Diff: lwip/core/tcp_out.c

Revision:

1:9d93f4dc2f46

Parent:

0:8b387bed54c2

diff -r 8b387bed54c2 -r 9d93f4dc2f46 lwip/core/tcp_out.c
--- a/lwip/core/tcp_out.c	Mon Jan 10 21:03:11 2011 +0000
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,1482 +0,0 @@
-/**
- * @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 <adam@sics.se>
- *
- */
-
-#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->dataptr = p->payload;
-  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;
-
-#if LWIP_NETIF_TX_SINGLE_PBUF
-  /* Always copy to try to create single pbufs for TX */
-  apiflags |= TCP_WRITE_FLAG_COPY;
-#endif /* LWIP_NETIF_TX_SINGLE_PBUF */
-
-  LWIP_DEBUGF(TCP_OUTPUT_DEBUG, ("tcp_write(pcb=%p, data=%p, len=%"U16_F", apiflags=%"U16_F")\n",
-    (void *)pcb, arg, len, (u16_t)apiflags));
-  LWIP_ERROR("tcp_write: arg == NULL (programmer violates API)", 
-             arg != NULL, return ERR_ARG;);
-
-  err = tcp_write_checks(pcb, len);
-  if (err != ERR_OK) {
-    return err;
-  }
-  queuelen = pcb->snd_queuelen;
-
-#if LWIP_TCP_TIMESTAMPS
-  if ((pcb->flags & TF_TIMESTAMP)) {
-    optflags = TF_SEG_OPTS_TS;
-    optlen = LWIP_TCP_OPT_LENGTH(TF_SEG_OPTS_TS);
-  }
-#endif /* LWIP_TCP_TIMESTAMPS */
-
-
-  /*
-   * TCP segmentation is done in three phases with increasing complexity:
-   *
-   * 1. Copy data directly into an oversized pbuf.
-   * 2. Chain a new pbuf to the end of pcb->unsent.
-   * 3. Create new segments.
-   *
-   * We may run out of memory at any point. In that case we must
-   * return ERR_MEM and not change anything in pcb. Therefore, all
-   * changes are recorded in local variables and committed at the end
-   * of the function. Some pcb fields are maintained in local copies:
-   *
-   * queuelen = pcb->snd_queuelen
-   * oversize = pcb->unsent_oversize
-   *
-   * These variables are set consistently by the phases:
-   *
-   * seg points to the last segment tampered with.
-   *
-   * pos records progress as data is segmented.
-   */
-
-  /* Find the tail of the unsent queue. */
-  if (pcb->unsent != NULL) {
-    u16_t space;
-    u16_t unsent_optlen;
-
-    /* @todo: this could be sped up by keeping last_unsent in the pcb */
-    for (last_unsent = pcb->unsent; last_unsent->next != NULL;
-         last_unsent = last_unsent->next);
-
-    /* Usable space at the end of the last unsent segment */
-    unsent_optlen = LWIP_TCP_OPT_LENGTH(last_unsent->flags);
-    space = pcb->mss - (last_unsent->len + unsent_optlen);
-
-    /*
-     * Phase 1: Copy data directly into an oversized pbuf.
-     *
-     * The number of bytes copied is recorded in the oversize_used
-     * variable. The actual copying is done at the bottom of the
-     * function.
-     */
-#if TCP_OVERSIZE
-#if TCP_OVERSIZE_DBGCHECK
-    /* check that pcb->unsent_oversize matches last_unsent->unsent_oversize */
-    LWIP_ASSERT("unsent_oversize mismatch (pcb vs. last_unsent)",
-                pcb->unsent_oversize == last_unsent->oversize_left);
-#endif /* TCP_OVERSIZE_DBGCHECK */
-    oversize = pcb->unsent_oversize;
-    if (oversize > 0) {
-      LWIP_ASSERT("inconsistent oversize vs. space", oversize_used <= space);
-      seg = last_unsent;
-      oversize_used = oversize < len ? oversize : len;
-      pos += oversize_used;
-      oversize -= oversize_used;
-      space -= oversize_used;
-    }
-    /* now we are either finished or oversize is zero */
-    LWIP_ASSERT("inconsistend oversize vs. len", (oversize == 0) || (pos == len));
-#endif /* TCP_OVERSIZE */
-
-    /*
-     * Phase 2: Chain a new pbuf to the end of pcb->unsent.
