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19.8. Debugging the Raw HTTP Exchange
19.8.1. Problem
Your CGI script is misbehaving strangely with your browser, and you suspect something in the HTTP header is missing. You want to find out exactly what your browser is sending to the server in the HTTP header.
19.8.2. Solution
Create your own fake web server and point your browser at it, as shown in Example 19-6.
Example 19-6. dummyhttpd
#!/usr/bin/perl -w
# dummyhttpd - start an HTTP daemon and print what the client sends
use strict;
use LWP 5.32; # minimal good version
use HTTP::Daemon;
my $server = HTTP::Daemon->new(Timeout => 60, LocalPort => 8989);
print "Please contact me at: <URL:", $server->url, ">\n";
while (my $client = $server->accept) {
CONNECTION:
while (my $answer = $client->get_request) {
print $answer->as_string;
$client->autoflush;
RESPONSE:
while (<STDIN>) {
last RESPONSE if $_ eq ".\n";
last CONNECTION if $_ eq "..\n";
print $client $_;
}
print "\nEOF\n";
}
print "CLOSE: ", $client->reason, "\n";
$client->close;
undef $client;
}19.8.3. Discussion
It's hard to keep track of which versions of all browsers still have which bugs. The fake server program can save you days of head scratching, because sometimes a misbehaving browser doesn't send the server the right thing. Historically, we have seen aberrant browsers lose their cookies, mis-escape a URL, send the wrong status line, and other blunders even less obvious.
The fake server is best run on the same machine as the real server. That way your browser still sends any cookies destined for that domain. Then instead of pointing your browser at:
http://somewhere.com/cgi-bin/whatever
use the alternate port given in the new constructor in the Solution. You don't need to be the superuser to run the server if you use the alternate port.
http://somewhere.com:8989/cgi-bin/whatever
If you convince yourself that the client is behaving properly but wonder about the server, it's easiest to use the telnet program to manually talk to the remote server.
% telnet www.perl.com 80 GET /bogotic HTTP/1.0 <<blank line here>> HTTP/1.1 404 File Not Found Date: Tue, 21 Apr 1998 11:25:43 GMT Server: Apache/1.2.4 Connection: close Content-Type: text/html <HTML><HEAD> <TITLE>404 File Not Found </TITLE> </HEAD><BODY> <H1>File Not Found</H1> The requested URL /bogotic was not found on this server.<P> </BODY></HTML>
If you have LWP installed on your system, you can use the GET alias for the lwp-request program. This will follow any redirection chains, which can shed light on your problem. For example:
% GET -esuSU http://mox.perl.com/perl/bogotic GET http://language.perl.com/bogotic Host: mox.perl.com User-Agent: lwp-request/1.32 GET http://mox.perl.com/perl/bogotic --> 302 Moved Temporarily GET http://www.perl.com/perl/bogotic --> 302 Moved Temporarily GET http://language.perl.com/bogotic --> 404 File Not Found Connection: close Date: Tue, 21 Apr 1998 11:29:03 GMT Server: Apache/1.2.4 Content-Type: text/html Client-Date: Tue, 21 Apr 1998 12:29:01 GMT Client-Peer: 208.201.239.47:80 Title: Broken perl.com Links <HTML> <HEAD><TITLE>An Error Occurred</TITLE></HEAD> <BODY> <H1>An Error Occurred</h1> 404 File Not Found </BODY> </HTML>
19.8.4. See Also
The documentation for the standard CGI module; Recipe 19.9; lwp-request(1)
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| 19.7. Redirecting to a Different Location |  | 19.9. Managing Cookies |
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