HTTP::Headers(3)

🌸 NAME 🌸

HTTP::Headers — the class that wraps up HTTP message headers, bestie 💌

(Also like, hi, this is the HTTP::Headers(3) page — User Contributed Perl Documentation, perl-core-coded, we love to see it.)

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⭐ VERSION ⭐

version 7.03 — periodt 💅

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✨ 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

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🦋 DESCRIPTION 🦋

okay so the HTTP::Headers class is literally the whole vibe of an HTTP-style message header, encapsulated 🫶. The headers are attribute-value pairs (also called fields, iykyk), they can be repeated, and they get printed in a very particular order. And the field names? Case insensitive, no cap.

Lowkey important detail: instances of this class are usually created as member variables of the HTTP::Request and HTTP::Response classes, internal to the library. So you're mostly meeting it through them 👀.

Here's every method available, bestie, no skips, no gatekeeping:

💖 $h = HTTP::Headers->new

Constructs a brand 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/');

Those constructor arguments get passed straight to the header method, which is described right below, so keep reading 💅.

💖 $h->clone

Returns a copy of this HTTP::Headers object. Iconic dupe behaviour, no notes 🌈.

💖 $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. And to make life easier for perl users who wanna avoid quoting before the => operator, you can use '_' as a replacement for '-' in header names — she's thoughtful like that 🎀.

The header() method accepts multiple ($field => $value) pairs, which means you can update several fields with a single invocation. Efficient queen 👑.

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. And 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. So like, heads up ⚠️.

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 — nothing gets deleted here, she's a collector 💜.

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. Respectful of boundaries, honestly 🌸.

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. Bye bye 👋.

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. 😭 like you get the receipts but not the labels.

💖 $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. She's giving you the leftovers in a lil container 🍓.

💖 $h->clear

This will remove all header fields. Full reset, clean slate, main character energy ✨.

💖 $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. So like, if you're gonna bail, you're on your own for catching it 💀.

💖 $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.

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💖 CONVENIENCE METHODS 💖

Okay bestie, so the headers you reach for literally all the time? They get their very own shortcut methods. Most of these can read AND write — if you pass an argument, congrats, you just set the header value. And the old value? Always handed back to you. If that header wasn't even there to begin with, you get undef. No drama.

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. So like, epoch seconds only, bestie. Don't be out here passing a string. 🫶

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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. ✨ Expired. Gone. Past its moment.

$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. The way it's giving "yeah no I already have that one" 💅

$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. Read-only, babes.

$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. Same deal. 🙈

$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. Yeah, also just for looking.

$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. So cute, so deprecated.

$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. Yeah. Also legacy.

$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. So heads up — those three will let the fragment ride along. 💀

$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 ':'. So like, don't do that. It's literally going to yell at you. 😭

$h->proxy_authorization_basic

Same as authorization_basic() but will set the "Proxy-Authorization" header instead. Same energy, different header. 👑

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🦋 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. Sneaky little colon. 🤫

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⭐ AUTHOR ⭐

Gisle Aas <gisle@activestate.com>

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👑 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.

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And that's a wrap on the whole page, bestie!! 💜 This bad boy is perl v5.42.2, dated 2026-07-23, and it lives at HTTP::Headers(3). Go forth and set some headers. Periodt. 🎀✨