Monday, August 6, 2012

Echo Server

Factor has nice cross-platform support for network programming. As is fairly typical, I am going to use an "echo server" to demonstrate how the libraries work.

The basic logic for an "echo server" is to read input from a client, write it back to them, and repeat until the client disconnects. Using the input and output stream abstraction, we can build a word which does this in a general manner, recursing until f is read indicating end-of-stream:

: echo-loop ( -- )
    1024 read-partial [ write flush echo-loop ] when* ;

Our "echo server" will use TCP (i.e., connection-oriented networking) and the general server abstraction that comes with Factor with a binary encoding. The server framework uses the name "echo.server" to automatically log client-related messages (such as connect and disconnect events as well as errors) to $FACTOR/logs/echo.server. We specify the echo-loop quotation as the handler for clients:

: <echo-server> ( port -- server )
    binary <threaded-server>
        swap >>insecure
        "echo.server" >>name
        [ echo-loop ] >>handler ;

We can start an echo server on, for example, port 12345:

IN: scratchpad 12345 <echo-server> start-server

Testing this is pretty easy using Netcat or a similar client:

$ nc localhost 12345
Hello, Factor
Hello, Factor

This is available as the echo-server vocabulary.

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