path: root/lib/stdlib/doc/src/uri_string.xml

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  <header>
    <copyright>
      <year>2017</year><year>2017</year>
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      Licensed under the Apache License, Version 2.0 (the "License");
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    <title>uri_string</title>
    <prepared>Péter Dimitrov</prepared>
    <docno>1</docno>
    <date>2017-10-24</date>
    <rev>A</rev>
  </header>
  <module>uri_string</module>
  <modulesummary>URI processing functions.</modulesummary>
  <description>
    <p>This module contains functions for parsing and handling URIs (RFC 3986) and
    form-urlencoded query strings (RFC 1866).</p>
    <p>A URI is an identifier consisting of a sequence of characters   matching the syntax
    rule named <em>URI</em> in <em>RFC 3986</em>.</p>
    <p>  The generic URI syntax consists of a hierarchical sequence of components referred
    to as the scheme, authority, path, query, and fragment:</p>
    <pre>
    URI         = scheme ":" hier-part [ "?" query ] [ "#" fragment ]
    hier-part   = "//" authority path-abempty
                   / path-absolute
                   / path-rootless
                   / path-empty
    scheme      = ALPHA *( ALPHA / DIGIT / "+" / "-" / "." )
    authority   = [ userinfo "@" ] host [ ":" port ]
    userinfo    = *( unreserved / pct-encoded / sub-delims / ":" )

    reserved    = gen-delims / sub-delims
    gen-delims  = ":" / "/" / "?" / "#" / "[" / "]" / "@"
    sub-delims  = "!" / "$" / "&amp;" / "'" / "(" / ")"
                / "*" / "+" / "," / ";" / "="

    unreserved  = ALPHA / DIGIT / "-" / "." / "_" / "~"
    </pre><br></br>
    <p>The interpretation of a URI depends only on the characters used and not on how those
    characters are represented in a network protocol.</p>
    <p>The functions implemented by this module covers the following use cases:</p>
    <list type="bulleted">
      <item>Parsing URIs<br></br>
      <c>parse/1</c></item>
      <item>Recomposing URIs<br></br>
      <c>recompose/2</c></item>
      <item>Transcoding URIs<br></br>
      <c>transcode/2</c></item>
      <item>Working with form-urlencoded query strings<br></br>
      <c>compose_query/[1,2], dissect_query/1</c></item>
    </list>
    <p>There are four different encodings present during the handling of URIs:</p>
    <list type="bulleted">
      <item>Inbound binary encoding in binaries</item>
      <item>Inbound percent-encoding in lists and binaries</item>
      <item>Outbound binary encoding in binaries</item>
      <item>Outbound percent-encoding in lists and binaries</item>
    </list>
    <p>Unless otherwise specified the return value type and encoding are the same as the input
    type and encoding. That is, binary input returns binary output, list input returns a list
    output but mixed input returns list output. Input and output encodings are the same except
    for <c>transcode/2</c>.</p>
    <p>All of the functions but <c>transcode/2</c> expects input as unicode codepoints in
    lists, UTF-8 encoding in binaries and UTF-8 encoding in percent-encoded URI parts.
    <c>transcode/2</c> provides the means to convert between the supported URI encodings.</p>
  </description>

  <datatypes>
    <datatype>
      <name name="uri_map"/>
      <desc>
        <p>URI map holding the main components of a URI.</p>
      </desc>
    </datatype>
    <datatype>
      <name name="uri_string"/>
      <desc>
        <p>List of unicode codepoints, UTF-8 encoded binary, or a mix of the two,
        representing an RFC 3986 compliant URI (<em>percent-encoded form</em>).
        A URI is a sequence of characters from a very limited set: the letters of
        the basic Latin alphabet, digits, and a few special characters.</p>
      </desc>
    </datatype>
  </datatypes>

  <funcs>

    <func>
      <name name="compose_query" arity="1"/>
      <fsummary>Compose urlencoded query string.</fsummary>
      <desc>
        <p>Composes a form-urlencoded <c><anno>QueryString</anno></c> based on a
	<c><anno>QueryList</anno></c>, a list of unescaped key-value pairs.
	Media type <c>application/x-www-form-urlencoded</c> is defined in section
	8.2.1 of <c>RFC 1866</c> (HTML 2.0). Reserved and unsafe characters, as
	defined by RFC 1738 (Uniform Resource Locators), are percent-encoded.
	</p>
        <p><em>Example:</em></p>
        <pre>
1> <input>uri_string:compose_query([{"foo bar","1"},{"city","örebro"}]).</input>
<![CDATA["foo+bar=1&amp;city=%C3%B6rebro"]]>
	</pre>
      </desc>
    </func>

