Provided by: libhttp-message-perl_6.45-1ubuntu1_all 
NAME
HTTP::Headers - Class encapsulating HTTP Message headers
VERSION
version 6.45
SYNOPSIS
require HTTP::Headers;
$h = HTTP::Headers->new;
$h->header('Content-Type' => 'text/plain'); # set
$ct = $h->header('Content-Type'); # get
$h->remove_header('Content-Type'); # delete
DESCRIPTION
The "HTTP::Headers" class encapsulates HTTP-style message headers. The headers consist of
attribute-value pairs also called fields, which may be repeated, and which are printed in
a particular order. The field names are cases insensitive.
Instances of this class are usually created as member variables of the "HTTP::Request" and
"HTTP::Response" classes, internal to the library.
The following methods are available:
$h = HTTP::Headers->new
Constructs a new "HTTP::Headers" object. You might pass some initial attribute-value
pairs as parameters to the constructor. E.g.:
$h = HTTP::Headers->new(
Date => 'Thu, 03 Feb 1994 00:00:00 GMT',
Content_Type => 'text/html; version=3.2',
Content_Base => 'http://www.perl.org/');
The constructor arguments are passed to the "header" method which is described below.
$h->clone
Returns a copy of this "HTTP::Headers" object.
$h->header( $field )
$h->header( $field => $value )
$h->header( $f1 => $v1, $f2 => $v2, ... )
Get or set the value of one or more header fields. The header field name ($field) is
not case sensitive. To make the life easier for perl users who wants to avoid quoting
before the => operator, you can use '_' as a replacement for '-' in header names.
The header() method accepts multiple ($field => $value) pairs, which means that you
can update several fields with a single invocation.
The $value argument may be a plain string or a reference to an array of strings for a
multi-valued field. If the $value is provided as "undef" then the field is removed.
If the $value is not given, then that header field will remain unchanged. In addition
to being a string, $value may be something that stringifies.
The old value (or values) of the last of the header fields is returned. If no such
field exists "undef" will be returned.
A multi-valued field will be returned as separate values in list context and will be
concatenated with ", " as separator in scalar context. The HTTP spec (RFC 2616)
promises that joining multiple values in this way will not change the semantic of a
header field, but in practice there are cases like old-style Netscape cookies (see
HTTP::Cookies) where "," is used as part of the syntax of a single field value.
Examples:
$header->header(MIME_Version => '1.0',
User_Agent => 'My-Web-Client/0.01');
$header->header(Accept => "text/html, text/plain, image/*");
$header->header(Accept => [qw(text/html text/plain image/*)]);
@accepts = $header->header('Accept'); # get multiple values
$accepts = $header->header('Accept'); # get values as a single string
$h->push_header( $field => $value )
$h->push_header( $f1 => $v1, $f2 => $v2, ... )
Add a new field value for the specified header field. Previous values for the same
field are retained.
As for the header() method, the field name ($field) is not case sensitive and '_' can
be used as a replacement for '-'.
The $value argument may be a scalar or a reference to a list of scalars.
$header->push_header(Accept => 'image/jpeg');
$header->push_header(Accept => [map "image/$_", qw(gif png tiff)]);
$h->init_header( $field => $value )
Set the specified header to the given value, but only if no previous value for that
field is set.
The header field name ($field) is not case sensitive and '_' can be used as a
replacement for '-'.
The $value argument may be a scalar or a reference to a list of scalars.
$h->remove_header( $field, ... )
This function removes the header fields with the specified names.
The header field names ($field) are not case sensitive and '_' can be used as a
replacement for '-'.
The return value is the values of the fields removed. In scalar context the number of
fields removed is returned.
Note that if you pass in multiple field names then it is generally not possible to
tell which of the returned values belonged to which field.
$h->remove_content_headers
This will remove all the header fields used to describe the content of a message. All
header field names prefixed with "Content-" fall into this category, as well as
"Allow", "Expires" and "Last-Modified". RFC 2616 denotes these fields as Entity
Header Fields.
The return value is a new "HTTP::Headers" object that contains the removed headers
only.
$h->clear
This will remove all header fields.
$h->header_field_names
Returns the list of distinct names for the fields present in the header. The field
names have case as suggested by HTTP spec, and the names are returned in the
recommended "Good Practice" order.
In scalar context return the number of distinct field names.
$h->scan( \&process_header_field )
Apply a subroutine to each header field in turn. The callback routine is called with
two parameters; the name of the field and a single value (a string). If a header
field is multi-valued, then the routine is called once for each value. The field name
passed to the callback routine has case as suggested by HTTP spec, and the headers
will be visited in the recommended "Good Practice" order.
Any return values of the callback routine are ignored. The loop can be broken by
raising an exception ("die"), but the caller of scan() would have to trap the
exception itself.
$h->flatten()
Returns the list of pairs of keys and values.
$h->as_string
$h->as_string( $eol )
Return the header fields as a formatted MIME header. Since it internally uses the
"scan" method to build the string, the result will use case as suggested by HTTP spec,
and it will follow recommended "Good Practice" of ordering the header fields. Long
header values are not folded.
The optional $eol parameter specifies the line ending sequence to use. The default is
"\n". Embedded "\n" characters in header field values will be substituted with this
line ending sequence.
CONVENIENCE METHODS
The most frequently used headers can also be accessed through the following convenience
methods. Most of these methods can both be used to read and to set the value of a header.
