[pocketbase#1628] fixed realtime panic on concurrent clients iteration

CHANGELOG.md

@@ -1,3 +1,14 @@
+## v0.11.3
+
+- Fix realtime API panic on concurrent clients iteration ([#1628](https://github.com/pocketbase/pocketbase/issues/1628))
+
+  - `app.SubscriptionsBroker().Clients()` now returns a shallow copy of the underlying map.
+
+  - Added `Discard()` and `IsDiscarded()` helper methods to the `subscriptions.Client` interface.
+
+  - Slow clients should no longer "block" the main action completion.
+
+
 ## v0.11.2
 
 - Fixed `fs.DeleteByPrefix()` hang on invalid S3 settings ([#1575](https://github.com/pocketbase/pocketbase/discussions/1575#discussioncomment-4661089)).

apis/realtime.go

@@ -15,6 +15,7 @@ import (
 	"github.com/pocketbase/pocketbase/forms"
 	"github.com/pocketbase/pocketbase/models"
 	"github.com/pocketbase/pocketbase/resolvers"
+	"github.com/pocketbase/pocketbase/tools/routine"
 	"github.com/pocketbase/pocketbase/tools/search"
 	"github.com/pocketbase/pocketbase/tools/subscriptions"
 )
@@ -43,10 +44,14 @@ func (api *realtimeApi) connect(c echo.Context) error {
 	client := subscriptions.NewDefaultClient()
 	api.app.SubscriptionsBroker().Register(client)
 	defer func() {
-		api.app.OnRealtimeDisconnectRequest().Trigger(&core.RealtimeDisconnectEvent{
+		disconnectEvent := &core.RealtimeDisconnectEvent{
 			HttpContext: c,
 			Client:      client,
-		})
+		}
+
+		if err := api.app.OnRealtimeDisconnectRequest().Trigger(disconnectEvent); err != nil && api.app.IsDebug() {
+			log.Println(err)
+		}
 
 		api.app.SubscriptionsBroker().Unregister(client.Id())
 	}()
@@ -259,21 +264,27 @@ func (api *realtimeApi) bindEvents() {
 
 	api.app.OnModelAfterCreate().PreAdd(func(e *core.ModelEvent) error {
 		if record, ok := e.Model.(*models.Record); ok {
-			api.broadcastRecord("create", record)
+			if err := api.broadcastRecord("create", record); err != nil && api.app.IsDebug() {
+				log.Println(err)
+			}
 		}
 		return nil
 	})
 
 	api.app.OnModelAfterUpdate().PreAdd(func(e *core.ModelEvent) error {
 		if record, ok := e.Model.(*models.Record); ok {
-			api.broadcastRecord("update", record)
+			if err := api.broadcastRecord("update", record); err != nil && api.app.IsDebug() {
+				log.Println(err)
+			}
 		}
 		return nil
 	})
 
 	api.app.OnModelBeforeDelete().Add(func(e *core.ModelEvent) error {
 		if record, ok := e.Model.(*models.Record); ok {
-			api.broadcastRecord("delete", record)
+			if err := api.broadcastRecord("delete", record); err != nil && api.app.IsDebug() {
+				log.Println(err)
+			}
 		}
 		return nil
 	})
@@ -370,6 +381,8 @@ func (api *realtimeApi) broadcastRecord(action string, record *models.Record) er
 	encodedData := string(dataBytes)
 
 	for _, client := range clients {
+		client := client
+
 		for subscription, rule := range subscriptionRuleMap {
 			if !client.HasSubscription(subscription) {
 				continue
@@ -398,7 +411,11 @@ func (api *realtimeApi) broadcastRecord(action string, record *models.Record) er
 				}
 			}
 
-			client.Channel() <- msg
+			routine.FireAndForget(func() {
+				if !client.IsDiscarded() {
+					client.Channel() <- msg
+				}
+			})
 		}
 	}
 

tools/subscriptions/broker.go

@@ -18,12 +18,19 @@ func NewBroker() *Broker {
 	}
 }
 
-// Clients returns all registered clients.
+// Clients returns a shallow copy of all registered clients indexed
+// with their connection id.
 func (b *Broker) Clients() map[string]Client {
 	b.mux.RLock()
 	defer b.mux.RUnlock()
 
