tcp_out.c

lwip-1.4.0

/**
 * @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 "lwip/opt.h"

#if LWIP_TCP /* don't build if not configured for use in lwipopts.h */

#include "lwip/tcp_impl.h"
#include "lwip/def.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_chksum.h"
#include "lwip/stats.h"
#include "lwip/snmp.h"

#include <string.h>

/* Define some copy-macros for checksum-on-copy so that the code looks
   nicer by preventing too many ifdef's. */
#if TCP_CHECKSUM_ON_COPY
#define TCP_DATA_COPY(dst, src, len, seg) do { \
  tcp_seg_add_chksum(LWIP_CHKSUM_COPY(dst, src, len), \
                     len, &seg->chksum, &seg->chksum_swapped); \
  seg->flags |= TF_SEG_DATA_CHECKSUMMED; } while(0)
#define TCP_DATA_COPY2(dst, src, len, chksum, chksum_swapped)  \
  tcp_seg_add_chksum(LWIP_CHKSUM_COPY(dst, src, len), len, chksum, chksum_swapped);
#else /* TCP_CHECKSUM_ON_COPY*/
#define TCP_DATA_COPY(dst, src, len, seg)                     MEMCPY(dst, src, len)
#define TCP_DATA_COPY2(dst, src, len, chksum, chksum_swapped) MEMCPY(dst, src, len)
#endif /* TCP_CHECKSUM_ON_COPY*/

/** Define this to 1 for an extra check that the output checksum is valid
 * (usefule when the checksum is generated by the application, not the stack) */
#ifndef TCP_CHECKSUM_ON_COPY_SANITY_CHECK
#define TCP_CHECKSUM_ON_COPY_SANITY_CHECK   0
#endif

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

/** Allocate a pbuf and create a tcphdr at p->payload, used for output
 * functions other than the default tcp_output -> tcp_output_segment
 * (e.g. tcp_send_empty_ack, etc.)
 *
 * @param pcb tcp pcb for which to send a packet (used to initialize tcp_hdr)
 * @param optlen length of header-options
 * @param datalen length of tcp data to reserve in pbuf
 * @param seqno_be seqno in network byte order (big-endian)
 * @return pbuf with p->payload being the tcp_hdr
 */
static struct pbuf *
tcp_output_alloc_header(struct tcp_pcb *pcb, u16_t optlen, u16_t datalen,
                      u32_t seqno_be /* already in network byte order */)
{
  struct tcp_hdr *tcphdr;
  struct pbuf *p = pbuf_alloc(PBUF_IP, TCP_HLEN + optlen + datalen, PBUF_RAM);
  if (p != NULL) {
    LWIP_ASSERT("check that first pbuf can hold struct tcp_hdr",
                 (p->len >= TCP_HLEN + optlen));
    tcphdr = (struct tcp_hdr *)p->payload;
    tcphdr->src = htons(pcb->local_port);
    tcphdr->dest = htons(pcb->remote_port);
    tcphdr->seqno = seqno_be;
    tcphdr->ackno = htonl(pcb->rcv_nxt);
    TCPH_HDRLEN_FLAGS_SET(tcphdr, (5 + optlen / 4), TCP_ACK);
    tcphdr->wnd = htons(pcb->rcv_ann_wnd);
    tcphdr->chksum = 0;
    tcphdr->urgp = 0;

    /* If we're sending a packet, update the announced right window edge */
    pcb->rcv_ann_right_edge = pcb->rcv_nxt + pcb->rcv_ann_wnd;
  }
  return p;
}

/**
 * Called by tcp_close() to send a segment including FIN flag but not data.
 *
 * @param pcb the tcp_pcb over which to send a segment
 * @return ERR_OK if sent, another err_t otherwise
 */
err_t
tcp_send_fin(struct tcp_pcb *pcb)
{
  /* first, try to add the fin to the last unsent segment */
  if (pcb->unsent != NULL) {
    struct tcp_seg *last_unsent;
    for (last_unsent = pcb->unsent; last_unsent->next != NULL;
         last_unsent = last_unsent->next);

    if ((TCPH_FLAGS(last_unsent->tcphdr) & (TCP_SYN | TCP_FIN | TCP_RST)) == 0) {
      /* no SYN/FIN/RST flag in the header, we can add the FIN flag */
      TCPH_SET_FLAG(last_unsent->tcphdr, TCP_FIN);
      return ERR_OK;
    }
  }
  /* no data, no length, flags, copy=1, no optdata */
  return tcp_enqueue_flags(pcb, TCP_FIN);
}

