pcap.cr

Crystal high level bindings for libpcap.

• crystal-libpcap(libpcap.cr) is a low level bindings for libpcap created by [puppetpies].

• pcap.cr is a wrapper for it and provides rich interface for packets like ruby-pcap.

• Crystal: 0.19.4

• Binary: https://github.com/maiha/pcap.cr/releases

require "pcap"

cap = Pcap::Capture.open_live("eth0")
cap.setfilter("tcp port 80")
cap.loop do |pkt|
  if pkt.tcp_data?
    p pkt.tcp_data.to_s
  end
end

"GET / HTTP/1.1\r\nHost: localhost\r\nUser-Agent: curl/7.47.0\r\nAccept: */*\r\n\r\n"
"HTTP/1.1 200 OK\r\nServer: nginx/1.10.0 (Ubuntu)\r\nDate: Mon, 13 Jun 2016 ...

Status

• support only tcp

TODO

• [x] libpcap api (0.1.0)
• [x] Crystal closure support in Pcap::Handler (0.2.0)
• [x] Ether Header (0.1.0)
  • [x] parse
  • [x] inspect
• [x] Ip Header (0.1.0)
  • [x] parse
  • [x] inspect
• [x] Tcp Header (0.1.0)
  • [x] parse
  • [x] inspect
• [ ] Udp Header
  • [ ] parse
  • [ ] inspect
• [ ] Other Headers
  • [ ] parse
  • [ ] inspect
• [ ] Test
  • [x] Pcap::Capture offline

Installation

Add this to your application's shard.yml:

dependencies:
  pcap:
    github: maiha/pcap.cr

And then

% crystal deps

Usage

require "pcap"

cap = Pcap::Capture.open_live("eth0")
cap.setfilter("tcp port 80")
cap.loop do |pkt|
  # p pkt.ether_header
  # p pkt.ip_header
  # p pkt.tcp_header
  if pkt.tcp_data?
    p pkt.tcp_data.to_s
  end
}

Examples

• (run as root)

tcpbody

• Sniffer redis commands

% crystal examples/tcpbody.cr -- 6379

# (or use compiled binary)
% tcpbody 6379                       

• run some redis command like redis-cli get foo

"*2\r\n$3\r\nget\r\n$3\r\nfoo\r\n"
"$-1\r\n"

tcpsniffer

% crystal examples/tcpsniffer.cr

# (or binary)
% tcpsniffier -p 6379
% tcpsniffier -f '(tcp port 80) or (tcp port 8080)' 
% tcpsniffier -i eth0 -p 10080

• send some packets to your specified port by curl localhost

12:29:01.445261 IP 127.0.0.1.56016 > 127.0.0.1.80: Flags [S], seq 746220255, win 43690, length 0
12:29:01.445282 IP 127.0.0.1.80 > 127.0.0.1.56016: Flags [SA], seq 4032610561, ack 746220256, win 43690, length 0

further output

• -x prints hexdump of packets

% tcpsniffer -x
12:30:12.305080 IP 127.0.0.1.56018 > 127.0.0.1.80: Flags [S], seq 4253528483, win 43690, length 0
        0x0000:  0000 0000 0000 0000 0000 0000 0800 4500  ..............E.
        0x0010:  003c 8c99 4000 4006 b020 7f00 0001 7f00  .<..@.@.. ......
        0x0020:  0001 dad2 0050 fd87 b1a3 0000 0000 a002  .....P..........
        0x0030:  aaaa fe30 0000 0204 ffd7 0402 080a 092a  ...0...........*
        0x0040:  3d3a 0000 0000 0103 0307                 =:........

• -v prints packet structures (calls inspect internally)

% tcpsniffer -v
--------------------------------------------------------------------------------
Packet Header
  Time         : 2016-06-11 22:42:09 +0900 (1465652529.994580)
  Packet Size  : 68 (total: 74) bytes

Ethernet Header
  Destination eth addr  : 00:00:00:00:00:00
  Source ether addr     : 00:00:00:00:00:00
  Packet type ID        : IPv4 (2048)

IpHeader
  Version         : 4
  Header Length   : 5 words (20 bytes)
  Service Type    : 0
  Total Length    : 60
  Identification  : 4307
  Flags           : 16384
  TTL             : 64
  Protocol        : 6
  Header Checksum : 11239
  Src IP Addr     : 127.0.0.1
  Dst IP Addr     : 127.0.0.1
...

• -d prints only packets where tcp data exist
• -b prints body oriented format (body mode)
• -x ignore all packets that contain only white spaces

% tcpsniffer -b -d
17:12:24.261729: "GET / HTTP/1.1\r\nHost: localhost\r\nUser-Agent: curl/7.47.0\r\nAccept: */*\r\n\r\n"
17:12:24.262003: "HTTP/1.1 200 OK\r\nServer: nginx/1.10.0 (Ubuntu)\r\nDate: Mon, 13 Jun 2016 ...

replay

• -r file reads from pcap file (same as tcpdump -r)

# record packets by root with tcpdump
% tcpdump -i lo -s 0 -w /tmp/redis.dump 'port 6379'

# in other shell
% redis-cli ping

# stop tcpdump by `Ctl-c`

# reply by tcpsniffer
% tcpsniffer -r /tmp/redis.dump -p 6379 -b -d
reading from file: /tmp/redis.dump
11:47:14.001208: "*1\r\n$4\r\nping\r\n"
11:47:14.001569: "+PONG\r\n"

Contributing

1. Fork it ( https://github.com/maiha/pcap.cr/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

Contributors

• [maiha] maiha - creator, maintainer
• [puppetpies] Brian Hood - libpcap.cr