each socket can have 4 states while reading or writing...well as far as i can
say....assuming is is nonblocking.
These can be checked via errno and return value.

			recv		send		errno
OK                      >0		>0		NOT SET
CLOSED REMOTELY		0		-1		(write)ECONNRESET
E_AGAIN			-1		-1		EAGAIN|EWOULDBLOCK
ERROR OTHER		-1		-1		AMYTHING ELSE

This means we need a slightly different handling for reading and writing.
It might be neccessary to distinguish other streams from sockets albeit I
would like to prevent this...
This might be tested with small test programs. Well, the only special thing
is ECONNRESET in write mode...because this is something that would not
happen to files open for writing.
We need to be more selective when to close the socket. In fact there are
some errors, as EINTR which does not mean our socket is closed at all.

Error which does not cause us to close the socket while writing:

EAGAIN  - go to poll
EINTR   - try again
ENOBUFS - try again (maybe only a few times....)
ENOMEM  - try again (maybe only a few times....)

All other errors will cause us to close the socket while writing to it.

Error which does not cause us to close the socket while reading:

EAGAIN - go to poll
EINTR  - try again
ENOMEM - try again (maybe only a few times....)

All other errors will cause us to close the socket while reading from it.

From a server view...
- read or write a socket as long as OK
- close if either indicated by read or write...maybe read or write themself
  could do the close.
- poll if all socket get EAGAIN on read and write.

So...read and write must be able to notify about 3 states at least.

1. I am fine...continue operation on me
2. I could not continue right now...please poll me
3. Don't do any further operation on me...please close me.

This could be simply done with return values...

for 1. Return value >= 0
for 2. Return -1  STREAM_DO_POLL
for 3. Return -2  STREAM_DO_CLOSE