-	return b.clients
+	copy := make(map[string]Client, len(b.clients))
+
+	for id, c := range b.clients {
+		copy[id] = c
+	}
+
+	return copy
 }
 
 // ClientById finds a registered client by its id.
@@ -56,9 +63,8 @@ func (b *Broker) Unregister(clientId string) {
 	b.mux.Lock()
 	defer b.mux.Unlock()
 
-	// Note:
-	// There is no need to explicitly close the client's channel since it will be GC-ed anyway.
-	// Addinitionally, closing the channel explicitly could panic when there are several
-	// subscriptions attached to the client that needs to receive the same event.
-	delete(b.clients, clientId)
+	if client, ok := b.clients[clientId]; ok {
+		client.Discard()
+		delete(b.clients, clientId)
+	}
 }

tools/subscriptions/broker_test.go

@@ -24,6 +24,13 @@ func TestClients(t *testing.T) {
 	b.Register(subscriptions.NewDefaultClient())
 	b.Register(subscriptions.NewDefaultClient())
 
+	// check if it is a shallow copy
+	clients := b.Clients()
+	for k := range clients {
+		delete(clients, k)
+	}
+
+	// should return a new copy
 	if total := len(b.Clients()); total != 2 {
 		t.Fatalf("Expected 2 clients, got %v", total)
 	}

tools/subscriptions/client.go

@@ -37,6 +37,16 @@ type Client interface {
 
 	// Get retrieves the key value from the client's context.
 	Get(key string) any
+
+	// Discard marks the client as "discarded", meaning that it
+	// shouldn't be used anymore for sending new messages.
+	//
+	// It is safe to call Discard() multiple times.
+	Discard()
+
+	// IsDiscarded indicates whether the client has been "discarded"
+	// and should no longer be used.
+	IsDiscarded() bool
 }
 
 // ensures that DefaultClient satisfies the Client interface
@@ -45,6 +55,7 @@ var _ Client = (*DefaultClient)(nil)
 // DefaultClient defines a generic subscription client.
 type DefaultClient struct {
 	mux           sync.RWMutex
+	isDiscarded   bool
 	id            string
 	store         map[string]any
 	channel       chan Message
@@ -63,11 +74,17 @@ func NewDefaultClient() *DefaultClient {
 
 // Id implements the [Client.Id] interface method.
 func (c *DefaultClient) Id() string {
+	c.mux.RLock()
+	defer c.mux.RUnlock()
+
 	return c.id
 }
 
 // Channel implements the [Client.Channel] interface method.
 func (c *DefaultClient) Channel() chan Message {
+	c.mux.RLock()
+	defer c.mux.RUnlock()
+
 	return c.channel
 }
 
@@ -139,3 +156,19 @@ func (c *DefaultClient) Set(key string, value any) {
 
 	c.store[key] = value
 }
+
+// Discard implements the [Client.Discard] interface method.
+func (c *DefaultClient) Discard() {
+	c.mux.Lock()
+	defer c.mux.Unlock()
+
+	c.isDiscarded = true
+}
+
+// IsDiscarded implements the [Client.IsDiscarded] interface method.
+func (c *DefaultClient) IsDiscarded() bool {
+	c.mux.RLock()
+	defer c.mux.RUnlock()
+
+	return c.isDiscarded
+}

tools/subscriptions/client_test.go

@@ -129,3 +129,17 @@ func TestSetAndGet(t *testing.T) {
 		t.Errorf("Expected 1, got %v", result)
 	}
 }
+
+func TestDiscard(t *testing.T) {
+	c := subscriptions.NewDefaultClient()
+
+	if v := c.IsDiscarded(); v {
+		t.Fatal("Expected false, got true")
+	}
+
+	c.Discard()
+
+	if v := c.IsDiscarded(); !v {
+		t.Fatal("Expected true, got false")
+	}
+}