resolvehostsproxy.go

/*
 * Copyright (c) 2014, Yasushi Abe
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package main

import (
	"flag"
	"github.com/elazarl/goproxy"
	"io/ioutil"
	"log"
	"net/http"
	"regexp"
	"strings"
)

func readHosts(hostsfile string) (map[string]string, error) {
	contents, err := ioutil.ReadFile(hostsfile)
	if err != nil {
		return nil, err
	}
	hosts := make(map[string]string)
	pattern := regexp.MustCompile("[ 	]+")
	for _, line := range strings.Split(string(contents), "\n") {
		if !strings.HasPrefix(line, "#") && len(line) > 0 {
			record := pattern.Split(line, -1)
			if len(record) > 1 {
				for _, name := range record[1:] {
					hosts[name] = record[0]
				}
			}
		}
	}
	return hosts, nil
}

func main() {
	verbose := flag.Bool("v", false, "should every proxy request be logged to stdout")
	addr := flag.String("addr", ":8080", "proxy listen address")
	hostsfile := flag.String("f", "hosts", "hosts file")
	flag.Parse()
	hosts, err := readHosts(*hostsfile)
	if err != nil {
		log.Fatal(err)
	}
	var condition goproxy.ReqConditionFunc = func(req *http.Request, ctx *goproxy.ProxyCtx) bool {
		_, ok := hosts[req.URL.Host]
		return ok
	}
	proxy := goproxy.NewProxyHttpServer()
	proxy.Verbose = *verbose
	proxy.OnRequest(condition).DoFunc(func(req *http.Request, ctx *goproxy.ProxyCtx) (*http.Request, *http.Response) {
		req.URL.Host = hosts[req.URL.Host]
		return req, nil
	})
	log.Fatal(http.ListenAndServe(*addr, proxy))
}