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. 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.
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) 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 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->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.
COPYRIGHT¶
Copyright 1995-2005 Gisle Aas.
This library is free software; you can redistribute it and/or modify it under
the same terms as Perl itself.