packet buffer binary processing

simple_capture.coffee

#global process require exports 
sys = require 'util'
pcap = require 'pcap'
require 'buffertools'
   
if process.argv.length > 4
    sys.error "usage: simple_capture interface filter"
    sys.error "Examples: "
    sys.error '  simple_capture "" "tcp port 80"'
    sys.error '  simple_capture eth1 ""'
    sys.error '  simple_capture lo0 "ip proto \\tcp and tcp port 80"'
    process.exit(1)

hwif = process.argv[2]
filter = process.argv[3]
pcap_session = pcap.createSession hwif, filter

# libpcap's internal version numnber
sys.puts pcap.lib_version

# Print all devices, currently listening device prefixed with an asterisk
pcap_session.findalldevs().forEach (dev)->
	if pcap_session.device_name == dev.name
		sys.print "* "
    
	sys.print dev.name+" "
	if dev.addresses.length > 0
		dev.addresses.forEach (address)->
			sys.print address.addr+"/"+address.netmask
		sys.print "\n"
	else
		sys.print "no address\n"
    
Binary = require 'binary'

is_spt_pkt = ( dmacbuf) ->
	prefix = new Buffer [ 0x01, 0x80, 0xc2 ]
	return dmacbuf.slice(0,3).equals(prefix)
	
decode_etherpkt = (pktbuf) ->
	Binary.parse(pktbuf).buffer('dmac', 6).buffer('smac',6).buffer('etype', 2).vars

decode_etherpkt2 = (pktbuf) ->
	dmacbuf = pktbuf.slice( 0,6)
	smacbuf = pktbuf.slice( 6,12)
	return { dmac: dmacbuf.toHex(), smac: smacbuf.toHex()}


# Listen for packets, decode them, and feed the simple printer.  No tricks.
pcap_session.on 'packet', (raw_packet)->
	#packet = pcap.decode.packet raw_packet
	#console.log 'dmac:', packet.link.dhost
	#console.log 'smac:', packet.link.shost
	#console.log 'etype:',packet.link.ethertype
	#sys.puts pcap.print.packet(packet)
	packet = decode_etherpkt raw_packet
	console.log packet
	if is_spt_pkt( packet.dmac)
		console.log 'got spanning tree'