Add proxy support (fixes #271)

lib/dialer/dialer.go

@@ -0,0 +1,88 @@
+// Copyright (C) 2015 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at http://mozilla.org/MPL/2.0/.
+
+package dialer
+
+import (
+	"net"
+	"os"
+	"strings"
+	"time"
+
+	"golang.org/x/net/proxy"
+
+	"github.com/syncthing/syncthing/lib/logger"
+)
+
+var (
+	l          = logger.DefaultLogger.NewFacility("dialer", "Dialing connections")
+	dialer     = proxy.FromEnvironment()
+	usingProxy = dialer != proxy.Direct
+)
+
+func init() {
+	l.SetDebug("dialer", strings.Contains(os.Getenv("STTRACE"), "dialer") || os.Getenv("STTRACE") == "all")
+	if usingProxy {
+		// Defer this, so that logging gets setup.
+		go func() {
+			time.Sleep(500 * time.Millisecond)
+			l.Infoln("Proxy settings detected")
+		}()
+	}
+}
+
+// Dial tries dialing via proxy if a proxy is configured, and falls back to
+// a direct connection if no proxy is defined, or connecting via proxy fails.
+func Dial(network, addr string) (net.Conn, error) {
+	if usingProxy {
+		conn, err := dialer.Dial(network, addr)
+		if err == nil {
+			l.Debugf("Dialing %s address %s via proxy - success, %s -> %s", network, addr, conn.LocalAddr(), conn.RemoteAddr())
+			return dialerConn{
+				conn, newDialerAddr(network, addr),
+			}, nil
+		}
+		l.Debugf("Dialing %s address %s via proxy - error %s", network, addr, err)
+	}
+
+	conn, err := proxy.Direct.Dial(network, addr)
+	if err == nil {
+		l.Debugf("Dialing %s address %s directly - success, %s -> %s", network, addr, conn.LocalAddr(), conn.RemoteAddr())
+	} else {
+		l.Debugf("Dialing %s address %s directly - error %s", network, addr, err)
+	}
+	return conn, err
+}
+
+type dialerConn struct {
+	net.Conn
+	addr net.Addr
+}
+
+func (c dialerConn) RemoteAddr() net.Addr {
+	return c.addr
+}
+
+func newDialerAddr(network, addr string) net.Addr {
+	netaddr, err := net.ResolveIPAddr(network, addr)
+	if err == nil {
+		return netaddr
+	}
+	return fallbackAddr{network, addr}
+}
+
+type fallbackAddr struct {
+	network string
+	addr    string
+}
+
+func (a fallbackAddr) Network() string {
+	return a.network
+}
+
+func (a fallbackAddr) String() string {
+	return a.addr
+}