sjmackenzie/enet

Pure Erlang network stack

ENet - A pure-Erlang network stack

ENet is a pure Erlang network stack that can be used to encode and decode a variety of common packet formats.

The project includes a port program that can be used to send and receive ethernet frames via the /dev/tap0 device.

Requirements

Mac OS X

libevent, OS X 10.6.1 (probably compatible with other versions), the tuntaposx driver ( http://tuntaposx.sourceforge.net ) loaded, sudo.

Linux

libevent, the tun module loaded, the tunctl program (usually in the uml-utilities package``), sudo.

Drivers

Mac OS X

The enet_tap port program. Takes a mandatory option -f to specify which tap device to use. (normally "/dev/tap0")

Linux

The enet_tap port program. Takes a mandatory -i argument that specifies which tap device to use. (normally "tap0")

Building the Driver

You'll need to edit the Makefile to set the appropriate CFLAGS and LDFLAGS for your machine and erts (32 or 64 bit build, location of libevent headers and libraries, ...).

Setting up the tap device

Mac OS X

For ease of use, you should probably change the ownership of /dev/tapN to yourself.

Linux

You should create a tap device that you can open as your user. The easiest way to do this is to install the tunctl program (in the uml-utilities package on debian systems), and then create the device:

tunctl -u yourusername -t tap0

Setup sudo

Enet currently uses the ifconfig command to configure the operating system side of the tap device. This is usually a privileged operation, so we need to configure sudo to allow erlang to do this without a password.

Add the following lines to /etc/sudoers:

Cmnd_Alias  ENET = /sbin/ifconfig tap0 *
yourusername ALL=(ALL) NOPASSWD: ENET

Starting Enet

From an erlang shell (erl -boot start_sasl -pa ebin):

1> {ok, Pid} = enet_iface:start("tap0", "192.168.2.1/24 up"),
   enet_if_dump:attach(Pid),
   enet_if_arp:attach(Pid),
   enet_if_arp:add_entry(Pid, "4A:6E:01:1B:19:8F", "192.168.2.2"),
   enet_if_icmp:attach(Pid).

You should now see decoded traffic in the erlang shell. If you ping the IP address of the erlang interface 192.168.2.2 in the example, you should see ping replies and an arp entry (arp -na):

? (192.168.2.2) at 4a:6e:1:1b:19:8f on tap0 ifscope [ethernet]

Debugging

There are a number of debugging aides available:

• enet_if_crtest -- Tries to re-encode decoded packets and writes erlang and pcap trace files if this fails.:

  2> {ok, Pid} = enet_iface:start("tap0", "192.168.2.1/24 up"),
     enet_if_dump:attach(Pid),
     enet_if_arp:attach(Pid),
     enet_if_arp:add_entry(Pid, "4A:6E:01:1B:19:8F", "192.168.2.2"),
     enet_if_icmp:attach(Pid),
     enet_if_crtest:attach(Pid, "priv/breakage").