package main

import (
	"io/ioutil"
	"log"
	"net"
	"net/http"
	"net/http/httputil"
	"net/url"
	"regexp"
	"strings"
	"time"
)

type LoggingTransport struct {
	transport *http.Transport
}

func (l *LoggingTransport) RoundTrip(req *http.Request) (resp *http.Response, err error) {
	log.Println("Request:", req)
	resp, err = l.transport.RoundTrip(req)

	if err != nil {
		log.Println("Err:", err)
		invalidContentLengthRegexp := regexp.MustCompile(`http: Request.ContentLength=\d+ with Body length \d+`)

		if invalidContentLengthRegexp.MatchString(err.Error()) {
			return &http.Response{
				Body:       ioutil.NopCloser(strings.NewReader("")),
				StatusCode: 400, // HTTP: Bad Request
			}, nil
		}

		return resp, err
	}

	return resp, err
}

func main() {
	connectTimeout, headerTimeout := 1*time.Second, 1*time.Second
	backendURL, _ := url.Parse("http://localhost:8081")

	proxy := httputil.NewSingleHostReverseProxy(backendURL)
	proxy.Transport = &LoggingTransport{&http.Transport{
		Dial: func(network, address string) (net.Conn, error) {
			log.Println("Dialling...", network, address, connectTimeout)
			return net.DialTimeout(network, address, connectTimeout)
		},
		ResponseHeaderTimeout: headerTimeout,
	}}

	log.Fatal(http.ListenAndServe(":9080", proxy))
}