cmd/gomote: allow creation of multiple VMs of the same type

For example:

	$ for i in 1 2 3; do gomote create linux-amd64; done
	$ gomote list
	linux-amd64	https://146.148.41.74
	linux-amd64-1	https://146.148.66.230
	linux-amd64-2	https://23.236.58.252

Change-Id: I3c84f455a8b0293056dd399ae34df0d39ccf29be
Reviewed-on: https://go-review.googlesource.com/6806
Reviewed-by: Russ Cox <rsc@golang.org>

cmd/gomote/create.go

@@ -63,7 +63,11 @@ func create(args []string) error {
 		}
 	}
 
-	instName := fmt.Sprintf("mote-%s-%s", username(), builderType)
+	instPrefix := fmt.Sprintf("mote-%s-", username())
+	instName, err := nextName(instPrefix + builderType)
+	if err != nil {
+		return err
+	}
 	client, err := buildlet.StartNewVM(projTokenSource(), instName, builderType, buildlet.VMOpts{
 		Zone:        *zone,
 		ProjectID:   *proj,
@@ -80,6 +84,6 @@ func create(args []string) error {
 	if err != nil {
 		return fmt.Errorf("failed to create VM: %v", err)
 	}
-	fmt.Printf("%s\t%s\n", builderType, client.URL())
+	fmt.Printf("%s\t%s\n", strings.TrimPrefix(instName, instPrefix), client.URL())
 	return nil
 }

cmd/gomote/list.go

@@ -34,7 +34,7 @@ func list(args []string) error {
 		if !strings.HasPrefix(vm.Name, prefix) {
 			continue
 		}
-		fmt.Printf("%s\thttps://%s\n", vm.Type, strings.TrimSuffix(vm.IPPort, ":443"))
+		fmt.Printf("%s\thttps://%s\n", strings.TrimPrefix(vm.Name, prefix), strings.TrimSuffix(vm.IPPort, ":443"))
 	}
 	return nil
 }
@@ -67,3 +67,29 @@ func namedClient(name string) (*buildlet.Client, error) {
 	}
 	return nil, fmt.Errorf("buildlet %q not running", name)
 }
+
+// nextName returns the next available numbered name or the given buildlet base
+// name. For example, if the provided prefix is "linux-amd64" and there's
+// already an instance named "linux-amd64", nextName will return
+// "linux-amd64-1".
+func nextName(prefix string) (string, error) {
+	vms, err := buildlet.ListVMs(projTokenSource(), *proj, *zone)
+	if err != nil {
+		return "", fmt.Errorf("error listing VMs: %v", err)
+	}
+	matches := map[string]bool{}
+	for _, vm := range vms {
+		if strings.HasPrefix(vm.Name, prefix) {
+			matches[vm.Name] = true
+		}
+	}
+	if len(matches) == 0 || !matches[prefix] {
+		return prefix, nil
+	}
+	for i := 1; ; i++ {
+		next := fmt.Sprintf("%v-%v", prefix, i)
+		if !matches[next] {
+			return next, nil
+		}
+	}
+}