Infinite loop that reads messages off of the socket while not closed.

        When a message is received its corresponding pending Future is set
        to have the message as its result.

        This is never used directly and is fired as a separate callback on the
        I/O loop via the `connect()` method.

def read_loop(self):
        """
        Infinite loop that reads messages off of the socket while not closed.

        When a message is received its corresponding pending Future is set
        to have the message as its result.

        This is never used directly and is fired as a separate callback on the
        I/O loop via the `connect()` method.
        """
        while not self.closing:
            try:
                xid, zxid, response = yield self.read_response()
            except iostream.StreamClosedError:
                return
            except Exception:
                log.exception("Error reading response.")
                self.abort()
                return

            payload_log.debug("[RECV] (xid: %s) %s", xid, response)

            if xid == protocol.WATCH_XID:
                self.watch_handler(response)
                continue
            elif xid in protocol.SPECIAL_XIDS:
                f = self.pending_specials[xid].pop()
            else:
                f = self.pending.pop(xid)

            if isinstance(response, Exception):
                f.set_exception(response)
            else:
                f.set_result((zxid, response))