*: Add progress notify request watch request

Documentation/dev-guide/api_reference_v3.md

@@ -740,7 +740,7 @@ Empty field.
 | ----- | ----------- | ---- |
 | cluster_id | cluster_id is the ID of the cluster which sent the response. | uint64 |
 | member_id | member_id is the ID of the member which sent the response. | uint64 |
-| revision | revision is the key-value store revision when the request was applied. | int64 |
+| revision | revision is the key-value store revision when the request was applied. For watch progress responses, the header.revision indicates progress. All future events recieved in this stream are guaranteed to have a higher revision number than the header.revision number. | int64 |
 | raft_term | raft_term is the raft term when the request was applied. | uint64 |
 
 
@@ -840,13 +840,22 @@ From google paxosdb paper: Our implementation hinges around a powerful primitive
 
 
 
+##### message `WatchProgressRequest` (etcdserver/etcdserverpb/rpc.proto)
+
+Requests the a watch stream progress status be sent in the watch response stream as soon as possible.
+
+Empty field.
+
+
+
 ##### message `WatchRequest` (etcdserver/etcdserverpb/rpc.proto)
 
 | Field | Description | Type |
 | ----- | ----------- | ---- |
 | request_union | request_union is a request to either create a new watcher or cancel an existing watcher. | oneof |
 | create_request |  | WatchCreateRequest |
 | cancel_request |  | WatchCancelRequest |
+| progress_request |  | WatchProgressRequest |
 
 
 

Documentation/dev-guide/apispec/swagger/rpc.swagger.json

@@ -2195,7 +2195,7 @@
           "format": "uint64"
         },
         "revision": {
-          "description": "revision is the key-value store revision when the request was applied.",
+          "description": "revision is the key-value store revision when the request was applied.\nFor watch progress responses, the header.revision indicates progress. All future events\nrecieved in this stream are guaranteed to have a higher revision number than the\nheader.revision number.",
           "type": "string",
           "format": "int64"
         }
@@ -2396,6 +2396,10 @@
         }
       }
     },
+    "etcdserverpbWatchProgressRequest": {
+      "description": "Requests the a watch stream progress status be sent in the watch response stream as soon as\npossible.",
+      "type": "object"
+    },
     "etcdserverpbWatchRequest": {
       "type": "object",
       "properties": {
@@ -2404,6 +2408,9 @@
         },
         "create_request": {
           "$ref": "#/definitions/etcdserverpbWatchCreateRequest"
+        },
+        "progress_request": {
+          "$ref": "#/definitions/etcdserverpbWatchProgressRequest"
         }
       }
     },

Documentation/dev-guide/apispec/swagger/v3election.swagger.json

@@ -168,7 +168,7 @@
         "revision": {
           "type": "string",
           "format": "int64",
-          "description": "revision is the key-value store revision when the request was applied."
+          "description": "revision is the key-value store revision when the request was applied.\nFor watch progress responses, the header.revision indicates progress. All future events\nrecieved in this stream are guaranteed to have a higher revision number than the\nheader.revision number."
         },
         "raft_term": {
           "type": "string",

Documentation/dev-guide/apispec/swagger/v3lock.swagger.json

@@ -87,7 +87,7 @@
         "revision": {
           "type": "string",
           "format": "int64",
-          "description": "revision is the key-value store revision when the request was applied."
+          "description": "revision is the key-value store revision when the request was applied.\nFor watch progress responses, the header.revision indicates progress. All future events\nrecieved in this stream are guaranteed to have a higher revision number than the\nheader.revision number."
         },
         "raft_term": {
           "type": "string",

