cp command from service to host: use the first container found to copy source on the host

Signed-off-by: Guillaume Lours <guillaume.lours@docker.com>

pkg/compose/cp.go

@@ -49,62 +49,73 @@ func (s *composeService) Copy(ctx context.Context, projectName string, options a
 
 	var direction copyDirection
 	var serviceName string
+	var copyFunc func(ctx context.Context, containerID string, srcPath string, dstPath string, opts api.CopyOptions) error
 	if srcService != "" {
 		direction |= fromService
 		serviceName = srcService
+		copyFunc = s.copyFromContainer
 
 		// copying from multiple containers of a services doesn't make sense.
 		if options.All {
 			return errors.New("cannot use the --all flag when copying from a service")
 		}
-		// due to remove of the --all flag, restore the default value to 1 when copying from a service container to the host.
-		if options.Index == 0 {
-			options.Index = 1
-		}
 	}
 	if destService != "" {
 		direction |= toService
 		serviceName = destService
+		copyFunc = s.copyToContainer
+	}
+	if direction == acrossServices {
+		return errors.New("copying between services is not supported")
 	}
-	var containers Containers
-	var err error
-	if direction == fromService || (direction == toService && options.Index > 0) {
-		container, err := s.getSpecifiedContainer(ctx, projectName, oneOffExclude, true, serviceName, options.Index)
-		if err != nil {
-			return err
-		}
-		containers = append(containers, container)
-	} else {
-		containers, err = s.getContainers(ctx, projectName, oneOffExclude, true, serviceName)
-		if err != nil {
-			return err
-		}
 
-		if len(containers) < 1 {
-			return fmt.Errorf("no container found for service %q", serviceName)
-		}
+	if direction == 0 {
+		return errors.New("unknown copy direction")
+	}
+
+	containers, err := s.listContainersTargetedForCopy(ctx, projectName, options.Index, direction, serviceName)
+	if err != nil {
+		return err
 	}
 
 	g := errgroup.Group{}
 	for _, container := range containers {
 		containerID := container.ID
 		g.Go(func() error {
-			switch direction {
-			case fromService:
-				return s.copyFromContainer(ctx, containerID, srcPath, dstPath, options)
-			case toService:
-				return s.copyToContainer(ctx, containerID, srcPath, dstPath, options)
-			case acrossServices:
-				return errors.New("copying between services is not supported")
-			default:
-				return errors.New("unknown copy direction")
-			}
+			return copyFunc(ctx, containerID, srcPath, dstPath, options)
 		})
 	}
 
 	return g.Wait()
 }
 
+func (s *composeService) listContainersTargetedForCopy(ctx context.Context, projectName string, index int, direction copyDirection, serviceName string) (Containers, error) {
+	var containers Containers
+	var err error
+	switch {
+	case index > 0:
+		container, err := s.getSpecifiedContainer(ctx, projectName, oneOffExclude, true, serviceName, index)
+		if err != nil {
+			return nil, err
+		}
+		return append(containers, container), nil
+	default:
+		containers, err = s.getContainers(ctx, projectName, oneOffExclude, true, serviceName)
+		if err != nil {
+			return nil, err
+		}
+
+		if len(containers) < 1 {
+			return nil, fmt.Errorf("no container found for service %q", serviceName)
+		}
+		if direction == fromService {
+			return containers[:1], err
+
+		}
+		return containers, err
+	}
+}
+
 func (s *composeService) copyToContainer(ctx context.Context, containerID string, srcPath string, dstPath string, opts api.CopyOptions) error {
 	var err error
 	if srcPath != "-" {