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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html lang="en"><head><title>URI Template</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta name="description" content="URI Template">
<meta name="generator" content="xml2rfc v1.33 (http://xml.resource.org/)">
<style type='text/css'><!--
body {
font-family: verdana, charcoal, helvetica, arial, sans-serif;
font-size: small; color: #000; background-color: #FFF;
margin: 2em;
}
h1, h2, h3, h4, h5, h6 {
font-family: helvetica, monaco, "MS Sans Serif", arial, sans-serif;
font-weight: bold; font-style: normal;
}
h1 { color: #900; background-color: transparent; text-align: right; }
h3 { color: #333; background-color: transparent; }
td.RFCbug {
font-size: x-small; text-decoration: none;
width: 30px; height: 30px; padding-top: 2px;
text-align: justify; vertical-align: middle;
background-color: #000;
}
td.RFCbug span.RFC {
font-family: monaco, charcoal, geneva, "MS Sans Serif", helvetica, verdana, sans-serif;
font-weight: bold; color: #666;
}
td.RFCbug span.hotText {
font-family: charcoal, monaco, geneva, "MS Sans Serif", helvetica, verdana, sans-serif;
font-weight: normal; text-align: center; color: #FFF;
}
table.TOCbug { width: 30px; height: 15px; }
td.TOCbug {
text-align: center; width: 30px; height: 15px;
color: #FFF; background-color: #900;
}
td.TOCbug a {
font-family: monaco, charcoal, geneva, "MS Sans Serif", helvetica, sans-serif;
font-weight: bold; font-size: x-small; text-decoration: none;
color: #FFF; background-color: transparent;
}
td.header {
font-family: arial, helvetica, sans-serif; font-size: x-small;
vertical-align: top; width: 33%;
color: #FFF; background-color: #666;
}
td.author { font-weight: bold; font-size: x-small; margin-left: 4em; }
td.author-text { font-size: x-small; }
/* info code from SantaKlauss at http://www.madaboutstyle.com/tooltip2.html */
a.info {
/* This is the key. */
position: relative;
z-index: 24;
text-decoration: none;
}
a.info:hover {
z-index: 25;
color: #FFF; background-color: #900;
}
a.info span { display: none; }
a.info:hover span.info {
/* The span will display just on :hover state. */
display: block;
position: absolute;
font-size: smaller;
top: 2em; left: -5em; width: 15em;
padding: 2px; border: 1px solid #333;
color: #900; background-color: #EEE;
text-align: left;
}
a { font-weight: bold; }
a:link { color: #900; background-color: transparent; }
a:visited { color: #633; background-color: transparent; }
a:active { color: #633; background-color: transparent; }
p { margin-left: 2em; margin-right: 2em; }
p.copyright { font-size: x-small; }
p.toc { font-size: small; font-weight: bold; margin-left: 3em; }
table.toc { margin: 0 0 0 3em; padding: 0; border: 0; vertical-align: text-top; }
td.toc { font-size: small; font-weight: bold; vertical-align: text-top; }
ol.text { margin-left: 2em; margin-right: 2em; }
ul.text { margin-left: 2em; margin-right: 2em; }
li { margin-left: 3em; }
/* RFC-2629 <spanx>s and <artwork>s. */
em { font-style: italic; }
strong { font-weight: bold; }
dfn { font-weight: bold; font-style: normal; }
cite { font-weight: normal; font-style: normal; }
tt { color: #036; }
tt, pre, pre dfn, pre em, pre cite, pre span {
font-family: "Courier New", Courier, monospace; font-size: small;
}
pre {
text-align: left; padding: 4px;
color: #000; background-color: #CCC;
}
pre dfn { color: #900; }
pre em { color: #66F; background-color: #FFC; font-weight: normal; }
pre .key { color: #33C; font-weight: bold; }
pre .id { color: #900; }
pre .str { color: #000; background-color: #CFF; }
