all: disable TCP keep-alives on iOS/Android

Updates #2442
Updates tailscale/corp#2750

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

net/netknob/netknob.go

@@ -0,0 +1,30 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package netknob has Tailscale network knobs.
+package netknob
+
+import (
+	"runtime"
+	"time"
+)
+
+// PlatformTCPKeepAlive returns the default net.Dialer.KeepAlive
+// value for the current runtime.GOOS.
+func PlatformTCPKeepAlive() time.Duration {
+	switch runtime.GOOS {
+	case "ios", "android":
+		// Disable TCP keep-alives on mobile platforms.
+		// See https://github.com/golang/go/issues/48622.
+		//
+		// TODO(bradfitz): in 1.17.x, try disabling TCP
+		// keep-alives on for all platforms.
+		return -1
+	}
+
+	// Otherwise, default to 30 seconds, which is mostly what we
+	// used to do. In some places we used the zero value, which Go
+	// defaults to 15 seconds. But 30 seconds is fine.
+	return 30 * time.Second
+}

net/netns/netns.go

@@ -19,6 +19,7 @@ import (
 	"net"
 
 	"inet.af/netaddr"
+	"tailscale.com/net/netknob"
 	"tailscale.com/syncs"
 )
 
@@ -45,7 +46,9 @@ func Listener() *net.ListenConfig {
 // namespace that doesn't route back into Tailscale. It also handles
 // using a SOCKS if configured in the environment with ALL_PROXY.
 func NewDialer() Dialer {
-	return FromDialer(new(net.Dialer))
+	return FromDialer(&net.Dialer{
+		KeepAlive: netknob.PlatformTCPKeepAlive(),
+	})
 }
 
 // FromDialer returns sets d.Control as necessary to run in a logical