

   Example of an attempt to retrieve an article using the NEXT command
   when the current article number is that of the last article in the
   group:

      [C] GROUP misc.test
      [S] 211 1234 3000234 3002322 misc.test
      [C] STAT 3002322
      [S] 223 3002322 <411@example.net> retrieved
      [C] NEXT
      [S] 421 No next article to retrieve

   Example of an attempt to retrieve an article using the NEXT command
   when the current selected newsgroup is empty:

      [C] GROUP example.empty.newsgroup
      [S] 211 0 0 0 example.empty.newsgroup
      [C] NEXT
      [S] 420 No current article selected


7.2 Retrieval of articles and article sections

   The ARTICLE, BODY, HEAD, and STAT commands are very similar.  They
   differ only in the parts of the article that are presented to the
   client and in the successful response code.  The ARTICLE command is
   described here in full, while the other commands are described in
   terms of the differences.  An article, as defined by RFC 1036,
   consists of two parts: the article headers and the article body.
   When responding to one of these commands, the server presents the
   entire article or appropriate part and does not attempt to alter or
   translate it in any way.

7.2.1 ARTICLE

7.2.1.1 Usage

   Syntax
      ARTICLE message-id
      ARTICLE [number]






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   Responses

      First form (message-id specified)
         220 0 message-id   Article follows (multiline)
         430                No article found with that message-id

      Second form (optional article number specified)
         220 n message-id   Article follows (multiline)
         412                No newsgroup selected
         420                Current article number is invalid [1]
         423                No such article in this newsgroup

   Parameters
      number     = Requested article number
      n          = Returned article number
      message-id = Article message-id

   [1] The 420 response can only occur if no article number has been
      specified.


7.2.1.2 Description

   The ARTICLE command selects an article based on the arguments and
   presents the header, a blank line, and the body of that article.  The
   command has two forms.

   In the first form, a message-id is specified (including the angle
   brackets), and the server presents the article with that message-id
   in its headers.  In this case, the server MUST NOT alter the current
   selected newsgroup or current article number.  This is both to
   facilitate the presentation of articles that may be referenced within
   another article being read, and because of the semantic difficulties
   of determining the proper sequence and membership of an article that
   may have been crossposted to more than one newsgroup.

   In the response, the article number is replaced with zero (that is,
   the server is not required to determine whether the article is in the
   current group or what article number(s) it has).

   In the second form, an article number may be specified.  If so, and
   if there is an article with that number in the currently selected
   newsgroup, the server MUST set the current article number to that
   number.

   Then, whether or not a number was specified, the article indicated by
   the current article number is presented to the client.




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   Note that a previously valid article number MAY become invalid if the
   article has been removed.  A previously invalid article number MAY
   become valid if the article has been reinstated, but such an article
   number MUST be no less than the reported low water mark for that
   group.

   The server MUST NOT change the current selected newsgroup as a result
   of this command.  The server MUST NOT change the current article
   number except when an article number argument was provided and the
   article exists; in particular, it MUST NOT change it following an
   unsuccessful response.

   The message-id of the article is taken from the message-id header
   line of the article (required by RFC 1036).  If there is no such
   line, the message-id "<0>" MUST be used instead (without the double
   quotes).

   Since the message-id field is unique for each article, it may be used
   by a client to skip duplicate displays of articles that have been
   posted more than once, or to more than one newsgroup.

   The article headers and body are returned as a multi-line response
   following the 220 response code.

   If the current article number is invalid, a 420 response MUST be
   returned.  If there is no article with the specified number, a 423
   response MUST be returned.  If the current selected newsgroup is
   invalid, a 412 response MUST be returned.

7.2.1.3 Examples

   Example of a successful retrieval of an article (using no article
   number):

      [C] GROUP misc.test
      [S] 211 1234 3000234 3002322 misc.test
      [C] ARTICLE
      [S] 220 3000234 <45223423@example.com>
      [S] Path: pathost!demo!whitehouse!not-for-mail
      [S] From: "Demo User" <nobody@example.net>
      [S] Newsgroups: misc.test
      [S] Subject: I am just a test article
      [S] Date: 6 Oct 1998 04:38:40 -0500
      [S] Organization: An Example Net, Uncertain, Texas
      [S] Message-ID: <411@example.net>
      [S]
      [S] This is just a test article.
      [S] .



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   Example of a successful retrieval of an article by message-id:

      [C] ARTICLE <45223423@example.com>
      [S] 220 0 <45223423@example.com>
      [S] Path: pathost!demo!whitehouse!not-for-mail
      [S] From: "Demo User" <nobody@example.net>
      [S] Newsgroups: misc.test
      [S] Subject: I am just a test article
      [S] Date: 6 Oct 1998 04:38:40 -0500
      [S] Organization: An Example Net, Uncertain, Texas
      [S] Message-ID: <411@example.net>
      [S]
      [S] This is just a test article.
      [S] .

   Example of an unsuccessful retrieval of an article by message-id:

      [C] ARTICLE <i.am.not.there@example.com>
      [S] 430 No Such Article Found

   Example of an unsuccessful retrieval of an article by number:

      [C] GROUP misc.test
      [S] 211 1234 3000234 3002322 news.groups
      [C] ARTICLE 300256
      [S] 423 No such article number in this group

   Example of an unsuccessful retrieval of an article by number because
   no newsgroup was selected first:

      [Assumes current selected newsgroup is invalid.]
      [C] ARTICLE 300256
      [S] 412 No newsgroup selected

   Example of an attempt to retrieve an article when the current
   selected newsgroup is empty:

      [C] GROUP example.empty.newsgroup
      [S] 211 0 0 0 example.empty.newsgroup
      [C] ARTICLE
      [S] 420 No current article selected


7.2.2 HEAD

7.2.2.1 Usage





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   Syntax
      HEAD message-id
      HEAD [number]

   Responses

      First form (message-id specified)
         221 0 message-id   Headers follow (multiline)
         430                No article found with that message-id

      Second form (optional article number specified)
         221 n message-id   Headers follow (multiline)
         412                No newsgroup selected
         420                Current article number is invalid [1]
         423                No such article in this newsgroup

   Parameters
      number     = Requested article number
      n          = Returned article number
      message-id = Article message-id

   [1] The 420 response can only occur if no article number has been
      specified.


7.2.2.2 Description

   The HEAD command behaves identically to the ARTICLE command except
   that, if the article exists, the response code is 221 instead of 220
   and only the headers are presented (the blank line separating the
   headers and body MUST NOT be included).

7.2.2.3 Examples

   Example of a successful retrieval of the headers in an article (using
   no article number):

      [C] GROUP misc.test
      [S] 211 1234 3000234 3002322 misc.test
      [C] HEAD
      [S] 221 3000234 <45223423@example.com>
      [S] Path: pathost!demo!whitehouse!not-for-mail
      [S] From: "Demo User" <nobody@example.net>
      [S] Newsgroups: misc.test
      [S] Subject: I am just a test article
      [S] Date: 6 Oct 1998 04:38:40 -0500
      [S] Organization: An Example Net, Uncertain, Texas
      [S] Message-ID: <411@example.net>



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      [S] .

   Example of a successful retrieval of the headers in an article by
   message-id:

      [C] HEAD <45223423@example.com>
      [S] 221 0 <45223423@example.com>
      [S] Path: pathost!demo!whitehouse!not-for-mail
      [S] From: "Demo User" <nobody@example.net>
      [S] Newsgroups: misc.test
      [S] Subject: I am just a test article
      [S] Date: 6 Oct 1998 04:38:40 -0500
      [S] Organization: An Example Net, Uncertain, Texas
      [S] Message-ID: <411@example.net>
      [S] .

   Example of an unsuccessful retrieval of the header of an article by
   message-id:

      [C] HEAD <i.am.not.there@example.com>
      [S] 430 No Such Article Found

   Example of an unsuccessful retrieval of the header of an article by
   number:

      [C] GROUP misc.test
      [S] 211 1234 3000234 3002322 misc.test
      [C] HEAD 300256
      [S] 423 No such article number in this group

   Example of an unsuccessful retrieval the header of an article by
   number because no newsgroup was selected first:

      [Assumes current selected newsgroup is invalid.]
      [C] HEAD 300256
      [S] 412 No newsgroup selected

   Example of an attempt to retrieve the header of an article when the
   current selected newsgroup is empty:

      [C] GROUP example.empty.newsgroup
      [S] 211 0 0 0 example.empty.newsgroup
      [C] HEAD
      [S] 420 No current article selected







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7.2.3 BODY

7.2.3.1 Usage

   Syntax
      BODY message-id
      BODY [number]

   Responses

      First form (message-id specified)
         222 0 message-id   Body follows (multiline)
         430                No article found with that message-id

      Second form (optional article number specified)
         222 n message-id   Body follows (multiline)
         412                No newsgroup selected
         420                Current article number is invalid [1]
         423                No such article in this newsgroup

   Parameters
      number     = Requested article number
      n          = Returned article number
      message-id = Article message-id

   [1] The 420 response can only occur if no article number has been
      specified.