/**
 * Create a TCP segment with prefilled header.
 *
 * Called by tcp_write and tcp_enqueue_flags.
 *
 * @param pcb Protocol control block for the TCP connection.
 * @param p pbuf that is used to hold the TCP header.
 * @param flags TCP flags for header.
 * @param seqno TCP sequence number of this packet
 * @param optflags options to include in TCP header
 * @return a new tcp_seg pointing to p, or NULL.
 * The TCP header is filled in except ackno and wnd.
 * p is freed on failure.
 */
static struct tcp_seg *
tcp_create_segment(struct tcp_pcb *pcb, struct pbuf *p, u8_t flags, u32_t seqno, u8_t optflags)
{
  struct tcp_seg *seg;
  u8_t optlen = LWIP_TCP_OPT_LENGTH(optflags);

  if ((seg = (struct tcp_seg *)memp_malloc(MEMP_TCP_SEG)) == NULL) {
    LWIP_DEBUGF(TCP_OUTPUT_DEBUG | 2, ("tcp_create_segment: no memory.\n"));
    pbuf_free(p);
    return NULL;
  }
  seg->flags = optflags;
  seg->next = NULL;
  seg->p = p;
  seg->len = p->tot_len - optlen;
#if TCP_OVERSIZE_DBGCHECK
  seg->oversize_left = 0;
#endif /* TCP_OVERSIZE_DBGCHECK */
#if TCP_CHECKSUM_ON_COPY
  seg->chksum = 0;
  seg->chksum_swapped = 0;
  /* check optflags */
  LWIP_ASSERT("invalid optflags passed: TF_SEG_DATA_CHECKSUMMED",
              (optflags & TF_SEG_DATA_CHECKSUMMED) == 0);
#endif /* TCP_CHECKSUM_ON_COPY */

  /* build TCP header */
  if (pbuf_header(p, TCP_HLEN)) {
    LWIP_DEBUGF(TCP_OUTPUT_DEBUG | 2, ("tcp_create_segment: no room for TCP header in pbuf.\n"));
    TCP_STATS_INC(tcp.err);
    tcp_seg_free(seg);
    return NULL;
  }
  seg->tcphdr = (struct tcp_hdr *)seg->p->payload;
  seg->tcphdr->src = htons(pcb->local_port);
  seg->tcphdr->dest = htons(pcb->remote_port);
  seg->tcphdr->seqno = htonl(seqno);
  /* ackno is set in tcp_output */
  TCPH_HDRLEN_FLAGS_SET(seg->tcphdr, (5 + optlen / 4), flags);
  /* wnd and chksum are set in tcp_output */
  seg->tcphdr->urgp = 0;
  return seg;
} 

/**
 * Allocate a PBUF_RAM pbuf, perhaps with extra space at the end.
 *
 * This function is like pbuf_alloc(layer, length, PBUF_RAM) except
 * there may be extra bytes available at the end.
 *
 * @param layer flag to define header size.
 * @param length size of the pbuf's payload.
 * @param max_length maximum usable size of payload+oversize.
 * @param oversize pointer to a u16_t that will receive the number of usable tail bytes.
 * @param pcb The TCP connection that willo enqueue the pbuf.
 * @param apiflags API flags given to tcp_write.
 * @param first_seg true when this pbuf will be used in the first enqueued segment.
 * @param 
 */
#if TCP_OVERSIZE
static struct pbuf *
tcp_pbuf_prealloc(pbuf_layer layer, u16_t length, u16_t max_length,
                  u16_t *oversize, struct tcp_pcb *pcb, u8_t apiflags,
                  u8_t first_seg)
{
  struct pbuf *p;
  u16_t alloc = length;

#if LWIP_NETIF_TX_SINGLE_PBUF
  LWIP_UNUSED_ARG(max_length);
  LWIP_UNUSED_ARG(pcb);
  LWIP_UNUSED_ARG(apiflags);
  LWIP_UNUSED_ARG(first_seg);
  /* always create MSS-sized pbufs */
  alloc = TCP_MSS;
#else /* LWIP_NETIF_TX_SINGLE_PBUF */
  if (length < max_length) {
    /* Should we allocate an oversized pbuf, or just the minimum
     * length required? If tcp_write is going to be called again
     * before this segment is transmitted, we want the oversized
     * buffer. If the segment will be transmitted immediately, we can
     * save memory by allocating only length. We use a simple
     * heuristic based on the following information:
     *
     * Did the user set TCP_WRITE_FLAG_MORE?
     *
     * Will the Nagle algorithm defer transmission of this segment?
     */
    if ((apiflags & TCP_WRITE_FLAG_MORE) ||
        (!(pcb->flags & TF_NODELAY) &&
         (!first_seg ||
          pcb->unsent != NULL ||
          pcb->unacked != NULL))) {
      alloc = LWIP_MIN(max_length, LWIP_MEM_ALIGN_SIZE(length + TCP_OVERSIZE));
    }
  }
#endif /* LWIP_NETIF_TX_SINGLE_PBUF */
  p = pbuf_alloc(layer, alloc, PBUF_RAM);
  if (p == NULL) {
    return NULL;
  }
  LWIP_ASSERT("need unchained pbuf", p->next == NULL);
  *oversize = p->len - length;
  /* trim p->len to the currently used size */
  p->len = p->tot_len = length;
  return p;
}
#else /* TCP_OVERSIZE */
#define tcp_pbuf_prealloc(layer, length, mx, os, pcb, api, fst) pbuf_alloc((layer), (length), PBUF_RAM)
#endif /* TCP_OVERSIZE */