    <func>
      <name name="compose_query" arity="2"/>
      <fsummary>Compose urlencoded query string.</fsummary>
      <desc>
        <p>Same as <c>compose_query/1</c> but with an additional
	<c><anno>Options</anno></c> parameter, that controls the type of separator used
	between key-value pairs. There are three supported separator types: <c>amp</c> (<![CDATA[&]]>), <c>escaped_amp</c> (<![CDATA[&amp;]]>) and <c>semicolon</c> (;). If the parameter <c><anno>Options</anno></c> is empty, separator takes the default value (<c>escaped_amp</c>).</p>
        <p><em>Example:</em></p>
        <pre>
1> <input>uri_string:compose_query([{"foo bar","1"},{"city","örebro"}],</input>
2> [{separator, semicolon}]).
"foo+bar=1;city=%C3%B6rebro"
	</pre>
      </desc>
    </func>

    <func>
      <name name="dissect_query" arity="1"/>
      <fsummary>Dissect query string.</fsummary>
      <desc>
        <p>Dissects an urlencoded <c><anno>QueryString</anno></c> and returns a
	<c><anno>QueryList</anno></c>, a list of unescaped key-value pairs.
	Media type <c>application/x-www-form-urlencoded</c> is defined in section
	8.2.1 of <c>RFC 1866</c> (HTML 2.0). Percent-encoded segments are decoded
	as defined by RFC 1738 (Uniform Resource Locators).
	</p>
        <p><em>Example:</em></p>
        <pre>
1> <input>uri_string:dissect_query("foo+bar=1;city=%C3%B6rebro").</input>
[{"foo bar","1"},{"city","örebro"}]
	</pre>
      </desc>
    </func>

    <func>
      <name name="parse" arity="1"/>
      <fsummary>Parse URI into a map.</fsummary>
      <desc>
        <p>Returns a <c>URIMap</c>, that is a <em>uri_map()</em> with the parsed components
	of the <c><anno>URIString</anno></c>.</p>
        <p>If parsing fails, an error tuple is returned.</p>
        <p><em>Example:</em></p>
        <pre>
1> <input>uri_string:parse("foo://[email protected]:8042/over/there?name=ferret#nose").</input>
#{fragment => "nose",host => "example.com",
  path => "/over/there",port => 8042,query => "name=ferret",
  scheme => foo,userinfo => "user"}
	</pre>
      </desc>
    </func>

    <func>
      <name name="recompose" arity="1"/>
      <fsummary>Recompose URI.</fsummary>
      <desc>
        <p>Returns an RFC 3986 compliant <c><anno>URIString</anno></c> (percent-encoded).</p>
	<p>If the <c><anno>URIMap</anno></c> is invalid, an error tuple is returned.</p>
        <p><em>Example:</em></p>
        <pre>
1> <input>URIMap = #{fragment => "nose", host => "example.com", path => "/over/there",</input>
port => 8042, query => "name=ferret", scheme => "foo", userinfo => "user"}.
#{fragment => "top",host => "example.com",
  path => "/over/there",port => 8042,query => "?name=ferret",
  scheme => foo,userinfo => "user"}

2> <input>uri_string:recompose(URIMap).</input>
"foo://example.com:8042/over/there?name=ferret#nose"</pre>
      </desc>
    </func>

    <func>
      <name name="transcode" arity="2"/>
      <fsummary>Transcode URI.</fsummary>
      <desc>
        <p>Transcodes an RFC 3986 compliant <c><anno>URIString</anno></c>,
	where <c><anno>Options</anno></c> is a list of tagged tuples, specifying the inbound
	(<c>in_encoding</c>) and outbound (<c>out_encoding</c>) encodings.</p>
	<p>If an argument is invalid, an error tuple is returned.</p>
        <p><em>Example:</em></p>
        <pre>
1> <input><![CDATA[uri_string:transcode(<<"foo%00%00%00%F6bar"/utf32>>,]]></input>
2> [{in_encoding, utf32},{out_encoding, utf8}]).
<![CDATA[<<"foo%C3%B6bar"/utf8>>]]>
	</pre>
      </desc>
    </func>

  </funcs>
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