Network Working Group                                        T. Hastings
Request for Comments: 2639                                     C. Manros
Category: Informational                                Xerox Corporation
                                                               July 1999

Internet Printing Protocol/1.0: Implementer's Guide

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

Abstract

   This document is one of a set of documents, which together describe
   all aspects of a new Internet Printing Protocol (IPP).  IPP is an
   application level protocol that can be used for distributed printing
   using Internet tools and technologies.  This document contains
   information that supplements the IPP Model and Semantics [RFC2566]
   and the IPP Transport and Encoding [RFC2565] documents.  It is
   intended to help implementers understand IPP/1.0 and some of the
   considerations that may assist them in the design of their client
   and/or IPP object implementations.  For example, a typical order of
   processing requests is given, including error checking.  Motivation
   for some of the specification decisions is also included.

   The full set of IPP documents includes:

     Design Goals for an Internet Printing Protocol [RFC2567]
     Rationale for the Structure and Model and Protocol for the Internet
        Printing Protocol [RFC2568]
     Internet Printing Protocol/1.0: Model and Semantics [RFC2566]
     Internet Printing Protocol/1.0: Encoding and Transport [RFC2565]
     Mapping between LPD and IPP Protocols [RFC2569]

   The document, "Design Goals for an Internet Printing Protocol", takes
   a broad look at distributed printing functionality, and it enumerates
   real-life scenarios that help to clarify the features that need to be
   included in a printing protocol for the Internet.  It identifies
   requirements for three types of users: end users, operators, and

   administrators.  The design goals document calls out a subset of end
   user requirements that are satisfied in IPP/1.0.  Operator and
   administrator requirements are out of scope for version 1.0.

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

   The document, "Internet Printing Protocol/1.0: Model and Semantics",
   describes a simplified model with abstract objects, their attributes,
   and their operations.  The model introduces a Printer and a Job.  The
   Job supports multiple documents per Job.  The model document also
   addresses how security, internationalization, and directory issues
   are addressed.

   The document, "Internet Printing Protocol/1.0: Encoding and
   Transport", is a formal mapping of the abstract operations and
   attributes defined in the model document onto HTTP/1.1.  It also
   defines the encoding rules for a new Internet media type called
   "application/ipp".

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

  1  Introduction......................................................4
   1.1 Conformance language............................................4
   1.2 Other terminology...............................................5
  2  Model and Semantics...............................................5
   2.1 Summary of Operation Attributes.................................5
   2.2 Suggested Operation Processing Steps for IPP Objects ..........10
       2.2.1 Suggested Operation Processing Steps for all Operations..11
       2.2.1.1  Validate version number...............................11
       2.2.1.2  Validate operation identifier.........................11
       2.2.1.3  Validate the request identifier.......................11
       2.2.1.4  Validate attribute group and attribute presence and
                order.................................................12
       2.2.1.5  Validate the values of the REQUIRED Operation
                attributes............................................19
       2.2.1.6  Validate the values of the OPTIONAL Operation
                attributes............................................23
     2.2.2 Suggested Additional Processing Steps for Operations that
           Create/Validate Jobs and Add Documents.....................26
       2.2.2.1  Default "ipp-attribute-fidelity" if not supplied......26

       2.2.2.2  Check that the Printer object is accepting jobs.......26
       2.2.2.3  Validate the values of the Job Template attributes....26
     2.2.3 Algorithm for job validation...............................27
       2.2.3.1  Check for conflicting Job Template attributes values..33
       2.2.3.2  Decide whether to REJECT the request..................33
       2.2.3.3  For the Validate-Job operation, RETURN one of the
                success status codes..................................34
       2.2.3.4  Create the Job object with attributes to support......34
       2.2.3.5  Return one of the success status codes................36
       2.2.3.6  Accept appended Document Content......................36
       2.2.3.7  Scheduling and Starting to Process the Job............36
       2.2.3.8  Completing the Job....................................37
       2.2.3.9  Destroying the Job after completion...................37
       2.2.3.10 Interaction with "ipp-attribute-fidelity".............37
   2.3 Status codes returned by operation ............................37
     2.3.1 Printer Operations.........................................38
       2.3.1.1  Print-Job.............................................38
       2.3.1.2  Print-URI.............................................40
       2.3.1.3  Validate-Job..........................................40
       2.3.1.4  Create-Job............................................41
       2.3.1.5  Get-Printer-Attributes................................41
       2.3.1.6  Get-Jobs..............................................42
     2.3.2 Job Operations.............................................43
       2.3.2.1  Send-Document.........................................43
       2.3.2.2  Send-URI..............................................44
       2.3.2.3  Cancel-Job............................................44
       2.3.2.4  Get-Job-Attributes....................................45
   2.4 Validate-Job...................................................46
   2.5 Case Sensitivity in URIs ......................................46
   2.6 Character Sets, natural languages, and internationalization....46
     2.6.1 Character set code conversion support .....................46
     2.6.2 What charset to return when an unsupported charset is
           requested?.................................................48
     2.6.3 Natural Language Override (NLO) ...........................48
   2.7 The "queued-job-count" Printer Description attribute...........50
     2.7.1 Why is "queued-job-count" RECOMMENDED?.....................50
     2.7.2 Is "queued-job-count" a good measure of how busy a printer
           is?........................................................50
   2.8 Sending empty attribute groups ................................50
   2.9 Returning unsupported attributes in Get-Xxxx responses ........51
   2.10 Returning job-state in Print-Job response ....................51
   2.11 Flow controlling the data portion of a Print-Job request .....52
   2.12 Multi-valued attributes ......................................53
   2.13 Querying jobs with IPP that were submitted using other job
        submission protocols .........................................53
   2.14 The 'none' value for empty sets ..............................54
   2.15 Get-Jobs, my-jobs='true', and 'requesting-user-name'?.........54

   2.16 The "multiple-document-handling" Job Template attribute and
        support of multiple document jobs.............................54
  3  Encoding and Transport...........................................55
   3.1 General Headers................................................56
   3.2 Request  Headers...............................................57
   3.3 Response Headers...............................................58
   3.4 Entity  Headers................................................59
   3.5 Optional support for HTTP/1.0..................................60
   3.6 HTTP/1.1 Chunking..............................................60
     3.6.1 Disabling IPP Server Response Chunking.....................60
     3.6.2 Warning About the Support of Chunked Requests..............60
  4  References.......................................................61
   4.1 Authors' Addresses.............................................62
  5  Security Considerations..........................................62
  6  Notices..........................................................62
  Full Copyright Statement............................................65

1 Introduction

  This document contains information that supplements the IPP Model and
  Semantics [RFC2566] and the IPP Transport and Encoding [RFC2565]
  documents.  As such this information is not part of the formal
  specifications.  Instead information is presented to help implementers
  understand the specification, including some of the motivation for
  decisions taken by the committee in developing the specification.
  Some of the implementation considerations are intended to help
  implementers design their client and/or IPP object implementations.
  If there are any contradictions between this document and [RFC2566] or
  [RFC2565], those documents take precedence over this document.

