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Internet Engineering Task Force (IETF)              Phillip Hallam-Baker
Internet-Draft                                         Comodo Group Inc.
Intended Status: Standards Track                        October 17, 2014
Expires: April 20, 2015


                      Protocol Specification Tool
                     draft-hallambaker-protogen-00

Abstract

   The syntax for the PROTOGEN protocol specification tool is described
   and the use of the tool to generate protocol specifications,
   prototype and production implementations. While the primary focus of
   PROTOGEN is to develop protocols using JSON message syntax, the
   PROTOGEN framework has been successfully applied to generate
   prototypes using ASN.1, TLS, XML and RFC822 style syntax.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   (http://trustee.ietf.org/license-info) in effect on the date of
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   to this document. Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.









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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
      1.1.  Previous work . . . . . . . . . . . . . . . . . . . . . .  3
      1.2.  Schema driven documentation . . . . . . . . . . . . . . .  3
      1.3.  Schema driven code generation . . . . . . . . . . . . . .  4
      1.4.  Application Examples  . . . . . . . . . . . . . . . . . .  4
   2.  Protocol Specification . . . . . . . . . . . . . . . . . . . .  6
      2.1.  Protocol  . . . . . . . . . . . . . . . . . . . . . . . .  6
      2.2.  Description . . . . . . . . . . . . . . . . . . . . . . .  7
      2.3.  Service . . . . . . . . . . . . . . . . . . . . . . . . .  7
      2.4.  Transaction . . . . . . . . . . . . . . . . . . . . . . .  7
      2.5.  Message . . . . . . . . . . . . . . . . . . . . . . . . .  8
      2.6.  Structure . . . . . . . . . . . . . . . . . . . . . . . .  8
      2.7.  Status  . . . . . . . . . . . . . . . . . . . . . . . . .  8
      2.8.  Using . . . . . . . . . . . . . . . . . . . . . . . . . .  8
   3.  Data Types . . . . . . . . . . . . . . . . . . . . . . . . . .  9
      3.1.  Abstract  . . . . . . . . . . . . . . . . . . . . . . . . 10
      3.2.  Inherits  . . . . . . . . . . . . . . . . . . . . . . . . 10
      3.3.  Null Values . . . . . . . . . . . . . . . . . . . . . . . 10
      3.4.  Lists . . . . . . . . . . . . . . . . . . . . . . . . . . 10
      3.5.  Decimal . . . . . . . . . . . . . . . . . . . . . . . . . 11
      3.6.  DateTime  . . . . . . . . . . . . . . . . . . . . . . . . 11
      3.7.  Binary  . . . . . . . . . . . . . . . . . . . . . . . . . 11
   4.  Further Work . . . . . . . . . . . . . . . . . . . . . . . . . 11
   5.  Acnowledgementstss . . . . . . . . . . . . . . . . . . . . . . 11
   6.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
      6.1.  Normative References  . . . . . . . . . . . . . . . . . . 11
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 11

























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1. Introduction

   The use of schemas to describe communication protocols is well
   established and plays a central role in the development of ASN.1 and
   XML based protocols. No such tools are currently widely used for
   writing JSON based protocols.

   It is the view of the author that the first, last and only purpose of
   a protocol schema language is to enable the use of tools to support
   the development effort. A schema language that delays rather than
   advances the development of correct code and consistent documentation
   has become a liabilty, not an enabler.

1.1. Previous work

   One of the main reasons for the lack of such a tool has been the
   widespread concern as to the complexity of traditional schema tools
   and in particular the tendency of such tools to impose a complex data
   model on simple problems.

   One major difference in the design of the Protogen schema language to
   its predecessors is that it does not attempt to support every feature
   of the JSON data model. Protogen is designed to allow programmers to
   design and implement network service protocols quickly using widely
   used programming languages such as C, C# and Java. JSON features that
   do not map conveniently to the majority of widely used languages are
   best ignored.

   The XML Schema language is particularly obtuse presenting a two level
   type system in which element definitions provide typing for data and
   element types provide a type system for elements. At least three
   different inheritance mechanisms are supported.

   The ASN.1 schema language introduces a distinction between lists and
   sets that is entirely frivolous in a serialization format and
   gratuitous distinctions between implicit and explict tagging.

   The lesson to be drawn from these abominations is clear: The primary
   purpose of a schema language should be to allow the programmer to
   forget and ignore the wireline representation of protocol messages.
   Features that allow fine tuning of the wireline representation should
   be avoided.

   While the notion of validating input data against a schema prior to
   passing data to an application is superficially attractive, schema
   constraints are rarely sufficient for this purpose. Thus applied to
   protocol design, schema validation rarely provides a meaningful
   benefit over checking that an encoding is well formed.

