Network Working Group E. Wilde
Internet-Draft June 27, 2016
Intended status: Informational
Expires: December 29, 2016
Home Documents for HTTP APIs: XML Syntax
draft-wilde-home-xml-04
Abstract
The specification for HTTP API Home Documents provides a JSON syntax
only. This specification provides an XML syntax for the same data
model, so that the concept of Home Documents can be consistently
exposed in both JSON- and XML-based HTTP APIs. It also defines the
link relation type "home" so that applications can identify links to
home documents.
Note to Readers
Please discuss this draft on the apps-discuss mailing list
(<https://www.ietf.org/mailman/listinfo/apps-discuss>).
Online access to all versions and files is available on GitHub
(<https://github.com/dret/I-D/tree/master/home-xml>).
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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."
This Internet-Draft will expire on December 29, 2016.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
Wilde Expires December 29, 2016 [Page 1]
Internet-Draft Home Documents XML June 2016
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. 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 Simplified BSD License.
1. Introduction
"Home Documents for HTTP APIs" [I-D.nottingham-json-home] proposes
the concept of "Home Documents" and describes them as follows:
"This document proposes a 'home document' format for non-browser HTTP
clients. [...] The goal of home documents is to serve as a starting
point for hypermedia APIs, where clients need to have an entry point,
and then can use the API by following links. Home documents thus
serve the same purpose as home pages on web sites: They are stable
entry points that provide starting points for clients with some
knowledge of the services linked from them."
While this general concept of a home document is independent of the
representation format, the specification only defines a JSON syntax.
In order to make this concept available across representations, this
specification defines an XML syntax for the concepts defined in
[I-D.nottingham-json-home].
One notable difference is the handling of links found in "href" or
"href-template" attributes of "resource" elements: In the JSON
syntax, these are (if they are relative URIs) resolved against the
URI of the home document itself. The XML syntax adds support for an
optional "xml:base" attribute [W3C.REC-xmlbase-20090128] on the
"resources" document element. If this attribute is present, it has
to be used according to its specification, and thus becomes part of a
possible resolution chain of relative URIs.
2. XML Example
The following Home Document in XML syntax uses the same data as the
Home Document shown in Section 2 [1] of [I-D.nottingham-json-home]
(but adding xml:base="http://example.com" to demonstrate the
mechanism):
Wilde Expires December 29, 2016 [Page 2]
Internet-Draft Home Documents XML June 2016
<?xml-stylesheet type="text/xsl" href="home-xml-02.xslt"?>
<resources xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:ietf:params:xml:ns:homedoc home-xml.xsd"
xmlns="urn:ietf:params:xml:ns:homedoc" xml:base="tag:me@example.com,2016:">
<resource rel="http://example.org/rel/widgets">
<link href="/widgets"/>
</resource>
<resource rel="widgets">
<template href-template="/widgets/{widget_id}">
<var name="widget_id" URI="widget"/>
</template>
<hints>
<allow>
<i>GET</i>
<i>PUT</i>
<i>DELETE</i>
<i>PATCH</i>
</allow>
<formats>
<format mediatype="application/json"/>
</formats>
<accept-patch>
<i>application/json-patch+json</i>
</accept-patch>
<accept-post>
<i>application/xml</i>
</accept-post>
<accept-ranges>
<i>bytes</i>
</accept-ranges>
</hints>
</resource>
</resources>
The mapping between JSON arrays and XML uses "item" elements <i/>,
where each of those elements represents one array item. For
properties that have a single values (i.e., they are not defined as
an array of values), this value is directly contained as content in
the corresponding element.
Currently, the draft does not specify an extension model (how to
represents hints that are not specified in the draft itself), and
therefore the extension model for XML is currently undefined as well.
The XML syntax will be updated to reflect the extension model once it
has been specified for the JSON syntax.
Wilde Expires December 29, 2016 [Page 3]
Internet-Draft Home Documents XML June 2016
3. XML Schema
The following XML Schema is describing the XML shown in Section 2.
Since there currently is no extension model, the XML Schema does
currently not contain any extension points.
