[racket] Intercepting WebSocket connections to the Racket web server?

From: Jay McCarthy (jay.mccarthy at gmail.com)
Date: Sat Mar 21 22:26:15 EDT 2015

The Web server models applications as "servlet : request -> response"
and there's no way to go from the request to the original HTTP

In contrast, the Web server has a lower level concept of a
"dispatcher" that receives a parsed HTTP request AND the connection
object (which has the I/O ports). If the WebSocket handshake has the
sender start with a correctly formatted HTTP request, then this is
what you want and you'd go from using something like serve/servlet to
using something like serve/launch/wait and dispatch/servlet with
another layer of dispatching.

On the other hand, if the handshake doesn't have a complete request,
then you'd need to customize the dispatching server directly with a
new kind of read-request and request structure that can stop in the
middle. I think what I'd do is make a super-struct and re-use
everything from the HTTP server when the handshake isn't there.


On Sat, Mar 21, 2015 at 8:44 PM, Alexis King <lexi.lambda at gmail.com> wrote:
> The WebSocket handshake is intentionally implemented in such a way so that WebSocket connections can be performed using the same port that the HTTP server is running on. This is implemented by making the handshake a standard HTTP 1.1 GET request with an “Upgrade: websocket” header.
> I’m interested in doing this using the Racket web server, but I’m not sure how to intercept websocket connections. I’m completely willing to implement all the websocket connection logic myself, I just need to know how to detect headers sent with that Upgrade header before the web server has a chance to handle them so that I can pass the connection off to my own websocket logic.
> What’s the proper way to achieve this sort of thing?
> Alexis
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Jay McCarthy

           "Wherefore, be not weary in well-doing,
      for ye are laying the foundation of a great work.
And out of small things proceedeth that which is great."
                          - D&C 64:33

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