I was wondering, imagine if there is no data to read from a TCP socket, then a whole frame of 1492 bytes arrives (full). In your code (C or any language supporting TCP) you have let’s say recv 4096 bytes, will the OS guarantee that the recv reads the whole 1492 bytes, or is it possible that the loading of the frame in memory and recv are “interleaved”, so the recv may get less ?
TCP is a stream oriented protocol. Data are received in order but you must not do any assumption about how many times you have to call recv until you receive all your data.
It is up to your application to repeat the calls to recv until you know you have received what you need.