Network Working Group A. Bryan, Ed. Internet-Draft T. Tsujikawa Intended status: Standards Track N. McNab Expires: February 22, 2010 Metalinker Project P. Poeml Novell, Inc. August 21, 2009 The Metalink Download Description Format draft-bryan-metalink-13 Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. 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 February 22, 2010. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the Bryan, et al. Expires February 22, 2010 [Page 1] Internet-Draft Metalink Download Description Format August 2009 document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license-info). 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. 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 . . . . . . . . . . . 8 4.1.2. The "metalink:file" Element . . . . . . . . . . . . . 9 4.1.3. The "metalink:pieces" Element . . . . . . . . . . . . 11 4.2. Metadata Elements . . . . . . . . . . . . . . . . . . . . 12 4.2.1. The "metalink:copyright" Element . . . . . . . . . . . 12 4.2.2. The "metalink:description" Element . . . . . . . . . . 12 4.2.3. The "metalink:dynamic" Element . . . . . . . . . . . . 12 4.2.4. The "metalink:generator" Element . . . . . . . . . . . 13 4.2.5. The "metalink:hash" Element . . . . . . . . . . . . . 13 4.2.6. The "metalink:identity" Element . . . . . . . . . . . 14 4.2.7. The "metalink:language" Element . . . . . . . . . . . 14 4.2.8. The "metalink:license" Element . . . . . . . . . . . . 15 4.2.9. The "metalink:logo" Element . . . . . . . . . . . . . 15 4.2.10. The "metalink:metaurl" Element . . . . . . . . . . . . 15 4.2.11. The "metalink:origin" Element . . . . . . . . . . . . 16 4.2.12. The "metalink:os" Element . . . . . . . . . . . . . . 17 4.2.13. The "metalink:published" Element . . . . . . . . . . . 17 4.2.14. The "metalink:publisher" Element . . . . . . . . . . . 17 4.2.15. The "metalink:signature" Element . . . . . . . . . . . 18 4.2.16. The "metalink:size" Element . . . . . . . . . . . . . 18 4.2.17. The "metalink:updated" Element . . . . . . . . . . . . 18 Bryan, et al. Expires February 22, 2010 [Page 2] Internet-Draft Metalink Download Description Format August 2009 4.2.18. The "metalink:url" Element . . . . . . . . . . . . . . 19 4.2.19. The "metalink:version" Element . . . . . . . . . . . . 19 5. Securing Metalink Documents . . . . . . . . . . . . . . . . . 19 6. Extending Metalink . . . . . . . . . . . . . . . . . . . . . . 20 6.1. Extensions from Non-Metalink Vocabularies . . . . . . . . 20 6.2. Extensions to the Metalink Vocabulary . . . . . . . . . . 20 6.3. Processing Foreign Markup . . . . . . . . . . . . . . . . 20 6.4. Extension Elements . . . . . . . . . . . . . . . . . . . . 21 6.4.1. Simple Extension Elements . . . . . . . . . . . . . . 21 6.4.2. Structured Extension Elements . . . . . . . . . . . . 21 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22 7.1. XML Namespace Registration . . . . . . . . . . . . . . . . 22 7.2. application/metalink+xml MIME type . . . . . . . . . . . . 22 8. Security Considerations . . . . . . . . . . . . . . . . . . . 23 8.1. URIs and IRIs . . . . . . . . . . . . . . . . . . . . . . 23 8.2. Spoofing . . . . . . . . . . . . . . . . . . . . . . . . . 23 8.3. Cryptographic Hashes . . . . . . . . . . . . . . . . . . . 23 8.4. Signing . . . . . . . . . . . . . . . . . . . . . . . . . 24 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24 9.1. Normative References . . . . . . . . . . . . . . . . . . . 24 9.2. Informative References . . . . . . . . . . . . . . . . . . 25 Appendix A. Acknowledgements and Contributors . . . . . . . . . . 26 Appendix B. RELAX NG Compact Schema . . . . . . . . . . . . . . . 27 Appendix C. Document History (to be removed by RFC Editor before publication) . . . . . . . . . . . . . . . . . 32 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 36 Bryan, et al. Expires February 22, 2010 [Page 3] Internet-Draft Metalink Download Description Format August 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: ftp://ftp.example.com/example.ext http://example.com/example.ext http://example.com/example.ext.torrent Bryan, et al. Expires February 22, 2010 [Page 4] Internet-Draft Metalink Download Description Format August 2009 A more extensive, single file Metalink Document: 2009-05-15T12:23:23Z Example 1.0 en A description of the example file for download. 