tcp_in.c

RT-Thread是发展中的下一代微内核嵌入式实时操作系统

        /* If there were no errors, we try to send something out. */
        if (err == ERR_OK) {
          tcp_output(pcb);
        }
      }
    }


    /* give up our reference to inseg.p */
    if (inseg.p != NULL)
    {
      pbuf_free(inseg.p);
      inseg.p = NULL;
    }
#if TCP_INPUT_DEBUG
#if TCP_DEBUG
    tcp_debug_print_state(pcb->state);
#endif /* TCP_DEBUG */
#endif /* TCP_INPUT_DEBUG */
      
  } else {

    /* If no matching PCB was found, send a TCP RST (reset) to the
       sender. */
    LWIP_DEBUGF(TCP_RST_DEBUG, ("tcp_input: no PCB match found, resetting.\n"));
    if (!(TCPH_FLAGS(tcphdr) & TCP_RST)) {
      TCP_STATS_INC(tcp.proterr);
      TCP_STATS_INC(tcp.drop);
      tcp_rst(ackno, seqno + tcplen,
        &(iphdr->dest), &(iphdr->src),
        tcphdr->dest, tcphdr->src);
    }
    pbuf_free(p);
  }

  LWIP_ASSERT("tcp_input: tcp_pcbs_sane()", tcp_pcbs_sane());
  PERF_STOP("tcp_input");
}

/**
 * Called by tcp_input() when a segment arrives for a listening
 * connection (from tcp_input()).
 *
 * @param pcb the tcp_pcb_listen for which a segment arrived
 * @return ERR_OK if the segment was processed
 *         another err_t on error
 *
 * @note the return value is not (yet?) used in tcp_input()
 * @note the segment which arrived is saved in global variables, therefore only the pcb
 *       involved is passed as a parameter to this function
 */
static err_t
tcp_listen_input(struct tcp_pcb_listen *pcb)
{
  struct tcp_pcb *npcb;
  u32_t optdata;

  /* In the LISTEN state, we check for incoming SYN segments,
     creates a new PCB, and responds with a SYN|ACK. */
  if (flags & TCP_ACK) {
    /* For incoming segments with the ACK flag set, respond with a
       RST. */
    LWIP_DEBUGF(TCP_RST_DEBUG, ("tcp_listen_input: ACK in LISTEN, sending reset\n"));
    tcp_rst(ackno + 1, seqno + tcplen,
      &(iphdr->dest), &(iphdr->src),
      tcphdr->dest, tcphdr->src);
  } else if (flags & TCP_SYN) {
    LWIP_DEBUGF(TCP_DEBUG, ("TCP connection request %"U16_F" -> %"U16_F".\n", tcphdr->src, tcphdr->dest));
#if TCP_LISTEN_BACKLOG
    if (pcb->accepts_pending >= pcb->backlog) {
      return ERR_ABRT;
    }
#endif /* TCP_LISTEN_BACKLOG */
    npcb = tcp_alloc(pcb->prio);
    /* If a new PCB could not be created (probably due to lack of memory),
       we don't do anything, but rely on the sender will retransmit the
       SYN at a time when we have more memory available. */
    if (npcb == NULL) {
      LWIP_DEBUGF(TCP_DEBUG, ("tcp_listen_input: could not allocate PCB\n"));
      TCP_STATS_INC(tcp.memerr);
      return ERR_MEM;
    }
#if TCP_LISTEN_BACKLOG
    pcb->accepts_pending++;
#endif /* TCP_LISTEN_BACKLOG */
    /* Set up the new PCB. */
    ip_addr_set(&(npcb->local_ip), &(iphdr->dest));
    npcb->local_port = pcb->local_port;
    ip_addr_set(&(npcb->remote_ip), &(iphdr->src));
    npcb->remote_port = tcphdr->src;
    npcb->state = SYN_RCVD;
    npcb->rcv_nxt = seqno + 1;
    npcb->snd_wnd = tcphdr->wnd;
    npcb->ssthresh = npcb->snd_wnd;
    npcb->snd_wl1 = seqno - 1;/* initialise to seqno-1 to force window update */
    npcb->callback_arg = pcb->callback_arg;
#if LWIP_CALLBACK_API
    npcb->accept = pcb->accept;
#endif /* LWIP_CALLBACK_API */
    /* inherit socket options */
    npcb->so_options = pcb->so_options & (SOF_DEBUG|SOF_DONTROUTE|SOF_KEEPALIVE|SOF_OOBINLINE|SOF_LINGER);
    /* Register the new PCB so that we can begin receiving segments
       for it. */
    TCP_REG(&tcp_active_pcbs, npcb);

    /* Parse any options in the SYN. */
    tcp_parseopt(npcb);
#if TCP_CALCULATE_EFF_SEND_MSS
    npcb->mss = tcp_eff_send_mss(npcb->mss, &(npcb->remote_ip));
#endif /* TCP_CALCULATE_EFF_SEND_MSS */

    snmp_inc_tcppassiveopens();

