sb-bsd-sockets:get-host-by-name gives NIL with only loopback active

[Ph. Marek]

I cannot readily start SWANK while being on the train, because the defined TCP
port isn't used.

Investigating gives this:
sb-bsd-sockets:get-host-by-name returns NIL if only the loopback interface
(lo, 127.0.0.1) is active.

As soon as I give eth0 an ipv4 address (no matter which one, even with link
down) it works again.

SBCL 1.0.47.0.debian
Linux 2.6.38-2-amd64 #1 SMP Thu Apr 7 04:28:07 UTC 2011 x86_64 GNU/Linux

Here's a transcript:

(defparameter *l* "127.0.0.1")

(defun resolve (n)
  (car (sb-bsd-sockets:host-ent-addresses
         (sb-bsd-sockets:get-host-by-name n))))

(let ((s (make-instance ' sb-bsd-sockets:inet-socket
                        :type :stream
                        :protocol :tcp)))
  (sb-bsd-sockets:socket-bind s
                              (resolve *l*) 8002) ; EINVAL without ip on eth0
  (print s))

;;; result:

(let ((s (make-instance ' sb-bsd-sockets:inet-socket
                        :type :stream
                        :protocol :tcp)))
  (sb-bsd-sockets:socket-bind s
                              (resolve *l*) 8002) ; EINVAL without ip on eth0
  (print s))
  0: (RESOLVE "127.0.0.1")
    1: (SB-BSD-SOCKETS:GET-HOST-BY-NAME "127.0.0.1")
    1: SB-BSD-SOCKETS:GET-HOST-BY-NAME returned
         #<SB-BSD-SOCKETS:HOST-ENT {1002BF2CC1}>
    1: (SB-BSD-SOCKETS:HOST-ENT-ADDRESSES
        #<SB-BSD-SOCKETS:HOST-ENT {1002BF2CC1}>)
    1: SB-BSD-SOCKETS:HOST-ENT-ADDRESSES returned NIL

#<SB-BSD-SOCKETS:INET-SOCKET 0.0.0.0:33173, fd: 18 {1003EF7101}> #<SB-BSD-SOCKETS:INET-SOCKET 0.0.0.0:33173, fd: 18 {1003EF7101}>

;; when ok:
  0: (RESOLVE "127.0.0.1")
    1: (SB-BSD-SOCKETS:GET-HOST-BY-NAME "127.0.0.1")
      2: (SB-BSD-SOCKETS:HOST-ENT-ADDRESSES
          #<SB-BSD-SOCKETS:HOST-ENT {100421CCA1}>)
      2: SB-BSD-SOCKETS:HOST-ENT-ADDRESSES returned NIL
      2: (SB-BSD-SOCKETS:HOST-ENT-ADDRESSES
          #<SB-BSD-SOCKETS:HOST-ENT {100421CCA1}>)
      2: SB-BSD-SOCKETS:HOST-ENT-ADDRESSES returned (#(127 0 0 1))
      2: (SB-BSD-SOCKETS:HOST-ENT-ADDRESSES
          #<SB-BSD-SOCKETS:HOST-ENT {100421CCA1}>)
      2: SB-BSD-SOCKETS:HOST-ENT-ADDRESSES returned (#(127 0 0 1))
    1: SB-BSD-SOCKETS:GET-HOST-BY-NAME returned
         #<SB-BSD-SOCKETS:HOST-ENT {100421CCA1}>
    1: (SB-BSD-SOCKETS:HOST-ENT-ADDRESSES
        #<SB-BSD-SOCKETS:HOST-ENT {100421CCA1}>)
    1: SB-BSD-SOCKETS:HOST-ENT-ADDRESSES returned (#(127 0 0 1))
  0: RESOLVE returned #(127 0 0 1)

#<SB-BSD-SOCKETS:INET-SOCKET 127.0.0.1:8002, fd: 19 {1004219341}> #<SB-BSD-SOCKETS:INET-SOCKET 127.0.0.1:8002, fd: 19 {1004219341}>

[Ph. Marek (ph-marek)]

It's not a DNS problem; 1) the eth0 link isn't necessary; 2) 127.0.0.1 doesn't need /etc/hosts; 3) the name of the machine would return 127.0.1.1 via /etc/hosts.

[Ph. Marek (ph-marek)]

I could argue that bind-socket is wrong; for NIL 4005 it should bind to port 4005 and not to some random one.

[Ph. Marek (ph-marek)]

fe[nl]ix commented that network-manager might rewrite /etc/hosts; I cannot confirm this yet.

BTW, gethostbyname("127.0.0.1") should always work, right?

[Ph. Marek (ph-marek)]

perl doesn't have this problem; I just checked. sbcl returns NIL for the host name, while perl works just fine:

strace perl -e 'use IO::Socket::INET; $x = IO::Socket::INET->new(Listen=>5,LocalAddr=>"127.0.0.1",LocalPort=>3332)'
...
bind(3, {sa_family=AF_INET, sin_port=htons(3332), sin_addr=inet_addr("127.0.0.1")}, 16) = 0