Web Applications

multipart/form-data

I asked a question on this on stackoverflow

package main

import (
	"fmt"
	"log"
	"mime/multipart"
	"net/http"
	"strings"
)

func handler(resp http.ResponseWriter, req *http.Request) {
	switch strings.Split(req.Header.Get("Content-Type"), ";")[0] {
	case "multipart/form-data":
		req.ParseMultipartForm(2097152)
		mw := multipart.NewWriter(resp)
		resp.Header().Set("Content-Type", mw.FormDataContentType())
		mw.WriteField("name", req.FormValue("user_name"))
		mw.WriteField("email", req.FormValue("user_email"))
		mw.WriteField("message", req.FormValue("user_message"))
		mw.Close()
	case "application/x-www-form-urlencoded":
		req.ParseForm()
		fmt.Fprintf(resp, "%#v", req.PostForm)
	case "application/json":
		fmt.Fprintf(resp, "%#v", req.Body)
	default:
		fmt.Fprintf(resp, "%#v", req.Body)
	}
}

func main() {
	http.HandleFunc("/", handler)
	log.Fatal(http.ListenAndServe(":8080", nil))
}

RFC 7230 Message Syntax and Routing

Request:

GET /hello.txt HTTP/1.1
User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
Host: www.example.com
Accept-Language: en, mi

To get the above in go

package main

import (
    "fmt"
    "log"
    "net/http"
)

func handler(response http.ResponseWriter, request *http.Request) {
    str := fmt.Sprintf("%v %v %v\n", request.Method, request.RequestURI, request.Proto)
	str = str + fmt.Sprintf("User-Agent: %v\n", request.Header["User-Agent"][0])
	str = str + fmt.Sprintf("Host: %v\n", request.Host)
	str = str + fmt.Sprintf("Accept-Language: %v\n", request.Header["Accept-Language"][0])
	fmt.Fprintf(response, str) 
}

func main() {
    http.HandleFunc("/", handler)
    log.Fatal(http.ListenAndServe(":4153", nil))
}

To access form key: values posted by the browser, request.ParseMultipartForm(maxBytes) is needed for multipart/form-data or request.ParseForm() for application/x-www-form-urlencoded

These values can then be access using request.FormValue(“key”)) or request.PostFormValue(“key”))

[NewWriter]

Response:

HTTP/1.1 200 OK
Date: Mon, 27 Jul 2009 12:28:53 GMT
Server: Apache
Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
ETag: "34aa387-d-1568eb00"
Accept-Ranges: bytes
Content-Length: 51
Vary: Accept-Encoding
Content-Type: text/plain

Hello World! My payload includes a trailing CRLF.

Writing Web Applications

https://stackoverflow.com/questions/20205796/post-data-using-the-content-type-multipart-form-data

Developing a RESTful API with Go and Gin

Gin Web Framework

Package

package main

import "github.com/gin-gonic/gin"

func main() {
	r := gin.Default()
	r.GET("/ping", func(c *gin.Context) {
		c.JSON(200, gin.H{
			"message": "pong",
		})
	})
	r.Run() // listen and serve on 0.0.0.0:8080
}

gin.Context is the most important part of Gin. It carries request details, validates and serializes JSON, and more. (Despite the similar name, this is different from Go’s built-in context package.)