INTERNET-DRAFT Roger deBry
<draft-ietf-ipp-collection-01.txt> Utah Valley State College
T. Hastings
Xerox Corporation
R. Herriot
Xerox Corporation
February 22, 2000
Internet Printing Protocol:
The 'collection' attribute syntax
Copyright (C) The Internet Society (2000). All Rights Reserved.
Status of this Memo:
This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of [RFC2026]. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas, and
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Abstract
This document specifies an OPTIONAL attribute syntax called
'collection' for use with the Internet Printing Protocol/1.0
(IPP) [RFC2565, RFC2566], IPP/1.1 [ipp-mod, ipp-pro], and
subsequent versions. A 'collection' is a container holding one or
more named values, which are called "member" attributes. A
collection allows data to be grouped like a PostScript dictionary
or a Java Map.
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The full set of IPP documents includes:
Design Goals for an Internet Printing Protocol [RFC2567]
Rationale for the Structure and Model and Protocol for the Internet
Printing Protocol [RFC2568]
Internet Printing Protocol/1.1: Model and Semantics (this document)
Internet Printing Protocol/1.1: Encoding and Transport [IPP-PRO]
Internet Printing Protocol/1.1: Implementer's Guide [IPP-IIG]
Mapping between LPD and IPP Protocols [RFC2569]
The "Design Goals for an Internet Printing Protocol" document 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. It calls out a subset of end user requirements that are
satisfied in IPP/1.0. A few OPTIONAL operator operations have been
added to IPP/1.1.
The "Rationale for the Structure and Model and Protocol for the Internet
Printing Protocol" document describes IPP from a high level view,
defines a roadmap for the various documents that form the suite of IPP
specification documents, and gives background and rationale for the IETF
working group's major decisions.
The "Internet Printing Protocol/1.1: Encoding and Transport" document is
a formal mapping of the abstract operations and attributes defined in
the model document onto HTTP/1.1 [RFC2616]. It defines the encoding
rules for a new Internet MIME media type called "application/ipp". This
document also defines the rules for transporting over HTTP a message
body whose Content-Type is "application/ipp". This document defines a
new scheme named 'ipp' for identifying IPP printers and jobs.
The "Internet Printing Protocol/1.1: Implementer's Guide" document gives
insight and advice to implementers of IPP clients and IPP objects. It
is intended to help them understand IPP/1.1 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 "Mapping between LPD and IPP Protocols" document gives some advice
to implementers of gateways between IPP and LPD (Line Printer Daemon)
implementations.
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Table of Contents
1 Problem Statement.................................................4
2 Solution..........................................................4
3 Definition of a Collection Type...................................5
4 Order of Member Attributes........................................6
5 New Operation Attribute...........................................6
5.1collection-syntax-recognized (boolean)...........................6
6 New Printer Attribute.............................................7
6.1collection-syntax-recognized (boolean)...........................7
7 New Out-of-band value.............................................7
7.1'none'...........................................................7
8 Unsupported Values................................................7
9 Encoding..........................................................8
10 Legacy issues.....................................................9
11 IANA Considerations..............................................10
12 Internationalization Considerations..............................10
13 Security Considerations..........................................10
14 References.......................................................10
15 Author's Addresses...............................................11
16 APPENDIX A: Example of collection usage..........................12
16.1"job-notify" Operation attribute..............................12
17 Appendix B: Full Copyright Statement.............................12
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1 Problem Statement
IPP supports most of the common data structures that are available in
programming languages. It lacks a mechanism for grouping several values
of different types. The Java language uses the Map to solve this
problem and PostScript has a dictionary.
2 Solution
The IPP 'collection' is a container holding one or more named values
(i.e. attributes), which are called member attributes. A collection also
has a type name, which identifies the expected member attributes, as
does a subclass of a Java Map. A collection value is similar to a group,
such as an operation group. They both consist of a set of attributes.
The name of each member attribute MUST be unique within a collection,
but MAY be the same as the name of a member attribute in another
collection type and/or MAY be the same as the name of an attribute that
is not a member of a collection.
A client or Printer is said to "recognize" collections as a single
attribute value if it can determine the beginning and end of a
collection value and if it can distinguish attributes within the
collection from attributes outside of the collection. In order to
support legacy IPP implementations, a client MUST indicate that it
"recognizes" collections by including the operation attribute
"collection-syntax-recognized" with the value of 'true' in each request.
