tcp_out.c

超轻量级TCP/IP协议栈源代码

    TCPH_SET_FLAG(seg->tcphdr, TCP_PSH);
  }

  return ERR_OK;
  memerr:
  TCP_STATS_INC(tcp.memerr);

  if (queue != NULL) {
    tcp_segs_free(queue);
  }
  if (pcb->snd_queuelen != 0) {
    LWIP_ASSERT("tcp_enqueue: valid queue length", pcb->unacked != NULL ||
      pcb->unsent != NULL);

  }
  LWIP_DEBUGF(TCP_QLEN_DEBUG | DBG_STATE, ("tcp_enqueue: %d (with mem err)\n", pcb->snd_queuelen));
  return ERR_MEM;
}

/* find out what we can send and send it */
err_t
tcp_output(struct tcp_pcb *pcb)
{
  struct pbuf *p;
  struct tcp_hdr *tcphdr;
  struct tcp_seg *seg, *useg;
  u32_t wnd;
#if TCP_CWND_DEBUG
  int i = 0;
#endif /* TCP_CWND_DEBUG */

  /* First, check if we are invoked by the TCP input processing
     code. If so, we do not output anything. Instead, we rely on the
     input processing code to call us when input processing is done
     with. */
  if (tcp_input_pcb == pcb) {
    return ERR_OK;
  }

  wnd = LWIP_MIN(pcb->snd_wnd, pcb->cwnd);


  seg = pcb->unsent;

  /* useg should point to last segment on unacked queue */
  useg = pcb->unacked;
  if (useg != NULL) {
    for (; useg->next != NULL; useg = useg->next);
  }                                                                             

   
  /* If the TF_ACK_NOW flag is set, we check if there is data that is
     to be sent. If data is to be sent out, we'll just piggyback our
     acknowledgement with the outgoing segment. If no data will be
     sent (either because the ->unsent queue is empty or because the
     window doesn't allow it) we'll have to construct an empty ACK
     segment and send it. */
  if (pcb->flags & TF_ACK_NOW &&
     (seg == NULL ||
      ntohl(seg->tcphdr->seqno) - pcb->lastack + seg->len > wnd)) {
    pcb->flags &= ~(TF_ACK_DELAY | TF_ACK_NOW);
    p = pbuf_alloc(PBUF_IP, TCP_HLEN, PBUF_RAM);
    if (p == NULL) {
      LWIP_DEBUGF(TCP_OUTPUT_DEBUG, ("tcp_output: (ACK) could not allocate pbuf\n"));
      return ERR_BUF;
    }
    LWIP_DEBUGF(TCP_OUTPUT_DEBUG, ("tcp_output: sending ACK for %lu\n", pcb->rcv_nxt));

    tcphdr = p->payload;
    tcphdr->src = htons(pcb->local_port);
    tcphdr->dest = htons(pcb->remote_port);
    tcphdr->seqno = htonl(pcb->snd_nxt);
    tcphdr->ackno = htonl(pcb->rcv_nxt);
    TCPH_FLAGS_SET(tcphdr, TCP_ACK);
    tcphdr->wnd = htons(pcb->rcv_wnd);
    tcphdr->urgp = 0;
    TCPH_HDRLEN_SET(tcphdr, 5);

    tcphdr->chksum = 0;
    tcphdr->chksum = inet_chksum_pseudo(p, &(pcb->local_ip), &(pcb->remote_ip),
          IP_PROTO_TCP, p->tot_len);


    ip_output(p, &(pcb->local_ip), &(pcb->remote_ip), pcb->ttl, pcb->tos,
        IP_PROTO_TCP);
    pbuf_free(p);

    return ERR_OK;
  }

#if TCP_OUTPUT_DEBUG
  if (seg == NULL) {
    LWIP_DEBUGF(TCP_OUTPUT_DEBUG, ("tcp_output: nothing to send (%p)\n", pcb->unsent));
  }
#endif /* TCP_OUTPUT_DEBUG */
#if TCP_CWND_DEBUG
  if (seg == NULL) {
    LWIP_DEBUGF(TCP_CWND_DEBUG, ("tcp_output: snd_wnd %lu, cwnd %lu, wnd %lu, seg == NULL, ack %lu\n",
                            pcb->snd_wnd, pcb->cwnd, wnd,
                            pcb->lastack));
  } else {
    LWIP_DEBUGF(TCP_CWND_DEBUG, ("tcp_output: snd_wnd %lu, cwnd %lu, wnd %lu, effwnd %lu, seq %lu, ack %lu\n",
                            pcb->snd_wnd, pcb->cwnd, wnd,
                            ntohl(seg->tcphdr->seqno) - pcb->lastack + seg->len,
                            ntohl(seg->tcphdr->seqno), pcb->lastack));
  }
#endif /* TCP_CWND_DEBUG */

