uip.c

完整的实现RS232与TCP/IP网络协议的转换

  /* Next, check if the incoming segment acknowledges any outstanding
     data. If so, we also reset the retransmission timer. */
  if(BUF->ackno[0] == uip_conn->ack_nxt[0] &&
     BUF->ackno[1] == uip_conn->ack_nxt[1] &&
     BUF->ackno[2] == uip_conn->ack_nxt[2] &&
     BUF->ackno[3] == uip_conn->ack_nxt[3]) {
    uip_conn->snd_nxt[0] = uip_conn->ack_nxt[0];
    uip_conn->snd_nxt[1] = uip_conn->ack_nxt[1];
    uip_conn->snd_nxt[2] = uip_conn->ack_nxt[2];
    uip_conn->snd_nxt[3] = uip_conn->ack_nxt[3];
    if(uip_conn->tcpstateflags & UIP_OUTSTANDING) {
      uip_flags = UIP_ACKDATA;
      uip_conn->tcpstateflags &= ~UIP_OUTSTANDING;
      uip_conn->timer = UIP_RTO;
    }
  }

  /* Do different things depending on in what state the connection is. */
  switch(uip_conn->tcpstateflags & TS_MASK) {
    /* CLOSED and LISTEN are not handled here. CLOSE_WAIT is not
	implemented, since we force the application to close when the
	peer sends a FIN (hence the application goes directly from
	ESTABLISHED to LAST_ACK). */
  case SYN_RCVD:
    /* In SYN_RCVD we have sent out a SYNACK in response to a SYN, and
       we are waiting for an ACK that acknowledges the data we sent
       out the last time. Therefore, we want to have the UIP_ACKDATA
       flag set. If so, we enter the ESTABLISHED state. */
    if(uip_flags & UIP_ACKDATA) {
      uip_conn->tcpstateflags = ESTABLISHED;
      uip_flags = UIP_CONNECTED;
      uip_len = 0;
      UIP_APPCALL();
      goto appsend;
    }
    goto drop;
#if UIP_ACTIVE_OPEN
  case SYN_SENT:
    /* In SYN_SENT, we wait for a SYNACK that is sent in response to
       our SYN. The rcv_nxt is set to sequence number in the SYNACK
       plus one, and we send an ACK. We move into the ESTABLISHED
       state. */
    if((uip_flags & UIP_ACKDATA) &&
       BUF->flags == (TCP_SYN | TCP_ACK)) {

      /* Parse the TCP MSS option, if present. */
      if((BUF->tcpoffset & 0xf0) > 0x50) {
	for(c = 0; c < ((BUF->tcpoffset >> 4) - 5) << 2 ;) {
	  opt = uip_buf[40 + UIP_LLH_LEN + c];
	  if(opt == 0x00) {
	    /* End of options. */	
	    break;
	  } else if(opt == 0x01) {
	    ++c;
	    /* NOP option. */
	  } else if(opt == 0x02 &&
		    uip_buf[40 + UIP_LLH_LEN + c + 1] == 0x04) {
	    /* An MSS option with the right option length. */
	    tmpport = (uip_buf[40 + UIP_LLH_LEN + c + 2] << 8) |
	      uip_buf[40 + UIP_LLH_LEN + c + 3];
	    uip_conn->mss = tmpport > UIP_TCP_MSS? UIP_TCP_MSS: tmpport;

	    /* And we are done processing options. */
	    break;
	  } else {
	    /* All other options have a length field, so that we easily
	       can skip past them. */
	    c += uip_buf[40 + UIP_LLH_LEN + c + 1];
	  }      
	}
      }  

      uip_conn->tcpstateflags = ESTABLISHED;      
      uip_conn->rcv_nxt[0] = BUF->seqno[0];
      uip_conn->rcv_nxt[1] = BUF->seqno[1];
      uip_conn->rcv_nxt[2] = BUF->seqno[2];
      uip_conn->rcv_nxt[3] = BUF->seqno[3];
      uip_add_rcv_nxt(1);
      uip_flags = UIP_CONNECTED | UIP_NEWDATA;
      uip_len = 0;
      UIP_APPCALL();
      goto appsend;
    }
    goto drop;
#endif /* UIP_ACTIVE_OPEN */
    
  case ESTABLISHED:
    /* In the ESTABLISHED state, we call upon the application to feed
    data into the uip_buf. If the UIP_ACKDATA flag is set, the
    application should put new data into the buffer, otherwise we are
    retransmitting an old segment, and the application should put that
    data into the buffer.

