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

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  <header>
    <copyright>
      <year>2017</year><year>2017</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      Licensed under the Apache License, Version 2.0 (the "License");
      you may not use this file except in compliance with the License.
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      distributed under the License is distributed on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      See the License for the specific language governing permissions and
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    </legalnotice>

    <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
    (<url href="https://www.ietf.org/rfc/rfc3986.txt">RFC 3986</url>) and
    form-urlencoded query strings (<url href="https://www.ietf.org/rfc/rfc1866.txt">RFC 1866</url>).
    </p>
    <p>A URI is an identifier consisting of a sequence of characters   matching the syntax
    rule named <em>URI</em> in <url href="https://www.ietf.org/rfc/rfc3986.txt">RFC 3986</url>.
    </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 cover the following use cases:</p>
    <list type="bulleted">
      <item>Parsing URIs into its components and returing a map<br></br>
      <seealso marker="#parse/1"><c>parse/1</c></seealso>
      </item>
      <item>Recomposing a map of URI components into a URI string<br></br>
      <seealso marker="#recompose/1"><c>recompose/1</c></seealso>
      </item>
      <item>Changing inbound binary and percent-encoding of URIs<br></br>
      <seealso marker="#transcode/2"><c>transcode/2</c></seealso>
      </item>
      <item>Transforming URIs into a normalized form<br></br>
      <seealso marker="#normalize/1"><c>normalize/1</c></seealso>
      </item>
      <item>Composing form-urlencoded query strings from a list of key-value pairs<br></br>
      <seealso marker="#compose_query/1"><c>compose_query/1</c></seealso><br></br>
      <seealso marker="#compose_query/2"><c>compose_query/2</c></seealso>
      </item>
      <item>Dissecting form-urlencoded query strings into a list of key-value pairs<br></br>
      <seealso marker="#dissect_query/1"><c>dissect_query/1</c></seealso>
      </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>Functions with <c>uri_string()</c> argument accept lists, binaries and
    mixed lists (lists with binary elements) as input type. All of the functions but
    <c>transcode/2</c> expects input as lists of unicode codepoints, UTF-8 encoded binaries
    and UTF-8 percent-encoded URI parts ("%C3%B6" corresponds to the unicode character "ö").</p>
    <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.</p>
    <p>In case of lists there is only percent-encoding. In binaries, however, both binary encoding
    and percent-encoding shall be considered. <c>transcode/2</c> provides the means to convert
    between the supported encodings, it takes a <c>uri_string()</c> and a list of options
    specifying inbound and outbound encodings.</p>
    <p><url href="https://www.ietf.org/rfc/rfc3986.txt">RFC 3986</url> does not mandate any specific
    character encoding and it is usually defined by the protocol or surrounding text. This library
    takes the same assumption, binary and percent-encoding are handled as one configuration unit,
    they cannot be set to different values.</p>
  </description>

  <datatypes>
    <datatype>
      <name name="error"/>
      <desc>
        <p>Error tuple indicating the type of error. Possible values of the second component:</p>
	<list type="bulleted">
	  <item><c>invalid_character</c></item>
	  <item><c>invalid_input</c></item>
	  <item><c>invalid_map</c></item>
	  <item><c>invalid_percent_encoding</c></item>
	  <item><c>invalid_scheme</c></item>
	  <item><c>invalid_uri</c></item>
	  <item><c>invalid_utf8</c></item>
	  <item><c>missing_value</c></item>
	</list>
	<p>The third component is a list or binary providing additional information about the
	cause of the error.</p>
      </desc>
    </datatype>
    <datatype>
      <name name="uri_map"/>
      <desc>
        <p>Map holding the main components of a URI.</p>
      </desc>
    </datatype>
    <datatype>
      <name name="uri_string"/>
      <desc>
        <p>List of unicode codepoints, a UTF-8 encoded binary, or a mix of the two,
        representing an <url href="https://www.ietf.org/rfc/rfc3986.txt">RFC 3986</url>
	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 non-percent-encoded key-value pairs.
        Form-urlencoding is defined in section
	8.2.1 of <url href="https://www.ietf.org/rfc/rfc1866.txt">RFC 1866</url>
	(HTML 2.0) for media type <c>application/x-www-form-urlencoded</c>.
	Reserved and unsafe characters, as
	defined by <url href="https://www.ietf.org/rfc/rfc1738.txt">RFC 1738</url>
	(Uniform Resource Locators), are percent-encoded.</p>
	<p>See also the opposite operation <seealso marker="#dissect_query/1">
	<c>dissect_query/1</c></seealso>.
	</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"]]>
2> <![CDATA[uri_string:compose_query([{<<"foo bar">>,<<"1">>},
2> {<<"city">>,<<"örebro"/utf8>>}]).]]>
<![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>See also the opposite operation <seealso marker="#dissect_query/1">
	<c>dissect_query/1</c></seealso>.
	</p>
        <p><em>Example:</em></p>
        <pre>
1> <input>uri_string:compose_query([{"foo bar","1"},{"city","örebro"}],</input>
1> [{separator, amp}]).
<![CDATA["foo+bar=1&city=%C3%B6rebro"
2> uri_string:compose_query([{<<"foo bar">>,<<"1">>},
2> {<<"city">>,<<"örebro"/utf8>>}], [{separator, escaped_amp}]).]]>
<![CDATA[<<"foo+bar=1&amp;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 non-percent-encoded key-value pairs.
        Form-urlencoding is defined in section
	8.2.1 of <url href="https://www.ietf.org/rfc/rfc1866.txt">RFC 1866</url>
	(HTML 2.0) for media type <c>application/x-www-form-urlencoded</c>.
	Percent-encoded segments are decoded as defined by
	<url href="https://www.ietf.org/rfc/rfc1738.txt">RFC 1738</url>
	(Uniform Resource Locators).</p>
	<p>Supported separator types: <c>amp</c> (<![CDATA[&]]>), <c>escaped_amp</c>
	(<![CDATA[&amp;]]>) and <c>semicolon</c> (;).</p>
	<p>See also the opposite operation <seealso marker="#compose_query/1">
	<c>compose_query/1</c></seealso>.
	</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"}]
2> <![CDATA[uri_string:dissect_query(<<"foo+bar=1&city=%C3%B6rebro">>).]]>
<![CDATA[[{<<"foo bar">>,<<"1">>},{<<"city">>,<<"örebro"/utf8>>}] ]]>
	</pre>
      </desc>
    </func>