7.2.3.2 Description

   The BODY command behaves identically to the ARTICLE command except
   that, if the article exists, the response code is 222 instead of 220
   and only the body is presented (the blank line separating the headers
   and body MUST NOT be included).

7.2.3.3 Examples

   Example of a successful retrieval of the body of an article (using no
   article number):

      [C] GROUP misc.test
      [S] 211 1234 3000234 3002322 misc.test
      [C] BODY
      [S] 222 3000234 <45223423@example.com>
      [S] This is just a test article.
      [S] .




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   Example of a successful retrieval of the body of an article by
   message-id:

      [C] BODY <45223423@example.com>
      [S] 222 0 <45223423@example.com>
      [S] This is just a test article.
      [S] .

   Example of an unsuccessful retrieval of the body of an article by
   message-id:

      [C] BODY <i.am.not.there@example.com>
      [S] 430 No Such Article Found

   Example of an unsuccessful retrieval of the body of an article by
   number:

      [C] GROUP misc.test
      [S] 211 1234 3000234 3002322 misc.test
      [C] BODY 300256
      [S] 423 No such article number in this group

   Example of an unsuccessful retrieval of the body of an article by
   number because no newsgroup was selected first:

      [Assumes current selected newsgroup is invalid.]
      [C] BODY 300256
      [S] 412 No newsgroup selected

   Example of an attempt to retrieve the body of an article when the
   current selected newsgroup is empty:

      [C] GROUP example.empty.newsgroup
      [S] 211 0 0 0 example.empty.newsgroup
      [C] BODY
      [S] 420 No current article selected


7.2.4 STAT

7.2.4.1 Usage

   Syntax
      STAT message-id
      STAT [number]






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   Responses

      First form (message-id specified)
         223 0 message-id   Article exists
         430                No article found with that message-id

      Second form (optional article number specified)
         223 n message-id   Article exists
         412                No newsgroup selected
         420                Current article number is invalid [1]
         423                No such article in this newsgroup

   Parameters
      number     = Requested article number
      n          = Returned article number
      message-id = Article message-id

   [1] The 420 response can only occur if no article number has been
      specified.


7.2.4.2 Description

   The STAT command behaves identically to the ARTICLE command except
   that, if the article exists, it is NOT presented to the client and
   the response code is 223 instead of 220.  Note that the response is
   NOT multi-line.

   This command allows the client to determine whether an article
   exists, and in the second form what its message-id is, without having
   to process an arbitrary amount of text.

7.2.4.3 Examples

   Example of STAT on an existing article (using no article number):

      [C] GROUP misc.test
      [S] 211 1234 3000234 3002322 misc.test
      [C] STAT
      [S] 223 3000234 <45223423@example.com>

   Example of a STAT of an existing article by message-id:

      [C] STAT <45223423@example.com>
      [S] 223 0 <45223423@example.com>

   Example of an STAT of an article not on the server by message-id:




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      [C] STAT <i.am.not.there@example.com>
      [S] 430 No Such Article Found

   Example of STAT of an article not in the server by number:

      [C] GROUP misc.test
      [S] 211 1234 3000234 3002322 misc.test
      [C] STAT 300256
      [S] 423 No such article number in this group

   Example of STAT of an article by number when no newsgroup was
   selected first:

      [Assumes current selected newsgroup is invalid.]
      [C] STAT 300256
      [S] 412 No newsgroup selected

   Example of STAT of an article when the current selected newsgroup is
   empty:

      [C] GROUP example.empty.newsgroup
      [S] 211 0 0 0 example.empty.newsgroup
      [C] STAT
      [S] 420 No current article selected


7.3 Article posting

   Article posting is done in one of two modes: individual article
   posting from news reading clients using POST, and article transfer
   from other news servers using IHAVE.

7.3.1 POST

7.3.1.1 Usage

   This command MUST NOT be pipelined.

   Syntax
      POST

   Responses

      Initial responses
         340   Send article to be posted
         440   Posting not permitted





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      Subsequent responses
         240   Article received OK
         441   Posting failed


7.3.1.2 Description

   If posting is allowed, a 340 response MUST be returned to indicate
   that the article to be posted should be sent.  If posting is
   prohibited for some installation-dependent reason, a 440 response
   MUST be returned.

   If posting is permitted, the article MUST be presented to the server
   by the client in the format specified by RFC 1036 (or by any of its
   successors or extensions).  The text forming the header and body of
   the message to be posted MUST be sent by the client in the format
   defined above (Section 3) for multi-line responses (except that there
   is no initial line containing a response code).  Thus a single dot
   (".") on a line indicates the end of the text, and lines starting
   with a dot in the original text have that dot doubled during
   transmission.

   Following the presentation of the termination sequence by the client,
   the server MUST return a response indicating success or failure of
   the article transfer.  Note that response codes 340 and 440 are used
   in direct response to the POST command.  Others are returned
   following the sending of the article.

   A response of 240 SHOULD indicate that, barring unforseen server
   errors, the posted article will be made available on the server and/
   or transferred to other servers as appropriate.  In other words,
   articles not wanted by the server SHOULD be rejected with a 411
   response and not accepted and silently discarded.

   No attempt shall be made by the server to filter characters, fold or
   limit lines, or otherwise process incoming text.  The intent is that
   the server just passes the incoming message to be posted to the
   server installation's news posting software, which is not defined by
   this document.

   The client SHOULD NOT assume that the article has been successfully
   transferred unless it receives an affirmative response from the
   server.  If the session is interrupted before the response is
   received, it is possible that an affirmative response was sent but
   has been lost.  Therefore, in any subsequent session the client
   SHOULD use the same message-id in the article when resending it or
   check whether the article was successfully posted before resending it
   to ensure that the resend will not result in a duplicate article.



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7.3.1.3 Examples

   Example of a successful posting:

      [C] POST
      [S] 340 Input article; end with <CR-LF>.<CR-LF>
      [C] From: "Demo User" <nobody@example.net>
      [C] Newsgroups: misc.test
      [C] Subject: I am just a test article
      [C] Organization: An Example Net
      [C]
      [C] This is just a test article.
      [C] .
      [S] 240 Article received OK

   Example of an unsuccessful posting:

      [C] POST
      [S] 340 Input article; end with <CR-LF>.<CR-LF>
      [C] From: "Demo User" <nobody@example.net>
      [C] Newsgroups: misc.test
      [C] Subject: I am just a test article
      [C] Organization: An Example Net
      [C]
      [C] This is just a test article.
      [C] .
      [S] 441 Posting failed

   Example of an attempt to post when posting is not allowed:

      [C] MODE READER
      [S] 201 NNTP Service Ready, posting prohibited
      [C] POST
      [S] 440 Posting not permitted


7.3.2 IHAVE

7.3.2.1 Usage

   This command MUST NOT be pipelined.

   Syntax
      IHAVE message-id

   Responses





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      Initial responses
         335   Send article to be transferred
         435   Article not wanted
         436   Transfer not possible; try again later

      Subsequent responses
         235   Article transferred OK
         436   Transfer failed; try again later
         437   Transfer rejected; do not retry

   Parameters
      message-id = Article message-id


7.3.2.2 Description

   The IHAVE command informs the server that the client has an article
   with the specified message-id.  If the server desires a copy of that
   article a 335 response MUST be returned, instructing the client to
   send the entire article.  If the server does not want the article
   (if, for example, the server already has a copy of it), a 435
   response MUST be returned, indicating that the article is not wanted.
   Finally, if the article isn't wanted immediately but the client
   should retry later if possible (if, for example, another client is in
   the process of sending the same article to the server), a 436
   response MUST be returned.

   If transmission of the article is requested, the client MUST send the
   entire article, including header and body, in the format defined
   above (Section 3) for multi-line responses (except that there is no
   initial line containing a response code).  Thus a single dot (".") on
   a line indicates the end of the text, and lines starting with a dot
   in the original text have that dot doubled during transmission.  The
   server MUST return either a 235 response, indicating that the article
   was successfully transferred, a 436 response, indicating that the
   transfer failed but should be tried again later, or a 437 response,
   indicating that the article was rejected.

   This function differs from the POST command in that it is intended
   for use in transferring already-posted articles between hosts.  It
   SHOULD NOT be used when the client is a personal news reading
   program, since this command indicates that the forthcoming article
   has already been posted at another site and is being forwarded from
   another host.  However, the server MAY elect not to post or forward
   the article if after further examination of the article it deems it
   inappropriate to do so.  Reasons for such subsequent rejection of an
   article may include such problems as inappropriate newsgroups or
   distributions, disc space limitations, article lengths, garbled



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   headers, and the like.  These are typically restrictions enforced by
   the server host's news software and not necessarily the NNTP server
   itself.

