Internet Services

Network programming is hard. The C socket library is the standard way of writing Internet clients and servers. Its like the file API descibed in Chapter 6, with its special flags and meager abstraction, only much more complicated. Its a shame because networked applications are the coolest kind of application. Only computer nerds like you and me care about XML or the best way to sort a list, but everyone uses Internet applications.

Fortunately, network programming is easy. Ruby provides bindings to the C socket library (in socket), but youll probably never need to use them. Existing Ruby libraries (some in the standard distribution) can speak every popular high-level Internet protocol.

The most popular Internet service is, of course, the Web, and Rubys most popular Internet library (or any kind of library, actually) is the Rails framework. Weve devoted the entire next chapter to Rails (Chapter 15) so that we can cover other technologies here.

Apart from Rails, most of the interesting stuff you can do with Ruby happens on the client end. We start with a set of recipes for requesting web pages (Recipes 14.1, 14.2, and 14.3), which are brought together at the end of the chapter with Recipe 14.20. Combine these recipes with one from Chapter 11 (probably Recipe 11.5), and you can make your own spider or web browser.

Then we present Ruby clients for the most popular Internet protocols. Ruby can do just about everything you do online: send and receive email, perform nameserver queries, even transfer files with FTP, SCP, or BitTorrent. With the Ruby interfaces, you can write custom clients for these protocols, or integrate them into larger programs.

Its less likely that youll be writing your own server in Ruby. A server only exists to service clients, so theres not much you can do but faithfully implement the appropriate protocol. If you do write a server, itll probably be for a custom protocol, one for which no other server exists.

Ruby provides two basic servers that you can use as a starting point. The gserver library described in Recipe 14.14 provides a generic framework for almost any kind of Internet server. Here you do have to do some socket programming, but only the easy parts. gserver takes care of all the socket-specific details, and you can just treat the sockets like read-write IO objects. You can use the techniques described in Chapter 6 to communicate with your clients.

The other basic server is WEBrick, a simple but powerful web server thats used as the basis for Rails and the Ruby SOAP server. If youve built a protocol on top of HTTP, WEBrick makes a good starting point for a server. Recipe 14.19 shows how to use WEBrick to hook pieces of Ruby code up to the Web.

Apart from Rails, web services are the major network-related topic not covered in this chapter. As with Rails, this is because they have their own chapter: Chapter 16.