Socket.Listen() does not support UNIX Domain Socket

[NonStatic2014]

According to https://github.com/dotnet/corefx/issues/10981, I copied the implementation from corefx/src/System.Net.Sockets/tests/FunctionalTests/UnixDomainSocketTest.cs and use it locally like below. (I'm using dotnet core 2.0.0 on Ubuntu)

Socket s = new Socket(AddressFamily.Unix, SocketType.Dgram, ProtocolType.Unspecified);
Console.WriteLine(s.SendBufferSize);
Console.WriteLine(s.ReceiveBufferSize);

var unixSocket = "./my.sock.1";
var ep = new UnixDomainSocketEndPoint(unixSocket);
Console.WriteLine(ep.AddressFamily);

try
{
    System.IO.File.Delete(unixSocket);
    s.Bind(ep);

    s.Listen(5);  //// **Operation not supported**

    while(true)
    {
        var newS = s.Accept();

        byte[] content = new byte[1000];
        var result = s.Receive(content);
        Console.WriteLine(result);
        Console.WriteLine(Encoding.Default.GetString(content));
        newS.Close();
    }
}
catch(Exception e)
{
    Console.WriteLine(e.Message);
    Console.WriteLine(e.StackTrace);
    s.Close();
}

The exception is something like below:

Operation not supported
   at System.Net.Sockets.Socket.UpdateStatusAfterSocketErrorAndThrowException(SocketError error, String callerName)
   at System.Net.Sockets.Socket.Listen(Int32 backlog)
   at test01.Program.Main(String[] args) in /home/klein/code/temp/test01/Program.cs:line 106

Is there any solution or workaround to let dotnet core build a domain socket server in Linux? Thanks!

[stephentoub]

You specified SocketType.Dgram. The error you're getting isn't coming from .NET, it's coming from the OS, saying it doesn't support that configuration. Did you try SocketType.Stream instead of SocketType.Dgram?

[stephentoub]

e.g. this C program works on my Ubuntu 17.10 VM:

#include <stdio.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <sys/types.h>

int main(void)
{
    unlink("./demo_socket");

    int socket_fd = socket(PF_UNIX, SOCK_STREAM, 0);
    if(socket_fd < 0) { perror("socket"); return 1; }

    struct sockaddr_un address;
    memset(&address, 0, sizeof(struct sockaddr_un));
    address.sun_family = AF_UNIX;
    snprintf(address.sun_path, sizeof(address.sun_path), "./demo_socket");

    if (bind(socket_fd, (struct sockaddr *)&address, sizeof(struct sockaddr_un)) != 0) { perror("bind"); return 1; }
    if (listen(socket_fd, 5) != 0) { perror("listen"); return 1; }

    printf("done\n");
    return 0;
}

and prints out "done", whereas changing that SOCK_STREAM to SOCK_DGRAM results in it printing out "listen: Operation not supported". listen returns EOPNOTSUPP when "The socket is not of a type that supports the listen() operation."

[NonStatic2014]

Thank you Stephen! I tried with STREAM + IP protocol and it worked. For IPC, which protocol would be the best one if I'm using SOCK_STREAM and the data between processes will be up to 10KB?

[stephentoub]

You'd need to read up on domain sockets. I'm not sure of what, if any, tradeoffs exist.