我在后端使用gin-gonic/gin web框架，在前端使用React axios。我试着解决它已经两天了，但我仍然得到下面同样的错误：

CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.

这个错误只在我尝试发送PATCH请求时发生，所以需要preflight OPTIONS请求的请求，但对于GET和POST，一切都按预期工作，不运行任何preflight检查。
下面是我的路由器配置代码：

package main

import (
    "book_renting/api"
    "log"
    "net/http"

    "github.com/gin-contrib/sessions"
    "github.com/gin-contrib/sessions/cookie"
    "github.com/gin-gonic/contrib/cors"
    "github.com/gin-gonic/gin"
    _ "github.com/lib/pq"
)

func main() {

    router := gin.Default()
    store := cookie.NewStore([]byte("your-secret-key"))
    store.Options(sessions.Options{MaxAge: 60 * 60 * 24})

    router.Use(cors.Default())
    router.Use(sessions.Sessions("sessions", store))

    router.Use(func(c *gin.Context) {
        host := c.Request.Header.Get("Origin")
        c.Writer.Header().Set("Access-Control-Allow-Origin", host)
        c.Writer.Header().Set("Access-Control-Allow-Credentials", "true")
        c.Writer.Header().Set("Access-Control-Allow-Headers", "Content-Type, Authorization")
        c.Writer.Header().Set("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, PATCH, OPTIONS")
        if c.Request.Method == "OPTIONS" {
            log.Println("Handling OPTIONS request")
            c.AbortWithStatus(http.StatusNoContent)
            return
        }
        log.Println("Executing CORS middleware")
        c.Next()
    })

    router.POST("/login", api.HandleLogin)
    router.GET("/logout", api.HandleLogout)
    router.POST("/register", api.HandleRegister)
    router.GET("/getCookie", api.GetCookieSession)

    router.GET("/books", api.GetBooksAPI)
    router.GET("/books/:id", api.BookByIdAPI)
    router.PATCH("/rent/:id", api.RentBookAPI)
    router.PATCH("/return/:id", api.ReturnBookAPI)
    router.Run("localhost:3000")
}

这里是前端：

import axios from 'axios'

const url = 'http://localhost:3000'

export const loginUser = async (credentials) => await axios.post(`${url}/login`, credentials, {withCredentials: true})
export const logoutUser = async () => await axios.get(`${url}/logout`, {withCredentials: true})
export const registerUser = () => axios.post(`${url}/register`)
export const fetchBooks = () => axios.get(`${url}/books`, { withCredentials: true })
export const fetchBookByID = (book_id) => axios.get(`${url}/books/${book_id}`, { withCredentials: true })
export const rentBook = (book_id) => axios.patch(`${url}/rent/${book_id}`, { withCredentials: true })
export const returnBook = (book_id) => axios.patch(`${url}/return/${book_id}`, { withCredentials: true })

我很确定我正确地设置了后端，它应该返回所有必要的头。
例如，对于GET请求，响应头看起来像这样：

HTTP/1.1 200 OK
Access-Control-Allow-Credentials: true
Access-Control-Allow-Headers: Content-Type, Authorization
Access-Control-Allow-Methods: GET, POST, PUT, DELETE, PATCH, OPTIONS
Access-Control-Allow-Origin: http://localhost:3001
Content-Type: application/json; charset=utf-8
Date: Sat, 10 Jun 2023 22:12:11 GMT
Content-Length: 495

而对于PATCH请求尝试，我没有任何响应（这并不奇怪），并且preflight响应头部是：

HTTP/1.1 200 OK
Date: Sat, 10 Jun 2023 22:12:12 GMT
Content-Length: 0

你有什么建议可能是什么问题？这两天，我已经不知道了。感谢您的评分
我也试着写了header：

c.Writer.Header().Set("Access-Control-Allow-Origin", host)
        c.Writer.Header().Set("Access-Control-Allow-Credentials", "true")
        c.Writer.Header().Set("Access-Control-Allow-Headers", "Content-Type, Authorization")
        c.Writer.Header().Set("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, PATCH, OPTIONS")

在if语句中：

if c.Request.Method == "OPTIONS" {
    log.Println("Handling OPTIONS request")
    c.AbortWithStatus(http.StatusNoContent)
    return
    }

但一点用都没有。事实上，在执行预检时，if语句并不执行，我从控制台知道服务器正在执行OPTIONS请求。

[GIN] 2023/06/11 - 00:12:13 | 200 |       7.708µs |       127.0.0.1 | OPTIONS  "/rent/2"

编辑：
下面是发送PATCH请求的cURL命令（实际上这里是preflight OPTIONS请求）：

curl 'http://localhost:3000/return/2' \
  -X 'OPTIONS' \
  -H 'Accept: */*' \
  -H 'Accept-Language: en-US,en;q=0.9,pl-PL;q=0.8,pl;q=0.7' \
  -H 'Access-Control-Request-Headers: content-type' \
  -H 'Access-Control-Request-Method: PATCH' \
  -H 'Cache-Control: no-cache' \
  -H 'Connection: keep-alive' \
  -H 'Origin: http://localhost:3001' \
  -H 'Pragma: no-cache' \
  -H 'Referer: http://localhost:3001/' \
  -H 'Sec-Fetch-Dest: empty' \
  -H 'Sec-Fetch-Mode: cors' \
  -H 'Sec-Fetch-Site: same-site' \
  -H 'User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/114.0.0.0 Safari/537.36' \
  --compressed

而对这一请求的回应是：

HTTP/1.1 200 OK
Date: Sun, 11 Jun 2023 01:22:57 GMT
Content-Length: 0