🤗 [Question]: Enable DisableHeaderNormalizing config will occur wrong cors middleware behaviour about fiber

[sixcolors]

It appears that the only effect that DisableHeaderNormalizing has is to set app.server.DisableHeaderNamesNormalizing = app.config.DisableHeaderNormalizing.

The fasthttp documentation for this setting is a bit more detailed on its effects:

	// Header names are passed as-is without normalization
	// if this option is set.
	//
	// Disabled header names' normalization may be useful only for proxying
	// incoming requests to other servers expecting case-sensitive
	// header names. See https://github.com/valyala/fasthttp/issues/57
	// for details.
	//
	// By default request and response header names are normalized, i.e.
	// The first letter and the first letters following dashes
	// are uppercased, while all the other letters are lowercased.
	// Examples:
	//
	//     * HOST -> Host
	//     * content-type -> Content-Type
	//     * cONTENT-lenGTH -> Content-Length
	DisableHeaderNamesNormalizing bool

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[gaby]

@Max-Cheng Which version of v2 are you running?

[Max-Cheng]

The main issue is whether Enable DisableHeaderNormalizing should affect the behavior of the CORS middleware or not.

[gaby]

Ping @sixcolors

[Max-Cheng]

@Max-Cheng Which version of v2 are you running?

github.com/gofiber/fiber/v2 v2.52.4

[Max-Cheng]

In my situation, I'm using a global middleware to enforce the Origin header to be in uppercase and process the correct logical path.

package main

import (
	"github.com/gofiber/fiber/v2"
	"github.com/gofiber/fiber/v2/log"
	"github.com/gofiber/fiber/v2/middleware/cors"
)

func main() {
	app := fiber.New(fiber.Config{
		DisableHeaderNormalizing: true,
	})
	app.Use(func(c *fiber.Ctx) error {
		if c.Get("origin") != "" {
			c.Request().Header.Set(fiber.HeaderOrigin, c.Get("origin"))
			return c.Next()
		}
		return c.Next()
	})
	app.Use(cors.New(cors.Config{
		AllowOrigins: "*",
		AllowMethods: "*",
		AllowHeaders: "*",
	}))
	app.Get("/", func(c *fiber.Ctx) error {
		return c.SendString("Hello, World!")
	})

	log.Fatal(app.Listen(":3000"))
}

[sixcolors]

This should not be the case. CORS middleware calls originHeader := strings.ToLower(c.Get(fiber.HeaderOrigin)), and c.Get is case insensitive, https://docs.gofiber.io/api/ctx/#get.

I will test and get back to you.

[sixcolors]

@Max-Cheng I understand what you mean now. If you set app := fiber.New(fiber.Config{ DisableHeaderNormalizing: true, }), it will impact headers in any fiber middleware.

Since the Cross-Origin Resource Sharing (CORS) and other middleware included with fiber use c.Get for headers, the middleware behaviour will follow this pattern. According to https://datatracker.ietf.org/doc/html/rfc2616#section-4.2, "Each header field consists of a name followed by a colon (":") and the field value. Field names are case-insensitive." Therefore, the default fiber behaviour is correct. However, the DisableHeaderNormalizing option allows users to disable this, which would cause the behaviour you noted.

However, the comment for DisableHeaderNormalizing does not seem to adequately capture this:

	// When set to true, disables header normalization.
	// By default all header names are normalized: conteNT-tYPE -> Content-Type.
	//
	// Default: false

Because https://docs.gofiber.io/api/ctx/#get notes that: "The match is case-insensitive." and the DisableHeaderNormalizing does not specify that it has other effects, I think we can address that in the documentation.

[Max-Cheng]

Yes. I don't think we should change the behaviour of the CORS middleware