You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: proxy_headers.go
    path of file: ./repos/handlers
    
    the code of the file until where you have to start completion: package handlers

import (
	"net/http"
	"regexp"
	"strings"
)

var (
	// De-facto standard header keys.
	xForwardedFor    = http.CanonicalHeaderKey("X-Forwarded-For")

    
func getScheme(r *http.Request) string {
	var scheme string

	// Retrieve the scheme from X-Forwarded-Proto.
	if proto := r.Header.Get(xForwardedProto); proto != "" {
		scheme = strings.ToLower(proto)
	} else if proto = r.Header.Get(xForwardedScheme); proto != "" {
		scheme = strings.ToLower(proto)
	} else if proto = r.Header.Get(forwarded); proto != "" {
		// match should contain at least two elements if the protocol was
		// specified in the Forwarded header. The first element will always be
		// the 'proto=' capture, which we ignore. In the case of multiple proto
		// parameters (invalid) we only extract the first.
		if match := protoRegex.FindStringSubmatch(proto); len(match) > 1 {
			scheme = strings.ToLower(match[1])
		}
	}

	return scheme
}