Bug Description

When using the proxy middleware to proxy.BalanceForward([]string{"http://localhost:5173"})) to a Vite/react dev server running on port 5173 the connection is refused with the following output Error: The HTTP request failed with error dial tcp4 127.0.0.1:5173: connect: connection refused

How to Reproduce

Clone https://github.com/sixcolors/FiberReactTest

cd frontend
npm install --include=dev && npm run dev

The proxy demonstrates this behaviour as can be seen in the main.go:

if DevMode {
		app.Get("*", proxy.BalancerForward([]string{"http://localhost:5173"}))

However the issue has been isolated to the fasthttp client.

To verify run the following:

package main

import (
	"io"
	"log"
	"net/http"

	"github.com/valyala/fasthttp"
)

func main() {
	// test connection to http://localhost:5173
	resp, err := http.Get("http://localhost:5173")
	if err != nil {
		log.Fatalf("Error: The HTTP request failed with error %s", err)
	} else {
		defer resp.Body.Close()
		data, err := io.ReadAll(resp.Body)
		if err != nil {
			log.Fatalf("Error reading body: %v", err)
		}
		log.Printf("HTTP Response Status: %d %s", resp.StatusCode, http.StatusText(resp.StatusCode))
		log.Printf("Response Body: %s", string(data))
	}

	statusCode, body, err := fasthttp.Get(nil, "http://localhost:5173")
	if err != nil {
		log.Fatalf("Error: The HTTP request failed with error %s", err)
	} else {
		log.Printf("HTTP Response Status: %d", statusCode)
		log.Printf("Response Body: %s", body)
	}
}

Expected Behavior

fasthttp client should connect to http://localhost:5173 and the proxy should work.

Actual Behavior

fasthttp client will not try dialing IPv6 by default and only IPv4 is tried, resulting in a connection refused error.

Fiber Version

v2.52.2

Code Snippet (optional)

No response

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.