1.1 Conformance language

  Usually, this document does not contain the terminology MUST, MUST
  NOT, MAY, NEED NOT, SHOULD, SHOULD NOT, REQUIRED, and OPTIONAL.
  However, when those terms do appear in this document, their intent is
  to repeat what the [RFC2566] and [RFC2565] documents require and
  allow, rather than specifying additional conformance requirements.
  These terms are defined in section 13 on conformance terminology in
  [RFC2566], most of which is taken from RFC 2119 [RFC2119].

  Implementers should read section 13 in [RFC2566] in order to
  understand these capitalized words.  The words MUST, MUST NOT, and
  REQUIRED indicate what implementations are required to support in a
  client or IPP object in order to be conformant to [RFC2566] and
  [RFC2565].  MAY, NEED NOT, and OPTIONAL indicate was is merely allowed
  as an implementer option.  The verbs SHOULD and SHOULD NOT indicate
  suggested behavior, but which is not required or disallowed,
  respectively, in order to conform to the specification.

1.2 Other terminology

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

2 Model and Semantics

This section discusses various aspects of IPP/1.0 Model and Semantics
[RFC2566].

2.1 Summary of Operation Attributes

  Legend for the following table:

      R indicates a REQUIRED operation or attribute for an
        implementation to support

      O indicates an OPTIONAL operation or attribute for an
        implementation to support

    Table 1.  Summary of operation attributes for Printer operations

                           Printer Operations

                         Requests                         Responses

     Operation           Print-   Pri  Crea Get-     Get- All
     Attributes          Job,     nt-  te-  Printer- Jobs Opera-
                         Validate URI  Job  Attribut      tions
                         -Job     (O)  (O)  es

     Operation parameters--REQUIRED to be supplied by the sender

     operation-id           R      R    R      R      R

     status-code                                            R

     request-id             R      R    R      R      R     R

     version-number         R      R    R      R      R     R

     Operation attributes-REQUIRED to be supplied by the sender

     attributes-charset     R      R    R      R      R     R

     attributes-            R      R    R      R      R     R
     natural-language

     document-uri                   R

     job-id*

     job-uri*

     last-document

     printer-uri            R      R    R      R      R

     Operation attributes-RECOMMENDED to be supplied by the sender

     job-name               R      R    R

     requesting-user-       R      R    R      R      R
     name

                           Printer Operations

                         Requests                        Responses

      Operation          Print-   Pri  Crea Get-    Get-  All
      Attributes         Job,     nt-  te-  Printer Jobs  Opera-
                         Vali-    URI  Job  Attri-        tions
                         date-Job (O)  (O)  butes

      Operation attributes-OPTIONAL to be supplied by the sender

      status-message                                         O

      compression           O     O

      document-format       R     R           O

      document-name         O     O

      document-natural-     O     O
      language

      ipp-attribute-        R     R    R
      fidelity

      job-impressions       O     O    O

      job-k-octets          O     O    O

      job-media-sheets      O     O    O

      limit                                           R

      message

      my-jobs                                         R

      requested-                               R      R
      attributes

      which-jobs                                      R

      *  "job-id" is REQUIRED only if used together with
      "printer-uri" to identify the target job; otherwise, "job-
      uri" is REQUIRED.

      Table 2.  Summary of operation attributes for Job operations

                         Requests                         Responses

      Operation          Send-    Send-  Cancel  Get-     All
      Attributes         Document URI    -Job    Job-     Opera-
                         (O)      (O)            Attri-   tions
                                                 butes

      Operation parameters--REQUIRED to be supplied by the sender

      operation-id          R       R      R       R

      status-code                                          R

      request-id            R       R      R       R       R

      version-number        R       R      R       R       R

      Operation attributes-REQUIRED to be supplied by the sender

      attributes-           R       R      R       R       R
      charset

      attributes-           R       R      R       R       R
      natural-language

      document-uri                   R

      job-id*               R       R      R       R

      job-uri*              R       R      R       R

      last-document         R       R

      printer-uri           R       R      R       R

      Operation attributes-RECOMMENDED to be supplied by the
      sender

      job-name

      requesting-user-      R       R      R       R
      name

                             Job Operations

                           Requests                      Responses

     Operation Attributes  Send-    Send-   Cance Get-    All
                           Document URI     l-Job Job-    Opera-
                           (O)      (O)           Attri-  tions
                                                  butes

     Operation attributes.OPTIONAL to be supplied by the sender

     status-message                                       O

     compression               O       O

     document-format           R       R

     document-name             O       O

     document-natural-         O       O
     language

     ipp-attribute-
     fidelity

     job-impressions

     job-k-octets

     job-media-sheets

     limit

     message                                   O

     my-jobs

     requested-attributes                             R

     which-jobs

     *  "job-id" is REQUIRED only if used together with "printer-
     uri" to identify the target job; otherwise, "job-uri" is
     REQUIRED.

2.2 Suggested Operation Processing Steps for IPP Objects

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

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

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

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

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

2.2.1 Suggested Operation Processing Steps for all Operations

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

2.2.1.1 Validate version number

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

   The checking of the minor version number is implementation dependent,
   however if the client supplied minor version is explicitly supported,
   the IPP object MUST respond using that identical minor version
   number.  If the requested minor version is not supported (the
   requested minor version is either higher or lower) than a supported
   minor version, the IPP object SHOULD return the closest supported
   minor version.

2.2.1.2 Validate operation identifier

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

2.2.1.3 Validate the request identifier

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

   Note: The "version-number",  "operation-id", and the "request-id"
   parameters are in fixed octet positions in the IPP/1.0 encoding.  The
   "version-number" parameter will be the same fixed octet position in
   all versions of the protocol.  These fields are validated before
   proceeding with the rest of the validation.

2.2.1.4 Validate attribute group and attribute presence and order

The order of the following validation steps depends on
implementation.

2.2.1.4.1 Validate the presence and order of attribute groups

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

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

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

2.2.1.4.2 Ignore unknown attribute groups in the expected position

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

   protocol document and in the request).  If the unknown group occurs
   in a different position, the IPP object REJECTS the request and
   RETURNS the 'client-error-bad-request' status code.

   Clients also ignore unknown attribute groups returned in a response.