  while (seg != NULL &&
  ntohl(seg->tcphdr->seqno) - pcb->lastack + seg->len <= wnd) {
#if TCP_CWND_DEBUG
    LWIP_DEBUGF(TCP_CWND_DEBUG, ("tcp_output: snd_wnd %lu, cwnd %lu, wnd %lu, effwnd %lu, seq %lu, ack %lu, i%d\n",
                            pcb->snd_wnd, pcb->cwnd, wnd,
                            ntohl(seg->tcphdr->seqno) + seg->len -
                            pcb->lastack,
                            ntohl(seg->tcphdr->seqno), pcb->lastack, i));
    ++i;
#endif /* TCP_CWND_DEBUG */

    pcb->unsent = seg->next;

    if (pcb->state != SYN_SENT) {
      TCPH_SET_FLAG(seg->tcphdr, TCP_ACK);
      pcb->flags &= ~(TF_ACK_DELAY | TF_ACK_NOW);
    }

    tcp_output_segment(seg, pcb);
    pcb->snd_nxt = ntohl(seg->tcphdr->seqno) + TCP_TCPLEN(seg);
    if (TCP_SEQ_LT(pcb->snd_max, pcb->snd_nxt)) {
      pcb->snd_max = pcb->snd_nxt;
    }
    /* put segment on unacknowledged list if length > 0 */
    if (TCP_TCPLEN(seg) > 0) {
      seg->next = NULL;
      if (pcb->unacked == NULL) {
        pcb->unacked = seg;
        useg = seg;
      } else {
        useg->next = seg;
        useg = useg->next;
      }
    } else {
      tcp_seg_free(seg);
    }
    seg = pcb->unsent;
  }
  return ERR_OK;
}

static void
tcp_output_segment(struct tcp_seg *seg, struct tcp_pcb *pcb)
{
  u16_t len;
  struct netif *netif;

  /* The TCP header has already been constructed, but the ackno and
   wnd fields remain. */
  seg->tcphdr->ackno = htonl(pcb->rcv_nxt);

  /* silly window avoidance */
  if (pcb->rcv_wnd < pcb->mss) {
    seg->tcphdr->wnd = 0;
  } else {
    /* advertise our receive window size in this TCP segment */
    seg->tcphdr->wnd = htons(pcb->rcv_wnd);
  }

  /* If we don't have a local IP address, we get one by
     calling ip_route(). */
  if (ip_addr_isany(&(pcb->local_ip))) {
    netif = ip_route(&(pcb->remote_ip));
    if (netif == NULL) {
      return;
    }
    ip_addr_set(&(pcb->local_ip), &(netif->ip_addr));
  }

  pcb->rtime = 0;

  if (pcb->rttest == 0) {
    pcb->rttest = tcp_ticks;
    pcb->rtseq = ntohl(seg->tcphdr->seqno);

    LWIP_DEBUGF(TCP_RTO_DEBUG, ("tcp_output_segment: rtseq %lu\n", pcb->rtseq));
  }
  LWIP_DEBUGF(TCP_OUTPUT_DEBUG, ("tcp_output_segment: %lu:%lu\n",
          htonl(seg->tcphdr->seqno), htonl(seg->tcphdr->seqno) +
          seg->len));

  len = (u16_t)((u8_t *)seg->tcphdr - (u8_t *)seg->p->payload);

  seg->p->len -= len;
  seg->p->tot_len -= len;

  seg->p->payload = seg->tcphdr;

  seg->tcphdr->chksum = 0;
  seg->tcphdr->chksum = inet_chksum_pseudo(seg->p,
             &(pcb->local_ip),
             &(pcb->remote_ip),
             IP_PROTO_TCP, seg->p->tot_len);
  TCP_STATS_INC(tcp.xmit);

  ip_output(seg->p, &(pcb->local_ip), &(pcb->remote_ip), pcb->ttl, pcb->tos,
      IP_PROTO_TCP);
}

