add digest sub-flag for list image

fix #162
Signed-off-by: yanxuean <yan.xuean@zte.com.cn>

cmd/crictl/image.go

@@ -92,6 +92,10 @@ var listImageCommand = cli.Command{
 			Name:  "output, o",
 			Usage: "Output format, One of: json|yaml|table",
 		},
+		cli.BoolFlag{
+			Name:  "digests",
+			Usage: "Show digests",
+		},
 	},
 	Action: func(context *cli.Context) error {
 		if err := getImageClient(context); err != nil {
@@ -121,15 +125,25 @@ var listImageCommand = cli.Command{
 				continue
 			}
 			if !verbose {
+				showDigest := context.Bool("digests")
 				if printHeader {
 					printHeader = false
-					fmt.Fprintln(w, "IMAGE\tTAG\tIMAGE ID\tSIZE")
+					if showDigest {
+						fmt.Fprintln(w, "IMAGE\tTAG\tDIGEST\tIMAGE ID\tSIZE")
+					} else {
+						fmt.Fprintln(w, "IMAGE\tTAG\tIMAGE ID\tSIZE")
+					}
 				}
+				repoDigest := normalizeRepoDigest(image.RepoDigests)
 				repoTagPairs := normalizeRepoTagPair(image.RepoTags, image.RepoDigests)
 				size := units.HumanSizeWithPrecision(float64(image.GetSize_()), 3)
 				trunctedImage := strings.TrimPrefix(image.Id, "sha256:")[:truncatedImageIDLen]
 				for _, repoTagPair := range repoTagPairs {
-					fmt.Fprintf(w, "%s\t%s\t%s\t%s\n", repoTagPair[0], repoTagPair[1], trunctedImage, size)
+					if showDigest {
+						fmt.Fprintf(w, "%s\t%s\t%s\t%s\t%s\n", repoTagPair[0], repoTagPair[1], repoDigest, trunctedImage, size)
+					} else {
+						fmt.Fprintf(w, "%s\t%s\t%s\t%s\n", repoTagPair[0], repoTagPair[1], trunctedImage, size)
+					}
 				}
 				continue
 			}
@@ -291,6 +305,17 @@ func normalizeRepoTagPair(repoTags []string, repoDigests []string) (repoTagPairs
 	return
 }
 
+func normalizeRepoDigest(repoDigests []string) string {
+	if len(repoDigests) == 0 {
+		return "<none>"
+	}
+	repoDigestPair := strings.Split(repoDigests[0],"@")
+	if len(repoDigestPair) != 2 {
+		return "errorRepoDigest"
+	}
+	return repoDigestPair[1]
+}
+
 // PullImage sends a PullImageRequest to the server, and parses
 // the returned PullImageResponse.
 func PullImage(client pb.ImageServiceClient, image string, auth *pb.AuthConfig) (*pb.PullImageResponse, error) {