lib::HTTP::HeadUser3Contributed Perl Documenlib::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
reference to an array of strings for a multi-valued
field. If the $value is undefined or not given, then
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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
values 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 cookies (see the HTTP::Cookies manpage) 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, $value)
Add a new field value for the specified header field.
Previous values for the same field are retained.
As for the header() method, the field name ($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 headers fields with the
specified names.
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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
recommended "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 Practice"
of ordering the header fieds. Long header values are
not folded.
The optional $endl parameter specifies the line ending
sequence to use. The default is "\n". Embedded "\n"
characters in header field values will be substitued
with this line ending sequence.
$h->clone
Returns a copy of this HTTP::Headers object.
CONVENIENCE METHODS
The most frequently used headers can also be accessed
through the following convenience methods. These methods
can both be used to read and to set the value of a header.
The header value is set if you pass an argument to the
method. The old header value is always returned. If the
given header did not exists then undef is returned.
Methods that deal with dates/times always convert their
value to system time (seconds since Jan 1, 1970) and they
also expect this kind of value when the header value is
set.
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$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.:
$h->content_type('text/html');
The value returned will be converted to lower case,
and potential parameters will be chopped off and
returned as a separate value if in an array context.
This makes it safe to do the following:
if ($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
modifier to the media type. When present, its value
indicates what additional encoding mechanism has been
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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/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:
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<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.
$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.
COPYRIGHT
Copyright 1995-2001 Gisle Aas.
This library is free software; you can redistribute it
and/or modify it under the same terms as Perl itself.
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