Ruby: How to detect when one side of a socket has been closed

Question

How can I detect that a socket is half-open? The case I'm dealing with is when the other side of a socket has sent a FIN and the Ruby app has ACKed that FIN. Is there a way for me to tell that the socket is in this condition?

Take, for example:

require 'socket'

s = TCPServer.new('0.0.0.0', 5010)

loop do
  c = s.accept

  until c.closed?
    p c.recv(1024)
  end
end

In this case, when I telnet into port 5010, I'll see all my input until I close the telnet session. At that point, it will print empty strings over and over as fast as it can.

This seems to be a duplicate of http://stackoverflow.com/questions/61675/recovering-from-a-broken-tcp-socket-in-ruby-when-in-gets, not sure if it helps any tho! — gaqzi, Apr 30 '09 at 16:02
I'd read up on socket communication. I'd advice the excellent book by Jesse Storimer: working with tcp sockets. I don't have any stocks or anything, just think it is a really good book on this topic. — Axe, Jul 20 '17 at 11:13

score 2 · Answer 1 · answered Jan 18 '16 at 20:43

2

You are using the blocking call recv, which will return nil when the other end closes. The socket won't be closed until you close it. Change

  until c.closed?
    p c.recv(1024)
  end

to

while (s = c.recv(1024)) && s > 0
   p s
end
c.close

answered Jan 18 '16 at 20:43

Rumbleweed

370
1
9

score 1 · Answer 2 · answered Jan 24 '21 at 22:54

1

You could combine IO#read and IO#eof? to check this.

require 'socket'

server = TCPServer.new('0.0.0.0', 5010)

loop do
  client = server.accept
  client.read(1024) until client.eof?
  puts 'client closed connection'
  client.close
end

answered Jan 24 '21 at 22:54

Panic

2,229
23
25

Ruby: How to detect when one side of a socket has been closed

2 Answers2