python - Connection refused when using abstract namespace unix sockets -

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i have strange problem unix socket (us) using so-called abstract namespaces when using python , "pure" c (python 3.x looks 2.x have same problem). "normal" socket works charm. "abstract" 1 code works when i'm using same "code platform" (c or python).

first thought has memset / str(n)cpy (see can not connect abstract unix socket in python) imho it's not case.

test matrix (srv - server, cli - client):

  • srv + cli @ "abstract" unix sock:
    • python + python = ok
    • c + c = ok
  • srv + cli @ "normal" unix sock:
    • python + python = ok
    • c + c = ok
  • srv + cli @ "normal" unix sock:
    • python + c = ok
    • c + python = ok
  • srv + cli @ "abstract" unix sock:
    • python + c = fail [cli / strace output: econnrefused (connection refused)]
    • c + python = fail [cli / raised exception: socket.error: [errno 111] connection refused]

/proc/net/unix / lsof or strace show nothing unusual:

  • working "normal" socket c client:
    // ...
    socket(pf_local, sock_stream, 0) = 3
    connect(3, {sa_family=af_local, sun_path=@"/var/tmp/sock.tmp"}, 110) = 0
    // ...

  • misbehaving "abstract" socket c client:
    // ...
    socket(pf_local, sock_stream, 0) = 3
    connect(3, {sa_family=af_local, sun_path=@"/var/tmp/sock.tmp"}, 110) = -1 econnrefused (connection refused)
    // ...

python bug or what...?

gist code samples my test matrix: https://gist.github.com/soutys/ffbe2e76a86835a9cc6b

original code / samples:

update 2015-11-02

more info system , compilations:

  • host system: ubuntu 14.04.3 lts (x64);
  • all c test files compiled gcc (example: gcc -wall -wextra -pedantic -o abs_cli abs_cli.c);
  • all programs (both compiled , built-in python) run non-root user;

when binding unix domain socket abstract name, addrlen argument should sizeof(struct sockaddr_un's sun_family) + number of characters in abstract name + 1. "+1" null byte in front of abstract name in sockaddr_un's sun_path. let's @ example:

  • server in c:

    int sockfd; struct sockaddr_un addr; /* create socket, set addr.sun_family, set addr.sun_path     null byte followed abstract_name */ bind(sockfd, (struct sockaddr *)&addr, sizeof(addr.sun_family) +      strlen(abstract_name) + 1);

  • client in python:

    client = socket.socket(socket.af_unix, ...) client.connect( "\0abstract_name" )

references:


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