Chapter 3. Bidirectional Chat

Your first full-fledged example is to build a bidirectional chat using WebSocket. The end result will be a server that accepts WebSocket connections and messages for your “chat room” and fans the messages out to connected clients. The WebSocket protocol itself is simple, so to write your chat application, you will manage the collection of message data in an array and hold the socket and unique UUID for the client in locally scoped variables.

Long Polling

Long polling is a process that keeps a connection to the server alive without having data immediately sent back to the client. Long polling (or a long-held HTTP request) sends a server request that is kept open until it has data, and the client will receive it and reopen a connection soon after receiving data from the server. This, in effect, allows for a persistent connection with the server to send data back and forth.

In practice, two common techniques are available for achieving this. In the first technique, XMLHttpRequest is initiated and then held open, waiting for a response from the server. Once this is received, another request is made to the server and held open, awaiting more data. The other technique involves writing out custom script tags possibly pointing to a different domain (cross-domain requests are not allowed with the first method). Requests are then handled in a similar manner and reopened in the typical long-polling fashion.

Long polling is the most common way of implementing ...

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