[lwip-users] Bug in tcp: 2*Odd length packets may cause 2 bytes of space in send-buffer to be lost

[Jan Ulvesten]

Version V 1.54 of tcp_in.c and V1.42 of tco_out.c fixed a bug with an unaligned send-buffer.

 

There seems to be a side-effect of the fix causing a “leak” in the send-buffer.

 

When sending for instance two packets each with one byte, snd_buf is decremented by 2 for each of the packets by tcp_out.c.  tcp_in.c is doing the reverse thing.. This works fine as long as every single packet is ackd. The peer will however ack both packets in a single packet, thus acking 2 bytes. The reverse action is not performed and two bytes of space in snd_buf is “lost”.

 

By the way, the FIN ACK problem is still present, Leon: See earlier postings on this topic. I can’t see that a bug report has been submitted.

 

Jan Ulvesten

Senior Software Engineer
SICOM  AS