Documentation/dev-guide/interacting_v3.md

@@ -355,6 +355,26 @@ foo         # key
 bar_latest  # value of foo key after modification
 ```
 
+## Watch progress
+
+Applications may want to check the progress of a watch to determine how up-to-date the watch stream is. For example, if a watch is used to update a cache, it can be useful to know if the cache is stale compared to the revision from a quorum read. 
+
+Progress requests can be issued using the "progress" command in interactive watch session to ask the etcd server to send a progress notify update in the watch stream:
+
+```bash
+$ etcdctl watch -i
+$ watch a
+$ progress
+progress notify: 1
+# in another terminal: etcdctl put x 0
+# in another terminal: etcdctl put y 1
+$ progress
+progress notify: 3
+```
+
+Note: The revision number in the progress notify response is the revision from the local etcd server node that the watch stream is connected to. If this node is partitioned and not part of quorum, this progress notify revision might be lower than 
+than the revision returned by a quorum read against a non-partitioned etcd server node.
+
 ## Compacted revisions
 
 As we mentioned, etcd keeps revisions so that applications can read past versions of keys. However, to avoid accumulating an unbounded amount of history, it is important to compact past revisions. After compacting, etcd removes historical revisions, releasing resources for future use. All superseded data with revisions before the compacted revision will be unavailable.

clientv3/integration/watch_test.go

@@ -582,6 +582,78 @@ func testWatchWithProgressNotify(t *testing.T, watchOnPut bool) {
 	}
 }
 
+func TestWatchRequestProgress(t *testing.T) {
+	testCases := []struct {
+		name     string
+		watchers []string
+	}{
+		{"0-watcher", []string{}},
+		{"1-watcher", []string{"/"}},
+		{"2-watcher", []string{"/", "/"}},
+	}
+
+	for _, c := range testCases {
+		t.Run(c.name, func(t *testing.T) {
+			defer testutil.AfterTest(t)
+
+			watchTimeout := 3 * time.Second
+
+			clus := integration.NewClusterV3(t, &integration.ClusterConfig{Size: 3})
+			defer clus.Terminate(t)
+
+			wc := clus.RandClient()
+
+			var watchChans []clientv3.WatchChan
+
+			for _, prefix := range c.watchers {
+				watchChans = append(watchChans, wc.Watch(context.Background(), prefix, clientv3.WithPrefix()))
+			}
+
+			_, err := wc.Put(context.Background(), "/a", "1")
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			for _, rch := range watchChans {
+				select {
+				case resp := <-rch: // wait for notification
+					if len(resp.Events) != 1 {
+						t.Fatalf("resp.Events expected 1, got %d", len(resp.Events))
+					}
+				case <-time.After(watchTimeout):
+					t.Fatalf("watch response expected in %v, but timed out", watchTimeout)
+				}
+			}
+
+			// put a value not being watched to increment revision
+			_, err = wc.Put(context.Background(), "x", "1")
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			err = wc.RequestProgress(context.Background())
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			// verify all watch channels receive a progress notify
+			for _, rch := range watchChans {
+				select {
+				case resp := <-rch:
+					if !resp.IsProgressNotify() {
+						t.Fatalf("expected resp.IsProgressNotify() == true")
+					}
+					if resp.Header.Revision != 3 {
+						t.Fatalf("resp.Header.Revision expected 3, got %d", resp.Header.Revision)
+					}
+				case <-time.After(watchTimeout):
+					t.Fatalf("progress response expected in %v, but timed out", watchTimeout)
+				}
+			}
+		})
+	}
+}
+
 func TestWatchEventType(t *testing.T) {
 	cluster := integration.NewClusterV3(t, &integration.ClusterConfig{Size: 1})
 	defer cluster.Terminate(t)

clientv3/watch.go

@@ -70,6 +70,9 @@ type Watcher interface {
 	// (see https://github.com/coreos/etcd/issues/8980)
 	Watch(ctx context.Context, key string, opts ...OpOption) WatchChan
 
+	// RequestProgress requests a progress notify response be sent in all watch channels.
+	RequestProgress(ctx context.Context) error
+
 	// Close closes the watcher and cancels all watch requests.
 	Close() error
 }
@@ -156,7 +159,7 @@ type watchGrpcStream struct {
 	resuming []*watcherStream
 
 	// reqc sends a watch request from Watch() to the main goroutine
-	reqc chan *watchRequest
+	reqc chan watchStreamRequest
 	// respc receives data from the watch client
 	respc chan *pb.WatchResponse
 	// donec closes to broadcast shutdown
@@ -174,6 +177,11 @@ type watchGrpcStream struct {
 	closeErr error
 }
 
+// watchStreamRequest is a union of the supported watch request operation types
+type watchStreamRequest interface {