pre .val { color: #066; }
pre .rep { color: #909; }
pre .oth { color: #000; background-color: #FCF; }
pre .err { background-color: #FCC; }
/* RFC-2629 <texttable>s. */
table.all, table.full, table.headers, table.none {
font-size: small; text-align: center; border-width: 2px;
vertical-align: top; border-collapse: collapse;
}
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table.headers, table.none { border-style: none; }
th {
font-weight: bold; border-color: black;
border-width: 2px 2px 3px 2px;
}
table.all th, table.full th { border-style: solid; }
table.headers th { border-style: none none solid none; }
table.none th { border-style: none; }
table.all td {
border-style: solid; border-color: #333;
border-width: 1px 2px;
}
table.full td, table.headers td, table.none td { border-style: none; }
hr { height: 1px; }
hr.insert {
width: 80%; border-style: none; border-width: 0;
color: #CCC; background-color: #CCC;
}
--></style>
</head>
<body>
<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></table>
<table summary="layout" width="66%" border="0" cellpadding="0" cellspacing="0"><tr><td><table summary="layout" width="100%" border="0" cellpadding="2" cellspacing="1">
<tr><td class="header">Network Working Group</td><td class="header">J. Gregorio, Ed.</td></tr>
<tr><td class="header">Internet-Draft</td><td class="header">Google</td></tr>
<tr><td class="header">Intended status: Standards Track</td><td class="header">M. Hadley, Ed.</td></tr>
<tr><td class="header">Expires: September 27, 2008</td><td class="header">Sun Microsystems</td></tr>
<tr><td class="header"> </td><td class="header">M. Nottingham, Ed.</td></tr>
<tr><td class="header"> </td><td class="header"> </td></tr>
<tr><td class="header"> </td><td class="header">D. Orchard</td></tr>
<tr><td class="header"> </td><td class="header">BEA Systems, Inc.</td></tr>
<tr><td class="header"> </td><td class="header">Mar 26, 2008</td></tr>
</table></td></tr></table>
<h1><br />URI Template<br />draft-gregorio-uritemplate-03</h1>
<h3>Status of this Memo</h3>
<p>
By submitting this Internet-Draft,
each author represents that any applicable patent or other IPR claims of which
he or she is aware have been or will be disclosed,
and any of which he or she becomes aware will be disclosed,
in accordance with Section 6 of BCP 79.</p>
<p>
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.</p>
<p>
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.”</p>
<p>
The list of current Internet-Drafts can be accessed at
<a href='http://www.ietf.org/ietf/1id-abstracts.txt'>http://www.ietf.org/ietf/1id-abstracts.txt</a>.</p>
<p>
The list of Internet-Draft Shadow Directories can be accessed at
<a href='http://www.ietf.org/shadow.html'>http://www.ietf.org/shadow.html</a>.</p>
<p>
This Internet-Draft will expire on September 27, 2008.</p>
<h3>Abstract</h3>
<p>
A URI Template is a compact sequence of characters
used for the construction of URIs.
This specification defines the URI Template
syntax and the process for expanding a URI Template into a
URI, along with guidelines and security considerations for the
use of URI Templates on the Internet.
The URI Template syntax allows for the construction
of strings that are a superset of URIs, allowing an implementation
to process any URI Template without knowing the scheme-specific
requirements of every possible resulting URI.
</p>
<h3>Editorial Note</h3>
<p>To provide feedback on this Internet-Draft, join the
<a href='http://lists.w3.org/Archives/Public/uri/'>W3C URI mailing
list (http://lists.w3.org/Archives/Public/uri/)</a>.
