water

README

water

water is a native Go library for TUN/TAP interfaces.

water is designed to be simple and efficient. It

• wraps almost only syscalls and uses only Go standard types;
• exposes standard interfaces; plays well with standard packages like io, bufio, etc..
• does not handle memory management (allocating/destructing slice). It's up to user to decide whether/how to reuse buffers.

water/waterutil has some useful functions to interpret MAC frame headers and IP packet headers. It also contains some constants such as protocol numbers and ethernet frame types.

See https://github.com/songgao/packets for functions for parsing various packets.

Supported Platforms

• Linux
• Windows (experimental; APIs might change)
• macOS (point-to-point TUN only)

Installation

go get -u github.com/songgao/water
go get -u github.com/songgao/water/waterutil

Documentation

http://godoc.org/github.com/songgao/water

Example

TAP on Linux:

package main

import (
	"log"

	"github.com/songgao/packets/ethernet"
	"github.com/songgao/water"
)

func main() {
	config := water.Config{
		DeviceType: water.TAP,
	}
	config.Name = "O_O"

	ifce, err := water.New(config)
	if err != nil {
		log.Fatal(err)
	}
	var frame ethernet.Frame

	for {
		frame.Resize(1500)
		n, err := ifce.Read([]byte(frame))
		if err != nil {
			log.Fatal(err)
		}
		frame = frame[:n]
		log.Printf("Dst: %s\n", frame.Destination())
		log.Printf("Src: %s\n", frame.Source())
		log.Printf("Ethertype: % x\n", frame.Ethertype())
		log.Printf("Payload: % x\n", frame.Payload())
	}
}

This piece of code creates a TAP interface, and prints some header information for every frame. After pull up the main.go, you'll need to bring up the interface and assign an IP address. All of these need root permission.

sudo go run main.go

In a new terminal:

sudo ip addr add 10.1.0.10/24 dev O_O
sudo ip link set dev O_O up

Wait until the output main.go terminal, try sending some ICMP broadcast message:

ping -c1 -b 10.1.0.255

You'll see output containing the IPv4 ICMP frame:

2016/10/24 03:18:16 Dst: ff:ff:ff:ff:ff:ff
2016/10/24 03:18:16 Src: 72:3c:fc:29:1c:6f
2016/10/24 03:18:16 Ethertype: 08 00
2016/10/24 03:18:16 Payload: 45 00 00 54 00 00 40 00 40 01 25 9f 0a 01 00 0a 0a 01 00 ff 08 00 01 c1 08 49 00 01 78 7d 0d 58 00 00 00 00 a2 4c 07 00 00 00 00 00 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f 20 21 22 23 24 25 26 27 28 29 2a 2b 2c 2d 2e 2f 30 31 32 33 34 35 36 37

TUN on macOS

package main

import (
	"log"

	"github.com/songgao/water"
)

func main() {
	ifce, err := water.New(water.Config{
		DeviceType: water.TUN,
	})
	if err != nil {
		log.Fatal(err)
	}

	log.Printf("Interface Name: %s\n", ifce.Name())

	packet := make([]byte, 2000)
	for {
		n, err := ifce.Read(packet)
		if err != nil {
			log.Fatal(err)
		}
		log.Printf("Packet Received: % x\n", packet[:n])
	}
}

Run it!

$ sudo go run main.go

This is a point-to-point only interface. Use ifconfig to see its attributes. You need to bring it up and assign IP addresses (apparently replace utun2 if needed):

$ sudo ifconfig utun2 10.1.0.10 10.1.0.20 up

Now send some ICMP packets to the interface:

$ ping 10.1.0.20

You'd see the ICMP packets printed out:

2017/03/20 21:17:30 Interface Name: utun2
2017/03/20 21:17:40 Packet Received: 45 00 00 54 e9 1d 00 00 40 01 7d 6c 0a 01 00 0a 0a 01 00 14 08 00 ee 04 21 15 00 00 58 d0 a9 64 00 08 fb a5 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f 20 21 22 23 24 25 26 27 28 29 2a 2b 2c 2d 2e 2f 30 31 32 33 34 35 36 37

Caveats

1. Only Point-to-Point user TUN devices are supported. TAP devices are not supported natively by macOS.
2. Custom interface names are not supported by macOS. Interface names are automatically generated serially, using the utun<#> naming convention.