+	toPB() *pb.WatchRequest
+}
+
 // watchRequest is issued by the subscriber to start a new watcher
 type watchRequest struct {
 	ctx context.Context
@@ -198,6 +206,10 @@ type watchRequest struct {
 	retc chan chan WatchResponse
 }
 
+// progressRequest is issued by the subscriber to request watch progress
+type progressRequest struct {
+}
+
 // watcherStream represents a registered watcher
 type watcherStream struct {
 	// initReq is the request that initiated this request
@@ -255,7 +267,7 @@ func (w *watcher) newWatcherGrpcStream(inctx context.Context) *watchGrpcStream {
 		cancel:     cancel,
 		substreams: make(map[int64]*watcherStream),
 		respc:      make(chan *pb.WatchResponse),
-		reqc:       make(chan *watchRequest),
+		reqc:       make(chan watchStreamRequest),
 		donec:      make(chan struct{}),
 		errc:       make(chan error, 1),
 		closingc:   make(chan *watcherStream),
@@ -361,6 +373,42 @@ func (w *watcher) Close() (err error) {
 	return err
 }
 
+// RequestProgress requests a progress notify response be sent in all watch channels.
+func (w *watcher) RequestProgress(ctx context.Context) (err error) {
+	ctxKey := streamKeyFromCtx(ctx)
+
+	w.mu.Lock()
+	if w.streams == nil {
+		return fmt.Errorf("no stream found for context")
+	}
+	wgs := w.streams[ctxKey]
+	if wgs == nil {
+		wgs = w.newWatcherGrpcStream(ctx)
+		w.streams[ctxKey] = wgs
+	}
+	donec := wgs.donec
+	reqc := wgs.reqc
+	w.mu.Unlock()
+
+	pr := &progressRequest{}
+
+	select {
+	case reqc <- pr:
+		return nil
+	case <-ctx.Done():
+		if err == nil {
+			return ctx.Err()
+		}
+		return err
+	case <-donec:
+		if wgs.closeErr != nil {
+			return wgs.closeErr
+		}
+		// retry; may have dropped stream from no ctxs
+		return w.RequestProgress(ctx)
+	}
+}
+
 func (w *watchGrpcStream) close() (err error) {
 	w.cancel()
 	<-w.donec
@@ -468,26 +516,31 @@ func (w *watchGrpcStream) run() {
 	for {
 		select {
 		// Watch() requested
-		case wreq := <-w.reqc:
-			outc := make(chan WatchResponse, 1)
-			// TODO: pass custom watch ID?
-			ws := &watcherStream{
-				initReq: *wreq,
-				id:      -1,
-				outc:    outc,
-				// unbuffered so resumes won't cause repeat events
-				recvc: make(chan *WatchResponse),
-			}
+		case req := <-w.reqc:
+			switch wreq := req.(type) {
+			case *watchRequest:
+				outc := make(chan WatchResponse, 1)
+				// TODO: pass custom watch ID?
+				ws := &watcherStream{
+					initReq: *wreq,
+					id:      -1,
+					outc:    outc,
+					// unbuffered so resumes won't cause repeat events
+					recvc: make(chan *WatchResponse),
+				}
 
-			ws.donec = make(chan struct{})
-			w.wg.Add(1)
-			go w.serveSubstream(ws, w.resumec)
+				ws.donec = make(chan struct{})
+				w.wg.Add(1)
+				go w.serveSubstream(ws, w.resumec)
 
-			// queue up for watcher creation/resume
-			w.resuming = append(w.resuming, ws)
-			if len(w.resuming) == 1 {
-				// head of resume queue, can register a new watcher
-				wc.Send(ws.initReq.toPB())
+				// queue up for watcher creation/resume
+				w.resuming = append(w.resuming, ws)
+				if len(w.resuming) == 1 {
+					// head of resume queue, can register a new watcher
+					wc.Send(ws.initReq.toPB())
+				}
+			case *progressRequest:
+				wc.Send(wreq.toPB())
 			}
 
 		// new events from the watch client
@@ -614,7 +667,28 @@ func (w *watchGrpcStream) dispatchEvent(pbresp *pb.WatchResponse) bool {
 		Canceled:        pbresp.Canceled,
 		cancelReason:    pbresp.CancelReason,
 	}
-	ws, ok := w.substreams[pbresp.WatchId]
+
+	if wr.IsProgressNotify() {
+		return w.broadcastResponse(wr)
+	}
+	return w.unicastResponse(wr, pbresp.WatchId)
+
+}
+
+// broadcastResponse send a watch response to all watch substreams.
+func (w *watchGrpcStream) broadcastResponse(wr *WatchResponse) bool {
+	for _, ws := range w.substreams {
+		select {
+		case ws.recvc <- wr:
+		case <-ws.donec:
+		}
+	}
+	return true
+}
+
+// unicastResponse sends a watch response to a specific watch substream.
+func (w *watchGrpcStream) unicastResponse(wr *WatchResponse, watchId int64) bool {
+	ws, ok := w.substreams[watchId]
 	if !ok {
 		return false
 	}
@@ -888,6 +962,13 @@ func (wr *watchRequest) toPB() *pb.WatchRequest {
 	return &pb.WatchRequest{RequestUnion: cr}
 }
 
+// toPB converts an internal progress request structure to its protobuf WatchRequest structure.
+func (pr *progressRequest) toPB() *pb.WatchRequest {
+	req := &pb.WatchProgressRequest{}
+	cr := &pb.WatchRequest_ProgressRequest{ProgressRequest: req}
+	return &pb.WatchRequest{RequestUnion: cr}
+}
+
 func streamKeyFromCtx(ctx context.Context) string {
 	if md, ok := metadata.FromOutgoingContext(ctx); ok {
 		return fmt.Sprintf("%+v", md)