http::headers(3)

NAME

HTTP::Headers - Class encapsulating HTTP Message headers

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.

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.; $h->header($field [=> $value],...)
Get or set the value of one or more header fields.
The header field name ($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 (this
behaviour can be suppressed by setting the
$HTTP::Headers::TRANSLATE_UNDERSCORE variable to a
FALSE value).

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 refer
ence to an array of strings for a multi-valued field.
If the $value is undefined or not given, then that
header field will remain unchanged.

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 retuned as separate val
ues in list context and will be concatenated with ", "
as separator in scalar context. The HTTP spec (RFC
2616) promise 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 cook
ies (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, im

age/*");
$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)

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 replace
ment 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 headers 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->scan(doit)

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 recom
mended "Good Practice" order.

Any return values of the callback routine are ignored.
The loop can be broken by raising an exception
("die").

$h->as_string([$endl])

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 Prac
tice" of ordering the header fieds. Long header val
ues are not folded.

The optional $endl parameter specifies the line ending
sequence to use. The default is "0. Embedded "0
characters in header field values will be substitued
with this line ending sequence.

$h->clone

Returns a copy of this "HTTP::Headers" object.

CONVENIENCE METHODS

The most frequently used headers can also be accessed
through the following convenience methods. 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 exists 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 condi
tional. 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.
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_encoding

The Content-Encoding header field is used as a modi
fier to the media type. When present, its value indi
cates 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 lan
guage 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 con
tains information about the user agent originating the
request. E.g.:

$h->user_agent('Mozilla/1.2');

$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 resouce 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 giv

en {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.

$h->www_authenticate

This header must be included as part of a "401 Unau
thorized" 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 Authenti
cation 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 head
ers.

$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.

COPYRIGHT

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

docs.sk