I read somewhere that every TCP connection has it's own 125kB output and input buffer. What happens if this buffer is full, and I still continue sending data on linux?
According to http://www.kernel.org/doc/man-pages/online/pages/man2/send.2.html the packets are just silently dropped, without notifying me. What can I do to stop this from happening? Is there any way to find out if at least some of my data has been sent correctly, so that I can continue at a later point in time?
Short answer is this. "send" calls on a TCP socket will just block until the TCP sliding window (or internal queue buffers) opens up as a result of the remote endpoint receiving and consuming data. It's not much different than trying to write bytes to a file faster than the disk can save it.
If your socket is configured for non-blocking mode, send will return EWOULDBLOCK or EAGAIN, until data can be sent. Standard poll, select, and epoll calls will work as expected so you know when to "send" again.
I don't know that the "packets are dropped". I think that what is more likely is that the calls that the program makes to write() will either block or return a failure.