80bc95fd391772fa61c91ed68567f0980bb45fd9 ftp://ftp.example.com/example.ext http://example.com/example.ext http://example.com/example.ext.torrent 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 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, Bryan, et al. Expires February 22, 2010 [Page 5] Internet-Draft Metalink Download Description Format August 2009 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. Any element defined by this specification MAY have an xml:lang attribute, whose content indicates the natural language for the Bryan, et al. Expires February 22, 2010 [Page 6] Internet-Draft Metalink Download Description Format August 2009 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 6 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: ... A description of the example file for download. ... Bryan, et al. Expires February 22, 2010 [Page 7] Internet-Draft Metalink Download Description Format August 2009 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, white space could be collapsed (including line breaks) and text could be displayed 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: 2009-05-15T18:30:02Z 2009-05-15T18:30:02.25Z 2009-05-15T18:30:02+01:00 2009-05-15T18:30:02.25+01:00 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 Metalink Documents that were published during the course of a single day. 4. Metalink Element Definitions 4.1. Container Elements 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 or more metalink:file child elements which consist of metadata elements. Bryan, et al. Expires February 22, 2010 [Page 8] Internet-Draft Metalink Download Description Format August 2009 metalinkMetalink = element metalink:metalink { metalinkCommonAttributes, (metalinkDynamic? & metalinkFile+ & metalinkGenerator? & metalinkOrigin? & metalinkPublished? & metalinkUpdated? & extensionElement*) } The following child elements are defined by this specification (note that the presence of some of these elements is required): o metalink:metalink elements MAY contain exactly one metalink: dynamic element. o metalink:metalink elements MUST contain one or more metalink:file elements. o metalink:metalink elements MAY contain exactly one metalink: generator element. o metalink:metalink elements SHOULD contain exactly one metalink: origin element. o metalink:metalink elements MAY contain exactly one metalink: published 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. 4.1.2. The "metalink:file" Element The "metalink:file" element represents an individual file, acting as a container for metadata and data associated with the file. All metalink:url elements SHOULD lead to identical files. That is, each metalink:url element should be an alternative location for the same file and each metalink:metaurl element should provide metadata Bryan, et al. Expires February 22, 2010 [Page 9] Internet-Draft Metalink Download Description Format August 2009 to retrieve the same file in another way, such as a peer to peer network. metalinkFile = element metalink:file { metalinkCommonAttributes, attribute name { text }, (metalinkCopyright? & metalinkDescription? & metalinkHash* & metalinkIdentity? & metalinkLanguage? & metalinkLicense? & metalinkLogo? & metalinkMetaURL* & metalinkURL* & metalinkOS? & metalinkPieces* & metalinkPublisher? & metalinkSignature? & metalinkSize? & metalinkVersion? & extensionElement*) } This specification assigns no significance to the order of metalink: file elements or to the order of metalink:url or metalink:metaurl elements. Significance is determined by the value of the "preference" attribute of the metalink:url or metalink:metaurl 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 MAY contain exactly one metalink:copyright element. o metalink:file elements MAY contain exactly one metalink: description element. o metalink:file elements MAY contain exactly one metalink:identity element. o metalink:file elements MAY contain one or more metalink:hash elements. o metalink:file elements MAY contain exactly one metalink:language element. o metalink:file elements MAY contain exactly one metalink:license element. Bryan, et al. Expires February 22, 2010 [Page 10] Internet-Draft Metalink Download Description Format August 2009 o metalink:file elements MAY contain exactly one metalink:logo element. o metalink:file elements MAY contain exactly one metalink:os element. o metalink:file elements MUST contain at least one metalink:url element or at least one metalink:metaurl element. Typically, metalink:file elements contains more than one metalink:url element to provide multiple download sources. o metalink:file elements MAY contain one or more metalink:pieces elements. o metalink:file elements MAY contain exactly one metalink:publisher element. o metalink:file elements MAY contain one or more metalink:signature elements. o metalink:file elements SHOULD contain exactly one metalink:size element. o metalink:file elements MAY contain exactly one metalink:version element. 4.1.2.1. The "name" Attribute metalink:file elements MUST have a "name" attribute, which contains the filename of the file to be downloaded. Directory information can also be contained in a "path/file" format only, as in: 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 NOT contain any directory traversal directives or information. The path MUST be relative. The path MUST NOT begin with a "/", "./" or "../", contain "/../", or end with "/..". 