   The client SHOULD NOT assume that the article has been successfully
   transferred unless it receives an affirmative response from the
   server.  A lack of response (such as a dropped network connection or
   a network timeout) SHOULD be treated the same as a 436 response.

   Because some news server software may not be able immediately to
   determine whether or not an article is suitable for posting or
   forwarding, an NNTP server MAY acknowledge the successful transfer of
   the article (with a 235 response) but later silently discard it.

7.3.2.3 Examples

   Example of successfully sending an article to another site:

      [C] IHAVE <i.am.an.article.you.will.want@example.com>
      [S] 335 Send it; end with <CR-LF>.<CR-LF>
      [C] Path: pathost!demo!somewhere!not-for-mail
      [C] From: "Demo User" <nobody@example.com>
      [C] Newsgroups: misc.test
      [C] Subject: I am just a test article
      [C] Date: 6 Oct 1998 04:38:40 -0500
      [C] Organization: An Example Com, San Jose, CA
      [C] Message-ID: <i.am.a.test.article@example.com>
      [C]
      [C] This is just a test article.
      [C] .
      [S] 235 Article transferred OK

   Example of sending an article to another site that rejects it:

      [C] IHAVE <i.am.an.article.you.will.want@example.com>
      [S] 335 Send it; end with <CR-LF>.<CR-LF>
      [C] Path: pathost!demo!somewhere!not-for-mail
      [C] From: "Demo User" <nobody@example.com>
      [C] Newsgroups: misc.test
      [C] Subject: I am just a test article
      [C] Date: 6 Oct 1998 04:38:40 -0500
      [C] Organization: An Example Com, San Jose, CA
      [C] Message-ID: <i.am.a.test.article@example.com>
      [C]
      [C] This is just a test article.
      [C] .
      [S] 437 Article rejected; don't send again




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   Example of sending an article to another site where the transfer
   fails:

      [C] IHAVE <i.am.an.article.you.will.want@example.com>
      [S] 335 Send it; end with <CR-LF>.<CR-LF>
      [C] Path: pathost!demo!somewhere!not-for-mail
      [C] From: "Demo User" <nobody@example.com>
      [C] Newsgroups: misc.test
      [C] Subject: I am just a test article
      [C] Date: 6 Oct 1998 04:38:40 -0500
      [C] Organization: An Example Com, San Jose, CA
      [C] Message-ID: <i.am.a.test.article@example.com>
      [C]
      [C] This is just a test article.
      [C] .
      [S] 436 Transfer failed

   Example of sending an article to a site that already has it:

      [C] IHAVE <i.am.an.article.you.have@example.com>
      [S] 435 Duplicate

   Example of sending an article to a site that requests the article be
   tried again later:

      [C] IHAVE <i.am.an.article.you.defer@example.com>
      [S] 436 Retry later
























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8. Information commands

   This section lists other commands that may be used at any time
   between the beginning of a session and its termination.  Using these
   commands does not alter any state information, but the response
   generated from their use may provide useful information to clients.

   All servers MUST implement these commands.

8.1 DATE

8.1.1 Usage

   Syntax
      DATE

   Responses
      111 yyyymmddhhmmss   server date and time

   Parameters
      yyyymmddHHmmss = Current UTC date and time on server


8.1.2 Description

   This command exists to help clients find out the current Coordinated
   Universal Time [9] from the server's perspective.  This command MUST
   NOT be used as a substitute for NTP [10], but to provide information
   that might be useful when using the NEWNEWS command (see Section
   8.4).  A system providing NNTP service SHOULD implement NTP for the
   purposes of keeping the system clock as accurate as possible.

   The server MUST return a 111 response specifying the date and time on
   the server in the form yyyymmddhhmmss.  This date and time is in
   Coordinated Universal Time.

8.1.3 Examples

      [C] DATE
      [S] 111 19990623135624


8.2 HELP

8.2.1 Usage






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   Syntax
      HELP

   Responses
      100   Help text follows (multiline)


8.2.2 Description

   This command provides a short summary of commands that are understood
   by this implementation of the server.  The help text will be
   presented as a multiline response following the 100 response code.

   This text is not guaranteed to be in any particular format and MUST
   NOT be used by clients as a replacement for the LIST EXTENSIONS
   command described in Section 6.1

8.2.3 Examples

      [C] HELP
      [S] 100 Help text follows
      [S] This is some help text.  There is no specific
      [S] formatting requirement for this test, though
      [S] it is customary for it to list the valid commands
      [S] and give a brief definition of what they do
      [S] .


8.3 NEWGROUPS

8.3.1 Usage

   Syntax
      NEWGROUPS date time [GMT]

   Responses
      231   List of new newsgroups follows (multiline)

   Parameters
      date = Date in yymmdd or yyyymmdd format
      time = Time in hhmmss format


8.3.2 Description

   This command returns a list of newsgroups created on the server since
   the specified date and time.  The results are in the same format as
   the LIST ACTIVE command (see Section 8.6.1).



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   OUTSTANDING ISSUE

      Does the output include high/low/status or not? If so, the
      examples are wrong.  If not, the above text is wrong.

   The date is specified as 6 or 8 digits in the format [xx]yymmdd,
   where xx is the first two digits of the year (19-99), yy is the last
   two digits of the year (00-99), mm is the month (01-12), and dd is
   the day of the month (01-31).  If the first two digits of the year
   are not specified, the year is to be taken from the current century
   if yy is smaller than or equal to the current year, otherwise the
   year is from the previous century.

   The time is specified as 6 digits in the format hhmmss, where hh is
   the hours in the 24-hour clock (00-23), mm is the minutes (00-59),
   and ss is the seconds (00-60, to allow for leap seconds).  The token
   "GMT" specifies that the date and time are given in Coordinated
   Universal Time; if it is omitted then the date and time are specified
   in the server's local timezone.  Note that there is no way using the
   protocol specified in this document to establish the server's local
   timezone.

   Note that an empty list is a possible valid response and indicates
   that there are no new newsgroups since that date-time.

   Clients SHOULD make all queries using Coordinated Universal Time
   (i.e.  by including the "GMT" parameter) when possible.

8.3.3 Examples

   Example where there are new groups:

      [C] NEWGROUPS 19990624 000000 GMT
      [S] 231 list of new newsgroups follows
      [S] alt.rfc-writers.recovery
      [S] tx.natives.recovery
      [S] .

   Example where there are no new groups:

      [C] NEWGROUPS 19990624 000000 GMT
      [S] 231 list of new newsgroups follows
      [S] .


8.4 NEWNEWS





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8.4.1 Usage

   Syntax
      NEWNEWS wildmat date time [GMT]

   Responses
      230   List of new articles follows (multiline)

   Parameters
      wildmat = Newsgroups of interest
      date    = Date in yymmdd or yyyymmdd format
      time    = Time in hhmmss format


8.4.2 Description

   This command returns a list of message-ids of articles posted or
   received on the server, in the newsgroups whose names match the
   wildmat, since the specified date and time.  One message-id is sent
   on each line; the order of the response has no specific significance
   and may vary from response to response in the same session.  A
   message-id MAY appear more than once; if it does so, it has the same
   meaning as if it appeared only once.

   Date and time are in the same format as the NEWGROUPS command (see
   Section 8.3).

   Note that an empty list is a possible valid response and indicates
   that there is currently no new news in the relevant groups.

   Clients SHOULD make all queries in Coordinated Universal Time (i.e.
   by using the "GMT" parameter) when possible.

8.4.3 Examples

   Example where there are new articles:

      [C] NEWNEWS news.*,sci.* 19990624 000000 GMT
      [S] 230 list of new articles by message-id follows
      [S] <i.am.a.new.article@example.com>
      [S] <i.am.another.new.article@example.com>
      [S] .

   Example where there are no new articles:

      [C] NEWNEWS alt.* 19990624 000000 GMT
      [S] 230 list of new articles by message-id follows
      [S] .



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8.5 Time

   As described in Section 7, each article has an arrival timestamp.
   Each newsgroup also has a creation timestamp.  These timestamps are
   used by the NEWNEWS and NEWGROUP commands to construct their
   reponses.

   The DATE command MUST return a timestamp from the same clock as is
   used for determining article arrival and group creation times.  This
   clock SHOULD be monotonic, and adjustments SHOULD be made by running
   it fast or slow compared to "real" time rather than by making sudden
   jumps.

   Clients can ensure that they do not have gaps in lists of articles or
   groups by using the DATE command in the following manner:

   First session:
      Issue DATE command and record result
      Issue NEWNEWS command using a previously chosen timestamp

   Subsequent sessions:
      Issue DATE command and hold result in temporary storage
      Issue NEWNEWS command using timestamp saved from previous session
      Overwrite saved timestamp with that currently in temporary storage

   In order to allow for minor errors, clients MAY want to adjust the
   timestamp back by two or three minutes before using it in NEWNEWS.

