- Introduction
- The Apache Request Object
- The HTTP Request Message
- The Client Request
- Accessing Client Request Headers
- Accessing HTML Form Fields
- Reading POSTed Data Manually
- Manipulating Cookies
- Handling File Uploads
- Setting Server Response Headers
- Controlling Caching Behavior
- Sending Server Response Headers
- Setting the Response Status
- Setting Error Headers
- Manipulating Headers with Multiple Like Fields
- Using Subrequests
- Setting Headers for Subrequests
- Short-Circuiting Subrequests
- Getting or Setting the Request Method
- Accessing the Request Object from XS
This chapter is from the book
This chapter is from the book
This chapter is from the book
Accessing Client Request Headers
You need to access the headers from the incoming request.
Technique
Use $r->headers_in() to obtain access to the header data.
sub handler {
my $r = shift;
# Grab all of the headers at once...
my %headers_in = $r->headers_in;
# ... or get a specific header and do something with it.
my $gzip = $r->headers_in->get('Accept-Encoding') =~ m/gzip/;
$r->send_http_header('text/plain');
print "The host in your URL is: ", $headers_in{'Host'}, "\n";
print "Your browser is: ", $headers_in{'User-Agent'}, "\n";
print "Your browser accepts gzip encoded data\n" if $gzip;;
return OK;
}
Comments
As shown in Recipe 3.3, parts of the incoming client request have their own accessor methods. For the request headers, all are stored together in a table in the Apache request record and are accessible through the headers_in() method. headers_in() returns an array of key/value pairs in a list context or an Apache::Table object in a scalar context; our sample code uses both forms.
Acceptable client request headers are defined in section 5.3 of RFC 2616 (with the exception of the Cookie header, which is described in RFC 2109). As already mentioned, in addition to the client request headers, some general and entity headers may also apply to a client request. These three classes of headers contain many more headers than those listed here in Table 3.3, but the following are the ones that you are most likely to find yourself programming against.
Table 3.3 Some HTTP Request Headers
|
Header |
Description |
|
Accept |
Lists acceptable media types for the server to present in response |
|
Accept-Charset |
Lists character sets the client will accept |
|
Accept-Encoding |
Lists encodings the client will accept |
|
Accept-Language |
Lists languages the client is most interested in |
|
Authorization |
A series of authorization fields |
|
Cookie |
Decribes a client cookie |
|
Host |
Name of the requested host server |
|
If-Match |
The entity tag of the client's cached version of the requested resource |
|
If-Modified-Since |
An HTTP-formatted date for the server to use in resource comparisons |
|
If-None-Match |
A list of entity tags representing the client's possible cached resources |
|
If-Unmodified-Since |
An HTTP-formatted date for the server to use in resource comparisons |
|
Referer |
An absolute or partial URI of the resource from which the current request was obtained |
|
User-Agent |
A string identifying the client software |
Note that the best way to access or alter a header isn't necessarily by going after the raw data with headers_in(). A multitude of methods are available in mod_perl that take care of the gory work of processing and parsing the incoming headers. For instance, the Apache::File class has methods for dealing with all the conditional If-* headers. Apache::File and these headers are discussed in detail in Chapter 6.