    /* Build an MSS option. */
    optdata = TCP_BUILD_MSS_OPTION();
    /* Send a SYN|ACK together with the MSS option. */
    tcp_enqueue(npcb, NULL, 0, TCP_SYN | TCP_ACK, 0, (u8_t *)&optdata, 4);
    return tcp_output(npcb);
  }
  return ERR_OK;
}

/**
 * Called by tcp_input() when a segment arrives for a connection in
 * TIME_WAIT.
 *
 * @param pcb the tcp_pcb for which a segment arrived
 *
 * @note the segment which arrived is saved in global variables, therefore only the pcb
 *       involved is passed as a parameter to this function
 */
static err_t
tcp_timewait_input(struct tcp_pcb *pcb)
{
  if (TCP_SEQ_GT(seqno + tcplen, pcb->rcv_nxt)) {
    pcb->rcv_nxt = seqno + tcplen;
  }
  if (tcplen > 0) {
    tcp_ack_now(pcb);
  }
  return tcp_output(pcb);
}

/**
 * Implements the TCP state machine. Called by tcp_input. In some
 * states tcp_receive() is called to receive data. The tcp_seg
 * argument will be freed by the caller (tcp_input()) unless the
 * recv_data pointer in the pcb is set.
 *
 * @param pcb the tcp_pcb for which a segment arrived
 *
 * @note the segment which arrived is saved in global variables, therefore only the pcb
 *       involved is passed as a parameter to this function
 */
static err_t
tcp_process(struct tcp_pcb *pcb)
{
  struct tcp_seg *rseg;
  u8_t acceptable = 0;
  err_t err;
  u8_t accepted_inseq;

  err = ERR_OK;

  /* Process incoming RST segments. */
  if (flags & TCP_RST) {
    /* First, determine if the reset is acceptable. */
    if (pcb->state == SYN_SENT) {
      if (ackno == pcb->snd_nxt) {
        acceptable = 1;
      }
    } else {
      if (TCP_SEQ_BETWEEN(seqno, pcb->rcv_nxt, 
                          pcb->rcv_nxt+pcb->rcv_ann_wnd)) {
        acceptable = 1;
      }
    }

    if (acceptable) {
      LWIP_DEBUGF(TCP_INPUT_DEBUG, ("tcp_process: Connection RESET\n"));
      LWIP_ASSERT("tcp_input: pcb->state != CLOSED", pcb->state != CLOSED);
      recv_flags = TF_RESET;
      pcb->flags &= ~TF_ACK_DELAY;
      return ERR_RST;
    } else {
      LWIP_DEBUGF(TCP_INPUT_DEBUG, ("tcp_process: unacceptable reset seqno %"U32_F" rcv_nxt %"U32_F"\n",
       seqno, pcb->rcv_nxt));
      LWIP_DEBUGF(TCP_DEBUG, ("tcp_process: unacceptable reset seqno %"U32_F" rcv_nxt %"U32_F"\n",
       seqno, pcb->rcv_nxt));
      return ERR_OK;
    }
  }

  /* Update the PCB (in)activity timer. */
  pcb->tmr = tcp_ticks;
  pcb->keep_cnt_sent = 0;

  /* Do different things depending on the TCP state. */
  switch (pcb->state) {
  case SYN_SENT:
    LWIP_DEBUGF(TCP_INPUT_DEBUG, ("SYN-SENT: ackno %"U32_F" pcb->snd_nxt %"U32_F" unacked %"U32_F"\n", ackno,
     pcb->snd_nxt, ntohl(pcb->unacked->tcphdr->seqno)));
    /* received SYN ACK with expected sequence number? */
    if ((flags & TCP_ACK) && (flags & TCP_SYN)
        && ackno == ntohl(pcb->unacked->tcphdr->seqno) + 1) {
      pcb->snd_buf++;
      pcb->rcv_nxt = seqno + 1;
      pcb->lastack = ackno;
      pcb->snd_wnd = tcphdr->wnd;
      pcb->snd_wl1 = seqno - 1; /* initialise to seqno - 1 to force window update */
      pcb->state = ESTABLISHED;

      /* Parse any options in the SYNACK before using pcb->mss since that
       * can be changed by the received options! */
      tcp_parseopt(pcb);
#if TCP_CALCULATE_EFF_SEND_MSS
      pcb->mss = tcp_eff_send_mss(pcb->mss, &(pcb->remote_ip));
#endif /* TCP_CALCULATE_EFF_SEND_MSS */

      /* Set ssthresh again after changing pcb->mss (already set in tcp_connect
       * but for the default value of pcb->mss) */
      pcb->ssthresh = pcb->mss * 10;

      pcb->cwnd = ((pcb->cwnd == 1) ? (pcb->mss * 2) : pcb->mss);
      LWIP_ASSERT("pcb->snd_queuelen > 0", (pcb->snd_queuelen > 0));
      --pcb->snd_queuelen;
      LWIP_DEBUGF(TCP_QLEN_DEBUG, ("tcp_process: SYN-SENT --queuelen %"U16_F"\n", (u16_t)pcb->snd_queuelen));
      rseg = pcb->unacked;
      pcb->unacked = rseg->next;

