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Block transmission by golang gin framework

2022-06-28 07:19:00 【nangonghen】

1） summary ： Block transmission

This is a kind of " break up the whole into parts " or " Divide and conquer " The idea of , stay HTTP The expression in the agreement is "chunked" Block transfer coding . stay http Header field in response message “Transfer-Encoding: chunked”, Represents the body It is not sent at one time , It's a lot of pieces （chunk） Send... One by one , Until it's sent .

2） Coding rules for block transmission

1） Each block consists of two parts ,< Length head > and < Data blocks >;
2）< Length head > In order to CRLF（ Carriage returns , namely \r\n） A line of clear text at the end , use 16 A decimal number means length ;
3）< Data blocks > Keep up with the < Length head > after , In the end CRLF ending , But the data doesn't contain CRLF;
4） Finally, we use a length of 0 The block of indicates the end of data transmission , namely “0\r\n\r\n”.
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3）golang Code

package main

import (
    "fmt"
    "github.com/gin-gonic/gin"
    "net/http"
    "time"
)

func main() {
    server := &APIServer{
        engine: gin.Default(),
    }
    server.registryApi()
    server.engine.Run(":38080")
}

type APIServer struct {
    engine *gin.Engine
}

func (s *APIServer) registryApi() {
    registryStream(s.engine)
}

func registryStream(engine *gin.Engine) {
    engine.GET("/stream", func(ctx *gin.Context) {
        w := ctx.Writer
        header := w.Header()
        // Add a block transfer header field to the response header Transfer-Encoding: chunked
        header.Set("Transfer-Encoding", "chunked")
        header.Set("Content-Type", "text/html")
        w.WriteHeader(http.StatusOK)
      
        //Flush() Method , For example, the server writes data to a file , The browser will see that the contents of this file are increasing .
        w.Write([]byte(`
            <html>
                    <body>
        `))
        w.(http.Flusher).Flush()


        for i:=0 ;i<10; i++{
            w.Write([]byte(fmt.Sprintf(`
                <h1>%d</h1>
            `,i)))
            w.(http.Flusher).Flush()
            time.Sleep(time.Duration(1) * time.Second)
        }

        w.Write([]byte(`
                    </body>
            </html>
        `))
        w.(http.Flusher).Flush()
    })
}

4） Browser Test

You can see that the browser interface gradually receives 0,1,2,3….
explain ： From the browser , Not a complete message , Because it is processed by the browser , With the block removed < Length head > Information .
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