tcp_out.c

lwip-1.4.0

          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;
#if CHECKSUM_GEN_TCP
#if TCP_CHECKSUM_ON_COPY
  {
    u32_t acc;
#if TCP_CHECKSUM_ON_COPY_SANITY_CHECK
    u16_t chksum_slow = inet_chksum_pseudo(seg->p, &(pcb->local_ip),
           &(pcb->remote_ip),
           IP_PROTO_TCP, seg->p->tot_len);
#endif /* TCP_CHECKSUM_ON_COPY_SANITY_CHECK */
    if ((seg->flags & TF_SEG_DATA_CHECKSUMMED) == 0) {
      LWIP_ASSERT("data included but not checksummed",
        seg->p->tot_len == (TCPH_HDRLEN(seg->tcphdr) * 4));
    }

    /* rebuild TCP header checksum (TCP header changes for retransmissions!) */
    acc = inet_chksum_pseudo_partial(seg->p, &(pcb->local_ip),
             &(pcb->remote_ip),
             IP_PROTO_TCP, seg->p->tot_len, TCPH_HDRLEN(seg->tcphdr) * 4);
    /* add payload checksum */
    if (seg->chksum_swapped) {
      seg->chksum = SWAP_BYTES_IN_WORD(seg->chksum);
      seg->chksum_swapped = 0;
    }
    acc += (u16_t)~(seg->chksum);
    seg->tcphdr->chksum = FOLD_U32T(acc);
#if TCP_CHECKSUM_ON_COPY_SANITY_CHECK
    if (chksum_slow != seg->tcphdr->chksum) {
      LWIP_DEBUGF(TCP_DEBUG | LWIP_DBG_LEVEL_WARNING,
                  ("tcp_output_segment: calculated checksum is %"X16_F" instead of %"X16_F"\n",
                  seg->tcphdr->chksum, chksum_slow));
      seg->tcphdr->chksum = chksum_slow;
    }
#endif /* TCP_CHECKSUM_ON_COPY_SANITY_CHECK */
  }
#else /* TCP_CHECKSUM_ON_COPY */
  seg->tcphdr->chksum = inet_chksum_pseudo(seg->p, &(pcb->local_ip),
         &(pcb->remote_ip),
         IP_PROTO_TCP, seg->p->tot_len);
#endif /* TCP_CHECKSUM_ON_COPY */
#endif /* CHECKSUM_GEN_TCP */
  TCP_STATS_INC(tcp.xmit);

#if LWIP_NETIF_HWADDRHINT
  ip_output_hinted(seg->p, &(pcb->local_ip), &(pcb->remote_ip), pcb->ttl, pcb->tos,
      IP_PROTO_TCP, &(pcb->addr_hint));
#else /* LWIP_NETIF_HWADDRHINT*/
  ip_output(seg->p, &(pcb->local_ip), &(pcb->remote_ip), pcb->ttl, pcb->tos,
      IP_PROTO_TCP);
#endif /* LWIP_NETIF_HWADDRHINT*/
}

/**
 * Send a TCP RESET packet (empty segment with RST flag set) either to
 * abort a connection or to show that there is no matching local connection
 * for a received segment.
 *
 * Called by tcp_abort() (to abort a local connection), tcp_input() (if no
 * matching local pcb was found), tcp_listen_input() (if incoming segment
 * has ACK flag set) and tcp_process() (received segment in the wrong state)
 *
 * Since a RST segment is in most cases not sent for an active connection,
 * tcp_rst() has a number of arguments that are taken from a tcp_pcb for
 * most other segment output functions.
 *
 * @param seqno the sequence number to use for the outgoing segment
 * @param ackno the acknowledge number to use for the outgoing segment
 * @param local_ip the local IP address to send the segment from
 * @param remote_ip the remote IP address to send the segment to
 * @param local_port the local TCP port to send the segment from
 * @param remote_port the remote TCP port to send the segment to
 */
void
tcp_rst(u32_t seqno, u32_t ackno,
  ip_addr_t *local_ip, ip_addr_t *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;
  }
  LWIP_ASSERT("check that first pbuf can hold struct tcp_hdr",
              (p->len >= sizeof(struct tcp_hdr)));

  tcphdr = (struct tcp_hdr *)p->payload;
  tcphdr->src = htons(local_port);
  tcphdr->dest = htons(remote_port);
  tcphdr->seqno = htonl(seqno);
  tcphdr->ackno = htonl(ackno);
  TCPH_HDRLEN_FLAGS_SET(tcphdr, TCP_HLEN/4, TCP_RST | TCP_ACK);
  tcphdr->wnd = PP_HTONS(TCP_WND);
  tcphdr->chksum = 0;
  tcphdr->urgp = 0;

