Function RedenormalizePath

handlers/path.go:42–77

RedenormalizePath undoes path normalization done by some browsers and revers proxies. Also trims leading slash if it is present.

(path string)

// RedenormalizePath undoes path normalization done by some browsers and revers proxies.
// Also trims leading slash if it is present.
func RedenormalizePath(path string) string {
	// Split path into options and plain URL parts
	var (
		options, plainURL string
		hasPlain          bool
	)
	if strings.HasPrefix(path, "plain/") {
		// If the path starts with `plain/`, it means that there are no options
		// and the entire path is a plain URL
		options = ""
		plainURL = path[6:]
		hasPlain = true
	} else {
		options, plainURL, hasPlain = strings.Cut(path, "/plain/")
	}

	// Some proxies/CDNs may encode `:` in options as `%3A`, so we need to unescape it first
	path = strings.ReplaceAll(options, "%3A", ":")

	if !hasPlain {
		return strings.TrimPrefix(path, "/")
	}

	// Some proxies/CDNs may "normalize" URLs by replacing `scheme://` with `scheme:/`
	// in the plain URL part, so we need to fix it back.
	if match := fixPathRe.FindStringSubmatch(plainURL); match != nil {
		repl := fmt.Sprintf("%s://", match[1])
		if match[1] == "local" {
			repl += "/"
		}
		repl += match[2]
		plainURL = strings.Replace(plainURL, match[0], repl, 1)
	}

	return strings.TrimPrefix(path+"/plain/"+plainURL, "/")
}