tcp_out.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, outgoing traffic
 *
 * The output functions of TCP.
 *
 */

/*
 * 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/def.h"
#include "lwip/opt.h"
#include "lwip/mem.h"
#include "lwip/memp.h"
#include "lwip/sys.h"
#include "lwip/ip_addr.h"
#include "lwip/netif.h"
#include "lwip/inet.h"
#include "lwip/tcp.h"
#include "lwip/stats.h"
#include "lwip/snmp.h"

#if LWIP_TCP

/* Forward declarations.*/
static void tcp_output_segment(struct tcp_seg *seg, struct tcp_pcb *pcb);

err_t
tcp_send_ctrl(struct tcp_pcb *pcb, u8_t flags)
{
  /* no data, no length, flags, copy=1, no optdata, no optdatalen */
  return tcp_enqueue(pcb, NULL, 0, flags, 1, NULL, 0);
}

/**
 * Write data for sending (but does not send it immediately).
 *
 * It waits in the expectation of more data being sent soon (as
 * it can send them more efficiently by combining them together).
 * To prompt the system to send data now, call tcp_output() after
 * calling tcp_write().
 * 
 * @arg pcb Protocol control block of the TCP connection to enqueue data for. 
 * 
 * @see tcp_write()
 */

err_t
tcp_write(struct tcp_pcb *pcb, const void *arg, u16_t len, u8_t copy)
{
  LWIP_DEBUGF(TCP_OUTPUT_DEBUG, ("tcp_write(pcb=%p, arg=%p, len=%"U16_F", copy=%"U16_F")\n", (void *)pcb,
    arg, len, (u16_t)copy));
  /* connection is in valid state for data transmission? */
  if (pcb->state == ESTABLISHED ||
     pcb->state == CLOSE_WAIT ||
     pcb->state == SYN_SENT ||
     pcb->state == SYN_RCVD) {
    if (len > 0) {
      return tcp_enqueue(pcb, (void *)arg, len, 0, copy, NULL, 0);
    }
    return ERR_OK;
  } else {
    LWIP_DEBUGF(TCP_OUTPUT_DEBUG | DBG_STATE | 3, ("tcp_write() called in invalid state\n"));
    return ERR_CONN;
  }
}

/**
 * Enqueue either data or TCP options (but not both) for tranmission
 * 
 * 
 * 
 * @arg pcb Protocol control block for the TCP connection to enqueue data for.
 * @arg arg Pointer to the data to be enqueued for sending.
 * @arg len Data length in bytes
 * @arg flags
 * @arg copy 1 if data must be copied, 0 if data is non-volatile and can be
 * referenced.
 * @arg optdata
 * @arg optlen
 */
err_t
tcp_enqueue(struct tcp_pcb *pcb, void *arg, u16_t len,
  u8_t flags, u8_t copy,
  u8_t *optdata, u8_t optlen)
{
  struct pbuf *p;
  struct tcp_seg *seg, *useg, *queue;
  u32_t left, seqno;
  u16_t seglen;
  void *ptr;
  u8_t queuelen;

  LWIP_DEBUGF(TCP_OUTPUT_DEBUG, ("tcp_enqueue(pcb=%p, arg=%p, len=%"U16_F", flags=%"X16_F", copy=%"U16_F")\n",
    (void *)pcb, arg, len, (u16_t)flags, (u16_t)copy));
  LWIP_ASSERT("tcp_enqueue: len == 0 || optlen == 0 (programmer violates API)",
      len == 0 || optlen == 0);
  LWIP_ASSERT("tcp_enqueue: arg == NULL || optdata == NULL (programmer violates API)",
      arg == NULL || optdata == NULL);
  /* fail on too much data */
  if (len > pcb->snd_buf) {
    LWIP_DEBUGF(TCP_OUTPUT_DEBUG | 3, ("tcp_enqueue: too much data (len=%"U16_F" > snd_buf=%"U16_F")\n", len, pcb->snd_buf));
    return ERR_MEM;
  }
  left = len;
  ptr = arg;

  /* seqno will be the sequence number of the first segment enqueued
   * by the call to this function. */
  seqno = pcb->snd_lbb;

  LWIP_DEBUGF(TCP_QLEN_DEBUG, ("tcp_enqueue: queuelen: %"U16_F"\n", (u16_t)pcb->snd_queuelen));

