Network Working Group A. Bryan Internet-Draft T. Tsujikawa Intended status: Standards Track N. McNab Expires: May 30, 2010 P. Poeml Novell, Inc. November 26, 2009 The Metalink Download Description Format draft-bryan-metalink-23 Abstract This document specifies Metalink, an XML-based download description format. Metalink describes download locations (mirrors), checksums, and other information. Clients can transparently use this information to reliably transfer files. 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 May 30, 2010. 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 Bryan, et al. Expires May 30, 2010 [Page 1] Internet-Draft Metalink Download Description Format November 2009 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. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the BSD License. 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. Bryan, et al. Expires May 30, 2010 [Page 2] Internet-Draft Metalink Download Description Format November 2009 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.2. Namespace and Version . . . . . . . . . . . . . . . . . . 7 1.3. Notational Conventions . . . . . . . . . . . . . . . . . . 7 2. Metalink Documents . . . . . . . . . . . . . . . . . . . . . . 7 3. Common Metalink Constructs . . . . . . . . . . . . . . . . . . 9 3.1. Text Constructs . . . . . . . . . . . . . . . . . . . . . 9 3.1.1. Text . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.2. Date Constructs . . . . . . . . . . . . . . . . . . . . . 9 4. Metalink Element Definitions . . . . . . . . . . . . . . . . . 10 4.1. Container Elements . . . . . . . . . . . . . . . . . . . . 10 4.1.1. The "metalink:metalink" Element . . . . . . . . . . . 10 4.1.2. The "metalink:file" Element . . . . . . . . . . . . . 11 4.1.3. 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:dynamic" Element . . . . . . . . . . . . 14 4.2.4. The "metalink:generator" Element . . . . . . . . . . . 15 4.2.5. The "metalink:hash" Element . . . . . . . . . . . . . 15 4.2.6. The "metalink:identity" Element . . . . . . . . . . . 16 4.2.7. The "metalink:language" Element . . . . . . . . . . . 17 4.2.8. The "metalink:license" Element . . . . . . . . . . . . 17 4.2.9. The "metalink:logo" Element . . . . . . . . . . . . . 17 4.2.10. The "metalink:metaurl" Element . . . . . . . . . . . . 18 4.2.11. The "metalink:origin" Element . . . . . . . . . . . . 19 4.2.12. The "metalink:os" Element . . . . . . . . . . . . . . 19 4.2.13. The "metalink:published" Element . . . . . . . . . . . 19 4.2.14. The "metalink:publisher" Element . . . . . . . . . . . 19 4.2.15. The "metalink:signature" Element . . . . . . . . . . . 20 4.2.16. The "metalink:size" Element . . . . . . . . . . . . . 20 4.2.17. The "metalink:updated" Element . . . . . . . . . . . . 21 4.2.18. The "metalink:url" Element . . . . . . . . . . . . . . 21 4.2.19. The "metalink:version" Element . . . . . . . . . . . . 21 5. Securing Metalink Documents . . . . . . . . . . . . . . . . . 22 6. Extending Metalink . . . . . . . . . . . . . . . . . . . . . . 22 6.1. Extensions from Non-Metalink Vocabularies . . . . . . . . 22 6.2. Extensions to the Metalink Vocabulary . . . . . . . . . . 22 6.3. Processing Foreign Markup . . . . . . . . . . . . . . . . 23 6.4. Extension Elements . . . . . . . . . . . . . . . . . . . . 23 6.4.1. Simple Extension Elements . . . . . . . . . . . . . . 23 6.4.2. Structured Extension Elements . . . . . . . . . . . . 23 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24 7.1. XML Namespace Registration . . . . . . . . . . . . . . . . 24 7.2. application/metalink4+xml MIME type . . . . . . . . . . . 24 8. Security Considerations . . . . . . . . . . . . . . . . . . . 25 Bryan, et al. Expires May 30, 2010 [Page 3] Internet-Draft Metalink Download Description Format November 2009 8.1. URIs and IRIs . . . . . . . . . . . . . . . . . . . . . . 25 8.2. Spoofing . . . . . . . . . . . . . . . . . . . . . . . . . 25 8.3. Cryptographic Hashes . . . . . . . . . . . . . . . . . . . 26 8.4. Signing . . . . . . . . . . . . . . . . . . . . . . . . . 26 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26 9.1. Normative References . . . . . . . . . . . . . . . . . . . 26 9.2. Informative References . . . . . . . . . . . . . . . . . . 28 Appendix A. Acknowledgements and Contributors . . . . . . . . . . 28 Appendix B. RELAX NG Compact Schema . . . . . . . . . . . . . . . 29 Appendix C. Document History (to be removed by RFC Editor before publication) . . . . . . . . . . . . . . . . . 