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

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

   Client requests and IPP object responses contain Operation attributes
   that [RFC2566] Section 3 requires to be present.  Attributes within a
   group may be in any order, except for the ordering of target,
   charset, and natural languages attributes.  These attributes MUST be
   first, and MUST be supplied in the following order: charset, natural
   language, and then target. An IPP object verifies that the attributes
   that Section 4 requires to be supplied by the client have been
   supplied in the request (attributes without an * in the following
   tables).  An asterisk (*) indicates groups and Operation attributes
   that the client may omit in a request or an IPP object may omit in a
   response.

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

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

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

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

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

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

   or a Job Template attribute to be supplied in an Operation Attribute
   group in a create request.  It is also an error to supply the
   "attributes-charset" attribute twice.

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

   The following tables list all the attributes for all the operations
   by attribute group in each request and each response.  The order of
   the groups is the order that the client supplies the groups as
   specified in [RFC2566] Section 3.  The order of the attributes within
   a group is arbitrary, except as noted for some of the special
   operation attributes (charset, natural language, and target).  The
   tables below use the following notation:

     R   indicates a REQUIRED attribute that an IPP object MUST support
     O   indicates an OPTIONAL attribute that an IPP object NEED NOT
               support
     *   indicates that a client MAY omit the attribute in a request
               and that an IPP object MAY omit the attribute in a
               response. The absence of an * means that a client MUST
               supply the attribute in a request and an IPP object MUST
               supply the attribute in a response.

                            Operation Requests

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

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

   Print-Job Request:
        Group 1: Operation Attributes (R)
             attributes-charset (R)
             attributes-natural-language (R)
             printer-uri (R)
             requesting-user-name (R*)
             job-name (R*)
             ipp-attribute-fidelity (R*)
             document-name (R*)
             document-format (R*)
             document-natural-language (O*)
             compression (O*)

             job-k-octets (O*)
             job-impressions (O*)
             job-media-sheets (O*)
        Group 2: Job Template Attributes (R*)
             <Job Template attributes> (O*)
                  (see [RFC2566] Section 4.2)
        Group 3: Document Content (R)
             <document content>

   Validate-Job Request:
        Group 1: Operation Attributes (R)
             attributes-charset (R)
             attributes-natural-language (R)
             printer-uri (R)
             requesting-user-name (R*)
             job-name (R*)
             ipp-attribute-fidelity (R*)
             document-name (R*)
             document-format (R*)
             document-natural-language (O*)
             compression (O*)
             job-k-octets (O*)
             job-impressions (O*)
             job-media-sheets (O*)
        Group 2: Job Template Attributes (R*)
             <Job Template attributes> (O*)
                  (see [RFC2566] Section 4.2)

   Create-Job Request:
        Group 1: Operation Attributes (R)
             attributes-charset (R)
             attributes-natural-language (R)
             printer-uri (R)
             requesting-user-name (R*)
             job-name (R*)
             ipp-attribute-fidelity (R*)
             job-k-octets (O*)
             job-impressions (O*)
             job-media-sheets (O*)
        Group 2: Job Template Attributes (R*)
             <Job Template attributes> (O*) (see
                  (see [RFC2566] Section 4.2)

   Print-URI Request:
        Group 1: Operation Attributes (R)
             attributes-charset (R)
             attributes-natural-language (R)
             printer-uri (R)

             document-uri (R)
             requesting-user-name (R*)
             job-name (R*)
             ipp-attribute-fidelity (R*)
             document-name (R*)
             document-format (R*)
             document-natural-language (O*)
             compression (O*)
             job-k-octets (O*)
             job-impressions (O*)
             job-media-sheets (O*)
        Group 2: Job Template Attributes (R*)
             <Job Template attributes> (O*) (see
                  (see [RFC2566] Section 4.2)

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

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

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

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

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

   Get-Jobs Request:
        Group 1: Operation Attributes (R)
             attributes-charset (R)
             attributes-natural-language (R)
             printer-uri (R)
             requesting-user-name (R*)
             limit (R*)
             requested-attributes (R*)
             which-jobs (R*)
             my-jobs (R*)

                            Operation Responses

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

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

   Print-Job Response:
   Print-URI Response:
   Create-Job Response:

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

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

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

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

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

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

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

   Get-Jobs Response:
        Group 1: Operation Attributes (R)
             attributes-charset (R)
             attributes-natural-language (R)
             status-message (O*)
        Group 2: Unsupported Attributes (R*) (see Note 4)
             <unsupported attributes> (R*)
        Group 3: Job Object Attributes(R*) (see Note 2, 5)
             <requested attributes> (R*)

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

2.2.1.5 Validate the values of the REQUIRED Operation attributes

   An IPP object validates the values supplied by the client of the
   REQUIRED Operation attribute that the IPP object MUST support.  The
   next section specifies the validation of the values of the OPTIONAL
   Operation attributes that IPP objects MAY support.

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

      a)that the length of each Operation attribute value is correct for
        the attribute syntax tag supplied by the client according to
        [RFC2566] Section 4.1,

      b)that the attribute syntax tag is correct for that Operation
        attribute according to [RFC2566] Section 3,

      c)that the value is in the range specified for that Operation
        attribute according to [RFC2566] Section 3,

      d)that multiple values are supplied by the client only for
        operation attributes that are multi-valued, i.e., that are
        1setOf X according to [RFC2566] Section 3.

   If any of these checks fail, the IPP object REJECTS the request and
   RETURNS the 'client-error-bad-request' or the 'client-error-request-
   value-too-long' status code.  Since such an error is most likely to
   be an error detected by a client developer, rather than by an end-
   user, the IPP object NEED NOT return an indication of which attribute
   had the error in either the Unsupported Attributes Group or the

   Status Message.  The description for each of these syntactic checks
   is explicitly expressed in the first IF statement in the following
   table.

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

   attributes-charset (charset)

      IF NOT a single non-empty 'charset' value, REJECT/RETURN 'client-
         error-bad-request'.

      IF the value length is greater than 63 octets, REJECT/RETURN '
         client-error-request-value-too-long'.
      IF NOT in the Printer object's "charset-supported" attribute,
         REJECT/RETURN "client-error-charset-not-supported".

   attributes-natural-language(naturalLanguage)

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

   requesting-user-name

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

   job-name(name)

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

   document-name (name)

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

   ipp-attribute-fidelity (boolean)

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

   document-format (mimeMediaType)

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

      IF NOT supplied by the client, the IPP object assumes the value of
         the Printer object's "document-format-default" attribute.

   document-uri (uri)

      IF NOT a single non-empty 'uri' value, REJECT/RETURN 'client-
         error-bad-request'.
      IF the value length is greater than 1023 octets, REJECT/RETURN
         'client-error-request-value-too-long'.
      IF the URI syntax is not valid, REJECT/RETURN 'client-error-bad-
         request'.
      IF scheme is NOT in the Printer object's "reference-uri-schemes-
         supported" attribute, REJECT/RETURN 'client-error-uri-scheme-
         not-supported'.
      The Printer object MAY check to see if the document exists and is
         accessible.  If the document is not found or is not accessible,
         REJECT/RETURN 'client-error-not found'.

   last-document (boolean)

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

   job-id (integer(1:MAX))

      IF NOT an single 'integer' value equal to 4 octets AND in the
         range 1 to MAX, REJECT/RETURN 'client-error-bad-request'.

