New command: "kubeadm token generate"

This surfaces the token generation logic so that users can first
generate and store a token, then pass it to kubeadm init/join.
Otherwise, users have to capture and parse the output of "kubeadm init"
to feed the token to "kubeadm join."

cmd/kubeadm/app/cmd/cmd.go

@@ -81,6 +81,7 @@ func NewKubeadmCommand(f cmdutil.Factory, in io.Reader, out, err io.Writer) *cob
 	cmds.AddCommand(NewCmdInit(out))
 	cmds.AddCommand(NewCmdJoin(out))
 	cmds.AddCommand(NewCmdReset(out))
+	cmds.AddCommand(NewCmdToken(out))
 	cmds.AddCommand(NewCmdVersion(out))
 
 	return cmds

cmd/kubeadm/app/cmd/token.go

@@ -0,0 +1,86 @@
+/*
+Copyright 2016 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package cmd
+
+import (
+	"errors"
+	"fmt"
+	"io"
+
+	"github.com/renstrom/dedent"
+	"github.com/spf13/cobra"
+
+	kubeadmapi "k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm"
+	"k8s.io/kubernetes/cmd/kubeadm/app/util"
+	kubeadmutil "k8s.io/kubernetes/cmd/kubeadm/app/util"
+)
+
+func NewCmdToken(out io.Writer) *cobra.Command {
+	cmd := &cobra.Command{
+		Use:   "token",
+		Short: "Manage tokens used by init/join",
+
+		// Without this callback, if a user runs just the "token"
+		// command without a subcommand, or with an invalid subcommand,
+		// cobra will print usage information, but still exit cleanly.
+		// We want to return an error code in these cases so that the
+		// user knows that their command was invalid.
+		RunE: func(cmd *cobra.Command, args []string) error {
+			if len(args) < 1 {
+				return errors.New("missing subcommand; 'token' is not meant to be run on its own")
+			} else {
+				return fmt.Errorf("invalid subcommand: %s", args[0])
+			}
+		},
+	}
+
+	cmd.AddCommand(NewCmdTokenGenerate(out))
+	return cmd
+}
+
+func NewCmdTokenGenerate(out io.Writer) *cobra.Command {
+	return &cobra.Command{
+		Use:   "generate",
+		Short: "Generate and print a token suitable for use with init/join",
+		Long: dedent.Dedent(`
+			This command will print out a randomly-generated token that you can use with
+			the "init" and "join" commands.
+
+			You don't have to use this command in order to generate a token, you can do so
+			yourself as long as it's in the format "<6 characters>.<16 characters>". This
+			command is provided for convenience to generate tokens in that format.
+
+			You can also use "kubeadm init" without specifying a token, and it will
+			generate and print one for you.
+		`),
+		Run: func(cmd *cobra.Command, args []string) {
+			err := RunGenerateToken(out)
+			kubeadmutil.CheckErr(err)
+		},
+	}
+}
+
+func RunGenerateToken(out io.Writer) error {
+	s := &kubeadmapi.Secrets{}
+	err := util.GenerateToken(s)
+	if err != nil {
+		return err
+	}
+
+	fmt.Fprintln(out, s.GivenToken)
+	return nil
+}

cmd/kubeadm/app/cmd/token_test.go

@@ -0,0 +1,46 @@
+/*
+Copyright 2016 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package cmd
+
+import (
+	"bytes"
+	"regexp"
+	"testing"
+)
+
+const (
+	TokenExpectedRegex = "^\\S{6}\\.\\S{16}\n$"
+)
+
+func TestRunGenerateToken(t *testing.T) {
+	var buf bytes.Buffer
+
+	err := RunGenerateToken(&buf)
+	if err != nil {
+		t.Errorf("RunGenerateToken returned an error: %v", err)
+	}
+
+	output := buf.String()
+
+	matched, err := regexp.MatchString(TokenExpectedRegex, output)
+	if err != nil {
+		t.Fatalf("encountered an error while trying to match RunGenerateToken's output: %v", err)
+	}
+	if !matched {
+		t.Errorf("RunGenerateToken's output did not match expected regex; wanted: [%s], got: [%s]", TokenExpectedRegex, output)
+	}
+}