How to connect to a Unix Domain Socket in .NET Core in C#

Question

I've created a unix socket in .NET Core on Linux (Ubuntu 16.04):

var unixSocket = "/var/run/mysqld/mysqld.sock";
var socket = new Socket(AddressFamily.Unix, SocketType.Stream, ProtocolType.IP);

Now how do I connect the socket?

The .NET Core API lists various Socket.Connect options, but all except for the first one deal with IP Addresses:

public void Connect(EndPoint remoteEP)
public void Connect(IPAddress address, int port)
public void Connect(IPAddress[] addresses, int port)
public void Connect(string host, int port)

The System.Net API defines a DNSEndpoint and an IPEndpoint, but I can't seem to find a UnixEndpoint or similar class to pass to Socket.Connect(EndPoint remoteEP)

Answer 1

Update: .NET Standard 2.1 / .NET Core 2.1 contains a UnixDomainSocketEndPoint Class

Original answer, applies to versions of .NET Standard / .NET Core prior to 2.1:

There does not seem to be a built-in UnixEndPoint class for .NET Core or a library that implements one at the time of this writing. The UnixEndPoint class from the Mono.Posix project can be easily adapted to work with .NET Core, however:

// copied from https://github.com/mono/mono/blob/master/mcs/class/Mono.Posix/Mono.Unix/UnixEndPoint.cs

//
// Mono.Unix.UnixEndPoint: EndPoint derived class for AF_UNIX family sockets.
//
// Authors:
//  Gonzalo Paniagua Javier ([email protected])
//
// (C) 2003 Ximian, Inc (http://www.ximian.com)
//

//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
//
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//

using System.Net.Sockets;
using System.Text;

namespace System.Net
{

    public class UnixEndPoint : EndPoint
    {
        string filename;

        public UnixEndPoint (string filename)
        {
            if (filename == null)
                throw new ArgumentNullException ("filename");

            if (filename == "")
                throw new ArgumentException ("Cannot be empty.", "filename");
            this.filename = filename;
        }

        public string Filename {
            get {
                return(filename);
            }
            set {
                filename=value;
            }
        }

        public override AddressFamily AddressFamily {
            get { return AddressFamily.Unix; }
        }

        public override EndPoint Create (SocketAddress socketAddress)
        {
            /*
             * Should also check this
             *
            int addr = (int) AddressFamily.Unix;
            if (socketAddress [0] != (addr & 0xFF))
                throw new ArgumentException ("socketAddress is not a unix socket address.");
            if (socketAddress [1] != ((addr & 0xFF00) >> 8))
                throw new ArgumentException ("socketAddress is not a unix socket address.");
             */

            if (socketAddress.Size == 2) {
                // Empty filename.
                // Probably from RemoteEndPoint which on linux does not return the file name.
                UnixEndPoint uep = new UnixEndPoint ("a");
                uep.filename = "";
                return uep;
            }
            int size = socketAddress.Size - 2;
            byte [] bytes = new byte [size];
            for (int i = 0; i < bytes.Length; i++) {
                bytes [i] = socketAddress [i + 2];
                // There may be junk after the null terminator, so ignore it all.
                if (bytes [i] == 0) {
                    size = i;
                    break;
                }
            }

            string name = Encoding.UTF8.GetString (bytes, 0, size);
            return new UnixEndPoint (name);
        }

        public override SocketAddress Serialize ()
        {
            byte [] bytes = Encoding.UTF8.GetBytes (filename);
            SocketAddress sa = new SocketAddress (AddressFamily, 2 + bytes.Length + 1);
            // sa [0] -> family low byte, sa [1] -> family high byte
            for (int i = 0; i < bytes.Length; i++)
                sa [2 + i] = bytes [i];

            //NULL suffix for non-abstract path
            sa[2 + bytes.Length] = 0;

            return sa;
        }

        public override string ToString() {
            return(filename);
        }

        public override int GetHashCode ()
        {
            return filename.GetHashCode ();
        }

        public override bool Equals (object o)
        {
            UnixEndPoint other = o as UnixEndPoint;
            if (other == null)
                return false;

            return (other.filename == filename);
        }
    }
}

With this class in your project, the socket can be connected like so:

var unixSocket = "/var/run/mysqld/mysqld.sock";
var socket = new Socket(AddressFamily.Unix, SocketType.Stream, ProtocolType.IP);
var unixEp = new UnixEndPoint(unixSocket);
socket.Connect(unixEp);