CORS Policy: Response to preflight request fails access control check: No 'Access-Control-Allow-Origin'

Question content

I use golang and gin-gonic/gin web framework on the backend and react axios on the frontend. I've been trying to solve it for two days and I'm still getting the same error below:

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

This error only occurs when I try to send a patch request, so that request requires a preflight options request, but everything with get and post works as expected, they don't run any preflight checks.

This is the code for my router configuration:

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")
}

This is the front end:

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 })

I'm pretty sure I've set up the backend correctly and it should return all the necessary headers.

For example, for a get request, the response headers look like this:

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

Although for the patch request attempt I get no response (unsurprisingly) and the preflight response headers are:

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

Do you have any suggestions for possible problems? After these two days I have no clue. Thank you in advance!

I also tried adding a title:

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")

...again in the if statement:

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

But this doesn't help at all. In fact, this if statement is not executed when the preflight is executed, I know from the console that the server is executing the options request.

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

edit:

This is the curl command that sends the patch request (so actually this is the preflight options request):

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

Response to this request:

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

Correct answer

It turns out you are using a deprecated packagegithub.com/gin-gonic/contrib/cors . You should use github.com/gin-contrib/cors instead. Here is a demo configuration using github.com/gin-contrib/cors:

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")
}

For some reason, the patch request headers are missing the "cookie" header, even though I used the withcredentials parameter.

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

Here { withcredentials: true } is treated as data and has no configuration. If you have no data to send to the server, you should write like this:

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

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