Network Working Group A. Bryan, Ed.
Internet-Draft Metalinker Project
Intended status: Standards Track January 13, 2009
Expires: July 17, 2009
The Metalink Download Description Format
draft-bryan-metalink-05
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on July 17, 2009.
Copyright Notice
Copyright (c) 2009 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document.
Abstract
This document specifies Metalink Documents, an XML-based download
description format.
Bryan Expires July 17, 2009 [Page 1]
Internet-Draft Metalink Download Description Format January 2009
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Namespace and Version . . . . . . . . . . . . . . . . . . 5
1.3. Notational Conventions . . . . . . . . . . . . . . . . . . 5
2. Metalink Documents . . . . . . . . . . . . . . . . . . . . . . 6
3. Common Metalink Constructs . . . . . . . . . . . . . . . . . . 7
3.1. Text Constructs . . . . . . . . . . . . . . . . . . . . . 7
3.1.1. Text . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2. Date Constructs . . . . . . . . . . . . . . . . . . . . . 8
4. Metalink Element Definitions . . . . . . . . . . . . . . . . . 8
4.1. Container Elements . . . . . . . . . . . . . . . . . . . . 8
4.1.1. The "metalink:metalink" Element . . . . . . . . . . . 9
4.1.2. The "metalink:files" Element . . . . . . . . . . . . . 10
4.1.3. The "metalink:file" Element . . . . . . . . . . . . . 11
4.1.4. The "metalink:resources" Element . . . . . . . . . . . 12
4.1.5. The "metalink:verification" Element . . . . . . . . . 13
4.1.6. The "metalink:pieces" Element . . . . . . . . . . . . 13
4.2. Metadata Elements . . . . . . . . . . . . . . . . . . . . 14
4.2.1. The "metalink:copyright" Element . . . . . . . . . . . 14
4.2.2. The "metalink:description" Element . . . . . . . . . . 14
4.2.3. The "metalink:generator" Element . . . . . . . . . . . 14
4.2.4. The "metalink:hash" Element . . . . . . . . . . . . . 15
4.2.5. The "metalink:identity" Element . . . . . . . . . . . 16
4.2.6. The "metalink:language" Element . . . . . . . . . . . 17
4.2.7. The "metalink:license" Element . . . . . . . . . . . . 17
4.2.8. The "metalink:logo" Element . . . . . . . . . . . . . 17
4.2.9. The "metalink:metadata" Element . . . . . . . . . . . 17
4.2.10. The "metalink:origin" Element . . . . . . . . . . . . 18
4.2.11. The "metalink:os" Element . . . . . . . . . . . . . . 18
4.2.12. The "metalink:published" Element . . . . . . . . . . . 19
4.2.13. The "metalink:publisher" Element . . . . . . . . . . . 19
4.2.14. The "metalink:signature" Element . . . . . . . . . . . 19
4.2.15. The "metalink:size" Element . . . . . . . . . . . . . 20
4.2.16. The "metalink:type" Element . . . . . . . . . . . . . 20
4.2.17. The "metalink:updated" Element . . . . . . . . . . . . 20
4.2.18. The "metalink:url" Element . . . . . . . . . . . . . . 21
4.2.19. The "metalink:version" Element . . . . . . . . . . . . 21
5. Client Implementation Considerations . . . . . . . . . . . . . 22
6. Securing Metalink Documents . . . . . . . . . . . . . . . . . 22
7. Extending Metalink . . . . . . . . . . . . . . . . . . . . . . 23
7.1. Extensions from Non-Metalink Vocabularies . . . . . . . . 23
7.2. Extensions to the Metalink Vocabulary . . . . . . . . . . 23
7.3. Processing Foreign Markup . . . . . . . . . . . . . . . . 23
7.4. Extension Elements . . . . . . . . . . . . . . . . . . . . 23
7.4.1. Simple Extension Elements . . . . . . . . . . . . . . 24
7.4.2. Structured Extension Elements . . . . . . . . . . . . 24
Bryan Expires July 17, 2009 [Page 2]
Internet-Draft Metalink Download Description Format January 2009
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
8.1. XML Namespace Registration . . . . . . . . . . . . . . . . 25
8.2. application/metalink+xml MIME type . . . . . . . . . . . . 25
9. Security Considerations . . . . . . . . . . . . . . . . . . . 26
9.1. URIs and IRIs . . . . . . . . . . . . . . . . . . . . . . 26
9.2. Spoofing . . . . . . . . . . . . . . . . . . . . . . . . . 26
9.3. Cryptographic Hashes . . . . . . . . . . . . . . . . . . . 26
9.4. Signing . . . . . . . . . . . . . . . . . . . . . . . . . 26
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 27
10.1. Normative References . . . . . . . . . . . . . . . . . . . 27
10.2. Informative References . . . . . . . . . . . . . . . . . . 28
Appendix A. Contributors . . . . . . . . . . . . . . . . . . . . 29
Appendix B. RELAX NG Compact Schema . . . . . . . . . . . . . . . 30
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 36
Bryan Expires July 17, 2009 [Page 3]
Internet-Draft Metalink Download Description Format January 2009
1. Introduction
Metalink is an XML-based document format that describes a file or
lists of files to be added to a download queue. Lists are composed
of a number of files, each with an extensible set of attached
metadata. For example, each file can have a description, checksum,
and list of URIs that it is available from.
The primary use case that Metalink addresses is the description of
downloadable content in a format so download agents can act
intelligently and recover from common errors with little or no user
interaction necessary. These errors can include multiple servers
going down and data corrupted in transmission.
Discussion of this draft should take place on discuss@apps.ietf.org
or the Metalink discussion mailing list located at
metalink-discussion@googlegroups.com. To join the list, visit
http://groups.google.com/group/metalink-discussion .
1.1. Examples
A brief, single file Metalink Document:
<?xml version="1.0" encoding="UTF-8"?>
<metalink xmlns="urn:ietf:params:xml:ns:metalink">
<files>
<file name="example.ext">
<resources>
<url>ftp://ftp.example.com/example.ext</url>
<url>http://example.com/example.ext</url>
<metadata type="torrent">
http://example.com/example.ext.torrent
</metadata>
</resources>
</file>
</files>
</metalink>
Bryan Expires July 17, 2009 [Page 4]
Internet-Draft Metalink Download Description Format January 2009
A more extensive, single file Metalink Document:
<?xml version="1.0" encoding="UTF-8"?>
<metalink xmlns="urn:ietf:params:xml:ns:metalink">
<published>2008-05-15T12:23:23Z</published>
<files>
<file name="example.ext">
<identity>Example</identity>
<version>1.0</version>
<description>A description of the example file for
download.</description>
<verification>
<hash type="sha-1">80bc95fd391772fa61c91ed68567f0980bb45fd9
</hash>
</verification>
<resources>
<url>ftp://ftp.example.com/example.ext</url>
<url>http://example.com/example.ext</url>
<metadata type="torrent">
http://example.com/example.ext.torrent
</metadata>
</resources>
</file>
</files>
</metalink>
1.2. Namespace and Version
The XML Namespaces URI [REC-xml-names] for the XML data format
described in this specification is:
urn:ietf:params:xml:ns:metalink
For convenience, this data format may be referred to as "Metalink",
which this specification uses internally.
