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watch_command.go
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watch_command.go
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// Copyright 2015 The etcd 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 command
import (
"bufio"
"context"
"errors"
"fmt"
"os"
"os/exec"
"strings"
"github.com/coreos/etcd/clientv3"
"github.com/spf13/cobra"
)
var (
errBadArgsNum = errors.New("bad number of arguments")
errBadArgsNumConflictEnv = errors.New("bad number of arguments (found conflicting environment key)")
errBadArgsNumSeparator = errors.New("bad number of arguments (found separator --, but no commands)")
errBadArgsInteractiveWatch = errors.New("args[0] must be 'watch' for interactive calls")
)
var (
watchRev int64
watchPrefix bool
watchInteractive bool
watchPrevKey bool
)
// NewWatchCommand returns the cobra command for "watch".
func NewWatchCommand() *cobra.Command {
cmd := &cobra.Command{
Use: "watch [options] [key or prefix] [range_end] [--] [exec-command arg1 arg2 ...]",
Short: "Watches events stream on keys or prefixes",
Run: watchCommandFunc,
}
cmd.Flags().BoolVarP(&watchInteractive, "interactive", "i", false, "Interactive mode")
cmd.Flags().BoolVar(&watchPrefix, "prefix", false, "Watch on a prefix if prefix is set")
cmd.Flags().Int64Var(&watchRev, "rev", 0, "Revision to start watching")
cmd.Flags().BoolVar(&watchPrevKey, "prev-kv", false, "get the previous key-value pair before the event happens")
return cmd
}
// watchCommandFunc executes the "watch" command.
func watchCommandFunc(cmd *cobra.Command, args []string) {
envKey, envRange := os.Getenv("ETCDCTL_WATCH_KEY"), os.Getenv("ETCDCTL_WATCH_RANGE_END")
if envKey == "" && envRange != "" {
ExitWithError(ExitBadArgs, fmt.Errorf("ETCDCTL_WATCH_KEY is empty but got ETCDCTL_WATCH_RANGE_END=%q", envRange))
}
if watchInteractive {
watchInteractiveFunc(cmd, os.Args, envKey, envRange)
return
}
watchArgs, execArgs, err := parseWatchArgs(os.Args, args, envKey, envRange, false)
if err != nil {
ExitWithError(ExitBadArgs, err)
}
c := mustClientFromCmd(cmd)
wc, err := getWatchChan(c, watchArgs)
if err != nil {
ExitWithError(ExitBadArgs, err)
}
printWatchCh(c, wc, execArgs)
if err = c.Close(); err != nil {
ExitWithError(ExitBadConnection, err)
}
ExitWithError(ExitInterrupted, fmt.Errorf("watch is canceled by the server"))
}
func watchInteractiveFunc(cmd *cobra.Command, osArgs []string, envKey, envRange string) {
c := mustClientFromCmd(cmd)
reader := bufio.NewReader(os.Stdin)
for {
l, err := reader.ReadString('\n')
if err != nil {
ExitWithError(ExitInvalidInput, fmt.Errorf("Error reading watch request line: %v", err))
}
l = strings.TrimSuffix(l, "\n")
args := argify(l)
if len(args) < 2 && envKey == "" {
fmt.Fprintf(os.Stderr, "Invalid command %s (command type or key is not provided)\n", l)
continue
}
if args[0] != "watch" {
fmt.Fprintf(os.Stderr, "Invalid command %s (only support watch)\n", l)
continue
}
watchArgs, execArgs, perr := parseWatchArgs(osArgs, args, envKey, envRange, true)
if perr != nil {
ExitWithError(ExitBadArgs, perr)
}
ch, err := getWatchChan(c, watchArgs)
if err != nil {
fmt.Fprintf(os.Stderr, "Invalid command %s (%v)\n", l, err)
continue
}
go printWatchCh(c, ch, execArgs)
}
}
func getWatchChan(c *clientv3.Client, args []string) (clientv3.WatchChan, error) {
if len(args) < 1 {
return nil, errBadArgsNum
}
key := args[0]
opts := []clientv3.OpOption{clientv3.WithRev(watchRev)}
if len(args) == 2 {
if watchPrefix {
return nil, fmt.Errorf("`range_end` and `--prefix` are mutually exclusive")
}
opts = append(opts, clientv3.WithRange(args[1]))
}
if watchPrefix {
opts = append(opts, clientv3.WithPrefix())
}
if watchPrevKey {
opts = append(opts, clientv3.WithPrevKV())
}
return c.Watch(clientv3.WithRequireLeader(context.Background()), key, opts...), nil
}
func printWatchCh(c *clientv3.Client, ch clientv3.WatchChan, execArgs []string) {
for resp := range ch {
if resp.Canceled {
fmt.Fprintf(os.Stderr, "watch was canceled (%v)\n", resp.Err())
}
display.Watch(resp)
if len(execArgs) > 0 {
for _, ev := range resp.Events {
cmd := exec.CommandContext(c.Ctx(), execArgs[0], execArgs[1:]...)
cmd.Env = os.Environ()
cmd.Env = append(cmd.Env, fmt.Sprintf("ETCD_WATCH_REVISION=%d", resp.Header.Revision))
cmd.Env = append(cmd.Env, fmt.Sprintf("ETCD_WATCH_EVENT_TYPE=%q", ev.Type))
cmd.Env = append(cmd.Env, fmt.Sprintf("ETCD_WATCH_KEY=%q", ev.Kv.Key))
cmd.Env = append(cmd.Env, fmt.Sprintf("ETCD_WATCH_VALUE=%q", ev.Kv.Value))
cmd.Stdout, cmd.Stderr = os.Stdout, os.Stderr
if err := cmd.Run(); err != nil {
fmt.Fprintf(os.Stderr, "command %q error (%v)\n", execArgs, err)
os.Exit(1)
}
}
}
}
}
// "commandArgs" is the command arguments after "spf13/cobra" parses
// all "watch" command flags, strips out special characters (e.g. "--").
