ServiceCreate/ServiceUpdate: refactor and fix potential NPE

- `ContainerSpec` and `PluginSpec` are mutually exclusive, so instead of using
  two separate if-statements, combine them in a switch.
- Use local variables (at cost of some slight duplication)
- Fix a potential NPE if image-digest resolution failed for a `PluginSpec`.
  The code was always using `ContainerSpec.Image` to create a `digestWarning`,
  but in case we're resoling the digest for a `PluginSpec`, `ContainerSpec`
  will be `nil` (as they're mutually exclusive). This issue was introduced in
  72c3bcf2a533a827402945e3a55872e2db4fb024, where the new `PluginSpec` path
  was added.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

client/service_create.go

@@ -15,8 +15,7 @@ import (
 
 // ServiceCreate creates a new Service.
 func (cli *Client) ServiceCreate(ctx context.Context, service swarm.ServiceSpec, options types.ServiceCreateOptions) (types.ServiceCreateResponse, error) {
-	var distErr error
-
+	var response types.ServiceCreateResponse
 	headers := map[string][]string{
 		"version": {cli.version},
 	}
@@ -31,46 +30,52 @@ func (cli *Client) ServiceCreate(ctx context.Context, service swarm.ServiceSpec,
 	}
 
 	if err := validateServiceSpec(service); err != nil {
-		return types.ServiceCreateResponse{}, err
+		return response, err
 	}
 
 	// ensure that the image is tagged
-	var imgPlatforms []swarm.Platform
-	if service.TaskTemplate.ContainerSpec != nil {
+	var resolveWarning string
+	switch {
+	case service.TaskTemplate.ContainerSpec != nil:
 		if taggedImg := imageWithTagString(service.TaskTemplate.ContainerSpec.Image); taggedImg != "" {
 			service.TaskTemplate.ContainerSpec.Image = taggedImg
 		}
 		if options.QueryRegistry {
-			var img string
-			img, imgPlatforms, distErr = imageDigestAndPlatforms(ctx, cli, service.TaskTemplate.ContainerSpec.Image, options.EncodedRegistryAuth)
-			if img != "" {
-				service.TaskTemplate.ContainerSpec.Image = img
+			if img, imgPlatforms, err := imageDigestAndPlatforms(ctx, cli, service.TaskTemplate.ContainerSpec.Image, options.EncodedRegistryAuth); err != nil {
+				resolveWarning = digestWarning(service.TaskTemplate.ContainerSpec.Image)
+			} else {
+				if img != "" {
+					service.TaskTemplate.ContainerSpec.Image = img
+				}
+				if len(imgPlatforms) > 0 {
+					if service.TaskTemplate.Placement == nil {
+						service.TaskTemplate.Placement = &swarm.Placement{}
+					}
+					service.TaskTemplate.Placement.Platforms = imgPlatforms
+				}
 			}
 		}
-	}
-
-	// ensure that the image is tagged
-	if service.TaskTemplate.PluginSpec != nil {
+	case service.TaskTemplate.PluginSpec != nil:
 		if taggedImg := imageWithTagString(service.TaskTemplate.PluginSpec.Remote); taggedImg != "" {
 			service.TaskTemplate.PluginSpec.Remote = taggedImg
 		}
 		if options.QueryRegistry {
-			var img string
-			img, imgPlatforms, distErr = imageDigestAndPlatforms(ctx, cli, service.TaskTemplate.PluginSpec.Remote, options.EncodedRegistryAuth)
-			if img != "" {
-				service.TaskTemplate.PluginSpec.Remote = img
+			if img, imgPlatforms, err := imageDigestAndPlatforms(ctx, cli, service.TaskTemplate.PluginSpec.Remote, options.EncodedRegistryAuth); err != nil {
+				resolveWarning = digestWarning(service.TaskTemplate.PluginSpec.Remote)
+			} else {
+				if img != "" {
+					service.TaskTemplate.PluginSpec.Remote = img
+				}
+				if len(imgPlatforms) > 0 {
+					if service.TaskTemplate.Placement == nil {
+						service.TaskTemplate.Placement = &swarm.Placement{}
+					}
+					service.TaskTemplate.Placement.Platforms = imgPlatforms
+				}
 			}
 		}
 	}
 