4.1.3. The "metalink:pieces" Element The "metalink:pieces" element acts as a container for a list of checksums of non-overlapping pieces of the file. The checksums MUST be listed in the same order as the corresponding pieces appear in the file, starting at the beginning of the file. metalinkPieces = element metalink:pieces { attribute length { xsd:integer }, attribute type { text }, metalinkHash+ } Bryan, et al. Expires February 22, 2010 [Page 11] Internet-Draft Metalink Download Description Format August 2009 4.1.3.1. The "type" Attribute metalink:pieces elements MUST have a "type" attribute. The IANA registry named "Hash Function Textual Names" defines values for hash types. If a Metalink Document contains hashes, it SHOULD include "sha-1" which is SHA-1 as specified in [RFC3174], or a stronger hash. It MAY also include other hashes. 4.1.3.2. The "length" Attribute metalink:pieces elements MUST have a "length" attribute, which is an integer that describes the length of the pieces of the file in octets. The whole file is divided into non-overlapping pieces of this length, starting from the beginning of the file. The last piece extends at most to the end of the file, and can therefore be shorter than the other pieces. 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:dynamic" Element The "metalink:dynamic" element is a Text construct that describes whether the IRI from "metalink:origin" in a Metalink will contain dynamic updated information or if it is static and not likely to be updated. Bryan, et al. Expires February 22, 2010 [Page 12] Internet-Draft Metalink Download Description Format August 2009 metalinkDynamic = element metalink:dynamic { "true" | "false" } 4.2.4. The "metalink:generator" Element The "metalink:generator" element's content identifies the generating agent name and version, separated by a "/", used to generate a Metalink Document, for debugging and other purposes. metalinkGenerator = element metalink:generator { metalinkTextConstruct } The content of this element, when present, MUST be a string that is a human-readable name and version, separated by a "/", for the generating agent. For example, "MirrorBrain/2.8.1", where "MirrorBrain" is the name and "2.8.1" is the version. Entities such as "&" and "<" represent their corresponding characters ("&" and "<" respectively), not markup. 4.2.5. 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. Hashes are used to verify the integrity of a complete file or portion of a file to determine if the file has been transferred without any errors. metalinkHash = element metalink:hash { attribute type { text }?, text } metalink:hash elements with a "type" attribute MUST contain a hash of the complete file. Metalink Documents can contain one or multiples hashes of a complete file. In this example, both SHA-1 and SHA-256 hashes are included. ... a97fcf6ba9358f8a6f62beee4421863d3e52b080 fc87941af7fd7f03e53b34af393f4c14923d74 825f51116ff591336af4880227 ... Bryan, et al. Expires February 22, 2010 [Page 13] Internet-Draft Metalink Download Description Format August 2009 Metalink Documents can also contain hashes for individual pieces of a file. metalink:hash elements that are inside a metalink:pieces container element have a hash for that specific piece or chunk of the file, and are of the same hash type as the metalink:pieces element they are contained in. metalink:hash elements without a "type" attribute MUST contain a hash for that specific piece or chunk of the file and MUST be listed in the same order as the corresponding pieces appear in the file, starting at the beginning of the file. ... a97fcf6ba9358f8a6f62beee4421863d3e52b080 fc87941af7fd7f03e53b34af393f4c14923d74 825f51116ff591336af4880227 d96b9a4b92a899c2099b7b31bddb5ca423bb9b30 10d68f4b1119014c123da2a0a6baf5c8a6d5ba1e 3e84219096435c34e092b17b70a011771c52d87a 67183e4c3ab892d3ebe8326b7d79eb62d077f487 ... 4.2.5.1. The "type" Attribute metalink:hash elements MUST have a "type" attribute, if and only if it contains a hash of the complete file. The IANA registry named "Hash Function Textual Names" defines values for hash types. If a Metalink Document contains hashes, it SHOULD include "sha-1" which is SHA-1 as specified in [RFC3174], or a stronger hash. It MAY also include other hashes. 4.2.6. 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 } 4.2.7. The "metalink:language" Element The "metalink:language" element is a Text construct that conveys a code for the language of a file, per [RFC4646]. Bryan, et al. Expires February 22, 2010 [Page 14] Internet-Draft Metalink Download Description Format August 2009 metalinkLanguage = element metalink:language { metalinkTextConstruct } 4.2.8. 