172 lines
3.8 KiB
Go
172 lines
3.8 KiB
Go
// Copyright 2015 The Prometheus Authors
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package cli
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import (
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"bytes"
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"fmt"
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"io"
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"sort"
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"strings"
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"text/template"
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)
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// Command represents a single command within an application.
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type Command struct {
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Desc string
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Run func(t Term, args ...string) int
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}
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// Term handles an application's output.
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type Term interface {
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Infof(format string, v ...interface{})
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Errorf(format string, v ...interface{})
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Out(format string)
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}
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type basicTerm struct {
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out, err io.Writer
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}
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// Infof implements Term.
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func (t *basicTerm) Infof(format string, v ...interface{}) {
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fmt.Fprintf(t.err, format, v...)
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fmt.Fprint(t.err, "\n")
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}
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// Errorf implements Term.
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func (t *basicTerm) Errorf(format string, v ...interface{}) {
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fmt.Fprintf(t.err, format, v...)
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fmt.Fprint(t.err, "\n")
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}
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// Out implements Term.
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func (t *basicTerm) Out(msg string) {
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fmt.Fprint(t.out, msg)
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fmt.Fprint(t.out, "\n")
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}
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// BasicTerm returns a Term writing Infof and Errorf to err and Out to out.
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func BasicTerm(out, err io.Writer) Term {
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return &basicTerm{out: out, err: err}
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}
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// App represents an application that may consist of multiple commands.
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type App struct {
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Name string
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Help func() string
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commands map[string]*Command
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}
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// NewApp creates a new application with a pre-registered help command.
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func NewApp(name string) *App {
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app := &App{
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Name: name,
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commands: map[string]*Command{},
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}
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app.Register("help", &Command{
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Desc: "prints this help text",
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Run: func(t Term, _ ...string) int {
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help := app.Help
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if help == nil {
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help = BasicHelp(app, tmpl)
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}
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t.Infof(help() + "\n")
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return 0
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},
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})
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return app
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}
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// Register adds a new command to the application.
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func (app *App) Register(name string, cmd *Command) {
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name = strings.TrimSpace(name)
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if name == "" {
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panic("command name must not be empty")
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}
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if _, ok := app.commands[name]; ok {
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panic("command cannot be registered twice")
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}
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app.commands[name] = cmd
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}
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// Run the application with the given arguments. Output is sent to t.
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func (app *App) Run(t Term, args ...string) int {
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help := app.commands["help"]
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if len(args) == 0 || strings.HasPrefix(args[0], "-") {
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help.Run(t)
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return 2
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}
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cmd, ok := app.commands[args[0]]
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if !ok {
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help.Run(t)
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return 2
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}
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return cmd.Run(t, args[1:]...)
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}
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var tmpl = `
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usage: {{ .Name }} <command> [<args>]
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Available commands:
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{{ range .Commands }}{{ .Name }} {{ .Desc }}
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{{ end }}
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`
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// BasicHelp returns a function that creates a basic help text for the application
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// with its commands.
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func BasicHelp(app *App, ts string) func() string {
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t := template.Must(template.New("help").Parse(ts))
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return func() string {
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type command struct {
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Name, Desc string
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}
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cmds := []command{}
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var maxLen int
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names := []string{}
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for name := range app.commands {
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names = append(names, name)
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if len(name) > maxLen {
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maxLen = len(name)
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}
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}
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sort.Strings(names)
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for _, name := range names {
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cmds = append(cmds, command{
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Name: name + strings.Repeat(" ", maxLen-len(name)),
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Desc: app.commands[name].Desc,
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})
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}
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var buf bytes.Buffer
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err := t.Execute(&buf, struct {
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Name string
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Commands []command
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}{
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Name: app.Name,
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Commands: cmds,
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})
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if err != nil {
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panic(fmt.Errorf("error executing help template: %s", err))
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}
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return strings.TrimSpace(buf.String())
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}
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}
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