Add dry-run mode to skopeo-sync

cmd/skopeo/sync.go

@@ -39,6 +39,7 @@ type syncOptions struct {
 	destination         string         // Destination registry name
 	scoped              bool           // When true, namespace copied images at destination using the source repository name
 	all                 bool           // Copy all of the images if an image in the source is a list
+	dryRun              bool           // Don't actually copy anything, just output what it would have done
 	keepGoing           bool           // Whether or not to abort the sync if there are any errors during syncing the images
 }
 
@@ -105,6 +106,7 @@ See skopeo-sync(1) for details.
 	flags.StringVarP(&opts.destination, "dest", "d", "", "DESTINATION transport type")
 	flags.BoolVar(&opts.scoped, "scoped", false, "Images at DESTINATION are prefix using the full source image path as scope")
 	flags.BoolVarP(&opts.all, "all", "a", false, "Copy all images if SOURCE-IMAGE is a list")
+	flags.BoolVar(&opts.dryRun, "dry-run", false, "Run without actually copying data")
 	flags.BoolVarP(&opts.keepGoing, "keep-going", "", false, "Do not abort the sync if any image copy fails")
 	flags.AddFlagSet(&sharedFlags)
 	flags.AddFlagSet(&deprecatedTLSVerifyFlags)
@@ -579,6 +581,11 @@ func (opts *syncOptions) run(args []string, stdout io.Writer) error {
 		OptimizeDestinationImageAlreadyExists: true,
 		ForceManifestMIMEType:                 manifestType,
 	}
+
+	if opts.dryRun {
+		logrus.Warn("Running in dry-run mode")
+	}
+
 	errorsPresent := false
 	imagesNumber := 0
 	for _, srcRepo := range srcRepoList {
@@ -606,26 +613,30 @@ func (opts *syncOptions) run(args []string, stdout io.Writer) error {
 			if err != nil {
 				return err
 			}
-
-			logrus.WithFields(logrus.Fields{
+			fromToFields := logrus.Fields{
 				"from": transports.ImageName(ref),
 				"to":   transports.ImageName(destRef),
-			}).Infof("Copying image ref %d/%d", counter+1, len(srcRepo.ImageRefs))
-
-			if err = retry.RetryIfNecessary(ctx, func() error {
-				_, err = copy.Image(ctx, policyContext, destRef, ref, &options)
-				return err
-			}, opts.retryOpts); err != nil {
-				if !opts.keepGoing {
-					return errors.Wrapf(err, "Error copying ref %q", transports.ImageName(ref))
-				}
-				// log the error, keep a note that there was a failure and move on to the next
-				// image ref
-				errorsPresent = true
-				logrus.WithError(err).Errorf("Error copying ref %q", transports.ImageName(ref))
-				continue
 			}
-			imagesNumber++
+			if opts.dryRun {
+				logrus.WithFields(fromToFields).Infof("Would have copied image ref %d/%d", counter+1, len(srcRepo.ImageRefs))
+			} else {
+				logrus.WithFields(fromToFields).Infof("Copying image ref %d/%d", counter+1, len(srcRepo.ImageRefs))
+        retryFunc := func() error {
+				  _, err = copy.Image(ctx, policyContext, destRef, ref, &options)
+				  return err
+			  }
+			  if err = retry.RetryIfNecessary(ctx, retryFunc, opts.retryOpts); err != nil {
+				  if !opts.keepGoing {
+					  return errors.Wrapf(err, "Error copying ref %q", transports.ImageName(ref))
+				  }
+				  // log the error, keep a note that there was a failure and move on to the next
+				  // image ref
+				  errorsPresent = true
+				  logrus.WithError(err).Errorf("Error copying ref %q", transports.ImageName(ref))
+				  continue
+        }
+        imagesNumber++
+			} 
 		}
 	}
 

docs/skopeo-sync.1.md

@@ -50,6 +50,10 @@ Path of the authentication file for the source registry. Uses path given by `--a
 
 Path of the authentication file for the destination registry. Uses path given by `--authfile`, if not provided.
 
+**--dry-run**
+
+Run the sync without actually copying data to the destination.
+
 **--src**, **-s** _transport_ Transport for the source repository.
 
 **--dest**, **-d** _transport_ Destination transport.