8.5.1 Examples

   First session:

      [C] DATE
      [S] 111 20010203112233
      [C] NEWNEWS local.chat 20001231 235959 GMT
      [S] 230 list follows
      [S] <article.1@local.service>
      [S] <article.2@local.service>
      [S] <article.3@local.service>
      [S] .

   Second session (the client has subtracted 3 minutes from the
   timestamp returned previously):

      [C] DATE
      [S] 111 20010204003344
      [C] NEWNEWS local.chat 20010203 111933 GMT
      [S] 230 list follows



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      [S] <article.3@local.service>
      [S] <article.4@local.service>
      [S] <article.5@local.service>
      [S] .

   Note how <article.3@local.service> arrived in the 3 minute gap and so
   is listed in both responses.

8.6 The LIST commands

8.6.1 LIST ACTIVE

8.6.1.1 Usage

   Syntax
      LIST ACTIVE [wildmat]

   Responses
      215   Information follows (multiline)

   Parameters
      wildmat = groups of interest


8.6.1.2 Description

   The LIST ACTIVE command with no parameters returns a list of valid
   newsgroups and associated information.  Each newsgroup is sent as a
   line of text in the following format:

   group first last status

   where:

   "group" is the name of the newsgroup;

   "first" is the current low water mark for the group;

   "last" is the current high water mark for the group;

   "status" is the current status of the group on this server; typically
      this is one of:

      "y" posting is permitted

      "n" posting is not permitted





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      "m" postings will be forwarded to the newsgroup moderator

      Other status strings may exist.  The definition of these other
      values and the circumstances under which they are returned is
      covered in other specifications.

      OUTSTANDING ISSUE

         Is the order "group first last status" or "group last first
         status"? The examples match the description above, but they
         don't match the news server I have tested.

   Each field in the line is separated from its neighboring fields by
   one or more US-ASCII spaces.

   The "first" and "last" fields correspond to the high and low water
   marks described in the GROUP command (see Section 7.1.1).

   The status of a newsgroup only indicates how posts to that newsgroup
   are processed.  It does not indicate if the current client is
   permitted to post.  That is indicated by the status code returned as
   part of the greeting.  Note that an empty list is a possible valid
   response, and indicates that there are currently no valid newsgroups.

   If the optional wildmat parameter is specified, the list is limited
   to only the groups whose names match the wildmat.  If no wildmat is
   specified, the keyword ACTIVE MAY be omitted without altering the
   effect of the command.

8.6.1.3 Examples

   Example of LIST ACTIVE returning a list of newsgroups:

      [C] LIST ACTIVE
      [S] 215 list of newsgroups follows
      [S] misc.test 3000234 3002322 y
      [S] alt.fc-writers.recovery 1 4 y
      [S] tx.natives.recovery 56 89 y
      [S] .

   Example of LIST ACTIVE omitting the second keyword and returning no
   newsgroups:

      [C] LIST
      [S] 215 list of newsgroups follows
      [S] .

   Example of LIST ACTIVE with a wildmat:



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      [C] LIST ACTIVE *.recovery
      [S] 215 list of newsgroups follows
      [S] alt.fc-writers.recovery 1 4 y
      [S] tx.natives.recovery 56 89 y
      [S] .


8.6.2 LIST ACTIVE.TIMES

8.6.2.1 Usage

   This command is optional.

   Syntax
      LIST ACTIVE.TIMES [wildmat]

   Responses
      215   Information follows (multiline)
      503   Facility not available

   Parameters
      wildmat = groups of interest


8.6.2.2 Description

   The active.times file is maintained by some news transport systems to
   contain information about who created a particular newsgroup and
   when.  Each line of this file consists of three fields separated from
   each other by one or more US-ASCII space characters.  The first field
   is the name of the newsgroup.  The second is the time when this group
   was created on this news server, measured in seconds since the start
   of January 1, 1970.  The third is the email address of the entity
   that created the newsgroup, and must be a mailbox as defined in RFC
   2822 [7].

   If the information is available, it is returned as a multi-line
   response following the 215 response code.  If the information is not
   available, a 503 response MUST be returned.  If the server does not
   recognize the command, a 501 response MUST be returned.

   If the optional wildmat parameter is specified, the list is limited
   to only the groups whose names match the wildmat (and therefore may
   be empty).

8.6.2.3 Examples

   Example of LIST ACTIVE.TIMES returning a list of newsgroups:



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      [C] LIST ACTIVE.TIMES
      [S] 215 information follows
      [S] misc.test 930445408 <creatme@isc.org>
      [S] alt.rfc-writers.recovery 930562309 <m@example.com>
      [S] tx.natives.recovery 930678923 <sob@academ.com>
      [S] .

   Example of LIST ACTIVE.TIMES returning an error where the command is
   recognised but the software does not maintain this information:

      [C] LIST ACTIVE.TIMES
      [S] 503 program error, function not performed

   Example of LIST ACTIVE.TIMES sent to a server that does not recognize
   this command:

      [C] LIST ACTIVE.TIMES
      [S] 501 Syntax Error


8.6.3 LIST DISTRIBUTIONS

8.6.3.1 Usage

   This command is optional.

   Syntax
      LIST DISTRIBUTIONS

   Responses
      215   Information follows (multiline)
      503   Facility not available


8.6.3.2 Description

   The distributions file is maintained by some news transport systems
   to contain information about valid values for the Distribution: line
   in a news article header and about what the values mean.  Each line
   of this file consists of two fields separated from each other by one
   or more US-ASCII space characters.  The first field is a value and
   the second is a short explanation of the meaning of that value.

   If the information is available, it is returned as a multi-line
   response following the 215 response code.  If the information is not
   available, a 503 response MUST be returned.  If the server does not
   recognize the command, a 501 response MUST be returned.




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8.6.3.3 Examples

   Example of LIST DISTRIBUTIONS returning a list of distributions:

      [C] LIST DISTRIBUTIONS
      [S] 215 information follows
      [S] usa United States of America
      [S] na North America
      [S] world All over the World
      [S] .

   Example of LIST DISTRIBUTIONS returning an error where the command is
   recognised but the software does not maintain this information:

      [C] LIST DISTRIBUTIONS
      [S] 503 program error, function not performed

   Example of LIST DISTRIBUTIONS sent to a server that does not
   recognize this command:

      [C] LIST DISTRIBUTIONS
      [S] 501 Syntax Error


8.6.4 LIST DISTRIB.PATS

8.6.4.1 Usage

   This command is optional.

   Syntax
      LIST DISTRIB.PATS

   Responses
      215   Information follows (multiline)
      503   Facility not available


8.6.4.2 Description

   The distrib.pats file is maintained by some news transport systems to
   choose a value for the Distribution: line in the header of a news
   article being posted.  Each line of this file consists of three
   fields separated from each other by a US-ASCII colon.  The first
   field is a weight, the second field is a wildmat (which may be a
   simple group name), and the third field is a value for the
   Distribution: header.




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   The client MAY use this information to select a Distribution: value
   based on the name of a newsgroup.  To do so, it should determine the
   lines whose second field matches the newsgroup name, select from
   among them the line with the highest weight (with 0 being the
   lowest), and use the value of the third field to construct the
   Distribution: header.

   If the information is available, it is returned as a multi-line
   response following the 215 response code.  If the information is not
   available, a 503 response MUST be returned.  If the server does not
   recognize the command, a 501 response MUST be returned.

8.6.4.3 Examples

   Example of LIST DISTRIB.PATS returning a list of newsgroups:

      [C] LIST DISTRIB.PATS
      [S] 215 information follows
      [S] 10:local.*:local
      [S] 5:*:world
      [S] 20:local.here.*:thissite
      [S] .

   Example of LIST DISTRIB.PATS returning an error where the command is
   recognised but the software does not maintain this information:

      [C] LIST DISTRIB.PATS
      [S] 503 program error, function not performed

   Example of LIST DISTRIB.PATS sent to a server that does not recognize
   this command:

      [C] LIST DISTRIB.PATS
      [S] 501 Syntax Error


8.6.5 LIST NEWSGROUPS

8.6.5.1 Usage

   This command is optional.

   Syntax
      LIST NEWSGROUPS [wildmat]

   Responses
      215   Information follows (multiline)
      503   Facility not available



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   Parameters
      wildmat = groups of interest


8.6.5.2 Description

   The newsgroups file is maintained by some news transport systems to
   contain the name of each newsgroup that is available on the server
   and a short description about the purpose of the group.  Each line of
   this file consists of two fields separated from each other by one or
   more US-ASCII space characters.  The first field is the name of the
   newsgroup and the second is a short description of the group.  Note
   that an empty list is a possible valid response, and indicates that
   there are currently no valid newsgroups.