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 url { metalinkUri }?, attribute name { text }? } The metalink:license element MAY have a "url" 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. 4.2.9. 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. 4.2.10. The "metalink:metaurl" Element The "metalink:metaurl" element contains the IRI of metadata about a resource to download. For example, this could be the IRI of a BitTorrent .torrent file or a Metalink Document. Note that the information in the metalink:hash element does not apply to these files, but to the files that are described by them. Bryan, et al. Expires February 22, 2010 [Page 15] Internet-Draft Metalink Download Description Format August 2009 metalinkMetaURL = element metalink:metaurl { metalinkCommonAttributes, attribute preference { xsd:integer }?, attribute type { text }, attribute name { text }?, metalinkUri } 4.2.10.1. The "preference" Attribute metalink:metaurl 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:metaurl elements can have the same preference, i.e. three BitTorrent .torrent files could have preference="100". See also the "preference" attribute of the metalink:url element. 4.2.10.2. The "type" Attribute metalink:metaurl 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. 4.2.10.3. The "name" Attribute metalink:metaurl elements MAY have a "name" attribute that indicates a specific file in a BitTorrent .torrent file or a Metalink Document that describes multiple files. Directory information can also be contained in a "path/file" format only, as in: In this example, a file named "Contents-amd64.gz" is indicated, in a "debian-amd64/sarge/" subdirectory. The path MUST NOT contain any directory traversal directives or information. The path MUST be relative. The path MUST NOT begin with a "/", "./" or "../", contain "/../", or end with "/..". 4.2.11. The "metalink:origin" Element The "metalink:origin" element is an IRI where the Metalink Document was originally published. If metalink:dynamic is "true", then updated versions of the Metalink can be found at this IRI. Bryan, et al. Expires February 22, 2010 [Page 16] Internet-Draft Metalink Download Description Format August 2009 metalinkOrigin = element metalink:origin { metalinkCommonAttributes, (metalinkUri) } 4.2.12. 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 } 4.2.13. 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. 4.2.14. The "metalink:publisher" Element The "metalink:publisher" element indicates a group or other entity which has published the file described in the Metalink Document. metalinkPublisher = element metalink:publisher { metalinkCommonAttributes, attribute url { metalinkUri }?, attribute name { text }? } The metalink:publisher element MAY have a "url" 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. Bryan, et al. Expires February 22, 2010 [Page 17] Internet-Draft Metalink Download Description Format August 2009 The metalink:publisher element MAY have a "name" attribute that indicates the name of the publisher. 4.2.15. 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. Digital signatures verify that a file is from the entity that has signed it. metalinkSignature = element metalink:signature { attribute type { "pgp" }, metalinkTextConstruct } 4.2.15.1. The "type" Attribute metalink:signature elements MUST have a "type" attribute. The initial 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. 4.2.16. 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. metalinkSize = element metalink:size { metalinkTextConstruct } 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, et al. Expires February 22, 2010 [Page 18] Internet-Draft Metalink Download Description Format August 2009 4.2.18. The "metalink:url" Element The "metalink:url" element contains the IRI of a file. Most Metalink Documents will contain multiple metalink:url elements, and each one SHOULD be a valid alternative to download the same file. 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". 4.2.18.2. The "location" Attribute metalink:url elements MAY have a "location" attribute, which is a [ISO3166-1] 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 would be "3.0". metalinkVersion = element metalink:version { metalinkTextConstruct } 5. Securing Metalink Documents Because Metalink is an XML-based format, existing XML security mechanisms can be used to secure its content. Producers of Metalink Documents may have sound reasons for signing otherwise-unprotected content. For example, a merchant might Bryan, et al. Expires February 22, 2010 [Page 19] Internet-Draft Metalink Download Description Format August 2009 digitally sign a Metalink that lists a file download to verify its origin. Other merchants may wish to sign and encrypt Metalink Documents that list digital songs that have been purchased. Of course, many other examples are conceivable 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]. 