The header value is set if you pass an argument to the method. The old header value is
always returned. If the given header did not exist then "undef" is returned.
Methods that deal with dates/times always convert their value to system time (seconds
since Jan 1, 1970) and they also expect this kind of value when the header value is set.
$h->date
This header represents the date and time at which the message was originated. E.g.:
$h->date(time); # set current date
$h->expires
This header gives the date and time after which the entity should be considered stale.
$h->if_modified_since
$h->if_unmodified_since
These header fields are used to make a request conditional. If the requested resource
has (or has not) been modified since the time specified in this field, then the server
will return a "304 Not Modified" response instead of the document itself.
$h->last_modified
This header indicates the date and time at which the resource was last modified. E.g.:
# check if document is more than 1 hour old
if (my $last_mod = $h->last_modified) {
if ($last_mod < time - 60*60) {
...
}
}
$h->content_type
The Content-Type header field indicates the media type of the message content. E.g.:
$h->content_type('text/html');
The value returned will be converted to lower case, and potential parameters will be
chopped off and returned as a separate value if in an array context. If there is no
such header field, then the empty string is returned. This makes it safe to do the
following:
if ($h->content_type eq 'text/html') {
# we enter this place even if the real header value happens to
# be 'TEXT/HTML; version=3.0'
...
}
$h->content_type_charset
Returns the upper-cased charset specified in the Content-Type header. In list context
return the lower-cased bare content type followed by the upper-cased charset. Both
values will be "undef" if not specified in the header.
$h->content_is_text
Returns TRUE if the Content-Type header field indicate that the content is textual.
$h->content_is_html
Returns TRUE if the Content-Type header field indicate that the content is some kind
of HTML (including XHTML). This method can't be used to set Content-Type.
$h->content_is_xhtml
Returns TRUE if the Content-Type header field indicate that the content is XHTML.
This method can't be used to set Content-Type.
$h->content_is_xml
Returns TRUE if the Content-Type header field indicate that the content is XML. This
method can't be used to set Content-Type.
$h->content_encoding
The Content-Encoding header field is used as a modifier to the media type. When
present, its value indicates what additional encoding mechanism has been applied to
the resource.
$h->content_length
A decimal number indicating the size in bytes of the message content.
$h->content_language
The natural language(s) of the intended audience for the message content. The value
is one or more language tags as defined by RFC 1766. Eg. "no" for some kind of
Norwegian and "en-US" for English the way it is written in the US.
$h->title
The title of the document. In libwww-perl this header will be initialized
automatically from the <TITLE>...</TITLE> element of HTML documents. This header is
no longer part of the HTTP standard.
$h->user_agent
This header field is used in request messages and contains information about the user
agent originating the request. E.g.:
$h->user_agent('Mozilla/5.0 (compatible; MSIE 7.0; Windows NT 6.0)');
$h->server
The server header field contains information about the software being used by the
originating server program handling the request.
$h->from
This header should contain an Internet e-mail address for the human user who controls
the requesting user agent. The address should be machine-usable, as defined by
RFC822. E.g.:
$h->from('King Kong <king@kong.com>');
This header is no longer part of the HTTP standard.
$h->referer
Used to specify the address (URI) of the document from which the requested resource
address was obtained.
The "Free On-line Dictionary of Computing" as this to say about the word referer:
<World-Wide Web> A misspelling of "referrer" which
somehow made it into the {HTTP} standard. A given {web
page}'s referer (sic) is the {URL} of whatever web page
contains the link that the user followed to the current
page. Most browsers pass this information as part of a
request.
(1998-10-19)
By popular demand "referrer" exists as an alias for this method so you can avoid this
misspelling in your programs and still send the right thing on the wire.
When setting the referrer, this method removes the fragment from the given URI if it
is present, as mandated by RFC2616. Note that the removal does not happen
automatically if using the header(), push_header() or init_header() methods to set the
referrer.
$h->www_authenticate
This header must be included as part of a "401 Unauthorized" response. The field
value consist of a challenge that indicates the authentication scheme and parameters
applicable to the requested URI.
$h->proxy_authenticate
This header must be included in a "407 Proxy Authentication Required" response.
$h->authorization
$h->proxy_authorization
A user agent that wishes to authenticate itself with a server or a proxy, may do so by
including these headers.
$h->authorization_basic
This method is used to get or set an authorization header that use the "Basic
Authentication Scheme". In array context it will return two values; the user name and
the password. In scalar context it will return "uname:password" as a single string
value.
When used to set the header value, it expects two arguments. E.g.:
$h->authorization_basic($uname, $password);
The method will croak if the $uname contains a colon ':'.
$h->proxy_authorization_basic
Same as authorization_basic() but will set the "Proxy-Authorization" header instead.
NON-CANONICALIZED FIELD NAMES
The header field name spelling is normally canonicalized including the '_' to '-'
translation. There are some application where this is not appropriate. Prefixing field
names with ':' allow you to force a specific spelling. For example if you really want a
header field name to show up as "foo_bar" instead of "Foo-Bar", you might set it like
this:
$h->header(":foo_bar" => 1);
These field names are returned with the ':' intact for $h->header_field_names and the
$h->scan callback, but the colons do not show in $h->as_string.
AUTHOR
Gisle Aas <gisle@activestate.com>
COPYRIGHT AND LICENSE
This software is copyright (c) 1994 by Gisle Aas.
This is free software; you can redistribute it and/or modify it under the same terms as
the Perl 5 programming language system itself.