uip.c

一个小的RTOS具有UIP网络功能

      if(uip_outstanding(uip_connr)) {
	--(uip_connr->timer);
	if(uip_connr->timer == 0) {
	  if(uip_connr->nrtx == UIP_MAXRTX ||
	     ((uip_connr->tcpstateflags == SYN_SENT ||
	       uip_connr->tcpstateflags == SYN_RCVD) &&
	      uip_connr->nrtx == UIP_MAXSYNRTX)) {
	    uip_connr->tcpstateflags = CLOSED;

	    /* We call UIP_APPCALL() with uip_flags set to
	       UIP_TIMEDOUT to inform the application that the
	       connection has timed out. */
	    uip_flags = UIP_TIMEDOUT;
	    UIP_APPCALL();

	    /* We also send a reset packet to the remote host. */
	    BUF->flags = TCP_RST | TCP_ACK;
	    goto tcp_send_nodata;
	  }

	  /* Exponential backoff. */
	  uip_connr->timer = UIP_RTO << (uip_connr->nrtx > 4?
					 4:
					 uip_connr->nrtx);
	  ++(uip_connr->nrtx);
	  
	  /* Ok, so we need to retransmit. We do this differently
	     depending on which state we are in. In ESTABLISHED, we
	     call upon the application so that it may prepare the
	     data for the retransmit. In SYN_RCVD, we resend the
	     SYNACK that we sent earlier and in LAST_ACK we have to
	     retransmit our FINACK. */
	  UIP_STAT(++uip_stat.tcp.rexmit);
	  switch(uip_connr->tcpstateflags & TS_MASK) {
	  case SYN_RCVD:
	    /* In the SYN_RCVD state, we should retransmit our
               SYNACK. */
	    goto tcp_send_synack;
	    
#if UIP_ACTIVE_OPEN
	  case SYN_SENT:
	    /* In the SYN_SENT state, we retransmit out SYN. */
	    BUF->flags = 0;
	    goto tcp_send_syn;
#endif /* UIP_ACTIVE_OPEN */
	    
	  case ESTABLISHED:
	    /* In the ESTABLISHED state, we call upon the application
               to do the actual retransmit after which we jump into
               the code for sending out the packet (the apprexmit
               label). */
	    uip_len = 0;
	    uip_slen = 0;
	    uip_flags = UIP_REXMIT;
	    UIP_APPCALL();
	    goto apprexmit;
	    
	  case FIN_WAIT_1:
	  case CLOSING:
	  case LAST_ACK:
	    /* In all these states we should retransmit a FINACK. */
	    goto tcp_send_finack;
	    
	  }
	}
      } else if((uip_connr->tcpstateflags & TS_MASK) == ESTABLISHED) {
	/* If there was no need for a retransmission, we poll the
           application for new data. */
	uip_len = 0;
	uip_slen = 0;
	uip_flags = UIP_POLL;
	UIP_APPCALL();
	goto appsend;
      }
    }
    goto drop;
  }
#if UIP_UDP 
  if(flag == UIP_UDP_TIMER) {
    if(uip_udp_conn->lport != 0) {
      uip_appdata = &uip_buf[UIP_LLH_LEN + 28];
      uip_len = uip_slen = 0;
      uip_flags = UIP_POLL;
      UIP_UDP_APPCALL();
      goto udp_send;
    } else {
      goto drop;
    }
  }
#endif

  /* This is where the input processing starts. */
  UIP_STAT(++uip_stat.ip.recv);


  /* Start of IPv4 input header processing code. */
  
  /* Check validity of the IP header. */  
  if(BUF->vhl != 0x45)  { /* IP version and header length. */
    UIP_STAT(++uip_stat.ip.drop);
    UIP_STAT(++uip_stat.ip.vhlerr);
    UIP_LOG("ip: invalid version or header length.");
    goto drop;
  }
  
  /* Check the size of the packet. If the size reported to us in
     uip_len doesn't match the size reported in the IP header, there
     has been a transmission error and we drop the packet. */
  
