URI(3)

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 (URI) references as specified in RFC 2396.

A Uniform Resource Identifier is a compact string of characters for identifying an abstract or physical resource. A Uniform Resource Identifier can be further classified either a Uniform Resource Locator (URL) or a Uniform Resource Name (URN). The distinction between URL and URN is not reflected by the URI class interface.

An absolute URI reference consist 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 URI 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 usage. 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 that a URI reference can be divided into depend on the scheme. The URI class provide methods to get and set the individual components. The methods available for a specific URI object depend on the scheme.

CONSTRUCTORS
The following methods to construct new URI objects are provided: This class method 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, will be automatically removed from the $str argument before it is processed further.

The constructor will determine the scheme, map this to an appropriate URI subclass, construct a new object of this class and return it.

The $scheme argument only makes a difference when $str takes a relative form. The $scheme can then either be 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 it is simply treated as a generic URI (no scheme specific methods available).

The set of characters available for building up URI references is restricted (see the URI::Escape manpage). Characters outside this set is automatically escaped by the URI constructor. This custructs a new absolute URI. This constructs a new file URI from a file name. See the URI::file manpage. This constructs a new absolute file URI from a file name. See the URI::file manpage. This returns the current working directory as a file URI. See the URI::file manpage. This method 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 will always return the old value of the component. The value returned will be 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 will update the corresponding component in addition to returning the old value of the component. Passing an undefined argument will remove the component (if possible). The description of the various accessor methods will tell if the component is passed as an escaped or an unescaped string. Components that can be futher divided into sub-parts are usually passed escaped, as unescaping might change its semantics.

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

Case distinctions does not matter for scheme names. The string returned by $uri->scheme is always lowercased. If you want the scheme just as it was written in the URI, i.e. not necessarily lowercased, you can use the $uri->_scheme method instead. The scheme specific part can be accessed with this method. The value is an escaped string. This method access the same stuff as $uri->opaque unless the URI support the generic syntax for hierarchical namespaces. Here the path is more restricted and $uri->opaque access everything that is found in between the scheme and the fragment. The fragment identifier of a URI reference can be accessed with this method. The value is escaped. This method convert a URI object to a plain string. URI objects are also converted to plain strings automatically by overloading. It means that $uri objects can be used as plain strings in most Perl constructs. This method will return a normalized version of the URI. The rules for normalization is scheme dependent. It usually involves lowercasing of the scheme and the Internet host name components, removal of explicit port specification that match the default port, upcasing of all escape sequences, and unescaping of octets that can be better represented by plain characters.

If the $uri already was in the normalized form, then a reference to itself is returned instead of a copy. This method test 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 and can then also test two string arguments.

If you need to test whether two URI object references denote the same object, you can use the '==' operator. This method will return an absolute URI reference. If $uri already is absolute, then a reference to itself is simply returned. If the $uri is relative then a new absolute URI is constructed, by combining the $uri and the $base, and returned. This method will return a relative URI reference if it is possible to make one that denotes the same resource as $uri relative to $base_uri. If not, then $uri is simply returned.

GENERIC METHODS
The following methods are available to schemes that use the common/generic syntax for hierarchical namespaces. The description of schemes below will tell which one these are. Unknown schemes are assumed to support the generic syntax, and therefore the following methods: This method can be used to get and set the escaped authority component of the $uri. This method can be used to get and set the escaped path component of the $uri. The path will never be undefined, but it can be the empty string. This method can be used to get and set the escaped path and query components as a single entity. The path and the query should be separated by a "?" character (but the query can itself contain "?"). This method can be used to get and set the path. In scalar context it returns the same value as $uri->path. In list context it will return 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. The anonymous array use overloading so it can be treated as a string too, and this string does not include the parameters. This method can be used to get and set the escaped query component of the $uri. This method can be used to get and set 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 with a "=" character. This method can be used to get and set query components that use the keywords separated by "+" format.

SERVER METHODS
Schemes where the authority component denote a Internet host will have the following methods available in addition to the generic methods. This method can be used to get and set the escaped userinfo part of the authority componenent. This method can be used to get and set the unescaped hostname.

If the $new_host string ends with a colon and a number, then this number will also set the port. This method will return the port specified in the URI or the default port for the URI scheme if no port is specified. If you don't want the default port substituted, then you can use the $uri->_port method instead. This method can be used to get and set the host and port as a single unit. The returned value will include a port, even if it matches the default port. The host part and the port part is separated with a colon; ":". This method will return the default port the URI scheme that $uri belongs to. For http this will be the number 80, for ftp this will be the number 21, etc.

SCHEME SPECIFIC SUPPORT
The following URI schemes are specifically supported. For URI objects not belonging to one of these you can only use the common and generic methods. 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 the URI::data manpage for details. An old speficication 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 to map file URI back to local file names; $uri->file and $uri->dir. See the URI::file manpage for details. 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 to access the userinfo sub-components: $uri->user and $uri->password. 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 to access gopher specific path components: $uri->gopher_type, $uri->selector, $uri->search, $uri->string. The http URI scheme is specified in <draft-ietf-http-v11-spec-rev-04> (which will become an RFC soon). 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. The https URI scheme is a Netscape invention which is commonly implemented. The scheme is used to reference HTTP servers through SSL connections. It's syntax is equal of that of http, but the default port is different. 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. The news, nntp and snews URI schemes are specified in <draft-gilman-news-url-01> and will hopefully be available as a 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. See news scheme. 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 An old speficication of the rlogin URI scheme is found in RFC 1738. URI objects belonging to the rlogin scheme support the common, generic and server methods. See news scheme. It's syntax is equal of that of news, but the default port is different. An old speficication of the telnet URI scheme is found in RFC 1738. URI objects belonging to the telnet scheme support the common, generic and server methods.

CONFIGURATION VARIABLES
The following configuration variables influence how the class and it's methods behave: 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"
You can also have the abs() method ignore if there is too many ".." 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::URL::ABS_REMOTE_LEADING_DOTS = 1;
  URI->new("../../../foo")->abs("http://host/a/b")
      ==> "http://host/foo"

SEE ALSO
the URI::file manpage, the URI::WithBase manpage, the URI::Escape manpage, the URI::Heuristic manpage

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

COPYRIGHT
Copyright 1995-1998 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.