1.3. Notational Conventions
This specification describes conformance of Metalink Documents.
Additionally, it places some requirements on Metalink Processors.
This specification uses the namespace prefix "metalink:" for the
Namespace URI identified in Section 1.2, above. Note that the choice
of namespace prefix is arbitrary and not semantically significant.
Metalink is specified using terms from the XML Infoset
[REC-xml-infoset]. However, this specification uses a shorthand for
two common terms: the phrase "Information Item" is omitted when
Bryan Expires July 17, 2009 [Page 5]
Internet-Draft Metalink Download Description Format January 2009
naming Element Information Items and Attribute Information Items.
Therefore, when this specification uses the term "element," it is
referring to an Element Information Item in Infoset terms. Likewise,
when it uses the term "attribute," it is referring to an Attribute
Information Item.
Some sections of this specification are illustrated with fragments of
a non-normative RELAX NG Compact schema [RELAX-NG]. However, the
text of this specification provides the definition of conformance. A
complete schema appears in Appendix B.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14, [RFC2119], as
scoped to those conformance targets.
2. Metalink Documents
This specification describes Metalink Documents.
A Metalink Document describes a file or group of files, how to access
them, and metadata that identifies them. Its root is the metalink:
metalink element.
namespace metalink = "urn:ietf:params:xml:ns:metalink"
start = metalinkMetalink
Metalink Documents are specified in terms of the XML Information Set,
serialized as XML 1.0 [REC-xml] and identified with the "application/
metalink+xml" media type.
Metalink Documents MUST be well-formed XML. This specification does
not define a DTD for Metalink Documents, and hence does not require
them to be valid (in the sense used by XML).
Metalink allows the use of IRIs [RFC3987]. Every URI [RFC3986] is
also an IRI, so a URI may be used wherever below an IRI is named.
There is one special consideration: when an IRI that is not also a
URI is given for dereferencing, it MUST be mapped to a URI using the
steps in Section 3.1 of [RFC3987].
Any element defined by this specification MAY have an xml:base
attribute [REC-xmlbase]. When xml:base is used in an Metalink
Document, it serves the function described in Section 5.1.1 of
[RFC3986], establishing the base URI (or IRI) for resolving any
relative references found within the effective scope of the xml:base
attribute.
Bryan Expires July 17, 2009 [Page 6]
Internet-Draft Metalink Download Description Format January 2009
Any element defined by this specification MAY have an xml:lang
attribute, whose content indicates the natural language for the
element and its descendents. The language context is only
significant for elements and attributes declared to be "Language-
Sensitive" by this specification. Requirements regarding the content
and interpretation of xml:lang are specified in XML 1.0 [REC-xml],
Section 2.12.
metalinkCommonAttributes =
attribute xml:base { metalinkUri }?,
attribute xml:lang { metalinkLanguageTag }?,
undefinedAttribute*
Metalink is an extensible format. See Section 7 of this document for
a full description of how Metalink Documents can be extended.
3. Common Metalink Constructs
Many of Metalink's elements share a few common structures. This
section defines those structures and their requirements for
convenient reference by the appropriate element definitions.
When an element is identified as being a particular kind of
construct, it inherits the corresponding requirements from that
construct's definition in this section.
Note that there MUST NOT be any white space in a Date construct or in
any IRI. Some XML-emitting implementations erroneously insert white
space around values by default, and such implementations will emit
invalid Metalink Documents.
3.1. Text Constructs
A Text construct contains human-readable text, usually in small
quantities. The content of Text constructs is Language-Sensitive.
metalinkTextConstruct =
metalinkCommonAttributes,
text
3.1.1. Text
Example metalink:description with text content:
Bryan Expires July 17, 2009 [Page 7]
Internet-Draft Metalink Download Description Format January 2009
...
<description>
A description of the example file for download.
</description>
...
The content of the Text construct MUST NOT contain child elements.
Such text is intended to be presented to humans in a readable
fashion. Thus, Metalink Processors MAY collapse white space
(including line breaks) and display the text using typographic
techniques such as justification and proportional fonts.
3.2. Date Constructs
A Date construct is an element whose content MUST conform to the
"date-time" production in [RFC3339]. In addition, an uppercase "T"
character MUST be used to separate date and time, and an uppercase
"Z" character MUST be present in the absence of a numeric time zone
offset.
metalinkDateConstruct =
metalinkCommonAttributes,
xsd:dateTime
Such date values happen to be compatible with the following
specifications: [ISO.8601.1988], [W3C.NOTE-datetime-19980827], and
[W3C.REC-xmlschema-2-20041028].
Example Date constructs:
<updated>2008-12-13T18:30:02Z</updated>
<updated>2008-12-13T18:30:02.25Z</updated>
<updated>2008-12-13T18:30:02+01:00</updated>
<updated>2008-12-13T18:30:02.25+01:00</updated>
Date values SHOULD be as accurate as possible. For example, it would
be generally inappropriate for a publishing system to apply the same
timestamp to several entries that were published during the course of
a single day.
4. Metalink Element Definitions
4.1. Container Elements
Bryan Expires July 17, 2009 [Page 8]
Internet-Draft Metalink Download Description Format January 2009
4.1.1. The "metalink:metalink" Element
The "metalink:metalink" element is the document (i.e., top-level)
element of a Metalink Document, acting as a container for metadata
and data associated with the listed files. It contains one
"metalink:files" element whose element children consist of metadata
elements followed by one or more metalink:file child elements.
metalinkMetalink =
element metalink:metalink {
metalinkCommonAttributes,
(metalinkPublished?
& metalinkOrigin?
& metalinkGenerator?
& metalinkUpdated?
& extensionElement*),
metalinkFiles
}
The following child elements are defined by this specification (note
that the presence of some of these elements is required):
o metalink:metalink elements MUST contain exactly one metalink:files
element.
o If metalink:type is "dynamic", metalink:metalink elements MAY
contain exactly one metalink:origin element.
o metalink:metalink elements MAY contain exactly one metalink:type
element.
o metalink:metalink elements MAY contain exactly one metalink:
generator element.
o metalink:metalink elements MAY contain exactly one metalink:
published element.
o If metalink:type is "dynamic", metalink:metalink elements MAY
contain exactly one metalink:updated element.
