Does recv() always return a complete data packet which has the expected length?

Question

I have a question regarding recv (C, Android).

Is recv guaranteed to return a complete UDP datagram when it returns?

In my case I am using recv to read RTP packets from a socket. The expected length of each RTP packet is 172 (160 bytes for payload and 12 for the header). However, I'm not sure whether I have a guarantee that I'll get the complete 172 bytes when recv returns with data.

Can anybody confirm/comment?

Answer 1

Per POSIX, recv returns the entire UDP packet, unless and error occurs or the buffer is too small for the entire packet. You can detect this by setting the MSG_TRUNC flag, which causes recv to return the frame's actual data length, which you can compare to the buffer size.