1.2. Schema driven documentation




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1.3. Schema driven code generation

1.4. Application Examples

   The following is based on an example from [RFC4627].

   [
          {
             "precision": "zip",
             "Latitude":  37.7668,
             "Longitude": -122.3959,
             "Address":   "",
             "City":      "SAN FRANCISCO",
             "State":     "CA",
             "Zip":       "94107",
             "Country":   "US"
          },
          {
             "precision": "zip",
             "Latitude":  37.371991,
             "Longitude": -122.026020,
             "Address":   "",
             "City":      "SUNNYVALE",
             "State":     "CA",
             "Zip":       "94085",
             "Country":   "US"
          }
      ]

   The corresponding Protogen schema is:

        Structure SiteList
                Description
                        |A list of sites
                Struct Site Sites
                        Multiple

        Structure Site
                Description
                        |A site location
                String          Country
                        Description
                                |ISO ALPHA-2 Country Code.
                String          precision
                Decimal         Latitude
                Decimal         Longitude
                String          Address
                String          City
                String          State
                String          Zip




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   For the sake of example, the description of the site structure
   entries is elided. While Protogen does not require description
   elements to be provided to produce code, descriptions are of course
   essential if useful documentation is to be generated.

   Protogen is built using the Goedel code metasynthesizer which
   attempts to eliminate all unnecessary clutter from the code
   specification to minimize error. By default, indentation and the off-
   side rule are used to denote block structure following the approach
   used in occam and Python. Punctuation characters are only used to
   delimit strings ("), text blocks (|) and comments (!).

   Note that the Latitude and Longitude are specified using the type
   Decimal rather than Float. This allows an implementation to avoid the
   loss of precision that inevitably occurs converting between a binary
   floating point representation such as IEEE 754 binary 64 and the
   decimal encoding used in JSON.

   The example fragment is sufficient to describe a data structure and
   generate methods for JSON serialization and deserializtion. It is not
   however sufficient to generate a useful implementation of a Web
   service or client access library. to do this we must define a
   protocol with services, transactions and messages defined as follows:

      Protocol
         A collection of related services.

      Service
         A set of transactions with a distinct DNS SRV prefix and HTTP
         well known service label.

      Transaction
         A defined sequence of protocol messages supported by a service.
         Currently only request-response design pattern is supported.

      Message
         A JSON document that corresponds to a request or response.

   To build a service using the Site structure, we prepend add following
   declaration:













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   Protocol Sitefinder STFND

        Service Finder "_siteFinder._wks" "SiteFinder" Request Response
                Description
                        |Find sites for new donut stores.

        Message Request
                Struct Site WhereIAm
        Message Response
                Struct Site WhereAreDonuts
                        Multiple

   We can now run Protogen to generate any of the following:

      *  Documentation in HTML

      *  Documentation in RFC2XML schema

      *  A C# client access library.

      *  A C# stub service library.

      *  A C header file describing corresponding C structures and data
         tables to enable serialization/deserialization.

   Support for partial classes makes C# a particularly attractive target
   language for code generation as it allows classes produced by
   generated code to be conveniently extended. Support for other modern
   languages aligned with the Java/.NET data model requires only
   straightforward modification of the code generator.

   While the C# generator is optimized for development of protocols and
   production code, the generator for C is intended for developing
   production code after the protocol architecture is largely static.
   The generator is intentionally biased towards flexibility rather than
   functionality since a modern programer using C is most likely to be
   doing so to build on a legacy code base. The ability to easily adapt
   the output of the generator to the existing coding style(s) is likely
   to be more highly valued than minimizing implementation effort.

2. Protocol Specification

2.1. Protocol

   Top level specification of a protocol. The Protocol element contains
   two attributes and a list of entries as follows:

      Namespace
         Namespace identifier for use in .NET and Java style programming
         environments




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      Prefix
         Prefix for use in C style programming environments.

      Entries
         A list of [Service Transaction Message Structure Description
         Using] elements

2.2. Description

   Describes the parent element. Multiple description elements may be
   specified in which case the first SHOULD be a standalone short
   description. The description element has one attribute:

      Text
         Text field data identified by use of the | prefix.

2.3. Service

   A service is a named set of transactions within a protocol namespace.

   At present, due to an implementation limitation, all request and
   response messages used in a service MUST inherit from a single
   message type. This is bogus and should be fixed.

   The service element has the following attributes:

      ID
         The code identifier of the service

      Discovery
         The DNS service prefix of the service for use in SRV, NAPTR
         style discovery

      WellKnown
         The HTTP well known service prefix.

      Request
         The parent class for all request messages supported by the
         service.

      Response
         The parent class for all response messages supported by the
         service.

      Entries
         A list of [Description Status] entries








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2.4. Transaction

   Specifies a Request-Response transaction supported by a specified
   service.

   At present transactions are specific to a service which is kind of
   bogus if multiple services were defined.