4.1.1.1. Providing Textual Content
Experience teaches that downloads providing textual content are in
general more useful than those that do not. Some applications (one
example is full-text indexers) require a minimum amount of text to
function reliably and predictably. Metalink publishers should be
aware of these issues. It is advisable that each metalink:file
element contain a non-empty metalink:description element, a non-empty
metalink:identity element when that element is present, and a non-
empty metalink:version element, and a non-empty metalink:publisher
element. However, the absence of metalink:description is not an
error, and Metalink Processors MUST NOT fail to function correctly as
a consequence of such an absence.
Bryan Expires July 17, 2009 [Page 9]
Internet-Draft Metalink Download Description Format January 2009
4.1.2. The "metalink:files" Element
The "metalink:files" element acts as a container for metadata and
data associated with the listed files. It contains one or more
metalink:file child elements. Certain elements can be listed either
under metalink:files or metalink:file. If under metalink:files, they
apply to all files listed in each metalink:file. If under metalink:
file, then they apply to just that specific file. If an element is
listed both under metalink:files and metalink:file, then the element
under metalink:file has precedence and the metalink:files element
does not apply to that particular file.
metalinkFiles =
element metalink:files {
metalinkCommonAttributes,
(metalinkIdentity?
& metalinkVersion?
& metalinkDescription?
& metalinkOS?
& metalinkLogo?
& metalinkLanguage?
& metalinkPublisher?
& metalinkCopyright?
& metalinkLicense?
& extensionElement*)
metalinkFile
}
The following child elements are defined by this specification (note
that the presence of some of these elements is required):
o metalink:files element MUST contain one or more metalink:file
elements.
o metalink:files elements SHOULD contain exactly one metalink:
identity element.
o metalink:files elements SHOULD contain exactly one metalink:
version element.
o metalink:files elements MAY contain exactly one metalink:
description element.
o metalink:files elements MAY contain exactly one metalink:os
element.
o metalink:files elements MAY contain exactly one metalink:logo
element.
o metalink:files elements MAY contain exactly one metalink:language
element.
o metalink:files elements MAY contain exactly one metalink:publisher
element.
Bryan Expires July 17, 2009 [Page 10]
Internet-Draft Metalink Download Description Format January 2009
o metalink:files elements MAY contain exactly one metalink:copyright
element.
o metalink:files elements MAY contain exactly one metalink:license
element.
4.1.3. The "metalink:file" Element
The "metalink:file" element represents an individual file, acting as
a container for metadata and data associated with the file.
metalinkFile =
element metalink:file {
metalinkCommonAttributes,
attribute name { metalinkTextConstruct },
(metalinkVerification?
& metalinkIdentity?
& metalinkVersion?
& metalinkDescription?
& metalinkSize?
& metalinkOS?
& metalinkLogo?
& metalinkLanguage?
& metalinkPublisher?
& metalinkCopyright?
& metalinkLicense?
& extensionElement*)
metalinkResources
}
This specification assigns no significance to the order of metalink:
file elements.
The following child elements are defined by this specification (note
that it requires the presence of some of these elements):
o metalink:file elements MUST contain exactly one metalink:resources
element.
o metalink:file elements SHOULD contain exactly one metalink:
verification element.
o metalink:file elements SHOULD contain exactly one metalink:
identity element.
o metalink:file elements SHOULD contain exactly one metalink:version
element.
o metalink:file elements MAY contain exactly one metalink:
description element.
o metalink:file elements SHOULD contain exactly one metalink:size
element.
Bryan Expires July 17, 2009 [Page 11]
Internet-Draft Metalink Download Description Format January 2009
o metalink:file elements MAY contain exactly one metalink:os
element.
o metalink:file elements MAY contain exactly one metalink:logo
element.
o metalink:file elements MAY contain exactly one metalink:language
element.
o metalink:file elements MAY contain exactly one metalink:publisher
element.
o metalink:file elements MAY contain exactly one metalink:copyright
element.
o metalink:file elements MAY contain exactly one metalink:license
element.
4.1.3.1. The "name" Attribute
metalink:file elements MUST have a "name" attribute, which contains
the filename of the file downloaded.
Directory information can also be contained in a "path/file" format
only, as in:
<file name="debian-amd64/sarge/Contents-amd64.gz">
In this example, a subdirectory debian-amd64/sarge/ will be created
and a file named Contents-amd64.gz will be created inside it. The
path MUST be relative. The path MUST NOT begin with a "/", "./" or
"../", contain "/../", or end with "/..". Metalink Processors MUST
NOT allow directory traversal.
A Metalink Processor MAY alter the name of the subdirectory or file
if they contain characters which are invalid in the destination
filesystem.
4.1.4. The "metalink:resources" Element
The "metalink:resources" element acts as a container for metadata and
data associated with the listed files. It contains one or more
metalink:url child elements. It can also contain one or more
metalink:metadata child elements.
metalinkResources =
element metalink:resources {
metalinkCommonAttributes,
extensionElement*
metalinkURL*
metalinkMetadata*
}
Bryan Expires July 17, 2009 [Page 12]
Internet-Draft Metalink Download Description Format January 2009
This specification assigns no significance to the order of metalink:
url elements. Significance is determined by the value of the
"preference" attribute of the metalink:url elements.
The following child elements are defined by this specification (note
that the presence of some of these elements is required):
o metalink:resources element MUST contain at least one metalink:
metadata element or at least one metalink:url element. Typically,
metalink:resources element contains more than one metalink:url
element to provide multiple download sources.
4.1.5. The "metalink:verification" Element
The "metalink:verification" element acts as a container for metadata
and data associated with verifying the listed files. This
information is in the form of checksums and digital signatures.
Checksums are used to verify the integrity of a complete file or
portion of a file to determine if the files have been transferred
without any errors. Digital signatures verify that a file is from
the entity that has signed it.
metalinkVerification =
element metalink:verification {
metalinkCommonAttributes,
(metalinkHash*
& metalinkPieces*
& metalinkSignature?
& extensionElement*)
}
The following child elements are defined by this specification:
o metalink:verification element MAY contain one or more metalink:
hash elements.
o metalink:verification element MAY contain one or more metalink:
pieces elements.
o metalink:verification element MAY contain one or more metalink:
signature elements.
4.1.6. The "metalink:pieces" Element
The "metalink:pieces" element acts as a container for metadata and
data associated with verifying the listed files. This information is
in the form of checksums for a portion of a file.
Bryan Expires July 17, 2009 [Page 13]
Internet-Draft Metalink Download Description Format January 2009
metalinkPieces =
element metalink:pieces {
attribute length { metalinkTextConstruct },
attribute type { metalinkTextConstruct },
hash+
}+,
4.1.6.1. The "type" Attribute
metalink:pieces elements MUST have a "type" attribute.
The IANA registry named "Hash Function Textual Names" defines values
for hash types. Metalink Generators and Processors supporting
verification SHOULD at least implement "sha-1" which is SHA1, as
specified in [RFC3174].
4.1.6.2. The "length" Attribute
metalink:pieces elements MUST have a "length" attribute, which is an
integer that describes the length of the piece of the file in octets.
