🐛 [Bug]: better error handling for file exceeding body size limit

[Abhinavbhar]

Bug Description

Limit for the fiber body is 4mb.
When a client send a file bigger than 4mb fiber returns a completely unrelated cors error.
This leads to confusion and wasting of developer time till developer lands on a page that explains this.

How to Reproduce

Steps to reproduce the behavior:

1. setup a basic fiber server and make a handler to receive multipart form
2. from browser send a file bigger than 4mb
3. this will give cors error completely unrelated anything that is actually happening

Expected Behavior

a error that clearly says that the request exceeds the allowed size limit and not a cors error.

Fiber Version

v2.52.9

Code Snippet (optional)

Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at http://localhost:8080/largefile. (Reason: CORS request did not succeed). Status code: (null).

//error got
which is completely unrelated and could not find any documentation about this error potentially being a size limit error.

Checklist:

• I agree to follow Fiber's Code of Conduct.
• I have checked for existing issues that describe my problem prior to opening this one.
• I understand that improperly formatted bug reports may be closed without explanation.

[gaby]

@Abhinavbhar Share an example code, are you sure your CORS is not misconfigured?

[Abhinavbhar]

yes i am sure i send all type of request on the same url {GET,POST,DELETE} from the same project everything works fine and the control reached the handler,
but when using multi-part form and file bigger than 4mb
returns this cors error and control dont reach handler
package main

import (
database "backend/dataBase"
"backend/handler"

"github.com/gofiber/fiber/v2"
"github.com/gofiber/fiber/v2/middleware/cors"

)

func main() {
app := fiber.New()

app.Use(cors.New(cors.Config{
	AllowOrigins: "*",
	AllowMethods: "GET,POST,PUT,DELETE,OPTIONS",
	AllowHeaders: "Origin, Content-Type, Accept, Authorization",
}))
database.ConnectDb()
app.Get("/", func(c *fiber.Ctx) error {
	return c.SendString("Hello, World!")
})
app.Post("/auth/google/signup", handler.Signup)
//add authentication middleware also
app.Post("/user/createbot", handler.CreateBot)
app.Listen("0.0.0.0:8080")

}

[Abhinavbhar]

The only difference between receiving a cors error and not receiving one is sending a file bigger than 4mb and a file smaller than 4mb from frontend

[gaby]

Ping @sixcolors

[Abhirup-99]

@gaby can I pick this up?