    If the incoming packet is a FIN, we should close the connection on
    this side as well, and we send out a FIN and enter the LAST_ACK
    state. We require that the FIN will have to acknowledge all
    outstanding data, otherwise we drop it. */

    if(BUF->flags & TCP_FIN) {
      uip_add_rcv_nxt(1 + uip_len);
      uip_flags = UIP_CLOSE;
      uip_len = 0;
      UIP_APPCALL();
      uip_add_ack_nxt(1);
      uip_conn->tcpstateflags = LAST_ACK | UIP_OUTSTANDING;
      uip_conn->nrtx = 0;
    tcp_send_finack:
      BUF->flags = TCP_FIN | TCP_ACK;      
      goto tcp_send_nodata;
    }

    
    /* If uip_len > 0 we have TCP data in the packet, and we flag this
       by setting the UIP_NEWDATA flag and update the sequence number
       we acknowledge. If the application has stopped the dataflow
       using uip_stop(), we must not accept any data packets from the
       remote host. */
    if(uip_len > 0 && !(uip_conn->tcpstateflags & UIP_STOPPED)) {
      uip_flags |= UIP_NEWDATA;
      uip_add_rcv_nxt(uip_len);
    }
    

    /* If this packet constitutes an ACK for outstanding data (flagged
       by the UIP_ACKDATA flag, we should call the application since it
       might want to send more data. If the incoming packet had data
       from the peer (as flagged by the UIP_NEWDATA flag), the
       application must also be notified.

       When the application is called, the global variable uip_len
       contains the length of the incoming data. The application can
       access the incoming data through the global pointer
       uip_appdata, which usually points 40 bytes into the uip_buf
       array.

       If the application wishes to send any data, this data should be
       put into the uip_appdata and the length of the data should be
       put into uip_len. If the application don't have any data to
       send, uip_len must be set to 0. */
    if(uip_flags & (UIP_NEWDATA | UIP_ACKDATA)) {
      UIP_APPCALL();

    appsend:
      if(uip_flags & UIP_ABORT) {
	uip_conn->tcpstateflags = CLOSED;
	BUF->flags = TCP_RST | TCP_ACK;
	goto tcp_send_nodata;
      }

      if(uip_flags & UIP_CLOSE) {
	uip_add_ack_nxt(1);
	uip_conn->tcpstateflags = FIN_WAIT_1 | UIP_OUTSTANDING;
	uip_conn->nrtx = 0;
	BUF->flags = TCP_FIN | TCP_ACK;
	goto tcp_send_nodata;	
      }

      /* If uip_len > 0, the application has data to be sent, in which
         case we set the UIP_OUTSTANDING flag in the connection
         structure. But we cannot send data if the application already
         has outstanding data. */
      if(uip_len > 0 &&
	 !(uip_conn->tcpstateflags & UIP_OUTSTANDING)) {
	uip_conn->tcpstateflags |= UIP_OUTSTANDING;
	uip_conn->nrtx = 0;
	uip_add_ack_nxt(uip_len);
      } else {
	uip_len = 0;
      }
    apprexmit:
      /* If the application has data to be sent, or if the incoming
         packet had new data in it, we must send out a packet. */
      if(uip_len > 0 || (uip_flags & UIP_NEWDATA)) {
	/* Add the length of the IP and TCP headers. */
	uip_len = uip_len + 40;
	/* We always set the ACK flag in response packets. */
	BUF->flags = TCP_ACK;
	/* Send the packet. */
	goto tcp_send_noopts;
      }
    }
    goto drop;
  case LAST_ACK:
    /* We can close this connection if the peer has acknowledged our
       FIN. This is indicated by the UIP_ACKDATA flag. */     
    if(uip_flags & UIP_ACKDATA) {
      uip_conn->tcpstateflags = CLOSED;
    }
    break;
    
  case FIN_WAIT_1:
    /* The application has closed the connection, but the remote host
       hasn't closed its end yet. Thus we do nothing but wait for a
       FIN from the other side. */
    if(uip_len > 0) {
      uip_add_rcv_nxt(uip_len);
    }
    if(BUF->flags & TCP_FIN) {
      if(uip_flags & UIP_ACKDATA) {
	uip_conn->tcpstateflags = TIME_WAIT;
	uip_conn->timer = 0;
      } else {
	uip_conn->tcpstateflags = CLOSING | UIP_OUTSTANDING;
      }
      uip_add_rcv_nxt(1);
      goto tcp_send_ack;
    } else if(uip_flags & UIP_ACKDATA) {
      uip_conn->tcpstateflags = FIN_WAIT_2;
      goto drop;
    }
    if(uip_len > 0) {
      goto tcp_send_ack;
    }
    goto drop;
      