   If the information is available, it is returned as a multi-line
   response following the 215 response code.  If the information is not
   available, a 503 response MUST be returned.  If the server does not
   recognize the command, a 501 response MUST be returned.

   If the optional wildmat parameter is specified, the list is limited
   to only the groups whose names match the wildmat.

8.6.5.3 Examples

   Example of LIST NEWSGROUPS returning a list of newsgroups:

      [C] LIST NEWSGROUPS
      [S] 215 information follows
      [S] misc.test General Usenet testing
      [S] alt.rfc-writers.recovery RFC Writers Recovery
      [S] tx.natives.recovery Texas Natives Recovery
      [S] .

   Example of LIST NEWSGROUPS returning an error where the command is
   recognised but the software does not maintain this information:

      [C] LIST NEWSGROUPS
      [S] 503 program error, function not performed

   Example of LIST NEWSGROUPS sent to a server that does not recognize
   this command:

      [C] LIST NEWSGROUPS
      [S] 501 Syntax error






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9. The CONCLUSION step

9.1 QUIT

9.1.1 Usage

   Syntax
      QUIT

   Responses
      205   Connection closing


9.1.2 Description

   The server process MUST acknowledge the QUIT command and then close
   the connection to the client.  This is the preferred method for a
   client to indicate that it has finished all its transactions with the
   NNTP server.

   If a client simply disconnects (or the connection times out or some
   other fault occurs), the server MUST gracefully cease its attempts to
   service the client, disconnecting from its end if necessary.

9.1.3 Examples

      [C] QUIT
      [S] 205 closing connection
      [Server closes connection.]






















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10. Framework for NNTP extensions

   Although NNTP is widely and robustly deployed, some parts of the
   Internet community might wish to extend the NNTP service.  This
   document defines a means whereby an extended NNTP client can query
   the server to determine the service extensions that it supports.

   It must be emphasized that any extension to the NNTP service should
   not be considered lightly.  NNTP's strength comes primarily from its
   simplicity.  Experience with many protocols has shown that:

      Protocols with few options tend towards ubiquity, whilst protocols
      with many options tend towards obscurity.

   This means that each and every extension, regardless of its benefits,
   must be carefully scrutinized with respect to its implementation,
   deployment, and interoperability costs.  In many cases, the cost of
   extending the NNTP service will likely outweigh the benefit.

   Given this environment, the framework for extensions described in
   this document consists of:

   o  a mechanism for clients to determine a server's available
      extensions

   o  a registry of NNTP service extensions

   The LIST EXTENSIONS command is described in this document (see
   Section 6.1) and is the mechanism for clients to use to determine
   what extensions are available.

   The IANA shall maintain a registry of NNTP service extensions.

   An extension is identified by a unique extension-label, which is a
   string of 1 to 12 uppercase letters.  The extension-label will often
   be the name of a new command that the extension adds.  However this
   is not a requirement: an extension might not add any new commands or
   keywords.

   An extension is either a private extension or else it is included in
   the IANA registry and is defined in an RFC.  Such RFCs either must be
   on the standards-track or must define an IESG-approved experimental
   protocol.

   The definition of an extension must include:

   o  a descriptive name for the extension




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   o  the extension-label (which is returned by LIST EXTENSIONS to
      indicate to the client that the server supports this particular
      extension)

   o  the syntax, values, and meanings of any parameters following the
      extension-label in the output of LIST EXTENSIONS

   o  any new NNTP commands associated with the extension

   o  the syntax and possible values of parameters associated with the
      new NNTP commands

   o  any new parameters the extension associates with any other
      pre-existing NNTP commands

   o  how support for the extension affects the behavior of a server and
      NNTP client

   o  any increase in the maximum length of commands over the value
      specified in this document

   o  a specific statement about the effect on pipelining this extension
      may have (if any)

   The extension-label of private extensions MUST begin with "X".  The
   extension-label of registered extensions MUST NOT begin with "X".

   A server MUST NOT provide any extension, whether or not listed in the
   output from LIST EXTENSIONS, unless it is either a registered
   extension or a private extension.

   Except where stated otherwise, the commands in this document are
   understood (even if not supported) by all servers and are not
   described in the list of features returned by the LIST EXTENSIONS
   command.

   A server MAY provide additional keywords - either for new commands or
   new variants of existing commands - as part of a private extension.
   These new keywords MUST begin with "X".

   A server MUST NOT send different response codes to basic NNTP
   commands documented here or commands documented in registered
   extensions in response to the availability or use of a private
   extension.







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10.1 Initial IANA registry

    The IANA's initial registry of NNTP service extensions consists of
   these entries:

     Extension                   Label        Added behavior
     Specific article numbers    LISTGROUP    Defined in this document
     Overview support            OVER         Defined in this document
     Header pattern matching     HDR          Defined in this document


10.2 Standard extensions

   Each of the following sections describes an extension that a server
   MAY provide.  If the server provides the extension, it MUST include
   the appropriate extension label in the response to LIST EXTENSIONS.
   If it does not provide it, it MUST NOT include the appropriate
   extension label.  The descriptions of facilities in each section are
   written as if the extension is provided.  If it is not provided, the
   entire section should be ignored.

   If the server provides an extension, it MUST implement all of the
   commands in the specification of the extension except for those
   marked as optional.  If it does not provide an extension, it MUST NOT
   implement any of the commands in the specification of that extension.

10.3 The LISTGROUP extension

   This extension provides one command and has the extension label
   LISTGROUP.

10.3.1 LISTGROUP

10.3.1.1 Usage

   Syntax
      LISTGROUP [ggg]

   Responses
      211   Article numbers follow (multiline)
      411   No such newsgroup
      412   No newsgroup selected [1]

   Parameters
      ggg = name of newsgroup






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   [1] The 412 response can only occur if no group has been specified.


10.3.1.2 Description

   The LISTGROUP command is used to get a listing of all the article
   numbers in a particular newsgroup.

   The optional parameter ggg is the name of the newsgroup to be
   selected (e.g.  "news.software.misc").  A list of valid newsgroups
   may be obtained from the LIST ACTIVE command.  If no group is
   specified, the current selected newsgroup is used.

   OUTSTANDING ISSUE

      On at least some servers the 211 response line is the same as with
      GROUP.  Should this be a requirement?

   The list of article numbers is returned as a multi-line response
   following the 211 response code.  It contains one number per line, is
   in numerical order, and lists precisely those articles that exist in
   the group.

   When a valid group is selected by means of this command, the current
   selected newsgroup MUST be set to that group and the current article
   number MUST be set to the first article in the group.  If an empty
   newsgroup is selected, the current article pointer is made invalid.
   If an invalid group is specified, the current selected newsgroup and
   current article number MUST NOT be changed.

   The LISTGROUP command MAY be used by a client as a replacement for
   the GROUP command in establishing a valid current selected newsgroup
   and current article number.

   If the group specified is not available on the server, a 411 response
   MUST be returned.  If no group is specified and the current selected
   newsgroup is invalid, a 412 response MUST be returned.

10.3.1.3 Examples

   Example of LISTGROUP on an empty group:

      [C] LISTGROUP example.empty.newsgroup
      [S] 211 list of article numbers follows
      [S] .

   Example of LISTGROUP on a valid current selected newsgroup:




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      [C] GROUP misc.test
      [S] 211 2000 3000234 3002322 misc.test selected
      [C] LISTGROUP
      [S] 211 list follows
      [S] 3000234
      [S] 3000237
      [S] 3000238
      [S] 3000239
      [S] 3002322
      [S] .

   Example of LISTGROUP failing because no group has been selected:

      [Assumes current selected newsgroup is invalid.]
      [C] LISTGROUP
      [S] 412 no current group
      [C] GROUP example.is.sob.bradner.or.barber
      [S] 411 no such group
      [C] LISTGROUP
      [S] 412 no current group


10.4 Article metadata

   The OVER and HDR extensions refer to the concept of "article
   metadata".  This is data about articles that does not occur within
   the article itself.  Each metadata item has a name which MUST begin
   with a colon.  Note that a historical feature of the LIST
   OVERVIEW.FMT command means that metadata names SHOULD NOT end with
   ":full".

   When generating a metadata item, the server MUST compute it for
   itself and MUST NOT trust any related value provided in the article.
   (In particular, a Lines: or Bytes: header in the article MUST NOT be
   assumed to specify the correct number of lines or bytes in the
   article.)

   This specification defines two metadata items: ":bytes" and ":lines".
   Implementations and other extensions may define other metadata items.

10.4.1 The :bytes metadata item

   The :bytes metadata item for an article is a decimal integer.  It
   MUST equal the number of octets in the entire article - headers,
   body, and separating blank line - except that the US-ASCII CRLF at
   the end of each line MAY (but SHOULD NOT) be counted as a single
   octet.




