| Rfc | 2639 |
|---|
| Title | Internet Printing Protocol/1.0: Implementer's Guide |
|---|
| Author | T. Hastings, C.
Manros |
|---|
| Date | July 1999 |
|---|
| Format: | TXT, HTML |
|---|
| Obsoleted by | RFC3196 |
|---|
| Status: | INFORMATIONAL |
|---|
|
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
Copyright (C) The Internet Society (1999). All Rights Reserved.
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.
Table of Contents
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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intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11 [BCP-11].
Copies of claims of rights made available for publication and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
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Full Copyright Statement
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