#if UIP_BUFSIZE > 255
  if(BUF->len[0] != (uip_len >> 8)) { /* IP length, high byte. */
    uip_len = (uip_len & 0xff) | (BUF->len[0] << 8);
  }
  if(BUF->len[1] != (uip_len & 0xff)) { /* IP length, low byte. */
    uip_len = (uip_len & 0xff00) | BUF->len[1];
  }
#else
  if(BUF->len[0] != 0) {        /* IP length, high byte. */
    UIP_STAT(++uip_stat.ip.drop);
    UIP_STAT(++uip_stat.ip.hblenerr);
    UIP_LOG("ip: invalid length, high byte.");
    goto drop;
  }
  if(BUF->len[1] != uip_len) {  /* IP length, low byte. */
    uip_len = BUF->len[1];
  }
#endif /* UIP_BUFSIZE > 255 */  

  if(BUF->ipoffset[0] & 0x3f) { /* We don't allow IP fragments. */
    UIP_STAT(++uip_stat.ip.drop);
    UIP_STAT(++uip_stat.ip.fragerr);
    UIP_LOG("ip: fragment dropped.");    
    goto drop;
  }

  /* If we are configured to use ping IP address configuration and
     hasn't been assigned an IP address yet, we accept all ICMP
     packets. */
#if UIP_PINGADDRCONF
  if((uip_hostaddr[0] | uip_hostaddr[1]) == 0) {
    if(BUF->proto == UIP_PROTO_ICMP) {
      UIP_LOG("ip: possible ping config packet received.");
      goto icmp_input;
    } else {
      UIP_LOG("ip: packet dropped since no address assigned..");
      goto drop;
    }
  }
#endif /* UIP_PINGADDRCONF */
  
  /* Check if the packet is destined for our IP address. */  
  if(BUF->destipaddr[0] != uip_hostaddr[0]) {
    UIP_STAT(++uip_stat.ip.drop);
    UIP_LOG("ip: packet not for us.");        
    goto drop;
  }
  if(BUF->destipaddr[1] != uip_hostaddr[1]) {
    UIP_STAT(++uip_stat.ip.drop);
    UIP_LOG("ip: packet not for us.");        
    goto drop;
  }

  if(uip_ipchksum() != 0xffff) { /* Compute and check the IP header
				    checksum. */
    UIP_STAT(++uip_stat.ip.drop);
    UIP_STAT(++uip_stat.ip.chkerr);
    UIP_LOG("ip: bad checksum.");    
    goto drop;
  }

  if(BUF->proto == UIP_PROTO_TCP)  /* Check for TCP packet. If so, jump
                                     to the tcp_input label. */
    goto tcp_input;

#if UIP_UDP
  if(BUF->proto == UIP_PROTO_UDP)
    goto udp_input;
#endif /* UIP_UDP */

  if(BUF->proto != UIP_PROTO_ICMP) { /* We only allow ICMP packets from
					here. */
    UIP_STAT(++uip_stat.ip.drop);
    UIP_STAT(++uip_stat.ip.protoerr);
    UIP_LOG("ip: neither tcp nor icmp.");        
    goto drop;
  }
  
 icmp_input:
  UIP_STAT(++uip_stat.icmp.recv);
  
  /* ICMP echo (i.e., ping) processing. This is simple, we only change
     the ICMP type from ECHO to ECHO_REPLY and adjust the ICMP
     checksum before we return the packet. */
  if(ICMPBUF->type != ICMP_ECHO) {
    UIP_STAT(++uip_stat.icmp.drop);
    UIP_STAT(++uip_stat.icmp.typeerr);
    UIP_LOG("icmp: not icmp echo.");
    goto drop;
  }

  /* If we are configured to use ping IP address assignment, we use
     the destination IP address of this ping packet and assign it to
     ourself. */
#if UIP_PINGADDRCONF
  if((uip_hostaddr[0] | uip_hostaddr[1]) == 0) {
    uip_hostaddr[0] = BUF->destipaddr[0];
    uip_hostaddr[1] = BUF->destipaddr[1];
  }
#endif /* UIP_PINGADDRCONF */  
  
  ICMPBUF->type = ICMP_ECHO_REPLY;
  
  if(ICMPBUF->icmpchksum >= HTONS(0xffff - (ICMP_ECHO << 8))) {
    ICMPBUF->icmpchksum += HTONS(ICMP_ECHO << 8) + 1;
  } else {
    ICMPBUF->icmpchksum += HTONS(ICMP_ECHO << 8);
  }
  
  /* Swap IP addresses. */
  tmpport = BUF->destipaddr[0];
  BUF->destipaddr[0] = BUF->srcipaddr[0];
  BUF->srcipaddr[0] = tmpport;
  tmpport = BUF->destipaddr[1];
  BUF->destipaddr[1] = BUF->srcipaddr[1];
  BUF->srcipaddr[1] = tmpport;

