golang 中允许使用 cors，代码如下

func register() *echo.echo {
    e := echo.new()
    e.get("/swagger/*", echoswagger.wraphandler) // swagger 등록
    validator.registervalidator(e)               // 유효성검사 등록
    e.use(middleware.cors())  // cors 등록
......

package middleware

import (
    "github.com/labstack/echo/v4"
    "github.com/labstack/echo/v4/middleware"
)

func cors() echo.middlewarefunc {
    return middleware.corswithconfig(middleware.corsconfig{
        alloworigins:  []string{"http://localhost:3000"},
        allowmethods:  []string{echo.get, echo.put, echo.post, echo.delete},
        allowheaders:  []string{echo.headerorigin, echo.headercontenttype, echo.headeraccept},
        exposeheaders: []string{echo.headercontentlength},
    })
}

但是，即使我在react项目中从(localhost:3000)发送请求，cors错误也不会停止。

func (serverInfo *ServerInfo) ServerStart() {

    var databaseSet database.DatabaseInterface = &mysql.MysqlInfo{} // Database
    databaseSet.InitDatabase()                                      // 데이터베이스를 초기화합니다
    hosts := map[string]*Host{}                                     // Hosts

    // API
    hosts[fmt.Sprintf("%v.%v:%v", "api.v1", os.Getenv(envkey.SERVER_URL), os.Getenv(envkey.PORT))] = &Host{apiV1Route.Register()}

    // Server
    e := echo.New()
    e.Use(middleware.Logger()) // 로거등록

    e.Any("/*", func(c echo.Context) (err error) {
        req := c.Request()
        res := c.Response()
        host := hosts[req.Host]

        if host == nil {
            err = echo.ErrNotFound
        } else {
            host.Echo.ServeHTTP(res, req)
        }
        return
    })

    // e.Logger.Fatal(e.StartTLS(fmt.Sprintf(":%v", os.Getenv(envkey.PORT)), "housewhale.com+3.pem", "housewhale.com+3-key.pem"))
    e.Logger.Fatal(e.Start(fmt.Sprintf(":%v", os.Getenv(envkey.PORT))))
}

这个问题我已经困扰了好几天了，如何解决？我已经尝试了在手册或谷歌中找到的所有内容，但 cors 错误并没有消失。

正确答案

有一个错误，没有附加错误，我附加了如下错误，当时问题就解决了。

access to fetch at 'https://api.v1.localhsot:8081/auth/retoken' from origin 'http://localhost:3000' has been blocked by cors policy: response to preflight request doesn't pass access control check: no 'access-control-allow-origin' header is present on the requested resource. if an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with cors disabled.

服务器端未正确允许cors，请配置服务器端以匹配请求

例如，如果客户端向标头发送授权数据，则服务器也允许在标头中进行授权。像这样设置必要的请求

package middleware

import (
    "github.com/labstack/echo/v4"
    "github.com/labstack/echo/v4/middleware"
)

func Cors() echo.MiddlewareFunc {
    return middleware.CORSWithConfig(middleware.CORSConfig{
        AllowOrigins:     []string{"http://localhost:3000"},
        AllowMethods:     []string{echo.GET, echo.PUT, echo.POST, echo.DELETE},
        AllowHeaders:     []string{echo.HeaderOrigin, echo.HeaderContentType, echo.HeaderAccept, echo.HeaderAuthorization},
        ExposeHeaders:    []string{echo.HeaderContentLength, echo.HeaderSetCookie},
        AllowCredentials: true, // Add this line to allow credentials
    })
}