6. Extending Metalink 6.1. 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. 6.2. 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". 6.3. 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, Bryan, et al. Expires February 22, 2010 [Page 20] Internet-Draft Metalink Download Description Format August 2009 software SHOULD ignore the markup and process any text content of foreign elements as though the surrounding markup were not present. 6.4. 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. 6.4.1. 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. 6.4.2. 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. Bryan, et al. Expires February 22, 2010 [Page 21] Internet-Draft Metalink Download Description Format August 2009 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. 7. IANA Considerations 7.1. 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. 7.2. 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: metalink4+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: Bryan, et al. Expires February 22, 2010 [Page 22] Internet-Draft Metalink Download Description Format August 2009 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. Base URI: As specified in [RFC3023], Section 6. Macintosh File Type code: TEXT Person and email address to contact for further information: Anthony Bryan Intended usage: COMMON Author/Change controller: IESG 8. 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. 8.1. 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. 8.2. Spoofing There is potential for spoofing attacks where the attacker publishes Metalink Documents 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. 8.3. 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 of the intended file and a substituted malicious file could match. If a Metalink Document contains hashes, it SHOULD include "sha-1" which is SHA-1, as specified in [RFC3174]. It MAY also include other Bryan, et al. Expires February 22, 2010 [Page 23] Internet-Draft Metalink Download Description Format August 2009 hashes. 8.4. Signing Metalink Documents SHOULD be signed using [REC-xmldsig-core] and are subject to the security considerations implied by its use. This addresses the issue of spoofing. Digital signatures provide authentication, message integrity, and non-repudiation with proof of origin. 9. References 9.1. Normative References [BITTORRENT] Cohen, B., "The BitTorrent Protocol Specification", BITTORRENT 11031, February 2008, . [ISO3166-1] International Organization for Standardization, "ISO 3166- 1:2006. Codes for the representation of names of countries and their subdivisions -- Part 1: Country codes", November 2006. [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, . [REC-xml-infoset] Cowan, J. and R. Tobin, "XML Information Set (Second Edition)", World Wide Web Consortium Recommendation REC- xml-infoset-20040204, February 2004, . [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, . [REC-xmlbase] Marsh, J., "XML Base", W3C REC W3C.REC-xmlbase-20010627, Bryan, et al. Expires February 22, 2010 [Page 24] Internet-Draft Metalink Download Description Format August 2009 June 2001, . [REC-xmldsig-core] Solo, D., Reagle, J., and D. Eastlake, "XML-Signature Syntax and Processing (Second Edition)", World Wide Web Consortium Recommendation REC-xmldsig-core-20080610, June 2008, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [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. [RFC4646] Phillips, A. and M. Davis, "Tags for Identifying Languages", BCP 47, RFC 4646, September 2006. 9.2. 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, . [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, . [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, . Appendix A. Acknowledgements and 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, A. Bram Neijt, Max Velasques, Manolo Valdes, Urs Wolfer, Frederick Cheung, Nils Maier, Hampus Wessman, Hayden Legendre, Danny Ayers, Nick Dominguez, Rene Leonhardt, Per Oyvind Karlsen, Gary Zellerbach, James Clark, Daniel Stenberg, Matt Domsch, Chris Newman, Lisa Dusseault, Ian Macfarlane, Dave Cridland, Julian Reschke, Barry Leiba, Uri Blumenthal, Paul Hoffman, Felix Sasaki, Matthias Fuchs, Eran Hammer-Lahav, and Mark Nottingham. 