-     *
-     * We don't extend segments containing SYN/FIN flags or options
-     * (len==0). The new pbuf is kept in concat_p and pbuf_cat'ed at
-     * the end.
-     */
-    if ((pos < len) && (space > 0) && (last_unsent->len > 0)) {
-      u16_t seglen = space < len - pos ? space : len - pos;
-      seg = last_unsent;
-
-      /* Create a pbuf with a copy or reference to seglen bytes. We
-       * can use PBUF_RAW here since the data appears in the middle of
-       * a segment. A header will never be prepended. */
-      if (apiflags & TCP_WRITE_FLAG_COPY) {
-        /* Data is copied */
-        if ((concat_p = tcp_pbuf_prealloc(PBUF_RAW, seglen, space, &oversize, pcb, apiflags, 1)) == NULL) {
-          LWIP_DEBUGF(TCP_OUTPUT_DEBUG | 2,
-                      ("tcp_write : could not allocate memory for pbuf copy size %"U16_F"\n",
-                       seglen));
-          goto memerr;
-        }
-#if TCP_OVERSIZE_DBGCHECK
-        last_unsent->oversize_left = oversize;
-#endif /* TCP_OVERSIZE_DBGCHECK */
-        TCP_DATA_COPY2(concat_p->payload, (u8_t*)arg + pos, seglen, &concat_chksum, &concat_chksum_swapped);
-#if TCP_CHECKSUM_ON_COPY
-        concat_chksummed += seglen;
-#endif /* TCP_CHECKSUM_ON_COPY */
-      } else {
-        /* Data is not copied */
-        if ((concat_p = pbuf_alloc(PBUF_RAW, seglen, PBUF_ROM)) == NULL) {
-          LWIP_DEBUGF(TCP_OUTPUT_DEBUG | 2,
-                      ("tcp_write: could not allocate memory for zero-copy pbuf\n"));
-          goto memerr;
-        }
-#if TCP_CHECKSUM_ON_COPY
-        /* calculate the checksum of nocopy-data */
-        tcp_seg_add_chksum(~inet_chksum((u8_t*)arg + pos, seglen), seglen,
-          &concat_chksum, &concat_chksum_swapped);
-        concat_chksummed += seglen;
-#endif /* TCP_CHECKSUM_ON_COPY */
-        /* reference the non-volatile payload data */
-        concat_p->payload = (u8_t*)arg + pos;
-      }
-
-      pos += seglen;
-      queuelen += pbuf_clen(concat_p);
-    }
-  } else {
-#if TCP_OVERSIZE
-    LWIP_ASSERT("unsent_oversize mismatch (pcb->unsent is NULL)",
-                pcb->unsent_oversize == 0);
-#endif /* TCP_OVERSIZE */
-  }
-
-  /*
-   * Phase 3: Create new segments.
-   *
-   * The new segments are chained together in the local 'queue'
-   * variable, ready to be appended to pcb->unsent.
-   */
-  while (pos < len) {
-    struct pbuf *p;
-    u16_t left = len - pos;
-    u16_t max_len = pcb->mss - optlen;
-    u16_t seglen = left > max_len ? max_len : left;
-#if TCP_CHECKSUM_ON_COPY
-    u16_t chksum = 0;
-    u8_t chksum_swapped = 0;
-#endif /* TCP_CHECKSUM_ON_COPY */
-
-    if (apiflags & TCP_WRITE_FLAG_COPY) {
-      /* If copy is set, memory should be allocated and data copied
-       * into pbuf */
-      if ((p = tcp_pbuf_prealloc(PBUF_TRANSPORT, seglen + optlen, pcb->mss, &oversize, pcb, apiflags, queue == NULL)) == NULL) {
-        LWIP_DEBUGF(TCP_OUTPUT_DEBUG | 2, ("tcp_write : could not allocate memory for pbuf copy size %"U16_F"\n", seglen));
-        goto memerr;
-      }
-      LWIP_ASSERT("tcp_write: check that first pbuf can hold the complete seglen",
-                  (p->len >= seglen));
-      TCP_DATA_COPY2((char *)p->payload + optlen, (u8_t*)arg + pos, seglen, &chksum, &chksum_swapped);
-    } else {
-      /* Copy is not set: 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.