  /* If total number of pbufs on the unsent/unacked queues exceeds the
   * configured maximum, return an error */
  queuelen = pcb->snd_queuelen;
  if (queuelen >= TCP_SND_QUEUELEN) {
    LWIP_DEBUGF(TCP_OUTPUT_DEBUG | 3, ("tcp_enqueue: too long queue %"U16_F" (max %"U16_F")\n", queuelen, TCP_SND_QUEUELEN));
    TCP_STATS_INC(tcp.memerr);
    return ERR_MEM;
  }
  if (queuelen != 0) {
    LWIP_ASSERT("tcp_enqueue: pbufs on queue => at least one queue non-empty",
      pcb->unacked != NULL || pcb->unsent != NULL);
  } else {
    LWIP_ASSERT("tcp_enqueue: no pbufs on queue => both queues empty",
      pcb->unacked == NULL && pcb->unsent == NULL);
  }

  /* First, break up the data into segments and tuck them together in
   * the local "queue" variable. */
  useg = queue = seg = NULL;
  seglen = 0;
  while (queue == NULL || left > 0) {

    /* The segment length should be the MSS if the data to be enqueued
     * is larger than the MSS. */
    seglen = left > pcb->mss? pcb->mss: left;

    /* Allocate memory for tcp_seg, and fill in fields. */
    seg = memp_malloc(MEMP_TCP_SEG);
    if (seg == NULL) {
      LWIP_DEBUGF(TCP_OUTPUT_DEBUG | 2, ("tcp_enqueue: could not allocate memory for tcp_seg\n"));
      goto memerr;
    }
    seg->next = NULL;
    seg->p = NULL;

    /* first segment of to-be-queued data? */
    if (queue == NULL) {
      queue = seg;
    }
    /* subsequent segments of to-be-queued data */
    else {
      /* Attach the segment to the end of the queued segments */
      LWIP_ASSERT("useg != NULL", useg != NULL);
      useg->next = seg;
    }
    /* remember last segment of to-be-queued data for next iteration */
    useg = seg;

    /* If copy is set, memory should be allocated
     * and data copied into pbuf, otherwise data comes from
     * ROM or other static memory, and need not be copied. If
     * optdata is != NULL, we have options instead of data. */
     
    /* options? */
    if (optdata != NULL) {
      if ((seg->p = pbuf_alloc(PBUF_TRANSPORT, optlen, PBUF_RAM)) == NULL) {
        goto memerr;
      }
      ++queuelen;
      seg->dataptr = seg->p->payload;
    }
    /* copy from volatile memory? */
    else if (copy) {
      if ((seg->p = pbuf_alloc(PBUF_TRANSPORT, seglen, PBUF_RAM)) == NULL) {
        LWIP_DEBUGF(TCP_OUTPUT_DEBUG | 2, ("tcp_enqueue : could not allocate memory for pbuf copy size %"U16_F"\n", seglen));
        goto memerr;
      }
      ++queuelen;
      if (arg != NULL) {
        memcpy(seg->p->payload, ptr, seglen);
      }
      seg->dataptr = seg->p->payload;
    }
    /* do not copy data */
    else {
      /* First, allocate a pbuf for holding the data.
       * since the referenced data is available at least until it is sent out on the
       * link (as it has to be ACKed by the remote party) we can safely use PBUF_ROM
       * instead of PBUF_REF here.
       */
      if ((p = pbuf_alloc(PBUF_TRANSPORT, seglen, PBUF_ROM)) == NULL) {
        LWIP_DEBUGF(TCP_OUTPUT_DEBUG | 2, ("tcp_enqueue: could not allocate memory for zero-copy pbuf\n"));
        goto memerr;
      }
      ++queuelen;
      /* reference the non-volatile payload data */
      p->payload = ptr;
      seg->dataptr = ptr;

      /* Second, allocate a pbuf for the headers. */
      if ((seg->p = pbuf_alloc(PBUF_TRANSPORT, 0, PBUF_RAM)) == NULL) {
        /* If allocation fails, we have to deallocate the data pbuf as
         * well. */
        pbuf_free(p);
        LWIP_DEBUGF(TCP_OUTPUT_DEBUG | 2, ("tcp_enqueue: could not allocate memory for header pbuf\n"));
        goto memerr;
      }
      ++queuelen;

      /* Concatenate the headers and data pbufs together. */
      pbuf_cat(seg->p/*header*/, p/*data*/);
      p = NULL;
    }

    /* Now that there are more segments queued, we check again if the
    length of the queue exceeds the configured maximum. */
    if (queuelen > TCP_SND_QUEUELEN) {
      LWIP_DEBUGF(TCP_OUTPUT_DEBUG | 2, ("tcp_enqueue: queue too long %"U16_F" (%"U16_F")\n", queuelen, TCP_SND_QUEUELEN));
      goto memerr;
    }

    seg->len = seglen;