-	if service.TaskTemplate.Placement == nil && len(imgPlatforms) > 0 {
-		service.TaskTemplate.Placement = &swarm.Placement{}
-	}
-	if len(imgPlatforms) > 0 {
-		service.TaskTemplate.Placement.Platforms = imgPlatforms
-	}
-
-	var response types.ServiceCreateResponse
 	resp, err := cli.post(ctx, "/services/create", nil, service, headers)
 	defer ensureReaderClosed(resp)
 	if err != nil {
@@ -78,9 +83,8 @@ func (cli *Client) ServiceCreate(ctx context.Context, service swarm.ServiceSpec,
 	}
 
 	err = json.NewDecoder(resp.body).Decode(&response)
-
-	if distErr != nil {
-		response.Warnings = append(response.Warnings, digestWarning(service.TaskTemplate.ContainerSpec.Image))
+	if resolveWarning != "" {
+		response.Warnings = append(response.Warnings, resolveWarning)
 	}
 
 	return response, err

client/service_update.go

@@ -15,8 +15,8 @@ import (
 // of swarm.Service, which can be found using ServiceInspectWithRaw.
 func (cli *Client) ServiceUpdate(ctx context.Context, serviceID string, version swarm.Version, service swarm.ServiceSpec, options types.ServiceUpdateOptions) (types.ServiceUpdateResponse, error) {
 	var (
-		query   = url.Values{}
-		distErr error
+		query    = url.Values{}
+		response = types.ServiceUpdateResponse{}
 	)
 
 	headers := map[string][]string{
@@ -38,46 +38,52 @@ func (cli *Client) ServiceUpdate(ctx context.Context, serviceID string, version
 	query.Set("version", strconv.FormatUint(version.Index, 10))
 
 	if err := validateServiceSpec(service); err != nil {
-		return types.ServiceUpdateResponse{}, err
+		return response, err
 	}
 
-	var imgPlatforms []swarm.Platform
 	// ensure that the image is tagged
-	if service.TaskTemplate.ContainerSpec != nil {
+	var resolveWarning string
+	switch {
+	case service.TaskTemplate.ContainerSpec != nil:
 		if taggedImg := imageWithTagString(service.TaskTemplate.ContainerSpec.Image); taggedImg != "" {
 			service.TaskTemplate.ContainerSpec.Image = taggedImg
 		}
 		if options.QueryRegistry {
-			var img string
-			img, imgPlatforms, distErr = imageDigestAndPlatforms(ctx, cli, service.TaskTemplate.ContainerSpec.Image, options.EncodedRegistryAuth)
-			if img != "" {
-				service.TaskTemplate.ContainerSpec.Image = img
+			if img, imgPlatforms, err := imageDigestAndPlatforms(ctx, cli, service.TaskTemplate.ContainerSpec.Image, options.EncodedRegistryAuth); err != nil {
+				resolveWarning = digestWarning(service.TaskTemplate.ContainerSpec.Image)
+			} else {
+				if img != "" {
+					service.TaskTemplate.ContainerSpec.Image = img
+				}
+				if len(imgPlatforms) > 0 {
+					if service.TaskTemplate.Placement == nil {
+						service.TaskTemplate.Placement = &swarm.Placement{}
+					}
+					service.TaskTemplate.Placement.Platforms = imgPlatforms
+				}
 			}
 		}
-	}
-
-	// ensure that the image is tagged
-	if service.TaskTemplate.PluginSpec != nil {
+	case service.TaskTemplate.PluginSpec != nil:
 		if taggedImg := imageWithTagString(service.TaskTemplate.PluginSpec.Remote); taggedImg != "" {
 			service.TaskTemplate.PluginSpec.Remote = taggedImg
 		}
 		if options.QueryRegistry {
-			var img string
-			img, imgPlatforms, distErr = imageDigestAndPlatforms(ctx, cli, service.TaskTemplate.PluginSpec.Remote, options.EncodedRegistryAuth)
-			if img != "" {
-				service.TaskTemplate.PluginSpec.Remote = img
+			if img, imgPlatforms, err := imageDigestAndPlatforms(ctx, cli, service.TaskTemplate.PluginSpec.Remote, options.EncodedRegistryAuth); err != nil {
+				resolveWarning = digestWarning(service.TaskTemplate.PluginSpec.Remote)
+			} else {
+				if img != "" {
+					service.TaskTemplate.PluginSpec.Remote = img
+				}
+				if len(imgPlatforms) > 0 {
+					if service.TaskTemplate.Placement == nil {
+						service.TaskTemplate.Placement = &swarm.Placement{}
+					}
+					service.TaskTemplate.Placement.Platforms = imgPlatforms
+				}
 			}
 		}
 	}
 
-	if service.TaskTemplate.Placement == nil && len(imgPlatforms) > 0 {
-		service.TaskTemplate.Placement = &swarm.Placement{}
-	}
-	if len(imgPlatforms) > 0 {
-		service.TaskTemplate.Placement.Platforms = imgPlatforms
-	}
-
-	var response types.ServiceUpdateResponse
 	resp, err := cli.post(ctx, "/services/"+serviceID+"/update", query, service, headers)
 	defer ensureReaderClosed(resp)
 	if err != nil {
@@ -85,9 +91,8 @@ func (cli *Client) ServiceUpdate(ctx context.Context, serviceID string, version
 	}
 
 	err = json.NewDecoder(resp.body).Decode(&response)
-
-	if distErr != nil {
-		response.Warnings = append(response.Warnings, digestWarning(service.TaskTemplate.ContainerSpec.Image))
+	if resolveWarning != "" {
+		response.Warnings = append(response.Warnings, resolveWarning)
 	}
 
 	return response, err