-       */
-      struct pbuf *p2;
-#if TCP_OVERSIZE
-      LWIP_ASSERT("oversize == 0", oversize == 0);
-#endif /* TCP_OVERSIZE */
-      if ((p2 = pbuf_alloc(PBUF_TRANSPORT, seglen, PBUF_ROM)) == NULL) {
-        LWIP_DEBUGF(TCP_OUTPUT_DEBUG | 2, ("tcp_write: could not allocate memory for zero-copy pbuf\n"));
-        goto memerr;
-      }
-#if TCP_CHECKSUM_ON_COPY
-      /* calculate the checksum of nocopy-data */
-      chksum = ~inet_chksum((u8_t*)arg + pos, seglen);
-#endif /* TCP_CHECKSUM_ON_COPY */
-      /* reference the non-volatile payload data */
-      p2->payload = (u8_t*)arg + pos;
-
-      /* Second, allocate a pbuf for the headers. */
-      if ((p = pbuf_alloc(PBUF_TRANSPORT, optlen, PBUF_RAM)) == NULL) {
-        /* If allocation fails, we have to deallocate the data pbuf as
-         * well. */
-        pbuf_free(p2);
-        LWIP_DEBUGF(TCP_OUTPUT_DEBUG | 2, ("tcp_write: could not allocate memory for header pbuf\n"));
-        goto memerr;
-      }
-      /* Concatenate the headers and data pbufs together. */
-      pbuf_cat(p/*header*/, p2/*data*/);
-    }
-
-    queuelen += pbuf_clen(p);
-
-    /* Now that there are more segments queued, we check again if the
-     * length of the queue exceeds the configured maximum or
-     * overflows. */
-    if ((queuelen > TCP_SND_QUEUELEN) || (queuelen > TCP_SNDQUEUELEN_OVERFLOW)) {
-      LWIP_DEBUGF(TCP_OUTPUT_DEBUG | 2, ("tcp_write: queue too long %"U16_F" (%"U16_F")\n", queuelen, TCP_SND_QUEUELEN));
-      pbuf_free(p);
-      goto memerr;
-    }
-
-    if ((seg = tcp_create_segment(pcb, p, 0, pcb->snd_lbb + pos, optflags)) == NULL) {
-      goto memerr;
-    }
-#if TCP_OVERSIZE_DBGCHECK
-    seg->oversize_left = oversize;
-#endif /* TCP_OVERSIZE_DBGCHECK */
-#if TCP_CHECKSUM_ON_COPY
-    seg->chksum = chksum;
-    seg->chksum_swapped = chksum_swapped;
-    seg->flags |= TF_SEG_DATA_CHECKSUMMED;
-#endif /* TCP_CHECKSUM_ON_COPY */
-    /* Fix dataptr for the nocopy case */
-    if ((apiflags & TCP_WRITE_FLAG_COPY) == 0) {
-      seg->dataptr = (u8_t*)arg + pos;
-    }
-
-    /* first segment of to-be-queued data? */
-    if (queue == NULL) {
-      queue = seg;
-    } else {
-      /* Attach the segment to the end of the queued segments */
-      LWIP_ASSERT("prev_seg != NULL", prev_seg != NULL);
-      prev_seg->next = seg;
-    }
-    /* remember last segment of to-be-queued data for next iteration */
-    prev_seg = seg;
-
-    LWIP_DEBUGF(TCP_OUTPUT_DEBUG | LWIP_DBG_TRACE, ("tcp_write: queueing %"U32_F":%"U32_F"\n",
-      ntohl(seg->tcphdr->seqno),
-      ntohl(seg->tcphdr->seqno) + TCP_TCPLEN(seg)));
-
-    pos += seglen;
-  }
-
-  /*
-   * All three segmentation phases were successful. We can commit the
-   * transaction.
-   */
-
-  /*
-   * Phase 1: If data has been added to the preallocated tail of
-   * last_unsent, we update the length fields of the pbuf chain.