      IF NOT a job-id of an existing Job object, REJECT/RETURN 'client-
         error-not-found' or 'client-error-gone' status code, if keep
         track of recently deleted jobs.

   requested-attributes (1setOf keyword)

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

   which-jobs (type2 keyword)

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

   my-jobs (boolean)

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

   limit (integer(1:MAX))

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

2.2.1.6 Validate the values of the OPTIONAL Operation attributes

   OPTIONAL Operation attributes are those that an IPP object MAY or MAY
   NOT support.  An IPP object validates the values of the OPTIONAL
   attributes supplied by the client.  The IPP object performs the same
   syntactic validation checks for each OPTIONAL attribute value as in
   Section 2.2.1.5.  As in Section 2.2.1.5, if any fail, the IPP object
   REJECTS the request and RETURNS the 'client-error-bad-request' or the
   'client-error-request-value-too-long' status code.

   In addition, the IPP object checks each Operation attribute value
   against some Printer attribute or some hard-coded value if there is
   no "xxx-supported" Printer attribute defined. If its value is not
   among those supported or is not in the range supported, then the IPP

   object REJECTS the request and RETURNS the error status code
   indicated in the table.  If the value of the Printer object's "xxx-
   supported" attribute is 'no-value' (because the system administrator
   hasn't configured a value), the check always fails.

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

   document-natural-language (naturalLanguage)

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

   compression (type3 keyword)

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

   job-k-octets (integer(0:MAX))

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

   job-impressions (integer(0:MAX))

      IF NOT a single 'integer' value equal to 4 octets,
      REJECT/RETURN 'client-error-bad-request'.

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

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

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

   message (text(127))

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

   unknown or unsupported attribute

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

      Note: Future Operation attributes may be added to the protocol
      specification that may occur anywhere in the specified group.
      When the operation is otherwise successful, the IPP object returns
      the 'successful-ok-ignored-or-substituted-attributes' status code.
      Ignoring unsupported Operation attributes in all operations is
      analogous to the handling of unsupported Job Template attributes
      in the create and Validate-Job operations when the client supplies
      the "ipp-attribute-fidelity" Operation attribute with the 'false'
      value.  This last rule is so that we can add OPTIONAL Operation
      attributes to future versions of IPP so that older clients can
      inter-work with new IPP objects and newer clients can inter-work
      with older IPP objects.  (If the new attribute cannot be ignored
      without performing unexpectedly, the major version number would

      have been increased in the protocol document and in the request).
      This rule for Operation attributes is independent of the value of
      the "ipp-attribute-fidelity" attribute.   For example, if an IPP
      object doesn't support the OPTIONAL "job-k-octets" attribute', the
      IPP object treats "job-k-octets" as an unknown attribute and only
      checks the length for the 'integer' attribute syntax supplied by
      the client.  If it is not four octets, the IPP object REJECTS the
      request and RETURNS the 'client-error-bad-request' status code,
      else the IPP object copies the attribute to the Unsupported
      Attribute response group, setting the value to the "out-of-band" '
      unsupported' value, but otherwise ignores the attribute.

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

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

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

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

2.2.2.2 Check that the Printer object is accepting jobs

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

2.2.2.3 Validate the values of the Job Template attributes

   An IPP object validates the values of all Job Template attribute
   supplied by the client.  The IPP object performs the analogous
   syntactic validation checks of each Job Template attribute value that
   it performs for Operation attributes (see Section 2.2.1.5.):

      a)that the length of each value is correct for the attribute
        syntax tag supplied by the client according to [RFC2566] Section
        4.1.

      b)that the attribute syntax tag is correct for that attribute
        according to [RFC2566] Sections 4.2 to 4.4.

      c)that multiple values are supplied only for multi-valued
        attributes, i.e., that are 1setOf  X according to [RFC2566]
        Sections 4.2 to 4.4.

   As in Section 2.2.1.5, if any of these syntactic checks fail, the IPP
   object REJECTS the request and RETURNS the 'client-error-bad-request'
   or 'client-error-request-value-too-long' status code as appropriate,
   independent of the value of the "ipp-attribute-fidelity".  Since such
   an error is most likely to be an error detected by a client
   developer, rather than by an end-user, the IPP object NEED NOT return
   an indication of which attribute had the error in either the
   Unsupported Attributes Group or the Status Message.  The description
   for each of these syntactic checks is explicitly expressed in the
   first IF statement in the following table.

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

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

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

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

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

2.2.3 Algorithm for job validation

   The process of validating a Job-Template attribute "xxx" against a
   Printer attribute "xxx-supported" can use the following validation
   algorithm (see section 3.2.1.2 in [RFC2566]).

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

      1.If U is multi-valued, validate each value X of U by performing
        the algorithm in Table 3 with each value X. Each validation is
        separate from the standpoint of returning unsupported values.

        Example: If U is "finishings" that the client supplies with
        'staple', 'bind' values, then X takes on the successive values:
        'staple', then 'bind'

      2.If V is multi-valued, validate X against each Z of V by
        performing the algorithm in Table 3 with each value Z.  If a
        value Z validates, the validation for the attribute value X
        succeeds. If it fails, the algorithm is applied to the next
        value Z of V. If there are no more values Z of V, validation
        fails.

        Example: If V is "sides-supported" with values: 'one-sided',
        'two-sided-long', and 'two-sided-short', then Z takes on the
        successive values: 'one-sided', 'two-sided-long', and
        'two-sided-short'.  If the client supplies "sides" with 'two-
        sided-long', the first comparison fails ('one-sided' is not
        equal to 'two-sided-long'), the second comparison succeeds
        ('two-sided-long' is equal to 'two-sided-long"), and the third
        comparison ('two-sided-short' with 'two-sided-long') is not even
        performed.

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

            Table 3 - Rules for validating single values X against Z

     attribute    attribute       validated if:
     syntax of X  syntax of Z

     integer      rangeOfInteger  X is within the range of
                                   Z

     uri          uriScheme       the uri scheme in X is
                                   equal to Z

     any          boolean         the value of Z is TRUE

     any          any             X and Z are of the same
                                   type and are equal.