</p><a name="toc"></a><br /><hr />
<h3>Table of Contents</h3>
<p class="toc">
<a href="#anchor1">1.</a>
Introduction<br />
<a href="#anchor2">1.1.</a>
Overview<br />
<a href="#anchor3">1.2.</a>
Design Considerations<br />
<a href="#anchor4">1.3.</a>
Applicability<br />
<a href="#anchor5">1.4.</a>
Notational Conventions<br />
<a href="#anchor6">2.</a>
Characters<br />
<a href="#anchor7">3.</a>
Terminology<br />
<a href="#anchor8">4.</a>
URI Template<br />
<a href="#variables">4.1.</a>
Variables<br />
<a href="#expansions">4.2.</a>
Template Expansions<br />
<a href="#error">4.3.</a>
Error Handling<br />
<a href="#evaluating">4.4.</a>
URI Template Substitution<br />
<a href="#var">4.4.1.</a>
('var') substitution<br />
<a href="#opt">4.4.2.</a>
The 'opt' operator<br />
<a href="#neg">4.4.3.</a>
The 'neg' operator<br />
<a href="#prefix">4.4.4.</a>
The 'prefix' operator<br />
<a href="#append">4.4.5.</a>
The 'suffix' operator<br />
<a href="#join">4.4.6.</a>
The 'join' operator<br />
<a href="#list">4.4.7.</a>
The 'list' operator<br />
<a href="#examples">4.5.</a>
Examples<br />
<a href="#anchor9">5.</a>
Security Considerations<br />
<a href="#iana">6.</a>
IANA Considerations<br />
<a href="#appendix_a">7.</a>
Appendix A - Parsing URI Template Expansions<br />
<a href="#rfc.references1">8.</a>
Normative References<br />
<a href="#anchor11">Appendix A.</a>
Contributors<br />
<a href="#anchor12">Appendix B.</a>
Revision History<br />
<a href="#rfc.authors">§</a>
Authors' Addresses<br />
<a href="#rfc.copyright">§</a>
Intellectual Property and Copyright Statements<br />
</p>
<br clear="all" />
<a name="anchor1"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></table>
<a name="rfc.section.1"></a><h3>1.
Introduction</h3>
<p>
A URI Template provides a simple and extensible format
for URI construction. A URI Template is a string that
contains embedded expansions, text marked off in matching
braces ('{', '}'), that denotes a part of the string that is
to be substituted by a template processor to
produce a URI. A URI Template is transformed into a URI by
substituting the expansions with their calculated value.
</p>
<p>
Several specifications have defined URI Templates
with varying levels of formality, such as WSDL, WADL and OpenSearch. This
specification is derived from these concepts, giving a
rigorous definition to such templates.
</p>
<p>
This specification uses the terms "character" and "coded
character set" in accordance with the definitions provided
in <a class='info' href='#RFC2978'>[RFC2978]<span> (</span><span class='info'>Freed, N. and J. Postel, “IANA Charset Registration Procedures,” October 2000.</span><span>)</span></a>, and "character encoding" in place of what
<a class='info' href='#RFC2978'>[RFC2978]<span> (</span><span class='info'>Freed, N. and J. Postel, “IANA Charset Registration Procedures,” October 2000.</span><span>)</span></a> refers to as a "charset".
</p>
<a name="anchor2"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></table>
<a name="rfc.section.1.1"></a><h3>1.1.
Overview</h3>
<p>
A URI Template allows a structural description of URIs
while allowing a consumer of the template to construct a
final URI by providing the values of the expansion
variables. For example, given the following URI Template:
</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
http://www.example.com/users/{userid}</pre></div>
<p>And the following variable value
</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
userid := "fred"</pre></div>
<p>The expansion of the URI Template is:
</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
http://www.example.com/users/fred</pre></div>
<p>
Here is an example that constructs a query
from multiple variables:
</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
http://www.example.com/?{-join|&|query,number}</pre></div>
<p>And the following variables
</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
query := "mycelium"
number := 100</pre></div>
<p>The expansion of the URI Template is:
</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
http://www.example.com/?query=mycelium&number=100</pre></div>
<p>
The template expansion describes in a machine
readable manner how the URI is to be constructed.
</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
http://www.example.com/?{-join|&|query,number}
\____________________/
|
|
Join 'var=value' for each variable
in ['query', 'number'] with '&'.
</pre></div>
<a name="anchor3"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></table>
<a name="rfc.section.1.2"></a><h3>1.2.
