gin 解決跨域問題

要想解決gin跨域的問題就需要給請求加上一個跨域請求中間件，代碼如下

package main

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

var (
	engine = gin.Default()
)

func main() {
	engine.Use(Cors())
	engine.GET("/ping", func(c *gin.Context) {
		c.JSON(http.StatusOK, gin.H{
			"message": "pong",
		})
	})
	engine.Run(":9001")
}

func Cors() gin.HandlerFunc {
	return func(c *gin.Context) {
		method := c.Request.Method               //請求方法
		origin := c.Request.Header.Get("Origin") //請求頭部
		var headerKeys []string                  // 聲明請求頭keys
		for k, _ := range c.Request.Header {
			headerKeys = append(headerKeys, k)
		}
		headerStr := strings.Join(headerKeys, ", ")
		if headerStr != "" {
			headerStr = fmt.Sprintf("access-control-allow-origin, access-control-allow-headers, %s", headerStr)
		} else {
			headerStr = "access-control-allow-origin, access-control-allow-headers"
		}
		if origin != "" {
			c.Writer.Header().Set("Access-Control-Allow-Origin", "*")
			c.Header("Access-Control-Allow-Origin", "*")                                       // 這是允許通路所有域
			c.Header("Access-Control-Allow-Methods", "POST, GET, OPTIONS, PUT, DELETE,UPDATE") //伺服器支援的所有跨域請求的方法,為了避免浏覽次請求的多次'預檢'請求
			//  header的類型
			c.Header("Access-Control-Allow-Headers", "Authorization, Content-Length, X-CSRF-Token, Token,session,X_Requested_With,Accept, Origin, Host, Connection, Accept-Encoding, Accept-Language,DNT, X-CustomHeader, Keep-Alive, User-Agent, X-Requested-With, If-Modified-Since, Cache-Control, Content-Type, Pragma")
			//				允許跨域設定																										可以傳回其他子段
			c.Header("Access-Control-Expose-Headers", "Content-Length, Access-Control-Allow-Origin, Access-Control-Allow-Headers,Cache-Control,Content-Language,Content-Type,Expires,Last-Modified,Pragma,FooBar") // 跨域關鍵設定 讓浏覽器可以解析
			c.Header("Access-Control-Max-Age", "172800")                                                                                                                                                           // 緩存請求資訊 機關為秒
			c.Header("Access-Control-Allow-Credentials", "false")                                                                                                                                                  //	跨域請求是否需要帶cookie資訊 預設設定為true
			c.Set("content-type", "application/json")                                                                                                                                                              // 設定傳回格式是json
		}

		//放行所有OPTIONS方法
		if method == "OPTIONS" {
			c.JSON(http.StatusOK, "Options Request!")
		}
		// 處理請求
		c.Next() //	處理請求
	}
}