kubectl 源码分析之exec

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目前刚开始写一个月，一共写了18篇原创文章，文章目录如下：

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不懂envoyfilter也敢说精通istio系列-03-http-csrf filter-再也不用再代码里写csrf逻辑了

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type ExecOptions struct {//exec结构体
	StreamOptions

	ResourceName string
	Command      []string

	ParentCommandName       string
	EnableSuggestedCmdUsage bool

	Builder          func() *resource.Builder
	ExecutablePodFn  polymorphichelpers.AttachablePodForObjectFunc
	restClientGetter genericclioptions.RESTClientGetter

	Pod           *corev1.Pod
	Executor      RemoteExecutor
	PodClient     coreclient.PodsGetter
	GetPodTimeout time.Duration
	Config        *restclient.Config
}

type StreamOptions struct {//stream结构体
	Namespace     string
	PodName       string
	ContainerName string
	Stdin         bool
	TTY           bool
	// minimize unnecessary output
	Quiet bool
	// InterruptParent, if set, is used to handle interrupts while attached
	InterruptParent *interrupt.Handler

	genericclioptions.IOStreams

	// for testing
	overrideStreams func() (io.ReadCloser, io.Writer, io.Writer)
	isTerminalIn    func(t term.TTY) bool
}

//创建exec命令
func NewCmdExec(f cmdutil.Factory, streams genericclioptions.IOStreams) *cobra.Command {
	options := &ExecOptions{//初始化结构体
		StreamOptions: StreamOptions{
			IOStreams: streams,
		},

		Executor: &DefaultRemoteExecutor{},
	}
	cmd := &cobra.Command{//创建cobra命令
		Use:                   "exec (POD | TYPE/NAME) [-c CONTAINER] [flags] -- COMMAND [args...]",
		DisableFlagsInUseLine: true,
		Short:                 i18n.T("Execute a command in a container"),
		Long:                  "Execute a command in a container.",
		Example:               execExample,
		Run: func(cmd *cobra.Command, args []string) {
			argsLenAtDash := cmd.ArgsLenAtDash()
			cmdutil.CheckErr(options.Complete(f, cmd, args, argsLenAtDash))//准备
			cmdutil.CheckErr(options.Validate())//校验
			cmdutil.CheckErr(options.Run())//运行
		},
	}
	cmdutil.AddPodRunningTimeoutFlag(cmd, defaultPodExecTimeout)//pod-running-timeout信息
	// TODO support UID
	cmd.Flags().StringVarP(&options.ContainerName, "container", "c", options.ContainerName, "Container name. If omitted, the first container in the pod will be chosen")// container选项
	cmd.Flags().BoolVarP(&options.Stdin, "stdin", "i", options.Stdin, "Pass stdin to the container")//-i选项
	cmd.Flags().BoolVarP(&options.TTY, "tty", "t", options.TTY, "Stdin is a TTY")//-t选项
	return cmd
}

//准备函数
func (p *ExecOptions) Complete(f cmdutil.Factory, cmd *cobra.Command, argsIn []string, argsLenAtDash int) error {
	// Let kubectl exec follow rules for `--`, see #13004 issue
	if len(argsIn) == 0 || argsLenAtDash == 0 {//没有参数报错
		return cmdutil.UsageErrorf(cmd, execUsageStr)
	}

	p.ResourceName = argsIn[0]//设置资源名称
	p.Command = argsIn[1:]//设置运行命令

	var err error

	p.Namespace, _, err = f.ToRawKubeConfigLoader().Namespace()//设置namespace
	if err != nil {
		return err
	}

	p.ExecutablePodFn = polymorphichelpers.AttachablePodForObjectFn//设置查找pod函数

	p.GetPodTimeout, err = cmdutil.GetPodRunningTimeoutFlag(cmd)//设置pod-running-timeout选项
	if err != nil {
		return cmdutil.UsageErrorf(cmd, err.Error())
	}

	p.Builder = f.NewBuilder//设置builder
	p.restClientGetter = f//设置restClientGetter

	cmdParent := cmd.Parent()//获取父命令
	if cmdParent != nil {
		p.ParentCommandName = cmdParent.CommandPath()//设置父命令名称
	}
	if len(p.ParentCommandName) > 0 && cmdutil.IsSiblingCommandExists(cmd, "describe") {
		p.EnableSuggestedCmdUsage = true//设置是否提示用法
	}

	p.Config, err = f.ToRESTConfig()//设置restConfig
	if err != nil {
		return err
	}

	clientset, err := f.KubernetesClientSet()//设置clientset
	if err != nil {
		return err
	}
	p.PodClient = clientset.CoreV1()//设置PodClient

	return nil
}

//校验
func (p *ExecOptions) Validate() error {
	if len(p.PodName) == 0 && len(p.ResourceName) == 0 {//resourcename和podName不能同时为空
		return fmt.Errorf("pod or type/name must be specified")
	}
	if len(p.Command) == 0 {//命令不能为空
		return fmt.Errorf("you must specify at least one command for the container")
	}
	if p.Out == nil || p.ErrOut == nil {//Out和ErrOut必须都不为空
		return fmt.Errorf("both output and error output must be provided")
	}
	return nil
}