-   */
-#if TCP_OVERSIZE
-  if (oversize_used > 0) {
-    struct pbuf *p;
-    /* Bump tot_len of whole chain, len of tail */
-    for (p = last_unsent->p; p; p = p->next) {
-      p->tot_len += oversize_used;
-      if (p->next == NULL) {
-        TCP_DATA_COPY((char *)p->payload + p->len, arg, oversize_used, last_unsent);
-        p->len += oversize_used;
-      }
-    }
-    last_unsent->len += oversize_used;
-#if TCP_OVERSIZE_DBGCHECK
-    last_unsent->oversize_left -= oversize_used;
-#endif /* TCP_OVERSIZE_DBGCHECK */
-  }
-  pcb->unsent_oversize = oversize;
-#endif /* TCP_OVERSIZE */
-
-  /*
-   * Phase 2: concat_p can be concatenated onto last_unsent->p
-   */
-  if (concat_p != NULL) {
-    LWIP_ASSERT("tcp_write: cannot concatenate when pcb->unsent is empty",
-      (last_unsent != NULL));
-    pbuf_cat(last_unsent->p, concat_p);
-    last_unsent->len += concat_p->tot_len;
-#if TCP_CHECKSUM_ON_COPY
-    if (concat_chksummed) {
-      tcp_seg_add_chksum(concat_chksum, concat_chksummed, &last_unsent->chksum,
-        &last_unsent->chksum_swapped);
-      last_unsent->flags |= TF_SEG_DATA_CHECKSUMMED;
-    }
-#endif /* TCP_CHECKSUM_ON_COPY */
-  }
-
-  /*
-   * Phase 3: Append queue to pcb->unsent. Queue may be NULL, but that
-   * is harmless
-   */
-  if (last_unsent == NULL) {
-    pcb->unsent = queue;
-  } else {
-    last_unsent->next = queue;
-  }
-
-  /*
-   * Finally update the pcb state.
-   */
-  pcb->snd_lbb += len;
-  pcb->snd_buf -= len;
-  pcb->snd_queuelen = queuelen;
-
-  LWIP_DEBUGF(TCP_QLEN_DEBUG, ("tcp_write: %"S16_F" (after enqueued)\n",
-    pcb->snd_queuelen));
-  if (pcb->snd_queuelen != 0) {
-    LWIP_ASSERT("tcp_write: valid queue length",
-                pcb->unacked != NULL || pcb->unsent != NULL);
-  }
-
-  /* Set the PSH flag in the last segment that we enqueued. */
-  if (seg != NULL && seg->tcphdr != NULL && ((apiflags & TCP_WRITE_FLAG_MORE)==0)) {
-    TCPH_SET_FLAG(seg->tcphdr, TCP_PSH);
-  }
-
-  return ERR_OK;
-memerr:
-  pcb->flags |= TF_NAGLEMEMERR;
-  TCP_STATS_INC(tcp.memerr);
-
-  if (concat_p != NULL) {
-    pbuf_free(concat_p);
-  }
-  if (queue != NULL) {
-    tcp_segs_free(queue);
-  }
-  if (pcb->snd_queuelen != 0) {
-    LWIP_ASSERT("tcp_write: valid queue length", pcb->unacked != NULL ||
-      pcb->unsent != NULL);
-  }
-  LWIP_DEBUGF(TCP_QLEN_DEBUG | LWIP_DBG_STATE, ("tcp_write: %"S16_F" (with mem err)\n", pcb->snd_queuelen));
-  return ERR_MEM;
-}
-
-/**
- * Enqueue TCP options for transmission.
- *
- * Called by tcp_connect(), tcp_listen_input(), and tcp_send_ctrl().
- *
- * @param pcb Protocol control block for the TCP connection.
- * @param flags TCP header flags to set in the outgoing segment.
- * @param optdata pointer to TCP options, or NULL.
- * @param optlen length of TCP options in bytes.
- */
-err_t
-tcp_enqueue_flags(struct tcp_pcb *pcb, u8_t flags)
-{
-  struct pbuf *p;
-  struct tcp_seg *seg;
-  u8_t optflags = 0;
-  u8_t optlen = 0;
-
-  LWIP_DEBUGF(TCP_QLEN_DEBUG, ("tcp_enqueue_flags: queuelen: %"U16_F"\n", (u16_t)pcb->snd_queuelen));
-
-  LWIP_ASSERT("tcp_enqueue_flags: need either TCP_SYN or TCP_FIN in flags (programmer violates API)",
-              (flags & (TCP_SYN | TCP_FIN)) != 0);
-
-  /* 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_enqueue_flags: 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 (flags & TCP_SYN) {
-    optflags = TF_SEG_OPTS_MSS;
-  }
-#if LWIP_TCP_TIMESTAMPS
-  if ((pcb->flags & TF_TIMESTAMP)) {
-    optflags |= TF_SEG_OPTS_TS;
-  }
-#endif /* LWIP_TCP_TIMESTAMPS */
-  optlen = LWIP_TCP_OPT_LENGTH(optflags);
-
-  /* tcp_enqueue_flags is always called with either SYN or FIN in flags.