34 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 40 Bryan, et al. Expires May 30, 2010 [Page 4] Internet-Draft Metalink Download Description Format November 2009 1. Introduction Metalink is an XML-based document format that describes a file or list of files to be downloaded from a server. Metalinks can list a number of files, each with an extensible set of attached metadata. Each listed file can have a description, checksum, and a list of URIs that it is available from. Often, identical copies of a file are accessible in multiple locations on the Internet over a variety of protocols (FTP, HTTP, and Peer-to-Peer). In some cases, users are shown a list of these multiple download locations (mirror servers) and must manually select one based on geographical location, priority, or bandwidth. This is done to distribute the load across multiple servers, and to give human users the opportunity to choose a download location that they expect to work best for them. At times, individual servers can be slow, outdated, or unreachable, but this can not be determined until the download has been initiated. This can lead to the user canceling the download and needing to restart it. During downloads, errors in transmission can corrupt the file. There are no easy ways to repair these files. For large downloads this can be especially troublesome. Any of the number of problems that can occur during a download lead to frustration on the part of users, and bandwith wasted with retransmission. Knowledge about availability of a download on mirror servers can be acquired and maintained by the operators of the origin server, or by third a party. This knowledge, together with checksums, digital signatures, and more can be stored in a machine-readable Metalink file. The Metalink file can transfer this knowledge to the user agent, which can peruse it in automatic ways or present the information to a human user. User agents can fall back to alternate mirrors if the current one has an issue. Thereby, clients are enabled to work their way to a successful download even under adverse circumstances. All this can be done transparently to the human user and the download is much more reliable and efficient. In contrast, a traditional HTTP redirect to one mirror conveys only comparatively minimal information - a referral to a single server, and there is no provision in the HTTP protocol to handle failures. Other features that some clients provide include multi-source downloads, where chunks of a file are downloaded from multiple mirrors (and optionally, Peer-to-Peer) simultaneously, which frequently results in a faster download. Metalinks can leverage HTTP, FTP and Peer-to-Peer protocols together, because regardless over which protocol the Metalink was obtained, it can make a resource accessible through other protocols. If the Metalink was obtained Bryan, et al. Expires May 30, 2010 [Page 5] Internet-Draft Metalink Download Description Format November 2009 from a trusted source, included verification metadata can solve trust issues when downloading files from replica servers operated by third parties. Metalinks also provide structured information about downloads that can be indexed by search engines. [[ Discussion of this draft should take place on discuss@apps.ietf.org. Past discussion has gone on at the Metalink discussion mailing list located at metalink-discussion@googlegroups.com / http://groups.google.com/group/metalink-discussion . ]] 1.1. Examples A brief, Metalink Document that describes a single file: 14471447 ftp://ftp.example.com/example.ext http://example.com/example.ext http://example.com/example.ext.torrent A more extensive, Metalink Document that describes two files: 2009-05-15T12:23:23Z 14471447 Example Bryan, et al. Expires May 30, 2010 [Page 6] Internet-Draft Metalink Download Description Format November 2009 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 14471447 Example 1.0 en Another description for a second file. 7f4afdc84bd1b79238703fb45cd045efd08bee4b ftp://ftp.example.com/example2.ext http://example.com/example2.ext http://example.com/example2.ext.torrent Bryan, et al. Expires May 30, 2010 [Page 7] Internet-Draft Metalink Download Description Format November 2009 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, 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 Bryan, et al. Expires May 30, 2010 [Page 8] Internet-Draft Metalink Download Description Format November 2009 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/ metalink4+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, encoded according to [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 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 Documents that do not follow this specification are invalid, and partially or wholly unusable to Metalink Processors. Metalink is an extensible format. See Section 6 of this document for a full description of how Metalink Documents can be extended. Bryan, et al. Expires May 30, 2010 [Page 9] Internet-Draft Metalink Download Description Format November 2009 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. ... 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. Bryan, et al. Expires May 30, 2010 [Page 10] Internet-Draft Metalink Download Description Format November 2009 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. 