socket: try removing if socket-location is a directory on Linux

sockets/unix_socket.go

@@ -86,8 +86,18 @@ func WithChmod(mask os.FileMode) SockOption {
 // this should only be for a short duration, it may affect other processes that
 // create files/directories during that period.
 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 {
+			// On Linux, attempting to remove a directory returns syscall.EISDIR,
+			// in which case we try to remove the directory. MacOS does not return
+			// this error, so we'll return immediately, see:
+			// https://github.com/golang/go/blob/6b420169d798c7ebe733487b56ea5c3fa4aab5ce/src/os/file_unix.go#L300-L311
+			return nil, err
+		}
+		if err := syscall.Rmdir(path); err != nil {
+			return nil, err
+		}
 	}
 
 	// net.Listen does not allow for permissions to be set. As a result, when

sockets/unix_socket_test.go

@@ -4,8 +4,11 @@ package sockets
 
 import (
 	"fmt"
+	"io/ioutil"
 	"net"
 	"os"
+	"path"
+	"runtime"
 	"syscall"
 	"testing"
 )
@@ -75,3 +78,48 @@ func TestUnixSocketWithOpts(t *testing.T) {
 	}
 	runTest(t, path, l, echoStr)
 }
+
+func TestUnixSocketConflictDirectory(t *testing.T) {
+	tmpDir, err := ioutil.TempDir("", t.Name())
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(tmpDir)
+
+	t.Run("conflicting directory", func(t *testing.T) {
+		if runtime.GOOS == "darwin" {
+			t.Skip("not supported on macOS")
+		}
+		path := path.Join(tmpDir, "test.sock")
+
+		// Create a conflicting directory at the socket location
+		err = os.MkdirAll(path, 0700)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		l, err := NewUnixSocketWithOpts(path)
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer l.Close()
+		runTest(t, path, l, "hello")
+	})
+
+	t.Run("conflicting file", func(t *testing.T) {
+		// Create a conflicting file at the socket location
+		path := path.Join(tmpDir, "test2.sock")
+		f, err := os.Create(path)
+		if err != nil {
+			t.Fatal(err)
+		}
+		f.Close()
+
+		l, err := NewUnixSocketWithOpts(path)
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer l.Close()
+		runTest(t, path, l, "hello")
+	})
+}