taildrop: implement asynchronous file deletion (#9844)

File resumption requires keeping partial files around for some time,
but we must still eventually delete them if never resumed.
Thus, we implement asynchronous file deletion, which could
spawn a background goroutine to delete the files.

We also use the same mechanism for deleting files on Windows,
where a file can't be deleted if there is still an open file handle.
We can enqueue those with the asynchronous file deleter as well.

Updates tailscale/corp#14772

Signed-off-by: Joe Tsai <joetsai@digital-static.net>

ipn/ipnlocal/local.go

@@ -646,6 +646,9 @@ func (b *LocalBackend) Shutdown() {
 	if b.sockstatLogger != nil {
 		b.sockstatLogger.Shutdown()
 	}
+	if b.peerAPIServer != nil {
+		b.peerAPIServer.taildrop.Shutdown()
+	}
 
 	b.unregisterNetMon()
 	b.unregisterHealthWatch()
@@ -3614,14 +3617,14 @@ func (b *LocalBackend) initPeerAPIListener() {
 
 	ps := &peerAPIServer{
 		b: b,
-		taildrop: &taildrop.Manager{
+		taildrop: taildrop.ManagerOptions{
 			Logf:             b.logf,
-			Clock:            tstime.DefaultClock{b.clock},
+			Clock:            tstime.DefaultClock{Clock: b.clock},
 			Dir:              fileRoot,
 			DirectFileMode:   b.directFileRoot != "",
 			AvoidFinalRename: !b.directFileDoFinalRename,
 			SendFileNotify:   b.sendFileNotify,
-		},
+		}.New(),
 	}
 	if dm, ok := b.sys.DNSManager.GetOK(); ok {
 		ps.resolver = dm.Resolver()

ipn/ipnlocal/peerapi_test.go

@@ -68,7 +68,7 @@ func bodyNotContains(sub string) check {
 
 func fileHasSize(name string, size int) check {
 	return func(t *testing.T, e *peerAPITestEnv) {
-		root := e.ph.ps.taildrop.Dir
+		root := e.ph.ps.taildrop.Dir()
 		if root == "" {
 			t.Errorf("no rootdir; can't check whether %q has size %v", name, size)
 			return
@@ -84,7 +84,7 @@ func fileHasSize(name string, size int) check {
 
 func fileHasContents(name string, want string) check {
 	return func(t *testing.T, e *peerAPITestEnv) {
-		root := e.ph.ps.taildrop.Dir
+		root := e.ph.ps.taildrop.Dir()
 		if root == "" {
 			t.Errorf("no rootdir; can't check contents of %q", name)
 			return
@@ -540,11 +540,11 @@ func TestHandlePeerAPI(t *testing.T) {
 			if !tt.omitRoot {
 				rootDir = t.TempDir()
 				if e.ph.ps.taildrop == nil {
-					e.ph.ps.taildrop = &taildrop.Manager{
+					e.ph.ps.taildrop = taildrop.ManagerOptions{
 						Logf: e.logBuf.Logf,
-					}
+						Dir:  rootDir,
+					}.New()
 				}
-				e.ph.ps.taildrop.Dir = rootDir
 			}
 			for _, req := range tt.reqs {
 				e.rr = httptest.NewRecorder()
@@ -583,10 +583,10 @@ func TestFileDeleteRace(t *testing.T) {
 			capFileSharing: true,
 			clock:          &tstest.Clock{},
 		},
-		taildrop: &taildrop.Manager{
+		taildrop: taildrop.ManagerOptions{
 			Logf: t.Logf,
 			Dir:  dir,
-		},
+		}.New(),
 	}
 	ph := &peerAPIHandler{
 		isSelf: true,