  UIP_STAT(++uip_stat.icmp.sent);
  goto send;

  /* End of IPv4 input header processing code. */
  

#if UIP_UDP
  /* UDP input processing. */
 udp_input:
  /* UDP processing is really just a hack. We don't do anything to the
     UDP/IP headers, but let the UDP application do all the hard
     work. If the application sets uip_slen, it has a packet to
     send. */
#if UIP_UDP_CHECKSUMS
  if(uip_udpchksum() != 0xffff) { 
    UIP_STAT(++uip_stat.udp.drop);
    UIP_STAT(++uip_stat.udp.chkerr);
    UIP_LOG("udp: bad checksum.");    
    goto drop;
  }  
#endif /* UIP_UDP_CHECKSUMS */

  /* Demultiplex this UDP packet between the UDP "connections". */
  for(uip_udp_conn = &uip_udp_conns[0];
      uip_udp_conn < &uip_udp_conns[UIP_UDP_CONNS];
      ++uip_udp_conn) {
    if(uip_udp_conn->lport != 0 &&
       UDPBUF->destport == uip_udp_conn->lport &&
       (uip_udp_conn->rport == 0 ||
        UDPBUF->srcport == uip_udp_conn->rport) &&
       BUF->srcipaddr[0] == uip_udp_conn->ripaddr[0] &&
       BUF->srcipaddr[1] == uip_udp_conn->ripaddr[1]) {
      goto udp_found; 
    }
  }
  goto drop;
  
 udp_found:
  uip_len = uip_len - 28;
  uip_appdata = &uip_buf[UIP_LLH_LEN + 28];
  uip_flags = UIP_NEWDATA;
  uip_slen = 0;
  UIP_UDP_APPCALL();
 udp_send:
  if(uip_slen == 0) {
    goto drop;      
  }
  uip_len = uip_slen + 28;

#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 */  
  BUF->proto = UIP_PROTO_UDP;

  UDPBUF->udplen = HTONS(uip_slen + 8);
  UDPBUF->udpchksum = 0;
#if UIP_UDP_CHECKSUMS 
  /* Calculate UDP checksum. */
  UDPBUF->udpchksum = ~(uip_udpchksum());
  if(UDPBUF->udpchksum == 0) {
    UDPBUF->udpchksum = 0xffff;
  }
#endif /* UIP_UDP_CHECKSUMS */

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

  BUF->srcipaddr[0] = uip_hostaddr[0];
  BUF->srcipaddr[1] = uip_hostaddr[1];
  BUF->destipaddr[0] = uip_udp_conn->ripaddr[0];
  BUF->destipaddr[1] = uip_udp_conn->ripaddr[1];
 
  uip_appdata = &uip_buf[UIP_LLH_LEN + 40];
  goto ip_send_nolen;
#endif /* UIP_UDP */
  
  /* TCP input processing. */  
 tcp_input:
  UIP_STAT(++uip_stat.tcp.recv);

  /* Start of TCP input header processing code. */
  
  if(uip_tcpchksum() != 0xffff) {   /* Compute and check the TCP
				       checksum. */
    UIP_STAT(++uip_stat.tcp.drop);
    UIP_STAT(++uip_stat.tcp.chkerr);
    UIP_LOG("tcp: bad checksum.");    
    goto drop;
  }
  
  /* Demultiplex this segment. */
  /* First check any active connections. */
  for(uip_connr = &uip_conns[0]; uip_connr < &uip_conns[UIP_CONNS]; ++uip_connr) {
    if(uip_connr->tcpstateflags != CLOSED &&
       BUF->destport == uip_connr->lport &&
       BUF->srcport == uip_connr->rport &&
       BUF->srcipaddr[0] == uip_connr->ripaddr[0] &&
       BUF->srcipaddr[1] == uip_connr->ripaddr[1]) {
      goto found;    
    }
  }

  /* If we didn't find and active connection that expected the packet,
     either this packet is an old duplicate, or this is a SYN packet
     destined for a connection in LISTEN. If the SYN flag isn't set,
     it is an old packet and we send a RST. */
  if((BUF->flags & TCP_CTL) != TCP_SYN)
    goto reset;
  
  tmpport = BUF->destport;
  /* Next, check listening connections. */  
  for(c = 0; c < UIP_LISTENPORTS; ++c) {
    if(tmpport == uip_listenports[c])
      goto found_listen;
  }
  
