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NAME

       uri_string - URI processing functions.

DESCRIPTION

       This  module  contains  functions  for  parsing  and  handling  URIs  (RFC 3986) and form-
       urlencoded query strings (HTML 5.2).

       Parsing and serializing non-UTF-8 form-urlencoded query strings are also  supported  (HTML
       5.0).

       A  URI  is  an  identifier consisting of a sequence of characters matching the syntax rule
       named URI in RFC 3986.

       The generic URI syntax consists of a hierarchical sequence of components  referred  to  as
       the scheme, authority, path, query, and fragment:

           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  = "!" / "$" / "&" / "'" / "(" / ")"
                       / "*" / "+" / "," / ";" / "="

           unreserved  = ALPHA / DIGIT / "-" / "." / "_" / "~"

       The  interpretation  of  a  URI  depends  only on the characters used and not on how those
       characters are represented in a network protocol.

       The functions implemented by this module cover the following use cases:

         * Parsing URIs into its components and returing a map
           parse/1

         * Recomposing a map of URI components into a URI string
           recompose/1

         * Changing inbound binary and percent-encoding of URIs
           transcode/2

         * Transforming URIs into a normalized form
           normalize/1
           normalize/2

         * Composing form-urlencoded query strings from a list of key-value pairs
           compose_query/1
           compose_query/2

         * Dissecting form-urlencoded query strings into a list of key-value pairs
           dissect_query/1

       There are four different encodings present during the handling of URIs:

         * Inbound binary encoding in binaries

         * Inbound percent-encoding in lists and binaries

         * Outbound binary encoding in binaries

         * Outbound percent-encoding in lists and binaries

       Functions with uri_string() argument accept lists, binaries and mixed  lists  (lists  with
       binary  elements)  as  input  type.  All of the functions but transcode/2 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").

       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.

       In  case  of  lists  there  is  only  percent-encoding.  In binaries, however, both binary
       encoding and percent-encoding shall be  considered.  transcode/2  provides  the  means  to
       convert  between  the  supported  encodings, it takes a uri_string() and a list of options
       specifying inbound and outbound encodings.

       RFC 3986 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.

DATA TYPES

       error() = {error, atom(), term()}

              Error tuple indicating the type of error. Possible values of the second component:

                * invalid_character

                * invalid_encoding

                * invalid_input

                * invalid_map

                * invalid_percent_encoding

                * invalid_scheme

                * invalid_uri

                * invalid_utf8

                * missing_value

              The third component is a term providing additional information about the  cause  of
              the error.

       uri_map() =
           #{fragment => unicode:chardata(),
             host => unicode:chardata(),
             path => unicode:chardata(),
             port => integer() >= 0 | undefined,
             query => unicode:chardata(),
             scheme => unicode:chardata(),
             userinfo => unicode:chardata()} |
           #{}

              Map holding the main components of a URI.

       uri_string() = iodata()

              List  of  unicode  codepoints,  a  UTF-8  encoded  binary,  or  a  mix  of the two,
              representing an RFC 3986 compliant URI (percent-encoded form). 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.

EXPORTS

       compose_query(QueryList) -> QueryString

              Types:

                 QueryList = [{unicode:chardata(), unicode:chardata() | true}]
                 QueryString = uri_string() | error()

              Composes a form-urlencoded QueryString based on a QueryList, a list of non-percent-
              encoded  key-value  pairs.  Form-urlencoding is defined in section 4.10.21.6 of the
              HTML 5.2 specification and in section 4.10.22.6 of the HTML 5.0  specification  for
              non-UTF-8 encodings.

              See also the opposite operation dissect_query/1.

              Example:

              1> uri_string:compose_query([{"foo bar","1"},{"city","örebro"}]).
              "foo+bar=1&city=%C3%B6rebro"
              2> uri_string:compose_query([{<<"foo bar">>,<<"1">>},
              2> {<<"city">>,<<"örebro"/utf8>>}]).
              <<"foo+bar=1&city=%C3%B6rebro">>

       compose_query(QueryList, Options) -> QueryString

              Types:

                 QueryList = [{unicode:chardata(), unicode:chardata() | true}]
                 Options = [{encoding, atom()}]
                 QueryString = uri_string() | error()

              Same as compose_query/1 but with an additional Options parameter, that controls the
              encoding ("charset") used by  the  encoding  algorithm.  There  are  two  supported
              encodings: utf8 (or unicode) and latin1.

              Each  character  in  the  entry's name and value that cannot be expressed using the
              selected character encoding, is  replaced  by  a  string  consisting  of  a  U+0026
              AMPERSAND  character  (&),  a  "#"  (U+0023)  character,  one  or more ASCII digits
              representing the Unicode code point of the character in base ten, and finally a ";"
              (U+003B) character.

              Bytes that are out of the range 0x2A, 0x2D, 0x2E, 0x30 to 0x39, 0x41 to 0x5A, 0x5F,
              0x61 to 0x7A, are percent-encoded (U+0025 PERCENT SIGN character  (%)  followed  by
              uppercase ASCII hex digits representing the hexadecimal value of the byte).

              See also the opposite operation dissect_query/1.

