Fix data race on the socket disconnect handler

.github/workflows/go.yml

@@ -33,7 +33,8 @@ jobs:
 
     - name: Install goimports
       run: |
-        go install golang.org/x/tools/cmd/goimports@latest
+        # Pinned: x/tools @latest needs go >= 1.26, the 1.25 job runs with GOTOOLCHAIN=local.
+        go install golang.org/x/tools/cmd/goimports@v0.49.0
         export PATH="$HOME/go/bin:$PATH"
 
     - name: Run pre-commit

socket/framesocket.go

@@ -31,7 +31,8 @@ type FrameSocket struct {
 	HTTPHeaders http.Header
 	HTTPClient  *http.Client
 
-	Frames       chan []byte
+	Frames chan []byte
+	// Use SetOnDisconnect to change the handler while the socket is in use.
 	OnDisconnect func(ctx context.Context, remote bool)
 
 	Header []byte
@@ -64,6 +65,14 @@ func (fs *FrameSocket) IsConnected() bool {
 	return fs.conn.Load() != nil
 }
 
+// SetOnDisconnect replaces the disconnect handler under the socket lock.
+// It does not cancel a callback already scheduled by Close.
+func (fs *FrameSocket) SetOnDisconnect(handler func(ctx context.Context, remote bool)) {
+	fs.lock.Lock()
+	defer fs.lock.Unlock()
+	fs.OnDisconnect = handler
+}
+
 func (fs *FrameSocket) Close(code websocket.StatusCode) {
 	fs.lock.Lock()
 	defer fs.lock.Unlock()

socket/noisesocket.go

@@ -45,9 +45,9 @@ func newNoiseSocket(
 		onFrame:      frameHandler,
 		stopConsumer: make(chan struct{}),
 	}
-	fs.OnDisconnect = func(ctx context.Context, remote bool) {
+	fs.SetOnDisconnect(func(ctx context.Context, remote bool) {
 		disconnectHandler(ctx, ns, remote)
-	}
+	})
 	go ns.consumeFrames(ctx, fs.Frames)
 	return ns, nil
 }
@@ -80,7 +80,7 @@ func (ns *NoiseSocket) Stop(disconnect, allowOnDisconnect bool) {
 	if ns.destroyed.CompareAndSwap(false, true) {
 		close(ns.stopConsumer)
 		if !allowOnDisconnect {
-			ns.fs.OnDisconnect = nil
+			ns.fs.SetOnDisconnect(nil)
 		}
 		if disconnect {
 			ns.fs.Close(websocket.StatusNormalClosure)

socket/noisesocket_test.go

@@ -0,0 +1,166 @@
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+package socket
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/coder/websocket"
+
+	waLog "github.com/polymorfa/hypermeow/util/log"
+)
+
+func newTestFrameSocket(t *testing.T) *FrameSocket {
+	t.Helper()
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		conn, err := websocket.Accept(w, r, &websocket.AcceptOptions{InsecureSkipVerify: true})
+		if err != nil {
+			t.Errorf("Failed to accept websocket: %v", err)
+			return
+		}
+		defer func() { _ = conn.CloseNow() }()
+		<-conn.CloseRead(r.Context()).Done()
+	}))
+	t.Cleanup(server.Close)
+	fs := NewFrameSocket(waLog.Noop, server.Client())
+	fs.URL = server.URL
+	if err := fs.Connect(t.Context()); err != nil {
+		t.Fatalf("Failed to connect websocket: %v", err)
+	}
+	t.Cleanup(func() { fs.Close(0) })
+	return fs
+}
+
+func TestNoiseSocketStopConcurrentClose(t *testing.T) {
+	for range 100 {
+		fs := newTestFrameSocket(t)
+		ns, err := newNoiseSocket(t.Context(), fs, nil, nil, nil, func(context.Context, *NoiseSocket, bool) {})
+		if err != nil {
+			t.Fatal(err)
+		}
+		var wg sync.WaitGroup
+		start := make(chan struct{})
+		wg.Go(func() {
+			<-start
+			fs.Close(0)
+		})
+		wg.Go(func() {
+			<-start
+			ns.Stop(true, false)
+		})
+		close(start)
+		wg.Wait()
+	}
+}
+
+func TestNewNoiseSocketConcurrentClose(t *testing.T) {
+	for range 100 {
+		fs := newTestFrameSocket(t)
+		var wg sync.WaitGroup
+		start := make(chan struct{})
+		wg.Go(func() {
+			<-start
+			fs.Close(0)
+		})
+		close(start)
+		ns, err := newNoiseSocket(t.Context(), fs, nil, nil, nil, func(context.Context, *NoiseSocket, bool) {})
+		if err != nil {
+			t.Fatal(err)
+		}
+		wg.Wait()
+		ns.Stop(false, false)
+	}
+}
+
+func TestNoiseSocketStop(t *testing.T) {
+	for _, tc := range []struct {
+		name              string
+		disconnect        bool
+		allowOnDisconnect bool
+	}{
+		{name: "local suppressed", disconnect: true},
+		{name: "local allowed", disconnect: true, allowOnDisconnect: true},
+		{name: "remote suppressed"},
+		{name: "remote allowed", allowOnDisconnect: true},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			fs := newTestFrameSocket(t)
+			called := make(chan bool, 2)
+			ns, err := newNoiseSocket(t.Context(), fs, nil, nil, nil, func(ctx context.Context, socket *NoiseSocket, remote bool) {
+				if ctx != t.Context() {
+					t.Error("Unexpected disconnect context")
+				}
+				socket.Stop(false, false)
+				fs.Close(0)
+				called <- remote
+			})
+			if err != nil {
+				t.Fatal(err)
+			}
+			ns.Stop(tc.disconnect, tc.allowOnDisconnect)
+			if fs.IsConnected() == tc.disconnect {
+				t.Fatalf("Unexpected connection state after Stop: %t", fs.IsConnected())
+			}
+			select {
+			case <-ns.stopConsumer:
+			default:
+				t.Fatal("Frame consumer was not stopped")
+			}
+			fs.lock.Lock()
+			hasHandler := fs.OnDisconnect != nil
+			fs.lock.Unlock()
+			if hasHandler != tc.allowOnDisconnect {
+				t.Fatalf("Unexpected disconnect handler after Stop: %t", hasHandler)
+			}
+			fs.Close(0)
+			fs.Close(0)
+			if tc.allowOnDisconnect {
+				select {
+				case remote := <-called:
+					if remote == tc.disconnect {
+						t.Errorf("Unexpected remote flag: %t", remote)
+					}
+				case <-time.After(5 * time.Second):
+					t.Fatal("Disconnect handler did not return")
+				}
+			}
+			select {
+			case <-called:
+				t.Fatal("Unexpected disconnect callback")
+			default:
+			}
+		})
+	}
+}
+
+func TestNoiseSocketRemoteDisconnect(t *testing.T) {
+	fs := newTestFrameSocket(t)
+	called := make(chan bool, 1)
+	ns, err := newNoiseSocket(t.Context(), fs, nil, nil, nil, func(ctx context.Context, socket *NoiseSocket, remote bool) {
+		socket.Stop(false, false)
+		fs.Close(0)
+		called <- remote
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	fs.Close(0)
+	select {
+	case remote := <-called:
+		if !remote {
+			t.Error("Expected remote disconnect")
+		}
+	case <-time.After(5 * time.Second):
+		t.Fatal("Disconnect handler did not return")
+	}
+	if !ns.destroyed.Load() {
+		t.Fatal("Disconnect handler did not stop the noise socket")
+	}
+}