[mqtt] Implements mqtt publish tooling

vendor/github.com/docker/go-connections/sockets/unix_socket.go

@@ -0,0 +1,32 @@
+// +build !windows
+
+package sockets
+
+import (
+	"net"
+	"os"
+	"syscall"
+)
+
+// NewUnixSocket creates a unix socket with the specified path and group.
+func NewUnixSocket(path string, gid int) (net.Listener, error) {
+	if err := syscall.Unlink(path); err != nil && !os.IsNotExist(err) {
+		return nil, err
+	}
+	mask := syscall.Umask(0777)
+	defer syscall.Umask(mask)
+
+	l, err := net.Listen("unix", path)
+	if err != nil {
+		return nil, err
+	}
+	if err := os.Chown(path, 0, gid); err != nil {
+		l.Close()
+		return nil, err
+	}
+	if err := os.Chmod(path, 0660); err != nil {
+		l.Close()
+		return nil, err
+	}
+	return l, nil
+}