4.2. Metadata Elements
4.2.1. The "metalink:copyright" Element
The "metalink:copyright" element is a Text construct that conveys a
human-readable copyright for a file.
metalinkCopyright =
element metalink:copyright {
metalinkTextConstruct
}
4.2.2. The "metalink:description" Element
The "metalink:description" element is a Text construct that conveys a
human-readable description for a file.
metalinkDescription =
element metalink:description {
metalinkTextConstruct
}
4.2.3. The "metalink:generator" Element
The "metalink:generator" element's content identifies the agent used
to generate a Metalink Document, for debugging and other purposes.
Bryan Expires July 17, 2009 [Page 14]
Internet-Draft Metalink Download Description Format January 2009
metalinkGenerator = element metalink:generator {
metalinkCommonAttributes,
attribute uri { metalinkUri }?,
attribute version { text }?,
text
}
The content of this element, when present, MUST be a string that is a
human-readable name for the generating agent. Entities such as
"&" and "<" represent their corresponding characters ("&" and
"<" respectively), not markup.
The metalink:generator element MAY have a "uri" attribute whose value
MUST be an IRI reference [RFC3987]. When dereferenced, the resulting
URI (mapped from an IRI, if necessary) SHOULD produce a
representation that is relevant to that agent.
The metalink:generator element MAY have a "version" attribute that
indicates the version of the generating agent.
4.2.4. The "metalink:hash" Element
The "metalink:hash" element is a Text construct that conveys a hash
for a file. All hashes are encoded in lowercase hexadecimal format.
metalinkHash =
element metalink:hash {
attribute piece { xsd:integer }?,
attribute type { metalinkTextConstruct },
text
}
Metalinks can contain multiples hashes for a complete file, for
example both SHA-1 and SHA-256.
...
<verification>
<hash type="sha-1">a97fcf6ba9358f8a6f62beee4421863d3e52b080</hash>
<hash type="sha-256">fc87941af7fd7f03e53b34af393f4c14923d74
825f51116ff591336af4880227</hash>
</verification>
...
Metalinks can also contain hashes for individual pieces of a file.
Bryan Expires July 17, 2009 [Page 15]
Internet-Draft Metalink Download Description Format January 2009
...
<verification>
<hash type="sha-1">a97fcf6ba9358f8a6f62beee4421863d3e52b080</hash>
<hash type="sha-256">fc87941af7fd7f03e53b34af393f4c14923d74
825f51116ff591336af4880227</hash>
<pieces length="1048576" type="sha-1">
<hash piece="0">d96b9a4b92a899c2099b7b31bddb5ca423bb9b30</hash>
<hash piece="1">10d68f4b1119014c123da2a0a6baf5c8a6d5ba1e</hash>
<hash piece="2">3e84219096435c34e092b17b70a011771c52d87a</hash>
<hash piece="3">67183e4c3ab892d3ebe8326b7d79eb62d077f487</hash>
</pieces>
</verification>
...
metalink:hash elements MUST have a "type" attribute or a "piece"
attribute. metalink:hash elements with a "type" attribute contain a
hash of the whole file. metalink:hash elements with a "piece"
attribute contain a hash for that specific piece or chunk of the
file.
4.2.4.1. The "type" Attribute
The IANA registry named "Hash Function Textual Names" defines values
for hash types. Metalink Generators and Processors supporting
verification SHOULD at least implement "sha-1" which is SHA1, as
specified in [RFC3174].
4.2.4.2. The "piece" Attribute
metalink:hash elements MAY have a "piece" attribute, only when they
are a sub element of metalink:pieces. The value of "piece" starts at
"0" and increases, depending on the "length" attribute of metalink:
pieces and the size of the file. Depending on the size of a file,
the last piece may not be the same size as the others.
4.2.5. The "metalink:identity" Element
The "metalink:identity" element is a Text construct that conveys a
human-readable identity for a file. The identity of OpenOffice.org
3.0 would be "OpenOffice.org".
metalinkIdentity =
element metalink:identity {
metalinkTextConstruct
}
Bryan Expires July 17, 2009 [Page 16]
Internet-Draft Metalink Download Description Format January 2009
4.2.6. The "metalink:language" Element
The "metalink:language" element is a Text construct that conveys a
code for the language of a file, per [ISO639-2].
metalinkLanguage =
element metalink:language {
metalinkTextConstruct
}
4.2.7. The "metalink:license" Element
The "metalink:license" element is a Text construct that conveys a
human-readable license name for a file.
metalinkLicense =
element metalink:license {
metalinkCommonAttributes,
attribute uri { metalinkUri }?,
attribute name { metalinkTextConstruct }?,
}
The metalink:license element MAY have a "uri" attribute whose value
MUST be an IRI reference [RFC3987]. When dereferenced, the resulting
URI (mapped from an IRI, if necessary) SHOULD produce a
representation that is relevant to that agent.
The metalink:license element MAY have a "name" attribute that
indicates the name of the license.
4.2.8. The "metalink:logo" Element
The "metalink:logo" element's content is an IRI reference [RFC3987]
that identifies an image that provides visual identification for a
file.
metalinkLogo = element metalink:logo {
metalinkCommonAttributes,
(metalinkUri)
}
The image SHOULD have an aspect ratio of one (horizontal) to one
(vertical) and SHOULD be suitable for presentation at a small size.
4.2.9. The "metalink:metadata" Element
The "metalink:metadata" element contains the IRI of metadata about a
resource to download. For example, this could be the IRI of a
Bryan Expires July 17, 2009 [Page 17]
Internet-Draft Metalink Download Description Format January 2009
BitTorrent .torrent file or a Metalink Document.
metalinkMetadata =
element metalink:metadata {
metalinkCommonAttributes,
attribute preference { xsd:integer }?,
attribute type { metalinkTextConstruct },
metalinkUri
}+
4.2.9.1. The "preference" Attribute
metalink:metadata elements MAY have a preference attribute, whose
value MUST be a number from 1 to 100 for priority, with 100 used
first and 1 used last. See the "preference" attribute of the
metalink:url element for more information.
4.2.9.2. The "type" Attribute
metalink:metadata elements MUST have a "type" attribute that
indicates the MIME type of the metadata available at the IRI. In the
case of BitTorrent as specified in [BITTORRENT], the value "torrent"
is required. Types without "/" are reserved. Currently, "torrent"
is the only reserved value.
Metalink Processors that do not support a specified type of metadata
about a resource to download MUST ignore that metadata.