TAP on Windows:

To use it with windows, you will need to install a tap driver, or OpenVPN client for windows.

It's compatible with the Linux code.

package main

import (
	"log"

	"github.com/songgao/packets/ethernet"
	"github.com/songgao/water"
)

func main() {
	ifce, err := water.New(water.Config{
		DeviceType: water.TAP,
	})
	if err != nil {
		log.Fatal(err)
	}
	var frame ethernet.Frame

	for {
		frame.Resize(1500)
		n, err := ifce.Read([]byte(frame))
		if err != nil {
			log.Fatal(err)
		}
		frame = frame[:n]
		log.Printf("Dst: %s\n", frame.Destination())
		log.Printf("Src: %s\n", frame.Source())
		log.Printf("Ethertype: % x\n", frame.Ethertype())
		log.Printf("Payload: % x\n", frame.Payload())
	}
}

Same as Linux version, but you don't need to bring up the device by hand, the only thing you need is to assign an IP address to it.

go run main.go

It will output a lot of lines because of some windows services and dhcp. You will need admin right to assign IP.

In a new cmd (admin right):

# Replace with your device name, it can be achieved by ifce.Name().
netsh interface ip set address name="Ehternet 2" source=static addr=10.1.0.10 mask=255.255.255.0 gateway=none

The main.go terminal should be silenced after IP assignment, try sending some ICMP broadcast message:

ping 10.1.0.255

You'll see output containing the IPv4 ICMP frame same as the Linux version.

TODO

• tuntaposx for TAP on Darwin

Alternatives

tuntap: https://code.google.com/p/tuntap/

Documentation

Index

• type Config
• type DevicePermissions
• type Interface
  • func New(config Config) (ifce *Interface, err error)
  • func (ifce *Interface) Name() string

Types

type Config

type Config struct {
	// Name is the name to be set for the interface to be created. This overrides
	// the default name assigned by OS such as tap0 or tun0. A zero-value of this
	// field, i.e. an empty string, indicates that the default name should be
	// used.
	Name string

	// Enable or disable persistence mode for the interface device.
	Persist bool

	// Owner and Group permissions for the device.
	// A zero-value of this field, i.e. nil, indicates that no changes to owner
	// or group will be made.
	Permissions *DevicePermissions

	// Support multiqueue tun/tap interface.
	// From version 3.8, Linux supports multiqueue tuntap which can uses multiple
	// file descriptors (queues) to parallelize packets sending or receiving.
	MultiQueue bool
}

type DevicePermissions

type DevicePermissions struct {
	// ID of the user which will be granted ownership of the device.
	// If set to a negative value, the owner value will not be changed.
	// By default, Linux sets the owner to -1, which allows any user.
	Owner uint

	// ID of the group which will be granted access to the device.
	// If set to a negative value, the group value will not be changed.
	// By default, Linux sets the group to -1, which allows any group.
	Group uint
}

type Interface

type Interface struct {
	*os.File
	// contains filtered or unexported fields
}

Interface is a TUN/TAP interface.

MultiQueue(Linux kernel > 3.8): With MultiQueue enabled, user should hold multiple interfaces to send/receive packet in parallel. Kernel document about MultiQueue: https://www.kernel.org/doc/Documentation/networking/tuntap.txt

func New

func New(config Config) (ifce *Interface, err error)

func (*Interface) Name

func (ifce *Interface) Name() string

Name returns the interface name of ifce, e.g. tun0, tap1, tun0, etc..