valyala/fasthttp · error

proxy: unknown scheme:

Error message

proxy: unknown scheme: 

What it means

getDialFunc in fasthttpproxy builds a dialer from a parsed proxy URL; when the URL scheme is not one of the supported ones (http, https, socks5) it returns this error with the offending scheme appended. It fails fast on proxy configurations the package cannot dial through.

Source

Thrown at fasthttpproxy/dialer.go:144

		if proxyURL == nil {
			// dial directly
			return func(addr string) (net.Conn, error) {
				return d.Dial(network, addr)
			}, nil
		}
		switch proxyURL.Scheme {
		case "socks5", "socks5h":
			proxyDialer, err = proxy.FromURL(proxyURL, d)
			if err != nil {
				return nil, err
			}
		case "http":
			proxyAddr, auth := addrAndAuth(proxyURL, nil)
			proxyDialer = DialerFunc(func(network, addr string) (conn net.Conn, err error) {
				return httpProxyDial(d, network, addr, proxyAddr, auth)
			})
		default:
			return nil, errors.New("proxy: unknown scheme: " + proxyURL.Scheme)
		}
		return func(addr string) (net.Conn, error) {
			return proxyDialer.Dial(network, addr)
		}, nil
	}
	// slow path when the proxyURL changes along with the request URL.
	var authCache sync.Map
	return func(addr string) (conn net.Conn, err error) {
		var proxyDialer proxy.Dialer
		var proxyURL *url.URL
		requestScheme := scheme
		if requestScheme == "" {
			requestScheme = httpsScheme
			if !strings.HasSuffix(addr, colonTLSPort) {
				requestScheme = httpScheme
			}
		}
		reqURL := &url.URL{Host: addr, Scheme: requestScheme}

View on GitHub (pinned to c96f600972)

Solutions

1. Use a supported scheme: http, https, or socks5 in the proxy URL
2. Fix the proxy URL: add an explicit scheme (http://host:port) if it is missing
3. Pre-parse the proxy URL (url.Parse) and reject unsupported schemes before calling GetDialFunc
4. Switch to socks4 via a different library or a local socks5 bridge if socks4 is required

Example fix

// before
proxy := os.Getenv("HTTPS_PROXY") // "socks4://proxy:1080"
dialFunc, err := fasthttpproxy.GetDialFunc(proxy)
// after
u, _ := url.Parse(os.Getenv("HTTPS_PROXY"))
switch u.Scheme {
case "http", "https", "socks5":
    dialFunc, err = fasthttpproxy.GetDialFunc(u.String())
default:
    err = fmt.Errorf("unsupported proxy scheme %q", u.Scheme)
}

u, err := url.Parse(proxyURL)
if err != nil || (u.Scheme != "http" && u.Scheme != "https" && u.Scheme != "socks5") {
    return fmt.Errorf("unsupported proxy scheme %q", u.Scheme)
}

When it happens

Trigger: Passing a proxy URL with an unsupported scheme (e.g. socks4, socks4a, ftp, or an empty scheme) to fasthttpproxy.GetDialFunc / fasthttp.ProxyFunc setup; environment variable HTTP_PROXY/HTTPS_PROXY containing an unsupported scheme.

Common situations: Corporate proxies configured as socks4; typos like 'https:...' vs 'http://'; env var set to 'localhost:8080' with no scheme at all; libraries reading standard proxy env vars that include schemes fasthttpproxy doesn't implement.

Related errors

• dont support the network:
• could not connect to proxy addr: %s status code: %d
• fasthttp: pipelined requests' queue has been overflowed. inc
• fasthttp: cannot find whitespace in the first line of respon
• fasthttp: unexpected char at the end of status code

AI-assisted analysis of valyala/fasthttp@c96f600972 (2026-08-31). Data as JSON: /api/errors/9a815fbaffa55380. Report an issue: GitHub.