socket: try removing is socket-location is a directory

Due to race-conditions between containers starting and the Docker
remote API being up, containers bind-mounting the docker-socket may
cause the socket-path to be created as a directory.

This patch will attempt to remove the directory in such situations.
Removing will fail if the directory is not empty.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Author: thaJeztah

sockets/unix_socket.go

@@ -79,8 +79,14 @@ func WithChmod(mask os.FileMode) SockOption {
 
 // NewUnixSocketWithOpts creates a unix socket with the specified options
 func NewUnixSocketWithOpts(path string, opts ...SockOption) (net.Listener, error) {
+	// Using syscall.Unlink(), not os.Remove() to prevent deleting the socket if it's in use
 	if err := syscall.Unlink(path); err != nil && !os.IsNotExist(err) {
-		return nil, err
+		if err != syscall.EISDIR {
+			return nil, err
+		}
+		if err := syscall.Rmdir(path); err != nil {
+			return nil, err
+		}
 	}
 	mask := syscall.Umask(0777)
 	defer syscall.Umask(mask)