tcp.c

《嵌入式网络系统设计-基于Atmel ARM7 系列》这个本书的光盘资料

/**
 * @file
 *
 * Transmission Control Protocol for IP
 *
 * This file contains common functions for the TCP implementation, such as functinos
 * for manipulating the data structures and the TCP timer functions. TCP functions
 * related to input and output is found in tcp_in.c and tcp_out.c respectively.
 *
 */

/*
 * Copyright (c) 2001-2004 Swedish Institute of Computer Science.
 * All rights reserved. 
 * 
 * Redistribution and use in source and binary forms, with or without modification, 
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission. 
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED 
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT 
 * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT 
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING 
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY 
 * OF SUCH DAMAGE.
 *
 * This file is part of the lwIP TCP/IP stack.
 * 
 * Author: Adam Dunkels <[e-mail]>
 *
 */

#include <string.h>

#include "lwip/opt.h"
#include "lwip/def.h"
#include "lwip/mem.h"
#include "lwip/memp.h"
#include "lwip/snmp.h"

#include "lwip/tcp.h"
#if LWIP_TCP

/* Incremented every coarse grained timer shot (typically every 500 ms). */
u32_t tcp_ticks;
const u8_t tcp_backoff[13] =
    { 1, 2, 3, 4, 5, 6, 7, 7, 7, 7, 7, 7, 7};

/* The TCP PCB lists. */

/** List of all TCP PCBs in LISTEN state */
union tcp_listen_pcbs_t tcp_listen_pcbs;
/** List of all TCP PCBs that are in a state in which
 * they accept or send data. */
struct tcp_pcb *tcp_active_pcbs;  
/** List of all TCP PCBs in TIME-WAIT state */
struct tcp_pcb *tcp_tw_pcbs;

struct tcp_pcb *tcp_tmp_pcb;

static u8_t tcp_timer;
static u16_t tcp_new_port(void);

/**
 * Initializes the TCP layer.
 */
void
tcp_init(void)
{
  /* Clear globals. */
  tcp_listen_pcbs.listen_pcbs = NULL;
  tcp_active_pcbs = NULL;
  tcp_tw_pcbs = NULL;
  tcp_tmp_pcb = NULL;
  
  /* initialize timer */
  tcp_ticks = 0;
  tcp_timer = 0;
  
}

/**
 * Called periodically to dispatch TCP timers.
 *
 */
void
tcp_tmr(void)
{
  /* Call tcp_fasttmr() every 250 ms */
  tcp_fasttmr();

  if (++tcp_timer & 1) {
    /* Call tcp_tmr() every 500 ms, i.e., every other timer
       tcp_tmr() is called. */
    tcp_slowtmr();
  }
}

/**
 * Closes the connection held by the PCB.
 *
 */
err_t
tcp_close(struct tcp_pcb *pcb)
{
  err_t err;

#if TCP_DEBUG
  LWIP_DEBUGF(TCP_DEBUG, ("tcp_close: closing in "));
  tcp_debug_print_state(pcb->state);
#endif /* TCP_DEBUG */

  switch (pcb->state) {
  case CLOSED:
    /* Closing a pcb in the CLOSED state might seem erroneous,
     * however, it is in this state once allocated and as yet unused
     * and the user needs some way to free it should the need arise.
     * Calling tcp_close() with a pcb that has already been closed, (i.e. twice)
     * or for a pcb that has been used and then entered the CLOSED state 
     * is erroneous, but this should never happen as the pcb has in those cases
     * been freed, and so any remaining handles are bogus. */
    err = ERR_OK;
    memp_free(MEMP_TCP_PCB, pcb);
    pcb = NULL;
    break;
  case LISTEN:
    err = ERR_OK;
    tcp_pcb_remove((struct tcp_pcb **)&tcp_listen_pcbs.pcbs, pcb);
    memp_free(MEMP_TCP_PCB_LISTEN, pcb);
    pcb = NULL;
    break;
  case SYN_SENT:
    err = ERR_OK;
    tcp_pcb_remove(&tcp_active_pcbs, pcb);
    memp_free(MEMP_TCP_PCB, pcb);
    pcb = NULL;
    snmp_inc_tcpattemptfails();
    break;
  case SYN_RCVD:
    err = tcp_send_ctrl(pcb, TCP_FIN);
    if (err == ERR_OK) {
      snmp_inc_tcpattemptfails();
      pcb->state = FIN_WAIT_1;
    }
    break;
  case ESTABLISHED:
    err = tcp_send_ctrl(pcb, TCP_FIN);
    if (err == ERR_OK) {
      snmp_inc_tcpestabresets();
      pcb->state = FIN_WAIT_1;
    }
    break;
  case CLOSE_WAIT:
    err = tcp_send_ctrl(pcb, TCP_FIN);
    if (err == ERR_OK) {
      snmp_inc_tcpestabresets();
      pcb->state = LAST_ACK;
    }
    break;
  default:
    /* Has already been closed, do nothing. */
    err = ERR_OK;
    pcb = NULL;
    break;
  }

