When reading from a stream, and that stream becomes closed at some point during the
reading, an IOException is signalled. The exception says "IOException: Error 0", which is completely useless in diagnosing the problem as reading from a closed file descriptor.

Additionally, the C code in io_md.c and the other files which are involved in reading from
a socket (socket.c?) are trashing errno before it gets to a point where it can be used
as part of the exception report (there are a lot of system calls between places in
io_md.c which set errno, and the place in socket.c where it's used).