From 61bad01726f6b7439cbc73154158e6cbcadee21a Mon Sep 17 00:00:00 2001
From: Frank Denis <github@pureftpd.org>
Date: Tue, 30 Jan 2018 15:51:07 +0100
Subject: [PATCH] Import xtransport

---
 dnscrypt-proxy/xtransport.go | 147 +++++++++++++++++++++++++++++++++++
 1 file changed, 147 insertions(+)
 create mode 100644 dnscrypt-proxy/xtransport.go

diff --git a/dnscrypt-proxy/xtransport.go b/dnscrypt-proxy/xtransport.go
new file mode 100644
index 00000000..b1a7f9be
--- /dev/null
+++ b/dnscrypt-proxy/xtransport.go
@@ -0,0 +1,147 @@
+package main
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"net"
+	"net/http"
+	"net/url"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/jedisct1/dlog"
+	"github.com/miekg/dns"
+)
+
+const DefaultFallbackResolver = "9.9.9.9:53"
+
+type CachedIPs struct {
+	sync.RWMutex
+	cache map[string]string
+}
+
+type XTransport struct {
+	transport        *http.Transport
+	timeout          time.Duration
+	cachedIPs        CachedIPs
+	fallbackResolver string
+}
+
+func NewXTransport(timeout time.Duration) *XTransport {
+	xTransport := XTransport{
+		cachedIPs:        CachedIPs{cache: make(map[string]string)},
+		timeout:          timeout,
+		fallbackResolver: DefaultFallbackResolver,
+	}
+	dialer := &net.Dialer{Timeout: timeout, KeepAlive: timeout, DualStack: true}
+	transport := &http.Transport{
+		DisableKeepAlives:      false,
+		DisableCompression:     true,
+		MaxIdleConns:           1,
+		IdleConnTimeout:        timeout,
+		ResponseHeaderTimeout:  timeout,
+		ExpectContinueTimeout:  timeout,
+		MaxResponseHeaderBytes: 4096,
+		DialContext: func(ctx context.Context, network, addrStr string) (net.Conn, error) {
+			host := addrStr[:strings.LastIndex(addrStr, ":")]
+			ipOnly := host
+			xTransport.cachedIPs.RLock()
+			cachedIP := xTransport.cachedIPs.cache[host]
+			xTransport.cachedIPs.RUnlock()
+			if len(cachedIP) > 0 {
+				ipOnly = cachedIP
+			} else {
+				dlog.Debugf("[%s] IP address was not cached", host)
+			}
+			addrStr = ipOnly + addrStr[strings.LastIndex(addrStr, ":"):]
+			return dialer.DialContext(ctx, network, addrStr)
+		},
+	}
+	xTransport.transport = transport
+	return &xTransport
+}
+
+func (xTransport *XTransport) Fetch(method string, url *url.URL, accept string, contentType string, body *io.ReadCloser, timeout time.Duration) (*http.Response, time.Duration, error) {
+	if timeout <= 0 {
+		timeout = xTransport.timeout
+	}
+	client := http.Client{Transport: xTransport.transport, Timeout: timeout}
+	header := map[string][]string{"User-Agent": {"dnscrypt-proxy"}}
+	if len(accept) > 0 {
+		header["Accept"] = []string{accept}
+	}
+	if len(contentType) > 0 {
+		header["Content-Type"] = []string{contentType}
+	}
+	req := &http.Request{
+		Method: method,
+		URL:    url,
+		Header: header,
+		Close:  false,
+	}
+	if body != nil {
+		req.Body = *body
+	}
+	start := time.Now()
+	resp, err := client.Do(req)
+	rtt := time.Since(start)
+	if err == nil {
+		if resp == nil {
+			err = errors.New("Webserver returned an error")
+		} else if resp.StatusCode < 200 || resp.StatusCode > 299 {
+			err = fmt.Errorf("Webserver returned code %d", resp.StatusCode)
+		}
+		return resp, rtt, err
+	}
+	host := url.Host
+	xTransport.cachedIPs.RLock()
+	cachedIP := xTransport.cachedIPs.cache[host]
+	xTransport.cachedIPs.RUnlock()
+	if len(cachedIP) > 0 {
+		dlog.Debugf("IP for [%s] was cached to [%s], but connection failed: [%s]", host, cachedIP, err)
+		return resp, rtt, err
+	}
+	dnsClient := new(dns.Client)
+	msg := new(dns.Msg)
+	msg.SetQuestion(dns.Fqdn(host), dns.TypeA)
+	msg.SetEdns0(4096, true)
+	dlog.Noticef("System DNS configuration not usable yet, exceptionally resolving [%s] using fallback resolver [%s]", host, xTransport.fallbackResolver)
+	in, _, err := dnsClient.Exchange(msg, xTransport.fallbackResolver)
+	if err != nil {
+		return resp, rtt, err
+	}
+	if len(in.Answer) <= 0 {
+		return resp, rtt, fmt.Errorf("No IP found for [%s]", host)
+	}
+	foundIP := in.Answer[0].(*dns.A).A.String()
+	xTransport.cachedIPs.Lock()
+	xTransport.cachedIPs.cache[host] = foundIP
+	xTransport.cachedIPs.Unlock()
+	dlog.Debugf("[%s] IP address [%s] added to the cache", host, foundIP)
+
+	start = time.Now()
+	resp, err = client.Do(req)
+	rtt = time.Since(start)
+	if err == nil {
+		if resp == nil {
+			err = errors.New("Webserver returned an error")
+		} else if resp.StatusCode < 200 || resp.StatusCode > 299 {
+			err = fmt.Errorf("Webserver returned code %d", resp.StatusCode)
+		}
+	}
+	return resp, rtt, err
+}
+
+func (xTransport *XTransport) Get(url *url.URL, timeout time.Duration) (*http.Response, time.Duration, error) {
+	return xTransport.Fetch("GET", url, "", "", nil, timeout)
+}
+
+func (xTransport *XTransport) Post(url *url.URL, accept string, contentType string, body []byte, timeout time.Duration) (*http.Response, time.Duration, error) {
+	bc := ioutil.NopCloser(bytes.NewReader(body))
+	return xTransport.Fetch("POST", url, accept, contentType, &bc, timeout)
+}