Fiddler Ideas

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Support Sec-WebSocket-Extensions: permessage-deflate

WebSockets offer a mechanism for doing compression of messages. Fiddler's WebSocket Inspector should provide a simpler means of viewing such content. 

The mechanism looks to be a simple DEFLATE operation:

  • Eric Lawrence
  • Nov 23 2016
  • Future consideration
  • Attach files
  • Eric Lawrence commented
    23 Nov, 2016 06:34pm

    Note, supporting permessage-deflate without the


    parameters (meaning that context takeover is allowed) likely would be pretty tricky because I don't think the DEFLATE code inside Fiddler is able to reuse a single compression context across multiple operations.

  • Eric Lawrence commented
    23 Nov, 2016 06:26pm

    Workarounds Today:

    Sec-WebSocket-Extensions: permessage-deflate;client_max_window_bits=15
    If you need to manipulate this stream, you could write a FiddlerScript rule that removes this header from the WebSocket handshake and this should force the communication to fall back to uncompressed traffic.
    Alternatively, on a one-off basis, you can use the Inspect As Response button to add a message to the WebSessions list:
    Inline image 1
    Use F2 to enable editing of the response and add a Content-Encoding: deflate header:
    Inline image 2
    Hit F2 to save the change, and you can now use the Transformer or yellow bar to decompress the text:
    Inline image 3
    Inline image 4