Now that you know how to write function interfaces to a web page (or in our case, a form), you can convert the data and functionality of any web page into something your programs can use easily in real time. Here are a few more things for you to consider.
A secondary benefit of creating a function interface to a webbot is that when a webbot uses a web page on another server as a resource, it allocates bandwidth and computational power across several computers. Since more resources are deployed, you can get more done in less time. You can use this technique to spread the burden of running complex webbots to more than one computer on your local or remote networks. This technique may also be used to make page requests from multiple IP addresses (for added stealth) or to spread bandwidth across multiple Internet nodes.
The interface described in this example is specific to PHP. Although scripts for Perl, Java, or C++ environments would be very similar to this one, you could not use this script directly in an environment other than PHP. You can solve this problem by returning data in a language-independent format like XML or SOAP (Simple Object Access Protocol). To learn more about these protocols, read Chapter 26.
Our example assumed that the target was not under our control, so we had to live within the constraints presented by the target website. When you control the website your interface targets, however, you can design the web page in such a way that you don't have to parse the data from HTML. In these instances, the data is returned as variables that your program can use directly. These techniques are also described in detail in Chapter 26.
If you're interested in creating your own ZIP code server (with a lightweight interface), you'll need a ZIP code database. You should be able to find one by performing a Google search for ZIP code database.