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

   If some Job Template attributes are supported for some document
   formats and not for others or the values are different for different
   document formats, the IPP object SHOULD take that into account in
   this validation using the value of the "document-format" supplied by
   the client (or defaulted to the value of the Printer's "document-
   format-default" attribute, if not supplied by the client).  For
   example, if "number-up" is supported for the 'text/plain' document
   format, but not for the 'application/postscript' document format, the
   check SHOULD (though it NEED NOT) depend on the value of the
   "document-format" operation attribute.  See "document-format" in
   [RFC2566] section 3.2.1.1 and 3.2.5.1.

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

   job-priority (integer(1:100))

      IF NOT a single 'integer' value with a length equal to 4 octets,
         REJECT/RETURN 'client-error-bad-request'.
      IF NOT supplied by the client, use the value of the Printer
         object's "job-priority-default" attribute at job submission
         time.
      IF NOT in the range 1 to 100, inclusive, copy the attribute and
         the unsupported value to the Unsupported Attributes response
         group.
      Map the value to the nearest supported value in the range 1:100 as
         specified by the number of discrete values indicated by the
         value of the Printer's "job-priority-supported" attribute.  See
         the formula in [RFC2566] Section 4.2.1.

   job-hold-until (type3 keyword | name)

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

   job-sheets (type3 keyword | name)

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

   multiple-document-handling (type2 keyword)

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

   copies (integer(1:MAX))

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

   finishings (1setOf type2 enum)

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

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

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

   sides (type2 keyword)

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

   number-up (integer(1:MAX))

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

   orientation-requested (type2 enum)

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

   media (type3 keyword | name)

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

   printer-resolution (resolution)

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

   print-quality (type2 enum)

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

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

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

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

   Name              Octet length check for read-write attributes
   -----------       --------------------------------------------
   'textWithLanguage    <= 1023 AND 'naturalLanguage'  <= 63
   'textWithoutLanguage' <= 1023
   'nameWithLanguage'    <= 255 AND 'naturalLanguage'  <= 63
   'nameWithoutLanguage' <= 255
   'keyword'             <= 255
   'enum'                = 4
   'uri'                 <= 1023
   'uriScheme'           <= 63
   'charset'             <= 63
   'naturalLanguage'     <= 63
   'mimeMediaType'       <= 255

   'octetString'         <= 1023
   'boolean'             = 1
   'integer'             = 4
   'rangeOfInteger'      = 8
   'dateTime'            = 11
   'resolution'          = 9
   '1setOf  X'

2.2.3.1 Check for conflicting Job Template attributes values

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

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

2.2.3.2 Decide whether to REJECT the request

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

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

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

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

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

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

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

2.2.3.4 Create the Job object with attributes to support

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

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

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

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

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

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

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

2.2.3.5 Return one of the success status codes

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

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

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

   The Printer object also returns Job status attributes that indicate
   the initial state of the Job ('pending', 'pending-held', '
   processing', etc.), etc.  See Print-Job Response, [RFC2566] section
   3.2.1.2.

2.2.3.6 Accept appended Document Content

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

2.2.3.7 Scheduling and Starting to Process the Job

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

2.2.3.8 Completing the Job

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

2.2.3.9 Destroying the Job after completion

   Once the Job moves to the 'completed', 'aborted', or 'canceled'
   state, it is an implementation decision as to when to destroy the Job
   object and release all associated resources.  Once the Job has been
   destroyed, the Printer would return either the "client-error-not-
   found" or "client-error-gone" status codes for operations directed at
   that Job.

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

2.2.3.10 Interaction with "ipp-attribute-fidelity"

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

2.3 Status codes returned by operation

   This section lists all status codes once in the first operation
   (Print-Job).  Then it lists the status codes that are different or
   specialized for subsequent operations under each operation.

2.3.1 Printer Operations

2.3.1.1 Print-Job

   The Printer object MUST return one of the following "status-code"
   values for the indicated reason.  Whether all of the document data
   has been accepted or not before returning the success or error
   response depends on implementation.  See Section 14 for a more
   complete description of each status code.

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

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

   [RFC2566] section 3.1.6 Operation Status Codes and Messages states:

         If the Printer object supports the "status-message" operation
         attribute, it SHOULD use the REQUIRED 'utf-8' charset to return
         a status message for the following error status codes (see
         section 14):  'client-error-bad-request', 'client-error-
         charset-not-supported', 'server-error-internal-error', '
         server-error-operation-not-supported', and 'server-error-
         version-not-supported'.  In this case, it MUST set the value of
         the "attributes-charset" operation attribute to 'utf-8' in the
         error response.

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

      client-error-bad-request:  The request syntax does not conform to
         the specification.

      client-error-forbidden:  The request is being refused for
         authorization or authentication reasons.  The implementation
         security policy is to not reveal whether the failure is one of
         authentication or authorization.
      client-error-not-authenticated:  Either the request requires
         authentication information to be supplied or the authentication
         information is not sufficient for authorization.
      client-error-not-authorized:  The requester is not authorized to
         perform the request on the target object.
      client-error-not-possible:  The request cannot be carried out
         because of the state of the system.  See also 'server-error-
         not-accepting-jobs' status code which MUST take precedence if
         the Printer object's "printer-accepting-jobs" attribute is '
         false'.
      client-error-timeout:  not applicable.
      client-error-not-found:  the target object does not exist.
      client-error-gone:  the target object no longer exists and no
         forwarding address is known.
      client-error-request-entity-too-large:  the size of the request
         and/or print data exceeds the capacity of the IPP Printer to
         process it.
      client-error-request-value-too-long:  the size of request variable
         length attribute values, such as 'text' and 'name' attribute
         syntaxes, exceed the maximum length specified in [RFC2566] for
         the attribute and MUST be returned in the Unsupported
         Attributes Group.
      client-error-document-format-not-supported:  the document format
         supplied is not supported.  The "document-format" attribute
         with the unsupported value MUST be returned in the Unsupported
         Attributes Group.  This error SHOULD take precedence over any
         other 'xxx-not-supported' error, except 'client-error-charset-
         not-supported'.
      client-error-attributes-or-values-not-supported:  one or more
         supplied attributes, attribute syntaxes, or values are not
         supported and the client supplied the "ipp-attributes-fidelity"
         operation attribute with a 'true' value.  They MUST be returned
         in the Unsupported Attributes Group as explained below.
      client-error-uri-scheme-not-supported:  not applicable.
      client-error-charset-not-supported:  the charset supplied in the
         "attributes-charset" operation attribute is not supported.  The
         Printer's "configured-charset" MUST be returned in the response
         as the value of the "attributes-charset" operation attribute
         and used for any 'text' and 'name' attributes returned in the
         error response.  This error SHOULD take precedence over any
         other error, unless the request syntax is so bad that the
         client's supplied "attributes-charset" cannot be determined.

