Add locking to ensure safe concurrent access to config file (#881)

Reviewed-on: https://gitea.com/gitea/tea/pulls/881
Co-authored-by: techknowlogick <techknowlogick@gitea.com>
Co-committed-by: techknowlogick <techknowlogick@gitea.com>

modules/config/lock_test.go

@@ -0,0 +1,182 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package config
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"sync"
+	"testing"
+	"time"
+)
+
+func TestConfigLock_BasicLockUnlock(t *testing.T) {
+	// Create a temp directory for test
+	tmpDir, err := os.MkdirTemp("", "tea-lock-test")
+	if err != nil {
+		t.Fatalf("failed to create temp dir: %v", err)
+	}
+	defer os.RemoveAll(tmpDir)
+
+	lockPath := filepath.Join(tmpDir, "config.yml.lock")
+
+	// Should be able to acquire lock
+	unlock, err := acquireConfigLock(lockPath, 5*time.Second)
+	if err != nil {
+		t.Fatalf("failed to acquire lock: %v", err)
+	}
+
+	// Should be able to release lock
+	err = unlock()
+	if err != nil {
+		t.Fatalf("failed to release lock: %v", err)
+	}
+}
+
+func TestConfigLock_MutexProtection(t *testing.T) {
+	// Create a temp directory for test
+	tmpDir, err := os.MkdirTemp("", "tea-lock-test")
+	if err != nil {
+		t.Fatalf("failed to create temp dir: %v", err)
+	}
+	defer os.RemoveAll(tmpDir)
+
+	lockPath := filepath.Join(tmpDir, "config.yml.lock")
+
+	// Acquire lock
+	unlock, err := acquireConfigLock(lockPath, 5*time.Second)
+	if err != nil {
+		t.Fatalf("failed to acquire lock: %v", err)
+	}
+
+	// Try to acquire again from same process - should block/timeout due to mutex
+	done := make(chan bool)
+	go func() {
+		_, err := acquireConfigLock(lockPath, 100*time.Millisecond)
+		done <- (err != nil) // Should timeout/fail
+	}()
+
+	select {
+	case failed := <-done:
+		if !failed {
+			t.Error("second lock acquisition should have failed due to mutex")
+		}
+	case <-time.After(2 * time.Second):
+		t.Error("test timed out")
+	}
+
+	if err := unlock(); err != nil {
+		t.Errorf("failed to unlock: %v", err)
+	}
+}
+
+func TestReloadConfigFromDisk(t *testing.T) {
+	// Save original config state
+	originalConfig := config
+
+	// Create a temp config file
+	tmpDir, err := os.MkdirTemp("", "tea-reload-test")
+	if err != nil {
+		t.Fatalf("failed to create temp dir: %v", err)
+	}
+	defer os.RemoveAll(tmpDir)
+
+	// We can't easily change GetConfigPath, so we test that reloadConfigFromDisk
+	// handles a missing file gracefully (returns nil and resets config)
+	config = LocalConfig{Logins: []Login{{Name: "test"}}}
+
+	// Call reload - since the actual config path likely exists or doesn't,
+	// we just verify it doesn't panic and returns without error or with expected error
+	err = reloadConfigFromDisk()
+	// The function should either succeed or return an error, not panic
+	if err != nil {
+		// This is acceptable - config file might not exist in test environment
+		t.Logf("reloadConfigFromDisk returned error (expected in test env): %v", err)
+	}
+
+	// Restore original config
+	config = originalConfig
+}
+
+func TestWithConfigLock(t *testing.T) {
+	executed := false
+	err := withConfigLock(func() error {
+		executed = true
+		return nil
+	})
+	if err != nil {
+		t.Errorf("withConfigLock returned error: %v", err)
+	}
+	if !executed {
+		t.Error("function was not executed")
+	}
+}
+
+func TestWithConfigLock_PropagatesError(t *testing.T) {
+	expectedErr := fmt.Errorf("test error")
+	err := withConfigLock(func() error {
+		return expectedErr
+	})
+
+	if err != expectedErr {
+		t.Errorf("expected error %v, got %v", expectedErr, err)
+	}
+}
+
+func TestDoubleCheckedLocking_SimulatedRefresh(t *testing.T) {
+	// This test simulates the double-checked locking pattern
+	// by having multiple goroutines try to "refresh" simultaneously
+
+	var (
+		refreshCount int
+		mu           sync.Mutex
+	)
+
+	// Simulate what RefreshOAuthToken does with double-check
+	simulatedRefresh := func(tokenExpiry *int64) error {
+		// First check (without lock)
+		if *tokenExpiry > time.Now().Unix() {
+			return nil // Token still valid
+		}
+
+		return withConfigLock(func() error {
+			// Double-check after acquiring lock
+			if *tokenExpiry > time.Now().Unix() {
+				return nil // Another goroutine refreshed it
+			}
+
+			// Simulate refresh
+			mu.Lock()
+			refreshCount++
+			mu.Unlock()
+
+			time.Sleep(50 * time.Millisecond) // Simulate API call
+			*tokenExpiry = time.Now().Add(1 * time.Hour).Unix()
+			return nil
+		})
+	}
+
+	// Start with expired token
+	tokenExpiry := time.Now().Add(-1 * time.Hour).Unix()
+
+	// Launch multiple goroutines trying to refresh
+	var wg sync.WaitGroup
+	for range 5 {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			if err := simulatedRefresh(&tokenExpiry); err != nil {
+				t.Errorf("refresh failed: %v", err)
+			}
+		}()
+	}
+
+	wg.Wait()
+
+	// Should only have refreshed once due to double-checked locking
+	if refreshCount != 1 {
+		t.Errorf("expected 1 refresh, got %d", refreshCount)
+	}
+}