netstack: introduce new module for gvisor tcp tun adapter

The Go linker isn't smart enough to prevent gvisor from being pulled
into modules that use other parts of tun/, due to the types exposed. So,
we put this into its own standalone module.

We use this as an opportunity to introduce some example code as well.

I'm still not happy that this not only clutters this repo's go.sum, but
all the other projects that consume it, but it seems like making a new
module inside of this repo will lead to even greater confusion.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

3 files changed, 106 insertions, 6 deletions

diff --git a/tun/netstack/examples/http_client.go b/tun/netstack/examples/http_client.go
new file mode 100644
index 0000000..2c1f8f4
--- /dev/null
+++ b/tun/netstack/examples/http_client.go
@@ -0,0 +1,50 @@
+// +build ignore
+
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright (C) 2019-2021 WireGuard LLC. All Rights Reserved.
+ */
+
+package main
+
+import (
+	"io"
+	"log"
+	"net"
+	"net/http"
+
+	"golang.zx2c4.com/wireguard/device"
+	"golang.zx2c4.com/wireguard/tun/netstack"
+)
+
+func main() {
+	tun, tnet, err := netstack.CreateNetTUN(
+		[]net.IP{net.ParseIP("192.168.4.29")},
+		[]net.IP{net.ParseIP("8.8.8.8")},
+		1420)
+	if err != nil {
+		log.Panic(err)
+	}
+	dev := device.NewDevice(tun, &device.Logger{log.Default(), log.Default(), log.Default()})
+	dev.IpcSet(`private_key=a8dac1d8a70a751f0f699fb14ba1cff7b79cf4fbd8f09f44c6e6a90d0369604f
+public_key=25123c5dcd3328ff645e4f2a3fce0d754400d3887a0cb7c56f0267e20fbf3c5b
+endpoint=163.172.161.0:12912
+allowed_ip=0.0.0.0/0
+`)
+	dev.Up()
+
+	client := http.Client{
+		Transport: &http.Transport{
+			DialContext: tnet.DialContext,
+		},
+	}
+	resp, err := client.Get("https://www.zx2c4.com/ip")
+	if err != nil {
+		log.Panic(err)
+	}
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		log.Panic(err)
+	}
+	log.Println(string(body))
+}
diff --git a/tun/netstack/examples/http_server.go b/tun/netstack/examples/http_server.go
new file mode 100644
index 0000000..e627e55
--- /dev/null
+++ b/tun/netstack/examples/http_server.go
@@ -0,0 +1,48 @@
+// +build ignore
+
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright (C) 2019-2021 WireGuard LLC. All Rights Reserved.
+ */
+
+package main
+
+import (
+	"golang.zx2c4.com/wireguard/device"
+	"golang.zx2c4.com/wireguard/tun/netstack"
+	"io"
+	"log"
+	"net"
+	"net/http"
+)
+
+func main() {
+	tun, tnet, err := netstack.CreateNetTUN(
+		[]net.IP{net.ParseIP("192.168.4.29")},
+		[]net.IP{net.ParseIP("8.8.8.8"), net.ParseIP("8.8.4.4")},
+		1420,
+	)
+	if err != nil {
+		log.Panic(err)
+	}
+	dev := device.NewDevice(tun, &device.Logger{log.Default(), log.Default(), log.Default()})
+	dev.IpcSet(`private_key=a8dac1d8a70a751f0f699fb14ba1cff7b79cf4fbd8f09f44c6e6a90d0369604f
+public_key=25123c5dcd3328ff645e4f2a3fce0d754400d3887a0cb7c56f0267e20fbf3c5b
+endpoint=163.172.161.0:12912
+allowed_ip=0.0.0.0/0
+persistent_keepalive_interval=25
+    `)
+	dev.Up()
+	listener, err := tnet.ListenTCP(&net.TCPAddr{Port: 80})
+	if err != nil {
+		log.Panicln(err)
+	}
+	http.HandleFunc("/", func(writer http.ResponseWriter, request *http.Request) {
+		log.Printf("> %s - %s - %s", request.RemoteAddr, request.URL.String(), request.UserAgent())
+		io.WriteString(writer, "Hello from userspace TCP!")
+	})
+	err = http.Serve(listener, nil)
+	if err != nil {
+		log.Panicln(err)
+	}
+}
diff --git a/tun/tun_net.go b/tun/netstack/tun.go
index 9a6f26f..6bdea23 100644
--- a/tun/tun_net.go
+++ b/tun/netstack/tun.go
@@ -3,7 +3,7 @@
  * Copyright (C) 2019-2021 WireGuard LLC. All Rights Reserved.
  */
 
-package tun
+package netstack
 
 import (
 	"context"
@@ -18,6 +18,8 @@ import (
 	"strings"
 	"time"
 
+	"golang.zx2c4.com/wireguard/tun"
+
 	"golang.org/x/net/dns/dnsmessage"
 	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/tcpip/adapters/gonet"
@@ -33,7 +35,7 @@ import (
 type netTun struct {
 	stack          *stack.Stack
 	dispatcher     stack.NetworkDispatcher
-	events         chan Event
+	events         chan tun.Event
 	incomingPacket chan buffer.VectorisedView
 	mtu            int
 	dnsServers     []net.IP
@@ -88,7 +90,7 @@ func (*endpoint) ARPHardwareType() header.ARPHardwareType {
 func (e *endpoint) AddHeader(local, remote tcpip.LinkAddress, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) {
 }
 
-func CreateNetTUN(localAddresses []net.IP, dnsServers []net.IP, mtu int) (Device, *Net, error) {
+func CreateNetTUN(localAddresses []net.IP, dnsServers []net.IP, mtu int) (tun.Device, *Net, error) {
 	opts := stack.Options{
 		NetworkProtocols:   []stack.NetworkProtocolFactory{ipv4.NewProtocol, ipv6.NewProtocol},
 		TransportProtocols: []stack.TransportProtocolFactory{tcp.NewProtocol, udp.NewProtocol},
@@ -96,7 +98,7 @@ func CreateNetTUN(localAddresses []net.IP, dnsServers []net.IP, mtu int) (Device
 	}
 	dev := &netTun{
 		stack:          stack.New(opts),
-		events:         make(chan Event, 10),
+		events:         make(chan tun.Event, 10),
 		incomingPacket: make(chan buffer.VectorisedView),
 		dnsServers:     dnsServers,
 		mtu:            mtu,
@@ -127,7 +129,7 @@ func CreateNetTUN(localAddresses []net.IP, dnsServers []net.IP, mtu int) (Device
 		dev.stack.AddRoute(tcpip.Route{Destination: header.IPv6EmptySubnet, NIC: 1})
 	}
 
-	dev.events <- EventUp
+	dev.events <- tun.EventUp
 	return dev, (*Net)(dev), nil
 }
 
@@ -139,7 +141,7 @@ func (tun *netTun) File() *os.File {
 	return nil
 }
 
-func (tun *netTun) Events() chan Event {
+func (tun *netTun) Events() chan tun.Event {
 	return tun.events
 }