Add dialer.DialTimeout support

lib/dialer/public.go

@@ -0,0 +1,48 @@
+// 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"
+	"time"
+)
+
+// 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 {
+		return dialWithFallback(proxyDialer.Dial, net.Dial, network, addr)
+	}
+	return net.Dial(network, addr)
+}
+
+// DialTimeout tries dialing via proxy with a timeout if a proxy is configured,
+// and falls back to a direct connection if no proxy is defined, or connecting
+// via proxy fails. The timeout can potentially be applied twice, once trying
+// to connect via the proxy connection, and second time trying to connect
+// directly.
+func DialTimeout(network, addr string, timeout time.Duration) (net.Conn, error) {
+	if usingProxy {
+		// Because the proxy package is poorly structured, we have to
+		// construct a struct that matches proxy.Dialer but has a timeout
+		// and reconstrcut the proxy dialer using that, in order to be able to
+		// set a timeout.
+		dd := &timeoutDirectDialer{
+			timeout: timeout,
+		}
+		// Check if the dialer we are getting is not timeoutDirectDialer we just
+		// created. It could happen that usingProxy is true, but getDialer
+		// returns timeoutDirectDialer due to env vars changing.
+		if timeoutProxyDialer := getDialer(dd); timeoutProxyDialer != dd {
+			directDialFunc := func(inetwork, iaddr string) (net.Conn, error) {
+				return net.DialTimeout(inetwork, iaddr, timeout)
+			}
+			return dialWithFallback(timeoutProxyDialer.Dial, directDialFunc, network, addr)
+		}
+	}
+	return net.DialTimeout(network, addr, timeout)
+}