  case FIN_WAIT_2:
    if(uip_len > 0) {
      uip_add_rcv_nxt(uip_len);
    }
    if(BUF->flags & TCP_FIN) {
      uip_conn->tcpstateflags = TIME_WAIT;
      uip_conn->timer = 0;
      uip_add_rcv_nxt(1);
      goto tcp_send_ack;
    }
    if(uip_len > 0) {
      goto tcp_send_ack;
    }
    goto drop;

  case TIME_WAIT:
    goto tcp_send_ack;
    
  case CLOSING:
    if(uip_flags & UIP_ACKDATA) {
      uip_conn->tcpstateflags = TIME_WAIT;
      uip_conn->timer = 0;
    }
  }  
  goto drop;
  

  /* We jump here when we are ready to send the packet, and just want
     to set the appropriate TCP sequence numbers in the TCP header. */
 tcp_send_ack:
  BUF->flags = TCP_ACK;
 tcp_send_nodata:
  uip_len = 40;
 tcp_send_noopts:
  BUF->tcpoffset = 5 << 4;
 tcp_send:
  /* We're done with the input processing. We are now ready to send a
     reply. Our job is to fill in all the fields of the TCP and IP
     headers before calculating the checksum and finally send the
     packet. */    
  BUF->ackno[0] = uip_conn->rcv_nxt[0];
  BUF->ackno[1] = uip_conn->rcv_nxt[1];
  BUF->ackno[2] = uip_conn->rcv_nxt[2];
  BUF->ackno[3] = uip_conn->rcv_nxt[3];
  
  BUF->seqno[0] = uip_conn->snd_nxt[0];
  BUF->seqno[1] = uip_conn->snd_nxt[1];
  BUF->seqno[2] = uip_conn->snd_nxt[2];
  BUF->seqno[3] = uip_conn->snd_nxt[3];

  BUF->srcport  = uip_conn->lport;
  BUF->destport = uip_conn->rport;

#if BYTE_ORDER == BIG_ENDIAN  
  BUF->srcipaddr[0] = ((UIP_IPADDR0 << 8) | UIP_IPADDR1);
  BUF->srcipaddr[1] = ((UIP_IPADDR2 << 8) | UIP_IPADDR3);
#else
  BUF->srcipaddr[0] = ((UIP_IPADDR1 << 8) | UIP_IPADDR0);
  BUF->srcipaddr[1] = ((UIP_IPADDR3 << 8) | UIP_IPADDR2);
#endif /* BYTE_ORDER == BIG_ENDIAN */

  BUF->destipaddr[0] = uip_conn->ripaddr[0];
  BUF->destipaddr[1] = uip_conn->ripaddr[1];

  if(uip_conn->tcpstateflags & UIP_STOPPED) {
    /* If the connection has issued uip_stop(), we advertise a zero
       window so that the remote host will stop sending data. */
    BUF->wnd[0] = BUF->wnd[1] = 0;
  } else {
#if (UIP_TCP_MSS) > 255
    BUF->wnd[0] = (uip_conn->mss >> 8);
#else
    BUF->wnd[0] = 0;
#endif /* UIP_MSS */
    BUF->wnd[1] = (uip_conn->mss & 0xff); 
  }
  
 tcp_send_noconn:

  BUF->vhl = 0x45;
  BUF->tos = 0;
  BUF->ipoffset[0] = BUF->ipoffset[1] = 0;
  BUF->ttl  = UIP_TTL;
  BUF->proto = IP_PROTO_TCP;

#if UIP_BUFSIZE > 255
  BUF->len[0] = (uip_len >> 8);
  BUF->len[1] = (uip_len & 0xff);
#else
  BUF->len[0] = 0;
  BUF->len[1] = uip_len;
#endif /* UIP_BUFSIZE > 255 */
  
  ++ipid;
  BUF->ipid[0] = ipid >> 8;
  BUF->ipid[1] = ipid & 0xff;
  
  /* Calculate IP and TCP checksums. */
  BUF->ipchksum = 0;
  BUF->ipchksum = ~(uip_ipchksum());
  BUF->tcpchksum = 0;
  BUF->tcpchksum = ~(uip_tcpchksum());

  UIP_STAT(++uip_stat.tcp.sent);
 send:
  UIP_STAT(++uip_stat.ip.sent);
  /* The data that should be sent is not present in the uip_buf, and
     the length of the data is in the variable uip_len. It is not our
     responsibility to do the actual sending of the data however. That
     is taken care of by the wrapper code, and only if uip_len > 0. */
  return;
 drop:
  uip_len = 0;
  return;
}
/*-----------------------------------------------------------------------------------*/