#if CHECKSUM_GEN_TCP
  tcphdr->chksum = inet_chksum_pseudo(p, local_ip, remote_ip,
              IP_PROTO_TCP, p->tot_len);
#endif
  TCP_STATS_INC(tcp.xmit);
  snmp_inc_tcpoutrsts();
   /* 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 %"U32_F" ackno %"U32_F".\n", seqno, ackno));
}

/**
 * Requeue all unacked segments for retransmission
 *
 * Called by tcp_slowtmr() for slow retransmission.
 *
 * @param pcb the tcp_pcb for which to re-enqueue all unacked segments
 */
void
tcp_rexmit_rto(struct tcp_pcb *pcb)
{
  struct tcp_seg *seg;

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

  /* Move all unacked segments to the head of the unsent queue */
  for (seg = pcb->unacked; seg->next != NULL; seg = seg->next);
  /* concatenate unsent queue after unacked queue */
  seg->next = pcb->unsent;
  /* unsent queue is the concatenated queue (of unacked, unsent) */
  pcb->unsent = pcb->unacked;
  /* unacked queue is now empty */
  pcb->unacked = NULL;

  /* increment number of retransmissions */
  ++pcb->nrtx;

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

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

/**
 * Requeue the first unacked segment for retransmission
 *
 * Called by tcp_receive() for fast retramsmit.
 *
 * @param pcb the tcp_pcb for which to retransmit the first unacked segment
 */
void
tcp_rexmit(struct tcp_pcb *pcb)
{
  struct tcp_seg *seg;
  struct tcp_seg **cur_seg;

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

  /* Move the first unacked segment to the unsent queue */
  /* Keep the unsent queue sorted. */
  seg = pcb->unacked;
  pcb->unacked = seg->next;

  cur_seg = &(pcb->unsent);
  while (*cur_seg &&
    TCP_SEQ_LT(ntohl((*cur_seg)->tcphdr->seqno), ntohl(seg->tcphdr->seqno))) {
      cur_seg = &((*cur_seg)->next );
  }
  seg->next = *cur_seg;
  *cur_seg = seg;

  ++pcb->nrtx;

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

  /* Do the actual retransmission. */
  snmp_inc_tcpretranssegs();
  /* No need to call tcp_output: we are always called from tcp_input()
     and thus tcp_output directly returns. */
}


/**
 * Handle retransmission after three dupacks received
 *
 * @param pcb the tcp_pcb for which to retransmit the first unacked segment
 */
void 
tcp_rexmit_fast(struct tcp_pcb *pcb)
{
  if (pcb->unacked != NULL && !(pcb->flags & TF_INFR)) {
    /* This is fast retransmit. Retransmit the first unacked segment. */
    LWIP_DEBUGF(TCP_FR_DEBUG, 
                ("tcp_receive: dupacks %"U16_F" (%"U32_F
                 "), fast retransmit %"U32_F"\n",
                 (u16_t)pcb->dupacks, pcb->lastack,
                 ntohl(pcb->unacked->tcphdr->seqno)));
    tcp_rexmit(pcb);

    /* Set ssthresh to half of the minimum of the current
     * cwnd and the advertised window */
    if (pcb->cwnd > pcb->snd_wnd) {
      pcb->ssthresh = pcb->snd_wnd / 2;
    } else {
      pcb->ssthresh = pcb->cwnd / 2;
    }
    
    /* The minimum value for ssthresh should be 2 MSS */
    if (pcb->ssthresh < 2*pcb->mss) {
      LWIP_DEBUGF(TCP_FR_DEBUG, 
                  ("tcp_receive: The minimum value for ssthresh %"U16_F
                   " should be min 2 mss %"U16_F"...\n",
                   pcb->ssthresh, 2*pcb->mss));
      pcb->ssthresh = 2*pcb->mss;
    }
    
    pcb->cwnd = pcb->ssthresh + 3 * pcb->mss;
    pcb->flags |= TF_INFR;
  } 
}


/**
 * Send keepalive packets to keep a connection active although
 * no data is sent over it.
 *
 * Called by tcp_slowtmr()
 *
 * @param pcb the tcp_pcb for which to send a keepalive packet
 */
void
tcp_keepalive(struct tcp_pcb *pcb)
{
  struct pbuf *p;
  struct tcp_hdr *tcphdr;

  LWIP_DEBUGF(TCP_DEBUG, ("tcp_keepalive: sending KEEPALIVE probe to %"U16_F".%"U16_F".%"U16_F".%"U16_F"\n",
                          ip4_addr1_16(&pcb->remote_ip), ip4_addr2_16(&pcb->remote_ip),
                          ip4_addr3_16(&pcb->remote_ip), ip4_addr4_16(&pcb->remote_ip)));