              Example:

              1> uri_string:compose_query([{"foo bar","1"},{"city","örebro"}],
              1> [{encoding, latin1}]).
              "foo+bar=1&city=%F6rebro"
              2> uri_string:compose_query([{<<"foo bar">>,<<"1">>},
              2> {<<"city">>,<<"東京"/utf8>>}], [{encoding, latin1}]).
              <<"foo+bar=1&city=%26%2326481%3B%26%2320140%3B">>

       dissect_query(QueryString) -> QueryList

              Types:

                 QueryString = uri_string()
                 QueryList =
                     [{unicode:chardata(), unicode:chardata() | true}] | error()

              Dissects  an urlencoded QueryString and returns a QueryList, a list of non-percent-
              encoded key-value pairs. Form-urlencoding is defined in section  4.10.21.6  of  the
              HTML  5.2  specification and in section 4.10.22.6 of the HTML 5.0 specification for
              non-UTF-8 encodings.

              See also the opposite operation compose_query/1.

              Example:

              1> uri_string:dissect_query("foo+bar=1&city=%C3%B6rebro").
              [{"foo bar","1"},{"city","örebro"}]
              2> uri_string:dissect_query(<<"foo+bar=1&city=%26%2326481%3B%26%2320140%3B">>).
              [{<<"foo bar">>,<<"1">>},
               {<<"city">>,<<230,157,177,228,186,172>>}]

       normalize(URI) -> NormalizedURI

              Types:

                 URI = uri_string() | uri_map()
                 NormalizedURI = uri_string() | error()

              Transforms an URI into  a  normalized  form  using  Syntax-Based  Normalization  as
              defined by RFC 3986.

              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.

              Example:

              1> uri_string:normalize("/a/b/c/./../../g").
              "/a/g"
              2> uri_string:normalize(<<"mid/content=5/../6">>).
              <<"mid/6">>
              3> uri_string:normalize("http://localhost:80").
              "https://localhost/"
              4> uri_string:normalize(#{scheme => "http",port => 80,path => "/a/b/c/./../../g",
              4> host => "localhost-örebro"}).
              "http://localhost-%C3%B6rebro/a/g"

       normalize(URI, Options) -> NormalizedURI

              Types:

                 URI = uri_string() | uri_map()
                 Options = [return_map]
                 NormalizedURI = uri_string() | uri_map()

              Same  as normalize/1 but with an additional Options parameter, that controls if the
              normalized URI shall be returned as an uri_map(). There is  one  supported  option:
              return_map.

              Example:

              1> uri_string:normalize("/a/b/c/./../../g", [return_map]).
              #{path => "/a/g"}
              2> uri_string:normalize(<<"mid/content=5/../6">>, [return_map]).
              #{path => <<"mid/6">>}
              3> uri_string:normalize("http://localhost:80", [return_map]).
              #{scheme => "http",path => "/",host => "localhost"}
              4> uri_string:normalize(#{scheme => "http",port => 80,path => "/a/b/c/./../../g",
              4> host => "localhost-örebro"}, [return_map]).
              #{scheme => "http",path => "/a/g",host => "localhost-örebro"}

       parse(URIString) -> URIMap

              Types:

                 URIString = uri_string()
                 URIMap = uri_map() | error()

              Parses  an  RFC 3986 compliant uri_string() into a uri_map(), that holds the parsed
              components of the URI. If parsing fails, an error tuple is returned.

              See also the opposite operation recompose/1.

              Example:

              1> uri_string:parse("foo://user@example.com:8042/over/there?name=ferret#nose").
              #{fragment => "nose",host => "example.com",
                path => "/over/there",port => 8042,query => "name=ferret",
                scheme => foo,userinfo => "user"}
              2> uri_string:parse(<<"foo://user@example.com:8042/over/there?name=ferret">>).
              #{host => <<"example.com">>,path => <<"/over/there">>,
                port => 8042,query => <<"name=ferret">>,scheme => <<"foo">>,
                userinfo => <<"user">>}

       recompose(URIMap) -> URIString

              Types:

                 URIMap = uri_map()
                 URIString = uri_string() | error()

              Creates an RFC 3986 compliant URIString (percent-encoded), based on the  components
              of URIMap. If the URIMap is invalid, an error tuple is returned.

              See also the opposite operation parse/1.

              Example:

              1> URIMap = #{fragment => "nose", host => "example.com", path => "/over/there",
              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> uri_string:recompose(URIMap).
              "foo://example.com:8042/over/there?name=ferret#nose"

       transcode(URIString, Options) -> Result

              Types:

                 URIString = uri_string()
                 Options =
                     [{in_encoding, unicode:encoding()} |
                      {out_encoding, unicode:encoding()}]
                 Result = uri_string() | error()

              Transcodes  an  RFC  3986  compliant  URIString,  where Options is a list of tagged
              tuples, specifying the inbound (in_encoding) and outbound (out_encoding) encodings.
              in_encoding  and  out_encoding  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.

              Example:

              1> uri_string:transcode(<<"foo%00%00%00%F6bar"/utf32>>,
              1> [{in_encoding, utf32},{out_encoding, utf8}]).
              <<"foo%C3%B6bar"/utf8>>
              2> uri_string:transcode("foo%F6bar", [{in_encoding, latin1},
              2> {out_encoding, utf8}]).
              "foo%C3%B6bar"