Design Considerations</h3>
<p>
The URI Template syntax has been designed to carefully balance
the need for a powerful substitution mechanism with ease
of implementation and security. The syntax is designed
to be easy to parse while at the same time providing
enough flexibility to express many common templating
scenarios.
</p>
<p>
Another consideration was to keep the syntax and processing
in-line with the pre-existing templating schemes present
in OpenSearch, WSDL and WADL.
</p>
<p>
The final design consideration was control over
the placement of reserved characters in the
URI generated from a URI Template. The reserved characters
in a URI Template can only appear in the non-expansion
text, or in the argument to an operator, both locations
are dictated by the URI Template author. Given
the percent-encoding rules for variable values
this means that the source of all structure, i.e
reserved characters, in a URI generated from a
URI Template is decided by the URI Template author.
</p>
<a name="anchor4"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></table>
<a name="rfc.section.1.3"></a><h3>1.3.
Applicability</h3>
<p>
While URI Templates use a notation that is similar to some URI path matching
notations in web frameworks, URI Templates were not designed for that use case,
nor are they appropriate for that purpose.
URI Templates are not URIs, they do not identify an abstract or physical
resource, they are not to be treated like URIs,
nor should not be used in places where a URI would be expected.
</p>
<a name="anchor5"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></table>
<a name="rfc.section.1.4"></a><h3>1.4.
Notational Conventions</h3>
<p>
This specification uses the Augmented Backus-Naur Form
(ABNF) notation of <a class='info' href='#RFC5234'>[RFC5234]<span> (</span><span class='info'>Crocker, D. and P. Overell, “Augmented BNF for Syntax Specifications: ABNF,” January 2008.</span><span>)</span></a>, including
the following core ABNF syntax rules defined by that
specification: ALPHA (letters) and DIGIT (decimal
digits). See <a class='info' href='#RFC3986'>[RFC3986]<span> (</span><span class='info'>Berners-Lee, T., Fielding, R., and L. Masinter, “Uniform Resource Identifier (URI): Generic Syntax,” January 2005.</span><span>)</span></a> for the
definitions of the URI-reference, percent-encoded,
reserved, and unreserved rules.
</p>
<p>
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 <a class='info' href='#RFC2119'>[RFC2119]<span> (</span><span class='info'>Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.</span><span>)</span></a>.
</p>
<a name="anchor6"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></table>
<a name="rfc.section.2"></a><h3>2.
Characters</h3>
<p>
A URI Template is a sequence of characters, and has the same
issues as URIs with regard to codepoints and character sets.
That is, URI Template characters are frequently encoded
as octets for transport or presentation. This specification
does not mandate any particular character encoding for
mapping between URI characters and the octets used to store
or transmit those characters. When a URI appears in a
protocol element, the character encoding is defined by that
protocol; without such a definition, a URI is assumed to be
in the same character encoding as the surrounding text.
</p>
<p>
The ABNF notation defines its terminal values to be
non-negative integers (codepoints) based on the US-ASCII
coded character set <a class='info' href='#ASCII'>[ASCII]<span> (</span><span class='info'>American National Standards Institute, “Coded Character Set - 7-bit American Standard Code for Information Interchange,” 1986.</span><span>)</span></a>. Because a URI is a sequence of
characters, we must invert that relation in order to
understand the URI syntax. Therefore, the integer values
used by the ABNF must be mapped back to their corresponding
characters via US-ASCII in order to complete the syntax
rules.
</p>
<a name="anchor7"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></table>
<a name="rfc.section.3"></a><h3>3.
Terminology</h3>
<p>
</p>
<ul class="text">
<li>
template processor - A program or library that converts a URI
Template into a URI.
</li>
<li>
template expansion - The text between '{' and '}', including the
enclosing brackets.
</li>
</ul><p>
</p>
<a name="anchor8"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></table>
<a name="rfc.section.4"></a><h3>4.
URI Template</h3>
<p>
A URI Template is a sequence of characters that contains any number of
embedded template expansions, see <a class='info' href='#expansions'>Section 4.2<span> (</span><span class='info'>Template Expansions</span><span>)</span></a>.
