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

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

lib/connections/config.go

@@ -0,0 +1,53 @@
+// Copyright (C) 2017 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 (
+	"io/ioutil"
+	"time"
+
+	"github.com/hashicorp/yamux"
+)
+
+const (
+	tcpPriority   = 10
+	kcpPriority   = 50
+	relayPriority = 200
+
+	// KCP filter priorities
+	kcpNoFilterPriority           = 100
+	kcpConversationFilterPriority = 20
+	kcpStunFilterPriority         = 10
+
+	// KCP SetNoDelay options
+
+	// 0 - disabled (default)
+	// 1 - enabled
+	kcpNoDelay        = 0
+	kcpUpdateInterval = 100 // ms (default)
+	// 0 - disable (default)
+	// 1 - enabled
+	kcpFastResend = 0
+	// 0 - enabled (default)
+	// 1 - disabled
+	kcpCongestionControl = 0
+
+	// KCP window sizes
+	kcpSendWindowSize    = 128
+	kcpReceiveWindowSize = 128
+)
+
+var (
+	yamuxConfig = &yamux.Config{
+		AcceptBacklog:          256,
+		EnableKeepAlive:        true,
+		KeepAliveInterval:      30 * time.Second,
+		ConnectionWriteTimeout: 10 * time.Second,
+		MaxStreamWindowSize:    256 * 1024,
+		LogOutput:              ioutil.Discard,
+	}
+)