HTTP::Headers - Class encapsulating HTTP Message headers
version 6.44
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
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:
Constructs a new HTTP::Headers object. You might pass
some initial attribute-value pairs as parameters to the constructor.
E.g.: $h = HTTP::Headers->new( Date => Thu, 03 Feb 1994
00:00:00 GMT, Content_Type => text/html; version=3.2, Content_Base
=> http://www.perl.org/); The constructor arguments are passed to the
header method which is described below.
Returns a copy of this HTTP::Headers object.
Get or set the value of one or more header fields. The header field
name ($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 =
$header->header(Accept); # get values as a single string
Add a new field value for the specified header field. Previous values
for the same field are retained. As for the header()
method, the field name ($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)]);
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
$value argument may be a scalar or a reference to a list of
scalars.
This function removes the header fields with the specified names. The header field names ($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.
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.
This will remove all header fields.
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.
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.
Returns the list of pairs of keys and values.
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.
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.
This header represents the date and time at which the message was originated. E.g.: $h->date(time); # set current date
This header gives the date and time after which the entity should be considered stale.
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.
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) { ... } }
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 ... }
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.
Returns TRUE if the Content-Type header field indicate that the content is textual.
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.
Returns TRUE if the Content-Type header field indicate that the content is XHTML. This method can't be used to set Content-Type.
Returns TRUE if the Content-Type header field indicate that the content is XML. This method can't be used to set Content-Type.
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.
A decimal number indicating the size in bytes of the message content.
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.
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.
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));
The server header field contains information about the software being used by the originating server program handling the request.
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.
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.
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.
This header must be included in a
407 Proxy Authentication Required response.
A user agent that wishes to authenticate itself with a server or a proxy, may do so by including these headers.
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 ':'.
Same as authorization_basic() but will set the Proxy-Authorization header instead.
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.
Gisle Aas <gisle@activestate.com>
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.