A printer MUST indicate that it "recognizes" collections by supporting
the attribute "collection-syntax-recognized" with the value of 'true'.
The fact that a Printer recognizes collections does not require the
printer to support collection values of attributes that are defined to
have values of collections and other attribute syntaxes. For example,
if an attribute is defined to have the attribute syntax: (type3 keyword
| name | collection), a Printer that recognizes collections MAY support
only keyword values of such an attribute.
Each member attribute can have any attribute syntax type, including
'collection', and can be either single-valued or multi-valued. The
length of a collection value is not limited. However, the length of each
member attribute MUST NOT exceed the limit of its attribute syntax.
The member attributes in a collection can be in any order. When a client
sends the Printer a collection, the order that the Printer stores the
value and the order returned in a response MAY be different from the
order sent by the client.
If a collection contains two or more member attributes with the same
attribute name, the collection is not well formed. The receiver of such
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a collection MAY either treat the collection as a bad value or ignore
all but one of the identically named member attributes.
3 Definition of a Collection Type
When a specification defines an attribute "xxx" whose syntax type is
'collection' or '1setOf collection', it must define following aspects of
the attribute.
1. The name of the attribute "xxx"
2. Its syntax type, which includes a collection syntax-type
3. Its default-value is specified by
a)the attribute's definition
b)an attribute, such as "xxx-default", which may have a collection
value
4. Its supported values, which may be specified by one of:
a)the attribute's definition
b)a boolean attribute, such as "xxx-supported", which is true if
the attribute is supported. The supported values are specified
by the attribute's definition which specifies the supported
values for each member of a collection or the "yyy-supported"
that specifies the value supported for the "yyy" member
attribute.
c)an attribute, such as "xxx-supported", which contains the
explicit collection values and other values supported.
5. the name of the collection type, whose characters are the same as
those for a keyword.
6. the following information about each "yyy" member attribute:
a)its name, which is a keyword like all attributes. It must be
unique within the collection type.
b)its syntax type, which may be any IPP syntax type, including
'collection'. If the attribute syntax type starts with "1setOf",
the member attribute is multi-valued.
c)its supported values, either enumerated explicitly or specified
by the values of a referenced attribute which may be specified
by either:
@ the attribute's definition
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@ an attribute, such as "yyy-supported", which contains the
explicit values supported. The "yyy-supported" attribute is
a Printer attribute and not in a collection. For example,
if a collection contains the "media" attribute and its
supported values are specified by the "media-supported"
attribute, the "media-supported" attribute is the same
Printer attribute that the "media" attribute uses.
d)whether "yyy" MUST be or MAY be supplied by a client in a
request.
e)the default value of "yyy" if it is OPTIONAL for a client to
supply the "yyy" attribute in a request. The default value is
specified by either:
@ the attribute's definition
@ an attribute, such as "yyy-default", which may have a
collection value
f)whether "yyy" MUST be or MAY be supported by the printer.
g)the semantics of "yyy".
4 Order of Member Attributes
The member attributes of a collection value are unordered. A Printer
and a client MUST accept member attributes of a collection in any order.
Therefore, a Printer and a client MAY send the member attributes of a
collection value in any order. A Printer NEED NOT return member
attributes to a client in the order received from a client.
5 New Operation Attribute
5.1 collection-syntax-recognized (boolean)
A client MUST include this operation attribute with a value of 'true' in
each request if it recognizes the collection-syntax. If a client does
not include this operation attribute or its value is not 'true' in a
request, then a Printer MUST NOT return a collection in a response.
ISSUE 01: If a Printer creates a notification subscription [ipp-ntfy]
with a request that does not include "collection-syntax-recognized"
(boolean) operation attribute with a value of 'true', then a Printer
MUST NOT send a collection in a Notification to a Notification
Recipient?
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6 New Printer Attribute
6.1 collection-syntax-recognized (boolean)
A Printer MUST support this attribute with a value of 'true' if it
recognizes the collection-syntax. If a Printer does not support this
attribute or its value is not 'true', then a client MUST NOT send a
collection in a request.
7 New Out-of-band value
7.1 'none'
'none' The specified Job Template attribute in the request MUST
NOT be applied to the job. Specifically, this value
overrides the Printer's "xxx-default" attribute value for
the Job Template attribute, if one exists.
This "out-of-band" value allows a client to specify "turn-off" a feature
that is specified by an attribute whose value is a collection. Because a
client specifies a value, the Printer uses the client-specified value
and not the Printer's default value.
