tcpsvr.go

package main

import (
	"bufio"
	"bytes"
	"encoding/binary"
	"fmt"
	"io"
	"log"
	"net"
)

func splitChunk(data []byte, atEOF bool) (int, []byte, error) {
	if len(data) == 0 && atEOF {
		return 0, nil, io.EOF
	}
	buf := bytes.NewReader(data)
	var dataSize uint32
	err := binary.Read(buf, binary.LittleEndian, &dataSize)
	if err != nil {
		if atEOF {
			return 0, nil, fmt.Errorf("too short data")
		}
		return 0, nil, nil // read more
	}
	dataSizeWithSizeHeader := dataSize + 4
	if uint32(len(data)) < dataSizeWithSizeHeader {
		if atEOF {
			return 0, nil, fmt.Errorf("too short data")
		}
		return 0, nil, nil // read more
	}
	return int(dataSizeWithSizeHeader), data[4:dataSizeWithSizeHeader], nil
}

type ClientID int

var lastClientID ClientID

type Client struct {
	ID   ClientID
	conn net.Conn
}

func NewClient(conn net.Conn) *Client {
	lastClientID++
	return &Client{ID: lastClientID, conn: conn}
}

func (c *Client) Activate() {
	defer c.conn.Close()
	scanner := bufio.NewScanner(c.conn)
	scanner.Split(splitChunk)
	for scanner.Scan() {
		log.Printf("client[%d]: %s", c.ID, scanner.Text())
	}
	if err := scanner.Err(); err != nil {
		log.Printf("client[%d]: %s", c.ID, err)
	} else {
		log.Printf("client[%d]: disconnected", c.ID)
	}
}

type App struct {
	clients map[ClientID]*Client
}

func NewApp() *App {
	return &App{
		clients: make(map[ClientID]*Client),
	}
}

func (a *App) HandleConnection(conn net.Conn) {
	log.Printf("app: new conection")
	c := NewClient(conn)
	a.clients[c.ID] = c
	c.Activate()
}

func main() {
	app := NewApp()
	log.Printf("listen to :5000")
	l, err := net.Listen("tcp", ":5000")
	if err != nil {
		log.Fatal(err)
	}
	for {
		conn, err := l.Accept()
		if err != nil {
			log.Fatal(err)
		}
		go app.HandleConnection(conn)
	}
}

tcpsvr_test.sh

#!/bin/bash
set -eux

# OK
printf "\x0D\x00\x00\x00%s" 'Hello, world!' | nc localhost 5000

# too short data
printf "\x0D\x00\x00\x00%s" 'Hello, world! ' | nc localhost 5000

# OK
printf "\x0D\x00\x00\x00%s\x03\x00\x00\x00%s" 'Hello, world!' 'Hi!' | nc localhost 5000