NAME
    URI - Uniform Resource Identifiers (absolute and relative)

SYNOPSIS
     $u1 = URI->new("http://www.perl.com");
     $u2 = URI->new("foo", "http");
     $u3 = $u2->abs($u1);
     $u4 = $u3->clone;
     $u5 = URI->new("HTTP://WWW.perl.com:80")->canonical;

     $str = $u->as_string;
     $str = "$u";

     $scheme = $u->scheme;
     $opaque = $u->opaque;
     $path   = $u->path;
     $frag   = $u->fragment;

     $u->scheme("ftp");
     $u->host("ftp.perl.com");
     $u->path("cpan/");

DESCRIPTION
    This module implements the "URI" class. Objects of this class represent
    "Uniform Resource Identifier references" as specified in RFC 2396 (and
    updated by RFC 2732).

    A Uniform Resource Identifier is a compact string of characters that
    identifies an abstract or physical resource. A Uniform Resource
    Identifier can be further classified as either a Uniform Resource
    Locator (URL) or a Uniform Resource Name (URN). The distinction between
    URL and URN does not matter to the "URI" class interface. A
    "URI-reference" is a URI that may have additional information attached
    in the form of a fragment identifier.

    An absolute URI reference consists of three parts: a *scheme*, a
    *scheme-specific part* and a *fragment* identifier. A subset of URI
    references share a common syntax for hierarchical namespaces. For these,
    the scheme-specific part is further broken down into *authority*, *path*
    and *query* components. These URIs can also take the form of relative
    URI references, where the scheme (and usually also the authority)
    component is missing, but implied by the context of the URI reference.
    The three forms of URI reference syntax are summarized as follows:

      <scheme>:<scheme-specific-part>#<fragment>
      <scheme>://<authority><path>?<query>#<fragment>
      <path>?<query>#<fragment>

    The components into which a URI reference can be divided depend on the
    *scheme*. The "URI" class provides methods to get and set the individual
    components. The methods available for a specific "URI" object depend on
    the scheme.

CONSTRUCTORS
    The following methods construct new "URI" objects:

    $uri = URI->new( $str )
    $uri = URI->new( $str, $scheme )
        Constructs a new URI object. The string representation of a URI is
        given as argument, together with an optional scheme specification.
        Common URI wrappers like "" and <>, as well as leading and trailing
        white space, are automatically removed from the $str argument before
        it is processed further.

        The constructor determines the scheme, maps this to an appropriate
        URI subclass, constructs a new object of that class and returns it.

        If the scheme isn't one of those that URI recognizes, you still get
        an URI object back that you can access the generic methods on. The
        "$uri->has_recognized_scheme" method can be used to test for this.

        The $scheme argument is only used when $str is a relative URI. It
        can be either a simple string that denotes the scheme, a string
        containing an absolute URI reference, or an absolute "URI" object.
        If no $scheme is specified for a relative URI $str, then $str is
        simply treated as a generic URI (no scheme-specific methods
        available).

        The set of characters available for building URI references is
        restricted (see URI::Escape). Characters outside this set are
        automatically escaped by the URI constructor.

    $uri = URI->new_abs( $str, $base_uri )
        Constructs a new absolute URI object. The $str argument can denote a
        relative or absolute URI. If relative, then it is absolutized using
        $base_uri as base. The $base_uri must be an absolute URI.

    $uri = URI::file->new( $filename )
    $uri = URI::file->new( $filename, $os )
        Constructs a new *file* URI from a file name. See URI::file.

    $uri = URI::file->new_abs( $filename )
    $uri = URI::file->new_abs( $filename, $os )
        Constructs a new absolute *file* URI from a file name. See
        URI::file.

    $uri = URI::file->cwd
        Returns the current working directory as a *file* URI. See
        URI::file.

    $uri->clone
        Returns a copy of the $uri.

COMMON METHODS
    The methods described in this section are available for all "URI"
    objects.

    Methods that give access to components of a URI always return the old
    value of the component. The value returned is "undef" if the component
    was not present. There is generally a difference between a component
    that is empty (represented as "") and a component that is missing
    (represented as "undef"). If an accessor method is given an argument, it
    updates the corresponding component in addition to returning the old
    value of the component. Passing an undefined argument removes the
    component (if possible). The description of each accessor method
    indicates whether the component is passed as an escaped
    (percent-encoded) or an unescaped string. A component that can be
    further divided into sub-parts are usually passed escaped, as unescaping
    might change its semantics.

