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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def receive_message(self):
 """Receive a message from the transport. Blocks until a message has been received. May return a context opaque to clients that should be passed to :py:func:`send_reply` to identify the client later on. :return: A tuple consisting of ``(context, message)``. """


        if not ('REQUEST_METHOD' in os.environ
                and os.environ['REQUEST_METHOD'] == 'POST'):
            print("Status: 405 Method not Allowed; only POST is accepted")
            exit(0)

        # POST
        content_length = int(os.environ['CONTENT_LENGTH'])
        request_json = sys.stdin.read(content_length)
        request_json = urlparse.unquote(request_json)
        # context isn't used with cgi
        return None, request_json