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

2.3.1.2 Print-URI

   All of the Print-Job status codes described in Section 3.2.1.2
   Print-Job Response are applicable to Print-URI with the following
   specializations and differences.  See Section 14 for a more complete
   description of each status code.

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

2.3.1.3 Validate-Job

   All of the Print-Job status codes described in Section 3.2.1.2
   Print-Job Response are applicable to Validate-Job.  See Section 14
   for a more complete description of each status code.

2.3.1.4 Create-Job

   All of the Print-Job status codes described in Section 3.2.1.2
   Print-Job Response are applicable to Create-Job with the following
   specializations and differences.  See Section 14 for a more complete
   description of each status code.

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

2.3.1.5 Get-Printer-Attributes

   All of the Print-Job status codes described in Section 3.2.1.2
   Print-Job Response are applicable to the Get-Printer-Attributes
   operation with the following specializations and differences.   See
   Section 14 for a more complete description of each status code.

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

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

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

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

      server-error-busy:  same as Print-Job, except the IPP object is
         too busy to accept even query requests.
      server-error-job-canceled:  not applicable.

2.3.1.6 Get-Jobs

   All of the Print-Job status codes described in Section 3.2.1.2
   Print-Job Response are applicable to the Get-Jobs operation with the
   following specializations and differences.   See Section 14 for a
   more complete description of each status code.

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

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

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

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

2.3.2 Job Operations

2.3.2.1 Send-Document

   All of the Print-Job status codes described in Section 3.2.1.2
   Print-Job Response are applicable to the Get-Printer-Attributes
   operation with the following specializations and differences.   See
   Section 14 for a more complete description of each status code.

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

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

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

      client-error-not-possible: Same as Print-Job, except that the
         Printer's "printer-is-accepting-jobs" attribute is not
         involved, so that the client is able to finish submitting a
         multi-document job after this attribute has been set to 'true'.
         Another condition is that the state of the job precludes Send-
         Document, i.e., the job has already been closed out by the
         client.  However, if the IPP Printer closed out the job due to
         timeout, the 'client-error-timeout' error status SHOULD  be
         returned instead.
      client-error-timeout:  This request was sent after the Printer
         closed the job, because it has not received a Send-Document or
         Send-URI operation within the Printer's "multiple-operation-
         time-out" period.
      client-error-request-entity-too-large:  same as Print-Job.
      client-error-conflicting-attributes:  same as Print-Job, except
         that "ipp-attributes-fidelity" operation attribute is not
         involved.
      server-error-operation-not-supported:  the Send-Document request
         is not supported.
      server-error-not-accepting-jobs:  not applicable.
      server-error-job-canceled:  the job has been canceled by an
         operator or the system while the client was transmitting the
         data.

2.3.2.2 Send-URI

   All of the Print-Job status code descriptions in Section 3.2.1.2
   Print-Job Response with the specializations described for Send-
   Document are applicable to Send-URI.  See Section 14 for a more
   complete description of each status code.

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

2.3.2.3 Cancel-Job

   All of the Print-Job status codes described in Section 3.2.1.2
   Print-Job Response are applicable to Cancel-Job with the following
   specializations and differences.  See Section 14 for a more complete
   description of each status code.

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

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

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

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

      server-error-operation-not-supported:  not applicable (Cancel-Job
         is REQUIRED).
      server-error-device-error:  same as Print-Job, except no document
         data is involved.
      server-error-temporary-error:  same as Print-Job, except no
         document data is involved.
      server-error-not-accepting-jobs:  not applicable.
      server-error-job-canceled:  not applicable.

2.3.2.4 Get-Job-Attributes

   All of the Print-Job status codes described in Section 3.2.1.2
   Print-Job Response are applicable to Get-Job-Attributes with the
   following specializations and differences.  See Section 14 for a more
   complete description of each status code.

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

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

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

      client-error-not-possible:  Same as Print-Job, in addition the
         Printer object is not accepting any requests.
      client-error-document-format-not-supported:  not applicable.
      client-error-attributes-or-values-not-supported:  not applicable.
      client-error-uri-scheme-not-supported:  not applicable.
      client-error-conflicting-attributes:  not applicable
      server-error-operation-not-supported:  not applicable (since Get-
         Job-Attributes is REQUIRED).
      server-error-device-error:  same as Print-Job, except no document
         data is involved.
      server-error-temporary-error:  sane as Print-Job, except no
         document data is involved.
      server-error-not-accepting-jobs:  not applicable.  server-error-
      job-canceled:  not applicable.

2.4 Validate-Job

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

2.5 Case Sensitivity in URIs

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

   The reason that the IPP specification does not make any restrictions
   on URIs, is so that implementations of IPP may use off-the-shelf
   components that conform to the standards that define URIs, such as
   RFC 2396 and the HTTP/1.1 specifications [RFC2068].  See these
   specifications for rules of matching, comparison, and case-
   sensitivity.

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

   The HTTP/1.1 specification [RFC2068] contains more details on
   comparing URLs.

2.6 Character Sets, natural languages, and internationalization

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

2.6.1 Character set code conversion support

   IPP clients and IPP objects are REQUIRED to support UTF-8.  They MAY
   support additional charsets.  It is RECOMMENDED that an IPP object
   also support US-ASCII, since many clients support US-ASCII, and
   indicate that UTF-8 and US-ASCII are supported by populating the

   Printer's "charset-supported" with 'utf-8' and 'us-ascii' values.  An
   IPP object is required to code covert with as little loss as possible
   between the charsets that it supports, as indicated in the Printer's
   "charsets-supported" attribute.

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

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

   According to the RFC2566 document (section 3.1.4.2), the value of the
   "attributes-charset" for the response of the second request must be
   "us-ascii" since that is the charset specified in the request.  The
   "job-name" value, however, is in "utf-8" format.  Should the request
   be rejected even though both "utf-8" and "us-ascii" charsets are
   supported by the server? or should the "job-name" value be converted
   to "us-ascii" and return "successful-ok-conflicting-attributes"
   (0x0002) as the status code?

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

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

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

2.6.2 What charset to return when an unsupported charset is requested?

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

      All clients and IPP objects MUST support the 'utf-8' charset
      [RFC2044] and MAY support additional charsets provided that they
      are registered with IANA [IANA-CS].  If the Printer object does
      not support the client supplied charset value, the Printer object
      MUST reject the request, set the "attributes-charset" to 'utf-8'
      in the response, and return the 'client-error-charset-not-
      supported' status code and any 'text' or 'name' attributes using
      the 'utf-8' charset.

