[lwip-users] Normal way how highlevel API interfaces with stack ?!

[Bonny Gijzen]

Hi,

 

 

I am trying to understand how (highlevel) BSD style API interfaces with any IP stack (like lwIP).

Let me try to explain my issue/question with an example.

 

Highlevel API:

 

if (SendSomeData(&send_buf, len, send_timeout)==RES_OK)

{

if (WaitForData(&receive_buf, 10, rec_timeout)==10)

{

  //successfully received my response, do something with it

} else {//some error like timeout or too few databytes received}

} else {//some error during sending of data}

 

My question is what will happen if one of the 2 highlevel functions fail?

Assume the SendSomeData() fails. This means normally (I think) that an ACK is not received yet in lowlevel land. This means this piece of data is being retransmitted some number of times.

 

Assume my timeout is set to 5 seconds.

So in highlevel land, after 5 seconds I fall through and do nothing (or some error code).

But in lowlevel land this data is still being retransmitted until the MAXRETRY.

 

In theory MAXRETRY can occur much later than the timeout value in highlevel land.

So it could be that the sent frame is successfully retransmitted, even after the highlevel function has failed and exitted.

 

I would think that the highlevel function needs to tell lwIP that this frame no longer needs to be retransmitted. But is this a normal way for a highlevel function to interface with the stack ?

Or are other approaches used?

 

(Similar thing can happen if the highlevel function timesout, tells lwIP to stop with this frame,

but at the same time the ACK arrives ... so the other side *has* received this frame, while the highlevel user thinks the other side hasn't)

 

 

Excuse my ignorance on this matter,

Bonny