    The common methods available for all URI are:

    $uri->scheme
    $uri->scheme( $new_scheme )
        Sets and returns the scheme part of the $uri. If the $uri is
        relative, then $uri->scheme returns "undef". If called with an
        argument, it updates the scheme of $uri, possibly changing the class
        of $uri, and returns the old scheme value. The method croaks if the
        new scheme name is illegal; a scheme name must begin with a letter
        and must consist of only US-ASCII letters, numbers, and a few
        special marks: ".", "+", "-". This restriction effectively means
        that the scheme must be passed unescaped. Passing an undefined
        argument to the scheme method makes the URI relative (if possible).

        Letter case does not matter for scheme names. The string returned by
        $uri->scheme is always lowercase. If you want the scheme just as it
        was written in the URI in its original case, you can use the
        $uri->_scheme method instead.

    $uri->has_recognized_scheme
        Returns TRUE if the URI scheme is one that URI recognizes.

        It will also be TRUE for relative URLs where a recognized scheme was
        provided to the constructor, even if "$uri->scheme" returns "undef"
        for these.

    $uri->opaque
    $uri->opaque( $new_opaque )
        Sets and returns the scheme-specific part of the $uri (everything
        between the scheme and the fragment) as an escaped string.

    $uri->path
    $uri->path( $new_path )
        Sets and returns the same value as $uri->opaque unless the URI
        supports the generic syntax for hierarchical namespaces. In that
        case the generic method is overridden to set and return the part of
        the URI between the *host name* and the *fragment*.

    $uri->fragment
    $uri->fragment( $new_frag )
        Returns the fragment identifier of a URI reference as an escaped
        string.

    $uri->as_string
        Returns a URI object to a plain ASCII string. URI objects are also
        converted to plain strings automatically by overloading. This means
        that $uri objects can be used as plain strings in most Perl
        constructs.

    $uri->as_iri
        Returns a Unicode string representing the URI. Escaped UTF-8
        sequences representing non-ASCII characters are turned into their
        corresponding Unicode code point.

    $uri->canonical
        Returns a normalized version of the URI. The rules for normalization
        are scheme-dependent. They usually involve lowercasing the scheme
        and Internet host name components, removing the explicit port
        specification if it matches the default port, uppercasing all escape
        sequences, and unescaping octets that can be better represented as
        plain characters.

        For efficiency reasons, if the $uri is already in normalized form,
        then a reference to it is returned instead of a copy.

    $uri->eq( $other_uri )
    URI::eq( $first_uri, $other_uri )
        Tests whether two URI references are equal. URI references that
        normalize to the same string are considered equal. The method can
        also be used as a plain function which can also test two string
        arguments.

        If you need to test whether two "URI" object references denote the
        same object, use the '==' operator.

    $uri->abs( $base_uri )
        Returns an absolute URI reference. If $uri is already absolute, then
        a reference to it is simply returned. If the $uri is relative, then
        a new absolute URI is constructed by combining the $uri and the
        $base_uri, and returned.

    $uri->rel( $base_uri )
        Returns a relative URI reference if it is possible to make one that
        denotes the same resource relative to $base_uri. If not, then $uri
        is simply returned.

    $uri->secure
        Returns a TRUE value if the URI is considered to point to a resource
        on a secure channel, such as an SSL or TLS encrypted one.

GENERIC METHODS
    The following methods are available to schemes that use the
    common/generic syntax for hierarchical namespaces. The descriptions of
    schemes below indicate which these are. Unrecognized schemes are assumed
    to support the generic syntax, and therefore the following methods:

    $uri->authority
    $uri->authority( $new_authority )
        Sets and returns the escaped authority component of the $uri.

    $uri->path
    $uri->path( $new_path )
        Sets and returns the escaped path component of the $uri (the part
        between the host name and the query or fragment). The path can never
        be undefined, but it can be the empty string.