   The Transaction element has the following attributes:

      Service
         The identifier of the service

      ID
         The identifier of the transaction

      Request
         The request message which must not be an abstract type.

      Response
         The response message returned for normal completion. An
         abstract type may be specified.

      Entries
         A list of [Description Status] entries

2.5. Message

   Specifies a protocol message. This is almost the same as a structure
   except that the name of a request message is a command to a server
   and the name of a response message identifies a response.

      Id
         The message identifier

      Entries
         A list of [Description Abstract Inherits Boolean Integer Binary
         Float Label Name String URI DateTime Struct Enum Status
         Authentication Format Decimal] entries

2.6. Structure

2.7. Status

   This feature is not yet implemented, the idea being that status codes
   should be represented at both the HTTP layer and JSON layer so that
   appropriate handling can be specified at either.







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2.8. Using

   Specifies a message or structure defined in another schema.

3. Data Types

   Protogen recognizes ten intrinsic data types. While this is
   considerably larger than the three intrinsic types supported in JSON,
   the additional expressive power allows the tools to do more work for
   the programmer. For example, distinguishing strings that represent
   date-time values from other strings allows the tool to perform the
   work of encoding/decoding these values.

   The following table sumarizes the Protogen schema types and their
   (default) corresponding C#/C equivalents.

   +----------+-----------------------------+-------------+------------+
   | Schema   | JSON                        | C#          | C          |
   +----------+-----------------------------+-------------+------------+
   | Boolean  | true | false                | bool        | bool       |
   |          |                             |             |            |
   | Float    | number                      | double      | double     |
   |          |                             |             |            |
   | Decimal  | number                      | Int64       | long long  |
   |          |                             |             |            |
   | Integer  | number                      | Int64       | int        |
   |          |                             |             |            |
   | Binary   | string (base64 encoded)     | byte[] Data | BinaryType |
   |          |                             |             |            |
   | Label    | string                      | string      | StringType |
   |          |                             |             |            |
   | Name     | string                      | string      | StringType |
   |          |                             |             |            |
   | String   | string                      | string      | StringType |
   |          |                             |             |            |
   | URI      | string                      | string      | StringType |
   |          |                             |             |            |
   | DateTime | string                      | DateTime    | struct tm  |
   +----------+-----------------------------+-------------+------------+

   Every data type supports the following options:

      Required
         The minimum number of occurrences is 1.

      Multiple
         Multiple values may be specified.

      Description
         Description of the element for use in code generation.




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      Deaful
         Default value for the element if unspecified.

   While the Protogen schema definition does include additional options
   for some data types (e.g. LengthBits, LengthFixed) these are only
   used in the TLS encoding generator and are ignored when JSON encoding
   is being used.

3.1. Abstract

   Messages and structures may be marked Abstract which means that they
   may be used as base classes for inheritance from other messages or
   structures but cannot appear on the wire.

3.2. Inherits

   Specifies that a message or structure inherits from another message
   or structure.

   Note that inheritance relationships are represented in the generated
   code for languages that support inheritance (e.g. C#) and flattened
   out in languages that do not (e.g. C).

3.3. Null Values

   No distinction is made between a value that is not present and a
   value that is present with the value null. Thus the following JSON
   documents are considered to specify the same object.

   { "Value": 1 }

   { "Value": 1,
     "Optional": null }

   An entry that has the 'Required' option set MUST always be specified
   even if the value is null.

3.4. Lists

   No distinction is made between a list that is not present, a list
   with the null value and an empty list. Thus the following encodings
   desribe the same object:












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   { "Value": 1 }

   { "Value": 1,
     "List": null }

   { "Value": 1,
     "List": [] }

   To simplify scripting language implementation an entry that has the
   'Multiple' option MUST be encoded as a list.

3.5. Decimal

   The decimal encoding provides an alternative to use of floating point
   to represent decimal fractions.

   Since 10 is not a power of 2, conversion between decimal and binary
   fractions is inexact and using Real32 or Real64 values for this
   purpose introduces an unnecessary loss of precision.

   Since modern programming languages lack support for a Decimal
   intrinsic type, this is implemented by mapping the datum to a 64 bit
   integer with an offset of 1,000,000,000. This approach allows for
   numbers up to 9,223,372 to be represented with nine digit precision.

3.6. DateTime

   Date Time Values are encoded as strings in IETF format.

3.7. Binary

   Binary values are encoded using BASE64URL encoding.

4. Further Work

5. Acnowledgementstss

6. References

6.1. Normative References

   [RFC4627]  Crockford, D., "The application/json Media Type for
              JavaScript Object Notation (JSON)", RFC 4627, July 2006.

Author's Address

   Phillip Hallam-Baker
   Comodo Group Inc.

   philliph@comodo.com




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