read len first.

test.go

package main

import "net"
import "io"
import "encoding/binary"
import "fmt"

func handleConnection(conn net.Conn) {
	defer conn.Close()
	p := make([]byte, 4)
	_, err := io.ReadFull(conn, p)
	if err != nil {
		return
	}
	len := binary.LittleEndian.Uint32(p)
	fmt.Println("len: ", len)
	s := make([]byte, len)
	_, err = io.ReadFull(conn, s)
	fmt.Printf("str: %s", string(s))
}

func main() {
	ln, _ := net.Listen("tcp", ":8888")
	defer ln.Close()
	for {
		conn, _ := ln.Accept()
		go handleConnection(conn)
	}
}