1HTTP::Headers(3) User Contributed Perl Documentation HTTP::Headers(3)
2
6 HTTP::Headers - Class encapsulating HTTP Message headers
7
9 require HTTP::Headers;
10 $h = HTTP::Headers->new;
11 $h->header('Content-Type' => 'text/plain'); # set
13 $ct = $h->header('Content-Type'); # get
14 $h->remove_header('Content-Type'); # delete
15
17 The "HTTP::Headers" class encapsulates HTTP-style message headers. The
18 headers consist of attribute-value pairs also called fields, which may
19 be repeated, and which are printed in a particular order. The field
20 names are cases insensitive.
21 Instances of this class are usually created as member variables of the
23 "HTTP::Request" and "HTTP::Response" classes, internal to the library.
24 The following methods are available:
26 $h = HTTP::Headers->new
28 Constructs a new "HTTP::Headers" object. You might pass some ini‐
29 tial attribute-value pairs as parameters to the constructor. E.g.:
30 $h = HTTP::Headers->new(
32 Date => 'Thu, 03 Feb 1994 00:00:00 GMT',
33 Content_Type => 'text/html; version=3.2',
34 Content_Base => 'http://www.perl.org/');
35 The constructor arguments are passed to the "header" method which
37 is described below.
38 $h->clone
40 Returns a copy of this "HTTP::Headers" object.
41 $h->header( $field )
43 $h->header( $field => $value, ... )
44 Get or set the value of one or more header fields. The header
45 field name ($field) is not case sensitive. To make the life easier
46 for perl users who wants to avoid quoting before the => operator,
47 you can use '_' as a replacement for '-' in header names.
48 The header() method accepts multiple ($field => $value) pairs,
50 which means that you can update several fields with a single invo‐
51 cation.
52 The $value argument may be a plain string or a reference to an
54 array of strings for a multi-valued field. If the $value is pro‐
55 vided as "undef" then the field is removed. If the $value is not
56 given, then that header field will remain unchanged.
57 The old value (or values) of the last of the header fields is
59 returned. If no such field exists "undef" will be returned.
60 A multi-valued field will be returned as separate values in list
62 context and will be concatenated with ", " as separator in scalar
63 context. The HTTP spec (RFC 2616) promise that joining multiple
64 values in this way will not change the semantic of a header field,
65 but in practice there are cases like old-style Netscape cookies
66 (see HTTP::Cookies) where "," is used as part of the syntax of a
67 single field value.
68 Examples:
70 $header->header(MIME_Version => '1.0',
72 User_Agent => 'My-Web-Client/0.01');
73 $header->header(Accept => "text/html, text/plain, image/*");
74 $header->header(Accept => [qw(text/html text/plain image/*)]);
75 @accepts = $header->header('Accept'); # get multiple values
76 $accepts = $header->header('Accept'); # get values as a single string
77 $h->push_header( $field => $value )
79 Add a new field value for the specified header field. Previous
80 values for the same field are retained.
81 As for the header() method, the field name ($field) is not case
83 sensitive and '_' can be used as a replacement for '-'.
84 The $value argument may be a scalar or a reference to a list of
86 scalars.
87 $header->push_header(Accept => 'image/jpeg');
89 $header->push_header(Accept => [map "image/$_", qw(gif png tiff)]);
90 $h->init_header( $field => $value )
92 Set the specified header to the given value, but only if no previ‐
93 ous value for that field is set.
94 The header field name ($field) is not case sensitive and '_' can be
96 used as a replacement for '-'.
97 The $value argument may be a scalar or a reference to a list of
99 scalars.
100 $h->remove_header( $field, ... )
102 This function removes the header fields with the specified names.
103 The header field names ($field) are not case sensitive and '_' can
105 be used as a replacement for '-'.
106 The return value is the values of the fields removed. In scalar
108 context the number of fields removed is returned.
109 Note that if you pass in multiple field names then it is generally
111 not possible to tell which of the returned values belonged to which
112 field.
113 $h->remove_content_headers
115 This will remove all the header fields used to describe the content
116 of a message. All header field names prefixed with "Content-"
117 falls into this category, as well as "Allow", "Expires" and
118 "Last-Modified". RFC 2616 denote these fields as Entity Header
119 Fields.
120 The return value is a new "HTTP::Headers" object that contains the
122 removed headers only.
123 $h->clear
125 This will remove all header fields.
126 $h->header_field_names
128 Returns the list of distinct names for the fields present in the
129 header. The field names have case as suggested by HTTP spec, and
130 the names are returned in the recommended "Good Practice" order.
131 In scalar context return the number of distinct field names.
133 $h->scan( \&process_header_field )
135 Apply a subroutine to each header field in turn. The callback rou‐
136 tine is called with two parameters; the name of the field and a
137 single value (a string). If a header field is multi-valued, then
138 the routine is called once for each value. The field name passed
139 to the callback routine has case as suggested by HTTP spec, and the
140 headers will be visited in the recommended "Good Practice" order.
141 Any return values of the callback routine are ignored. The loop
143 can be broken by raising an exception ("die"), but the caller of
144 scan() would have to trap the exception itself.
145 $h->as_string
147 $h->as_string( $eol )
148 Return the header fields as a formatted MIME header. Since it
149 internally uses the "scan" method to build the string, the result
150 will use case as suggested by HTTP spec, and it will follow recom‐
151 mended "Good Practice" of ordering the header fields. Long header
152 values are not folded.
153 The optional $eol parameter specifies the line ending sequence to
155 use. The default is "\n". Embedded "\n" characters in header
156 field values will be substituted with this line ending sequence.
