exec_watch_command.go

/*
   Copyright 2014 CoreOS, Inc.

   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 command

import (
	"errors"
	"fmt"
	"io"
	"os"
	"os/exec"
	"os/signal"

	"github.com/coreos/etcd/Godeps/_workspace/src/github.com/codegangsta/cli"
	"github.com/coreos/etcd/Godeps/_workspace/src/github.com/coreos/go-etcd/etcd"
)

// NewExecWatchCommand returns the CLI command for "exec-watch".
func NewExecWatchCommand() cli.Command {
	return cli.Command{
		Name:  "exec-watch",
		Usage: "watch a key for changes and exec an executable",
		Flags: []cli.Flag{
			cli.IntFlag{Name: "after-index", Value: 0, Usage: "watch after the given index"},
			cli.BoolFlag{Name: "recursive", Usage: "watch all values for key and child keys"},
		},
		Action: func(c *cli.Context) {
			handleKey(c, execWatchCommandFunc)
		},
	}
}

// execWatchCommandFunc executes the "exec-watch" command.
func execWatchCommandFunc(c *cli.Context, client *etcd.Client) (*etcd.Response, error) {
	_ = io.Copy
	_ = exec.Command
	args := c.Args()
	argsLen := len(args)

	if argsLen < 2 {
		return nil, errors.New("Key and command to exec required")
	}

	key := args[argsLen-1]
	cmdArgs := args[:argsLen-1]

	index := 0
	if c.Int("after-index") != 0 {
		index = c.Int("after-index") + 1
		key = args[0]
		cmdArgs = args[2:]
	}

	recursive := c.Bool("recursive")
	if recursive != false {
		key = args[0]
		cmdArgs = args[2:]
	}

	sigch := make(chan os.Signal, 1)
	signal.Notify(sigch, os.Interrupt)
	stop := make(chan bool)

	go func() {
		<-sigch
		stop <- true
		os.Exit(0)
	}()

	receiver := make(chan *etcd.Response)
	go client.Watch(key, uint64(index), recursive, receiver, stop)

	for {
		resp := <-receiver
		cmd := exec.Command(cmdArgs[0], cmdArgs[1:]...)
		cmd.Env = environResponse(resp, os.Environ())

		stdout, err := cmd.StdoutPipe()
		if err != nil {
			fmt.Fprintf(os.Stderr, err.Error())
			os.Exit(1)
		}
		stderr, err := cmd.StderrPipe()
		if err != nil {
			fmt.Fprintf(os.Stderr, err.Error())
			os.Exit(1)
		}
		err = cmd.Start()
		if err != nil {
			fmt.Fprintf(os.Stderr, err.Error())
			os.Exit(1)
		}
		go io.Copy(os.Stdout, stdout)
		go io.Copy(os.Stderr, stderr)
		cmd.Wait()
	}
}

func environResponse(resp *etcd.Response, env []string) []string {
	env = append(env, "ETCD_WATCH_ACTION="+resp.Action)
	env = append(env, "ETCD_WATCH_MODIFIED_INDEX="+fmt.Sprintf("%d", resp.Node.ModifiedIndex))
	env = append(env, "ETCD_WATCH_KEY="+resp.Node.Key)
	env = append(env, "ETCD_WATCH_VALUE="+resp.Node.Value)
	return env
}