Check validity of an image tag (#143)

sonar/cmd/layers_list.go

@@ -20,6 +20,11 @@ var layersListCmd = &cobra.Command{
 			return fmt.Errorf("%s", err)
 		}
 
+		if validity, err := image.Valid(); validity != true {
+
+			return err
+		}
+
 		image.ShowTag = false
 
 		dockerLayers, err := docker.GetAllLayers(image.String(), image.Tag)

sonar/docker/image.go

@@ -8,7 +8,10 @@ import (
 	"strings"
 )
 
-var ErrImageName = errors.New("Error: Invalid image name.")
+var (
+	ErrImageName = errors.New("Error: Invalid image name.")
+	ErrImageTag  = errors.New("Error: Image tag doesn't exist.")
+)
 
 type ImageRef struct {
 	Namespace string `json:"namesapce"`
@@ -26,6 +29,29 @@ func (this *ImageRef) String() string {
 	return fmt.Sprintf("%s/%s", this.Namespace, this.Name)
 }
 
+/* Returns true if the image tag exists for an image. */
+func (this *ImageRef) Valid() (bool, error) {
+
+	reqURL := "https://hub.docker.com/v2/repositories/" + this.Namespace + "/" + this.Name + "/tags/" + this.Tag
+
+	req, err := http.NewRequest("GET", reqURL, nil)
+	if err != nil {
+		return false, err
+	}
+
+	resp, err := SendRequest(req, "", "")
+	if err != nil {
+		return false, err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode == http.StatusOK {
+		return true, nil
+	} else {
+		return false, ErrImageTag
+	}
+}
+
 // NewImageRef creates a new reference to a Docker image.
 // Namespace and tag can be empty strings in order to use Docker defaults of 'library' and 'latest'.
 func NewImageRef(namespace, name, tag string) (*ImageRef, error) {