Received Packet Size Differ From transmitted TCP Packet

That code won't work (as you've found out).

As I said, TCP is a bytestream protocol.

The data from the send() calls will very likely be merged together then split into full sized ethernet frames.

The recv() will be given a partial length if it 'catches up' with the receive data stream.

If you put a marker at the start of each 640 byte block you'll find that you receiver is misaligned on the rx data for most of the trace.