    /* build TCP header */
    if (pbuf_header(seg->p, TCP_HLEN)) {
      LWIP_DEBUGF(TCP_OUTPUT_DEBUG | 2, ("tcp_enqueue: no room for TCP header in pbuf.\n"));
      TCP_STATS_INC(tcp.err);
      goto memerr;
    }
    seg->tcphdr = seg->p->payload;
    seg->tcphdr->src = htons(pcb->local_port);
    seg->tcphdr->dest = htons(pcb->remote_port);
    seg->tcphdr->seqno = htonl(seqno);
    seg->tcphdr->urgp = 0;
    TCPH_FLAGS_SET(seg->tcphdr, flags);
    /* don't fill in tcphdr->ackno and tcphdr->wnd until later */

    /* Copy the options into the header, if they are present. */
    if (optdata == NULL) {
      TCPH_HDRLEN_SET(seg->tcphdr, 5);
    }
    else {
      TCPH_HDRLEN_SET(seg->tcphdr, (5 + optlen / 4));
      /* Copy options into data portion of segment.
       Options can thus only be sent in non data carrying
       segments such as SYN|ACK. */
      memcpy(seg->dataptr, optdata, optlen);
    }
    LWIP_DEBUGF(TCP_OUTPUT_DEBUG | DBG_TRACE, ("tcp_enqueue: queueing %"U32_F":%"U32_F" (0x%"X16_F")\n",
      ntohl(seg->tcphdr->seqno),
      ntohl(seg->tcphdr->seqno) + TCP_TCPLEN(seg),
      (u16_t)flags));

    left -= seglen;
    seqno += seglen;
    ptr = (void *)((u8_t *)ptr + seglen);
  }

  /* Now that the data to be enqueued has been broken up into TCP
  segments in the queue variable, we add them to the end of the
  pcb->unsent queue. */
  if (pcb->unsent == NULL) {
    useg = NULL;
  }
  else {
    for (useg = pcb->unsent; useg->next != NULL; useg = useg->next);
  }
  /* { useg is last segment on the unsent queue, NULL if list is empty } */

  /* If there is room in the last pbuf on the unsent queue,
  chain the first pbuf on the queue together with that. */
  if (useg != NULL &&
    TCP_TCPLEN(useg) != 0 &&
    !(TCPH_FLAGS(useg->tcphdr) & (TCP_SYN | TCP_FIN)) &&
    !(flags & (TCP_SYN | TCP_FIN)) &&
    /* fit within max seg size */
    useg->len + queue->len <= pcb->mss) {
    /* Remove TCP header from first segment of our to-be-queued list */
    pbuf_header(queue->p, -TCP_HLEN);
    pbuf_cat(useg->p, queue->p);
    useg->len += queue->len;
    useg->next = queue->next;

    LWIP_DEBUGF(TCP_OUTPUT_DEBUG | DBG_TRACE | DBG_STATE, ("tcp_enqueue: chaining segments, new len %"U16_F"\n", useg->len));
    if (seg == queue) {
      seg = NULL;
    }
    memp_free(MEMP_TCP_SEG, queue);
  }
  else {
    /* empty list */
    if (useg == NULL) {
      /* initialize list with this segment */
      pcb->unsent = queue;
    }
    /* enqueue segment */
    else {
      useg->next = queue;
    }
  }
  if ((flags & TCP_SYN) || (flags & TCP_FIN)) {
    ++len;
  }
  pcb->snd_lbb += len;

  pcb->snd_buf -= len;

  /* update number of segments on the queues */
  pcb->snd_queuelen = queuelen;
  LWIP_DEBUGF(TCP_QLEN_DEBUG, ("tcp_enqueue: %"S16_F" (after enqueued)\n", pcb->snd_queuelen));
  if (pcb->snd_queuelen != 0) {
    LWIP_ASSERT("tcp_enqueue: valid queue length",
      pcb->unacked != NULL || pcb->unsent != NULL);
  }

  /* Set the PSH flag in the last segment that we enqueued, but only
  if the segment has data (indicated by seglen > 0). */
  if (seg != NULL && seglen > 0 && seg->tcphdr != NULL) {
    TCPH_SET_FLAG(seg->tcphdr, TCP_PSH);
  }

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

  if (queue != NULL) {
    tcp_segs_free(queue);
  }