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import hashlib
from twisted.internet import reactor

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


class MessageBasedHashServerProtocol(WebSocketServerProtocol):

    """
    Message-based WebSockets server that computes a SHA-256 for every
    message it receives and sends back the computed digest.
    """

    def onMessage(self, payload, isBinary):
        sha256 = hashlib.sha256()
        sha256.update(payload)
        digest = sha256.hexdigest()
        self.sendMessage(digest.encode('utf8'))
        print("Sent digest for message: {}".format(digest))


if __name__ == '__main__':
    factory = WebSocketServerFactory("ws://127.0.0.1:9000")
    factory.protocol = MessageBasedHashServerProtocol
    listenWS(factory)
    reactor.run()
