What causes a recv syscall for a socket to sometimes return less than the request len?

Hi!

On 17:20 Wed 21 Sep     , Daniel Ellis wrote:

Howdy,

I understand that data fragmentation happens across TCP packets, and in my
case that is what is happening.  The packets I'm seeing usually run around
1450 in length, and are always cut into two packets at the 1400 mark.  This
works fine most of the time, since the call to recv is being passed a len
of 4096 (via Python's socket.recv, which I'm assuming is just a wrapper
around the system call).  But sometimes I'll get all of the data I request,
even across TCP packet boundaries (so the full 1450 bytes), and other
times, it stops at a single packet, at which point I need to make another
recv call.

The recv() call currently returns:
- as soon as there is some data in the receive queue
- all the data which is in the queue, up your buffer size.

	-Michi
-- 
programing a layer 3+4 network protocol for mesh networks
see http://michaelblizek.twilightparadox.com