Go Content-Type

What is the “idempotence”? 冪

idempotence中文翻成「冪」

HTTP/1.1 規範提到

Methods can also have the property of “idempotence” in that (aside from error or expiration issues) the side-effects of N > 0 identical requests is the same as for a single request.

也就是如果他具有冪的特性，撇開送錯誤或者已到期的不談，那麼您送出N次的請求應該和送1次的請求是相同的

Request

  • GET : 具有idempotence的特性
  • DELETE : 具有idempotence的特性 (理論上刪除1次和N次是一樣的結果)
  • POST : 非idempotence 創建資源 (其實也能更新)
  • PUT : idempotence 更新資源(需要傳入完整的對象) (其實也能創建)
  • PATCH : 非idempotence 局部更新

Go中如何接收Form的資料

http.Request有三種方式可以接收Form的資料

  1. ParseForm
  2. ParseMultipartForm
  3. PostFormValue

ParseForm

For all requests, ParseForm parses the raw query from the URL and updates r.Form.

For

  • POST
  • PUT
  • PATCH : 局部

requests, it also reads the request body,

parses it as a form and puts the results into both r.PostForm and r.Form.

Request body parameters take precedence over URL query string values in r.Form.

If the request Body’s size has not already been limited by MaxBytesReader, the size is capped at ❗10MB❗.

For other HTTP methods, or when the Content-Type is not application/x-www-form-urlencoded,

the request Body is not read, and r.PostForm is initialized to a non-nil, empty value.

建議這個只用在

application/x-www-form-urlencoded

ParseMultipartForm

func (r *Request) ParseMultipartForm(maxMemory int64) error

ParseMultipartForm parses a request body as

multipart/form-data.

The whole request body is parsed and up to a total of maxMemory bytes of its file parts are stored in memory,

因此會需要指定maxMemory的大小去讀，這部分讀到的東西保留在記憶體中

with the remainder stored on disk in temporary files.

不曉得臨時文件在哪?

PostFormValue

PostFormValue returns the first value for the named component of the POST, PATCH, or PUT request body.

URL query parameters are ignored.

總結

說明看看就好，說明講得天花亂墜，還不如實際上去看一下代碼

例如您想查看 ParseMultipartForm

說明只講一點點，你實際上點過去 代碼連結

會發現如下

func (r *Request) ParseMultipartForm(maxMemory int64) error {
	if r.MultipartForm == multipartByReader {
		return errors.New("http: multipart handled by MultipartReader")
	}
	if r.Form == nil {
		err := r.ParseForm()
		if err != nil {
			return err
		}
	}
	if r.MultipartForm != nil {
		return nil
	}

	mr, err := r.multipartReader(false)
	if err != nil {
		return err
	}

	f, err := mr.ReadForm(maxMemory)  // 🔔 您可以發現原來也是有大小上的限制
	if err != nil {
		return err
	}

	if r.PostForm == nil {
		r.PostForm = make(url.Values)
	}
	for k, v := range f.Value {
		r.Form[k] = append(r.Form[k], v...)
		// r.PostForm should also be populated. See Issue 9305.
		r.PostForm[k] = append(r.PostForm[k], v...)
	}

	r.MultipartForm = f

	return nil
}

你會發現很多細節，然後在debug進去會收入更多

關於boundary

通常是1~70各字元組成開頭

最後一個段落會再補上兩個-破折號

POST /foo HTTP/1.1
Content-Length: 68137
Content-Type: multipart/form-data; boundary=---------------------------974767299852498929531610575

-----------------------------974767299852498929531610575
Content-Disposition: form-data; name="description"

some text
-----------------------------974767299852498929531610575
Content-Disposition: form-data; name="myFile"; filename="foo.txt"
Content-Type: text/plain

(content of the uploaded file foo.txt)
-----------------------------974767299852498929531610575--

如果您用xmlHTTPRequest送POST

如果補上Content-Type

xhr.setRequestHeader(“Content-Type”, “multipart/form-data; charset=utf-8”)

可能會遇到

ErrMissingBoundary = &ProtocolError{“no multipart boundary param in Content-Type”}

就是缺少boundary，一個是不寫Content-Type讓瀏覽器自己幫您解決

不然可能要參考這篇的做法

How to send multipart/form-data form content by ajax (no jquery)?

參考資料

comments powered by Disqus