  LWIP_DEBUGF(TCP_DEBUG, ("tcp_keepalive: tcp_ticks %"U32_F"   pcb->tmr %"U32_F" pcb->keep_cnt_sent %"U16_F"\n", 
                          tcp_ticks, pcb->tmr, pcb->keep_cnt_sent));
   
  p = tcp_output_alloc_header(pcb, 0, 0, htonl(pcb->snd_nxt - 1));
  if(p == NULL) {
    LWIP_DEBUGF(TCP_DEBUG, 
                ("tcp_keepalive: could not allocate memory for pbuf\n"));
    return;
  }
  tcphdr = (struct tcp_hdr *)p->payload;

#if CHECKSUM_GEN_TCP
  tcphdr->chksum = inet_chksum_pseudo(p, &pcb->local_ip, &pcb->remote_ip,
                                      IP_PROTO_TCP, p->tot_len);
#endif
  TCP_STATS_INC(tcp.xmit);

  /* Send output to IP */
#if LWIP_NETIF_HWADDRHINT
  ip_output_hinted(p, &pcb->local_ip, &pcb->remote_ip, pcb->ttl, 0, IP_PROTO_TCP,
    &(pcb->addr_hint));
#else /* LWIP_NETIF_HWADDRHINT*/
  ip_output(p, &pcb->local_ip, &pcb->remote_ip, pcb->ttl, 0, IP_PROTO_TCP);
#endif /* LWIP_NETIF_HWADDRHINT*/

  pbuf_free(p);

  LWIP_DEBUGF(TCP_DEBUG, ("tcp_keepalive: seqno %"U32_F" ackno %"U32_F".\n",
                          pcb->snd_nxt - 1, pcb->rcv_nxt));
}


/**
 * Send persist timer zero-window probes to keep a connection active
 * when a window update is lost.
 *
 * Called by tcp_slowtmr()
 *
 * @param pcb the tcp_pcb for which to send a zero-window probe packet
 */
void
tcp_zero_window_probe(struct tcp_pcb *pcb)
{
  struct pbuf *p;
  struct tcp_hdr *tcphdr;
  struct tcp_seg *seg;
  u16_t len;
  u8_t is_fin;

  LWIP_DEBUGF(TCP_DEBUG, 
              ("tcp_zero_window_probe: sending ZERO WINDOW probe to %"
               U16_F".%"U16_F".%"U16_F".%"U16_F"\n",
               ip4_addr1_16(&pcb->remote_ip), ip4_addr2_16(&pcb->remote_ip),
               ip4_addr3_16(&pcb->remote_ip), ip4_addr4_16(&pcb->remote_ip)));

  LWIP_DEBUGF(TCP_DEBUG, 
              ("tcp_zero_window_probe: tcp_ticks %"U32_F
               "   pcb->tmr %"U32_F" pcb->keep_cnt_sent %"U16_F"\n", 
               tcp_ticks, pcb->tmr, pcb->keep_cnt_sent));

  seg = pcb->unacked;

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

  is_fin = ((TCPH_FLAGS(seg->tcphdr) & TCP_FIN) != 0) && (seg->len == 0);
  /* we want to send one seqno: either FIN or data (no options) */
  len = is_fin ? 0 : 1;

  p = tcp_output_alloc_header(pcb, 0, len, seg->tcphdr->seqno);
  if(p == NULL) {
    LWIP_DEBUGF(TCP_DEBUG, ("tcp_zero_window_probe: no memory for pbuf\n"));
    return;
  }
  tcphdr = (struct tcp_hdr *)p->payload;

  if (is_fin) {
    /* FIN segment, no data */
    TCPH_FLAGS_SET(tcphdr, TCP_ACK | TCP_FIN);
  } else {
    /* Data segment, copy in one byte from the head of the unacked queue */
    struct tcp_hdr *thdr = (struct tcp_hdr *)seg->p->payload;
    char *d = ((char *)p->payload + TCP_HLEN);
    pbuf_copy_partial(seg->p, d, 1, TCPH_HDRLEN(thdr) * 4);
  }

#if CHECKSUM_GEN_TCP
  tcphdr->chksum = inet_chksum_pseudo(p, &pcb->local_ip, &pcb->remote_ip,
                                      IP_PROTO_TCP, p->tot_len);
#endif
  TCP_STATS_INC(tcp.xmit);

  /* Send output to IP */
#if LWIP_NETIF_HWADDRHINT
  ip_output_hinted(p, &pcb->local_ip, &pcb->remote_ip, pcb->ttl, 0, IP_PROTO_TCP,
    &(pcb->addr_hint));
#else /* LWIP_NETIF_HWADDRHINT*/
  ip_output(p, &pcb->local_ip, &pcb->remote_ip, pcb->ttl, 0, IP_PROTO_TCP);
#endif /* LWIP_NETIF_HWADDRHINT*/

  pbuf_free(p);

  LWIP_DEBUGF(TCP_DEBUG, ("tcp_zero_window_probe: seqno %"U32_F
                          " ackno %"U32_F".\n",
                          pcb->snd_nxt - 1, pcb->rcv_nxt));
}
#endif /* LWIP_TCP */