Each expansion references one or
more variables whose values are used when determining the
substition value for an expansion. A URI Template becomes a
URI when all the template expansions are substituted with their
values (see <a class='info' href='#evaluating'>Section 4.4<span> (</span><span class='info'>URI Template Substitution</span><span>)</span></a>). The generated
URI will be a URI-reference, i.e. either an absolute
URI or a relative reference.
</p>
<a name="variables"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></table>
<a name="rfc.section.4.1"></a><h3>4.1.
Variables</h3>
<p>
Every variable is either a Unicode string or a list of Unicode strings.
</p>
<p>
A template expansion MAY reference variables that are unknown
to the template processor. Those variables are 'undefined'
and template expansion takes into consideration 'undefined' variables.
Conversely, every variable that he template processor knows about
is considered 'defined'.
</p>
<p>
A variable that contains a string
of length zero MUST NOT be considered 'undefined' by the template processor.
A list variable that contains no members, that is of zero length, MUST NOT
be considered 'undefined' by the template processor.
</p>
<p>
Beyond the scope of this
specification is the allowable programming constructs
that can be used for a list variable. For example, a Python
implementation might allow only built-in list types, or
it may allow any iterable to be used as the source for a
list variable.
</p>
<p>
Some variables may be supplied with default values. The default
value must comde from ( unreserved / pct-encoded ). Note that
there is no notation for supplying default values to list variables.
</p>
<p>
A variable may appear in more than one expansion in a
URI Template. The value used for that variable MUST
remain the same for every template expansion when
converting a URI Template into a URI.
</p>
<a name="expansions"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></table>
<a name="rfc.section.4.2"></a><h3>4.2.
Template Expansions</h3>
<p>
Template expansions are the parameterized components of a URI Template.
A template expansion MUST match the 'expansion' rule.
</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
op = 1*ALPHA
arg = *(reserved / unreserved / pct-encoded)
var = varname [ "=" vardefault ]
vars = var [ *("," var) ]
varname = (ALPHA / DIGIT)*(ALPHA / DIGIT / "." / "_" / "-" )
vardefault = *(unreserved / pct-encoded)
operator = "-" op "|" arg "|" vars
expansion = "{" ( var / operator ) "}"
</pre></div>
<a name="error"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></table>
<a name="rfc.section.4.3"></a><h3>4.3.
Error Handling</h3>
<p>
During template substitution error conditions may arise.
The exact circumstances for those errors are described in
<a class='info' href='#evaluating'>Section 4.4<span> (</span><span class='info'>URI Template Substitution</span><span>)</span></a>. When an error occurs the
template processor MUST NOT return a URI. It is language
specific and beyond the scope of this document how the
template processor signals that an error has occured and that
a URI will not be generated from the template.
</p>
<a name="evaluating"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></table>
<a name="rfc.section.4.4"></a><h3>4.4.
URI Template Substitution</h3>
<p>
Template substitution is the process of turning
a URI Template into a URI given definitions
for the variables used in the template. Substitution
replaces each expansion with its calculated value.
A template processor take two inputs, a URI Template and
a set of variables, and returns a URI-reference.
</p>
<p>
Before substitution the template processor MUST convert
every variable value into a sequence of characters in ( unreserved / pct-encoded ).
The template processor does that using the following algorithm:
The template processor normalizes the string using NFKC, converts it to
UTF-8 <a class='info' href='#RFC3629'>[RFC3629]<span> (</span><span class='info'>Yergeau, F., “UTF-8, a transformation format of ISO 10646,” November 2003.</span><span>)</span></a>, and then
every octet of the UTF-8 string that falls outside of
( unreserved ) MUST be percent-encoded, as
per <a class='info' href='#RFC3986'>[RFC3986]<span> (</span><span class='info'>Berners-Lee, T., Fielding, R., and L. Masinter, “Uniform Resource Identifier (URI): Generic Syntax,” January 2005.</span><span>)</span></a>, section 2.1.
