###############################################################################
#
# The MIT License (MIT)
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# Copyright (c) Tavendo GmbH
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# of this software and associated documentation files (the "Software"), to deal
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import hashlib
from twisted.internet import reactor

from autobahn.twisted.websocket import WebSocketServerFactory, \
    WebSocketServerProtocol, \
    listenWS


class FrameBasedHashServerProtocol(WebSocketServerProtocol):

    """
    Frame-based WebSockets server that computes a running SHA-256 for message
    data received. It will respond after every frame received with the digest
    computed up to that point. It can receive messages of unlimited number
    of frames. Digest is reset upon new message.
    """

    def onMessageBegin(self, isBinary):
        WebSocketServerProtocol.onMessageBegin(self, isBinary)
        self.sha256 = hashlib.sha256()

    def onMessageFrame(self, payload):
        l = 0
        for data in payload:
            l += len(data)
            self.sha256.update(data)
        digest = self.sha256.hexdigest()
        print("Received frame with payload length {}, compute digest: {}".format(l, digest))
        self.sendMessage(digest.encode('utf8'))

    def onMessageEnd(self):
        self.sha256 = None


if __name__ == '__main__':

    factory = WebSocketServerFactory("ws://localhost:9000")
    factory.protocol = FrameBasedHashServerProtocol

    enableCompression = False
    if enableCompression:
        from autobahn.websocket.compress import PerMessageDeflateOffer, \
            PerMessageDeflateOfferAccept
        # Function to accept offers from the client ..

        def accept(offers):
            for offer in offers:
                if isinstance(offer, PerMessageDeflateOffer):
                    return PerMessageDeflateOfferAccept(offer)

        factory.setProtocolOptions(perMessageCompressionAccept=accept)

    listenWS(factory)
    reactor.run()
