golang多次读取http request body的问题分析

type APIContext struct {
	Action   string
	ID       string
	Type     string
	Link     string
	Method   string
	Version  *APIVersion
	Request  *http.Request
	Response http.ResponseWriter
	...
}

type Request struct {
    Method string
    URL *url.URL
    Header Header
    Body io.ReadCloser
    GetBody func() (io.ReadCloser, error)
    Response *Response
    ctx context.Context
    ...
}

func ApiHandler() (error) {
    ...
    bodyBytes, err := ioutil.ReadAll(request.Request.Body)
    // fmt.Printf("bodyBytes: %+v", bodyBytes) 结果为[]
    if err != nil {
        ...
    }
    ...
}

func ApiHandler2() (error) {
    input, err := parse.ReadBody(request.Request)
    ...
}

// ReadAll reads from r until an error or EOF and returns the data it read.
// A successful call returns err == nil, not err == EOF. Because ReadAll is
// defined to read from src until EOF, it does not treat an EOF from Read
// as an error to be reported.
func ReadAll(r Reader) ([]byte, error) {
	b := make([]byte, 0, 512)
	for {
		if len(b) == cap(b) {
			// Add more capacity (let append pick how much).
			b = append(b, 0)[:len(b)]
		}
		n, err := r.Read(b[len(b):cap(b)])
		b = b[:len(b)+n]
		if err != nil {
			if err == EOF {
				err = nil
			}
			return b, err
		}
	}
}

type Reader interface {
    Read(p []byte) (n int, err error)
}

func ReadFile(filename string) ([]byte, error){}