@Override
    public GuacamoleInstruction filter(GuacamoleInstruction instruction)
            throws GuacamoleException {

        // Intercept "ack" instructions for in-progress streams
        if (instruction.getOpcode().equals("ack"))
            handleAck(instruction);

        // Pass instruction through untouched
        return instruction;

    }
Handles a single "ack" instruction, sending yet more blobs or closing the
stream depending on whether the "ack" indicates success or failure. If no
InputStream is associated with the stream index within the "ack"
instruction, the instruction is ignored.

@param instruction
    The "ack" instruction being handled.
guacamole/src/main/java/org/apache/guacamole/tunnel/InputStreamInterceptingFilter.java