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): Bryan, et al. Expires May 30, 2010 [Page 11] Internet-Draft Metalink Download Description Format November 2009 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 to retrieve the same file in another way, such as a peer to peer network. Bryan, et al. Expires May 30, 2010 [Page 12] Internet-Draft Metalink Download Description Format November 2009 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 "priority" 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. o metalink:file elements MAY contain exactly one metalink:logo element. o metalink:file elements MAY contain one or more metalink:os element. Bryan, et al. Expires May 30, 2010 [Page 13] Internet-Draft Metalink Download Description Format November 2009 o metalink:file elements MUST contain at least one metalink:url element or at least one metalink:metaurl element. Typically, metalink:file elements contain 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:positiveInteger }, attribute type { text }, metalinkHash+ } Bryan, et al. Expires May 30, 2010 [Page 14] Internet-Draft Metalink Download Description Format November 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 positive 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. That is, every piece should be the same size, apart from the last piece which is the remainder. The last piece extends 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 May 30, 2010 [Page 15] Internet-Draft Metalink Download Description Format November 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/2.9.2", where "MirrorBrain" is the name and "2.9.2" 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 May 30, 2010 [Page 16] Internet-Draft Metalink Download Description Format November 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. The size of the piece is equal to the value of the "length" attribute of the metalink:pieces element. The whole file is divided into non- overlapping pieces of this length, starting from the beginning of the file. That is, every piece should be the same size, apart from the last piece which is the remainder. The last piece extends to the end of the file, and can therefore be shorter than the other pieces. ... 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 additional hash types. 4.2.6. The "metalink:identity" Element The "metalink:identity" element is a Text construct that conveys a human-readable identity for a file. For example, the identity of Firefox 3.5 would be "Firefox". metalinkIdentity = element metalink:identity { metalinkTextConstruct } Bryan, et al. Expires May 30, 2010 [Page 17] Internet-Draft Metalink Download Description Format November 2009 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 [RFC5646]. 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. Bryan, et al. Expires May 30, 2010 [Page 18] Internet-Draft Metalink Download Description Format November 2009 4.2.10. The "metalink:metaurl" Element The "metalink:metaurl" element contains the IRI of a metadata file, also known as a metainfo file, about a resource to download. For example, this could be the IRI of a BitTorrent .torrent file, a Metalink Document, or other type of metadata file. Note that the information in the metalink:hash element does not apply to these metadata files, but to the files that are described by them. metalinkMetaURL = element metalink:metaurl { metalinkCommonAttributes, attribute priority { xsd:positiveInteger }?, attribute type { text }, attribute name { text }?, metalinkUri } 4.2.10.1. The "priority" Attribute metalink:metaurl elements MAY have a priority attribute. Values MUST be positive integers. Lower values indicate a higher priority. Multiple metalink:metaurl elements can have the same priority, i.e. three BitTorrent .torrent files could have priority="1". See also the "priority" 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 media type [RFC4288] 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 Bryan, et al. Expires May 30, 2010 [Page 19] Internet-Draft Metalink Download Description Format November 2009 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. 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. Bryan, et al. Expires May 30, 2010 [Page 20] Internet-Draft Metalink Download Description Format November 2009 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. 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. This value MUST be a non-negative integer. metalinkSize = element metalink:size { xsd:nonNegativeInteger } Bryan, et al. Expires May 30, 2010 [Page 21] Internet-Draft Metalink Download Description Format November 2009 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. 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 priority { xsd:positiveInteger }?, metalinkUri } 4.2.18.1. The "priority" Attribute metalink:url elements MAY have a priority attribute. Values MUST be positive integers. Lower values indicate a higher priority. Multiple metalink:url elements can have the same priority, i.e. ten mirrors could have priority="1". 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 Firefox 3.5 would be "3.5". Bryan, et al. Expires May 30, 2010 [Page 22] Internet-Draft Metalink Download Description Format November 2009 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 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". Bryan, et al. Expires May 30, 2010 [Page 23] Internet-Draft Metalink Download Description Format November 2009 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, 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. 