Behaviour of recv on a non-blocking TCP socket before connection completion

Question

Friends,

I have a non-blocking TCP socket (on AIX). When I attempted connect() I got EINPROGRESS. My question is if I call recv() before connection completion, what would be the (most apprpriate) error code?

I saw that, in case connection fails, and I call recv(), I got ECONNREFUSED; means I got an error corresponding to my earlier connect() attempt. Taking same logic I should get EINPROGRESS for recv(). Am I right in my approach ?

If yes, this raises another question - Why such error codes are not included amongst error codes of recv()?

Answer 1

I have only seen EAGAIN returned in this case, just as you would see in the case where there's no data to read. For writing to a non-connected socket, you typically get ENOTCONN, though I believe some platforms might give you EAGAIN.

Here's a trivial Python script to demonstrate:

import socket
# Any address that does not succeed or fail right away will do
ADDR = "192.168.100.100"
PORT = 23
s = socket.socket()
s.setblocking(False)
try:
    s.connect((ADDR, PORT))
except socket.error, e:
    print "Connect gave us",e
try:
    s.recv(1)
except socket.error, e:
    print "Read gave us",e
try:
    s.send("x")
except socket.error, e:
    print "Write gave us",e

For me, it gives: Connect gave us (36, 'Operation now in progress') Read gave us (35, 'Resource temporarily unavailable') Write gave us (57, 'Socket is not connected')

These are EINPROGRESS, EAGAIN, and ENOTCONN respectively.