      /* If there's nothing left to acknowledge, stop the retransmit
         timer, otherwise reset it to start again */
      if(pcb->unacked == NULL)
        pcb->rtime = -1;
      else {
        pcb->rtime = 0;
        pcb->nrtx = 0;
      }

      tcp_seg_free(rseg);

      /* Call the user specified function to call when sucessfully
       * connected. */
      TCP_EVENT_CONNECTED(pcb, ERR_OK, err);
      tcp_ack_now(pcb);
    }
    /* received ACK? possibly a half-open connection */
    else if (flags & TCP_ACK) {
      /* send a RST to bring the other side in a non-synchronized state. */
      tcp_rst(ackno, seqno + tcplen, &(iphdr->dest), &(iphdr->src),
        tcphdr->dest, tcphdr->src);
    }
    break;
  case SYN_RCVD:
    if (flags & TCP_ACK &&
       !(flags & TCP_RST)) {
      /* expected ACK number? */
      if (TCP_SEQ_BETWEEN(ackno, pcb->lastack+1, pcb->snd_nxt)) {
        u16_t old_cwnd;
        pcb->state = ESTABLISHED;
        LWIP_DEBUGF(TCP_DEBUG, ("TCP connection established %"U16_F" -> %"U16_F".\n", inseg.tcphdr->src, inseg.tcphdr->dest));
#if LWIP_CALLBACK_API
        LWIP_ASSERT("pcb->accept != NULL", pcb->accept != NULL);
#endif
        /* Call the accept function. */
        TCP_EVENT_ACCEPT(pcb, ERR_OK, err);
        if (err != ERR_OK) {
          /* If the accept function returns with an error, we abort
           * the connection. */
          tcp_abort(pcb);
          return ERR_ABRT;
        }
        old_cwnd = pcb->cwnd;
        /* If there was any data contained within this ACK,
         * we'd better pass it on to the application as well. */
        accepted_inseq = tcp_receive(pcb);

        pcb->cwnd = ((old_cwnd == 1) ? (pcb->mss * 2) : pcb->mss);

        if ((flags & TCP_FIN) && accepted_inseq) {
          tcp_ack_now(pcb);
          pcb->state = CLOSE_WAIT;
        }
      }
      /* incorrect ACK number */
      else {
        /* send RST */
        tcp_rst(ackno, seqno + tcplen, &(iphdr->dest), &(iphdr->src),
                tcphdr->dest, tcphdr->src);
      }
    }
    break;
  case CLOSE_WAIT:
    /* FALLTHROUGH */
  case ESTABLISHED:
    accepted_inseq = tcp_receive(pcb);
    if ((flags & TCP_FIN) && accepted_inseq) { /* passive close */
      tcp_ack_now(pcb);
      pcb->state = CLOSE_WAIT;
    }
    break;
  case FIN_WAIT_1:
    tcp_receive(pcb);
    if (flags & TCP_FIN) {
      if (flags & TCP_ACK && ackno == pcb->snd_nxt) {
        LWIP_DEBUGF(TCP_DEBUG,
          ("TCP connection closed %"U16_F" -> %"U16_F".\n", inseg.tcphdr->src, inseg.tcphdr->dest));
        tcp_ack_now(pcb);
        tcp_pcb_purge(pcb);
        TCP_RMV(&tcp_active_pcbs, pcb);
        pcb->state = TIME_WAIT;
        TCP_REG(&tcp_tw_pcbs, pcb);
      } else {
        tcp_ack_now(pcb);
        pcb->state = CLOSING;
      }
    } else if (flags & TCP_ACK && ackno == pcb->snd_nxt) {
      pcb->state = FIN_WAIT_2;
    }
    break;
  case FIN_WAIT_2:
    tcp_receive(pcb);
    if (flags & TCP_FIN) {
      LWIP_DEBUGF(TCP_DEBUG, ("TCP connection closed %"U16_F" -> %"U16_F".\n", inseg.tcphdr->src, inseg.tcphdr->dest));
      tcp_ack_now(pcb);
      tcp_pcb_purge(pcb);
      TCP_RMV(&tcp_active_pcbs, pcb);
      pcb->state = TIME_WAIT;
      TCP_REG(&tcp_tw_pcbs, pcb);
    }
    break;
  case CLOSING:
    tcp_receive(pcb);
    if (flags & TCP_ACK && ackno == pcb->snd_nxt) {
      LWIP_DEBUGF(TCP_DEBUG, ("TCP connection closed %"U16_F" -> %"U16_F".\n", inseg.tcphdr->src, inseg.tcphdr->dest));
      tcp_ack_now(pcb);
      tcp_pcb_purge(pcb);
      TCP_RMV(&tcp_active_pcbs, pcb);