lwip_tcp_out.c

00001 /**
00002  * @file
00003  * Transmission Control Protocol, outgoing traffic
00004  *
00005  * The output functions of TCP.
00006  *
00007  * There are two distinct ways for TCP segments to get sent:
00008  * - queued data: these are segments transferring data or segments containing
00009  *   SYN or FIN (which both count as one sequence number). They are created as
00010  *   struct @ref pbuf together with a struct tcp_seg and enqueue to the
00011  *   unsent list of the pcb. They are sent by tcp_output:
00012  *   - @ref tcp_write : creates data segments
00013  *   - @ref tcp_split_unsent_seg : splits a data segment
00014  *   - @ref tcp_enqueue_flags : creates SYN-only or FIN-only segments
00015  *   - @ref tcp_output / tcp_output_segment : finalize the tcp header
00016  *      (e.g. sequence numbers, options, checksum) and output to IP
00017  *   - the various tcp_rexmit functions shuffle around segments between the
00018  *     unsent an unacked lists to retransmit them
00019  *   - tcp_create_segment and tcp_pbuf_prealloc allocate pbuf and
00020  *     segment for these functions
00021  * - direct send: these segments don't contain data but control the connection
00022  *   behaviour. They are created as pbuf only and sent directly without
00023  *   enqueueing them:
00024  *   - @ref tcp_send_empty_ack sends an ACK-only segment
00025  *   - @ref tcp_rst sends a RST segment
00026  *   - @ref tcp_keepalive sends a keepalive segment
00027  *   - @ref tcp_zero_window_probe sends a window probe segment
00028  *   - tcp_output_alloc_header allocates a header-only pbuf for these functions
00029  */
00030 
00031 /*
00032  * Copyright (c) 2001-2004 Swedish Institute of Computer Science.
00033  * All rights reserved.
00034  *
00035  * Redistribution and use in source and binary forms, with or without modification,
00036  * are permitted provided that the following conditions are met:
00037  *
00038  * 1. Redistributions of source code must retain the above copyright notice,
00039  *    this list of conditions and the following disclaimer.
00040  * 2. Redistributions in binary form must reproduce the above copyright notice,
00041  *    this list of conditions and the following disclaimer in the documentation
00042  *    and/or other materials provided with the distribution.
00043  * 3. The name of the author may not be used to endorse or promote products
00044  *    derived from this software without specific prior written permission.
00045  *
00046  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
00047  * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
00048  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
00049  * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
00050  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
00051  * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
00052  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
00053  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
00054  * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
00055  * OF SUCH DAMAGE.
00056  *
00057  * This file is part of the lwIP TCP/IP stack.
00058  *
00059  * Author: Adam Dunkels <adam@sics.se>
00060  *
00061  */
00062 
00063 #include "lwip/opt.h"
00064 
00065 #if LWIP_TCP /* don't build if not configured for use in lwipopts.h */
00066 
00067 #include "lwip/priv/tcp_priv.h"
00068 #include "lwip/def.h"
00069 #include "lwip/mem.h"
00070 #include "lwip/memp.h"
00071 #include "lwip/ip_addr.h"
00072 #include "lwip/netif.h"
00073 #include "lwip/inet_chksum.h"
00074 #include "lwip/stats.h"
00075 #include "lwip/ip6.h"
00076 #include "lwip/ip6_addr.h"
00077 #if LWIP_TCP_TIMESTAMPS
00078 #include "lwip/sys.h"
