tcp_in.c

网络服务器上实现操作系统和嵌入式协议栈的 结合

          pcb->snd_nxt = htonl(pcb->unsent->tcphdr->seqno);
        }
      }
      
    /* End of ACK for new data processing. */
    
    DEBUGF(TCP_RTO_DEBUG, ("tcp_receive: pcb->rttest %d rtseq %lu ackno %lu\n",
	   pcb->rttest, pcb->rtseq, ackno));
    
    /* RTT estimation calculations. This is done by checking if the
       incoming segment acknowledges the segment we use to take a
       round-trip time measurement. */
    if(pcb->rttest && TCP_SEQ_LT(pcb->rtseq, ackno)) {
      m = tcp_ticks - pcb->rttest;

      DEBUGF(TCP_RTO_DEBUG, ("tcp_receive: experienced rtt %d ticks (%d msec).\n",
	     m, m * TCP_SLOW_INTERVAL));

      /* This is taken directly from VJs original code in his paper */      
      m = m - (pcb->sa >> 3);
      pcb->sa += m;
      if(m < 0) {
	m = -m;
      }
      m = m - (pcb->sv >> 2);
      pcb->sv += m;
      pcb->rto = (pcb->sa >> 3) + pcb->sv;
      
      DEBUGF(TCP_RTO_DEBUG, ("tcp_receive: RTO %d (%d miliseconds)\n",
			     pcb->rto, pcb->rto * TCP_SLOW_INTERVAL));

      pcb->rttest = 0;
    } 
  }
  
  /* If the incoming segment contains data, we must process it
     further. */
  if(tcplen > 0) {
    /* This code basically does three things:

     +) If the incoming segment contains data that is the next
        in-sequence data, this data is passed to the application. This
        might involve trimming the first edge of the data. The rcv_nxt
        variable and the advertised window are adjusted.       

     +) If the incoming segment has data that is above the next
        sequence number expected (->rcv_nxt), the segment is placed on
        the ->ooseq queue. This is done by finding the appropriate
        place in the ->ooseq queue (which is ordered by sequence
        number) and trim the segment in both ends if needed. An
        immediate ACK is sent to indicate that we received an
        out-of-sequence segment.

     +) Finally, we check if the first segment on the ->ooseq queue
        now is in sequence (i.e., if rcv_nxt >= ooseq->seqno). If
        rcv_nxt > ooseq->seqno, we must trim the first edge of the
        segment on ->ooseq before we adjust rcv_nxt. The data in the
        segments that are now on sequence are chained onto the
        incoming segment so that we only need to call the application
        once.
    */

    /* First, we check if we must trim the first edge. We have to do
       this if the sequence number of the incoming segment is less
       than rcv_nxt, and the sequence number plus the length of the
       segment is larger than rcv_nxt. */
    if(TCP_SEQ_LT(seqno, pcb->rcv_nxt)){
      if(TCP_SEQ_LT(pcb->rcv_nxt, seqno + tcplen)) {
	/* Trimming the first edge is done by pushing the payload
	   pointer in the pbuf downwards. This is somewhat tricky since
	   we do not want to discard the full contents of the pbuf up to
	   the new starting point of the data since we have to keep the
	   TCP header which is present in the first pbuf in the chain.
	   
	   What is done is really quite a nasty hack: the first pbuf in
	   the pbuf chain is pointed to by inseg.p. Since we need to be
	   able to deallocate the whole pbuf, we cannot change this
	   inseg.p pointer to point to any of the later pbufs in the
	   chain. Instead, we point the ->payload pointer in the first
	   pbuf to data in one of the later pbufs. We also set the
	   inseg.data pointer to point to the right place. This way, the
	   ->p pointer will still point to the first pbuf, but the
	   ->p->payload pointer will point to data in another pbuf.
	   
	   After we are done with adjusting the pbuf pointers we must
	   adjust the ->data pointer in the seg and the segment
	   length.*/
	off = pcb->rcv_nxt - seqno;
	if(inseg.p->len < off) {
	  p = inseg.p;
	  while(p->len < off) {
	    off -= p->len;
	    inseg.p->tot_len -= p->len;
	    p->len = 0;
	    p = p->next;
	  }
	  pbuf_header(p, -off);
	} else {
	  pbuf_header(inseg.p, -off);
	}
	inseg.dataptr = inseg.p->payload;
	inseg.len -= pcb->rcv_nxt - seqno;      
	inseg.tcphdr->seqno = seqno = pcb->rcv_nxt;
      }
      else{
	/* the whole segment is < rcv_nxt */
	/* must be a duplicate of a packet that has already been correctly handled */
	
	DEBUGF(TCP_INPUT_DEBUG, ("tcp_receive: duplicate seqno %lu\n", seqno));
	tcp_ack_now(pcb);
      }
    }

