fix connection leak with redis pub/sub

router/pkg/pubsub/redis/adapter.go

@@ -99,18 +99,22 @@ func (p *ProviderAdapter) Subscribe(ctx context.Context, conf datasource.Subscri
 	sub := p.conn.PSubscribe(ctx, subConf.Channels...)
 	msgChan := sub.Channel()
 
-	cleanup := func() {
-		err := sub.PUnsubscribe(ctx, subConf.Channels...)
-		if err != nil {
-			log.Error(fmt.Sprintf("error unsubscribing from redis for topics %v", subConf.Channels), zap.Error(err))
-		}
-	}
-
 	p.closeWg.Add(1)
 
 	go func() {
 		defer p.closeWg.Done()
 
+		// Always release the dedicated pub/sub connection on every exit path,
+		// otherwise each subscription leaks a connection. Closing the PubSub
+		// also unsubscribes from all channels server-side, so an explicit
+		// PUnsubscribe is unnecessary (and would fail anyway once the context
+		// driving teardown is cancelled).
+		defer func() {
+			if err := sub.Close(); err != nil {
+				log.Error(fmt.Sprintf("error closing redis subscription for topics %v", subConf.Channels), zap.Error(err))
+			}
+		}()
+
 		for {
 			select {
 			case msg, ok := <-msgChan:
@@ -137,12 +141,10 @@ func (p *ProviderAdapter) Subscribe(ctx context.Context, conf datasource.Subscri
 			case <-p.ctx.Done():
 				// When the application context is done, we stop the subscription if it is not already done
 				log.Debug("application context done, stopping subscription")
-				cleanup()
 				return
 			case <-ctx.Done():
 				// When the subscription context is done, we stop the subscription if it is not already done
 				log.Debug("subscription context done, stopping subscription")
-				cleanup()
 				return
 			}
 		}

router/pkg/pubsub/redis/adapter_test.go

@@ -0,0 +1,70 @@
+package redis
+
+import (
+	"context"
+	"fmt"
+	"testing"
+	"time"
+
+	"github.com/alicebob/miniredis/v2"
+	"github.com/stretchr/testify/require"
+	"github.com/wundergraph/cosmo/router/pkg/pubsub/datasource"
+	"go.uber.org/zap/zaptest"
+)
+
+// noopUpdater satisfies datasource.SubscriptionEventUpdater for tests.
+type noopUpdater struct{}
+
+func (noopUpdater) Update(events []datasource.StreamEvent) {}
+func (noopUpdater) Complete()                              {}
+func (noopUpdater) Done()                                  {}
+func (noopUpdater) SetHooks(hooks datasource.Hooks)        {}
+
+func newTestAdapter(t *testing.T) (*ProviderAdapter, *miniredis.Miniredis) {
+	t.Helper()
+
+	mr := miniredis.RunT(t)
+
+	adapter := NewProviderAdapter(
+		context.Background(),
+		zaptest.NewLogger(t),
+		[]string{fmt.Sprintf("redis://%s", mr.Addr())},
+		false,
+		datasource.ProviderOpts{},
+	)
+	require.NoError(t, adapter.Startup(context.Background()))
+	t.Cleanup(func() { _ = adapter.Shutdown(context.Background()) })
+
+	return adapter.(*ProviderAdapter), mr
+}
+
+// TestProviderAdapter_Subscribe_ReleasesConnectionOnCancel guards against the
+// connection leak where each subscription's dedicated pub/sub connection was
+// never closed (only PUnsubscribe was called, with an already-cancelled
+// context). After every subscription context is cancelled, the pool's total
+// connection count must return to its pre-subscribe baseline.
+func TestProviderAdapter_Subscribe_ReleasesConnectionOnCancel(t *testing.T) {
+	p, _ := newTestAdapter(t)
+
+	baseline := p.conn.PoolStats().TotalConns
+
+	const subscriptions = 10
+	for i := 0; i < subscriptions; i++ {
+		subCtx, cancel := context.WithCancel(context.Background())
+		err := p.Subscribe(subCtx, &SubscriptionEventConfiguration{
+			Provider: "test-provider",
+			Channels: []string{fmt.Sprintf("channel-%d", i)},
+		}, noopUpdater{})
+		require.NoError(t, err)
+
+		// Cancelling the subscription context must tear the subscription down
+		// and release its dedicated connection.
+		cancel()
+	}
+
+	require.Eventually(t, func() bool {
+		return p.conn.PoolStats().TotalConns <= baseline
+	}, 5*time.Second, 10*time.Millisecond,
+		"redis pub/sub connections leaked: have %d, baseline %d",
+		p.conn.PoolStats().TotalConns, baseline)
+}