Matches URL for a particular scheme and domain and replaces them with a new URL

urlrewriter.go

package main

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

// URLRewriter rewrites URL
type URLRewriter struct {
	re     *regexp.Regexp
	newURL string
}

// NewURLRewriter creates an instance of a URLRewriter
func NewURLRewriter(oldURL, newURL string) (*URLRewriter, error) {
	o, err := url.Parse(oldURL)
	if err != nil {
		return nil, err
	}

	n, err := url.Parse(newURL)
	if err != nil {
		return nil, err
	}

	r := &URLRewriter{}
	// Create regex pattern to match old URL.
	// The pattern purposely ingores the specified port and matches purely based on the scheme an hostname
	pattern := `(?i)(` + o.Scheme + `://)?` + strings.Replace(o.Hostname(), `.`, `\.`, -1) + `:?\d*`
	re, err := regexp.Compile(pattern)
	if err != nil {
		return nil, err
	}
	r.re = re
	r.newURL = n.String()
	return r, nil
}

// Rewrite rewrites the body with the replacement URL
func (r *URLRewriter) Rewrite(body string) string {
	return r.re.ReplaceAllString(body, r.newURL)
}