    /* The sequence number must be within the window (above rcv_nxt
       and below rcv_nxt + rcv_wnd) in order to be further
       processed. */
    if(TCP_SEQ_GEQ(seqno, pcb->rcv_nxt) &&
       TCP_SEQ_LT(seqno, pcb->rcv_nxt + pcb->rcv_wnd)) {
      if(pcb->rcv_nxt == seqno) {			
	/* The incoming segment is the next in sequence. We check if
           we have to trim the end of the segment and update rcv_nxt
           and pass the data to the application. */
#if TCP_QUEUE_OOSEQ
	if(pcb->ooseq != NULL &&
	   TCP_SEQ_LEQ(pcb->ooseq->tcphdr->seqno, seqno + inseg.len)) {
	  /* We have to trim the second edge of the incoming
             segment. */
	  inseg.len = pcb->ooseq->tcphdr->seqno - seqno;
	  pbuf_realloc(inseg.p, inseg.len);
	}
#endif /* TCP_QUEUE_OOSEQ */

	tcplen = TCP_TCPLEN(&inseg);
	
	pcb->rcv_nxt += tcplen;
	
	/* Update the receiver's (our) window. */
	if(pcb->rcv_wnd < tcplen) {
	  pcb->rcv_wnd = 0;
	} else {
	  pcb->rcv_wnd -= tcplen;
	}
	
	/* If there is data in the segment, we make preparations to
	   pass this up to the application. The ->recv_data variable
	   is used for holding the pbuf that goes to the
	   application. The code for reassembling out-of-sequence data
	   chains its data on this pbuf as well.
	   
	   If the segment was a FIN, we set the TF_GOT_FIN flag that will
	   be used to indicate to the application that the remote side has
	   closed its end of the connection. */      
	if(inseg.p->tot_len > 0) {
	  recv_data = inseg.p;
	  /* Since this pbuf now is the responsibility of the
	     application, we delete our reference to it so that we won't
	     (mistakingly) deallocate it. */
	  inseg.p = NULL;
	}
	if(TCPH_FLAGS(inseg.tcphdr) & TCP_FIN) {
	  DEBUGF(TCP_INPUT_DEBUG, ("tcp_receive: received FIN."));
	  recv_flags = TF_GOT_FIN;
	}
	
#if TCP_QUEUE_OOSEQ
	/* We now check if we have segments on the ->ooseq queue that
           is now in sequence. */
	while(pcb->ooseq != NULL &&
	      pcb->ooseq->tcphdr->seqno == pcb->rcv_nxt) {

	  cseg = pcb->ooseq;
	  seqno = pcb->ooseq->tcphdr->seqno;
	  
	  pcb->rcv_nxt += TCP_TCPLEN(cseg);
	  if(pcb->rcv_wnd < TCP_TCPLEN(cseg)) {
	    pcb->rcv_wnd = 0;
	  } else {
	    pcb->rcv_wnd -= TCP_TCPLEN(cseg);
	  }
	  if(cseg->p->tot_len > 0) {
	    /* Chain this pbuf onto the pbuf that we will pass to
	       the application. */
	    if(recv_data) {
	      pbuf_chain(recv_data, cseg->p);
	    } else {
	      recv_data = cseg->p;
	    }
	    cseg->p = NULL;
	  }
	  if(flags & TCP_FIN) {
	    DEBUGF(TCP_INPUT_DEBUG, ("tcp_receive: dequeued FIN."));
	    recv_flags = TF_GOT_FIN;
	  }	    
	  

	  pcb->ooseq = cseg->next;
	  tcp_seg_free(cseg);
	}
#endif /* TCP_QUEUE_OOSEQ */


	/* Acknowledge the segment(s). */
	tcp_ack(pcb);

      } else {
	/* We get here if the incoming segment is out-of-sequence. */
	tcp_ack_now(pcb);
#if TCP_QUEUE_OOSEQ
	/* We queue the segment on the ->ooseq queue. */
	if(pcb->ooseq == NULL) {
	  pcb->ooseq = tcp_seg_copy(&inseg);
	} else {
	  /* If the queue is not empty, we walk through the queue and
	  try to find a place where the sequence number of the
	  incoming segment is between the sequence numbers of the
	  previous and the next segment on the ->ooseq queue. That is
	  the place where we put the incoming segment. If needed, we
	  trim the second edges of the previous and the incoming
	  segment so that it will fit into the sequence.