For variables that are lists, the above algorithm is applied
to each value in the list.
</p>
<p>
The Unicode Standard <a class='info' href='#UNIV4'>[UNIV4]<span> (</span><span class='info'>The Unicode Consortium, “The Unicode Standard, Version 4.0.1, defined by: The Unicode Standard, Version 4.0 (Reading, MA, Addison-Wesley, 2003. ISBN 0-321-18578-1), as amended by Unicode 4.0.1 (http://www.unicode.org/versions/Unicode4.0.1/),” March 2004.</span><span>)</span></a> defines various
equivalences between sequences of characters for various
purposes. Unicode Standard Annex #15 <a class='info' href='#UTR15'>[UTR15]<span> (</span><span class='info'>Davis, M. and M. Duerst, “Unicode Normalization Forms,” April 2003.</span><span>)</span></a> defines
various Normalization Forms for these equivalences, in
particular Normalization Form KC (NFKC, Compatibility
Decomposition, followed by Canonical Composition). Since
different Normalized Forms unicode strings will have
different UTF-8 represenations the only way to guarantee
that template processors will produce the same URI is to
require a common Normalized Form.
</p>
<p>
Requiring that all characters outside of ( unreserved ) be
percent encoded means that the only characters outside of
( unreserved ) that will appear in the generated URI-reference
will come from outside the template expansions in the URI Template or
from the argument of a template expansion. This means that the
designer of the URI Template determines the placement of reserved characters in the
resulting URI, and thus the structure of the resulting generated URI-reference.
</p>
<p>
If the expansion is an operator then the substitution value
is determined by the given operator. Each operator
works only on the variables that are defined within
their expansion.
</p>
<p>
The result of substitution
MUST match the URI-reference rule and SHOULD also match
any known rules for the scheme of the resulting URI.
</p>
<p>
If a template processor encounters an operator that it does not
understand then it MUST fail and MUST NOT produce a URI from
the URI Template. The list of operators that a template processor
knows is not constrained by this specification, that is, later
specifications may add new operators.
</p>
<p>
Every expansion consists of either a variable ('var') or
an operator expression ('operator'), and the rules for how
to expand each of these is given below. For every expansion
a template MUST have at least one variable name in the
template expansion. It is an error if no variables are supplied.
All of the variables supplied to a template expansion MAY be undefined
and the expansion rules below specify how to process the template expansion
in that situation.
</p>
<a name="var"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></table>
<a name="rfc.section.4.4.1"></a><h3>4.4.1.
('var') substitution</h3>
<p>
In a variable ('var')
expansion, if the variable is defined then
substitute the value of the variable, otherwise
substitute the default value. If no default value is
given then substitute with the empty string.
</p>
<p>
Example:
</p>
<div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
foo := "fred"
"{foo}" -> "fred"
"{bar=wilma}" -> "wilma"
"{baz}" -> ""
</pre></div><p>
</p>
<a name="opt"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></table>
<a name="rfc.section.4.4.2"></a><h3>4.4.2.
The 'opt' operator</h3>
<p>
If each variable is undefined or an empty list
then substitute the empty string, otherwise
substitute the value of 'arg'.
</p>
<p>
Example:
</p>
<div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
foo := "fred"
"{-opt|[email protected]|foo}" -> "[email protected]"
"{-opt|[email protected]|bar}" -> ""
</pre></div><p>
</p>
<a name="neg"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></table>
<a name="rfc.section.4.4.3"></a><h3>4.4.3.
The 'neg' operator</h3>
<p>
If each variable is undefined or an empty list
then substitute the value of arg, otherwise
substitute the empty string.
</p>
<p>
Example:
</p>
<div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
foo := "fred"
"{-neg|[email protected]|foo}" -> ""
"{-neg|[email protected]|bar}" -> "[email protected]"
</pre></div><p>
</p>
<a name="prefix"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></table>
<a name="rfc.section.4.4.4"></a><h3>4.4.4.
The 'prefix' operator</h3>
<p>
The prefix operator MUST only have one variable in
its expansion. More than one variable is an error condition.