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   OUTSTANDING ISSUE

      Should this be called ":octets" instead? Or should it be a count
      of UTF characters rather than octets?


10.4.2 The :lines metadata item

   The :lines metadata item for an article is a decimal integer.  It
   MUST equal the number of lines in the article body (excluding the
   blank line separating headers and body); equivalently, it is two less
   than the number of US-ASCII CRLF pairs that the BODY command would
   return for that article (the extra two are those following the
   response code and the termination octet).

10.5 The OVER extension

   This extension provides two commands, OVER and LIST OVERVIEW.FMT.
   The label for this extension is OVER.

   The OVER extension provides access to the overview database [8],
   which is a database of header lines extracted from incoming articles.
   Only certain headers are included in the database.  The database also
   includes some article metadata.

   The information stored in the database may change over time.  The
   LIST OVERVIEW.FMT command describes the information that would be
   stored for an article arriving at the same time as the command was
   executed.

10.5.1 OVER

10.5.1.1 Usage

   Syntax
      OVER [range]

   Responses
      224   Overview information follows (multiline)
      412   No newsgroup selected
      420   Current article number is invalid
      423   No articles in that range

   Parameters
      range = Article(s) to return information for






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10.5.1.2 Description

   The OVER command returns the contents of the headers and metadata in
   the database for the article(s) specified from the current selected
   newsgroup.

   The optional range argument may be any of the following:

   o  an article number

   o  an article number followed by a dash to indicate all following

   o  an article number followed by a dash followed by another article
      number

   If no argument is specified, then the current article number is used.

   If the information is available, it is returned as a multi-line
   response following the 224 response code.  If the current selected
   newsgroup is invalid, a 412 response MUST be returned.  If there are
   no articles in the range specified, a 423 response MUST be returned.
   If OVER is sent without any arguments and the current article number
   is invalid, a 420 response MUST be returned.  If the client does not
   have permission to access the overview database, a 502 response MUST
   be returned.

   OUTSTANDING ISSUE

      Should this be 502 ("not permitted") or 503 ("there is no overview
      database")? In which case, why provide the command?

   For a successful response, the output consists of one line per
   article, sorted in numerical order of article number.  Each line
   consists of a number of fields separated by an US-ASCII TAB
   character.  A field may be empty (in which case there will be two
   adjacent US-ASCII TABs), and a sequence of trailing US-ASCII TABs may
   be omitted.

   The first 8 fields MUST be the following, in order:

      article number
      "Subject" header
      "From" header
      "Date" header
      "Message-ID" header
      "References" header
      :bytes metadata item
      :lines metadata item



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   Any subsequent fields are the contents of the other headers and
   metadata held in the database.

   For the five mandatory headers, the content of each field MUST be
   based on the original header with the header name and following colon
   and space removed.  If the article does not contain that header, or
   if there is nothing following the colon and space, the field MUST be
   empty.  For the two mandatory metadata items, the content of the
   field MUST be just the value, with no other text.

   For all subsequent fields that contain headers, the content MUST be
   based on the entire header including the name.  For all subsequent
   fields that contain metadata, the field consists of the metadata
   name, a single US-ASCII space, and then the value.

   For all fields, the value is processed by first removing all US-ASCII
   CRLF pairs and then replacing each remaining US-ASCII NUL, TAB, CR,
   or LF character with a single US-ASCII space (for example, CR LF LF
   TAB will become two spaces).  If there is no such header in the
   article, or no such metadata item, or no header or item stored in the
   database for that article, the corresponding field MUST be empty.

   The server SHOULD NOT produce output for articles that no longer
   exist.

10.5.1.3 Examples

   In the first two examples, US-ASCII tab has been replaced by vertical
   bar and some lines have been folded for readability.

   Example of a successful retrieval of overview information for an
   article (using no article number):

      [C] GROUP misc.test
      [S] 211 1234 3000234 3002322 misc.test
      [C] OVER
      [S] 224 Overview information follows
      [S] 300234|I am just a test article|"Demo User"
      <nobody@example.com>|6 Oct 1998 04:38:40 -0500|
      <45223423@example.com>|<45454@example.net>|1234|
      17|Xref: news.example.com misc.test:3000363
      [S] .

   Example of a successful retrieval of overview information for a range
   of articles:

      [C] GROUP misc.test
      [S] 211 1234 3000234 3002322 misc.test



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      [C] OVER 3000234-3000240
      [S] 224 Overview information follows
      [S] 300234|I am just a test article|"Demo User"
      <nobody@example.com>|6 Oct 1998 04:38:40 -0500|
      <45223423@example.com>|<45454@example.net>|1234|
      17|Xref: news.example.com misc.test:3000363
      [S] 3000235|Another test article|nobody@nowhere.to
      (Demo User)|6 Oct 1998 04:38:45 -0500|<45223425@to.to>||
      4818|37||Distribution: fi
      [S] 3000238|Re: I am just a test article|somebody@elsewhere.to|
      7 Oct 1998 11:38:40 +1200|<kfwer3v@elsewhere.to>|
      <45223423@to.to>|9234|51
      [S] .

   Note the missing "References" and Xref headers in the second line,
   the missing trailing field(s) in the first and last lines, and that
   there are only results for those articles that still exist.

   Example of an unsuccessful retrieval of overview information on an
   article by number:

      [C] GROUP misc.test
      [S] 211 1234 3000234 3002322 misc.test
      [C] OVER 300256
      [S] 420 No such article in this group

   Example of an unsuccessful retrieval of overview information by
   number because no newsgroup was selected first:

      [Assumes current selected newsgroup is invalid.]
      [C] OVER
      [S] 412 No newsgroup selected

   Example of an attempt to retrieve information when the current
   selected newsgroup is empty:

      [C] GROUP example.empty.newsgroup
      [S] 211 0 0 0 example.empty.newsgroup
      [C] OVER
      [S] 420 No current article selected


10.5.2 LIST OVERVIEW.FMT

10.5.2.1 Usage






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   Syntax
      LIST OVERVIEW.FMT

   Responses
      215   Information follows (multiline)
      503   Facility not available


10.5.2.2 Description

   OUTSTANDING ISSUE

      Should this be optional even when the OVER extension is provided?
      If so, is there a point in the 503 response?

   The LIST OVERVIEW.FMT command returns a description of the fields in
   the database.  The fields MUST be listed in the order that they will
   be returned by the OVER command for a newly-received article (the
   information stored for articles may change over time).

   If the information is available, it is returned as a multi-line
   response following the 215 response code.  If the information is not
   available, a 503 response MUST be returned.  The information contains
   one line per field in the order they are returned by the OVER
   command; he first 7 lines MUST be exactly:

       Subject:
       From:
       Date:
       Message-ID:
       References:
       :bytes
       :lines

    except that, for compatibility with existing implementations, the
   last two lines MAY instead be:

       Bytes:
       Lines:

    even though they refer to metadata, not headers.

   All subsequent lines MUST consist of either a header name followed by
   ":full", or the name of a piece of metadata.

   There are no leading or trailing spaces in the output.

   Note that the 7 fixed lines describe the 2nd to 8th fields of the



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   OVER output.  The "full" suffix is a reminder that the corresponding
   fields include the header name.

   This command MAY generate different results if used more than once in
   a session.

10.5.2.3 Examples

   Example of LIST OVERVIEW.FMT output corresponding to the example OVER
   output above, using the preferred format:

      [C] LIST OVERVIEW.FMT
      [S] 215 Order of fields in overview database.
      [S] Subject:
      [S] From:
      [S] Date:
      [S] Message-ID:
      [S] References:
      [S] :bytes
      [S] :lines
      [S] Xref:full
      [S] Distribution:full
      [S] .

   Example of LIST OVERVIEW.FMT output corresponding to the example OVER
   output above, using the alternative format:

      [C] LIST OVERVIEW.FMT
      [S] 215 Order of fields in overview database.
      [S] Subject:
      [S] From:
      [S] Date:
      [S] Message-ID:
      [S] References:
      [S] Bytes:
      [S] Lines:
      [S] Xref:full
      [S] Distribution:full
      [S] .

   Example of LIST OVERVIEW.FMT returning an error:

      [C] LIST OVERVIEW.FMT
      [S] 503 overview.fmt not available







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10.6 The HDR extension

   This extension provides one new command: HDR.  The label for this
   extension is HDR.

10.6.1 HDR

10.6.1.1 Usage

   Syntax
      HDR header range
      HDR header message-id
      HDR header

   Responses

      First form (range specified)
         225   Headers follow (multiline)
         412   No newsgroup selected
         423   No articles in that range

      Second form (message-id specified)
         225   Headers follow (multiline)
         430   No article with that message-id

      Third form (current article number used)
         225   Headers follow (multiline)
         412   No newsgroup selected
         420   Current article number is invalid

   Parameters
      header     = name of header, without the colon
      range      = number(s) of articles
      message-id = message-id of article


10.6.1.2 Description

   The HDR command retrieves specific headers from an article or
   specified range of articles in the current selected newsgroup, or
   from an article specified by message-id.  It can also return certain
   metadata about the article or articles.