	  If the incoming segment has the same sequence number as a
	  segment on the ->ooseq queue, we discard the segment that
	  contains less data. */

	  prev = NULL;
	  for(next = pcb->ooseq; next != NULL; next = next->next) {
	    if(seqno == next->tcphdr->seqno) {
	      /* The sequence number of the incoming segment is the
                 same as the sequence number of the segment on
                 ->ooseq. We check the lengths to see which one to
                 discard. */
	      if(inseg.len > next->len) {
		/* The incoming segment is larger than the old
                   segment. We replace the old segment with the new
                   one. */
		cseg = tcp_seg_copy(&inseg);
		if(cseg != NULL) {
		  cseg->next = next->next;
		  if(prev != NULL) {
		    prev->next = cseg;
		  } else {
		    pcb->ooseq = cseg;
		  }
		}
		break;
	      } else {
		/* Either the lenghts are the same or the incoming
                   segment was smaller than the old one; in either
                   case, we ditch the incoming segment. */
		break;
	      } 
	    } else {
	      if(prev == NULL) {
		if(TCP_SEQ_LT(seqno, next->tcphdr->seqno)) {
		  /* The sequence number of the incoming segment is lower
		     than the sequence number of the first segment on the
		     queue. We put the incoming segment first on the
		     queue. */
		  
		  if(TCP_SEQ_GT(seqno + inseg.len, next->tcphdr->seqno)) {
		    /* We need to trim the incoming segment. */
		    inseg.len = next->tcphdr->seqno - seqno;
		    pbuf_realloc(inseg.p, inseg.len);
		  }
		  cseg = tcp_seg_copy(&inseg);
		  if(cseg != NULL) {
		    cseg->next = next;
		    pcb->ooseq = cseg;
		  }
		  break;
		}
	      } else if(TCP_SEQ_LT(prev->tcphdr->seqno, seqno) &&
		 TCP_SEQ_LT(seqno, next->tcphdr->seqno)) {
		/* The sequence number of the incoming segment is in
                   between the sequence numbers of the previous and
                   the next segment on ->ooseq. We trim and insert the
                   incoming segment and trim the previous segment, if
                   needed. */
		if(TCP_SEQ_GT(seqno + inseg.len, next->tcphdr->seqno)) {
		  /* We need to trim the incoming segment. */
		  inseg.len = next->tcphdr->seqno - seqno;
		  pbuf_realloc(inseg.p, inseg.len);
		}

		cseg = tcp_seg_copy(&inseg);
		if(cseg != NULL) {		 		  
		  cseg->next = next;
		  prev->next = cseg;
		  if(TCP_SEQ_GT(prev->tcphdr->seqno + prev->len, seqno)) {
		    /* We need to trim the prev segment. */
		    prev->len = seqno - prev->tcphdr->seqno;
		    pbuf_realloc(prev->p, prev->len);
		  }
		}
		break;
		}
	      /* If the "next" segment is the last segment on the
                 ooseq queue, we add the incoming segment to the end
                 of the list. */
	      if(next->next == NULL &&
		 TCP_SEQ_GT(seqno, next->tcphdr->seqno)) {
		next->next = tcp_seg_copy(&inseg);
		if(next->next != NULL) {		
		  if(TCP_SEQ_GT(next->tcphdr->seqno + next->len, seqno)) {
		    /* We need to trim the last segment. */
		    next->len = seqno - next->tcphdr->seqno;
		    pbuf_realloc(next->p, next->len);
		  }
		}
		break;
	      }
	    }
	    prev = next;
	  }    
	} 
#endif /* TCP_QUEUE_OOSEQ */
	     
      }    
    }
  } else {
    /* Segments with length 0 is taken care of here. Segments that
       fall out of the window are ACKed. */
    if(TCP_SEQ_GT(pcb->rcv_nxt, seqno) ||
       TCP_SEQ_GEQ(seqno, pcb->rcv_nxt + pcb->rcv_wnd)) {
      tcp_ack_now(pcb);
    }      
  }
}
/*-----------------------------------------------------------------------------------*/
/*
 * tcp_parseopt:
 *
 * Parses the options contained in the incoming segment. (Code taken
 * from uIP with only small changes.)
 * 
 */
/*-----------------------------------------------------------------------------------*/
static void
tcp_parseopt(struct tcp_pcb *pcb)
{
  u8_t c;
  u8_t *opts, opt;
  u16_t mss;

  opts = (u8_t *)tcphdr + TCP_HLEN;
  
  /* Parse the TCP MSS option, if present. */
  if((TCPH_OFFSET(tcphdr) & 0xf0) > 0x50) {
    for(c = 0; c < ((TCPH_OFFSET(tcphdr) >> 4) - 5) << 2 ;) {
      opt = opts[c];
      if(opt == 0x00) {
        /* End of options. */   
	break;
      } else if(opt == 0x01) {
        ++c;
        /* NOP option. */
      } else if(opt == 0x02 &&
                opts[c + 1] == 0x04) {
        /* An MSS option with the right option length. */       
        mss = (opts[c + 2] << 8) | opts[c + 3];
        pcb->mss = mss > TCP_MSS? TCP_MSS: mss;
        
        /* And we are done processing options. */
        break;
      } else {
	if(opts[c + 1] == 0) {
          /* If the length field is zero, the options are malformed
             and we don't process them further. */
          break;
        }
        /* All other options have a length field, so that we easily
           can skip past them. */
        c += opts[c + 1];
      }      
    }
  }
}
#endif /* LWIP_TCP */
/*-----------------------------------------------------------------------------------*/