feat: Replace SSE with WebSocket for UI notifications (#36965)

* Closes #36942
* Fixes #19265 

Replaces the SSE-based push channel (`/user/events`) with a WebSocket
endpoint (`/-/ws`).

### What changes

- **New `/-/ws` endpoint** (authenticated). One WebSocket per origin,
shared across tabs via a single `SharedWorker`.
- **Pubsub broker** (`services/pubsub`) for fan-out by topic, behind a
`Broker` interface. `MemoryBroker` is the default (single process); a
Redis backend is available for multi-process setups, configured via
`[websocket].PUBSUB_TYPE` / `PUBSUB_CONN_STR`. The internal Gitea queue
was not usable here because it has FIFO/single-consumer semantics.
- **Push-only event production.** Events are emitted by write-triggered
notifiers — `NotificationCountChange`, `PublishStopwatchesForUser`, and
the logout publisher — wired into the existing `notify.Notifier`
interface. No server-side pollers.
- **Typed pub/sub on the client.** `web_src/js/modules/worker.ts` is a
singleton transport; features subscribe per event type via
`onUserEvent('notification-count', cb)` instead of branching on
`event.data.type`.
- **Wire contract** (`UserEventType` union) is shared between the worker
and consumers via `web_src/js/types.ts`, kept in sync with
`services/websocket/events.go`.
- **Client-side periodic polling fallback** kicks in only when the
WebSocket cannot be established (e.g. proxy blocks WS, browser lacks
module-SharedWorker support).

### What's removed

- `modules/eventsource` (SSE manager, run loop, messenger).
- `/user/events` route and `tests/integration/eventsource_test.go`.
- All server-side polling for stopwatches and notification counts.

### Stopwatch multi-tab fix

The navbar stopwatch icon was previously rendered conditionally on `{{if
$activeStopwatch}}`, so tabs loaded before the timer started had no DOM
element to update. The icon and popup are now always rendered (toggled
with `tw-hidden`), and the start/stop/cancel handlers POST silently so
all open tabs reflect the change in real time.

### Deployment note

WebSocket needs the upgrade headers to pass through a reverse proxy,
e.g. for nginx:

```nginx
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection "upgrade";
```

Without them the WebSocket cannot be established, and after 3
consecutive failed opens the shared worker signals `push-unavailable`:
the notification count and stopwatch fall back to periodic polling on
the existing `[ui.notification]` timeouts. Real-time push is lost, the
features keep working. The reverse-proxy docs need the same note (see
the `docs-update-needed` label).

---------

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Epid <rexmrj@gmail.com>

modules/setting/setting.go

@@ -221,6 +221,7 @@ func LoadSettings() {
 	loadServiceFrom(CfgProvider)
 	loadOAuth2ClientFrom(CfgProvider)
 	loadCacheFrom(CfgProvider)
+	loadWebsocketFrom(CfgProvider)
 	loadSessionFrom(CfgProvider)
 	loadCorsFrom(CfgProvider)
 	loadMailsFrom(CfgProvider)

modules/setting/ui.go

@@ -52,10 +52,9 @@ var UI = struct {
 	DefaultShowFullName bool
 
 	Notification struct {
-		MinTimeout            time.Duration
-		TimeoutStep           time.Duration
-		MaxTimeout            time.Duration
-		EventSourceUpdateTime time.Duration
+		MinTimeout  time.Duration
+		TimeoutStep time.Duration
+		MaxTimeout  time.Duration
 	} `ini:"ui.notification"`
 
 	SVG struct {
@@ -107,15 +106,13 @@ var UI = struct {
 	AmbiguousUnicodeDetection: true,
 
