fix mem leak in hubConnectionIndex (#22560)

server/channels/app/platform/web_hub.go

@@ -599,6 +599,8 @@ func (i *hubConnectionIndex) Remove(wc *WebConn) {
 	last := userConnections[len(userConnections)-1]
 	// set the slot that we are trying to remove to be the last connection.
 	userConnections[userConnIndex] = last
+	// remove the last connection pointer from slice.
+	userConnections[len(userConnections)-1] = nil
 	// remove the last connection from the slice.
 	i.byUserId[wc.UserId] = userConnections[:len(userConnections)-1]
 	// set the index of the connection that was moved to the new index.

server/channels/app/platform/web_hub_test.go

@@ -8,6 +8,7 @@ import (
 	"net"
 	"net/http"
 	"net/http/httptest"
+	"runtime"
 	"testing"
 	"time"
 
@@ -539,6 +540,42 @@ func BenchmarkHubConnIndex(b *testing.B) {
 	})
 }
 
+func TestHubConnIndexRemoveMemLeak(t *testing.T) {
+	th := Setup(t)
+	defer th.TearDown()
+
+	connIndex := newHubConnectionIndex(1 * time.Second)
+
+	wc := &WebConn{
+		Platform: th.Service,
+		Suite:    th.Suite,
+	}
+	wc.SetConnectionID(model.NewId())
+	wc.SetSession(&model.Session{})
+
+	ch := make(chan struct{})
+
+	runtime.SetFinalizer(wc, func(*WebConn) {
+		close(ch)
+	})
+
+	connIndex.Add(wc)
+	connIndex.Remove(wc)
+
+	runtime.GC()
+
+	timer := time.NewTimer(3 * time.Second)
+	defer timer.Stop()
+
+	select {
+	case <-ch:
+	case <-timer.C:
+		require.Fail(t, "timeout waiting for collection of wc")
+	}
+
+	assert.Len(t, connIndex.byConnection, 0)
+}
+
 var hubSink *Hub
 
 func BenchmarkGetHubForUserId(b *testing.B) {