[rohc] input bytes beyond message

["Lajos Zaccomer (ETH)" <Lajos.Zaccomer@eth.ericsson.se>]

Hi,

At SIPit, an interesting interpretation problem was found regarding the INPUT-BYTES instruction. Namely: what to do with the bytes read if there aren't as many in the message as was requested?

The RFC says: "If the instruction requests data that lies beyond the end of the SigComp message, no data is returned.  Instead the UDVM moves program execution to the address specified by the address operand."

In my interpretation this sentence means that ONLY data that lies beyond the end of the message should be discarded. Others interpreted this to discard even those bytes that were part of the message.

Why is this important? Because it may be a very nice feature to eliminate implementing a loop or passing the length of the data block, resulting in shorter bytecodes:
	INPUT-BYTES maximum_length, destination, continue_address
This instructions reads a maximum of maximum_length bytes from the message without knowing how many bytes there are.

I don't think this may impose security risk compared to the other solution, when all the bytes are discarded, if the available cpb is increased with the number of the actually read bytes, instead of the value of the length parameter (the same way as it is done in the INPUT-HUFFMAN instruction).

As I need some statement regarding this question in one or two weeks, I call all interested parties, standardizers and implementors, to start a discussion on this question.

BR/Zacco
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