Access-Control-Allow-Headers CORS Error

[hussainhyder23]

I am trying to use the below code to upload my file using Uppy. However, When I am trying to do that, I'm getting CORS origin error.
Output in console : [GIN] 2020/11/21 - 00:56:46 | 204 | 337.339µs | ::1 | OPTIONS "/files/"
This is the error I am getting in my browser's console : "'http://localhost:8080/files/' from origin 'http://localhost:3000' has been blocked by CORS policy: Request header field tus-resumable is not allowed by Access-Control-Allow-Headers in preflight response."
I used router.Use(cors.Default()) as well

router.POST("/files", func(c *gin.Context) {

		s3Locker := s3store.New("edisontestbucket1", s3.New(session.Must(session.NewSession()), s3Config))
		composer := tusd.NewStoreComposer()
		s3Locker.UseIn(composer)

		handler, err := tusd.NewHandler(tusd.Config{
			BasePath:              "/files/",
			StoreComposer:         composer,
			NotifyCompleteUploads: true,
			// NotifyTerminatedUploads: true,
			// NotifyUploadProgress:    true,
			// NotifyCreatedUploads:    true,
		})
		if err != nil {
			panic(fmt.Errorf("Unable to create handler: %s", err))
		}
		go func() {
			for {
				event := <-handler.CompleteUploads
				fmt.Printf("Upload %s finished\n", event.Upload.ID)
			}
		}()
	})

[rangerthegood]

I just ran into the same problem. The issue was the ordering of the lines in my function.

See below, The line r.Use must come before the r.GET. If it was the other way, I didn't get the Access-Control-Allow-Headers header set.

`func main() {
r := gin.Default()

r.Use(cors.Default())
r.GET("/ping", func(c *gin.Context) {
	c.JSON(200, gin.H{
		"message": "pong",
	})
})

r.Run(":3000") // listen and serve on 0.0.0.0:8080 (for windows "localhost:8080")

}`

[JiahuiChen99]

@rangerthegood This solved the CORS error, what a dumb mistake it was. Thank you! 👍