 	Notification: struct {
-		MinTimeout            time.Duration
-		TimeoutStep           time.Duration
-		MaxTimeout            time.Duration
-		EventSourceUpdateTime time.Duration
+		MinTimeout  time.Duration
+		TimeoutStep time.Duration
+		MaxTimeout  time.Duration
 	}{
-		MinTimeout:            10 * time.Second,
-		TimeoutStep:           10 * time.Second,
-		MaxTimeout:            60 * time.Second,
-		EventSourceUpdateTime: 10 * time.Second,
+		MinTimeout:  10 * time.Second,
+		TimeoutStep: 10 * time.Second,
+		MaxTimeout:  60 * time.Second,
 	},
 	SVG: struct {
 		Enabled bool `ini:"ENABLE_RENDER"`

modules/setting/websocket.go

@@ -0,0 +1,34 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package setting
+
+import "gitea.dev/modules/log"
+
+const (
+	PubsubTypeMemory = "memory"
+	PubsubTypeRedis  = "redis"
+)
+
+// Websocket holds the settings for the websocket event delivery. The pubsub
+// backend is scoped to websocket messages only, it is not a general-purpose
+// pubsub service.
+type WebsocketConfig struct {
+	PubsubType    string
+	PubsubConnStr string
+}
+
+var Websocket = WebsocketConfig{
+	PubsubType: PubsubTypeMemory,
+}
+
+func loadWebsocketFrom(rootCfg ConfigProvider) {
+	sec := rootCfg.Section("websocket")
+	Websocket.PubsubType = sec.Key("PUBSUB_TYPE").In(PubsubTypeMemory, []string{PubsubTypeMemory, PubsubTypeRedis})
+	if Websocket.PubsubType == PubsubTypeRedis {
+		Websocket.PubsubConnStr = sec.Key("PUBSUB_CONN_STR").MustString(Redis.ConnStr)
+		if Websocket.PubsubConnStr == "" {
+			log.Fatal("[websocket].PUBSUB_CONN_STR is required when PUBSUB_TYPE = redis")
+		}
+	}
+}

modules/setting/websocket_test.go

@@ -0,0 +1,63 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package setting
+
+import (
+	"testing"
+
+	"gitea.dev/modules/test"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestLoadWebsocketConfig(t *testing.T) {
+	cases := []struct {
+		name     string
+		ini      string
+		wantType string
+		wantConn string
+	}{
+		{
+			name:     "defaults to memory",
+			wantType: PubsubTypeMemory,
+		},
+		{
+			name:     "redis with its own conn str",
+			ini:      "[websocket]\nPUBSUB_TYPE = redis\nPUBSUB_CONN_STR = redis://127.0.0.1:6379/0",
+			wantType: PubsubTypeRedis,
+			wantConn: "redis://127.0.0.1:6379/0",
+		},
+		{
+			name:     "redis falls back to the shared [redis] section",
+			ini:      "[redis]\nCONN_STR = redis://127.0.0.1:6379/0\n[websocket]\nPUBSUB_TYPE = redis",
+			wantType: PubsubTypeRedis,
+			wantConn: "redis://127.0.0.1:6379/0",
+		},
+		{
+			name:     "own conn str wins over the shared one",
+			ini:      "[redis]\nCONN_STR = redis://127.0.0.1:6379/0\n[websocket]\nPUBSUB_TYPE = redis\nPUBSUB_CONN_STR = redis://10.0.0.1:6379/1",
+			wantType: PubsubTypeRedis,
+			wantConn: "redis://10.0.0.1:6379/1",
+		},
+		{
+			name:     "memory ignores the shared [redis] section",
+			ini:      "[redis]\nCONN_STR = redis://127.0.0.1:6379/0\n[websocket]\nPUBSUB_TYPE = memory",
+			wantType: PubsubTypeMemory,
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			defer test.MockVariableValue(&Websocket)()
+			defer test.MockVariableValue(&Redis)()
+			cfg, err := NewConfigProviderFromData(tc.ini)
+			assert.NoError(t, err)
+
+			loadRedisFrom(cfg)
+			loadWebsocketFrom(cfg)
+			assert.Equal(t, tc.wantType, Websocket.PubsubType)
+			assert.Equal(t, tc.wantConn, Websocket.PubsubConnStr)
+		})
+	}
+}