  /* No matching connection found, so we send a RST packet. */
  UIP_STAT(++uip_stat.tcp.synrst);
 reset:

  /* We do not send resets in response to resets. */
  if(BUF->flags & TCP_RST) 
    goto drop;

  UIP_STAT(++uip_stat.tcp.rst);
  
  BUF->flags = TCP_RST | TCP_ACK;
  uip_len = 40;
  BUF->tcpoffset = 5 << 4;

  /* Flip the seqno and ackno fields in the TCP header. */
  c = BUF->seqno[3];
  BUF->seqno[3] = BUF->ackno[3];  
  BUF->ackno[3] = c;
  
  c = BUF->seqno[2];
  BUF->seqno[2] = BUF->ackno[2];  
  BUF->ackno[2] = c;
  
  c = BUF->seqno[1];
  BUF->seqno[1] = BUF->ackno[1];
  BUF->ackno[1] = c;
  
  c = BUF->seqno[0];
  BUF->seqno[0] = BUF->ackno[0];  
  BUF->ackno[0] = c;

  /* We also have to increase the sequence number we are
     acknowledging. If the least significant byte overflowed, we need
     to propagate the carry to the other bytes as well. */
  if(++BUF->ackno[3] == 0) {
    if(++BUF->ackno[2] == 0) {
      if(++BUF->ackno[1] == 0) {
	++BUF->ackno[0];
      }
    }
  }
 
  /* Swap port numbers. */
  tmpport = BUF->srcport;
  BUF->srcport = BUF->destport;
  BUF->destport = tmpport;
  
  /* Swap IP addresses. */
  tmpport = BUF->destipaddr[0];
  BUF->destipaddr[0] = BUF->srcipaddr[0];
  BUF->srcipaddr[0] = tmpport;
  tmpport = BUF->destipaddr[1];
  BUF->destipaddr[1] = BUF->srcipaddr[1];
  BUF->srcipaddr[1] = tmpport;

  
  /* And send out the RST packet! */
  goto tcp_send_noconn;

  /* This label will be jumped to if we matched the incoming packet
     with a connection in LISTEN. In that case, we should create a new
     connection and send a SYNACK in return. */
 found_listen:
  /* First we check if there are any connections avaliable. Unused
     connections are kept in the same table as used connections, but
     unused ones have the tcpstate set to CLOSED. Also, connections in
     TIME_WAIT are kept track of and we'll use the oldest one if no
     CLOSED connections are found. Thanks to Eddie C. Dost for a very
     nice algorithm for the TIME_WAIT search. */
  uip_connr = 0;
  for(c = 0; c < UIP_CONNS; ++c) {
    if(uip_conns[c].tcpstateflags == CLOSED) {
      uip_connr = &uip_conns[c];
      break;
    }
    if(uip_conns[c].tcpstateflags == TIME_WAIT) {
      if(uip_connr == 0 ||
	 uip_conns[c].timer > uip_connr->timer) {
	uip_connr = &uip_conns[c];
      }
    }
  }

  if(uip_connr == 0) {
    /* All connections are used already, we drop packet and hope that
       the remote end will retransmit the packet at a time when we
       have more spare connections. */
    UIP_STAT(++uip_stat.tcp.syndrop);
    UIP_LOG("tcp: found no unused connections.");
    goto drop;
  }
  uip_conn = uip_connr;
  
  /* Fill in the necessary fields for the new connection. */
  uip_connr->timer = UIP_RTO;
  uip_connr->nrtx = 0;
  uip_connr->lport = BUF->destport;
  uip_connr->rport = BUF->srcport;
  uip_connr->ripaddr[0] = BUF->srcipaddr[0];
  uip_connr->ripaddr[1] = BUF->srcipaddr[1];
  uip_connr->tcpstateflags = SYN_RCVD;

  uip_connr->snd_nxt[0] = iss[0];
  uip_connr->snd_nxt[1] = iss[1];
  uip_connr->snd_nxt[2] = iss[2];
  uip_connr->snd_nxt[3] = iss[3];
  uip_connr->len = 1;

  /* rcv_nxt should be the seqno from the incoming packet + 1. */
  uip_connr->rcv_nxt[3] = BUF->seqno[3];
  uip_connr->rcv_nxt[2] = BUF->seqno[2];
  uip_connr->rcv_nxt[1] = BUF->seqno[1];
  uip_connr->rcv_nxt[0] = BUF->seqno[0];
  uip_add_rcv_nxt(1);

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