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:xml="http://www.w3.org/XML/1998/namespace" targetNamespace="urn:ietf:params:xml:ns:homedoc" elementFormDefault="qualified" xmlns:home="urn:ietf:params:xml:ns:homedoc">
<xs:import namespace="http://www.w3.org/XML/1998/namespace" schemaLocation="http://www.w3.org/2001/xml.xsd"/>
<xs:element name="resources">
<xs:complexType>
<xs:sequence maxOccurs="unbounded" minOccurs="0">
<xs:element name="resource">
<xs:complexType>
<xs:sequence>
<xs:choice>
<xs:element name="link">
<xs:complexType>
<xs:attribute name="href" type="xs:anyURI" use="required"/>
</xs:complexType>
</xs:element>
<xs:element name="template">
<xs:complexType>
<xs:sequence maxOccurs="unbounded" minOccurs="0">
<xs:element name="var">
<xs:complexType>
<xs:attribute name="name" use="required"/>
<xs:attribute name="URI" type="xs:anyURI" use="required"/>
</xs:complexType>
</xs:element>
</xs:sequence>
<xs:attribute name="href-template" use="required"/>
</xs:complexType>
</xs:element>
</xs:choice>
<xs:element minOccurs="0" name="hints">
<xs:complexType>
<xs:choice maxOccurs="unbounded" minOccurs="0">
<xs:element name="allow" type="home:arrayType"/>
<xs:element name="formats">
<xs:complexType>
<xs:sequence>
<xs:element name="format">
<xs:complexType>
<xs:attribute name="mediatype" type="home:mediaTypeType"/>
</xs:complexType>
</xs:element>
</xs:sequence>
Wilde Expires December 29, 2016 [Page 4]
Internet-Draft Home Documents XML June 2016
</xs:complexType>
</xs:element>
<xs:element name="accept-patch" type="home:mediaTypeArrayType"/>
<xs:element name="accept-post" type="home:mediaTypeArrayType"/>
<xs:element name="accept-ranges" type="home:arrayType"/>
<xs:element name="accept-prefer" type="home:arrayType"/>
<xs:element name="docs" type="xs:anyURI"/>
<xs:element name="precondition-req" type="home:arrayType"/>
<xs:element name="auth-req">
<xs:complexType>
<xs:sequence maxOccurs="unbounded" minOccurs="0">
<xs:element name="scheme">
<xs:complexType>
<xs:sequence maxOccurs="unbounded" minOccurs="0">
<xs:element name="realm"/>
</xs:sequence>
<xs:attribute name="name" type="xs:token"/>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name="status">
<xs:simpleType>
<xs:restriction base="xs:token">
<xs:enumeration value="deprecated"/>
<xs:enumeration value="gone"/>
</xs:restriction>
</xs:simpleType>
</xs:element>
</xs:choice>
</xs:complexType>
</xs:element>
</xs:sequence>
<xs:attribute name="rel" type="xs:anyURI" use="required"/>
</xs:complexType>
</xs:element>
</xs:sequence>
<xs:attribute ref="xml:base" use="optional"/>
</xs:complexType>
</xs:element>
<xs:simpleType name="mediaTypeType">
<xs:restriction base="xs:string"/>
</xs:simpleType>
<xs:complexType name="arrayType">
<xs:sequence maxOccurs="unbounded" minOccurs="0">
<xs:element name="i"/>
</xs:sequence>
Wilde Expires December 29, 2016 [Page 5]
Internet-Draft Home Documents XML June 2016
</xs:complexType>
<xs:complexType name="mediaTypeArrayType">
<xs:sequence maxOccurs="unbounded" minOccurs="0">
<xs:element name="i" type="home:mediaTypeType"/>
</xs:sequence>
</xs:complexType>
</xs:schema>
4. IANA Considerations
This specification registers a media type and an XML namespace URI
for the XML syntax of Home Documents (as defined in
[I-D.nottingham-json-home]).
4.1. Media Type application/home+xml
The Internet media type [RFC6838] for a Home Document in XML syntax
is application/home+xml.
Type name: application
Subtype name: home+xml
Required parameters: none
Optional parameters: Same as charset parameter for the media type
"application/xml" as specified in RFC 3023 [RFC3023].
Encoding considerations: Same as encoding considerations of media
type "application/xml" as specified in RFC 3023 [RFC3023].
Security considerations: This media type has all of the security
considerations described in RFC 3023 [RFC3023] and
[I-D.nottingham-json-home].
Interoperability considerations: N/A
Published specification: RFC XXXX
Applications that use this media type: Applications that publish Home
Documents for HTTP services using XML syntax.
Additional information:
Magic number(s): N/A
File extension(s): XML documents should use ".xml" as the file
extension.