If a Printer supports the use of the 'collection' attribute syntax for
an attribute, a Printer MUST support the use of the "out-of-band" value
'none'.
A Printer MUST support the "out-of-band" value 'none' as the value for
an attribute "xxx" if:
@ the definition of the attribute specifies 'none' MUST be
supported AND
@ the definition of the attribute specifies 'none' MAY be
supported and it is a value of the attribute "xxx-supported".
8 Unsupported Values
The rules for returning an unsupported collection attribute are an
extension to the current rules.
If a collection contains unrecognized, unsupported member attributes
and/or conflicting values, the attribute returned in the Unsupported
Group is a collection containing the unrecognized, unsupported member
attributes, and/or conflicting values. The unrecognized member
attributes have an out-of-band value of 'unsupported' (see the
beginning of [ipp-mod] section 4.1). The unsupported member
attributes and conflicting values have their unsupported values.
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9 Encoding
This section defines the encoding of a collection syntax type. A
collection is encoded by using three new tags:
Tag name Tag Meaning
value
beginCollection 0x34 Begin the named collection.
endCollection 0x37 End the named collection.
A collection value is encoded as a sequence of attribute values
preceded by a beginCollection value and followed by an endCollection
value. The value field of a beginCollection and an endCollection both
contain the name of the collection type, which is a string of ASCII
characters. These values allow a receiver to optionally match an
endCollection value with a beginCollection. A 1setOf collection is
encoded using the rules for 1setOf and collection. The name field for
the endCollection must be empty. The following example is written in the
style of the IPP/1.1 "Encoding and Transport" document [ipp-pro]. The
following example is for a job-notify attribute containing a set of 2
collections.
Octets Symbolic Protocol comments
Value field
0x34 beginCollecti value-tag Beginning of the
on collection
0x000a name-length
job-notify job-notify Name
0x000f Value-length
job-notify-coll job-notify- Value Collection type
coll
0x45 uri type value-tag "notify-recipients"
attribute
0x0010 name-length
notify-recipient notify- Name
recipient
0x0013 value-length
ipp- Value
notify:port=700
0x44 keyword type value-tag "notify-event-groups"
attribute
0x000d name-length
notify-events Name
0x0d value-length
job-completed Value
0x44 keyword type value-tag 2nd "notify-event-
groups" attribute
0x0000 name-length 0 length means next
multiple value
0x0011 value-length
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Octets Symbolic Protocol comments
Value field
job-state-changed job- Value
completion
0x37 endCollection value-tag
0x0000 name-length
0x000f value-length
job-notify-coll Value Matches value of
beginCollection
0x34 beginCollecti value-tag Separator between
on collection values
0x0000 name-length
0x000f value-length
job-notify-coll Value Matches value of
beginCollection
0x45 uri type value-tag "notify-recipients"
attribute
0x0010 name-length
notify-recipient Name
0x0014 value-length
mailto:smith@foo.c Value
om
0x44 keyword type value-tag "notify-event-groups"
attribute
0x000d name-length
notify-events Name
0x0d value-length
job-completed Value
0x37 endCollection value-tag End of last collection
0x0000 name-length
0x000f value-length
job-notify-coll Value Matches value of
beginCollection
10 Legacy issues
If a client recognizes collections in responses, it MUST include the
"collection-syntax-recognized" operation attribute with the value of
'true' in each operation whether or not the request contains a
collection.
If a Printer recognizes collections in requests, it MUST support the
"collection-syntax-recognized" Printer Description attribute with the
value of 'true'.
A client that supports collections MUST NOT send collections in a
request to a Printer that does not recognize collections.
A Printer that supports collections MUST NOT return collections in a
response to a client that does not recognize collections.
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Although a client or Printer that doesn't recognize collections will
skip over the beginCollection and endCollection tags as unrecognized
syntax types, the client or Printer will mistakenly assume that the
member attributes are outside of the unrecognized collection. Thus it
is important that clients and Printers that don't recognize collections
not receive them.
11 IANA Considerations
This attribute syntax will be registered with IANA after the WG approves
its specification according to the procedures for extension of the
IPP/1.1 Model and Semantics [ipp-mod].
12 Internationalization Considerations
This attribute syntax by itself has no impact on internationalization.
However, the member attributes that are subsequently defined for use in
a collection may have internationalization considerations, as may any
attribute, according to [ipp-mod].
