LionNatsu / dgtcp

An implementation of TCP-based datagram-style protocol

DGTCP

Overview

Datagram Transmission Control Protocol (DGTCP) is an TCP-based datagram-style protocol. It provide a datagram model over TCP (which is stream model).

DGTCP can handle packets not larger than 65536 bytes.

Protocol Details

For sending a packet, DGTCP sends two bytes firstly, to show the length of the following data, in network order i.e. big-endian byte order.

Here is an example of 2 packets sent in DGTCP.

[ packet #1: 00 01 02 ...(0x1FF bytes) ]
[ packet #2: 23 12 AB ]
...

The following chart shows how these two packets was sent in the underlying TCP stream.

<len> <          data         >   <len> < data >   ...
01 FF 00 01 02 ...(0x1FF bytes)   00 03 23 12 AB   ...

Golang Package

Package dgtcp overrides Read() and Write() methods of net.TCPConn.

Usage & Example

Client:

package main

import (
	"net"

	"github.com/LionNatsu/dgtcp"
)

func main() {
	connRaw, _ := net.Dial("tcp", "[::1]:50000")
	conn := dgtcp.New(connRaw) // <=
	buf := make([]byte, 20000)
	conn.Write(buf)
	conn.Close()
}

Server:

package main

import (
	"fmt"
	"net"

	"github.com/LionNatsu/dgtcp"
)

func main() {
	listener, _ := net.Listen("tcp", "[::1]:50000")
	defer listener.Close()
	for {
		conn, _ := listener.Accept()
		go process(conn)
	}
}

func process(connRaw net.Conn) {
	conn := dgtcp.New(connRaw)
	buf := make([]byte, 65536)
	size, _ := conn.Read(buf)
	fmt.Println("recieved:", buf[:size], "from", conn.RemoteAddr())
	conn.Close()
}