cmd中Geth重要衔接包代码简析

Geth中的main函数中调用了一个Run方法，该方法属于包cli中的类App的一个成员方法，下面是Run函数的具体实现

func (a *App) Run(arguments []string) (err error) {
	a.Setup()

	// handle the completion flag separately from the flagset since
	// completion could be attempted after a flag, but before its value was put
	// on the command line. this causes the flagset to interpret the completion
	// flag name as the value of the flag before it which is undesirable
	// note that we can only do this because the shell autocomplete function
	// always appends the completion flag at the end of the command
	shellComplete, arguments := checkShellCompleteFlag(a, arguments)

	// parse flags
	set, err := flagSet(a.Name, a.Flags)
	if err != nil {
		return err
	}

	set.SetOutput(ioutil.Discard)
	err = set.Parse(arguments[1:])
	nerr := normalizeFlags(a.Flags, set)
	context := NewContext(a, set, nil)
	if nerr != nil {
		fmt.Fprintln(a.Writer, nerr)
		ShowAppHelp(context)
		return nerr
	}
	context.shellComplete = shellComplete

	if checkCompletions(context) {
		return nil
	}

	if err != nil {
		if a.OnUsageError != nil {
			err := a.OnUsageError(context, err, false)
			HandleExitCoder(err)
			return err
		}
		fmt.Fprintf(a.Writer, "%s %s\n\n", "Incorrect Usage.", err.Error())
		ShowAppHelp(context)
		return err
	}

	if !a.HideHelp && checkHelp(context) {
		ShowAppHelp(context)
		return nil
	}

	if !a.HideVersion && checkVersion(context) {
		ShowVersion(context)
		return nil
	}

	if a.After != nil {
		defer func() {
			if afterErr := a.After(context); afterErr != nil {
				if err != nil {
					err = NewMultiError(err, afterErr)
				} else {
					err = afterErr
				}
			}
		}()
	}

	if a.Before != nil {
		beforeErr := a.Before(context)
		if beforeErr != nil {
			fmt.Fprintf(a.Writer, "%v\n\n", beforeErr)
			ShowAppHelp(context)
			HandleExitCoder(beforeErr)
			err = beforeErr
			return err
		}
	}

	args := context.Args()
	if args.Present() {
		name := args.First()
		c := a.Command(name)
		if c != nil {
			return c.Run(context)
		}
	}

	if a.Action == nil {
		a.Action = helpCommand.Action
	}

	// Run default Action
	err = HandleAction(a.Action, context)

	HandleExitCoder(err)
	return err
}

a.Setup仅仅是做了些简单的处理，比如相关的Auther、Email、重新创建Command切片等等.接下来我们看看下面的这个if判断

if args.Present() {
		name := args.First()
		c := a.Command(name)
		if c != nil {
			return c.Run(context)
		}
	}

由于我们前面在控制台输入的命令（启动命令 geth + 参数）长度不为0，因此执行

c.Run(context)

操作，此时的命令其实就是我们的console命令。接下来我们看看Run方法，Run方法的代码如下：

func (c Command) Run(ctx *Context) (err error) {
	if len(c.Subcommands) > 0 {
		return c.startApp(ctx)
	}

	if !c.HideHelp && (HelpFlag != BoolFlag{}) {
		// append help to flags
		c.Flags = append(
			c.Flags,
			HelpFlag,
		)
	}

	set, err := flagSet(c.Name, c.Flags)
	if err != nil {
		return err
	}
	set.SetOutput(ioutil.Discard)

	if c.SkipFlagParsing {
		err = set.Parse(append([]string{"--"}, ctx.Args().Tail()...))
	} else if !c.SkipArgReorder {
		firstFlagIndex := -1
		terminatorIndex := -1
		for index, arg := range ctx.Args() {
			if arg == "--" {
				terminatorIndex = index
				break
			} else if arg == "-" {
				// Do nothing. A dash alone is not really a flag.
				continue
			} else if strings.HasPrefix(arg, "-") && firstFlagIndex == -1 {
				firstFlagIndex = index
			}
		}

		if firstFlagIndex > -1 {
			args := ctx.Args()
			regularArgs := make([]string, len(args[1:firstFlagIndex]))
			copy(regularArgs, args[1:firstFlagIndex])

			var flagArgs []string
			if terminatorIndex > -1 {
				flagArgs = args[firstFlagIndex:terminatorIndex]
				regularArgs = append(regularArgs, args[terminatorIndex:]...)
			} else {
				flagArgs = args[firstFlagIndex:]
			}

			err = set.Parse(append(flagArgs, regularArgs...))
		} else {
			err = set.Parse(ctx.Args().Tail())
		}
	} else {
		err = set.Parse(ctx.Args().Tail())
	}

	nerr := normalizeFlags(c.Flags, set)
	if nerr != nil {
		fmt.Fprintln(ctx.App.Writer, nerr)
		fmt.Fprintln(ctx.App.Writer)
		ShowCommandHelp(ctx, c.Name)
		return nerr
	}

	context := NewContext(ctx.App, set, ctx)
	if checkCommandCompletions(context, c.Name) {
		return nil
	}

	if err != nil {
		if c.OnUsageError != nil {
			err := c.OnUsageError(ctx, err, false)
			HandleExitCoder(err)
			return err
		}
		fmt.Fprintln(ctx.App.Writer, "Incorrect Usage:", err.Error())
		fmt.Fprintln(ctx.App.Writer)
		ShowCommandHelp(ctx, c.Name)
		return err
	}

	if checkCommandHelp(context, c.Name) {
		return nil
	}

	if c.After != nil {
		defer func() {
			afterErr := c.After(context)
			if afterErr != nil {
				HandleExitCoder(err)
				if err != nil {
					err = NewMultiError(err, afterErr)
				} else {
					err = afterErr
				}
			}
		}()
	}

	if c.Before != nil {
		err = c.Before(context)
		if err != nil {
			fmt.Fprintln(ctx.App.Writer, err)
			fmt.Fprintln(ctx.App.Writer)
			ShowCommandHelp(ctx, c.Name)
			HandleExitCoder(err)
			return err
		}
	}

	if c.Action == nil {
		c.Action = helpSubcommand.Action
	}

	context.Command = c
	err = HandleAction(c.Action, context)

	if err != nil {
		HandleExitCoder(err)
	}
	return err
}

该主要是设置flag、解析输入的命令行参数、创建全局的context、将当前命令保存到全局context中,接下来调用HandleAction来处理命令，HandleAction的函数实现如下：

func HandleAction(action interface{}, context *Context) (err error) 	{
	if a, ok := action.(ActionFunc); ok {
		return a(context)
	} else if a, ok := action.(func(*Context) error); ok {
		return a(context)
	} else if a, ok := action.(func(*Context)); ok { // deprecated function signature
		a(context)
		return nil
	} else {
		return errInvalidActionType
	}
}

通过该函数代码重新经过相应的Init函数中的命令初始化方式进入相应的命令执行，当然，这只是简单的分析，实际的执行过程比这锅复杂得多。

GitHub地址：

https://github.com/guoshijiang/go-ethereum-code-analysis

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