-   * We need one available snd_buf byte to do that.
-   * This means we can't send FIN while snd_buf==0. A better fix would be to
-   * not include SYN and FIN sequence numbers in the snd_buf count. */
-  if (pcb->snd_buf == 0) {
-    LWIP_DEBUGF(TCP_OUTPUT_DEBUG | 3, ("tcp_enqueue_flags: no send buffer available\n"));
-    TCP_STATS_INC(tcp.memerr);
-    return ERR_MEM;
-  }
-
-  /* Allocate pbuf with room for TCP header + options */
-  if ((p = pbuf_alloc(PBUF_TRANSPORT, optlen, PBUF_RAM)) == NULL) {
-    pcb->flags |= TF_NAGLEMEMERR;
-    TCP_STATS_INC(tcp.memerr);
-    return ERR_MEM;
-  }
-  LWIP_ASSERT("tcp_enqueue_flags: check that first pbuf can hold optlen",
-              (p->len >= optlen));
-
-  /* Allocate memory for tcp_seg, and fill in fields. */
-  if ((seg = tcp_create_segment(pcb, p, flags, pcb->snd_lbb, optflags)) == NULL) {
-    pcb->flags |= TF_NAGLEMEMERR;
-    TCP_STATS_INC(tcp.memerr);
-    return ERR_MEM;
-  }
-  LWIP_ASSERT("tcp_enqueue_flags: invalid segment length", seg->len == 0);
-
-  LWIP_DEBUGF(TCP_OUTPUT_DEBUG | LWIP_DBG_TRACE,
-              ("tcp_enqueue_flags: queueing %"U32_F":%"U32_F" (0x%"X16_F")\n",
-               ntohl(seg->tcphdr->seqno),
-               ntohl(seg->tcphdr->seqno) + TCP_TCPLEN(seg),
-               (u16_t)flags));
-
-  /* Now append seg to pcb->unsent queue */
-  if (pcb->unsent == NULL) {
-    pcb->unsent = seg;
-  } else {
-    struct tcp_seg *useg;
-    for (useg = pcb->unsent; useg->next != NULL; useg = useg->next);
-    useg->next = seg;
-  }
-#if TCP_OVERSIZE
-  /* The new unsent tail has no space */
-  pcb->unsent_oversize = 0;
-#endif /* TCP_OVERSIZE */
-
-  /* SYN and FIN bump the sequence number */
-  if ((flags & TCP_SYN) || (flags & TCP_FIN)) {
-    pcb->snd_lbb++;
-    /* optlen does not influence snd_buf */
-    pcb->snd_buf--;
-  }
-  if (flags & TCP_FIN) {
-    pcb->flags |= TF_FIN;
-  }
-
-  /* update number of segments on the queues */
-  pcb->snd_queuelen += pbuf_clen(seg->p);
-  LWIP_DEBUGF(TCP_QLEN_DEBUG, ("tcp_enqueue_flags: %"S16_F" (after enqueued)\n", pcb->snd_queuelen));
-  if (pcb->snd_queuelen != 0) {
-    LWIP_ASSERT("tcp_enqueue_flags: invalid queue length",
-      pcb->unacked != NULL || pcb->unsent != NULL);
-  }
-
-  return ERR_OK;
-}
- 
-
-#if LWIP_TCP_TIMESTAMPS
-/* Build a timestamp option (12 bytes long) at the specified options pointer)
- *
- * @param pcb tcp_pcb
- * @param opts option pointer where to store the timestamp option
- */
-static void
-tcp_build_timestamp_option(struct tcp_pcb *pcb, u32_t *opts)
-{
-  /* Pad with two NOP options to make everything nicely aligned */
-  opts[0] = PP_HTONL(0x0101080A);
-  opts[1] = htonl(sys_now());
-  opts[2] = htonl(pcb->ts_recent);
-}
-#endif
-
-/** Send an ACK without data.
