fix: better error messages when there's another instance of Pocket ID running

See https://github.com/pocket-id/pocket-id/issues/1274#issuecomment-4015888747

backend/internal/bootstrap/bootstrap.go

@@ -2,6 +2,7 @@ package bootstrap
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"log/slog"
 	"time"
@@ -11,6 +12,7 @@ import (
 
 	"github.com/pocket-id/pocket-id/backend/internal/common"
 	"github.com/pocket-id/pocket-id/backend/internal/job"
+	"github.com/pocket-id/pocket-id/backend/internal/service"
 	"github.com/pocket-id/pocket-id/backend/internal/storage"
 	"github.com/pocket-id/pocket-id/backend/internal/utils"
 )
@@ -60,7 +62,9 @@ func Bootstrap(ctx context.Context) error {
 	}
 
 	waitUntil, err := svc.appLockService.Acquire(ctx, false)
-	if err != nil {
+	if errors.Is(err, service.ErrLockUnavailable) {
+		return errors.New("it appears that there's already one instance of Pocket ID running; running multiple replicas of Pocket ID is currently not supported")
+	} else if err != nil {
 		return fmt.Errorf("failed to acquire application lock: %w", err)
 	}
 

backend/internal/cmds/import.go

@@ -119,11 +119,10 @@ func acquireImportLock(ctx context.Context, db *gorm.DB, force bool) error {
 	defer cancel()
 
 	waitUntil, err := appLockService.Acquire(opCtx, force)
-	if err != nil {
-		if errors.Is(err, service.ErrLockUnavailable) {
-			//nolint:staticcheck
-			return errors.New("Pocket ID must be stopped before importing data; please stop the running instance or run with --forcefully-acquire-lock to terminate the other instance")
-		}
+	if errors.Is(err, service.ErrLockUnavailable) {
+		//nolint:staticcheck
+		return errors.New("Pocket ID must be stopped before importing data; please stop the running instance or run with --forcefully-acquire-lock to terminate the other instance")
+	} else if err != nil {
 		return fmt.Errorf("failed to acquire application lock: %w", err)
 	}
 

backend/internal/service/app_lock_service.go

@@ -96,7 +96,8 @@ func (s *AppLockService) Acquire(ctx context.Context, force bool) (waitUntil tim
 
 	var prevLock lockValue
 	if prevLockRaw != "" {
-		if err := prevLock.Unmarshal(prevLockRaw); err != nil {
+		err = prevLock.Unmarshal(prevLockRaw)
+		if err != nil {
 			return time.Time{}, fmt.Errorf("decode existing lock value: %w", err)
 		}
 	}
@@ -142,7 +143,8 @@ func (s *AppLockService) Acquire(ctx context.Context, force bool) (waitUntil tim
 		return time.Time{}, fmt.Errorf("lock acquisition failed: %w", res.Error)
 	}
 
-	if err := tx.Commit().Error; err != nil {
+	err = tx.Commit().Error
+	if err != nil {
 		return time.Time{}, fmt.Errorf("commit lock acquisition: %w", err)
 	}