[lwip-devel] [bug #20515] TCP delayed ack does not work as expected

[Jim Pettinato]

Follow-up Comment #9, bug #20515 (project lwip):



Okay, I've taken a look at this issue, since I'm sick of settling for a
separate ACK packet being sent for every Modbus/TCP command received when I
KNOW I'm going to reply with data anyway. The delayed ACK feature is
essentially useless in this type of application.

I've got a 64K window, it's reduced by 12-255 bytes by an incoming Modbus
command, and lwIP wants to send an immediate window update? That seems awfully
silly to me.

And, if you actually follow all of the program flow, at the point tcp_recved
is called by the app, the TF_ACK_DELAY flag is ALWAYS set for the pcb... it's
set when the segment is handled in tcp_receive(). It appears to me that there
is no need to test the previous state of the pcb's flags here, just call
tcp_ack_now() when you need an immediate window update sent. 

Of course, we still have to determine the precise definition of when we need
an immediate window update sent... ;)

Now that 1.3.0 has been released, I'd like to form a consensus on how to
proceed on this bug. 



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