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

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

   Furthermore, [RFC2566] section 14.1.4.14 client-error-charset-not-
   supported (0x040D) was clarified in November 1998 as follows:

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

2.6.3 Natural Language Override (NLO)

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

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

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

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

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

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

   Early drafts of [RFC2566] contained a job-level natural language
   override (NLO) for the Get-Jobs response.  A job-level (NLO) is an
   (unrequested) Job Attribute which then specified the implicit natural

   language for any other WithoutLanguage job attributes returned in the
   response for that job.  Interoperability testing of early
   implementations showed that no one was implementing the job-level NLO
   in Get-Job responses.  So the job-level NLO was eliminated from the
   Get- Jobs response.  This simplification makes all requests and
   responses consistent in that the implicit natural language for any
   WithoutLanguage 'text' or 'name' form is always supplied in the
   request's or response's "attributes-natural-language" operation
   attribute.

2.7 The "queued-job-count" Printer Description attribute

2.7.1 Why is "queued-job-count" RECOMMENDED?

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

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

2.7.2 Is "queued-job-count" a good measure of how busy a printer is?

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

2.8 Sending empty attribute groups

   The [RFC2566] and [RFC2565] specifications RECOMMEND that a sender
   not send an empty attribute group in a request or a response.
   However, they REQUIRE a receiver to accept an empty attribute group
   as equivalent to the omission of that group.  So a client SHOULD omit
   the Job Template Attributes group entirely in a create operation that
   is not supplying any Job Template attributes.  Similarly, an IPP
   object SHOULD omit an empty Unsupported Attributes group if there are
   no unsupported attributes to be returned in a response.

   The [RFC2565] specification REQUIRES a receiver to be able to receive
   either an empty attribute group or an omitted attribute group and
   treat them equivalently.  The term "receiver" means an IPP object for
   a request and a client for a response.  The term "sender' means a
   client for a request and an IPP object for a response.

   There is an exception to the rule for Get-Jobs when there are no
   attributes to be returned.  [RFC2565] contains the following
   paragraph:

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

2.9 Returning unsupported attributes in Get-Xxxx responses

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

2.10 Returning job-state in Print-Job response

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

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

   This issue comes up for the implementation of an IPP Printer object
   as a server that forwards jobs to devices that do not provide job
   status back to the server.  If the server is reasonably certain that
   the job completed successfully, then it should return the job-state
   as 'completed'.  Also the server can keep the job in its "job
   history" long after the job is no longer in the device.  Then a user

   could query the server and see that the job was in the 'completed'
   state and completed as specified by the job's "time-at-completed"
   time which would be the same as the server submitted the job to the
   device.

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

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

   On the other hand, if the server is able to query the device and/or
   setup some sort of event notification that the device initiates when
   the job makes state transitions, then the server can return the
   current job state in the Print-Job response and in subsequent queries
   because the server knows what the job state is in the device (or can
   query the device).

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

2.11 Flow controlling the data portion of a Print-Job request

   A paused printer (or one that is stopped due to paper out or jam or
   spool space full or buffer space full, may flow control the data of a
   Print-Job operation (at the TCP/IP layer), so that the client is not
   able to send all the document data.  Consequently, the Printer will
   not return a response until the condition is changed.

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

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

2.12 Multi-valued attributes

   What is the attribute syntax for a multi-valued attribute?  Since
   some attributes support values in more than one data type, such as
   "media", "job-hold-until", and "job-sheets", IPP semantics associate

   the attribute syntax with each value, not with the attribute as a
   whole.  The protocol associates the attribute syntax tag with each
   value.  Don't be fooled, just because the attribute syntax tag comes
   before the attribute keyword.  All attribute values after the first
   have a zero length attribute keyword as the indication of a
   subsequent value of the same attribute.

2.13 Querying jobs with IPP that were submitted using other job
submission protocols

The following clarification was added to [RFC2566] section 8.5:

8.5 Queries on jobs submitted using non-IPP protocols

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

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

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

2.14 The 'none' value for empty sets

   [RFC2566] states that the 'none' value should be used as the value of
   a 1SetOf when the set is empty. In most cases, sets that are
   potentially empty contain keywords so the keyword 'none' is used, but
   for the 3 finishings attributes, the values are enums and thus the
   empty set is represented by the enum 3.  Currently there are no other
   attributes with 1SetOf values which can be empty and can contain
   values that are not keywords.  This exception requires special code
   and is a potential place for bugs.  It would have been better if we
   had chosen an out-of-band value, either "no-value" or some new value,
   such as 'none'.  Since we didn't, implementations have to deal with
   the different representations of 'none', depending on the attribute
   syntax.

2.15 Get-Jobs, my-jobs='true', and 'requesting-user-name'?

   In [RFC2566] section 3.2.6.1 'Get-Jobs Request', if the attribute '
   my-jobs' is present and set to TRUE, MUST the 'requesting-user-name'
   attribute be there to, and if it's not present what should the IPP
   printer do?

   [RFC2566] Section 8.3 describes the various cases of "requesting-
   user-name" being present or not for any operation.  If the client
   does not supply a value for "requesting-user-name", the printer MUST
   assume that the client is supplying some anonymous name, such as
   "anonymous".

2.16 The "multiple-document-handling" Job Template attribute and support
of multiple document jobs

   ISSUE:  IPP/1.0 is silent on which of the four effects an
   implementation would perform if it supports Create-Job, but does not
   support "multiple-document-handling".

   A fix to IPP/1.0 would be to require implementing all four values of
   "multiple-document-handling" if Create-Job is supported at all.  Or
   at least 'single-document-new-sheet' and 'separate-documents-
   uncollated-copies'.  In any case, an implementation that supports
   Create-Job SHOULD also support "multiple-document-handling".  Support
   for all four values is RECOMMENDED, but at least the 'single-
   document-new-sheet' and 'separate-documents-uncollated-copies'
   values, along with the "multiple-document-handling-default"
   indicating the default behavior and "multiple-document-handling-
   supported" values.  If an implementation spools the data, it should
   also support the 'separate-documents-collated-copies' value as well.

3 Encoding and Transport

   This section discusses various aspects of IPP/1.0 Encoding and
   Transport [RFC2565].

   A server is not required to send a response until after it has
   received the client.s entire request.  Hence, a client must not
   expect a response until after it has sent the entire request.
   However, we recommend that the server return a response as soon as
   possible if an error is detected while the client is still sending
   the data, rather than waiting until all of the data is received.
   Therefore, we also recommend that a client listen for an error
   response that an IPP server MAY send before it receives all the data.
   In this case a client, if chunking the data, can send a premature
   zero-length chunk to end the request before sending all the data (and
   so the client can keep the connection open for other requests, rather
   than closing it). If the request is blocked for some reason, a client
   MAY determine the reason by opening another connection to query the
   server using Get-Printer-Attributes.