Wilde Expires December 29, 2016 [Page 6]
Internet-Draft Home Documents XML June 2016
Macintosh file type code(s): TEXT
Person & email address to contact for further information: Erik Wilde
<erik.wilde@emc.com>
Intended usage: COMMON
Restrictions on usage: none
Author: Erik Wilde <erik.wilde@emc.com>
Change controller: IETF
4.2. XML Namespace Registration
This document registers the following XML namespaces in the IETF XML
registry defined in [RFC3688].
URI: urn:ietf:params:xml:ns:homedoc
Registrant: The IESG.
XML: N/A, the requested URI is an XML namespace defined by an RFC.
4.3. Link Relation Type
The link relation type below has been registered by IANA per
Section 6.2.1 of RFC 5988 [RFC5988]:
4.3.1. Link Relation Type: home
Relation Name: home
Description: Identifies a resource that provides a "home" document
for the context resource. Home documents often serve as starting
points for a certain resource context, such as for Web APIs where
the home resource provides access to a number of "entry points" to
the Web API.
Reference: RFC XXXX
5. Implementation Status
Note to RFC Editor: Please remove this section before publication.
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in RFC 6982
Wilde Expires December 29, 2016 [Page 7]
Internet-Draft Home Documents XML June 2016
[RFC6982]. The description of implementations in this section is
intended to assist the IETF in its decision processes in progressing
drafts to RFCs. Please note that the listing of any individual
implementation here does not imply endorsement by the IETF.
Furthermore, no effort has been spent to verify the information
presented here that was supplied by IETF contributors. This is not
intended as, and must not be construed to be, a catalog of available
implementations or their features. Readers are advised to note that
other implementations may exist.
According to RFC 6982, "this will allow reviewers and working groups
to assign due consideration to documents that have the benefit of
running code, which may serve as evidence of valuable experimentation
and feedback that have made the implemented protocols more mature.
It is up to the individual working groups to use this information as
they see fit".
For a list of implementations, please refer to the wiki that tracks
implementations for the Home Document specification in general:
<https://github.com/mnot/I-D/wiki/json-home>
6. Security Considerations
The general security considerations for XML home documents are the
same as those for JSON home documents, as described in the "Security
Considerations" of [I-D.nottingham-json-home]. The specific security
considerations introduced by XML as a representation format are
described in the "Security Considerations" of [RFC3023].
7. Open Issues
o The move from a predefined list of hints to a hint registry is not
yet reflected in the XML; in particular because the draft defines
the hint data model to be JSON-specific.
o What is the extension model for the XML syntax? Should processing
of other namespaces be defined as "should ignore", so that same-
namespace extensions are encouraged?
o Should the XML syntax provide support for embedded human-readable
documentation? This would probably not be supported in the JSON
syntax, but could be marked as strictly optional and XML-specific.
Wilde Expires December 29, 2016 [Page 8]
Internet-Draft Home Documents XML June 2016
8. References
8.1. Normative References
[I-D.nottingham-json-home]
Nottingham, M., "Home Documents for HTTP APIs", draft-
nottingham-json-home-04 (work in progress), May 2016.
[RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media
Types", RFC 3023, January 2001.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
DOI 10.17487/RFC3688, January 2004,
<http://www.rfc-editor.org/info/rfc3688>.
[RFC5988] Nottingham, M., "Web Linking", RFC 5988, October 2010.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, January 2013.
[W3C.REC-xml-20081126]
Sperberg-McQueen, C., Yergeau, F., Paoli, J., Maler, E.,
and T. Bray, "Extensible Markup Language (XML) 1.0 (Fifth
Edition)", World Wide Web Consortium Recommendation REC-
xml-20081126, November 2008,
<http://www.w3.org/TR/2008/REC-xml-20081126>.
[W3C.REC-xmlbase-20090128]
Marsh, J. and R. Tobin, "XML Base (Second Edition)", World
Wide Web Consortium Recommendation REC-xmlbase-20090128,
January 2009,
<http://www.w3.org/TR/2009/REC-xmlbase-20090128>.
8.2. Informative References
[W3C.REC-xslt-19991116]
Clark, J., "XSL Transformations (XSLT) Version 1.0", World
Wide Web Consortium Recommendation REC-xslt-19991116,
November 1999,
<http://www.w3.org/TR/1999/REC-xslt-19991116>.
