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Re: [tor-dev] [Stegotorus] Strange comparison in chop_circuit_t::send_targeted(conn, blocksize)
On 2012-08-10 8:11 AM, vmon wrote:
Hey Zack,
Please take a look at this comparison in
chop_circuit_t::send_targeted(conn, blocksize):
if (avail > blocksize - lo)
avail = blocksize - lo;
else if (avail > SECTION_LEN)
avail = SECTION_LEN;
else if (upstream_eof && !sent_fin)
// this block will carry the last byte of real data to be sent in
// this direction; mark it as such
op = op_FIN;
Assume SECTION_LEN = 65536 suppose
avail = 67000 blocksize - lo = 66500 => avail = 66500
avail = 67000 blocksize - lo = 67500 => avail = 65536
it's like that if avail is very big then the it is OK if it's bigger than
SECTION_LEN but if it's moderately big then it shouldn't be bigger than
SECTION_LEN, which seems very arbitrary.
The *intent* here is to clamp 'avail' to
min(blocksize - lo, SECTION_LEN) because: we can't fit more than
SECTION_LEN bytes of data in a block under any circumstances, and we
were asked to provide a block which is no larger than 'blocksize' but we
have 'lo' bytes of overhead to cope with.
So your rewrite is correct. I think maybe the control flow here could
do with some going-over for clarity but that needn't happen right now.
if ((avail > blocksize - lo) || (avail > SECTION_LEN))
The nested parentheses are unnecessary in this case.
{
avail = min(blocksize - lo, SECTION_LEN);
}
No curly braces around one-statement blocks.
zw
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