- *
- * @param pcb Protocol control block for the TCP connection to send the ACK
- */
-err_t
-tcp_send_empty_ack(struct tcp_pcb *pcb)
-{
-  struct pbuf *p;
-  struct tcp_hdr *tcphdr;
-  u8_t optlen = 0;
-
-#if LWIP_TCP_TIMESTAMPS
-  if (pcb->flags & TF_TIMESTAMP) {
-    optlen = LWIP_TCP_OPT_LENGTH(TF_SEG_OPTS_TS);
-  }
-#endif
-
-  p = tcp_output_alloc_header(pcb, optlen, 0, htonl(pcb->snd_nxt));
-  if (p == NULL) {
-    LWIP_DEBUGF(TCP_OUTPUT_DEBUG, ("tcp_output: (ACK) could not allocate pbuf\n"));
-    return ERR_BUF;
-  }
-  tcphdr = (struct tcp_hdr *)p->payload;
-  LWIP_DEBUGF(TCP_OUTPUT_DEBUG, 
-              ("tcp_output: sending ACK for %"U32_F"\n", pcb->rcv_nxt));
-  /* remove ACK flags from the PCB, as we send an empty ACK now */
-  pcb->flags &= ~(TF_ACK_DELAY | TF_ACK_NOW);
-
-  /* NB. MSS option is only sent on SYNs, so ignore it here */
-#if LWIP_TCP_TIMESTAMPS
-  pcb->ts_lastacksent = pcb->rcv_nxt;
-
-  if (pcb->flags & TF_TIMESTAMP) {
-    tcp_build_timestamp_option(pcb, (u32_t *)(tcphdr + 1));
-  }
-#endif 
-
-#if CHECKSUM_GEN_TCP
-  tcphdr->chksum = inet_chksum_pseudo(p, &(pcb->local_ip), &(pcb->remote_ip),
-        IP_PROTO_TCP, p->tot_len);
-#endif
-#if LWIP_NETIF_HWADDRHINT
-  ip_output_hinted(p, &(pcb->local_ip), &(pcb->remote_ip), pcb->ttl, pcb->tos,
-      IP_PROTO_TCP, &(pcb->addr_hint));
-#else /* LWIP_NETIF_HWADDRHINT*/
-  ip_output(p, &(pcb->local_ip), &(pcb->remote_ip), pcb->ttl, pcb->tos,
-      IP_PROTO_TCP);
-#endif /* LWIP_NETIF_HWADDRHINT*/
-  pbuf_free(p);
-
-  return ERR_OK;
-}
-
-/**
- * Find out what we can send and send it
- *
- * @param pcb Protocol control block for the TCP connection to send data
- * @return ERR_OK if data has been sent or nothing to send
- *         another err_t on error
- */
-err_t
-tcp_output(struct tcp_pcb *pcb)
-{
-  struct tcp_seg *seg, *useg;
-  u32_t wnd, snd_nxt;
-#if TCP_CWND_DEBUG
-  s16_t i = 0;
-#endif /* TCP_CWND_DEBUG */
-
-  /* First, check if we are invoked by the TCP input processing
-     code. If so, we do not output anything. Instead, we rely on the
-     input processing code to call us when input processing is done
-     with. */
-  if (tcp_input_pcb == pcb) {
-    return ERR_OK;
-  }
-
-  wnd = LWIP_MIN(pcb->snd_wnd, pcb->cwnd);
-
-  seg = pcb->unsent;
-
-  /* If the TF_ACK_NOW flag is set and no data will be sent (either
-   * because the ->unsent queue is empty or because the window does
-   * not allow it), construct an empty ACK segment and send it.
-   *
-   * If data is to be sent, we will just piggyback the ACK (see below).
