Diffing between 4.3.1 and Mar 13 STABLE it appears
you are already working on this bug.  In network.c:
php_sockop_write, you had previously declared didwrite
as size_t, which is unsigned on some OS (e.g. Linux).
Therefore, an error in the send system call was not
detected.  The STABLE release changes didwrite to an
int but in streams.c:_php_stream_write, the return
value still gets assigned into size_t justwrote, and
therefore you get stuck in an endless loop because the
check justwrote>0 i.e. (unsigned)0xFFFFFFFF>0 is true.

Fix is to either change justwrote to an int, or
to add the following to the end of sockop_write:
return didwrite<0?0:didwrite;