If the variable is undefined or an empty
list then substitute the empty string. If the variable
is a defined non-list then substitute the value of arg preceeded
by the value of the variable. If the variable is a defined list
then substitute the concatenation of every list value preceeded
by the arg.
</p>
<p>
Example:
</p>
<div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
foo := "fred"
bar := ["fee", "fi", "fo", "fum"]
baz := []
"{-prefix|/|foo}" -> "/fred"
"{-prefix|/|bar}" -> "/fee/fi/fo/fum"
"{-prefix|/|baz}" -> ""
"{-prefix|/|qux}" -> ""
</pre></div><p>
</p>
<a name="append"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></table>
<a name="rfc.section.4.4.5"></a><h3>4.4.5.
The 'suffix' operator</h3>
<p>
The prefix operator MUST only have one variable in
its expansion. More than one variable is an error condition.
If the variable is undefined or an empty
list then substitute the empty string. If the variable
is a defined non-list then substitute the value of arg followed
by the value of the variable. If the variable is a defined list
then substitute the concatenation of every list value followed
by the arg.
</p>
<p>
Example:
</p>
<div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
foo := "fred"
bar := ["fee", "fi", "fo", "fum"]
baz := []
"{-suffix|/|foo}" -> "fred/"
"{-suffix|/|bar}" -> "fee/fi/fo/fum/"
"{-suffix|/|baz}" -> ""
"{-suffix|/|qux}" -> ""
</pre></div><p>
</p>
<a name="join"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></table>
<a name="rfc.section.4.4.6"></a><h3>4.4.6.
The 'join' operator</h3>
<p>
Supplying a list variable to the join operator
is an error. For each variable that is defined and non-empty
create a keyvalue string that is the concatenation
of the variable name, "=", and the
variable value. Concatenate more than one keyvalue
string with intervening values of arg to
create the substitution value. The order of variables
MUST be preserved during substitution.
</p>
<p>
Example:
</p>
<div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
foo := "fred"
bar := "barney"
baz := ""
"{-join|&|foo,bar,baz,qux}" -> "foo=fred&bar=barney&baz="
"{-join|&|bar}" -> "bar=barney"
"{-join|&|qux}" -> ""
</pre></div><p>
</p>
<a name="list"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></table>
<a name="rfc.section.4.4.7"></a><h3>4.4.7.
The 'list' operator</h3>
<p>
The listjoin operator MUST have only one variable
in its expansion and that variable must be a list.
More than one variable is an error.
If the list is non-empty then substitute
the concatenation of all the list members with intervening
values of arg. If the list is empty or the variable is undefined them
substitute the empty string.
</p>
<p>
Example:
</p>
<div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
foo := ["fred", "barney", "wilma"]
bar := ["a", "", "c"]
baz := ["betty"]
qux := []
"{-list|/|foo}" -> "fred/barney/wilma"
"{-list|/|bar}" -> "a//c"
"{-list|/|baz}" -> "betty"
"{-list|/|qux}" -> ""
"{-list|/|corge}" -> ""
</pre></div><p>
</p>
<a name="examples"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></table>
<a name="rfc.section.4.5"></a><h3>4.5.