    $uri->path_query
    $uri->path_query( $new_path_query )
        Sets and returns the escaped path and query components as a single
        entity. The path and the query are separated by a "?" character, but
        the query can itself contain "?".

    $uri->path_segments
    $uri->path_segments( $segment, ... )
        Sets and returns the path. In a scalar context, it returns the same
        value as $uri->path. In a list context, it returns the unescaped
        path segments that make up the path. Path segments that have
        parameters are returned as an anonymous array. The first element is
        the unescaped path segment proper; subsequent elements are escaped
        parameter strings. Such an anonymous array uses overloading so it
        can be treated as a string too, but this string does not include the
        parameters.

        Note that absolute paths have the empty string as their first
        *path_segment*, i.e. the *path* "/foo/bar" have 3 *path_segments*;
        "", "foo" and "bar".

    $uri->query
    $uri->query( $new_query )
        Sets and returns the escaped query component of the $uri.

    $uri->query_form
    $uri->query_form( $key1 => $val1, $key2 => $val2, ... )
    $uri->query_form( $key1 => $val1, $key2 => $val2, ..., $delim )
    $uri->query_form( \@key_value_pairs )
    $uri->query_form( \@key_value_pairs, $delim )
    $uri->query_form( \%hash )
    $uri->query_form( \%hash, $delim )
        Sets and returns query components that use the
        *application/x-www-form-urlencoded* format. Key/value pairs are
        separated by "&", and the key is separated from the value by a "="
        character.

        The form can be set either by passing separate key/value pairs, or
        via an array or hash reference. Passing an empty array or an empty
        hash removes the query component, whereas passing no arguments at
        all leaves the component unchanged. The order of keys is undefined
        if a hash reference is passed. The old value is always returned as a
        list of separate key/value pairs. Assigning this list to a hash is
        unwise as the keys returned might repeat.

        The values passed when setting the form can be plain strings or
        references to arrays of strings. Passing an array of values has the
        same effect as passing the key repeatedly with one value at a time.
        All the following statements have the same effect:

            $uri->query_form(foo => 1, foo => 2);
            $uri->query_form(foo => [1, 2]);
            $uri->query_form([ foo => 1, foo => 2 ]);
            $uri->query_form([ foo => [1, 2] ]);
            $uri->query_form({ foo => [1, 2] });

        The $delim parameter can be passed as ";" to force the key/value
        pairs to be delimited by ";" instead of "&" in the query string.
        This practice is often recommended for URLs embedded in HTML or XML
        documents as this avoids the trouble of escaping the "&" character.
        You might also set the $URI::DEFAULT_QUERY_FORM_DELIMITER variable
        to ";" for the same global effect.

        The "URI::QueryParam" module can be loaded to add further methods to
        manipulate the form of a URI. See URI::QueryParam for details.

    $uri->query_keywords
    $uri->query_keywords( $keywords, ... )
    $uri->query_keywords( \@keywords )
        Sets and returns query components that use the keywords separated by
        "+" format.

        The keywords can be set either by passing separate keywords directly
        or by passing a reference to an array of keywords. Passing an empty
        array removes the query component, whereas passing no arguments at
        all leaves the component unchanged. The old value is always returned
        as a list of separate words.

SERVER METHODS
    For schemes where the *authority* component denotes an Internet host,
    the following methods are available in addition to the generic methods.

    $uri->userinfo
    $uri->userinfo( $new_userinfo )
        Sets and returns the escaped userinfo part of the authority
        component.

        For some schemes this is a user name and a password separated by a
        colon. This practice is not recommended. Embedding passwords in
        clear text (such as URI) has proven to be a security risk in almost
        every case where it has been used.

    $uri->host
    $uri->host( $new_host )
        Sets and returns the unescaped hostname.

        If the $new_host string ends with a colon and a number, then this
        number also sets the port.

        For IPv6 addresses the brackets around the raw address is removed in
        the return value from $uri->host. When setting the host attribute to
        an IPv6 address you can use a raw address or one enclosed in
        brackets. The address needs to be enclosed in brackets if you want
        to pass in a new port value as well.

    $uri->ihost
        Returns the host in Unicode form. Any IDNA A-labels are turned into
        U-labels.

