Cannot connect to a listener on 0.0.0.0

[informatimago]

Related to #75 but here, characterised as a bug.

This is in the context of IPv6, with both IPv6 and IPv4 interfaces.

Notably, localhost has a A and an AAAA records!

17:48[pjb@despina org.xquartz:0 ~ 17Gi]$ ping -c 3 localhost
PING localhost (127.0.0.1): 56 data bytes
64 bytes from 127.0.0.1: icmp_seq=0 ttl=64 time=0.053 ms
64 bytes from 127.0.0.1: icmp_seq=1 ttl=64 time=0.046 ms
64 bytes from 127.0.0.1: icmp_seq=2 ttl=64 time=0.054 ms

--- localhost ping statistics ---
3 packets transmitted, 3 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 0.046/0.051/0.054/0.004 ms

17:48[pjb@despina org.xquartz:0 ~ 17Gi]$ ping6 -c 3 localhost
PING6(56=40+8+8 bytes) ::1 --> ::1
16 bytes from ::1, icmp_seq=0 hlim=64 time=0.088 ms
16 bytes from ::1, icmp_seq=1 hlim=64 time=0.074 ms
16 bytes from ::1, icmp_seq=2 hlim=64 time=0.073 ms

--- localhost ping6 statistics ---
3 packets transmitted, 3 packets received, 0.0% packet loss
round-trip min/avg/max/std-dev = 0.073/0.078/0.088/0.007 ms

Listening to localhost and connecting to localhost works:

(usocket:with-socket-listener (listen  "localhost"   9999 :element-type '(unsigned-byte 8) :reuseaddress t :backlog 1)
  (usocket:with-client-socket (client client-stream  "localhost" 9999 :element-type '(unsigned-byte 8))
    (usocket:with-server-socket (server (usocket:socket-accept listen))
      (write-byte 42  client-stream)
      (force-output client-stream)
      (read-byte  (usocket:socket server)))))

42

But listening on all the IPv4 addresses, and connecting to localhost does not work:

(usocket:with-socket-listener (listen  "0.0.0.0"   9999 :element-type '(unsigned-byte 8) :reuseaddress t :backlog 1)
  (usocket:with-client-socket (client client-stream  "localhost" 9999 :element-type '(unsigned-byte 8))
    (usocket:with-server-socket (server (usocket:socket-accept listen))
      (write-byte 42  client-stream)
      (force-output client-stream)
      (read-byte  (usocket:socket server)))))

> Debug: Error #<usocket:connection-refused-error #x3020051CEBCD>
> While executing: (:internal swank::invoke-default-debugger), in process worker(470).
> Type :POP to abort, :R for a list of available restarts.
> Type :? for other options.

$ macosx-netstat-tnpl |grep 9999
tcp4       0      0  *.9999                 *.*                    LISTEN

That's because as mentionned in #75, usocket:socket-connect only tries IPv6 and not both IPv6 and IPv4 addresses. Cf. patch provided in #75.

[binghe]

Hi Pascal J. Bourguignon,

I'm sorry that I overlooked your code provided in #75. Now I have committed your version (for Clozure CL since its IPv6 support), and added the above two tests into the test suite. I'm also on macOS, now it seems worked:

? (usocket:with-socket-listener (listen  "localhost"   9999 :element-type '(unsigned-byte 8) :reuseaddress t :backlog 1)
  (usocket:with-client-socket (client client-stream  "localhost" 9999 :element-type '(unsigned-byte 8))
    (usocket:with-server-socket (server (usocket:socket-accept listen))
      (write-byte 42  client-stream)
      (force-output client-stream)
      (read-byte  (usocket:socket server)))))
42
? (usocket:with-socket-listener (listen  "0.0.0.0"   9999 :element-type '(unsigned-byte 8) :reuseaddress t :backlog 1)
  (usocket:with-client-socket (client client-stream  "localhost" 9999 :element-type '(unsigned-byte 8))
    (usocket:with-server-socket (server (usocket:socket-accept listen))
      (write-byte 42  client-stream)
      (force-output client-stream)
      (read-byte  (usocket:socket server)))))
42

Thanks again for your patch.

Regards,

Chun Tian

[binghe]

And I will test and adapt your algorithm also on other Lisp platforms (which supports IPv6, especially LispWorks and SBCL) to see if they suffer from the issue.

[informatimago]

Thank you.