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, Sebastien Willemijns, Micah Cowan, Yazsoft, 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, 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 Hofmann, Dan Bryan, et al. Expires February 22, 2010 [Page 26] Internet-Draft Metalink Download Description Format August 2009 Connolly, Tim Berners-Lee, Louis Suarez-Potts, Ross Smith, Jeff Covey, Ed Lee, Shawn Wilsher, Mike Connor, Johan Svedberg, Dedric Carter, James Antill, 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 6.2 and 6.3. # -*- rnc -*- # RELAX NG Compact Syntax Grammar for the # Metalink Format Specification Version 4 namespace local = "" 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 start = metalinkMetalink metalinkMetalink = element metalink:metalink { metalinkCommonAttributes, (metalinkDynamic? Bryan, et al. Expires February 22, 2010 [Page 27] Internet-Draft Metalink Download Description Format August 2009 & metalinkFile+ & metalinkGenerator? & metalinkOrigin? & metalinkPublished? & metalinkUpdated? & extensionElement*) } metalinkFile = element metalink:file { metalinkCommonAttributes, attribute name { text }, (metalinkCopyright? & metalinkDescription? & metalinkIdentity? & metalinkHash* & metalinkLanguage? & metalinkLicense? & metalinkLogo? & metalinkMetaURL* & metalinkURL* & metalinkOS? & metalinkPieces* & metalinkPublisher? & metalinkSignature? & metalinkSize? & metalinkVersion? & extensionElement*) } metalinkPieces = element metalink:pieces { attribute length { xsd:integer }, attribute type { text }, metalinkHash+ } metalinkCopyright = element metalink:copyright { metalinkTextConstruct } metalinkDescription = element metalink:description { metalinkTextConstruct } metalinkDynamic = Bryan, et al. Expires February 22, 2010 [Page 28] Internet-Draft Metalink Download Description Format August 2009 element metalink:dynamic { "true" | "false" } metalinkGenerator = element metalink:generator { metalinkTextConstruct } metalinkHash = element metalink:hash { attribute type { text }?, text } metalinkIdentity = element metalink:identity { metalinkTextConstruct } metalinkLanguage = element metalink:language { metalinkTextConstruct } metalinkLicense = element metalink:license { metalinkCommonAttributes, attribute url { metalinkUri }?, attribute name { text }? } metalinkLogo = element metalink:logo { metalinkCommonAttributes, (metalinkUri) } metalinkMetaURL = element metalink:metaurl { metalinkCommonAttributes, attribute preference { xsd:integer }?, attribute type { text }, attribute name { text }?, metalinkUri } metalinkOrigin = Bryan, et al. Expires February 22, 2010 [Page 29] Internet-Draft Metalink Download Description Format August 2009 element metalink:origin { metalinkCommonAttributes, (metalinkUri) } metalinkOS = element metalink:os { metalinkTextConstruct } metalinkPublished = element metalink:published { metalinkDateConstruct } metalinkPublisher = element metalink:publisher { metalinkCommonAttributes, attribute url { metalinkUri }?, attribute name { text }? } metalinkSignature = element metalink:signature { attribute type { "pgp" }, metalinkTextConstruct } metalinkSize = element metalink:size { metalinkTextConstruct } metalinkUpdated = element metalink:updated { metalinkDateConstruct } metalinkURL = element metalink:url { metalinkCommonAttributes, attribute location { xsd:string { minLength = "2" maxLength="2"} }?, attribute preference { xsd:integer }?, metalinkUri } Bryan, et al. Expires February 22, 2010 [Page 30] Internet-Draft Metalink Download Description Format August 2009 metalinkVersion = element metalink:version { metalinkTextConstruct } # As defined in RFC 3066 and compatible with RFC 4646 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 undefinedAttribute = attribute * - (xml:base | xml:lang | local:*) { text } undefinedContent = (text|anyForeignElement)* anyElement = element * { (attribute * { text } | text | anyElement)* } Bryan, et al. Expires February 22, 2010 [Page 31] Internet-Draft Metalink Download Description Format August 2009 anyForeignElement = element * - metalink:* { (attribute * { text } | text | anyElement)* } # EOF Appendix C. Document History (to be removed by RFC Editor before publication) [[ to be removed by the RFC editor before publication as an RFC. ]] Updated versions can be found at http://tools.ietf.org/html/draft-bryan-metalink with frequent updates in Subversion at http://metalinks.svn.sourceforge.net/viewvc/metalinks/internetdraft/ Known issues concerning this draft: o None. -13 : August 21, 2009. o Remove files, resources, verification container elements. o MIME type: application/metalink4+xml -12 : August 18, 2009. o Remove "piece" attribute from hash elements in pieces container elements. o Rename "uri" attribute of license and publisher elements to "url". -11 : August 08, 2009. o Renamed type element (static or dynamic values) to dynamic element (true or false values). o Removed metadata inheritance and most other elements from files element. -10 : July 28, 2009. o Schema fixes. o Rename metadata element to metaurl, add name attribute to it similar to file element's name attribute. o Update REC-xmldsig-core