I'd say that's a matter of interpretation. I did consider the situation where no ETX existed; however, jagexCoder wrote "... packets of interest that are within STX and ETX endings.". Accordingly, I coded for STX and ETX to always be present. Perhaps wait for the OP to clarify this.
[Aside: You appear to have removed the original typo, so I don't know what you're apologising for. Regardless, I accept your apology. :-) ]
Oh dear! Having posted this, I see I've also introduced a typo such that it made no sense.
s/Perhaps wait for to OP can clarify this./Perhaps wait for the OP to clarify this./