kubectl源码分析之explain

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type ExplainOptions struct {//explain结构体
  genericclioptions.IOStreams

  CmdParent  string
  APIVersion string
  Recursive  bool

  Mapper meta.RESTMapper
  Schema openapi.Resources
}

func NewExplainOptions(parent string, streams genericclioptions.IOStreams) *ExplainOptions {
  return &ExplainOptions{//初始化explain结构体
    IOStreams: streams,
    CmdParent: parent,
  }
}

//创建explain命令
func NewCmdExplain(parent string, f cmdutil.Factory, streams genericclioptions.IOStreams) *cobra.Command {
  o := NewExplainOptions(parent, streams)//初始化结构体

  cmd := &cobra.Command{//创建cobra命令
    Use:                   "explain RESOURCE",
    DisableFlagsInUseLine: true,
    Short:                 i18n.T("Documentation of resources"),
    Long:                  explainLong + "\n\n" + cmdutil.SuggestAPIResources(parent),
    Example:               explainExamples,
    Run: func(cmd *cobra.Command, args []string) {
      cmdutil.CheckErr(o.Complete(f, cmd))//准备
      cmdutil.CheckErr(o.Validate(args))//校验
      cmdutil.CheckErr(o.Run(args))//运行
    },
  }
  cmd.Flags().BoolVar(&o.Recursive, "recursive", o.Recursive, "Print the fields of fields (Currently only 1 level deep)")//recursive选项
  cmd.Flags().StringVar(&o.APIVersion, "api-version", o.APIVersion, "Get different explanations for particular API version")//api-version选项
  return cmd
}

//准备方法
func (o *ExplainOptions) Complete(f cmdutil.Factory, cmd *cobra.Command) error {
  var err error
  o.Mapper, err = f.ToRESTMapper()//设置mapper
  if err != nil {
    return err
  }

  o.Schema, err = f.OpenAPISchema()//设置schema
  if err != nil {
    return err
  }
  return nil
}

//校验
func (o *ExplainOptions) Validate(args []string) error {
  if len(args) == 0 {//参数不能为空
    return fmt.Errorf("You must specify the type of resource to explain. %s\n", cmdutil.SuggestAPIResources(o.CmdParent))
  }
  if len(args) > 1 {//参数不能大于一个
    return fmt.Errorf("We accept only this format: explain RESOURCE\n")
  }

  return nil
}

//运行
func (o *ExplainOptions) Run(args []string) error {
  recursive := o.Recursive
  apiVersionString := o.APIVersion

  // TODO: After we figured out the new syntax to separate group and resource, allow
  // the users to use it in explain (kubectl explain <group><syntax><resource>).
  // Refer to issue #16039 for why we do this. Refer to PR #15808 that used "/" syntax.
  inModel, fieldsPath, err := explain.SplitAndParseResourceRequest(args[0], o.Mapper)//用.分割resource和字段
  if err != nil {
    return err
  }

  // TODO: We should deduce the group for a resource by discovering the supported resources at server.
  fullySpecifiedGVR, groupResource := schema.ParseResourceArg(inModel)//解析groupversionresource
  gvk := schema.GroupVersionKind{}
  if fullySpecifiedGVR != nil {
    gvk, _ = o.Mapper.KindFor(*fullySpecifiedGVR)//从gvr获取gvk
  }
  if gvk.Empty() {//如果gvk为空，则获取版本为空的gvk
    gvk, err = o.Mapper.KindFor(groupResource.WithVersion(""))
    if err != nil {
      return err
    }
  }

  if len(apiVersionString) != 0 {//如果api-version不为空，则再次获取gvk
    apiVersion, err := schema.ParseGroupVersion(apiVersionString)
    if err != nil {
      return err
    }
    gvk = apiVersion.WithKind(gvk.Kind)
  }

  schema := o.Schema.LookupResource(gvk)//获取schema
  if schema == nil {
    return fmt.Errorf("Couldn't find resource for %q", gvk)
  }

  return explain.PrintModelDescription(fieldsPath, o.Out, schema, gvk, recursive)//打印结果
}