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

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

   The table for .request headers. does not have columns for responses,
   and the table for .response headers. does not have columns for
   requests.

   The following is an explanation of the values in the .request/client.
   and .response/ server. columns.

      - must: the client or server MUST send the header,
      - must-if: the client or server MUST send the header when the
        condition described in the .values and conditions. column is
        met,

      - may: the client or server MAY send the header
      - not: the client or server SHOULD NOT send the header. It is not
        relevant to an IPP implementation.

   The following is an explanation of the values in the
   .response/client.  and .request/ server. columns.

      - must: the client or server MUST support the header,
      - may: the client or server MAY support the header
      - not: the client or server SHOULD NOT support the header. It is
        not relevant to an IPP implementation.

3.1 General Headers

   The following is a table for the general headers.

   General-     Request         Response       Values and Conditions
   Header

                Client  Server Server Client

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

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

   Date         may     may    must   may     per RFC 1123 [RFC1123]
                                                from RFC 2068
                                                [RFC2068]

   Pragma       must    not    must   not     .no-cache. only

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

Upgrade not not not not

Via not not not not

3.2 Request Headers

   The following is a table for the request headers.

   Request-Header   Client   Server  Request Values and Conditions

   Accept           may      must    .application/ipp. only.  This
                                      value is the default if the

   Request-Header   Client   Server  Request Values and Conditions

                                      client omits it

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

   Accept-Encoding  may      must    empty and per RFC 2068 [RFC2068]
                                      and IANA registry for content-
                                      codings

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

   Authorization    must-if  must    per RFC 2068. A client MUST send
                                      this header when it receives a
                                      401 .Unauthorized. response and
                                      does not receive a  .Proxy-
                                      Authenticate. header.

   From             not      not     per RFC 2068. Because RFC
                                      recommends sending this header
                                      only with the user.s approval, it
                                      is not very useful

   Host             must     must    per RFC 2068

   If-Match         not      not

   If-Modified-     not      not
   Since

   If-None-Match    not      not

   If-Range         not      not

   If-Unmodified-   not      not
   Since

   Max-Forwards     not      not

   Proxy-           must-if  not     per RFC 2068. A client MUST send
   Authorization                      this header when it receives a
                                      401 .Unauthorized. response and a
                                      .Proxy-Authenticate. header.

   Range            not      not

   Referer          not      not

   User-Agent       not      not

3.3 Response Headers

   The following is a table for the request headers.

   Response-      Server  Client  Response Values and Conditions
   Header

   Accept-Ranges  not     not

   Age            not     not

   Location       must-if may     per RFC 2068. When URI needs
                                   redirection.

   Proxy-         not     must    per RFC 2068
   Authenticate

   Public         may     may     per RFC 2068

   Retry-After    may     may     per RFC 2068

   Server         not     not

   Vary           not     not

   Warning        may     may     per RFC 2068

WWW- must-if must per RFC 2068. When a server needs to
Authenticate authenticate a client.

3.4 Entity Headers

   The following is a table for the entity headers.

   Entity-Header  Request         Response        Values and Conditions

                  Client  Server Server  Client

   Allow          not     not    not     not

   Content-Base   not     not    not     not

   Content-       may     must   must    must   per RFC 2068 and IANA
   Encoding                                       registry for content
                                                  codings.

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

   Content-       must-if must   must-if must   the length of the
   Length                                         message-body per RFC
                                                  2068. Header MUST be
                                                  present if Transfer-

   Entity-Header  Request         Response        Values and Conditions

                  Client  Server Server  Client

                                                  Encoding is absent.

   Content-       not     not    not     not
   Location

   Content-MD5    may     may    may     may    per RFC 2068

   Content-Range  not     not    not     not

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

   ETag           not     not    not     not

   Expires        not     not    not     not

Last-Modified not not not not

3.5 Optional support for HTTP/1.0

   IPP implementations consist of an HTTP layer and an IPP layer.  In
   the following discussion, the term "client" refers to the HTTP client
   layer and the term "server" refers to the HTTP server layer.  The
   Encoding and Transport document [RFC2565] requires that HTTP 1.1 MUST
   be supported by all clients and all servers.  However, a client
   and/or a server implementation may choose to also support HTTP 1.0.

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

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

3.6 HTTP/1.1 Chunking

3.6.1 Disabling IPP Server Response Chunking

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

        TE: identity

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

3.6.2 Warning About the Support of Chunked Requests

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

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

   Some HTTP/1.1 implementations that support CGI scripts [CGI] and/or
   servlets [Servlet] require that the client supply a Content-Length.
   These implementations might reject a chunked POST method and return a
   411 status code (Length Required), might attempt to buffer the
   request and run out of room returning a 413 status code (Request
   Entity Too Large), or might successfully accept the chunked request.

   Because of this lack of conformance of HTTP servers to the HTTP/1.1
   standard, the IPP standard [RFC2565] REQUIRES that a conforming IPP
   Printer object implementation support chunked requests and that
   conforming clients accept chunked responses.  Therefore, IPP object
   implementers are warned to seek HTTP server implementations that
   support chunked POST requests in order to conform to the IPP standard
   and/or use implementation techniques that support chunked POST
   requests.

4 References

   [CGI]     Coar, K. and D. Robinson, "The WWW Common Gateway Interface
             Version 1.1 (CGI/1.1)", Work in Progress.

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

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

   [RFC2566] deBry, R., Hastings, T., Herriot, R., Isaacson, S. and P.
             Powell, "Internet Printing Protocol/1.0: Model and
             Semantics", RFC 2566, April 1999.

   [RFC2565] Herriot, R., Butler, S., Moore, P. and R. Tuner, "Internet
             Printing Protocol/1.0: Encoding and Transport", RFC 2565,
             April 1999.

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

   [RFC2567] Wright, D., "Design Goals for an Internet Printing
             Protocol", RFC 2567, April 1999.

   [RFC1123] Braden, S., "Requirements for Internet Hosts - Application
             and Support", STD 3, RFC 1123, October 1989.

   [RFC2026] Bradner, S., "The Internet Standards Process -- Revision
             3", BCP 9, RFC 2026, October 1996.

   [RFC2068] Fielding, R., Gettys, J., Mogul, J., Frystyk, H. and T.
             Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC
             2068, January 1997.

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

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

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

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

4.1 Authors' Addresses

   Thomas N. Hastings
   Xerox Corporation
   701 Aviation Blvd.
   El Segundo, CA 90245

   EMail: hastings@cp10.es.xerox.com

   Carl-Uno Manros
   Xerox Corporation
   701 Aviation Blvd.
   El Segundo, CA 90245

   EMail: manros@cp10.es.xerox.com

5 Security Considerations

Security issues are discussed in sections 2.2, 2.3.1, and 8.5.

6 Notices

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