ipn{,/ipnlocal}, client/tailscale: move Taildrop recv notifications to LocalAPI HTTP method

Updates #6417

Change-Id: Iec544c477a0e5e9f1c6bf23555afec06255e2e22
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

client/tailscale/localclient.go

@@ -426,8 +426,20 @@ func (lc *LocalClient) IDToken(ctx context.Context, aud string) (*tailcfg.TokenR
 	return decodeJSON[*tailcfg.TokenResponse](body)
 }
 
+// WaitingFiles returns the list of received Taildrop files that have been
+// received by the Tailscale daemon in its staging/cache directory but not yet
+// transferred by the user's CLI or GUI client and written to a user's home
+// directory somewhere.
 func (lc *LocalClient) WaitingFiles(ctx context.Context) ([]apitype.WaitingFile, error) {
-	body, err := lc.get200(ctx, "/localapi/v0/files/")
+	return lc.AwaitWaitingFiles(ctx, 0)
+}
+
+// AwaitWaitingFiles is like WaitingFiles but takes a duration to await for an answer.
+// If the duration is 0, it will return immediately. The duration is respected at second
+// granularity only. If no files are available, it returns (nil, nil).
+func (lc *LocalClient) AwaitWaitingFiles(ctx context.Context, d time.Duration) ([]apitype.WaitingFile, error) {
+	path := "/localapi/v0/files/?waitsec=" + fmt.Sprint(int(d.Seconds()))
+	body, err := lc.get200(ctx, path)
 	if err != nil {
 		return nil, err
 	}

cmd/tailscale/cli/file.go

@@ -26,7 +26,6 @@ import (
 	"golang.org/x/time/rate"
 	"tailscale.com/client/tailscale/apitype"
 	"tailscale.com/envknob"
-	"tailscale.com/ipn"
 	"tailscale.com/net/tsaddr"
 	"tailscale.com/tailcfg"
 	"tailscale.com/util/quarantine"
@@ -529,30 +528,16 @@ func wipeInbox(ctx context.Context) error {
 }
 
 func waitForFile(ctx context.Context) error {
-	c, bc, pumpCtx, cancel := connect(ctx)
+	for {
-	defer cancel()
+		ff, err := localClient.AwaitWaitingFiles(ctx, time.Hour)
-	fileWaiting := make(chan bool, 1)
+		if len(ff) > 0 {
-	notifyError := make(chan error, 1)
-	bc.SetNotifyCallback(func(n ipn.Notify) {
-		if n.ErrMessage != nil {
-			notifyError <- fmt.Errorf("Notify.ErrMessage: %v", *n.ErrMessage)
-		}
-		if n.FilesWaiting != nil {
-			select {
-			case fileWaiting <- true:
-			default:
-			}
-		}
-	})
-	go pump(pumpCtx, bc, c)
-	select {
-	case <-fileWaiting:
 			return nil
-	case <-pumpCtx.Done():
+		}
-		return pumpCtx.Err()
+		if err := ctx.Err(); err != nil {
-	case <-ctx.Done():
-		return ctx.Err()
-	case err := <-notifyError:
 			return err
 		}
+		if err != nil && !errors.Is(err, context.DeadlineExceeded) && !errors.Is(err, context.Canceled) {
+			return err
+		}
+	}
 }

ipn/backend.go

@@ -76,6 +76,8 @@ type Notify struct {
 	// FilesWaiting if non-nil means that files are buffered in
 	// the Tailscale daemon and ready for local transfer to the
 	// user's preferred storage location.
+	//
+	// Deprecated: use LocalClient.AwaitWaitingFiles instead.
 	FilesWaiting *empty.Message `json:",omitempty"`
 
 	// IncomingFiles, if non-nil, specifies which files are in the
@@ -83,6 +85,8 @@ type Notify struct {
 	// Notify should not update the state of file transfers. A non-nil
 	// but empty IncomingFiles means that no files are in the middle
 	// of being transferred.
+	//
+	// Deprecated: use LocalClient.AwaitWaitingFiles instead.
 	IncomingFiles []PartialFile `json:",omitempty"`
 