-   */
-  if (pcb->flags & TF_ACK_NOW &&
-     (seg == NULL ||
-      ntohl(seg->tcphdr->seqno) - pcb->lastack + seg->len > wnd)) {
-     return tcp_send_empty_ack(pcb);
-  }
-
-  /* useg should point to last segment on unacked queue */
-  useg = pcb->unacked;
-  if (useg != NULL) {
-    for (; useg->next != NULL; useg = useg->next);
-  }
-
-#if TCP_OUTPUT_DEBUG
-  if (seg == NULL) {
-    LWIP_DEBUGF(TCP_OUTPUT_DEBUG, ("tcp_output: nothing to send (%p)\n",
-                                   (void*)pcb->unsent));
-  }
-#endif /* TCP_OUTPUT_DEBUG */
-#if TCP_CWND_DEBUG
-  if (seg == NULL) {
-    LWIP_DEBUGF(TCP_CWND_DEBUG, ("tcp_output: snd_wnd %"U16_F
-                                 ", cwnd %"U16_F", wnd %"U32_F
-                                 ", seg == NULL, ack %"U32_F"\n",
-                                 pcb->snd_wnd, pcb->cwnd, wnd, pcb->lastack));
-  } else {
-    LWIP_DEBUGF(TCP_CWND_DEBUG, 
-                ("tcp_output: snd_wnd %"U16_F", cwnd %"U16_F", wnd %"U32_F
-                 ", effwnd %"U32_F", seq %"U32_F", ack %"U32_F"\n",
-                 pcb->snd_wnd, pcb->cwnd, wnd,
-                 ntohl(seg->tcphdr->seqno) - pcb->lastack + seg->len,
-                 ntohl(seg->tcphdr->seqno), pcb->lastack));
-  }
-#endif /* TCP_CWND_DEBUG */
-  /* data available and window allows it to be sent? */
-  while (seg != NULL &&
-         ntohl(seg->tcphdr->seqno) - pcb->lastack + seg->len <= wnd) {
-    LWIP_ASSERT("RST not expected here!", 
-                (TCPH_FLAGS(seg->tcphdr) & TCP_RST) == 0);
-    /* Stop sending if the nagle algorithm would prevent it
-     * Don't stop:
-     * - if tcp_write had a memory error before (prevent delayed ACK timeout) or
-     * - if FIN was already enqueued for this PCB (SYN is always alone in a segment -
-     *   either seg->next != NULL or pcb->unacked == NULL;
-     *   RST is no sent using tcp_write/tcp_output.
-     */
-    if((tcp_do_output_nagle(pcb) == 0) &&
-      ((pcb->flags & (TF_NAGLEMEMERR | TF_FIN)) == 0)){
-      break;
-    }
-#if TCP_CWND_DEBUG
-    LWIP_DEBUGF(TCP_CWND_DEBUG, ("tcp_output: snd_wnd %"U16_F", cwnd %"U16_F", wnd %"U32_F", effwnd %"U32_F", seq %"U32_F", ack %"U32_F", i %"S16_F"\n",
-                            pcb->snd_wnd, pcb->cwnd, wnd,
-                            ntohl(seg->tcphdr->seqno) + seg->len -
-                            pcb->lastack,
-                            ntohl(seg->tcphdr->seqno), pcb->lastack, i));
-    ++i;
-#endif /* TCP_CWND_DEBUG */
-
-    pcb->unsent = seg->next;
-
-    if (pcb->state != SYN_SENT) {
-      TCPH_SET_FLAG(seg->tcphdr, TCP_ACK);
-      pcb->flags &= ~(TF_ACK_DELAY | TF_ACK_NOW);
-    }
-
-    tcp_output_segment(seg, pcb);
-       
-    snd_nxt = ntohl(seg->tcphdr->seqno) + TCP_TCPLEN(seg);
-    
-    LWIP_DEBUGF(TCP_OUTPUT_DEBUG, ("tcp_output: pcb->snd_nxt was %"U32_F" seqno=%"U32_F" len=%"U32_F" new snd_nxt=%"U32_F"\n", //DG
-                                    pcb->snd_nxt, ntohl(seg->tcphdr->seqno), TCP_TCPLEN(seg), snd_nxt));
-    
-    if (TCP_SEQ_LT(pcb->snd_nxt, snd_nxt)) {
-      pcb->snd_nxt = snd_nxt;
-    }
-    /* put segment on unacknowledged list if length > 0 */
-    if (TCP_TCPLEN(seg) > 0) {
-      seg->next = NULL;
-      /* unacked list is empty? */
-      if (pcb->unacked == NULL) {
-        pcb->unacked = seg;
-        useg = seg;
-      /* unacked list is not empty? */
-      } else {
-        /* In the case of fast retransmit, the packet should not go to the tail
-         * of the unacked queue, but rather somewhere before it. We need to check for
-         * this case. -STJ Jul 27, 2004 */
-        if (TCP_SEQ_LT(ntohl(seg->tcphdr->seqno), ntohl(useg->tcphdr->seqno))) {
-          /* add segment to before tail of unacked list, keeping the list sorted */
-          struct tcp_seg **cur_seg = &(pcb->unacked);
-          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;
-        } else {
-          /* add segment to tail of unacked list */
-          useg->next = seg;
-          useg = useg->next;
-        }
-      }
-    /* do not queue empty segments on the unacked list */
-    } else {
-      tcp_seg_free(seg);
-    }
-    seg = pcb->unsent;
-  }
-#if TCP_OVERSIZE
-  if (pcb->unsent == NULL) {
-    /* last unsent has been removed, reset unsent_oversize */
-    pcb->unsent_oversize = 0;
-  }
-#endif /* TCP_OVERSIZE */
-
-  if (seg != NULL && pcb->persist_backoff == 0 && 
-      ntohl(seg->tcphdr->seqno) - pcb->lastack + seg->len > pcb->snd_wnd) {
-    /* prepare for persist timer */
-    pcb->persist_cnt = 0;
-    pcb->persist_backoff = 1;
-  }
-
-  pcb->flags &= ~TF_NAGLEMEMERR;
-  return ERR_OK;
-}
-
-/**
- * Called by tcp_output() to actually send a TCP segment over IP.
