Add support for HTTP/HTTPS proxies

Fixes #638

dnscrypt-proxy/config.go

@@ -6,6 +6,7 @@ import (
 	"flag"
 	"fmt"
 	"net"
+	"net/http"
 	"net/url"
 	"os"
 	"path"
@@ -71,6 +72,7 @@ type Config struct {
 	NetprobeAddress          string                     `toml:"netprobe_address"`
 	NetprobeTimeout          int                        `toml:"netprobe_timeout"`
 	OfflineMode              bool                       `toml:"offline_mode"`
+	HTTPProxyURL             string                     `toml:"http_proxy"`
 }
 
 func newConfig() Config {
@@ -254,11 +256,18 @@ func ConfigLoad(proxy *Proxy, svcFlag *string) error {
 	proxy.xTransport.useIPv4 = config.SourceIPv4
 	proxy.xTransport.useIPv6 = config.SourceIPv6
 	proxy.xTransport.keepAlive = time.Duration(config.KeepAlive) * time.Second
+	if len(config.HTTPProxyURL) > 0 {
+		httpProxyURL, err := url.Parse(config.HTTPProxyURL)
+		if err != nil {
+			dlog.Fatalf("Unable to parse the HTTP proxy URL [%v]", config.HTTPProxyURL)
+		}
+		proxy.xTransport.httpProxyFunction = http.ProxyURL(httpProxyURL)
+	}
 
 	if len(config.Proxy) > 0 {
 		proxyDialerURL, err := url.Parse(config.Proxy)
 		if err != nil {
-			dlog.Fatalf("Unable to parse proxy url [%v]", config.Proxy)
+			dlog.Fatalf("Unable to parse the proxy URL [%v]", config.Proxy)
 		}
 		proxyDialer, err := netproxy.FromURL(proxyDialerURL, netproxy.Direct)
 		if err != nil {

dnscrypt-proxy/example-dnscrypt-proxy.toml

@@ -85,13 +85,18 @@ require_nofilter = true
 force_tcp = false
 
 
-## HTTP / SOCKS proxy
+## SOCKS proxy
 ## Uncomment the following line to route all TCP connections to a local Tor node
 ## Tor doesn't support UDP, so set `force_tcp` to `true` as well.
 
 # proxy = "socks5://127.0.0.1:9050"
 
 
+## HTTP/HTTPS proxy
+## Only for DoH servers
+
+# http_proxy = "http://127.0.0.1:8888"
+
 
 ## How long a DNS query will wait for a response, in milliseconds
 

dnscrypt-proxy/xtransport.go

@@ -43,6 +43,7 @@ type XTransport struct {
 	tlsDisableSessionTickets bool
 	tlsCipherSuite           []uint16
 	proxyDialer              *netproxy.Dialer
+	httpProxyFunction        func(*http.Request) (*url.URL, error)
 }
 
 var DefaultKeepAlive = 5 * time.Second
@@ -104,6 +105,9 @@ func (xTransport *XTransport) rebuildTransport() {
 			}
 		},
 	}
+	if xTransport.httpProxyFunction != nil {
+		transport.Proxy = xTransport.httpProxyFunction
+	}
 	if xTransport.tlsDisableSessionTickets || xTransport.tlsCipherSuite != nil {
 		tlsClientConfig := tls.Config{
 			SessionTicketsDisabled: xTransport.tlsDisableSessionTickets,