//运行
func (p *ExecOptions) Run() error {
	var err error
	// we still need legacy pod getter when PodName in ExecOptions struct is provided,
	// since there are any other command run this function by providing Podname with PodsGetter
	// and without resource builder, eg: `kubectl cp`.
	if len(p.PodName) != 0 {//pod名称不为空
		p.Pod, err = p.PodClient.Pods(p.Namespace).Get(p.PodName, metav1.GetOptions{})//通过podClient获取pod
		if err != nil {
			return err
		}
	} else {
		builder := p.Builder().
			WithScheme(scheme.Scheme, scheme.Scheme.PrioritizedVersionsAllGroups()...).
			NamespaceParam(p.Namespace).DefaultNamespace().ResourceNames("pods", p.ResourceName)//用构造器获取result对象

		obj, err := builder.Do().Object()//从result获取Object
		if err != nil {
			return err
		}

		p.Pod, err = p.ExecutablePodFn(p.restClientGetter, obj, p.GetPodTimeout)//从obj获取可执行的pod
		if err != nil {
			return err
		}
	}

	pod := p.Pod

	if pod.Status.Phase == corev1.PodSucceeded || pod.Status.Phase == corev1.PodFailed {//如果pod为complete状态返回错误
		return fmt.Errorf("cannot exec into a container in a completed pod; current phase is %s", pod.Status.Phase)
	}

	containerName := p.ContainerName
	if len(containerName) == 0 {//指定了container
		if len(pod.Spec.Containers) > 1 {// 如果pod container大于1个，提示信息
			fmt.Fprintf(p.ErrOut, "Defaulting container name to %s.\n", pod.Spec.Containers[0].Name)
			if p.EnableSuggestedCmdUsage {
				fmt.Fprintf(p.ErrOut, "Use '%s describe pod/%s -n %s' to see all of the containers in this pod.\n", p.ParentCommandName, pod.Name, p.Namespace)
			}
		}
		containerName = pod.Spec.Containers[0].Name//容器名称为第0个容器名称
	}

	// ensure we can recover the terminal while attached
	t := p.SetupTTY()//设置tty

	var sizeQueue remotecommand.TerminalSizeQueue
	if t.Raw {
		// this call spawns a goroutine to monitor/update the terminal size
		sizeQueue = t.MonitorSize(t.GetSize())

		// unset p.Err if it was previously set because both stdout and stderr go over p.Out when tty is
		// true
		p.ErrOut = nil
	}

	fn := func() error {//exec函数
		restClient, err := restclient.RESTClientFor(p.Config)//获取client
		if err != nil {
			return err
		}

		// TODO: consider abstracting into a client invocation or client helper
		req := restClient.Post().
			Resource("pods").
			Name(pod.Name).
			Namespace(pod.Namespace).
			SubResource("exec")// 构造request对象
		req.VersionedParams(&corev1.PodExecOptions{
			Container: containerName,
			Command:   p.Command,
			Stdin:     p.Stdin,
			Stdout:    p.Out != nil,
			Stderr:    p.ErrOut != nil,
			TTY:       t.Raw,
		}, scheme.ParameterCodec)

		return p.Executor.Execute("POST", req.URL(), p.Config, p.In, p.Out, p.ErrOut, t.Raw, sizeQueue)//执行exec
	}

	if err := t.Safe(fn); err != nil {//执行t safe
		return err
	}

	return nil
}

//执行exec
func (*DefaultRemoteExecutor) Execute(method string, url *url.URL, config *restclient.Config, stdin io.Reader, stdout, stderr io.Writer, tty bool, terminalSizeQueue remotecommand.TerminalSizeQueue) error {
	exec, err := remotecommand.NewSPDYExecutor(config, method, url)//创建executer
	if err != nil {
		return err
	}
	return exec.Stream(remotecommand.StreamOptions{//执行stream
		Stdin:             stdin,
		Stdout:            stdout,
		Stderr:            stderr,
		Tty:               tty,
		TerminalSizeQueue: terminalSizeQueue,
	})
}