Maintain state for the advertised window length, and only ever increase
it (instead of calculating it afresh on each transmit). This avoids
triggering "treason uncloaked" messages on Linux peers.
Respond to zero-length TCP keepalives (i.e. empty data packets
transmitted outside the window). Even if the peer wouldn't otherwise
expect an ACK (because its packet consumed no sequence space), force an
ACK if it was outside the window.
We don't yet generate TCP keepalives. It could be done, but it's unclear
what benefit this would have. (Linux, for example, doesn't start sending
keepalives until the connection has been idle for two hours.)
Modify data-xfer semantics: it is no longer necessary to call one of
request(), seek() or deliver_xxx() in order to start the data flow.
Autonomous generators must be genuinely autonomous (having their own
process), or otherwise arrange to be called. TCP does this by
starting the retry timer immediately.
Add some debugging statements.
Make TCP give up immediately when it receives -ENETUNREACH from
tcpip_tx(). This avoids the irritating wait when you accidentally type
"kernel pxelinux.0" before bringing up the network interface.
Add ENETUNREACH to strerror()'s list.
"when SYN is ACKed and we have already received SYN", or
"when SYN is received and we have already had SYN ACKed"
rather than just
"when SYN is ACKed"
This avoids spuriously calling the connected() method when we receive
a RST,ACK in response to a SYN.
Truncate TX length to TCP window at time of transmission rather than at
time of adding to TX packet; this is conceptually cleaner and also allows
the application to call tcp_send() multiple times to build up a single
packet.
Redefine TCP state to include "flags that have been sent" rather than
"flags that are currently being sent". This allows at least one special
case (checking that we haven't already sent a FIN in tcp_rx_fin()) to be
collapsed.
Don't call stop_timer() from within the timer expiry callback; it's
already stopped.
Don't call start_timer() when sending a dataless ACK. This may or may
not be the right thing to do; I can't tell.
Back out broken "send ACK only if required to" logic temporarily.