[lwip-users] TCP retransmit bug

[Karl Jeacle]

Hi all,

There appears to be a problem with how lwIP handles TCP retransmissions.

When a retransmission is triggered via tcp_slowtmr(), tcp_rexmit()
is called, and does the following:

1. checks that pcb->unacked is not null
2. moves all segments from pcb->unacked to pcb->unsent
3. sets some variables
4. calls tcp_output()

But if further timeouts occur, and no acks have been received, both
tcp_slowtmr() and tcp_rexmit() find that pcb->unacked is null, and
therefore no subsequent retransmission is attempted.

Shouldn't both of these functions be modifed to check for segments
on pcb->unsent in addition to pcb->unacked?

Karl