From: Eric Wong <normalperson@...>
Date: 2015-12-16T10:43:42+00:00
Subject: [ruby-core:72184] EOF behavior for socket recv* methods?

Background: IO#read with length arg returns nil on EOF;
and read_nonblock raises EOFError or returns nil depending
on how the `exception' keyword is specified:

a, b = IO.pipe
b.close
p a.read(1) # => nil
p begin; a.read_nonblock(1); rescue => e; e; end # => nil EOFError
p a.read_nonblock(1, exception: false) # => nil


However, using the analogous recv/recv_nonblock calls return
an empty string, similar to IO#read w/o length arg...

require 'socket'
a, b = UNIXSocket.pair(:SEQPACKET)
b.close
p a.recv(1) # => ""
p a.recv_nonblock(1) # => ""
p a.recv_nonblock(1, exception: false) # => ""

I've noticed this for many years and always forgot to bring it
up, but what was the reasoning for this?


In any case, I'm not sure if we can change it at this point.
This mistake (if it was one) has been with us for many years.

Linux manpage for recv/recvfrom/recvmsg says:

RETURN VALUE
  These calls return the number of bytes received,  or  -1  if  an  error
  occurred.   The  return  value will be 0 when the peer has performed an
  orderly shutdown.

So the same thing as read(2)...