Bug #12674
closedio/wait: not handling the case when the socket is closed before doing wait_readable/writable with timeout
Description
I wrote the following script to show the problem:
require 'socket'
require 'io/wait'
Thread.new do
server = TCPServer.new 2000 # Server bind to port 2000
loop do
client = server.accept # Wait for a client to connect
client.puts "Hello !"
client.puts "Time is #{Time.now}"
sleep 3
client.close
end
end
puts "server is starting..."
sleep 2
puts "connecting now"
s = TCPSocket.new 'localhost', 2000
puts "connected"
10.times do
k = s.wait_readable(2)
puts "wait: #{k.inspect}"
v = s.read_nonblock(8, exception: false)
puts "val: #{v.inspect}"
break if v == nil
end
# server is starting...
# connecting now
# connected
# wait: #<TCPSocket:fd 11>
# val: "Hello !\n"
# wait: #<TCPSocket:fd 11>
# val: "Time is "
# wait: #<TCPSocket:fd 11>
# val: "2016-08-"
# wait: #<TCPSocket:fd 11>
# val: "14 16:30"
# wait: #<TCPSocket:fd 11>
# val: ":35 +020"
# wait: #<TCPSocket:fd 11>
# val: "0\n"
# wait: nil
# val: :wait_readable
# ISSUE!
# wait: nil
# val: nil
The problem there is, I'm going to wait_readable(timeout)
on the socket, and it's going to return nil. This nil is ambiguous, as it can mean in the spec "timed out on wait" or "server has closed the socket". The only way I have to know exactly what it means is to call read_nonblock again. If nil, it's EOF. If wait_readable, it timed out. So I can't fail early.
The wait methods could benefit from a more explicit return value for #wait. This might have been subject to discussion previously, as "false" was removed as of ruby 2.3 from the possible return values, but I think it's an issue that might prevent correctness in socket programming. Take the example from the standard library: https://github.com/ruby/ruby/blob/trunk/lib/net/protocol.rb#L154-L159
If the server closes after :wait_readable was returned, wait_readable will return nil, and this will be interpreted as a timeout, instead of EOF. I don't know of any real-world issues with this using net/http, but there was one here.
Updated by shyouhei (Shyouhei Urabe) over 7 years ago
- Description updated (diff)
Updated by nobu (Nobuyoshi Nakada) over 7 years ago
- Status changed from Open to Feedback
What's your platform?
IIRC, it depends on platforms.
Updated by chucke (Tiago Cardoso) over 7 years ago
this was executed on a MAC (darwin, I guess).
Updated by chucke (Tiago Cardoso) over 7 years ago
Just tested on linux (x86_64-linux), same output.
Updated by nobu (Nobuyoshi Nakada) over 7 years ago
- Status changed from Feedback to Assigned
- Assignee set to nobu (Nobuyoshi Nakada)
Updated by nobu (Nobuyoshi Nakada) over 6 years ago
- Status changed from Assigned to Rejected
IO#wait_readable
should return the receiver at EOF, since 2.3.
nil
before EOF is the behavior of the OS.