fix(api): Protects DisableConfigDir from concurrent access using mutex

pkg/api/api.go

@@ -37,6 +37,7 @@ import (
 	"bufio"
 	"io"
 	"os"
+	"sync"
 	"time"
 
 	"github.com/pdfcpu/pdfcpu/pkg/log"
@@ -160,11 +161,19 @@ func EnsureDefaultConfigAt(path string) error {
 	return model.EnsureDefaultConfigAt(path)
 }
 
+var (
+	// mutexDisableConfigDir protects DisableConfigDir from concurrent access.
+	// NOTE: This is not a guard for model.ConfigPath variable.
+	mutexDisableConfigDir sync.Mutex
+)
+
 // DisableConfigDir disables the configuration directory.
 // Any needed default configuration will be loaded from configuration.go
 // Since the config dir also contains the user font dir, this also limits font usage to the default core font set
 // No user fonts will be available.
 func DisableConfigDir() {
+	mutexDisableConfigDir.Lock()
+	defer mutexDisableConfigDir.Unlock()
 	// Call if you don't want to use a specific configuration
 	// and also do not need to use user fonts.
 	model.ConfigPath = "disable"

pkg/api/api_test.go

@@ -0,0 +1,32 @@
+package api
+
+import (
+	"sync"
+	"testing"
+
+	"github.com/pdfcpu/pdfcpu/pkg/pdfcpu/model"
+)
+
+func TestDisableConfigDir(t *testing.T) {
+	t.Parallel()
+	DisableConfigDir()
+
+	if model.ConfigPath != "disable" {
+		t.Errorf("model.ConfigPath != \"disable\" (%s)", model.ConfigPath)
+	}
+}
+
+func TestDisableConfigDir_Parallel(t *testing.T) {
+	t.Parallel()
+
+	var wg sync.WaitGroup
+	for i := 0; i < 100; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			DisableConfigDir()
+		}()
+	}
+	wg.Wait()
+	t.Log("DisableConfigDir is passed")
+}

pkg/pdfcpu/model/configuration.go

@@ -212,6 +212,10 @@ type Configuration struct {
 //
 //	default:	Ensure config dir at default location
 //	disable:	Disable config dir usage
+//
+// WARNING: This is a global variable and should be safe for concurrent use.
+// If you want to change disable config dir,
+// call api.DisableConfigDir() that is concurrency safe instead of changing directly.
 var ConfigPath string = "default"
 
 var loadedDefaultConfig *Configuration