我在后端使用 golang 和 gin-gonic/gin web 框架，在前端使用 react axios。我已经尝试解决它两天了，但我仍然遇到以下相同的错误：

cors policy: response to preflight request doesn't pass access control check: no 'access-control-allow-origin' header is present on the requested resource.

仅当我尝试发送 patch 请求时才会发生此错误，因此该请求需要预检 options 请求，但 get 和 post 一切都按预期工作，它们不运行任何预检检查。

这是我的路由器配置的代码：

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 })

我非常确定我正确设置了后端，它应该返回所有必要的标头。

例如，对于 get 请求，响应标头如下所示：

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

虽然对于 patch 请求尝试，我没有任何响应（毫不奇怪），并且预检响应标头是：

http/1.1 200 ok
date: sat, 10 jun 2023 22:12:12 gmt
content-length: 0

您对可能出现的问题有什么建议吗？经过这两天我已经毫无头绪了。预先感谢您！

我还尝试添加标题：

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")

...再次在 if 语句中：

if c.request.method == "options" {
    log.println("handling options request")
    c.abortwithstatus(http.statusnocontent)
    return
    }

但这根本没有帮助。事实上，这个if语句在执行预检时并没有执行，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：

这是发送 patch 请求的 curl 命令（因此实际上这是预检 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

对此请求的响应：

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

正确答案

事实证明，您正在使用已弃用的软件包 github.com/gin-gonic/contrib/cors。您应该使用 github.com/gin-contrib/cors 代替。这是使用 github.com/gin-contrib/cors 的演示配置：

package main

import (
    "github.com/gin-contrib/cors"
    "github.com/gin-contrib/sessions"
    "github.com/gin-contrib/sessions/cookie"
    "github.com/gin-gonic/gin"
)

func main() {
    router := gin.default()

    config := cors.defaultconfig()
    config.addallowheaders("authorization")
    config.allowcredentials = true
    config.allowallorigins = false
    // i think you should whitelist a limited origins instead:
    //  config.allowallorigins = []{"xxxx", "xxxx"}
    config.alloworiginfunc = func(origin string) bool {
        return true
    }
    router.use(cors.new(config))

    store := cookie.newstore([]byte("your-secret-key"))
    store.options(sessions.options{maxage: 60 * 60 * 24})
    router.use(sessions.sessions("sessions", store))

    // routes below

    router.run("localhost:3000")
}

由于某种原因，patch 请求标头缺少“cookie”标头，尽管我使用了 withcredentials 参数。

axios.patch(`${url}/rent/${book_id}`, { withcredentials: true })

这里 { withcredentials: true } 被视为数据，并且没有配置。如果你没有数据发送到服务器，你应该这样写：

axios.patch(`${url}/rent/${book_id}`, null, { withCredentials: true })