157
159 The most frequently used headers can also be accessed through the fol‐
160 lowing convenience methods. These methods can both be used to read and
161 to set the value of a header. The header value is set if you pass an
162 argument to the method. The old header value is always returned. If
163 the given header did not exist then "undef" is returned.
164 Methods that deal with dates/times always convert their value to system
166 time (seconds since Jan 1, 1970) and they also expect this kind of
167 value when the header value is set.
168 $h->date
170 This header represents the date and time at which the message was
171 originated. E.g.:
172 $h->date(time); # set current date
174 $h->expires
176 This header gives the date and time after which the entity should
177 be considered stale.
178 $h->if_modified_since
180 $h->if_unmodified_since
181 These header fields are used to make a request conditional. If the
182 requested resource has (or has not) been modified since the time
183 specified in this field, then the server will return a "304 Not
184 Modified" response instead of the document itself.
185 $h->last_modified
187 This header indicates the date and time at which the resource was
188 last modified. E.g.:
189 # check if document is more than 1 hour old
191 if (my $last_mod = $h->last_modified) {
192 if ($last_mod < time - 60*60) {
193 ...
194 }
195 }
196 $h->content_type
198 The Content-Type header field indicates the media type of the mes‐
199 sage content. E.g.:
200 $h->content_type('text/html');
202 The value returned will be converted to lower case, and potential
204 parameters will be chopped off and returned as a separate value if
205 in an array context. If there is no such header field, then the
206 empty string is returned. This makes it safe to do the following:
207 if ($h->content_type eq 'text/html') {
209 # we enter this place even if the real header value happens to
210 # be 'TEXT/HTML; version=3.0'
211 ...
212 }
213 $h->content_encoding
215 The Content-Encoding header field is used as a modifier to the
216 media type. When present, its value indicates what additional
217 encoding mechanism has been applied to the resource.
218 $h->content_length
220 A decimal number indicating the size in bytes of the message con‐
221 tent.
222 $h->content_language
224 The natural language(s) of the intended audience for the message
225 content. The value is one or more language tags as defined by RFC
226 1766. Eg. "no" for some kind of Norwegian and "en-US" for English
227 the way it is written in the US.
228 $h->title
230 The title of the document. In libwww-perl this header will be ini‐
231 tialized automatically from the <TITLE>...</TITLE> element of HTML
232 documents. This header is no longer part of the HTTP standard.
233 $h->user_agent
235 This header field is used in request messages and contains informa‐
236 tion about the user agent originating the request. E.g.:
237 $h->user_agent('Mozilla/1.2');
239 $h->server
241 The server header field contains information about the software
242 being used by the originating server program handling the request.
243 $h->from
245 This header should contain an Internet e-mail address for the human
246 user who controls the requesting user agent. The address should be
247 machine-usable, as defined by RFC822. E.g.:
248 $h->from('King Kong <king@kong.com>');
250 This header is no longer part of the HTTP standard.
252 $h->referer
254 Used to specify the address (URI) of the document from which the
255 requested resource address was obtained.
256 The "Free On-line Dictionary of Computing" as this to say about the
258 word referer:
259 <World-Wide Web> A misspelling of "referrer" which
261 somehow made it into the {HTTP} standard. A given {web
262 page}'s referer (sic) is the {URL} of whatever web page
263 contains the link that the user followed to the current
264 page. Most browsers pass this information as part of a
265 request.
266 (1998-10-19)
268 By popular demand "referrer" exists as an alias for this method so
270 you can avoid this misspelling in your programs and still send the
271 right thing on the wire.
272 When setting the referrer, this method removes the fragment from
274 the given URI if it is present, as mandated by RFC2616. Note that
275 the removal does not happen automatically if using the header(),
276 push_header() or init_header() methods to set the referrer.
277 $h->www_authenticate
279 This header must be included as part of a "401 Unauthorized"
280 response. The field value consist of a challenge that indicates
281 the authentication scheme and parameters applicable to the
282 requested URI.
283 $h->proxy_authenticate
285 This header must be included in a "407 Proxy Authentication
286 Required" response.
287 $h->authorization
289 $h->proxy_authorization
290 A user agent that wishes to authenticate itself with a server or a
291 proxy, may do so by including these headers.
292 $h->authorization_basic
294 This method is used to get or set an authorization header that use
295 the "Basic Authentication Scheme". In array context it will return
296 two values; the user name and the password. In scalar context it
297 will return "uname:password" as a single string value.
298 When used to set the header value, it expects two arguments. E.g.:
300 $h->authorization_basic($uname, $password);
302 The method will croak if the $uname contains a colon ':'.
304 $h->proxy_authorization_basic
306 Same as authorization_basic() but will set the "Proxy-Authoriza‐
307 tion" header instead.
308
310 The header field name spelling is normally canonicalized including the
311 '_' to '-' translation. There are some application where this is not
312 appropriate. Prefixing field names with ':' allow you to force a spe‐
313 cific spelling. For example if you really want a header field name to
314 show up as "foo_bar" instead of "Foo-Bar", you might set it like this:
315 $h->header(":foo_bar" => 1);
317 These field names are returned with the ':' intact for
319 $h->header_field_names and the $h->scan callback, but the colons do not
320 show in $h->as_string.
321
323 Copyright 1995-2005 Gisle Aas.
324 This library is free software; you can redistribute it and/or modify it
326 under the same terms as Perl itself.
327perl v5.8.8 2004-04-06 HTTP::Headers(3)