The HTTP echo server with an HTTP driver

The time has come to rewrite the HTTP echo server as a functional and reactive application. This application contains an observable cycle. The HTTP server driver returns HTTP requests and takes HTTP responses as input, while the server logic takes HTTP requests as input and returns HTTP responses:

Figure 3.5: The echo server reactivity diagram

ReactiveX operators

This new implementation of the echo server makes use of two new ReactiveX operators: empty and merge. Let's see what they do before going into the new implementation of the server.

The empty operator

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