Examples</h3>
<br /><hr class="insert" />
<a name="example-table"></a>
<p style='text-align: center'>
Given the following template variable names and
values:
</p><table class="full" align="center" border="0" cellpadding="2" cellspacing="2">
<col align="left"><col align="left">
<tr><th align="left">Name</th><th align="left">Value</th></tr>
<tr>
<td align="left">foo</td>
<td align="left">\u03d3</td>
</tr>
<tr>
<td align="left">bar</td>
<td align="left">fred</td>
</tr>
<tr>
<td align="left">baz</td>
<td align="left">10,20,30</td>
</tr>
<tr>
<td align="left">qux</td>
<td align="left">["10","20","30"]</td>
</tr>
<tr>
<td align="left">corge</td>
<td align="left">[]</td>
</tr>
<tr>
<td align="left">grault</td>
<td align="left"> </td>
</tr>
<tr>
<td align="left">garply</td>
<td align="left">a/b/c</td>
</tr>
<tr>
<td align="left">waldo</td>
<td align="left">ben & jerrys</td>
</tr>
<tr>
<td align="left">fred</td>
<td align="left">["fred", "", "wilma"]</td>
</tr>
<tr>
<td align="left">plugh</td>
<td align="left">["\u017F\u0307", "\u0073\u0307"]</td>
</tr>
<tr>
<td align="left">1-a_b.c</td>
<td align="left">200</td>
</tr>
</table>
<br clear="all" />
<table border="0" cellpadding="0" cellspacing="2" align="center"><tr><td align="center"><font face="monaco, MS Sans Serif" size="1"><b> Table 1 </b></font><br /></td></tr></table><hr class="insert" />
<p>
The variable 'foo' is the unicode character GREEK UPSILON WITH ACUTE AND HOOK SYMBOL.
This character was chosen because it is one of only three characters that has
a different normal form for each of the four normalization forms (NFC, NFD, NFKC, NFKD).
The name 'xyzzy' has not been defined, the value of 'grault' is the empty string.
The variables qux, corge, fred, and plugh are lists.
</p>
<p>The following URI Templates will be expanded as shown:
</p>
<p> ----
</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
http://example.org/?q={bar}
http://example.org/?q=fred
/{xyzzy}
/
http://example.org/?{-join|&|foo,bar,xyzzy,baz}
http://example.org/?foo=%CE%8E&bar=fred&baz=10%2C20%2C30
http://example.org/?d={-list|,|qux}
http://example.org/?d=10,20,30
http://example.org/?d={-list|&d=|qux}
http://example.org/?d=10&d=20&d=30
http://example.org/{bar}{bar}/{garply}
http://example.org/fredfred/a%2Fb%2Fc
http://example.org/{bar}{-prefix|/|fred}
http://example.org/fred/fred//wilma
{-neg|:|corge}{-suffix|:|plugh}
:%E1%B9%A1:%E1%B9%A1:
../{waldo}/
../ben%20%26%20jerrys/
telnet:192.0.2.16{-opt|:80|grault}
telnet:192.0.2.16:80
:{1-a_b.c}:
:200:
</pre></div>
<p> ----
</p>
<a name="anchor9"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></table>
<a name="rfc.section.5"></a><h3>5.
Security Considerations</h3>
<p>
A URI Template does not contain active or executable content. Other
security considerations are the same as those for URIs, see section 7
of RFC3986.
</p>
<a name="iana"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></table>
<a name="rfc.section.6"></a><h3>6.
IANA Considerations</h3>
<p>
In common with RFC3986, URI scheme names form a registered
namespace that is managed by IANA according to the
procedures defined in <a class='info' href='#RFC4395'>[RFC4395]<span> (</span><span class='info'>Hansen, T., Hardie, T., and L. Masinter, “Guidelines and Registration Procedures for New URI Schemes,” February 2006.</span><span>)</span></a>. No IANA
actions are required by this document.
</p>
<a name="appendix_a"></a><br /><hr />
<table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></table>
<a name="rfc.section.7"></a><h3>7.
Appendix A - Parsing URI Template Expansions</h3>
<p>
Parsing a valid URI Template expansion does not require
building a parser from the given ABNF. Instead, the set of allowed
characters in each part of URI Template expansion has been
chosen to avoid complex parsing, and breaking an expansion into
its component parts can be achieved by a series of splits
of the character string.
</p>
<p>
Here is example Python code that parses a URI Template
expansion and returns the operator, argument, and
variables as a tuple. The variables are returned
as a dictionary of variable names mapped to their
default values. If no default is given then the
name maps to None.
</p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
def parse_expansion(expansion):
if "|" in expansion:
(op, arg, vars_) = expansion.split("|")
op = op[1:]
else:
(op, arg, vars_) = (None, None, expansion)
vars_ = vars_.split(",")
variables = {}