lib/connections: Add KCP support (fixes #804)

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3489

lib/connections/kcp_dial.go

@@ -0,0 +1,106 @@
+// Copyright (C) 2016 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 connections
+
+import (
+	"crypto/tls"
+	"net/url"
+	"time"
+
+	"github.com/hashicorp/yamux"
+	"github.com/syncthing/syncthing/lib/config"
+	"github.com/syncthing/syncthing/lib/protocol"
+	"github.com/xtaci/kcp-go"
+)
+
+func init() {
+	factory := &kcpDialerFactory{}
+	for _, scheme := range []string{"kcp", "kcp4", "kcp6"} {
+		dialers[scheme] = factory
+	}
+}
+
+type kcpDialer struct {
+	cfg    *config.Wrapper
+	tlsCfg *tls.Config
+}
+
+func (d *kcpDialer) Dial(id protocol.DeviceID, uri *url.URL) (internalConn, error) {
+	uri = fixupPort(uri, config.DefaultKCPPort)
+
+	var conn *kcp.UDPSession
+	var err error
+
+	// Try to dial via an existing listening connection
+	// giving better changes punching through NAT.
+	if f := getDialingFilter(); f != nil {
+		conn, err = kcp.NewConn(uri.Host, nil, 0, 0, f.NewConn(kcpConversationFilterPriority, &kcpConversationFilter{}))
+		l.Debugf("dial %s using existing conn on %s", uri.String(), conn.LocalAddr())
+	} else {
+		conn, err = kcp.DialWithOptions(uri.Host, nil, 0, 0)
+	}
+	if err != nil {
+		l.Debugln(err)
+		conn.Close()
+		return internalConn{}, err
+	}
+
+	conn.SetKeepAlive(0) // yamux and stun service does keep-alives.
+	conn.SetStreamMode(true)
+	conn.SetACKNoDelay(false)
+	conn.SetWindowSize(kcpSendWindowSize, kcpReceiveWindowSize)
+	conn.SetNoDelay(kcpNoDelay, kcpUpdateInterval, kcpFastResend, kcpCongestionControl)
+
+	ses, err := yamux.Client(conn, yamuxConfig)
+	if err != nil {
+		conn.Close()
+		return internalConn{}, err
+	}
+	stream, err := ses.OpenStream()
+	if err != nil {
+		ses.Close()
+		return internalConn{}, err
+	}
+
+	tc := tls.Client(&sessionClosingStream{stream, ses}, d.tlsCfg)
+	tc.SetDeadline(time.Now().Add(time.Second * 10))
+	err = tc.Handshake()
+	if err != nil {
+		tc.Close()
+		return internalConn{}, err
+	}
+	tc.SetDeadline(time.Time{})
+
+	return internalConn{tc, connTypeKCPClient, kcpPriority}, nil
+}
+
+func (d *kcpDialer) RedialFrequency() time.Duration {
+	// For restricted NATs, the UDP mapping will potentially only be open for 20-30 seconds
+	// hence try dialing just as often.
+	return time.Duration(d.cfg.Options().StunKeepaliveS) * time.Second
+}
+
+type kcpDialerFactory struct{}
+
+func (kcpDialerFactory) New(cfg *config.Wrapper, tlsCfg *tls.Config) genericDialer {
+	return &kcpDialer{
+		cfg:    cfg,
+		tlsCfg: tlsCfg,
+	}
+}
+
+func (kcpDialerFactory) Priority() int {
+	return kcpPriority
+}
+
+func (kcpDialerFactory) Enabled(cfg config.Configuration) bool {
+	return true
+}
+
+func (kcpDialerFactory) String() string {
+	return "KCP Dialer"
+}