[lwip-users] Non-blocking I/O in lwip

[Francesco Sacchi]

Hello,
we are currently using lwip 1.3.2 and we are aware that non-blocking IO 
while *sending* tcp data is not supported in that version.

We have integrated lwip in our operating system (bertos.org) for now 
usign only the cooperative kernel.

Here is the scenario:
our application has a listening tcp socket, used by the user in order to 
send telnet commands, and, in another process, the application sends 
data to a remote tcp server.

Sometimes this server crashes in a manner that connection stalls. The 
socket is still open on the server side, but the server application does 
not read from it.
This server is not under our control, so we have to handle this case on 
our side.

Lwip tries to buffer the data, but at some point the memory finishes and 
the lwip_send() function blocks indefinitely; and worse, since there is 
no more memory, the listening telnet socket cannot handle requests anymore.

We tried to close the blocked socket with lwip_close() from another 
process, but lwip_send() did not return nor the memory allocated was freed.

We see that non-blocking sending has been implemented in lwip-1.4, and 
here is our question: if we upgrade will this issue be solved?

In other words, if I open a socket in non-blocking mode, I suppose that 
the lwip_send() will return an error in case it would block 
(EWOULDBLOCK), but then, if I close the socket, will the memory 
allocated be freed correctly?



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  |/ Francesco Sacchi - Develer S.r.l.
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