reference to second edition. -09 : July 11, 2009. o Replace ISO639-2 references with RFC 4646. Bryan, et al. Expires February 22, 2010 [Page 32] Internet-Draft Metalink Download Description Format August 2009 o Add ISO3166-1. -08 : July 04, 2009. o Clarifications. o Remove "uri" and "version" attributes from generator element. -07 : June 18, 2009. o This ID describes the Metalink document format/schema. o Remove "Client Implementation Considerations" section. o Expand "Known issues" section of Document History. -06 : March 3, 2009. o Add authors and this Document History section. -05 : January 13, 2009. o Clarifications. -04 : December 31, 2008. o New IPR notice as required by IETF. o Correct "metalink:pieces" Element text. o Add hash examples. o Slim down "Securing Metalink Documents" section. o Recommend at least SHA-1. -03 : September 19, 2008. o New namespace - urn:ietf:params:xml:ns:metalink o Use the IANA registry named "Operating System Names" to define values for OS types. o Add "Client Implementation Considerations" section, which includes Content Negotiation. -02 : September 4, 2008. o Use the IANA registry named "Hash Function Textual Names" for hash types. o metadata Element for listing .torrent, .metalink, etc. o Remove type attribute for url Element. -01 : August 28, 2008. o Clarify directory info in name attribute, hash types, add text for preference attribute. -00 : August 23, 2008. o Initial draft; Text largely based on RFC 4287, ideas from Metalink 3.0 specification. Index Bryan, et al. Expires February 22, 2010 [Page 33] Internet-Draft Metalink Download Description Format August 2009 A application/metalink+xml Media Type 22 C copyright XML element 12 D description XML element 12 F file XML element 9 G generator XML element 13 Grammar metalinkCommonAttributes 7 metalinkCopyright 12 metalinkDateConstruct 8 metalinkDescription 12 metalinkFile 10 metalinkGenerator 13 metalinkHash 13 metalinkIdentity 14 metalinkLanguage 15 metalinkLicense 15 metalinkLogo 15 metalinkMetalink 9 metalinkOrigin 17 metalinkOS 17 metalinkPieces 11 metalinkPublished 17 metalinkPublisher 17 metalinkSignature 18 metalinkSize 18 metalinkTextConstruct 7 metalinkType 13 metalinkUpdated 18 metalinkURL 16, 19 metalinkVersion 19 simpleExtensionElement 21 structuredExtensionElement 21 H hash XML element 13 I identity XML element 14 Bryan, et al. Expires February 22, 2010 [Page 34] Internet-Draft Metalink Download Description Format August 2009 L language XML element 14 license XML element 15 logo XML element 15 M Media Type application/metalink+xml 22 metadata XML element 15 metalink XML element 8 metalinkCommonAttributes grammar production 7 metalinkCopyright grammar production 12 metalinkDateConstruct grammar production 8 metalinkDescription grammar production 12 metalinkFile grammar production 10 metalinkGenerator grammar production 13 metalinkHash grammar production 13 metalinkIdentity grammar production 14 metalinkLanguage grammar production 15 metalinkLicense grammar production 15 metalinkLogo grammar production 15 metalinkMetalink grammar production 9 metalinkOrigin grammar production 17 metalinkOS grammar production 17 metalinkPieces grammar production 11 metalinkPublished grammar production 17 metalinkPublisher grammar production 17 metalinkSignature grammar production 18 metalinkSize grammar production 18 metalinkTextConstruct grammar production 7 metalinkType grammar production 13 metalinkUpdated grammar production 18 metalinkURL grammar production 16, 19 metalinkVersion grammar production 19 O origin XML element 16 os XML element 17 P pieces XML element 11 published XML element 17 publisher XML element 17 S signature XML element 18 simpleExtensionElement grammar production 21 size XML element 18 Bryan, et al. Expires February 22, 2010 [Page 35] Internet-Draft Metalink Download Description Format August 2009 structuredExtensionElement grammar production 21 T type XML element 12 U updated XML element 18 url XML element 19 V version XML element 19 X XML Elements copyright 12 description 12 entry 9 generator 13 hash 13 identity 14 language 14 license 15 logo 15 metadata 15 metalink 8 origin 16 os 17 pieces 11 published 17 publisher 17 signature 18 size 18 type 12 updated 18 url 19 version 19 Authors' Addresses Anthony Bryan (editor) Metalinker Project Email: anthonybryan@gmail.com URI: http://www.metalinker.org Bryan, et al. Expires February 22, 2010 [Page 36] Internet-Draft Metalink Download Description Format August 2009 Tatsuhiro Tsujikawa Metalinker Project Email: tatsuhiro.t@gmail.com URI: http://aria2.sourceforge.net Neil McNab Metalinker Project Email: nabber00@gmail.com URI: http://www.nabber.org Peter Poeml Novell, Inc. Email: info@mirrorbrain.org URI: http://www.mirrorbrain.org/ Bryan, et al. Expires February 22, 2010 [Page 37]