So we can intercept the _make_request() method if we want to sublass Mechanize and it appears to return an HTTP::Response object (you have to read the code to really see that). I am subclassing to be able to use Mechanize to test Mason code, but the following minimal test script fails:

package WWW::Mechanize::Mason;
use strict;

use HTTP::Status qw/RC_OK RC_NOT_FOUND/;
use base 'WWW::Mechanize'; # we can make it work by also inheriting fr
+om Clone

sub _make_request
{
    my ($self,$request,@rest) = @_;
    my $uri = $request->uri->as_string;
    my $response_content = "foobar\n";

    # we'll probably have to build in support for redirects at some po
+int
    my $response = HTTP::Response->new(
        defined $response_content ? RC_OK : RC_NOT_FOUND,
    );
    $response->request($request);
    $response->push_header('Content-Type', 'text/html');
    $response->content($response_content);
    return $response;
}

package main;
my $browser = WWW::Mechanize::Mason->new;
$browser->get('/TEST/mason.txt');
print $browser->content;
$browser->get('/TEST/mason.txt');
print $browser->content;
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After the second call to get(), the program dies with this message:

Can't use an undefined value as a HASH reference at /dp/usr/cxp/perl/lib/LWP/UserAgent.pm line 1036

Digging into this, I find that the program dies after the call to to _make_request() and I see that the problem lies with LWP::UserAgent::clone expecting its object to have a 'proxy' key, but the value is undef and the code can't dereference it. The quick workaround was to have my stuff also inherit from Clone, but that was causing some problems with a different, much larger script that I've had trouble reducing down.

The troublesome method in LWP::UserAgent:

sub clone
{
    my $self = shift;
    my $copy = bless { %$self }, ref $self;  # copy most fields

    # elements that are references must be handled in a special way
    $copy->{'proxy'} = { %{$self->{'proxy'}} }; # here's where we die!
    $copy->{'no_proxy'} = [ @{$self->{'no_proxy'}} ];  # copy array

    # remove reference to objects for now
    delete $copy->{cookie_jar};
    delete $copy->{conn_cache};

    $copy;
}
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Suggestions for the best way to fix this are welcome. I can make Clone work, but it doesn't seem like a clean fix.