   The required header parameter is the name of a header (e.g.
   "subject") in an article, or the name of a metadata item, and is
   case-insensitive.  See RFC 1036 [6] for a list of valid header lines.
   Names of metadata items always include a colon.  Except where stated
   otherwise, metadata items are treated as if they were header values,



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   and references to headers in this description apply equally to
   metadata items.

   OUTSTANDING ISSUE

      Should this be changed to require the name to *begin* with a
      colon?

   The range parameter may be any of the following:

   o  an article number

   o  an article number followed by a dash to indicate all following

   o  an article number followed by a dash followed by another article
      number

   The message-id argument indicates a specific article.  As shown by
   the syntax, the range and message-id arguments are mutually
   exclusive; if neither are specified, the current article number is
   used.

   If the information is available, it is returned as a multi-line
   response following the 225 response code and contains one line for
   each article where the relevant header line exists.  The line
   consists of the article number, a US-ASCII space, and then the
   contents of the header (without the header name or the colon and
   space that follow it) or metadata item.  If the article is specified
   by message-id rather than by article range, the article number is
   given as "0".

   Header contents are modified as follows: all US-ASCII CRLF pairs are
   removed, and then each remaining US-ASCII NUL, TAB, CR, or LF
   character is replaced with a single US-ASCII space.  (Note that this
   is the same transformation as is performed by the OVER extension.)

   The header content is in all cases taken from the article.  This
   means that, for example, a request for the header "Lines" returns the
   contents of the "Lines" header of the specified articles, if any, not
   the line count metadata or any other server-generated value.  If the
   header occurs in a given article multiple times, only the value of
   the first occurrence is returned by HDR.

   If the requested header is not present in the article or if it is
   present but empty, a line for that article is included in the output
   but the header content portion of the line is empty (the space after
   the article number MAY be retained or omitted).  If any article
   number in the provided range does not exist in the group, no line for



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   that article number is included in the output.

   If the optional argument is a message-id and no such article exists,
   a 430 response MUST be returned.  If the optional argument is not a
   message-id and the current selected newsgroup is invalid, a 412
   response MUST be returned.  If the optional argument is an article
   number or number range and no article with that number or in that
   number range exists in the current selected newsgroup, a 423 response
   MUST be returned.  If HDR is sent without any arguments and the
   current article number is invalid, a 420 response MUST be returned.
   A server MAY only allow HDR commands for a limited set of headers and
   metadata items (such as those present in the overview database).  If
   so, it MUST respond with a 503 response to attempts to request other
   headers, rather than returning erroneous results such as a successful
   empty response.

10.6.1.3 Examples

   Example of a successful retrieval of subject lines from a range of
   articles (3000235 has no Subject header, and 3000236 is missing):

      [C] GROUP misc.test
      [S] 211 1234 3000234 3002322 misc.test
      [C] HDR Subject 3000234-300238
      [S] 225 Headers follow
      [S] 3000234 I am just a test article
      [S] 3000235
      [S] 3000237 Re: I am just a test article
      [S] 3000238 Ditto
      [S] .

   Example of a successful retrieval of line counts from a range of
   articles:

      [C] GROUP misc.test
      [S] 211 1234 3000234 3002322 misc.test
      [C] HDR :lines 3000234-300238
      [S] 225 Headers follow
      [S] 3000234 42
      [S] 3000235 5
      [S] 3000237 11
      [S] 3000238 2378
      [S] .

   Example of a successful retrieval of the subject line from an article
   by message-id:

      [C] GROUP misc.test



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      [S] 211 1234 3000234 3002322 misc.test
      [C] HDR subject <i.am.a.test.article@example.com>
      [S] 225 Header information follows
      [S] 0 I am just a test article
      [S] .

   Example of a successful retrieval of the subject line from the
   current article:

      [C] GROUP misc.test
      [S] 211 1234 3000234 3002322 misc.test
      [C] HDR subject
      [S] 225 Header information follows
      [S] 3000234 I am just a test article
      [S] .

   Example of an unsuccessful retrieval of a header from an article by
   message-id:

      [C] HDR subject <i.am.not.there@example.com>
      [S] 430 No Such Article Found

   Example of an unsuccessful retrieval of headers from articles by
   number because no newsgroup was selected first:

      [Assumes current selected newsgroup is invalid.]
      [C] HDR subject 300256-
      [S] 412 No newsgroup selected

   Example of an unsuccessful retrieval of headers because the current
   selected newsgroup is empty:

      [C] GROUP example.empty.newsgroup
      [S] 211 0 0 0 example.empty.newsgroup
      [C] HDR subject 1-
      [S] 423 No articles in that range

   Example of an unsuccessful retrieval of headers because the server
   does not allow HDR commands for that header:

      [C] GROUP misc.test
      [S] 211 1234 3000234 3002322 misc.test
      [C] HDR Content-Type 3000234-300238
      [S] 503 HDR not permitted on Content-Type







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11. Augmented BNF Syntax for NNTP Commands

   This syntax defines the non-terminal "command-line".  Note that ABNF
   strings are case insensitive.

     command-line = command EOL
     command = article-command /
           body-command /
           date-command /
           group-command /
           hdr-command /
           head-command /
           help-command /
           ihave-command /
           last-command /
           list-active-command /
           list-active-times-command /
           list-distrib-pats-command /
           list-distributions-command /
           list-extensions-command /
           list-newsgroups-command /
           list-overview-fmt-command /
           listgroup-command /
           mode-reader-command /
           newgroups-command /
           newnews-command /
           next-command /
           over-command /
           post-command /
           quit-command /
           stat-command /
           x-command
     article-command = "ARTICLE" [article-ref]
     body-command = "BODY" [article-ref]
     date-command = "DATE"
     group-command = "GROUP" WS newsgroup-name
     hdr-command = "HDR" WS header-meta-name [range-ref]
     head-command = "HEAD" [article-ref]
     help-command = "HELP"
     ihave-command = "IHAVE" WS message-id
     last-command = "LAST"
     list-active-command = "LIST" [WS "ACTIVE" [WS wildmat]]
     list-active-times-command = "LIST" WS "ACTIVE.TIMES" [WS wildmat]
     list-distrib-pats-command = "LIST" WS "DISTRIB.PATS"
     list-distributions-command = "LIST" WS "DISTRIBUTIONS"
     list-extensions-command = "LIST" WS "EXTENSIONS"
     list-newsgroups-command = "LIST" WS "NEWSGROUPS" [WS wildmat]
     list-overview-fmt-command = "LIST" WS "OVERVIEW.FMT"



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     listgroup-command = "LISTGROUP" [WS newsgroup-name]
     mode-reader-command = "MODE" WS "READER"
     newgroups-command = "NEWGROUPS" WS date-time
     newnews-command = "NEWNEWS" WS wildmat WS date-time
     next-command = "NEXT"
     over-command = "OVER" [WS range]
     post-command = "POST"
     quit-command = "QUIT"
     stat-command = "STAT" [article-ref]
     x-command = x-command-name *(WS x-argument)
         ; Each extension command is specified fully elsewhere
     article-ref = WS (article-number / message-id)
     article-number = 1*16DIGIT
     date = [2DIGIT] 6DIGIT
     date-time = date WS time [WS "GMT"]
     header-meta-name = header-name / metadata-name
     header-name = 1*header-name-char
     header-name-char = %x21-39 / %x3B-7E ; exclude SP and :
     message-id = "<" 1*248message-id-char ">"
       ; subject to requirements in
   Section 7
   >
     message-id-char = %x21-3B / %x3C / %x3E-7E ; exclude SP < >
     metadata-name = ":" 1*header-name-char
     newsgroup-name = 1*wildmat-exact
     range = article-number ["-" [article-number]]
     range-ref = WS (range / message-id)
     time = 6DIGIT
     x-command-name = 3*12%x21-7E
     x-argument = 1*(%x21-7E / UTF-8-non-ascii)
     wildmat = wildmat-pattern *("," ["!"] wildmat-pattern)
     wildmat-pattern = 1*wildmat-item
     wildmat-item = wildmat-exact / wildmat-wild
     wildmat-exact = %x21-29 / %x2B / %x2D-3E / %x40-5A / %x5E-7E /
          UTF-8-non-ascii  ; exclude * , ? [ \ ]
     wildmat-wild = "*" / "?"
     CR = %x0D
     CRLF = CR LF
     DIGIT = %x30-39
     EOL = *(SP / HT) CRLF
     HT = %x09
     LF = %x0A
     SP = %x20
     UTF-8-non-ascii = UTF8-2 / UTF8-3 / UTF8-4 / UTF8-5 / UTF8-6
     UTF8-1 = %x80-BF
     UTF8-2 = %xC2-DF UTF8-1
     UTF8-3 = %xE0 %A0-BF UTF8-1 / %xE1-EC 2UTF8-1 /
              %xED %80-9F UTF8-1 / %xEE-EF 2UTF8-1



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     UTF8-4 = %xF0 %90-BF 2UTF8-1 / %xF1-F7 3UTF8-1
     UTF8-5 = %xF8 %88-BF 3UTF8-1 / %xF9-FB 4UTF8-1
     UTF8-6 = %xFC %84-BF 4UTF8-1 / %xFD    5UTF8-1
     WS = 1*(SP / HT)















































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12. Security Considerations

   This section is meant to inform application developers, information
   providers, and users of the security limitations in NNTP as described
   by this document.  The discussion does not include definitive
   solutions to the problems revealed, though it does make some
   suggestions for reducing security risks.