    $uri->port
    $uri->port( $new_port )
        Sets and returns the port. The port is a simple integer that should
        be greater than 0.

        If a port is not specified explicitly in the URI, then the URI
        scheme's default port is returned. If you don't want the default
        port substituted, then you can use the $uri->_port method instead.

    $uri->host_port
    $uri->host_port( $new_host_port )
        Sets and returns the host and port as a single unit. The returned
        value includes a port, even if it matches the default port. The host
        part and the port part are separated by a colon: ":".

        For IPv6 addresses the bracketing is preserved; thus
        URI->new("http://[::1]/")->host_port returns "[::1]:80". Contrast
        this with $uri->host which will remove the brackets.

    $uri->default_port
        Returns the default port of the URI scheme to which $uri belongs.
        For *http* this is the number 80, for *ftp* this is the number 21,
        etc. The default port for a scheme can not be changed.

SCHEME-SPECIFIC SUPPORT
    Scheme-specific support is provided for the following URI schemes. For
    "URI" objects that do not belong to one of these, you can only use the
    common and generic methods.

    data:
        The *data* URI scheme is specified in RFC 2397. It allows inclusion
        of small data items as "immediate" data, as if it had been included
        externally.

        "URI" objects belonging to the data scheme support the common
        methods and two new methods to access their scheme-specific
        components: $uri->media_type and $uri->data. See URI::data for
        details.

    file:
        An old specification of the *file* URI scheme is found in RFC 1738.
        A new RFC 2396 based specification in not available yet, but file
        URI references are in common use.

        "URI" objects belonging to the file scheme support the common and
        generic methods. In addition, they provide two methods for mapping
        file URIs back to local file names; $uri->file and $uri->dir. See
        URI::file for details.

    ftp:
        An old specification of the *ftp* URI scheme is found in RFC 1738. A
        new RFC 2396 based specification in not available yet, but ftp URI
        references are in common use.

        "URI" objects belonging to the ftp scheme support the common,
        generic and server methods. In addition, they provide two methods
        for accessing the userinfo sub-components: $uri->user and
        $uri->password.

    gopher:
        The *gopher* URI scheme is specified in
        <draft-murali-url-gopher-1996-12-04> and will hopefully be available
        as a RFC 2396 based specification.

        "URI" objects belonging to the gopher scheme support the common,
        generic and server methods. In addition, they support some methods
        for accessing gopher-specific path components: $uri->gopher_type,
        $uri->selector, $uri->search, $uri->string.

    http:
        The *http* URI scheme is specified in RFC 2616. The scheme is used
        to reference resources hosted by HTTP servers.

        "URI" objects belonging to the http scheme support the common,
        generic and server methods.

    https:
        The *https* URI scheme is a Netscape invention which is commonly
        implemented. The scheme is used to reference HTTP servers through
        SSL connections. Its syntax is the same as http, but the default
        port is different.

    ldap:
        The *ldap* URI scheme is specified in RFC 2255. LDAP is the
        Lightweight Directory Access Protocol. An ldap URI describes an LDAP
        search operation to perform to retrieve information from an LDAP
        directory.

        "URI" objects belonging to the ldap scheme support the common,
        generic and server methods as well as ldap-specific methods:
        $uri->dn, $uri->attributes, $uri->scope, $uri->filter,
        $uri->extensions. See URI::ldap for details.

    ldapi:
        Like the *ldap* URI scheme, but uses a UNIX domain socket. The
        server methods are not supported, and the local socket path is
        available as $uri->un_path. The *ldapi* scheme is used by the
        OpenLDAP package. There is no real specification for it, but it is
        mentioned in various OpenLDAP manual pages.

    ldaps:
        Like the *ldap* URI scheme, but uses an SSL connection. This scheme
        is deprecated, as the preferred way is to use the *start_tls*
        mechanism.

    mailto:
        The *mailto* URI scheme is specified in RFC 2368. The scheme was
        originally used to designate the Internet mailing address of an
        individual or service. It has (in RFC 2368) been extended to allow
        setting of other mail header fields and the message body.

        "URI" objects belonging to the mailto scheme support the common
        methods and the generic query methods. In addition, they support the
        following mailto-specific methods: $uri->to, $uri->headers.