4.2.10. The "metalink:origin" Element
The "metalink:origin" element is an IRI where the Metalink Document
was originally published. If metalink:type is "dynamic", then
updated versions of the Metalink can be found at this IRI.
metalinkOrigin = element metalink:origin {
metalinkCommonAttributes,
(metalinkUri)
}
4.2.11. The "metalink:os" Element
The "metalink:os" element is a Text construct that conveys a human-
readable Operating System for a file. The IANA registry named
"Operating System Names" defines values for OS types.
metalinkOS =
element metalink:os {
metalinkTextConstruct
Bryan Expires July 17, 2009 [Page 18]
Internet-Draft Metalink Download Description Format January 2009
}
4.2.12. The "metalink:published" Element
The "metalink:published" element is a Date construct indicating an
instant in time associated with an event early in the life cycle of
the entry.
metalinkPublished =
element metalink:published {
metalinkDateConstruct
}
Typically, metalink:published will be associated with the initial
creation or first availability of the resource.
4.2.13. The "metalink:publisher" Element
The "metalink:publisher" element indicates a group or other entity
which has published the file.
metalinkPublisher =
element metalink:publisher {
metalinkCommonAttributes,
attribute uri { metalinkUri }?,
attribute name { metalinkTextConstruct }?,
}
The metalink:publisher element MAY have a "uri" attribute whose value
MUST be an IRI reference [RFC3987]. When dereferenced, the resulting
URI (mapped from an IRI, if necessary) SHOULD produce a
representation that is relevant to that agent.
The metalink:publisher element MAY have a "name" attribute that
indicates the name of the publisher.
4.2.14. The "metalink:signature" Element
The "metalink:signature" element is a Text construct that conveys a
digital signature for a file described in a Metalink Document.
metalinkSignature =
element metalink:signature {
attribute type { "pgp" },
metalinkTextConstruct
}
Bryan Expires July 17, 2009 [Page 19]
Internet-Draft Metalink Download Description Format January 2009
4.2.14.1. The "type" Attribute
metalink:signature elements MUST have a "type" attribute. The inital
value of "type" is the string that is non-empty and matches "pgp".
It may be useful to extend Metalink documents with new types of
digital signatures, so unknown types are allowed.
4.2.15. The "metalink:size" Element
The "metalink:size" element indicates the length of the linked
content in octets; it is a hint about the content length of the
representation returned when the IRI is mapped to a URI and
dereferenced. Note that the "metalink:size" element MUST override
the actual content length of the representation as reported by the
underlying protocol, i.e. files with different sizes should be
discarded.
metalinkSize =
element metalink:size {
metalinkTextConstruct
}
4.2.16. The "metalink:type" Element
The "metalink:type" element is a Text construct that describes
whether the IRI from "metalink:origin" a Metalink will contain
dynamic updated Metalinks or static content that is not updated.
metalinkType =
element metalink:type {
"static" | "dynamic"
}
4.2.17. The "metalink:updated" Element
The "metalink:updated" element is a Date construct indicating the
most recent instant in time when a Metalink was modified in a way the
publisher considers significant. Therefore, not all modifications
necessarily result in a changed metalink:updated value.
metalinkUpdated =
element metalink:updated {
metalinkDateConstruct
}
Publishers MAY change the value of this element over time.
Bryan Expires July 17, 2009 [Page 20]
Internet-Draft Metalink Download Description Format January 2009
4.2.18. The "metalink:url" Element
The "metalink:url" element contains the IRI of a file. All IRIs MUST
lead to identical files.
metalinkURL =
element metalink:url {
metalinkCommonAttributes,
attribute location { xsd:string {
minLength = "2" maxLength="2"}
}?,
attribute preference { xsd:integer }?,
metalinkUri
}+
4.2.18.1. The "preference" Attribute
metalink:url elements MAY have a preference attribute, whose value
MUST be a number from 1 to 100 for priority, with 100 used first and
1 used last. Multiple metalink:url elements can have the same
preference, i.e. ten mirrors could have preference="100". A Metalink
Processor MAY download different segments of a file from more than
one IRI simultaneously, and when doing so SHOULD first use the
highest priority IRIs and then use lower ones.
When one or more metalink:url elements have a preference attribute
value of "100", other metalink:url elements SHOULD NOT be used,
unless the elements with a preference of 100 cannot be processed
(e.g. if they are of a metalink:metadata element type which is not
supported by the Metalink Processor, such as BitTorrent, or if the
servers are unavailable).
Any metalink:url elements with a preference attribute value of "1"
SHOULD NOT be used unless all other metalink:url elements cannot be
processed (e.g. if they are of a metalink:metadata element type which
is not supported by the Metalink Processor, such as BitTorrent, or if
the servers are unavailable).
4.2.18.2. The "location" Attribute
metalink:url elements MAY have a "location" attribute, which is a
[ISO3166] alpha-2 two letter country code for the geographical
location of the physical server an IRI is used to access.
4.2.19. The "metalink:version" Element
The "metalink:version" element is a Text construct that conveys a
human-readable version for a file. The version of OpenOffice.org 3.0
Bryan Expires July 17, 2009 [Page 21]
Internet-Draft Metalink Download Description Format January 2009
would be "3.0".
metalinkVersion =
element metalink:version {
metalinkTextConstruct
}
5. Client Implementation Considerations
Metalink Processors that support HTTP MUST support transparent
content negotiation with HTTP [RFC2295]. Transparent content
negotiation is accomplished by adding the Metalink media type to the
Accept request header. Metalink Processors MUST check the returned
content type, and if the Metalink media type is used, it MUST process
the Metalink. If the content type does not match the Metalink media
type, then Metalink Processors SHOULD handle the response as a normal
response. Metalink Processors MUST NOT add the Metalink media type
to Accept when requesting a URI from a metalink:url element, thus
avoiding loops. Metalink Processors SHOULD handle external redirects
that might lead to a Metalink.
When multiple hash types methods are provided, a Metalink Processor
MAY verify using more than one of these hash types. Metalink
Processors are encouraged to check all hash types given which they
are able to verify.
6. Securing Metalink Documents
Because Metalink is an XML-based format, existing XML security
mechanisms can be used to secure its content.
Producers of Metalinks may have sound reasons for signing otherwise-
unprotected content. For example, a merchant might digitally sign a
Metalink that lists a file download to verify its origin. Other
merchants may wish to sign and encypt Metalinks that list digital
songs that have been purchased. Of course, many other examples exist
as well.
The algorithm requirements in this section pertain to the Metalink
Processor. They require that a recipient, at a minimum, be able to
handle messages that use the specified cryptographic algorithms.
These requirements do not limit the algorithms that the sender can
choose.
Metalink Processors that verify signed Metalink Documents MUST at
least support XML-Signature and Syntax Processing [REC-xmldsig-core].
Bryan Expires July 17, 2009 [Page 22]
Internet-Draft Metalink Download Description Format January 2009
7. Extending Metalink
7.1. Extensions from Non-Metalink Vocabularies
This specification describes Metalink's XML markup vocabulary.
Markup from other vocabularies ("foreign markup") can be used in an
Metalink Document.
7.2. Extensions to the Metalink Vocabulary
The Metalink namespace is reserved for future forward-compatible
revisions of Metalink. Future versions of this specification could
add new elements and attributes to the Metalink markup vocabulary.
