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https://github.com/maiha/pcap.cr
Crystal bindings for libpcap
https://github.com/maiha/pcap.cr
crystal packets pcap
Last synced: 4 days ago
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Crystal bindings for libpcap
- Host: GitHub
- URL: https://github.com/maiha/pcap.cr
- Owner: maiha
- License: mit
- Created: 2016-06-11T13:51:35.000Z (over 8 years ago)
- Default Branch: master
- Last Pushed: 2020-05-17T09:36:58.000Z (over 4 years ago)
- Last Synced: 2024-08-01T17:32:17.484Z (3 months ago)
- Topics: crystal, packets, pcap
- Language: Crystal
- Size: 58.6 KB
- Stars: 25
- Watchers: 5
- Forks: 3
- Open Issues: 2
-
Metadata Files:
- Readme: README.md
- License: LICENSE
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README
# pcap.cr [](https://travis-ci.org/maiha/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: 0.31.1 0.32.1 0.33.0 0.34.0
- x86_64 binary: https://github.com/maiha/pcap.cr/releases
## Usage : loop with handler
- `Pcap::Capture#loop` : `NoReturn`
is a easiest way to read all packets, and loop forever.
`tcpdump` uses this style to capture packets.
```crystal
require "pcap"
pcap = Pcap::Capture.open_live("eth0")
pcap.setfilter("tcp port 80")
pcap.loop do |pkt|
if pkt.tcp_data?
# p pkt.ether_header
# p pkt.ip_header
# p pkt.tcp_header
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 ...
```
## Usage : reads a packet without blocking
- `Pcap::Capture#next_ex` : `Pcap::NextError` | `Pcap::Packet`
reads a next packet without blocking.
```crystal
pkt = pcap.next_ex
case pkt
when Pcap::Packet ; # use pkt as you like
when Pcap::NextError::Timeout; # try again
when Pcap::NextError::Error ; abort "libpcap error"
when Pcap::NextError::EOF ; # found only in offline mode
end
```
- `Pcap::Capture#get?` : `Pcap::Packet?`
is a easiest way to read a packet. This api would block because `get?` = `next_ex` + timeout retry.
```crystal
if pkt = pcap.get?
puts pkt
else
abort "EOF reached"
end
```
```
22:36:51.327153 IP 127.0.0.1.56903 > 127.0.0.1.6379: Flags [S], seq 3742863884, win 43690, length 0
```
## 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`:
```yaml
dependencies:
pcap:
github: maiha/pcap.cr
version: 0.6.1
```
And then
```console
$ shards update
```
## Example applications
#### `filtertest`
Test a string of `pcap-filter`.
```console
$ filtertest 'tcp'
$ filtertest 'tcp 80'
syntax error
$ filtertest 'tcp port 80'
$ filtertest -f filter.data # for large string
```
(As it works, this command will not display any output.)
#### `tcpsniffer`
- (run as root)
```console
$ 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
```console
$ 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)
```console
$ 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
```console
$ 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 ...
```
- `-W DIR` writes each tcp data by file in the DIR
```console
$ tcpsniffer -p 6379 -d -W pcap
16:37:03.683540 IP 127.0.0.1.52182 > 127.0.0.1.6379: Flags [PA], seq 3176296709, ack 3372892385, win 342, length 14
16:37:03.683611 IP 127.0.0.1.6379 > 127.0.0.1.52182: Flags [PA], seq 3372892385, ack 3176296723, win 342, length 7
$ redis-cli ping
PONG
$ ls -l pcap
-rw-r--r-- 1 root root 14 Mar 6 16:37 1.pcap
-rw-r--r-- 1 root root 7 Mar 6 16:37 2.pcap
$ hd pcap/1.pcap
00000000 2a 31 0d 0a 24 34 0d 0a 50 49 4e 47 0d 0a |*1..$4..PING..|
0000000e
$ hd pcap/2.pcap
00000000 2b 50 4f 4e 47 0d 0a |+PONG..|
00000007
```
##### replay
- `-r file` reads from pcap file (same as `tcpdump -r`)
```console
# 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](https://github.com/maiha) maiha - creator, maintainer
- [puppetpies](https://github.com/puppetpies) Brian Hood - `libpcap.cr`