在微信多模板消息推送的时候会panic，Handler crashed with error http: wrote more than the declared Content-Length

[chaegumi]

问题及现象

不是每次都报错，我观察了下，是render里边的性能不够高

//Render render from bytes
func (ctx *Context) Render(bytes []byte) {
	//debug
	//fmt.Println("response msg = ", string(bytes))
	ctx.Writer.WriteHeader(200)
	_, err := ctx.Writer.Write(bytes)
	if err != nil {
		panic(err)
	}
}

看了beego的源码，再结合stackoverflow上搜索到的回答https://stackoverflow.com/questions/29664720/golang-map-of-http-responsewriters

就是这个问题了。

The goroutine responsible for the ResponseWriter exits. A 'better' way would be to trigger the work, block in the handler, write the work to a buffer, and then io.Copy(buf, w) to write it out back in the handler. Set a timeout to prevent the HTTP connection from timing out on the client side.

beego

func (output *BeegoOutput) Body(content []byte) error {
	var encoding string
	var buf = &bytes.Buffer{}
	if output.EnableGzip {
		encoding = ParseEncoding(output.Context.Request)
	}
	if b, n, _ := WriteBody(encoding, buf, content); b {
		output.Header("Content-Encoding", n)
		output.Header("Content-Length", strconv.Itoa(buf.Len()))
	} else {
		output.Header("Content-Length", strconv.Itoa(len(content)))
	}
	// Write status code if it has been set manually
	// Set it to 0 afterwards to prevent "multiple response.WriteHeader calls"
	if output.Status != 0 {
		output.Context.ResponseWriter.WriteHeader(output.Status)
		output.Status = 0
	} else {
		output.Context.ResponseWriter.Started = true
	}
	io.Copy(output.Context.ResponseWriter, buf)
	return nil
}