        Note that the "foo@example.com" part of a mailto is *not* the
        "userinfo" and "host" but instead the "path". This allows a mailto
        URI to contain multiple comma separated email addresses.

    mms:
        The *mms* URL specification can be found at <http://sdp.ppona.com/>.
        "URI" objects belonging to the mms scheme support the common,
        generic, and server methods, with the exception of userinfo and
        query-related sub-components.

    news:
        The *news*, *nntp* and *snews* URI schemes are specified in
        <draft-gilman-news-url-01> and will hopefully be available as an RFC
        2396 based specification soon.

        "URI" objects belonging to the news scheme support the common,
        generic and server methods. In addition, they provide some methods
        to access the path: $uri->group and $uri->message.

    nntp:
        See *news* scheme.

    pop:
        The *pop* URI scheme is specified in RFC 2384. The scheme is used to
        reference a POP3 mailbox.

        "URI" objects belonging to the pop scheme support the common,
        generic and server methods. In addition, they provide two methods to
        access the userinfo components: $uri->user and $uri->auth

    rlogin:
        An old specification of the *rlogin* URI scheme is found in RFC
        1738. "URI" objects belonging to the rlogin scheme support the
        common, generic and server methods.

    rtsp:
        The *rtsp* URL specification can be found in section 3.2 of RFC
        2326. "URI" objects belonging to the rtsp scheme support the common,
        generic, and server methods, with the exception of userinfo and
        query-related sub-components.

    rtspu:
        The *rtspu* URI scheme is used to talk to RTSP servers over UDP
        instead of TCP. The syntax is the same as rtsp.

    rsync:
        Information about rsync is available from <http://rsync.samba.org/>.
        "URI" objects belonging to the rsync scheme support the common,
        generic and server methods. In addition, they provide methods to
        access the userinfo sub-components: $uri->user and $uri->password.

    sip:
        The *sip* URI specification is described in sections 19.1 and 25 of
        RFC 3261. "URI" objects belonging to the sip scheme support the
        common, generic, and server methods with the exception of path
        related sub-components. In addition, they provide two methods to get
        and set *sip* parameters: $uri->params_form and $uri->params.

    sips:
        See *sip* scheme. Its syntax is the same as sip, but the default
        port is different.

    snews:
        See *news* scheme. Its syntax is the same as news, but the default
        port is different.

    telnet:
        An old specification of the *telnet* URI scheme is found in RFC
        1738. "URI" objects belonging to the telnet scheme support the
        common, generic and server methods.

    tn3270:
        These URIs are used like *telnet* URIs but for connections to IBM
        mainframes. "URI" objects belonging to the tn3270 scheme support the
        common, generic and server methods.

    ssh:
        Information about ssh is available at <http://www.openssh.com/>.
        "URI" objects belonging to the ssh scheme support the common,
        generic and server methods. In addition, they provide methods to
        access the userinfo sub-components: $uri->user and $uri->password.

    sftp:
        "URI" objects belonging to the sftp scheme support the common,
        generic and server methods. In addition, they provide methods to
        access the userinfo sub-components: $uri->user and $uri->password.

    urn:
        The syntax of Uniform Resource Names is specified in RFC 2141. "URI"
        objects belonging to the urn scheme provide the common methods, and
        also the methods $uri->nid and $uri->nss, which return the Namespace
        Identifier and the Namespace-Specific String respectively.

        The Namespace Identifier basically works like the Scheme identifier
        of URIs, and further divides the URN namespace. Namespace Identifier
        assignments are maintained at
        <http://www.iana.org/assignments/urn-namespaces>.

        Letter case is not significant for the Namespace Identifier. It is
        always returned in lower case by the $uri->nid method. The
        $uri->_nid method can be used if you want it in its original case.

    urn:isbn:
        The "urn:isbn:" namespace contains International Standard Book
        Numbers (ISBNs) and is described in RFC 3187. A "URI" object
        belonging to this namespace has the following extra methods (if the
        Business::ISBN module is available): $uri->isbn,
        $uri->isbn_publisher_code, $uri->isbn_group_code (formerly
        isbn_country_code, which is still supported by issues a deprecation
        warning), $uri->isbn_as_ean.

    urn:oid:
        The "urn:oid:" namespace contains Object Identifiers (OIDs) and is
        described in RFC 3061. An object identifier consists of sequences of
        digits separated by dots. A "URI" object belonging to this namespace
        has an additional method called $uri->oid that can be used to
        get/set the oid value. In a list context, oid numbers are returned
        as separate elements.