- *
- * @param seg the tcp_seg to send
- * @param pcb the tcp_pcb for the TCP connection used to send the segment
- */
-static void
-tcp_output_segment(struct tcp_seg *seg, struct tcp_pcb *pcb)
-{
-  u16_t len;
-  struct netif *netif;
-  u32_t *opts;
-
-  /** @bug Exclude retransmitted segments from this count. */
-  snmp_inc_tcpoutsegs();
-
-  /* The TCP header has already been constructed, but the ackno and
-   wnd fields remain. */
-  seg->tcphdr->ackno = htonl(pcb->rcv_nxt);
-
-  /* advertise our receive window size in this TCP segment */
-  seg->tcphdr->wnd = htons(pcb->rcv_ann_wnd);
-
-  pcb->rcv_ann_right_edge = pcb->rcv_nxt + pcb->rcv_ann_wnd;
-
-  /* Add any requested options.  NB MSS option is only set on SYN
-     packets, so ignore it here */
-  LWIP_ASSERT("seg->tcphdr not aligned", ((mem_ptr_t)(seg->tcphdr + 1) % 4) == 0);
-  opts = (u32_t *)(void *)(seg->tcphdr + 1);
-  if (seg->flags & TF_SEG_OPTS_MSS) {
-    TCP_BUILD_MSS_OPTION(*opts);
-    opts += 1;
-  }
-#if LWIP_TCP_TIMESTAMPS
-  pcb->ts_lastacksent = pcb->rcv_nxt;
-
-  if (seg->flags & TF_SEG_OPTS_TS) {
-    tcp_build_timestamp_option(pcb, opts);
-    opts += 3;
-  }
-#endif
-
-  /* If we don't have a local IP address, we get one by
-     calling ip_route(). */
-  if (ip_addr_isany(&(pcb->local_ip))) {
-    netif = ip_route(&(pcb->remote_ip));
-    if (netif == NULL) {
-      return;
-    }
-    ip_addr_copy(pcb->local_ip, netif->ip_addr);
-  }
-
-  /* Set retransmission timer running if it is not currently enabled */
-  if(pcb->rtime == -1) {
-    pcb->rtime = 0;
-  }
-
-  if (pcb->rttest == 0) {
-    pcb->rttest = tcp_ticks;
-    pcb->rtseq = ntohl(seg->tcphdr->seqno);
-
-    LWIP_DEBUGF(TCP_RTO_DEBUG, ("tcp_output_segment: rtseq %"U32_F"\n", pcb->rtseq));
-  }
-  LWIP_DEBUGF(TCP_OUTPUT_DEBUG, ("tcp_output_segment: %"U32_F":%"U32_F"\n",
-          htonl(seg->tcphdr->seqno), htonl(seg->tcphdr->seqno) +
-          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);
-  
-  LWIP_DEBUGF(TCP_OUTPUT_DEBUG, ("tcp_output_segment: Before ip_out seqno = %"U32_F"\n",
-        htonl(seg->tcphdr->seqno))); //DG
-
-#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*/
-
-  LWIP_DEBUGF(TCP_OUTPUT_DEBUG, ("tcp_output_segment: After ip_out seqno = %"U32_F"\n",
-        htonl(seg->tcphdr->seqno))); //DG
-
-
-}
-
-/**
- * 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 */
-    *((char *)p->payload + TCP_HLEN) = *(char *)seg->dataptr;
-  }
-
-#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 */