Software written to conform to this version of the specification will
not be able to process such markup correctly and, in fact, will not
be able to distinguish it from markup error. For the purposes of
this discussion, unrecognized markup from the Metalink vocabulary
will be considered "foreign markup".
7.3. Processing Foreign Markup
Metalink Processors that encounter foreign markup in a location that
is legal according to this specification MUST NOT stop processing or
signal an error. It might be the case that the Metalink Processor is
able to process the foreign markup correctly and does so. Otherwise,
such markup is termed "unknown foreign markup".
When unknown foreign markup is encountered as a child of metalink:
file, metalink:metalink, Metalink Processors MAY bypass the markup
and any textual content and MUST NOT change their behavior as a
result of the markup's presence.
When unknown foreign markup is encountered in a Text Construct,
software SHOULD ignore the markup and process any text content of
foreign elements as though the surrounding markup were not present.
7.4. Extension Elements
Metalink allows foreign markup anywhere in an Metalink document,
except where it is explicitly forbidden. Child elements of metalink:
file and metalink:metalink are considered Metadata elements and are
described below. Child elements of Person constructs are considered
to apply to the construct. The role of other foreign markup is
undefined by this specification.
Bryan Expires July 17, 2009 [Page 23]
Internet-Draft Metalink Download Description Format January 2009
7.4.1. Simple Extension Elements
A Simple Extension element MUST NOT have any attributes or child
elements. The element MAY contain character data or be empty.
Simple Extension elements are not Language-Sensitive.
simpleExtensionElement =
element * - metalink:* {
text
}
The element can be interpreted as a simple property (or name/value
pair) of the parent element that encloses it. The pair consisting of
the namespace-URI of the element and the local name of the element
can be interpreted as the name of the property. The character data
content of the element can be interpreted as the value of the
property. If the element is empty, then the property value can be
interpreted as an empty string.
7.4.2. Structured Extension Elements
The root element of a Structured Extension element MUST have at least
one attribute or child element. It MAY have attributes, it MAY
contain well-formed XML content (including character data), or it MAY
be empty. Structured Extension elements are Language-Sensitive.
structuredExtensionElement =
element * - metalink:* {
(attribute * { text }+,
(text|anyElement)*)
| (attribute * { text }*,
(text?, anyElement+, (text|anyElement)*))
}
The structure of a Structured Extension element, including the order
of its child elements, could be significant.
This specification does not provide an interpretation of a Structured
Extension element. The syntax of the XML contained in the element
(and an interpretation of how the element relates to its containing
element) is defined by the specification of the Metalink extension.
8. IANA Considerations
Bryan Expires July 17, 2009 [Page 24]
Internet-Draft Metalink Download Description Format January 2009
8.1. XML Namespace Registration
This document makes use of the XML registry specified in [RFC3688].
Accordingly, IANA has made the following registration:
Registration request for the Metalink namespace:
URI: urn:ietf:params:xml:ns:metalink
Registrant Contact: See the "Author's Address" section of this
document.
XML: None. Namespace URIs do not represent an XML specification.
8.2. application/metalink+xml MIME type
A Metalink Document, when serialized as XML 1.0, can be identified
with the following media type:
MIME media type name: application
MIME subtype name: metalink+xml
Mandatory parameters: None.
Optional parameters:
"charset": This parameter has semantics identical to the charset
parameter of the "application/xml" media type as specified in
[RFC3023].
Encoding considerations: Identical to those of "application/xml" as
described in [RFC3023], Section 3.2.
Security considerations: As defined in this specification.
In addition, as this media type uses the "+xml" convention, it
shares the same security considerations as described in [RFC3023],
Section 10.
Interoperability considerations: There are no known interoperability
issues.
Published specification: This specification.
Applications that use this media type: No known applications
currently use this media type.
Additional information:
Magic number(s): As specified for "application/xml" in [RFC3023],
Section 3.2.
File extension: .metalink
Fragment identifiers: As specified for "application/xml" in
[RFC3023], Section 5.
Bryan Expires July 17, 2009 [Page 25]
Internet-Draft Metalink Download Description Format January 2009
Base URI: As specified in [RFC3023], Section 6.
Macintosh File Type code: TEXT
Person and email address to contact for further information: Anthony
Bryan <anthonybryan@gmail.com>
Intended usage: COMMON
Author/Change controller: IESG
9. Security Considerations
Publishers are encouraged to offer Metalink documents via
authenticated HTTP under TLS as specified in [RFC2818]. Publishers
are also encouraged to include digital signatures of the files within
the Metalink Documents if they are available.
9.1. URIs and IRIs
Metalink Processors handle URIs and IRIs. See Section 7 of [RFC3986]
and Section 8 of [RFC3987] for security considerations related to
their handling and use.
9.2. Spoofing
Metalink Processors should be aware of the potential for spoofing
attacks where the attacker publishes Metalinks with false
information. Malicious publishers might create Metalink Documents
containing inaccurate information anywhere in the document. At best,
this could deceive unaware downloaders that they are downloading a
malicious or worthless file. At worst, malicious publishers could
attempt a distributed denial of service attack by inserting unrelated
IRIs into Metalink Documents.
9.3. Cryptographic Hashes
Currently, some of the hash types defined in the IANA registry named
"Hash Function Textual Names" are considered insecure. These include
the whole Message Digest family of algorithms which are not suitable
for cryptographically strong verification. Malicious people could
provide files that appear to be identical to another file because of
a collision, i.e. the weak cryptographic hashes match.
Metalink Generators and Processors supporting verification SHOULD at
least implement "sha-1" which is SHA1, as specified in [RFC3174].
9.4. Signing
Metalink Documents SHOULD be signed using [REC-xmldsig-core] and are
subject to the security considerations implied by its use. This
Bryan Expires July 17, 2009 [Page 26]
Internet-Draft Metalink Download Description Format January 2009
addresses the issue of spoofing.
Digital signatures provide authentication, message integrity, and
non-repudiation with proof of origin.
10. References
10.1. Normative References
[BITTORRENT]
Cohen, B., "The BitTorrent Protocol Specification",
BITTORRENT 11031, February 2008,
<http://www.bittorrent.org/beps/bep_0003.html>.
[ISO3166] International Organization for Standardization, "ISO 3166:
1988 (E/F) - Codes for the representation of names of
countries - The International Organization for
Standardization, 3rd edition, 1988-08-15.", ISO Standard
3166, 1988.
[ISO639-2]
International Organization for Standardization, "ISO 639-
2:1998 - Codes for the representation of names of
languages -- Part 2: Alpha-3 code - edition 1,
1998-11-01, 66 pages, prepared by a Joint Working Group of
ISO TC46/SC4 and ISO TC37/SC2.", ISO Standard 639-2, 1998.
