Mastering Perl/Tk

Library for WWW Access in Perl

LWP is a Perl library providing access to the Web, used primarily for writing client applications. It “speaks” Hypertext Transfer Protocol (HTTP),^[1] and one of its most basic duties is fetching the content of URLs. The beauty of LWP is that it hides all the operational details while allowing us to do our work with simple objects and methods.

In essence, a user agent object working on our behalf takes a request object and does whatever low-level communication and error handling is required to send a request for web content on its way. The user agent then waits for the reply (or error) and hands it back to our program in the form of a response object. Our job is to create the user agent, then use various LWP methods to manipulate requests and responses. But if all we want to do is simply fetch web content, we can use LWP in “simple” mode and just say “fetch this URL,” and LWP creates the user agent and request/response objects internally, eventually returning content data to our program.

At first glance, the simple LWP mechanism would appear to suffice for a client such as tkcomics, but it has some drawbacks. As you might suspect, they have to do with blocking, because there might be a considerable time delay between a request and when the network finally delivers the response. Even handling LWP’s user agent manually can’t surmount all of these problems. Thus, eventually, we’ll have to resort to a multiprocess scheme. So let’s begin and see ...