Gotcp

Gotcp is user space tcp/ip protocol stack implementation by golang for learing purpose. This project is inspired by microps

Features

Gotcp work on Linux only. To run this, You have to be root. Supported protocol is berow.

• Ethernet
  • tuntap
  • ap_packet
• ARP
• IPv4
• ICMP
• TCP

Tutorial

You can run Gotcp with virtual machines or docker containers.

Environment

Virtual machine

I prepare the virtual machines in vm/. You can setup vm via Vagrant.

Container

I also prepare docker-compose.yml. This way is easier than using virtual machines.

Run

To buil this, execute go build .

I prepare some command to run sample application.

./gotcp help
Usage: gotcp <flags> <subcommand> <subcommand args>

Subcommands:
        commands         list all command names
        dump             dump
        flags            describe all known top-level flags
        help             describe subcommands and their syntax
        ids              ids
        ping             ping
        tcpclient        tcp client
        tcpserver        tcp server

ping

# ./gotcp ping -h
goctp ping -i <interface name> -dest <destination address>:
        send icmp echo request packets and receive reply packets  -debug
        output debug messages
  -dest string
        destination address
  -i string
        interface

# ./gotcp ping -i eth0 -dest 172.20.0.3
172.20.0.3
47 bytes from 172.20.0.3: icmp_seq=0 ttl=64 time=%!f(int64=6953) ms
47 bytes from 172.20.0.3: icmp_seq=0 ttl=64 time=%!f(int64=1011073) ms
47 bytes from 172.20.0.3: icmp_seq=0 ttl=64 time=%!f(int64=2013006) ms
47 bytes from 172.20.0.3: icmp_seq=0 ttl=64 time=%!f(int64=3018657) ms
47 bytes from 172.20.0.3: icmp_seq=0 ttl=64 time=%!f(int64=4019847) ms
47 bytes from 172.20.0.3: icmp_seq=0 ttl=64 time=%!f(int64=5020866) ms

tcp client

You can run a sample tcp client application.

# ./gotcp tcpclient -h
gotcp tcpclient -i <interface name> -addr <ip address> -port <port>
        tcp client to destination host  -addr string
        destination host address
  -debug
        output debug message
  -i string
        interface name
  -port int
        destination host port

Before running this application, you have to execute these commands on the client and server side.

• server

   $ ethtool -K eth0 tso off gso off # stop kernel nic offloading
   $ cd app/standard/tcp-server-big
   $ go run main.go # run server program

• client

   $ mkdir data
   $ head -c 20000 /dev/urandom > data/random-data # generate random data
   $ iptables -A OUTPUT -p tcp --dport 8888 -j DROP # stop processing packets by kernel
   $ ./gotcp tcpclient -debug -i eth0 -addr 172.20.0.3 -port 8888 # run gotcp tcpclient

log

INFO[0000] tcp server running at 8888                    command="tcp client"
INFO[0000] [start to listen]                             protocol=tcp
DEBU[0000] [LISTEN]                                      protocol=tcp
DEBU[0003] [SYN_RECVD]                                   protocol=tcp
DEBU[0003] [ESTABLISHED]                                 protocol=tcp
DEBU[0003] [retransmission routine start ]               protocol=tcp
Server> Connection from 172.20.0.3:8888
Server> Read 1448 bytes
Server> Read 1448 bytes
Server> Read 1448 bytes
Server> Read 1448 bytes
Server> Read 1448 bytes
Server> Read 1448 bytes
Server> Read 1448 bytes
Server> Read 1448 bytes
Server> Read 1448 bytes
Server> Read 1448 bytes
Server> Read 1448 bytes
Server> Read 1448 bytes
Server> Read 1448 bytes
Server> Read 1448 bytes
Server> Read 208 bytes
Server> recv all buf 21720 bytes
Server> Write 20272 bytes
DEBU[0008] [CLOSE_WAIT]                                  protocol=tcp
DEBU[0008] [LAST_ACK]                                    protocol=tcp
DEBU[0008] [CLOSED]                                      protocol=tcp
INFO[0008] [received packet is not handled. invalid peer.]  protocol=tcp
Server> close

tcp server

You can run a sample tcp server application.

$ ./gotcp tcpserver -h
gotcp tcpserver -i <interface name> -port <port>
        tcp server binding port  -debug
        output debug message
  -i string
        interface
  -port int
        binding port

Befor you run this application, you have to execute these commands.

• server

   $ iptables -A INPUT -p tcp --dport 4000:65000 -j DROP # stop packets processing by kernel
   $ ./gotcp tcpserver -debug -i eth0 -port 8888

• client

   $ ethtool -K eth0 tso off gso off # stop kernel nic offloading
   $ cd app/standard/tcp-client-big
   $ go run main.go # run client program

log

INFO[0000] tcp server running at 8888                    command="tcp client"
INFO[0000] [start to listen]                             protocol=tcp
DEBU[0000] [LISTEN]                                      protocol=tcp
DEBU[0004] [SYN_RECVD]                                   protocol=tcp
DEBU[0005] [ESTABLISHED]                                 protocol=tcp
DEBU[0005] [retransmission routine start ]               protocol=tcp
Server> Connection from 172.20.0.3:8888
Server> Read 1448 bytes
Server> Read 1448 bytes
Server> Read 1448 bytes
Server> Read 1448 bytes
Server> Read 1448 bytes
Server> Read 1448 bytes
Server> Read 1448 bytes
Server> Read 1448 bytes
Server> Read 1448 bytes
Server> Read 1448 bytes
Server> Read 1448 bytes
Server> Read 1448 bytes
Server> Read 1448 bytes
Server> Read 1448 bytes
Server> Read 208 bytes
Server> recv all buf 21720 bytes
Server> Write 20272 bytes
DEBU[0015] [CLOSED]                                      protocol=tcp
Server> close

License

Gotcp is under the MIT License: See LICENSE file.