Just in case anyone's interested.
After a bit of thought,it wasn't so hard to check the partial-send pathway.
Every check on loopback and simple LAN always sent as much as was in the buffer.
So it was impossible to check the partial-send path directly.
So all I did was create a simple pseudo "mysend" function in a debug version of the server.
Instead of writing to the socket it writes to another file whose size is easy to check.
The number of bytes written is determined randomly on each call and returned to the writecount variable.
So it simulates a very dodgy send() function.
Hey Presto!, path checked.
