* Creates a key for the specified request for response matching.
     *
     * @param request the request to create a key for
     * @throws IOException if an I/O error occurs
     */
    protected abstract void makeKey(Request request) throws IOException;

    /**
     * Reads and returns the key of the next message without consuming it.
     *
     * @return the request key of the next message

            socket.close();
        } finally {
            digest = null;
            socket = null;
            tconHostName = null;
        }
    }

    @Override
    protected void makeKey(final Request request) throws IOException {
        /* The request *is* the key */
        if (++mid == 32000) {
            mid = 1;
        }
        ((ServerMessageBlock) request).mid = mid;
    }

     *
     * @param request the request to generate a key for
     * @return the generated key
     * @throws IOException if an I/O error occurs
     */
    protected abstract long makeKey(Request request) throws IOException;

    /**
     * Peek at the next key without removing it from the input stream
     *
     * @return the next key or null if none available