最近的项目出现了一个问题，前端发来一个 GET请求，但是后端只接收到了一个 OPTIONS请求，并返回 404，经过简单分析后，发现这是跨域问题，这里我们前端用的框架是Vue3，在修改 header后，会先发送一个 OPTIONS请求，再发送 GET请求，我就是卡在了这里。解决的方法很简单，在路由使用之前添加一个中间件即可

附上当时的Log：

2021-09-17T23:05:20.954+0800    INFO    zap@v0.0.1/zap.go:46    /xxx   {"status": 404, "method": "OPTIONS", "path": "/xxx", "query": "", "ip": "120.236.177.100", "user-agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/93.0.4577.82 Safari/537.36", "time": "2021-09-17T23:05:20+08:00", "latency": 0.000011207}

middleware/cros/Cros.go

package cros

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

func Cors() gin.HandlerFunc {
    return func(c *gin.Context) {
        method := c.Request.Method
  
        c.Header("Access-Control-Allow-Origin", "*")
        c.Header("Access-Control-Allow-Headers", "Content-Type,AccessToken,X-CSRF-Token, Authorization, Token")
        c.Header("Access-Control-Allow-Methods", "POST, GET, OPTIONS")
        c.Header("Access-Control-Expose-Headers", "Content-Length, Access-Control-Allow-Origin, Access-Control-Allow-Headers, Content-Type")
        c.Header("Access-Control-Allow-Credentials", "true")

        //放行所有OPTIONS方法
        if method == "OPTIONS" {
            c.AbortWithStatus(http.StatusNoContent)
        }
        // 处理请求
        c.Next()
    }
}

routers/router.go

package routers

import (
    "kakkk-test/common/middleware/cros"
    "kakkk-test/controller"
    "github.com/gin-gonic/gin"
)

func SetupRouter() *gin.Engine {
    r := gin.New()
    r.Use(cros.Cors())
    r.GET("xxx", controller.XXXHandler)
    //一些其他代码
    return r
}