  if (pcb != NULL && err == ERR_OK) {
    err = tcp_output(pcb);
  }
  return err;
}

/**
 * Aborts a connection by sending a RST to the remote host and deletes
 * the local protocol control block. This is done when a connection is
 * killed because of shortage of memory.
 *
 */
void
tcp_abort(struct tcp_pcb *pcb)
{
  u32_t seqno, ackno;
  u16_t remote_port, local_port;
  struct ip_addr remote_ip, local_ip;
#if LWIP_CALLBACK_API  
  void (* errf)(void *arg, err_t err);
#endif /* LWIP_CALLBACK_API */
  void *errf_arg;

  
  /* Figure out on which TCP PCB list we are, and remove us. If we
     are in an active state, call the receive function associated with
     the PCB with a NULL argument, and send an RST to the remote end. */
  if (pcb->state == TIME_WAIT) {
    tcp_pcb_remove(&tcp_tw_pcbs, pcb);
    memp_free(MEMP_TCP_PCB, pcb);
  } else {
    seqno = pcb->snd_nxt;
    ackno = pcb->rcv_nxt;
    ip_addr_set(&local_ip, &(pcb->local_ip));
    ip_addr_set(&remote_ip, &(pcb->remote_ip));
    local_port = pcb->local_port;
    remote_port = pcb->remote_port;
#if LWIP_CALLBACK_API
    errf = pcb->errf;
#endif /* LWIP_CALLBACK_API */
    errf_arg = pcb->callback_arg;
    tcp_pcb_remove(&tcp_active_pcbs, pcb);
    if (pcb->unacked != NULL) {
      tcp_segs_free(pcb->unacked);
    }
    if (pcb->unsent != NULL) {
      tcp_segs_free(pcb->unsent);
    }
#if TCP_QUEUE_OOSEQ    
    if (pcb->ooseq != NULL) {
      tcp_segs_free(pcb->ooseq);
    }
#endif /* TCP_QUEUE_OOSEQ */
    memp_free(MEMP_TCP_PCB, pcb);
    TCP_EVENT_ERR(errf, errf_arg, ERR_ABRT);
    LWIP_DEBUGF(TCP_RST_DEBUG, ("tcp_abort: sending RST\n"));
    tcp_rst(seqno, ackno, &local_ip, &remote_ip, local_port, remote_port);
  }
}

/**
 * Binds the connection to a local portnumber and IP address. If the
 * IP address is not given (i.e., ipaddr == NULL), the IP address of
 * the outgoing network interface is used instead.
 *
 */

err_t
tcp_bind(struct tcp_pcb *pcb, struct ip_addr *ipaddr, u16_t port)
{
  struct tcp_pcb *cpcb;

  if (port == 0) {
    port = tcp_new_port();
  }
  /* Check if the address already is in use. */
  for(cpcb = (struct tcp_pcb *)tcp_listen_pcbs.pcbs;
      cpcb != NULL; cpcb = cpcb->next) {
    if (cpcb->local_port == port) {
      if (ip_addr_isany(&(cpcb->local_ip)) ||
        ip_addr_isany(ipaddr) ||
        ip_addr_cmp(&(cpcb->local_ip), ipaddr)) {
          return ERR_USE;
      }
    }
  }
  for(cpcb = tcp_active_pcbs;
      cpcb != NULL; cpcb = cpcb->next) {
    if (cpcb->local_port == port) {
      if (ip_addr_isany(&(cpcb->local_ip)) ||
   ip_addr_isany(ipaddr) ||
   ip_addr_cmp(&(cpcb->local_ip), ipaddr)) {
  return ERR_USE;
      }
    }
  }