void
tcp_rst(u32_t seqno, u32_t ackno,
  struct ip_addr *local_ip, struct ip_addr *remote_ip,
  u16_t local_port, u16_t remote_port)
{
  struct pbuf *p;
  struct tcp_hdr *tcphdr;
  p = pbuf_alloc(PBUF_IP, TCP_HLEN, PBUF_RAM);
  if (p == NULL) {
      LWIP_DEBUGF(TCP_DEBUG, ("tcp_rst: could not allocate memory for pbuf\n"));
      return;
  }

  tcphdr = p->payload;
  tcphdr->src = htons(local_port);
  tcphdr->dest = htons(remote_port);
  tcphdr->seqno = htonl(seqno);
  tcphdr->ackno = htonl(ackno);
  TCPH_FLAGS_SET(tcphdr, TCP_RST | TCP_ACK);
  tcphdr->wnd = htons(TCP_WND);
  tcphdr->urgp = 0;
  TCPH_HDRLEN_SET(tcphdr, 5);

  tcphdr->chksum = 0;
  tcphdr->chksum = inet_chksum_pseudo(p, local_ip, remote_ip,
              IP_PROTO_TCP, p->tot_len);

  TCP_STATS_INC(tcp.xmit);
   /* Send output with hardcoded TTL since we have no access to the pcb */
  ip_output(p, local_ip, remote_ip, TCP_TTL, 0, IP_PROTO_TCP);
  pbuf_free(p);
  LWIP_DEBUGF(TCP_RST_DEBUG, ("tcp_rst: seqno %lu ackno %lu.\n", seqno, ackno));
}

void
tcp_rexmit(struct tcp_pcb *pcb)
{
  struct tcp_seg *seg;

  if (pcb->unacked == NULL) {
    return;
  }

  /* Move all unacked segments to the unsent queue. */
  for (seg = pcb->unacked; seg->next != NULL; seg = seg->next);

  seg->next = pcb->unsent;
  pcb->unsent = pcb->unacked;

  pcb->unacked = NULL;


  pcb->snd_nxt = ntohl(pcb->unsent->tcphdr->seqno);

  ++pcb->nrtx;

  /* Don't take any rtt measurements after retransmitting. */
  pcb->rttest = 0;

  /* Do the actual retransmission. */
  tcp_output(pcb);

}

void
tcp_keepalive(struct tcp_pcb *pcb)
{
   struct pbuf *p;
   struct tcp_hdr *tcphdr;

   LWIP_DEBUGF(TCP_DEBUG, ("tcp_keepalive: sending KEEPALIVE probe to %u.%u.%u.%u\n",
                           ip4_addr1(&pcb->remote_ip), ip4_addr2(&pcb->remote_ip),
                           ip4_addr3(&pcb->remote_ip), ip4_addr4(&pcb->remote_ip)));

   LWIP_DEBUGF(TCP_DEBUG, ("tcp_keepalive: tcp_ticks %ld   pcb->tmr %ld  pcb->keep_cnt %ld\n", tcp_ticks, pcb->tmr, pcb->keep_cnt));
   
   p = pbuf_alloc(PBUF_IP, TCP_HLEN, PBUF_RAM);

   if(p == NULL) {
      LWIP_DEBUGF(TCP_DEBUG, ("tcp_keepalive: could not allocate memory for pbuf\n"));
      return;
   }

   tcphdr = p->payload;
   tcphdr->src = htons(pcb->local_port);
   tcphdr->dest = htons(pcb->remote_port);
   tcphdr->seqno = htonl(pcb->snd_nxt - 1);
   tcphdr->ackno = htonl(pcb->rcv_nxt);
   tcphdr->wnd = htons(pcb->rcv_wnd);
   tcphdr->urgp = 0;
   TCPH_HDRLEN_SET(tcphdr, 5);
   
   tcphdr->chksum = 0;
   tcphdr->chksum = inet_chksum_pseudo(p, &pcb->local_ip, &pcb->remote_ip, IP_PROTO_TCP, p->tot_len);

  TCP_STATS_INC(tcp.xmit);

   /* Send output to IP */
  ip_output(p, &pcb->local_ip, &pcb->remote_ip, pcb->ttl, 0, IP_PROTO_TCP);

  pbuf_free(p);

  LWIP_DEBUGF(TCP_RST_DEBUG, ("tcp_keepalive: seqno %lu ackno %lu.\n", pcb->snd_nxt - 1, pcb->rcv_nxt));
}

#endif /* LWIP_TCP */