13 Security Considerations
This attribute syntax causes no more security concerns than any other
attribute syntax. It is only the attributes that are subsequently
defined to use this or any other attribute syntax that may have security
concerns, depending on the semantics of the attribute, according to
[ipp-mod].
14 References
[ipp-mod]
Isaacson, S., deBry, R., Hastings, T., Herriot, R., Powell, P.,
"Internet Printing Protocol/1.1: Model and Semantics" draft-ietf-
ipp-model-v11-04.txt, June 23, 1999.
[ipp-ntfy]
Isaacson, S., Martin, J., deBry, R., Hastings, T., Shepherd, M.,
Bergman, R. " Internet Printing Protocol/1.0 & 1.1: IPP Event
Notification Specification" draft-ietf-ipp-not-spec-02.txt, work in
progress, February 2, 2000.
[ipp-pro]
Herriot, R., Butler, S., Moore, P., Turner, R., "Internet Printing
Protocol/1.1: Encoding and Transport", draft-ietf-ipp-protocol-v11-
03.txt, June 23, 1999.
[RFC2565]
Herriot, R., Butler, S., Moore, P., Tuner, R., "Internet Printing
Protocol/1.0: Encoding and Transport", RFC 2565, April 1999.
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[RFC2566]
R. deBry, T. Hastings, R. Herriot, S. Isaacson, P. Powell,
"Internet Printing Protocol/1.0: Model and Semantics", RFC 2566,
April 1999.
[RFC2567]
Wright, D., "Design Goals for an Internet Printing Protocol", RFC
2567, April 1999.
[RFC2568]
Zilles, S., "Rationale for the Structure and Model and Protocol for
the Internet Printing Protocol", RFC 2568, April 1999.
[RFC2569]
Herriot, R., Hastings, T., Jacobs, N., Martin, J., "Mapping between
LPD and IPP Protocols", RFC 2569, April 1999.
[RFC2616]
R. Fielding, J. Gettys, J. Mogul, H. Frystyk, L. Masinter, P.
Leach, T. Berners-Lee, "Hypertext Transfer Protocol - HTTP/1.1",
RFC 2616, June 1999.
15 Author's Addresses
Tom Hastings
Xerox Corporation
737 Hawaii St. ESAE 231
El Segundo, CA 90245
Phone: 310-333-6413
Fax: 310-333-5514
e-mail: hastings@cp10.es.xerox.com
Robert Herriot
Xerox Corp.
3400 Hill View Ave, Building 1
Palo Alto, CA 94304
Phone: 650-813-7696
Fax: 650-813-6860
e-mail: robert.herriot@pahv.xerox.com
Roger deBry
Utah Valley State College
Orem, UT 84058
Phone: (801) 222-8000
EMail: debryro@uvsc.edu
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16 APPENDIX A: Example of collection usage
This section describes one collection Job Template example.
16.1"job-notify" Operation attribute
The following example illustrates the definition of a collection
attribute for the "job-notify" operation attribute (see [ipp-ntfy]).
Each column of the table corresponds to information that is required for
member attributes. Only the semantics have been omitted.
Member name Member type Supported- Client Printer
values supplied/ support
default
notify- uri notify- MUST MUST
recipient recipient-
schemes-
supported
notify-events 1setOf type2 notify-events- notify-events- MUST
keyword supported default
subscriber- octetString(63) <any octet <empty MUST
user-data string> octetString>
notify- charset charset- attributes- MAY
attributes- supported charset in
charset operation
group
notify- naturalLanguage generated- attributes- MAY
attributes- natural- natural-
natural- language- language in
language supported operation
group
Note: for the "client supplied/default" column, the default is specified
if it is OPTIONAL for the client to supply the member attribute in a
request.
17 Appendix B: Full Copyright Statement
Copyright (C) The Internet Society (1998,1999). All Rights Reserved
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it or
assist in its implementation may be prepared, copied, published and
distributed, in whole or in part, without restriction of any kind,
provided that the above copyright notice and this paragraph are included
on all such copies and derivative works. However, this document itself
may not be modified in any way, such as by removing the copyright notice
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or references to the Internet Society or other Internet organizations,
except as needed for the purpose of developing Internet standards in
which case the procedures for copyrights defined in the Internet
Standards process must be followed, or as required to translate it into
languages other than English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an "AS
IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK
FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT
LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT
INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR
FITNESS FOR A PARTICULAR PURPOSE.
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