  if (!ip_addr_isany(ipaddr)) {
    pcb->local_ip = *ipaddr;
  }
  pcb->local_port = port;
  LWIP_DEBUGF(TCP_DEBUG, ("tcp_bind: bind to port %"U16_F"\n", port));
  return ERR_OK;
}
#if LWIP_CALLBACK_API
static err_t
tcp_accept_null(void *arg, struct tcp_pcb *pcb, err_t err)
{
  (void)arg;
  (void)pcb;
  (void)err;

  return ERR_ABRT;
}
#endif /* LWIP_CALLBACK_API */

/**
 * Set the state of the connection to be LISTEN, which means that it
 * is able to accept incoming connections. The protocol control block
 * is reallocated in order to consume less memory. Setting the
 * connection to LISTEN is an irreversible process.
 *
 */
struct tcp_pcb *
tcp_listen(struct tcp_pcb *pcb)
{
  struct tcp_pcb_listen *lpcb;

  /* already listening? */
  if (pcb->state == LISTEN) {
    return pcb;
  }
  lpcb = memp_malloc(MEMP_TCP_PCB_LISTEN);
  if (lpcb == NULL) {
    return NULL;
  }
  lpcb->callback_arg = pcb->callback_arg;
  lpcb->local_port = pcb->local_port;
  lpcb->state = LISTEN;
  lpcb->so_options = pcb->so_options;
  lpcb->so_options |= SOF_ACCEPTCONN;
  lpcb->ttl = pcb->ttl;
  lpcb->tos = pcb->tos;
  ip_addr_set(&lpcb->local_ip, &pcb->local_ip);
  memp_free(MEMP_TCP_PCB, pcb);
#if LWIP_CALLBACK_API
  lpcb->accept = tcp_accept_null;
#endif /* LWIP_CALLBACK_API */
  TCP_REG(&tcp_listen_pcbs.listen_pcbs, lpcb);
  return (struct tcp_pcb *)lpcb;
}

/**
 * This function should be called by the application when it has
 * processed the data. The purpose is to advertise a larger window
 * when the data has been processed.
 *
 */
void
tcp_recved(struct tcp_pcb *pcb, u16_t len)
{
  if ((u32_t)pcb->rcv_wnd + len > TCP_WND) {
    pcb->rcv_wnd = TCP_WND;
  } else {
    pcb->rcv_wnd += len;
  }
  if (!(pcb->flags & TF_ACK_DELAY) &&
     !(pcb->flags & TF_ACK_NOW)) {
    /*
     * We send an ACK here (if one is not already pending, hence
     * the above tests) as tcp_recved() implies that the application
     * has processed some data, and so we can open the receiver's
     * window to allow more to be transmitted.  This could result in
     * two ACKs being sent for each received packet in some limited cases
     * (where the application is only receiving data, and is slow to
     * process it) but it is necessary to guarantee that the sender can
     * continue to transmit.
     */
    tcp_ack(pcb);
  } 
  else if (pcb->flags & TF_ACK_DELAY && pcb->rcv_wnd >= TCP_WND/2) {
    /* If we can send a window update such that there is a full
     * segment available in the window, do so now.  This is sort of
     * nagle-like in its goals, and tries to hit a compromise between
     * sending acks each time the window is updated, and only sending
     * window updates when a timer expires.  The "threshold" used
     * above (currently TCP_WND/2) can be tuned to be more or less
     * aggressive  */
    tcp_ack_now(pcb);
  }

  LWIP_DEBUGF(TCP_DEBUG, ("tcp_recved: recveived %"U16_F" bytes, wnd %"U16_F" (%"U16_F").\n",
         len, pcb->rcv_wnd, TCP_WND - pcb->rcv_wnd));
}

/**
 * A nastly hack featuring 'goto' statements that allocates a
 * new TCP local port.
 */
static u16_t
tcp_new_port(void)
{
  struct tcp_pcb *pcb;
#ifndef TCP_LOCAL_PORT_RANGE_START
#define TCP_LOCAL_PORT_RANGE_START 4096
#define TCP_LOCAL_PORT_RANGE_END   0x7fff
#endif
  static u16_t port = TCP_LOCAL_PORT_RANGE_START;
  
 again:
  if (++port > TCP_LOCAL_PORT_RANGE_END) {
    port = TCP_LOCAL_PORT_RANGE_START;
  }
  
  for(pcb = tcp_active_pcbs; pcb != NULL; pcb = pcb->next) {
    if (pcb->local_port == port) {
      goto again;
    }