// "orArgs" is the raw arguments passed to "watch" command
// (e.g. ./bin/etcdctl watch foo --rev 1 bar).
// "--" characters are invalid arguments for "spf13/cobra" library,
// so no need to handle such cases.
func parseWatchArgs(osArgs, commandArgs []string, envKey, envRange string, interactive bool) (watchArgs []string, execArgs []string, err error) {
rawArgs := make([]string, len(osArgs))
copy(rawArgs, osArgs)
watchArgs = make([]string, len(commandArgs))
copy(watchArgs, commandArgs)
// remove preceding commands (e.g. ./bin/etcdctl watch)
// handle "./bin/etcdctl watch foo -- echo watch event"
for idx := range rawArgs {
if rawArgs[idx] == "watch" {
rawArgs = rawArgs[idx+1:]
break
}
}
// remove preceding commands (e.g. "watch foo bar" in interactive mode)
// handle "./bin/etcdctl watch foo -- echo watch event"
if interactive {
if watchArgs[0] != "watch" {
// "watch" not found
watchPrefix, watchRev, watchPrevKey = false, 0, false
return nil, nil, errBadArgsInteractiveWatch
}
watchArgs = watchArgs[1:]
}
execIdx, execExist := 0, false
if !interactive {
for execIdx = range rawArgs {
if rawArgs[execIdx] == "--" {
execExist = true
break
}
}
if execExist && execIdx == len(rawArgs)-1 {
// "watch foo bar --" should error
return nil, nil, errBadArgsNumSeparator
}
// "watch" with no argument should error
if !execExist && len(rawArgs) < 1 && envKey == "" {
return nil, nil, errBadArgsNum
}
if execExist && envKey != "" {
// "ETCDCTL_WATCH_KEY=foo watch foo -- echo 1" should error
// (watchArgs==["foo","echo","1"])
widx, ridx := len(watchArgs)-1, len(rawArgs)-1
for ; widx >= 0; widx-- {
if watchArgs[widx] == rawArgs[ridx] {
ridx--
continue
}
// watchArgs has extra:
// ETCDCTL_WATCH_KEY=foo watch foo -- echo 1
// watchArgs: foo echo 1
if ridx == execIdx {
return nil, nil, errBadArgsNumConflictEnv
}
}
}
// check conflicting arguments
// e.g. "watch --rev 1 -- echo Hello World" has no conflict
if !execExist && len(watchArgs) > 0 && envKey != "" {
// "ETCDCTL_WATCH_KEY=foo watch foo" should error
// (watchArgs==["foo"])
return nil, nil, errBadArgsNumConflictEnv
}
} else {
for execIdx = range watchArgs {
if watchArgs[execIdx] == "--" {
execExist = true
break
}
}
if execExist && execIdx == len(watchArgs)-1 {
// "watch foo bar --" should error
watchPrefix, watchRev, watchPrevKey = false, 0, false
return nil, nil, errBadArgsNumSeparator
}
flagset := NewWatchCommand().Flags()
if err := flagset.Parse(watchArgs); err != nil {
watchPrefix, watchRev, watchPrevKey = false, 0, false
return nil, nil, err
}
pArgs := flagset.Args()
// "watch" with no argument should error
if !execExist && envKey == "" && len(pArgs) < 1 {
watchPrefix, watchRev, watchPrevKey = false, 0, false
return nil, nil, errBadArgsNum
}
// check conflicting arguments
// e.g. "watch --rev 1 -- echo Hello World" has no conflict
if !execExist && len(pArgs) > 0 && envKey != "" {
// "ETCDCTL_WATCH_KEY=foo watch foo" should error
// (watchArgs==["foo"])
watchPrefix, watchRev, watchPrevKey = false, 0, false
return nil, nil, errBadArgsNumConflictEnv
}
}
argsWithSep := rawArgs
if interactive {
// interactive mode directly passes "--" to the command args
argsWithSep = watchArgs
}
idx, foundSep := 0, false
for idx = range argsWithSep {
if argsWithSep[idx] == "--" {
foundSep = true
break
}
}
if foundSep {
execArgs = argsWithSep[idx+1:]
}
if interactive {
flagset := NewWatchCommand().Flags()
if err := flagset.Parse(argsWithSep); err != nil {
return nil, nil, err
}
watchArgs = flagset.Args()
watchPrefix, err = flagset.GetBool("prefix")
if err != nil {
return nil, nil, err
}
watchRev, err = flagset.GetInt64("rev")
if err != nil {
return nil, nil, err
}
watchPrevKey, err = flagset.GetBool("prev-kv")
if err != nil {
return nil, nil, err
}
}
// "ETCDCTL_WATCH_KEY=foo watch -- echo hello"
// should translate "watch foo -- echo hello"
// (watchArgs=["echo","hello"] should be ["foo","echo","hello"])
if envKey != "" {
ranges := []string{envKey}
if envRange != "" {
ranges = append(ranges, envRange)
}
watchArgs = append(ranges, watchArgs...)
}
if !foundSep {
return watchArgs, nil, nil
}
// "watch foo bar --rev 1 -- echo hello" or "watch foo --rev 1 bar -- echo hello",
// then "watchArgs" is "foo bar echo hello"
// so need ignore args after "argsWithSep[idx]", which is "--"
endIdx := 0
for endIdx = len(watchArgs) - 1; endIdx >= 0; endIdx-- {
if watchArgs[endIdx] == argsWithSep[idx+1] {
break
}
}
watchArgs = watchArgs[:endIdx]
return watchArgs, execArgs, nil
}