12.1 Personal and Proprietary Information

   NNTP, because it was created to distribute network news articles,
   will forward whatever information is stored in those articles.
   Specification of that information is outside this scope of this
   document, but it is likely that some personal and/or proprietary
   information is available in some of those articles.  It is very
   important that designers and implementers provide informative
   warnings to users so personal and/or proprietary information in
   material that is added automatically to articles (e.g.  in headers)
   is not disclosed inadvertently.  Additionally, effective and easily
   understood mechanisms to manage the distribution of news articles
   SHOULD be provided to NNTP Server administrators, so that they are
   able to report with confidence the likely spread of any particular
   set of news articles.

12.2 Abuse of Server Log Information

   A server is in the position to save session data about a user's
   requests that might identify their reading patterns or subjects of
   interest.  This information is clearly confidential in nature and its
   handling can be constrained by law in certain countries.  People
   using the NNTP protocol to provide data are responsible for ensuring
   that such material is not distributed without the permission of any
   individuals that are identifiable by the published results.

12.3 Weak Authentication and Access Control

   There is no user-based or token-based authentication in the basic
   NNTP specification.  Access is normally controlled by server
   configuration files.  Those files specify access by using domain
   names or IP addresses.  However, this specification does permit the
   creation of extensions to the NNTP protocol itself for such purposes.
   While including such mechanisms is optional, doing so is strongly
   encouraged.

   Other mechanisms are also available.  For example, a proxy server
   could be put in place that requires authentication before connecting
   via the proxy to the NNTP server.




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12.4 DNS Spoofing

   Many existing NNTP implementations authorize incoming connections by
   checking the IP address of that connection against the IP addresses
   obtained via DNS lookups of lists of domain names given in local
   configuration files.  Servers that use this type of authentication,
   and clients that find a server by doing a DNS lookup of the server
   name, rely very heavily on the Domain Name Service, and are thus
   generally prone to security attacks based on the deliberate
   misassociation of IP addresses and DNS names.  Clients and servers
   need to be cautious in assuming the continuing validity of an IP
   number/DNS name association.

   In particular, NNTP clients and servers SHOULD rely on their name
   resolver for confirmation of an IP number/DNS name association,
   rather than caching the result of previous host name lookups.  Many
   platforms already can cache host name lookups locally when
   appropriate, and they SHOULD be configured to do so.  It is proper
   for these lookups to be cached, however, only when the TTL (Time To
   Live) information reported by the name server makes it likely that
   the cached information will remain useful.

   If NNTP clients or servers cache the results of host name lookups in
   order to achieve a performance improvement, they MUST observe the TTL
   information reported by DNS.  If NNTP clients or servers do not
   observe this rule, they could be spoofed when a previously accessed
   server's IP address changes.  As network renumbering is expected to
   become increasingly common, the possibility of this form of attack
   will grow.  Observing this requirement thus reduces this potential
   security vulnerability.

   This requirement also improves the load-balancing behavior of clients
   for replicated servers using the same DNS name and reduces the
   likelihood of a user's experiencing failure in accessing sites that
   use that strategy.

12.5 UTF-8 issues

   The UTF-8 specification [2] permits only certain sequences of octets
   and designates others as either malformed or "illegal".  The Unicode
   standard identifies a number of security issues related to illegal
   sequences and forbids their generation by conforming implementations.

   Implementations of this specification MUST NOT generate malformed or
   illegal sequences and SHOULD detect them and take some appropriate
   action.  This could include:

   o  replacing such sequences by a "guessed" valid sequence (based on



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      properties of the UTF-8 encoding);

   o  replacing such sequences by the sequence %xEF.BF.BD, which encodes
      the "replacement character";

   o  closing the connection;

   o  generating a 501 response code.











































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13. Acknowledgments

   The author acknowledges the original authors of NNTP as documented in
   RFC 977: Brian Kantor and Phil Lapsey.

   The author gratefully acknowledges the work of the NNTP committee
   chaired by Eliot Lear.  The organization of this document was
   influenced by the last available draft from this working group.  A
   special thanks to Eliot for generously providing the original
   machine-readable sources for that document.

   The author gratefully acknowledges the work of Marshall Rose & John
   G.  Meyers in RFC 1939 and the work of the DRUMS working group,
   specifically RFC 1869, which is the basis of the NNTP extensions
   mechanism detailed in this document.

   OUTSTANDING ISSUE

      Why RFC 1939?

   The author gratefully acknowledges the authors of RFC 2616 for
   providing specific and relevant examples of security issues that
   should be considered for HTTP.  Since many of the same considerations
   exist for NNTP, those examples that are relevant have been included
   here with some minor rewrites.

   The author gratefully acknowledges the comments and additional
   information provided by the following individuals in preparing one or
   more of the progenitors of this document:

      Russ Allbery <rra@stanford.edu>
      Wayne Davison <davison@armory.com>
      Chris Lewis <clewis@bnr.ca>
      Tom Limoncelli <tal@mars.superlink.net>
      Eric Schnoebelen <eric@egsner.cirr.com>
      Rich Salz <rsalz@osf.org>

   This work was motivated by the work of various news reader authors
   and news server authors, which includes those listed below:

   Rick Adams
      Original author of the NNTP extensions to the RN news reader and
      last maintainer of Bnews

   Stan Barber
      Original author of the NNTP extensions to the news readers that
      are part of Bnews




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   Geoff Collyer
      Original author of the OVERVIEW database proposal and one of the
      original authors of CNEWS

   Dan Curry
      Original author of the xvnews news reader

   Wayne Davison
      Author of the first threading extensions to the RN news reader
      (commonly called TRN)

   Geoff Huston
      Original author of ANU NEWS

   Phil Lapsey
      Original author of the UNIX reference implementation for NNTP

   Iain Lea
      Original maintainer of the TIN news reader

   Chris Lewis
      First known implementer of the AUTHINFO GENERIC extension

   Rich Salz
      Original author of INN

   Henry Spencer
      One of the original authors of CNEWS

   Kim Storm
      Original author of the NN news reader

   Finally, the present author gratefully acknowledges the vast amount
   of work put into previous drafts by the previous author:

      Stan Barber <sob@academ.com>















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Normative References

   [1]   Kantor, B. and P. Lapsley, "Network News Transfer Protocol",
         RFC 977, February 1986.

   [2]   Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC
         2279, January 1998.

   [3]   American National Standards Institute, "Coded Character Set -
         7-bit American Standard Code for Information Interchange", ANSI
         X3.4, 1986.

   [4]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
         Levels", BCP 14, RFC 2119, March 1997.

   [5]   Crocker, D. and P. Overell, "Augmented BNF for Syntax
         Specifications: ABNF", RFC 2234, November 1997.

   [6]   Horton, M. and R. Adams, "Standard for interchange of USENET
         messages", RFC 1036, December 1987.

   [7]   Resnick, P., "Internet Message Format", RFC 2822, April 2001.

   [8]   Robertson, R., "FAQ: Overview database / NOV General
         Information", January 1995.

   [9]   International Telecommunications Union - Radio, "Glossary,
         ITU-R Recommendation TF.686-1", ITU-R Recommendation TF.686-1,
         October 1997.

   [10]  Mills, D., "Network Time Protocol (Version 3) Specification,
         Implementation", RFC 1305, March 1992.



















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Informative References

   [11]  Salz, R., "Manual Page for wildmat(3) from the INN 1.4
         distribution, Revision 1.10", April 1992.

   [12]  Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629, June
         1999.


Author's Address

   Clive D.W. Feather
   Thus plc
   322 Regents Park Road
   London  N3 2QQ
   GB

   Phone: +44 20 8371 1138
   Fax:   +44 870 051 9937
   URI:   http://www.davros.org/































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Intellectual Property Statement

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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.











































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