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 Bryan, et al. Expires May 30, 2010 [Page 24] Internet-Draft Metalink Download Description Format November 2009 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. 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/metalink4+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. Bryan, et al. Expires May 30, 2010 [Page 25] Internet-Draft Metalink Download Description Format November 2009 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: .meta4 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 Bryan, et al. Expires May 30, 2010 [Page 26] Internet-Draft Metalink Download Description Format November 2009 might create Metalink Documents containing inaccurate information anywhere in the document. Unaware downloaders could be deceived into downloading a malicious or worthless file. 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], or stronger. It MAY also include other hashes from the IANA registry named "Hash Function Textual Names". 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 Bryan, et al. Expires May 30, 2010 [Page 27] Internet-Draft Metalink Download Description Format November 2009 (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, 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. [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 Bryan, et al. Expires May 30, 2010 [Page 28] Internet-Draft Metalink Download Description Format November 2009 Identifiers (IRIs)", RFC 3987, January 2005. [RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and Registration Procedures", BCP 13, RFC 4288, December 2005. [RFC5646] Phillips, A. and M. Davis, "Tags for Identifying Languages", BCP 47, RFC 5646, September 2009. 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, . [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, January 2004. [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 content and concepts within are a product of the Metalink community. The Metalink community has dozens of contributors who proposed ideas Bryan, et al. Expires May 30, 2010 [Page 29] Internet-Draft Metalink Download Description Format November 2009 and wording for this document, or contributed to the evolution of Metalink, including: 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, Yazsoft, KGet developers, FDM Team, Orbit Team, Arne Babenhauserheide, Mathias Berchtold, Xienzhenyu and TheWorld Browser Team, Xi Software, Nicolas Alvarez, Patrick Ruckstuhl, Sebastien Willemijns, Micah Cowan, Bridget and Ethan Fletcher, Ruben Kerkhof, Agostino Russo, Salvatore Musumeci, Steve Eshelman, Lucas Hewett, Ryan 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 & Sandra Sowder, Tom Mainville, Janie Wargo, Jason Hansen, Tim Bray, Dan Brickley, Markus Hofmann, Dan 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, Chris Newman, Lisa Dusseault, Ian Macfarlane, Dave Cridland, Julian Reschke, Barry Leiba, Uri Blumenthal, Paul Hoffman, Felix Sasaki, Matthias Fuchs, Mark Baker, Eran Hammer-Lahav, Mark Nottingham, and Peter Saint- Andre. We also thank 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 }?, Bryan, et al. Expires May 30, 2010 [Page 30] Internet-Draft Metalink Download Description Format November 2009 attribute xml:lang { metalinkLanguageTag }?, undefinedAttribute* # Text Constructs metalinkTextConstruct = metalinkCommonAttributes, text # Date Construct metalinkDateConstruct = metalinkCommonAttributes, xsd:dateTime start = metalinkMetalink metalinkMetalink = element metalink:metalink { metalinkCommonAttributes, (metalinkDynamic? & 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? Bryan, et al. Expires May 30, 2010 [Page 31] Internet-Draft Metalink Download Description Format November 2009 & extensionElement*) } metalinkPieces = element metalink:pieces { attribute length { xsd:positiveInteger }, attribute type { text }, metalinkHash+ } metalinkCopyright = element metalink:copyright { metalinkTextConstruct } metalinkDescription = element metalink:description { metalinkTextConstruct } metalinkDynamic = 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 { Bryan, et al. Expires May 30, 2010 [Page 32] Internet-Draft Metalink Download Description Format November 2009 metalinkCommonAttributes, attribute url { metalinkUri }?, attribute name { text }? } metalinkLogo = element metalink:logo { metalinkCommonAttributes, (metalinkUri) } metalinkMetaURL = element metalink:metaurl { metalinkCommonAttributes, attribute priority { xsd:positiveInteger }?, attribute type { text }, attribute name { text }?, metalinkUri } metalinkOrigin = 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 } Bryan, et al. Expires May 30, 2010 [Page 33] Internet-Draft Metalink Download Description Format November 2009 metalinkSize = element metalink:size { xsd:nonNegativeInteger } metalinkUpdated = element metalink:updated { metalinkDateConstruct } metalinkURL = element metalink:url { metalinkCommonAttributes, attribute location { xsd:string { minLength = "2" maxLength="2"} }?, attribute priority { xsd:positiveInteger }?, metalinkUri } metalinkVersion = element metalink:version { metalinkTextConstruct } # As defined in RFC 3066 and compatible with RFC 5646 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 }*, Bryan, et al. Expires May 30, 2010 [Page 34] Internet-Draft Metalink Download Description Format November 2009 (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)* } 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. -23 : November 26, 2009. o Apps Area AD review changes, Change RFC3688 from Normative to Informative Reference. Bryan, et al. Expires May 30, 2010 [Page 35] Internet-Draft Metalink Download Description Format November 2009 o Schema: integer changed to positiveInteger or nonNegativeInteger where fitting. -22 : November 09, 2009. o Clarifications. -21 : October 13, 2009. o Update author details. -20 : October 12, 2009. o RFC 5646 updates RFC 4646. -19 : October 5, 2009. o Remove organization for independent authors. -18 : October 4, 2009. o File extension: .meta4 o Hashes clarification, modified to allow multiple metalink:os elements, add size element to example. -17 : September 28, 2009. o Typo correction. -16 : August 31, 2009. o Clarifications. -15 : August 26, 2009. o Rename "preference" attribute of metaurl and url elements to "priority", where lower values indicate higher priority. -14 : August 24, 2009. o Update abstract and introduction. -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. Bryan, et al. Expires May 30, 2010 [Page 36] Internet-Draft Metalink Download Description Format November 2009 -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. 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. Bryan, et al. Expires May 30, 2010 [Page 37] Internet-Draft Metalink Download Description Format November 2009 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 A application/metalink4+xml Media Type 25 C copyright XML element 15 D description XML element 15 F file XML element 12 G generator XML element 16 Grammar metalinkCommonAttributes 9 metalinkCopyright 15 metalinkDateConstruct 11 metalinkDescription 15 metalinkFile 13 metalinkGenerator 16 metalinkHash 16 metalinkIdentity 17 metalinkLanguage 18 metalinkLicense 18 metalinkLogo 18 metalinkMetalink 11 metalinkOrigin 20 metalinkOS 20 metalinkPieces 14 metalinkPublished 20 metalinkPublisher 21 metalinkSignature 21 metalinkSize 21 metalinkTextConstruct 10 metalinkType 16 metalinkUpdated 22 metalinkURL 19, 22 Bryan, et al. Expires May 30, 2010 [Page 38] Internet-Draft Metalink Download Description Format November 2009 metalinkVersion 23 simpleExtensionElement 24 structuredExtensionElement 25 H hash XML element 16 I identity XML element 17 L language XML element 18 license XML element 18 logo XML element 18 M Media Type application/metalink4+xml 25 metadata XML element 19 metalink XML element 11 metalinkCommonAttributes grammar production 9 metalinkCopyright grammar production 15 metalinkDateConstruct grammar production 11 metalinkDescription grammar production 15 metalinkFile grammar production 13 metalinkGenerator grammar production 16 metalinkHash grammar production 16 metalinkIdentity grammar production 17 metalinkLanguage grammar production 18 metalinkLicense grammar production 18 metalinkLogo grammar production 18 metalinkMetalink grammar production 11 metalinkOrigin grammar production 20 metalinkOS grammar production 20 metalinkPieces grammar production 14 metalinkPublished grammar production 20 metalinkPublisher grammar production 21 metalinkSignature grammar production 21 metalinkSize grammar production 21 metalinkTextConstruct grammar production 10 metalinkType grammar production 16 metalinkUpdated grammar production 22 metalinkURL grammar production 19, 22 metalinkVersion grammar production 23 O origin XML element 20 os XML element 20 Bryan, et al. Expires May 30, 2010 [Page 39] Internet-Draft Metalink Download Description Format November 2009 P pieces XML element 14 published XML element 20 publisher XML element 20 S signature XML element 21 simpleExtensionElement grammar production 24 size XML element 21 structuredExtensionElement grammar production 25 T type XML element 15 U updated XML element 22 url XML element 22 V version XML element 22 X XML Elements copyright 15 description 15 entry 12 generator 16 hash 16 identity 17 language 18 license 18 logo 18 metadata 19 metalink 11 origin 20 os 20 pieces 14 published 20 publisher 20 signature 21 size 21 type 15 updated 22 url 22 version 22 Bryan, et al. Expires May 30, 2010 [Page 40] Internet-Draft Metalink Download Description Format November 2009 Authors' Addresses Anthony Bryan Pompano Beach, FL USA Email: anthonybryan@gmail.com URI: http://www.metalinker.org Tatsuhiro Tsujikawa Email: tatsuhiro.t@gmail.com URI: http://aria2.sourceforge.net Neil McNab Email: neil@nabber.org URI: http://www.nabber.org Peter Poeml Novell, Inc. Email: poeml@mirrorbrain.org URI: http://www.mirrorbrain.org/ Bryan, et al. Expires May 30, 2010 [Page 41]