net: add (*UnixListener).SetUnlinkOnClose

Let users control whether unix listener socket file is unlinked on close.

Fixes #13877.

Change-Id: I9d1cb47e31418d655f164d15c67e188656a67d1c
Reviewed-on: https://go-review.googlesource.com/32099
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/unixsock_posix.go

@@ -190,6 +190,18 @@ func (ln *UnixListener) file() (*os.File, error) {
 	return f, nil
 }
 
+// SetUnlinkOnClose sets whether the underlying socket file should be removed
+// from the file system when the listener is closed.
+//
+// The default behavior is to unlink the socket file only when package net created it.
+// That is, when the listener and the underlying socket file were created by a call to
+// Listen or ListenUnix, then by default closing the listener will remove the socket file.
+// but if the listener was created by a call to FileListener to use an already existing
+// socket file, then by default closing the listener will not remove the socket file.
+func (l *UnixListener) SetUnlinkOnClose(unlink bool) {
+	l.unlink = unlink
+}
+
 func listenUnix(ctx context.Context, network string, laddr *UnixAddr) (*UnixListener, error) {
 	fd, err := unixSocket(ctx, network, laddr, nil, "listen")
 	if err != nil {

src/net/unixsock_test.go

@@ -415,44 +415,104 @@ func TestUnixUnlink(t *testing.T) {
 		t.Skip("unix test")
 	}
 	name := testUnixAddr()
+
+	listen := func(t *testing.T) *UnixListener {
 		l, err := Listen("unix", name)
 		if err != nil {
 			t.Fatal(err)
 		}
-	if _, err := os.Stat(name); err != nil {
-		t.Fatalf("cannot stat unix socket after ListenUnix: %v", err)
-	}
-	f, _ := l.(*UnixListener).File()
-	l1, err := FileListener(f)
-	if err != nil {
-		t.Fatal(err)
+		return l.(*UnixListener)
 	}
+	checkExists := func(t *testing.T, desc string) {
 		if _, err := os.Stat(name); err != nil {
-		t.Fatalf("cannot stat unix socket after FileListener: %v", err)
+			t.Fatalf("unix socket does not exist %s: %v", desc, err)
 		}
-	if err := l1.Close(); err != nil {
-		t.Fatalf("closing file listener: %v", err)
 	}
-	if _, err := os.Stat(name); err != nil {
-		t.Fatalf("cannot stat unix socket after closing FileListener: %v", err)
+	checkNotExists := func(t *testing.T, desc string) {
+		if _, err := os.Stat(name); err == nil {
+			t.Fatalf("unix socket does exist %s: %v", desc, err)
 		}
-	f.Close()
-	if _, err := os.Stat(name); err != nil {
-		t.Fatalf("cannot stat unix socket after closing FileListener and fd: %v", err)
 	}
+
+	// Listener should remove on close.
+	t.Run("Listen", func(t *testing.T) {
+		l := listen(t)
+		checkExists(t, "after Listen")
 		l.Close()
-	if _, err := os.Stat(name); err == nil {
-		t.Fatal("closing unix listener did not remove unix socket")
-	}
+		checkNotExists(t, "after Listener close")
+	})
+
+	// FileListener should not.
+	t.Run("FileListener", func(t *testing.T) {
+		l := listen(t)
+		f, _ := l.File()
+		l1, _ := FileListener(f)
+		checkExists(t, "after FileListener")
+		f.Close()
+		checkExists(t, "after File close")
+		l1.Close()
+		checkExists(t, "after FileListener close")
+		l.Close()
+		checkNotExists(t, "after Listener close")
+	})
+
+	// Only first call to l.Close should remove.
+	t.Run("SecondClose", func(t *testing.T) {
+		l := listen(t)
+		checkExists(t, "after Listen")
+		l.Close()
+		checkNotExists(t, "after Listener close")
 		if err := ioutil.WriteFile(name, []byte("hello world"), 0666); err != nil {
 			t.Fatalf("cannot recreate socket file: %v", err)
 		}
-	if _, err := os.Stat(name); err != nil {
-		t.Fatal("recreating unix listener as file failed: %v", err)
-	}
+		checkExists(t, "after writing temp file")
 		l.Close()
-	if _, err := os.Stat(name); err != nil {
-		t.Fatalf("second close of unix socket did second remove: %v", err)
-	}
+		checkExists(t, "after second Listener close")
 		os.Remove(name)
+	})
+
+	// SetUnlinkOnClose should do what it says.
+
+	t.Run("Listen/SetUnlinkOnClose(true)", func(t *testing.T) {
+		l := listen(t)
+		checkExists(t, "after Listen")
+		l.SetUnlinkOnClose(true)
+		l.Close()
+		checkNotExists(t, "after Listener close")
+	})
+
+	t.Run("Listen/SetUnlinkOnClose(false)", func(t *testing.T) {
+		l := listen(t)
+		checkExists(t, "after Listen")
+		l.SetUnlinkOnClose(false)
+		l.Close()
+		checkExists(t, "after Listener close")
+		os.Remove(name)
+	})
+
+	t.Run("FileListener/SetUnlinkOnClose(true)", func(t *testing.T) {
+		l := listen(t)
+		f, _ := l.File()
+		l1, _ := FileListener(f)
+		checkExists(t, "after FileListener")
+		l1.(*UnixListener).SetUnlinkOnClose(true)
+		f.Close()
+		checkExists(t, "after File close")
+		l1.Close()
+		checkNotExists(t, "after FileListener close")
+		l.Close()
+	})
+
+	t.Run("FileListener/SetUnlinkOnClose(false)", func(t *testing.T) {
+		l := listen(t)
+		f, _ := l.File()
+		l1, _ := FileListener(f)
+		checkExists(t, "after FileListener")
+		l1.(*UnixListener).SetUnlinkOnClose(false)
+		f.Close()
+		checkExists(t, "after File close")
+		l1.Close()
+		checkExists(t, "after FileListener close")
+		l.Close()
+	})
 }