Node.js the Right Way

Responding to Requests

The REQ/REP (request/reply) pattern is quite common in networked programming, particularly in Node. We’ll use this pattern often in the next couple of chapters, and ØMQ has great support for it. As you’ll see in a minute, this is where the “Q” of ØMQ becomes apparent.

In ØMQ, a REQ/REP pair communicates in lockstep. A request comes in, then a reply goes out. Additional incoming requests are queued and later dispatched by ØMQ. Your application, however, is only aware of one request at a time.

Let’s see how this works, again using the file system as a source of information for building a service. In this scenario, a responder waits for a request for file data, then serves up the content when asked. We’ll start with the responder—the ...