CONFIGURATION VARIABLES
    The following configuration variables influence how the class and its
    methods behave:

    $URI::ABS_ALLOW_RELATIVE_SCHEME
        Some older parsers used to allow the scheme name to be present in
        the relative URL if it was the same as the base URL scheme. RFC 2396
        says that this should be avoided, but you can enable this old
        behaviour by setting the $URI::ABS_ALLOW_RELATIVE_SCHEME variable to
        a TRUE value. The difference is demonstrated by the following
        examples:

          URI->new("http:foo")->abs("http://host/a/b")
              ==>  "http:foo"

          local $URI::ABS_ALLOW_RELATIVE_SCHEME = 1;
          URI->new("http:foo")->abs("http://host/a/b")
              ==>  "http:/host/a/foo"

    $URI::ABS_REMOTE_LEADING_DOTS
        You can also have the abs() method ignore excess ".." segments in
        the relative URI by setting $URI::ABS_REMOTE_LEADING_DOTS to a TRUE
        value. The difference is demonstrated by the following examples:

          URI->new("../../../foo")->abs("http://host/a/b")
              ==> "http://host/../../foo"

          local $URI::ABS_REMOTE_LEADING_DOTS = 1;
          URI->new("../../../foo")->abs("http://host/a/b")
              ==> "http://host/foo"

    $URI::DEFAULT_QUERY_FORM_DELIMITER
        This value can be set to ";" to have the query form "key=value"
        pairs delimited by ";" instead of "&" which is the default.

BUGS
    There are some things that are not quite right:

    *   Using regexp variables like $1 directly as arguments to the URI
        accessor methods does not work too well with current perl
        implementations. I would argue that this is actually a bug in perl.
        The workaround is to quote them. Example:

           /(...)/ || die;
           $u->query("$1");

    *   The escaping (percent encoding) of chars in the 128 .. 255 range
        passed to the URI constructor or when setting URI parts using the
        accessor methods depend on the state of the internal UTF8 flag (see
        utf8::is_utf8) of the string passed. If the UTF8 flag is set the
        UTF-8 encoded version of the character is percent encoded. If the
        UTF8 flag isn't set the Latin-1 version (byte) of the character is
        percent encoded. This basically exposes the internal encoding of
        Perl strings.

PARSING URIs WITH REGEXP
    As an alternative to this module, the following (official) regular
    expression can be used to decode a URI:

      my($scheme, $authority, $path, $query, $fragment) =
      $uri =~ m|(?:([^:/?#]+):)?(?://([^/?#]*))?([^?#]*)(?:\?([^#]*))?(?:#(.*))?|;

    The "URI::Split" module provides the function uri_split() as a readable
    alternative.

SEE ALSO
    URI::file, URI::WithBase, URI::QueryParam, URI::Escape, URI::Split,
    URI::Heuristic

    RFC 2396: "Uniform Resource Identifiers (URI): Generic Syntax",
    Berners-Lee, Fielding, Masinter, August 1998.

    <http://www.iana.org/assignments/uri-schemes>

    <http://www.iana.org/assignments/urn-namespaces>

    <http://www.w3.org/Addressing/>

COPYRIGHT
    Copyright 1995-2009 Gisle Aas.

    Copyright 1995 Martijn Koster.

    This program is free software; you can redistribute it and/or modify it
    under the same terms as Perl itself.

AUTHORS / ACKNOWLEDGMENTS
    This module is based on the "URI::URL" module, which in turn was
    (distantly) based on the "wwwurl.pl" code in the libwww-perl for perl4
    developed by Roy Fielding, as part of the Arcadia project at the
    University of California, Irvine, with contributions from Brooks Cutter.

    "URI::URL" was developed by Gisle Aas, Tim Bunce, Roy Fielding and
    Martijn Koster with input from other people on the libwww-perl mailing
    list.

    "URI" and related subclasses was developed by Gisle Aas.