How can I explicitly wait for a TCP ACK before proceeding?

Question

Is there a way to get send() to wait until all the data that has been sent has been ACK-ed (or return -1 if the timeout for an ACK has been reached), or is there some other mechanism to wait for the ACK after the send() but before doing something else?

I am using the standard Unix Berkeley sockets API.

I know I could implement an application-layer ACK, but I'd rather not do that when TCP's ACK serves the purpose perfectly well.

Answer 1

AFAIK there is no way.

Also, it wouldn't be reliable, the ACK means only that the kernel received the data, in the meantime the client or its machine could have crashed. You would think the client received the data, but actually it never processed it.

Answer 2

Unfortunately standard API doesn't reserve any appropriate way to do this. There could be a way to query the current TCP send window size/usage, but unfortunately it may not be queried by the standard means.

Of course there are tricky ways to achieve what you want. For instance on Windows one may create a network filter driver to monitor packet-level trafic.