    <func>
      <name name="normalize" arity="1"/>
      <fsummary>Syntax-based normalization.</fsummary>
      <desc>
        <p>Transforms <c><anno>URIString</anno></c> into a normalized form
	using Syntax-Based Normalization as defined by
	<url href="https://www.ietf.org/rfc/rfc3986.txt">RFC 3986</url>.</p>
	<p>This function implements case normalization, percent-encoding
	normalization, path segment normalization and scheme based normalization
	for HTTP(S) with basic support for FTP, SSH, SFTP and TFTP.</p>
        <p><em>Example:</em></p>
        <pre>
1> <input>uri_string:normalize("/a/b/c/./../../g").</input>
"/a/g"
2> <![CDATA[uri_string:normalize(<<"mid/content=5/../6">>).]]>
<![CDATA[<<"mid/6">>]]>
3> uri_string:normalize("http://localhost:80").
"https://localhost/"
	</pre>
      </desc>
    </func>

    <func>
      <name name="parse" arity="1"/>
      <fsummary>Parse URI into a map.</fsummary>
      <desc>
        <p>Parses an <url href="https://www.ietf.org/rfc/rfc3986.txt">RFC 3986</url>
	compliant <c>uri_string()</c> into a <c>uri_map()</c>, that holds the parsed
	components of the <c>URI</c>.
	If parsing fails, an error tuple is returned.</p>
	<p>See also the opposite operation <seealso marker="#recompose/1">
	<c>recompose/1</c></seealso>.</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"}
2> <![CDATA[uri_string:parse(<<"foo://[email protected]:8042/over/there?name=ferret">>).]]>
<![CDATA[#{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>Creates an <url href="https://www.ietf.org/rfc/rfc3986.txt">RFC 3986</url> compliant
	<c><anno>URIString</anno></c> (percent-encoded), based on the components of
	<c><anno>URIMap</anno></c>.
	If the <c><anno>URIMap</anno></c> is invalid, an error tuple is returned.</p>
	<p>See also the opposite operation <seealso marker="#parse/1">
	<c>parse/1</c></seealso>.</p>
        <p><em>Example:</em></p>
        <pre>
1> <input>URIMap = #{fragment => "nose", host => "example.com", path => "/over/there",</input>
1> 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 <url href="https://www.ietf.org/rfc/rfc3986.txt">RFC 3986</url>
	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. <c>in_encoding</c>
	and <c>out_encoding</c> specifies both binary encoding and percent-encoding for the
	input and output data. Mixed encoding, where binary encoding is not the same as
	percent-encoding, is not supported.
	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>
1> [{in_encoding, utf32},{out_encoding, utf8}]).
<![CDATA[<<"foo%C3%B6bar"/utf8>>]]>
2> uri_string:transcode("foo%F6bar", [{in_encoding, latin1},
2> {out_encoding, utf8}]).
"foo%C3%B6bar"
	</pre>
      </desc>
    </func>

  </funcs>
</erlref>