[W3C.REC-xml-stylesheet-20101028]
Pieters, S., Clark, J., and H. Thompson, "Associating
Style Sheets with XML documents 1.0 (Second Edition)",
World Wide Web Consortium Recommendation REC-xml-
stylesheet-20101028, October 2010,
<http://www.w3.org/TR/2010/REC-xml-stylesheet-20101028>.
Wilde Expires December 29, 2016 [Page 9]
Internet-Draft Home Documents XML June 2016
[RFC6982] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", RFC 6982, July
2013.
8.3. URIs
[1] http://tools.ietf.org/html/draft-nottingham-json-home-
04#section-2
Appendix A. XML-to-HTML for Home Documents
The following XSLT 1.0 stylesheet [W3C.REC-xslt-19991116] transforms
XML Home Documents to very simple HTML renditions. By associating
this stylesheet [W3C.REC-xml-stylesheet-20101028] with an XML Home
Document, it is possible to serve XML Home Documents that will be
rendered in a human-friendly way when viewed in a browser.
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:xml="http://www.w3.org/XML/1998/namespace" version="1.0" xmlns:home="urn:ietf:params:xml:ns:homedoc" exclude-result-prefixes="home">
<xsl:output method="html"/>
<xsl:template match="home:resources">
<html>
<head>
<title>Home Document</title>
</head>
<body>
<h1>Home Document</h1>
<ul>
<xsl:for-each select="home:resource">
<li>
<xsl:text>Link Relation </xsl:text>
<code><xsl:value-of select="@rel"/></code>
<xsl:text>: Link </xsl:text>
<code>
<xsl:choose>
<xsl:when test="home:link">
<xsl:variable name="link-URI">
<xsl:call-template name="resolve-URI">
<xsl:with-param name="URI" select="home:link/@href"/>
</xsl:call-template>
</xsl:variable>
<a href="{$link-URI}" title="URI"><xsl:value-of select="$link-URI"/></a>
</xsl:when>
<xsl:otherwise>
<xsl:variable name="template-URI">
<xsl:call-template name="resolve-URI">
<xsl:with-param name="URI" select="home:template/@href-template"/>
</xsl:call-template>
Wilde Expires December 29, 2016 [Page 10]
Internet-Draft Home Documents XML June 2016
</xsl:variable>
<a href="{$template-URI}" title="URI template"><xsl:value-of select="$template-URI"/></a>
</xsl:otherwise>
</xsl:choose>
</code>
<dl>
<xsl:if test="home:template/home:var">
<dt>Variables: </dt>
<dd>
<ul>
<xsl:for-each select="home:template/home:var">
<xsl:sort select="@name"/>
<li>
<span title="Variable Name"><xsl:value-of select="@name"/></span>
<xsl:text>: </xsl:text>
<span title="Associated URI"><xsl:value-of select="@URI"/></span>
</li>
</xsl:for-each>
</ul>
</dd>
</xsl:if>
<xsl:if test="home:hints">
<dt>Hints: </dt>
<dd>
<ul>
<xsl:for-each select="home:hints/home:*">
<xsl:sort select="local-name()"/>
<li>
<span title="Hint Name"><xsl:value-of select="local-name()"/></span>
<xsl:text>: </xsl:text>
<xsl:choose>
<xsl:when test="home:i">
<xsl:for-each select="home:i">
<xsl:value-of select="."/>
<xsl:if test="position() != last()">
<xsl:text>, </xsl:text>
</xsl:if>
</xsl:for-each>
</xsl:when>
<xsl:otherwise>
<xsl:value-of select="."/>
</xsl:otherwise>
</xsl:choose>
</li>
</xsl:for-each>
</ul>
</dd>
</xsl:if>
Wilde Expires December 29, 2016 [Page 11]
Internet-Draft Home Documents XML June 2016
</dl>
</li>
</xsl:for-each>
</ul>
</body>
</html>
</xsl:template>
<xsl:template name="resolve-URI">
<xsl:param name="URI"/>
<!-- This is not how URI resolution should be done; http://tools.ietf.org/html/rfc3986#section-5 describes the correct process. -->
<xsl:value-of select="concat(/home:resources/@xml:base, $URI)"/>
</xsl:template>
</xsl:stylesheet>
Author's Address
Erik Wilde
Email: erik.wilde@dret.net
URI: http://dret.net/netdret/
Wilde Expires December 29, 2016 [Page 12]