 	// LocalTCPPort, if non-nil, informs the UI frontend which

ipn/ipnlocal/local.go

@@ -180,6 +180,7 @@ type LocalBackend struct {
 	peerAPIListeners []*peerAPIListener
 	loginFlags       controlclient.LoginFlags
 	incomingFiles    map[*incomingFile]bool
+	fileWaiters      map[*mapSetHandle]context.CancelFunc // handle => func to call on file received
 	lastStatusTime   time.Time                            // status.AsOf value of the last processed status update
 	// directFileRoot, if non-empty, means to write received files
 	// directly to this directory, without staging them in an
@@ -1709,6 +1710,9 @@ func (b *LocalBackend) sendFileNotify() {
 	var n ipn.Notify
 
 	b.mu.Lock()
+	for _, wakeWaiter := range b.fileWaiters {
+		wakeWaiter()
+	}
 	notifyFunc := b.notify
 	apiSrv := b.peerAPIServer
 	if notifyFunc == nil || apiSrv == nil {
@@ -3579,6 +3583,20 @@ func (b *LocalBackend) TestOnlyPublicKeys() (machineKey key.MachinePublic, nodeK
 	return mk, nk
 }
 
+// mapSetHandle is a minimal (but non-zero) value whose address serves as a map
+// key for sets of non-comparable values that can't be map keys themselves.
+type mapSetHandle byte
+
+func (b *LocalBackend) setFileWaiter(handle *mapSetHandle, wakeWaiter context.CancelFunc) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	if wakeWaiter == nil {
+		delete(b.fileWaiters, handle)
+	} else {
+		mak.Set(&b.fileWaiters, handle, wakeWaiter)
+	}
+}
+
 func (b *LocalBackend) WaitingFiles() ([]apitype.WaitingFile, error) {
 	b.mu.Lock()
 	apiSrv := b.peerAPIServer
@@ -3586,6 +3604,42 @@ func (b *LocalBackend) WaitingFiles() ([]apitype.WaitingFile, error) {
 	return apiSrv.WaitingFiles()
 }
 
+// AwaitWaitingFiles is like WaitingFiles but blocks while ctx is not done,
+// waiting for any files to be available.
+//
+// On return, exactly one of the results will be non-empty or non-nil,
+// respectively.
+func (b *LocalBackend) AwaitWaitingFiles(ctx context.Context) ([]apitype.WaitingFile, error) {
+	if ff, err := b.WaitingFiles(); err != nil || len(ff) > 0 {
+		return ff, err
+	}
+
+	for {
+		gotFile, gotFileCancel := context.WithCancel(context.Background())
+		defer gotFileCancel()
+
+		handle := new(mapSetHandle)
+		b.setFileWaiter(handle, gotFileCancel)
+		defer b.setFileWaiter(handle, nil)
+
+		// Now that we've registered ourselves, check again, in case
+		// of race. Otherwise there's a small window where we could
+		// miss a file arrival and wait forever.
+		if ff, err := b.WaitingFiles(); err != nil || len(ff) > 0 {
+			return ff, err
+		}
+
+		select {
+		case <-gotFile.Done():
+			if ff, err := b.WaitingFiles(); err != nil || len(ff) > 0 {
+				return ff, err
+			}
+		case <-ctx.Done():
+			return nil, ctx.Err()
+		}
+	}
+}
+
 func (b *LocalBackend) DeleteFile(name string) error {
 	b.mu.Lock()
 	apiSrv := b.peerAPIServer

ipn/localapi/localapi.go

@@ -7,6 +7,7 @@ package localapi
 
 import (
 	"bytes"
+	"context"
 	"crypto/rand"
 	"encoding/hex"
 	"encoding/json"
@@ -680,8 +681,20 @@ func (h *Handler) serveFiles(w http.ResponseWriter, r *http.Request) {
 			http.Error(w, "want GET to list files", 400)
 			return
 		}
-		wfs, err := h.b.WaitingFiles()
+		ctx := r.Context()
+		if s := r.FormValue("waitsec"); s != "" && s != "0" {
+			d, err := strconv.Atoi(s)
 			if err != nil {
+				http.Error(w, "invalid waitsec", http.StatusBadRequest)
+				return
+			}
+			deadline := time.Now().Add(time.Duration(d) * time.Second)
+			var cancel context.CancelFunc
+			ctx, cancel = context.WithDeadline(ctx, deadline)
+			defer cancel()
+		}
+		wfs, err := h.b.AwaitWaitingFiles(ctx)
+		if err != nil && ctx.Err() == nil {
 			http.Error(w, err.Error(), 500)
 			return
 		}