[REC-xml] Yergeau, F., Paoli, J., Bray, T., Sperberg-McQueen, C.,
and E. Maler, "Extensible Markup Language (XML) 1.0
(Fourth Edition)", World Wide Web Consortium
Recommendation REC-xml-20060816, August 2006,
<http://www.w3.org/TR/2006/REC-xml-20060816>.
[REC-xml-infoset]
Cowan, J. and R. Tobin, "XML Information Set (Second
Edition)", World Wide Web Consortium Recommendation REC-
xml-infoset-20040204, February 2004,
<http://www.w3.org/TR/2004/REC-xml-infoset-20040204>.
[REC-xml-names]
Hollander, D., Bray, T., Tobin, R., and A. Layman,
"Namespaces in XML 1.0 (Second Edition)", World Wide Web
Consortium Recommendation REC-xml-names-20060816,
August 2006,
<http://www.w3.org/TR/2006/REC-xml-names-20060816>.
[REC-xmlbase]
Bryan Expires July 17, 2009 [Page 27]
Internet-Draft Metalink Download Description Format January 2009
Marsh, J., "XML Base", W3C REC W3C.REC-xmlbase-20010627,
June 2001,
<http://www.w3.org/TR/2001/REC-xmlbase-20010627>.
[REC-xmldsig-core]
Solo, D., Reagle, J., and D. Eastlake, "XML-Signature
Syntax and Processing", World Wide Web Consortium
Recommendation REC-xmldsig-core-20020212, February 2002,
<http://www.w3.org/TR/2002/REC-xmldsig-core-20020212>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2295] Holtman, K. and A. Mutz, "Transparent Content Negotiation
in HTTP", RFC 2295, March 1998.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media
Types", RFC 3023, January 2001.
[RFC3174] Eastlake, D. and P. Jones, "US Secure Hash Algorithm 1
(SHA1)", RFC 3174, September 2001.
[RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet:
Timestamps", RFC 3339, July 2002.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
January 2004.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource
Identifiers (IRIs)", RFC 3987, January 2005.
10.2. Informative References
[ISO.8601.1988]
International Organization for Standardization, "Data
elements and interchange formats - Information interchange
- Representation of dates and times", ISO Standard 8601,
June 1988.
[RELAX-NG]
Clark, J., "RELAX NG Compact Syntax", December 2001, <http
://www.oasis-open.org/committees/relax-ng/
Bryan Expires July 17, 2009 [Page 28]
Internet-Draft Metalink Download Description Format January 2009
compact-20021121.html>.
[RFC4287] Nottingham, M. and R. Sayre, "The Atom Syndication
Format", RFC 4287, December 2005.
[W3C.NOTE-datetime-19980827]
Wolf, M. and C. Wicksteed, "Date and Time Formats", W3C
NOTE NOTE-datetime-19980827, August 1998,
<http://www.w3.org/TR/1998/NOTE-datetime-19980827>.
[W3C.REC-xmlschema-2-20041028]
Malhotra, A. and P. Biron, "XML Schema Part 2: Datatypes
Second Edition", W3C REC REC-xmlschema-2-20041028,
October 2004,
<http://www.w3.org/TR/2004/REC-xmlschema-2-20041028>.
Appendix A. Contributors
The layout and content of this document relies heavily on work
pioneered in the Atom Syndication Format as specified in [RFC4287].
The following people contributed to preliminary versions of this
document: Paul Burkhead, Kristian Weston, Darius Liktorius, Michael
Burford, Giorgio Maone, Manuel Subredu, Tatsuhiro Tsujikawa, A. Bram
Neijt, Max Velasques, Manolo Valdes, Urs Wolfer, Frederick Cheung,
Nils Maier, Hampus Wessman, Neil McNab, Hayden Legendre, Danny Ayers,
Nick Dominguez, Rene Leonhardt, Per Oyvind Karlsen, Gary Zellerbach,
James Clark, Daniel Stenberg, Peter Poeml, Matt Domsch, Chris Newman,
Lisa Dusseault, Ian Macfarlane, Dave Cridland, Julian Reschke, Barry
Leiba, Uri Blumenthal, and Paul Hoffman. The content and concepts
within are a product of the Metalink community.
The Metalink community has dozens of contributors who proposed ideas
and wording for this document, or contributed to the evolution of
Metalink, including:
Nicolas Alvarez, Patrick Ruckstuhl, Mike Wells, Sebastien Willemijns,
Micah Cowan, Dan Fandrich, Francis Giannaros, Yazsoft, Lukas
Appelhans, KGet developers, FDM Team, Orbit Team, Arne
Babenhauserheide, Mathias Berchtold, Xienzhenyu and TheWorld Browser
Team, Xi Software, Bridget and Ethan Fletcher, Ruben Kerkhof,
Agostino Russo, Gervase Markham, Salvatore and Robin Musumeci, Steve
and Rachel Eshelman, Lucas Hewett, Ryan and Darren Cronin, Dave
Winquist, Bob Denison, Wes Shelton, Kees Cook, Josh Colbert, Steve
Kleisath, Chad Neptune, Nick Carrabba, Chris Carrabba, Erin Solari,
Derick Cordoba, Ryan Alexander, John Sowder, Sandra Amisano, Tom
Mainville, Janie Wargo, Jason Hansen, Tim Bray, Dan Brickley, Markus
Bryan Expires July 17, 2009 [Page 29]
Internet-Draft Metalink Download Description Format January 2009
Hofmann, Dan Connolly, Tim Berners-Lee, Harry Chen, Adrien Macneil,
Louis Suarez-Potts, Ross Smith, Rahul Sundaram, Jesse Keating, Michal
Bentkowski, Andrew Pantyukhin, Judd Vinet, Charles Landemaine, Pascal
Bleser, Jeff@BLAG, Yuichiro Nakada, Jereme Hancock, Marcel Hauser,
Jeff Covey, Doug Lang, Seth Brown, Alexander Lazic, Mayank Sharma,
Robin Heggelund Hansen, Steve Langasek, Federico Parodi, Stefano
Verna, Jason Green, James Linden, Matt Nederlanden, Aren Olsen, Dag
Odenhall, Troy Sobotka, Corey Farwell, Ed Lee, Shawn Wilsher, Mike
Connor, Anand Muttagi, Dedric Carter, Debi Goulding, the Anthony
Family, the Bryan Family, Juanita Anthony and Zimmy Bryan.
Appendix B. RELAX NG Compact Schema
This appendix is informative.
The Relax NG schema explicitly excludes elements in the Metalink
namespace that are not defined in this revision of the specification.
Requirements for Metalink Processors encountering such markup are
given in Sections 7.2 and 7.3.
