docker save: fix the 'repositories' file

For various use cases, the 'repositories' file does not match expected
behavior.

Like,

	docker save busybox:latest | tar t

Before:

	[...]
	busybox:latest/
	busybox:latest/VERSION
	busybox:latest/json
	busybox:latest/layer.tar
	# note, the layer name, and lack of 'repositories' file

Now:

	[...]
	a9eb172552348a9a49180694790b33a1097f546456d041b6e82e4d7716ddb721/
	a9eb172552348a9a49180694790b33a1097f546456d041b6e82e4d7716ddb721/VERSION
	a9eb172552348a9a49180694790b33a1097f546456d041b6e82e4d7716ddb721/json
	a9eb172552348a9a49180694790b33a1097f546456d041b6e82e4d7716ddb721/layer.tar
	repositories
	# and the repositories file is correct for the single tagged
	# image.
	#> {"busybox":{"latest":"a9eb172552348a9a49180694790b33a1097f546456d041b6e82e4d7716ddb721"}}

and

	docker save a9eb17255234 | tar t

Before:
	[...]
	a9eb17255234/
	a9eb17255234/VERSION
	a9eb17255234/json
	a9eb17255234/layer.tar
	# Note the truncated layer name

Now:
	[...]
	a9eb172552348a9a49180694790b33a1097f546456d041b6e82e4d7716ddb721/
	a9eb172552348a9a49180694790b33a1097f546456d041b6e82e4d7716ddb721/VERSION
	a9eb172552348a9a49180694790b33a1097f546456d041b6e82e4d7716ddb721/json
	a9eb172552348a9a49180694790b33a1097f546456d041b6e82e4d7716ddb721/layer.tar
	# There is no 'repositories' file, because there is no named repo

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)

server/server.go

@@ -351,29 +351,52 @@ func (srv *Server) ImageExport(job *engine.Job) engine.Status {
 
 	utils.Debugf("Serializing %s", name)
 
+	rootRepoMap := map[string]graph.Repository{}
 	rootRepo, err := srv.daemon.Repositories().Get(name)
 	if err != nil {
 		return job.Error(err)
 	}
 	if rootRepo != nil {
+		// this is a base repo name, like 'busybox'
+
 		for _, id := range rootRepo {
 			if err := srv.exportImage(job.Eng, id, tempdir); err != nil {
 				return job.Error(err)
 			}
 		}
-
-		// write repositories
-		rootRepoMap := map[string]graph.Repository{}
 		rootRepoMap[name] = rootRepo
+	} else {
+		img, err := srv.daemon.Repositories().LookupImage(name)
+		if err != nil {
+			return job.Error(err)
+		}
+		if img != nil {
+			// This is a named image like 'busybox:latest'
+			repoName, repoTag := utils.ParseRepositoryTag(name)
+			if err := srv.exportImage(job.Eng, img.ID, tempdir); err != nil {
+				return job.Error(err)
+			}
+			// check this length, because a lookup of a truncated has will not have a tag
+			// and will not need to be added to this map
+			if len(repoTag) > 0 {
+				rootRepoMap[repoName] = graph.Repository{repoTag: img.ID}
+			}
+		} else {
+			// this must be an ID that didn't get looked up just right?
+			if err := srv.exportImage(job.Eng, name, tempdir); err != nil {
+				return job.Error(err)
+			}
+		}
+	}
+	// write repositories, if there is something to write
+	if len(rootRepoMap) > 0 {
 		rootRepoJson, _ := json.Marshal(rootRepoMap)
 
 		if err := ioutil.WriteFile(path.Join(tempdir, "repositories"), rootRepoJson, os.FileMode(0644)); err != nil {
 			return job.Error(err)
 		}
 	} else {
-		if err := srv.exportImage(job.Eng, name, tempdir); err != nil {
-			return job.Error(err)
-		}
+		utils.Debugf("There were no repositories to write")
 	}
 
 	fs, err := archive.Tar(tempdir, archive.Uncompressed)