#if TCP_CHECKSUM_ON_COPY
/** Add a checksum of newly added data to the segment */
static void
tcp_seg_add_chksum(u16_t chksum, u16_t len, u16_t *seg_chksum,
                   u8_t *seg_chksum_swapped)
{
  u32_t helper;
  /* add chksum to old chksum and fold to u16_t */
  helper = chksum + *seg_chksum;
  chksum = FOLD_U32T(helper);
  if ((len & 1) != 0) {
    *seg_chksum_swapped = 1 - *seg_chksum_swapped;
    chksum = SWAP_BYTES_IN_WORD(chksum);
  }
  *seg_chksum = chksum;
}
#endif /* TCP_CHECKSUM_ON_COPY */

/** Checks if tcp_write is allowed or not (checks state, snd_buf and snd_queuelen).
 *
 * @param pcb the tcp pcb to check for
 * @param len length of data to send (checked agains snd_buf)
 * @return ERR_OK if tcp_write is allowed to proceed, another err_t otherwise
 */
static err_t
tcp_write_checks(struct tcp_pcb *pcb, u16_t len)
{
  /* connection is in invalid state for data transmission? */
  if ((pcb->state != ESTABLISHED) &&
      (pcb->state != CLOSE_WAIT) &&
      (pcb->state != SYN_SENT) &&
      (pcb->state != SYN_RCVD)) {
    LWIP_DEBUGF(TCP_OUTPUT_DEBUG | LWIP_DBG_STATE | LWIP_DBG_LEVEL_SEVERE, ("tcp_write() called in invalid state\n"));
    return ERR_CONN;
  } else if (len == 0) {
    return ERR_OK;
  }

  /* fail on too much data */
  if (len > pcb->snd_buf) {
    LWIP_DEBUGF(TCP_OUTPUT_DEBUG | 3, ("tcp_write: too much data (len=%"U16_F" > snd_buf=%"U16_F")\n",
      len, pcb->snd_buf));
    pcb->flags |= TF_NAGLEMEMERR;
    return ERR_MEM;
  }

  LWIP_DEBUGF(TCP_QLEN_DEBUG, ("tcp_write: 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 */
  /* check for configured max queuelen and possible overflow */
  if ((pcb->snd_queuelen >= TCP_SND_QUEUELEN) || (pcb->snd_queuelen > TCP_SNDQUEUELEN_OVERFLOW)) {
    LWIP_DEBUGF(TCP_OUTPUT_DEBUG | 3, ("tcp_write: too long queue %"U16_F" (max %"U16_F")\n",
      pcb->snd_queuelen, TCP_SND_QUEUELEN));
    TCP_STATS_INC(tcp.memerr);
    pcb->flags |= TF_NAGLEMEMERR;
    return ERR_MEM;
  }
  if (pcb->snd_queuelen != 0) {
    LWIP_ASSERT("tcp_write: pbufs on queue => at least one queue non-empty",
      pcb->unacked != NULL || pcb->unsent != NULL);
  } else {
    LWIP_ASSERT("tcp_write: no pbufs on queue => both queues empty",
      pcb->unacked == NULL && pcb->unsent == NULL);
  }
  return ERR_OK;
}

/**
 * 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().
 *
 * @param pcb Protocol control block for the TCP connection to enqueue data for.
 * @param arg Pointer to the data to be enqueued for sending.
 * @param len Data length in bytes
 * @param apiflags combination of following flags :
 * - TCP_WRITE_FLAG_COPY (0x01) data will be copied into memory belonging to the stack
 * - TCP_WRITE_FLAG_MORE (0x02) for TCP connection, PSH flag will be set on last segment sent,
 * @return ERR_OK if enqueued, another err_t on error
 */
err_t
tcp_write(struct tcp_pcb *pcb, const void *arg, u16_t len, u8_t apiflags)
{
  struct pbuf *concat_p = NULL;
  struct tcp_seg *last_unsent = NULL, *seg = NULL, *prev_seg = NULL, *queue = NULL;
  u16_t pos = 0; /* position in 'arg' data */
  u16_t queuelen;
  u8_t optlen = 0;
  u8_t optflags = 0;
#if TCP_OVERSIZE
  u16_t oversize = 0;
  u16_t oversize_used = 0;
#endif /* TCP_OVERSIZE */
#if TCP_CHECKSUM_ON_COPY
  u16_t concat_chksum = 0;
  u8_t concat_chksum_swapped = 0;
  u16_t concat_chksummed = 0;
#endif /* TCP_CHECKSUM_ON_COPY */
  err_t err;