gen_unix is an Erlang interface to Unix sockets. The main purpose of gen_unix is to allow access to socket ancillary data required for fd and credential passing.

WARNING: gen_unix is still under development and going through a lot of change.

Examples

• File descriptor passing

  Open 2 shell prompts and start an Erlang VM in each:

    # VM 1
    $ rebar shell
    1> {ok, Ref} = gen_unix:start().
    {ok,<0.35.0>}
  
    2> {ok, Listen} = gen_unix:listen(Ref, "/tmp/test").
    {ok,8}
  
    # VM 2
    $ sudo rebar shell
    1> {ok, Ref} = gen_unix:start().
    {ok,<0.35.0>}
  
    2> {ok, Socket} = gen_unix:connect(Ref, "/tmp/test").
    {ok,7}
  
    2> {ok, FD1} = procket:socket(inet,raw,icmp).
    {ok,8}
  
    3> {ok, FD2} = procket:socket(inet6,raw,icmp6).
    {ok,9}
  
    4> {ok, Msg} = unixsock:msg({fdsend, [FD1,FD2]}).
    {ok,{msghdr,<<0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,160,114,0,
                  232,20,127,0,0,1,...>>,
                  [{msg_iov,<<>>},{msg_control,<<>>},{iov,[<<>>]}]}}
  
    5> gen_unix:sendmsg(Ref, Socket, Msg).
    ok
  
    # Open another shell and send a few ping's
  
    # Back in VM 1
    2> {ok, Socket} = gen_unix:accept(Ref, Listen).
    {ok,9}
  
    3> {ok, Msg} = unixsock:msg({fdrecv, 2}).
    {ok,{msghdr,<<0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,160,114,0,
                  128,198,127,0,0,1,...>>,
                  [{msg_iov,<<>>},{msg_control,<<>>},{iov,[<<>>]}]}}
  
    4> gen_unix:recvmsg(Ref, Socket, Msg).
    {ok,1}
  
    % [8,9]
    5> {ok, [FD1, FD2]} = unixsock:msg(Msg).
    {ok,"\t\n"}
  
    5> procket:read(FD1, 1024).
    {ok,<<69,0,0,84,236,114,0,0,56,1,38,238,173,194,43,69,
          192,168,213,152,0,0,98,95,21,173,0,...>>}
  

• Credential passing

    # VM 1
    $ rebar shell
    1> {ok, Ref} = gen_unix:start().
    {ok,<0.35.0>}
  
    2> {ok, Listen} = gen_unix:listen(Ref, "/tmp/test").
    {ok,8}
  
    # VM 2
    $ rebar shell
    1> {ok, Ref} = gen_unix:start().
    {ok,<0.35.0>}
  
    2> {ok, Socket} = gen_unix:connect(Ref, "/tmp/test").
    {ok,7}
  
    2> {ok, Msg} = unixsock:msg(credsend).
    {ok,{msghdr,<<0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,115,0,232,
                  20,127,0,0,1,...>>,
                  [{msg_iov,<<>>},{iov,[<<>>]}]}}
  
    3> gen_unix:sendmsg(Ref, Socket, Msg).
    ok
  
    # Back in VM 1
    2> {ok, Socket} = gen_unix:accept(Ref, Listen).
    {ok,9}
  
    3> {ok, Msg} = unixsock:msg(credrecv).
    {ok,{msghdr,<<0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,115,0,128,
                  198,127,0,0,1,...>>,
                  [{msg_iov,<<>>},{msg_control,<<>>},{iov,[<<>>]}]}}
  
    4> unixsock:setsockopt(Socket, {credrecv, open}).
    ok
  
    5> gen_unix:recvmsg(Ref, Socket, Msg).
    {ok,1}
  
    6> unixsock:msg(Msg).
    {ok, [{pid,12866},{uid,1000},{gid,1000}]}
  
    7> unixsock:setsockopt(Socket, {credrecv, close}).
    ok