# -*- rnc -*-
# RELAX NG Compact Syntax Grammar for the
# Metalink Format Specification Version 2
namespace metalink = "urn:ietf:params:xml:ns:metalink"
namespace xsd = "http://www.w3.org/2001/XMLSchema"
# Common attributes
metalinkCommonAttributes =
attribute xml:base { metalinkUri }?,
attribute xml:lang { metalinkLanguageTag }?,
undefinedAttribute*
# Text Constructs
metalinkTextConstruct =
metalinkCommonAttributes,
text
# Date Construct
metalinkDateConstruct =
metalinkCommonAttributes,
xsd:dateTime
Bryan Expires July 17, 2009 [Page 30]
Internet-Draft Metalink Download Description Format January 2009
start =
element metalink:metalink {
element metalink:generator {
attribute uri { metalinkUri }?,
attribute version { text }?,
metalinkTextConstruct
}
element metalink:origin { metalinkUri }?,
element metalink:type { "static" | "dynamic" }?,
element metalink:published { metalinkDateConstruct }?,
element metalink:updated { metalinkDateConstruct }?,
element metalink:files {
element metalink:file {
attribute name { metalinkTextConstruct },
element metalink:identity { metalinkTextConstruct }?,
element metalink:version { metalinkTextConstruct }?,
element metalink:size { xsd:integer }?,
element metalink:description { metalinkTextConstruct }?,
element metalink:license {
attribute uri { metalinkUri }?,
attribute name { metalinkTextConstruct }?,
}?,
element metalink:logo { metalinkUri }?,
element metalink:publisher {
attribute uri { metalinkUri }?,
attribute name { metalinkTextConstruct }?,
}?,
element metalink:language { metalinkTextConstruct }?,
element metalink:copyright { metalinkTextConstruct }?,
element metalink:license { metalinkTextConstruct }?,
element metalink:os { metalinkTextConstruct }?,
element metalink:verification {
hash+,
element metalink:pieces {
attribute length { metalinkTextConstruct },
attribute type { metalinkTextConstruct },
hash+
}+,
element metalink:signature {
attribute type { "pgp" },
text
}+
}?,
element metalink:resources {
element metalink:metadata {
attribute preference { xsd:integer }?,
attribute type { metalinkTextConstruct },
metalinkUri
Bryan Expires July 17, 2009 [Page 31]
Internet-Draft Metalink Download Description Format January 2009
element metalink:url {
attribute location { xsd:string {
minLength = "2" maxLength="2"}
}?,
attribute preference { xsd:integer }?,
metalinkUri
}+
}
}+
}
}
hash =
element metalink:hash {
attribute piece { metalinkTextConstruct }?,
attribute type { metalinkTextConstruct },
text
}
# As defined in RFC 3066
metalinkLanguageTag = xsd:string {
pattern = "[A-Za-z]{1,8}(-[A-Za-z0-9]{1,8})*"
}
# Unconstrained; it's not entirely clear how IRI fit into
# xsd:anyURI so let's not try to constrain it here
metalinkUri = text
# Simple Extension
simpleExtensionElement =
element * - metalink:* {
text
}
# Structured Extension
structuredExtensionElement =
element * - metalink:* {
(attribute * { text }+,
(text|anyElement)*)
| (attribute * { text }*,
(text?, anyElement+, (text|anyElement)*))
}
# Other Extensibility
extensionElement =
simpleExtensionElement | structuredExtensionElement
Bryan Expires July 17, 2009 [Page 32]
Internet-Draft Metalink Download Description Format January 2009
undefinedAttribute =
attribute * - (xml:base | xml:lang | local:*) { text }
undefinedContent = (text|anyForeignElement)*
anyElement =
element * {
(attribute * { text }
| text
| anyElement)*
}
anyForeignElement =
element * - metalink:* {
(attribute * { text }
| text
| anyElement)*
}
# EOF
Index
A
application/metalink+xml Media Type 25
C
copyright XML element 14
D
description XML element 14
F
file XML element 11
files XML element 10
G
generator XML element 14
Grammar
metalinkCommonAttributes 7
metalinkCopyright 14
metalinkDateConstruct 8
metalinkDescription 14
metalinkFile 11
metalinkFiles 10
metalinkGenerator 15
metalinkHash 15
Bryan Expires July 17, 2009 [Page 33]
Internet-Draft Metalink Download Description Format January 2009
metalinkIdentity 16
metalinkLanguage 17
metalinkLicense 17
metalinkLogo 17
metalinkMetalink 9
metalinkOrigin 18
metalinkOS 18
metalinkPieces 14
metalinkPublished 19
metalinkPublisher 19
metalinkResources 12
metalinkSignature 19
metalinkSize 20
metalinkTextConstruct 7
metalinkType 20
metalinkUpdated 20
metalinkURL 18, 21
metalinkVerification 13
metalinkVersion 22
simpleExtensionElement 24
structuredExtensionElement 24
H
hash XML element 15
I
identity XML element 16
L
language XML element 17
license XML element 17
logo XML element 17
M
Media Type
application/metalink+xml 25
metadata XML element 17
metalink XML element 9
metalinkCommonAttributes grammar production 7
metalinkCopyright grammar production 14
metalinkDateConstruct grammar production 8
metalinkDescription grammar production 14
metalinkFile grammar production 11
metalinkFiles grammar production 10
metalinkGenerator grammar production 15
metalinkHash grammar production 15
metalinkIdentity grammar production 16
metalinkLanguage grammar production 17
Bryan Expires July 17, 2009 [Page 34]
Internet-Draft Metalink Download Description Format January 2009
metalinkLicense grammar production 17
metalinkLogo grammar production 17
metalinkMetalink grammar production 9
metalinkOrigin grammar production 18
metalinkOS grammar production 18
metalinkPieces grammar production 14
metalinkPublished grammar production 19
metalinkPublisher grammar production 19
metalinkResources grammar production 12
metalinkSignature grammar production 19
metalinkSize grammar production 20
metalinkTextConstruct grammar production 7
metalinkType grammar production 20
metalinkUpdated grammar production 20
metalinkURL grammar production 18, 21
metalinkVerification grammar production 13
metalinkVersion grammar production 22
O
origin XML element 18
os XML element 18
P
pieces XML element 13
published XML element 19
publisher XML element 19
R
resources XML element 12
S
signature XML element 19
simpleExtensionElement grammar production 24
size XML element 20
structuredExtensionElement grammar production 24
T
type XML element 20
U
updated XML element 20
url XML element 21
V
verification XML element 13
version XML element 21
X
Bryan Expires July 17, 2009 [Page 35]
Internet-Draft Metalink Download Description Format January 2009
XML Elements
copyright 14
description 14
entry 11
files 10
generator 14
hash 15
identity 16
language 17
license 17
logo 17
metadata 17
metalink 9
origin 18
os 18
pieces 13
published 19
publisher 19
resources 12
signature 19
size 20
type 20
updated 20
url 21
verification 13
version 21
Author's Address
Anthony Bryan (editor)
Metalinker Project
Email: anthonybryan@gmail.com
URI: http://www.metalinker.org
Bryan Expires July 17, 2009 [Page 36]
