Handling partial return from recv() TCP in C

Question

I\'ve been reading through Beej\'s Guide to Network Programming to get a handle on TCP connections. In one of the samples the client code for a simple TCP stream cl

Answer 1

The first thing you need to learn when doing TCP/IP programming: 1 write/send call might take several recv calls to receive, and several write/send calls might need just 1 recv call to receive. And anything in-between.

You'll need to loop until you have all data. The return value of recv() tells you how much data you received. If you simply want to receive all data on the TCP connection, you can loop until recv() returns 0 - provided that the other end closes the TCP connection when it is done sending.

If you're sending records/lines/packets/commands or something similar, you need to make your own protocol over TCP, which might be as simple as "commands are delimited with \n".

The simple way to read/parse such a command would be to read 1 byte at a time, building up a buffer with the received bytes and check for a \n byte every time. Reading 1 byte is extremely inefficient, so you should read larger chunks at a time.

Since TCP is stream oriented and does not provide record/message boundaries it becomes a bit more tricky - you'd have to recv a piece of bytes, check in the received buffer for a \n byte, if it's there - append the bytes to previously received bytes and output that message. Then check the remainder of the buffer after the \n - which might contain another whole message or just the start of another message.