Add TypingCache to maintain a list of users typing (#559)

* Add typing cache

Signed-off-by: Anant Prakash <anantprakashjsr@gmail.com>

* Add tests for typingCache

* Make test stricter

* Handle cases where expireTime is updated

* Make the slice comparisons sturdy

* Use timers to call removeUser after timeout

* Add test for TypingCache.removeUser

Signed-Off-By: Matthias Kesler <krombel@krombel.de>

* Write deterministic test

src/github.com/matrix-org/dendrite/typingserver/cache/cache.go

@@ -0,0 +1,108 @@
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package cache
+
+import (
+	"sync"
+	"time"
+)
+
+const defaultTypingTimeout = 10 * time.Second
+
+// userSet is a map of user IDs to a timer, timer fires at expiry.
+type userSet map[string]*time.Timer
+
+// TypingCache maintains a list of users typing in each room.
+type TypingCache struct {
+	sync.RWMutex
+	data map[string]userSet
+}
+
+// NewTypingCache returns a new TypingCache initialized for use.
+func NewTypingCache() *TypingCache {
+	return &TypingCache{data: make(map[string]userSet)}
+}
+
+// GetTypingUsers returns the list of users typing in a room.
+func (t *TypingCache) GetTypingUsers(roomID string) (users []string) {
+	t.RLock()
+	usersMap, ok := t.data[roomID]
+	t.RUnlock()
+	if ok {
+		users = make([]string, 0, len(usersMap))
+		for userID := range usersMap {
+			users = append(users, userID)
+		}
+	}
+
+	return
+}
+
+// AddTypingUser sets an user as typing in a room.
+// expire is the time when the user typing should time out.
+// if expire is nil, defaultTypingTimeout is assumed.
+func (t *TypingCache) AddTypingUser(userID, roomID string, expire *time.Time) {
+	expireTime := getExpireTime(expire)
+	if until := time.Until(expireTime); until > 0 {
+		timer := time.AfterFunc(until, t.timeoutCallback(userID, roomID))
+		t.addUser(userID, roomID, timer)
+	}
+}
+
+// addUser with mutex lock & replace the previous timer.
+func (t *TypingCache) addUser(userID, roomID string, expiryTimer *time.Timer) {
+	t.Lock()
+	defer t.Unlock()
+
+	if t.data[roomID] == nil {
+		t.data[roomID] = make(userSet)
+	}
+
+	// Stop the timer to cancel the call to timeoutCallback
+	if timer, ok := t.data[roomID][userID]; ok {
+		// It may happen that at this stage timer fires but now we have a lock on t.
+		// Hence the execution of timeoutCallback will happen after we unlock.
+		// So we may lose a typing state, though this event is highly unlikely.
+		// This can be mitigated by keeping another time.Time in the map and check against it
+		// before removing. This however is not required in most practical scenario.
+		timer.Stop()
+	}
+
+	t.data[roomID][userID] = expiryTimer
+}
+
+// Returns a function which is called after timeout happens.
+// This removes the user.
+func (t *TypingCache) timeoutCallback(userID, roomID string) func() {
+	return func() {
+		t.removeUser(userID, roomID)
+	}
+}
+
+// removeUser with mutex lock & stop the timer.
+func (t *TypingCache) removeUser(userID, roomID string) {
+	t.Lock()
+	defer t.Unlock()
+
+	if timer, ok := t.data[roomID][userID]; ok {
+		timer.Stop()
+		delete(t.data[roomID], userID)
+	}
+}
+
+func getExpireTime(expire *time.Time) time.Time {
+	if expire != nil {
+		return *expire
+	}
+	return time.Now().Add(defaultTypingTimeout)
+}

src/github.com/matrix-org/dendrite/typingserver/cache/cache_test.go

@@ -0,0 +1,99 @@
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package cache
+
+import (
+	"testing"
+	"time"
+
+	"github.com/matrix-org/dendrite/common/test"
+)
+
+func TestTypingCache(t *testing.T) {
+	tCache := NewTypingCache()
+	if tCache == nil {
+		t.Fatal("NewTypingCache failed")
+	}
+
+	t.Run("AddTypingUser", func(t *testing.T) {
+		testAddTypingUser(t, tCache)
+	})
+
+	t.Run("GetTypingUsers", func(t *testing.T) {
+		testGetTypingUsers(t, tCache)
+	})
+
+	t.Run("removeUser", func(t *testing.T) {
+		testRemoveUser(t, tCache)
+	})
+}
+
+func testAddTypingUser(t *testing.T, tCache *TypingCache) {
+	present := time.Now()
+	tests := []struct {
+		userID string
+		roomID string
+		expire *time.Time
+	}{ // Set four users typing state to room1
+		{"user1", "room1", nil},
+		{"user2", "room1", nil},
+		{"user3", "room1", nil},
+		{"user4", "room1", nil},
+		//typing state with past expireTime should not take effect or removed.
+		{"user1", "room2", &present},
+	}
+
+	for _, tt := range tests {
+		tCache.AddTypingUser(tt.userID, tt.roomID, tt.expire)
+	}
+}
+
+func testGetTypingUsers(t *testing.T, tCache *TypingCache) {
+	tests := []struct {
+		roomID    string
+		wantUsers []string
+	}{
+		{"room1", []string{"user1", "user2", "user3", "user4"}},
+		{"room2", []string{}},
+	}
+
+	for _, tt := range tests {
+		gotUsers := tCache.GetTypingUsers(tt.roomID)
+		if !test.UnsortedStringSliceEqual(gotUsers, tt.wantUsers) {
+			t.Errorf("TypingCache.GetTypingUsers(%s) = %v, want %v", tt.roomID, gotUsers, tt.wantUsers)
+		}
+	}
+}
+
+func testRemoveUser(t *testing.T, tCache *TypingCache) {
+	tests := []struct {
+		roomID  string
+		userIDs []string
+	}{
+		{"room3", []string{"user1"}},
+		{"room4", []string{"user1", "user2", "user3"}},
+	}
+
+	for _, tt := range tests {
+		for _, userID := range tt.userIDs {
+			tCache.AddTypingUser(userID, tt.roomID, nil)
+		}
+
+		length := len(tt.userIDs)
+		tCache.removeUser(tt.userIDs[length-1], tt.roomID)
+		expLeftUsers := tt.userIDs[:length-1]
+		if leftUsers := tCache.GetTypingUsers(tt.roomID); !test.UnsortedStringSliceEqual(leftUsers, expLeftUsers) {
+			t.Errorf("Response after removal is unexpected. Want = %s, got = %s", leftUsers, expLeftUsers)
+		}
+	}
+}