From 342cd47e6a2a083c215f61aeea743dcbdce9d197 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Luk=C3=A1=C5=A1=20Lipinsk=C3=BD?=
 <6032558+Mr-Tao@users.noreply.github.com>
Date: Sat, 29 Aug 2026 21:24:49 +0200
Subject: [PATCH] fix(player): snapshot device timestamps safely

---
 .../soundtouchweb/device_projection.go        |  2 +-
 .../soundtouchweb/device_projection_test.go   | 47 ++++++++++++++++++-
 pkg/service/soundtouchweb/handler.go          | 21 +++++----
 3 files changed, 60 insertions(+), 10 deletions(-)

diff --git a/pkg/service/soundtouchweb/device_projection.go b/pkg/service/soundtouchweb/device_projection.go
index e5e28b8f..332b8b4a 100644
--- a/pkg/service/soundtouchweb/device_projection.go
+++ b/pkg/service/soundtouchweb/device_projection.go
@@ -83,7 +83,7 @@ func captureDeviceProjectionEntries(snapshot []DeviceEntry) []deviceProjectionEn
 			ID:       entry.ID,
 			Info:     entry.Device.DeviceInfo,
 			Status:   entry.Device.Status(),
-			LastSeen: entry.Device.LastSeen,
+			LastSeen: entry.LastSeen,
 		})
 	}
 
diff --git a/pkg/service/soundtouchweb/device_projection_test.go b/pkg/service/soundtouchweb/device_projection_test.go
index 2989db30..2a9c0b30 100644
--- a/pkg/service/soundtouchweb/device_projection_test.go
+++ b/pkg/service/soundtouchweb/device_projection_test.go
@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"net/http"
 	"net/http/httptest"
+	"sync"
 	"testing"
 	"time"
 
@@ -19,7 +20,7 @@ func projectionDevice(host, deviceID, name string, connected bool, group *models
 	})
 	conn.SetStatus(&webtypes.DeviceStatus{IsConnected: connected, Group: group})
 
-	return DeviceEntry{ID: host, Device: conn}
+	return DeviceEntry{ID: host, Device: conn, LastSeen: conn.LastSeen}
 }
 
 func testStereoGroup() *models.Group {
@@ -173,6 +174,50 @@ func TestProjectCapturedDeviceEntriesUsesOneCoherentStatusPerDevice(t *testing.T
 	}
 }
 
+func TestDeviceViewSnapshotConcurrentTouchUsesCapturedLastSeen(t *testing.T) {
+	app := NewWebApp()
+	conn := newRegistryDevice("Living Room")
+	if !app.AddDevice("192.0.2.10", conn) {
+		t.Fatal("AddDevice returned false on first insert")
+	}
+
+	stale := app.DeviceSnapshot()
+	if len(stale) != 1 {
+		t.Fatalf("DeviceSnapshot len = %d, want 1", len(stale))
+	}
+
+	if !app.TouchDevice("192.0.2.10") {
+		t.Fatal("TouchDevice returned false for registered device")
+	}
+	if got := projectDeviceEntries(stale)["192.0.2.10"].LastSeen; got != stale[0].LastSeen {
+		t.Fatalf("projection LastSeen = %s, want captured value %s", got, stale[0].LastSeen)
+	}
+
+	const iterations = 1000
+	start := make(chan struct{})
+	var wg sync.WaitGroup
+	wg.Add(2)
+
+	go func() {
+		defer wg.Done()
+		<-start
+		for i := 0; i < iterations; i++ {
+			app.TouchDevice("192.0.2.10")
+		}
+	}()
+
+	go func() {
+		defer wg.Done()
+		<-start
+		for i := 0; i < iterations; i++ {
+			_ = app.deviceViewSnapshot()
+		}
+	}()
+
+	close(start)
+	wg.Wait()
+}
+
 func TestHandleAPIDevicesUsesLogicalStereoProjection(t *testing.T) {
 	app := NewWebApp()
 	group := testStereoGroup()
diff --git a/pkg/service/soundtouchweb/handler.go b/pkg/service/soundtouchweb/handler.go
index 34401063..222e07c4 100644
--- a/pkg/service/soundtouchweb/handler.go
+++ b/pkg/service/soundtouchweb/handler.go
@@ -114,11 +114,12 @@ func (app *WebApp) proxyServiceURL() string {
 	return app.ServiceURL
 }
 
-// DeviceEntry pairs a device id with its connection. Used by
-// DeviceSnapshot so callers can iterate without holding the lock.
+// DeviceEntry pairs a device id with its connection and the LastSeen value
+// captured by DeviceSnapshot under the registry lock.
 type DeviceEntry struct {
-	ID     string
-	Device *webtypes.DeviceConnection
+	ID       string
+	Device   *webtypes.DeviceConnection
+	LastSeen time.Time
 }
 
 // NewWebApp creates a new WebApp instance for SPA mode
@@ -142,9 +143,9 @@ func (app *WebApp) GetDevice(id string) (*webtypes.DeviceConnection, bool) {
 	return device, ok
 }
 
-// DeviceSnapshot returns a list of (id, *DeviceConnection) pairs taken
-// under a single read lock. Callers can iterate the result without
-// holding any registry lock. Devices added or removed after the call
+// DeviceSnapshot returns device entries taken under a single read lock.
+// Callers can iterate the result without holding any registry lock.
+// Devices added or removed after the call
 // are not reflected. A pointer captured here stays valid even if the
 // device is later removed (RemoveDevice only detaches it from the map
 // and stops its goroutines), so iterating a stale snapshot is safe.
@@ -154,7 +155,11 @@ func (app *WebApp) DeviceSnapshot() []DeviceEntry {
 
 	out := make([]DeviceEntry, 0, len(app.devices))
 	for id, device := range app.devices {
-		out = append(out, DeviceEntry{ID: id, Device: device})
+		out = append(out, DeviceEntry{
+			ID:       id,
+			Device:   device,
+			LastSeen: device.LastSeen,
+		})
 	}
 
 	return out