如何基于udp实现tcp协议栈

//定义枚举：
enmu state{
CLOSED，//没有连接
SYN-SENT，//发送了syn，等代服务器ack
ACK_RECEIVE,//接到服务器ack
SYNACK_SEND,//恢复服务器的ack，确认
ESTABLISHED，//成功建立
}
//定义你自己的用udp连接函数
int newconnect( int sd, const struct sockaddr * sa, int namelen )
{
int err = -1;
int state = CLOSED；
char ** buff[128] = {"syn","synack"};
char buffrom[128];
memset(buff,0,128);
while(true)//开始状态机转换
{
if( state == ESTABLISHED )
break;
switch(state)
{
case CLOSED:
err = sendto( sd, buff[0], strlen(buff[0]), 0, sa, namelen );
if( err == SOCKET_ERROR )
goto error；
state = SYN-SENT；
break;
case SYN-SENT:
err = recvfrom( sd, buffrom, strlen(buffrom), sa, namelen );
if( err == SOCKET_ERROR )
goto error；
if( !strcmp(buffom,"ack",3) )
state = ACK_RECEIVE；
break；
case ACK_RECEIVE:
err = sendto( sd, buff[1], strlen(buff[1]), 0, sa, namelen );
if( err == SOCKET_ERROR )
goto error；
state = ESTABLISHED:
break;
case ESTABLISHED:
break;
default:
break;
}

}
return sd;
err:
closesocket(sd);
return NULL;
}