00079 #endif
00080 
00081 #include <string.h>
00082 
00083 #ifdef LWIP_HOOK_FILENAME
00084 #include LWIP_HOOK_FILENAME
00085 #endif
00086 
00087 /* Allow to add custom TCP header options by defining this hook */
00088 #ifdef LWIP_HOOK_TCP_OUT_TCPOPT_LENGTH
00089 #define LWIP_TCP_OPT_LENGTH_SEGMENT(flags, pcb) LWIP_HOOK_TCP_OUT_TCPOPT_LENGTH(pcb, LWIP_TCP_OPT_LENGTH(flags))
00090 #else
00091 #define LWIP_TCP_OPT_LENGTH_SEGMENT(flags, pcb) LWIP_TCP_OPT_LENGTH(flags)
00092 #endif
00093 
00094 /* Define some copy-macros for checksum-on-copy so that the code looks
00095    nicer by preventing too many ifdef's. */
00096 #if TCP_CHECKSUM_ON_COPY
00097 #define TCP_DATA_COPY(dst, src, len, seg) do { \
00098   tcp_seg_add_chksum(LWIP_CHKSUM_COPY(dst, src, len), \
00099                      len, &seg->chksum, &seg->chksum_swapped); \
00100   seg->flags |= TF_SEG_DATA_CHECKSUMMED; } while(0)
00101 #define TCP_DATA_COPY2(dst, src, len, chksum, chksum_swapped)  \
00102   tcp_seg_add_chksum(LWIP_CHKSUM_COPY(dst, src, len), len, chksum, chksum_swapped);
00103 #else /* TCP_CHECKSUM_ON_COPY*/
00104 #define TCP_DATA_COPY(dst, src, len, seg)                     MEMCPY(dst, src, len)
00105 #define TCP_DATA_COPY2(dst, src, len, chksum, chksum_swapped) MEMCPY(dst, src, len)
00106 #endif /* TCP_CHECKSUM_ON_COPY*/
00107 
00108 /** Define this to 1 for an extra check that the output checksum is valid
00109  * (usefule when the checksum is generated by the application, not the stack) */
00110 #ifndef TCP_CHECKSUM_ON_COPY_SANITY_CHECK
00111 #define TCP_CHECKSUM_ON_COPY_SANITY_CHECK   0
00112 #endif
00113 /* Allow to override the failure of sanity check from warning to e.g. hard failure */
00114 #if TCP_CHECKSUM_ON_COPY_SANITY_CHECK
00115 #ifndef TCP_CHECKSUM_ON_COPY_SANITY_CHECK_FAIL
00116 #define TCP_CHECKSUM_ON_COPY_SANITY_CHECK_FAIL(msg) LWIP_DEBUGF(TCP_DEBUG | LWIP_DBG_LEVEL_WARNING, msg)
00117 #endif
00118 #endif
00119 
00120 #if TCP_OVERSIZE
00121 /** The size of segment pbufs created when TCP_OVERSIZE is enabled */
00122 #ifndef TCP_OVERSIZE_CALC_LENGTH
00123 #define TCP_OVERSIZE_CALC_LENGTH(length) ((length) + TCP_OVERSIZE)
00124 #endif
00125 #endif
00126 
00127 /* Forward declarations.*/
00128 static err_t tcp_output_segment(struct tcp_seg *seg, struct tcp_pcb *pcb, struct netif *netif);
00129 
00130 /* tcp_route: common code that returns a fixed bound netif or calls ip_route */
00131 static struct netif *
00132 tcp_route(const struct tcp_pcb *pcb, const ip_addr_t *src, const ip_addr_t *dst)
00133 {
00134   LWIP_UNUSED_ARG(src); /* in case IPv4-only and source-based routing is disabled */
00135 
00136   if ((pcb != NULL) && (pcb->netif_idx != NETIF_NO_INDEX)) {
00137     return netif_get_by_index(pcb->netif_idx);
00138   } else {
00139     return ip_route(src, dst);
00140   }
00141 }
00142 
00143 /**
00144  * Create a TCP segment with prefilled header.
00145  *
00146  * Called by @ref tcp_write, @ref tcp_enqueue_flags and @ref tcp_split_unsent_seg
00147  *
00148  * @param pcb Protocol control block for the TCP connection.
00149  * @param p pbuf that is used to hold the TCP header.
00150  * @param hdrflags TCP flags for header.
00151  * @param seqno TCP sequence number of this packet
00152  * @param optflags options to include in TCP header
00153  * @return a new tcp_seg pointing to p, or NULL.
00154  * The TCP header is filled in except ackno and wnd.
00155  * p is freed on failure.
00156  */
00157 static struct tcp_seg *
00158 tcp_create_segment(const struct tcp_pcb *pcb, struct pbuf *p, u8_t hdrflags, u32_t seqno, u8_t optflags)
00159 {
00160   struct tcp_seg *seg;
00161   u8_t optlen;
00162 
00163   LWIP_ASSERT("tcp_create_segment: invalid pcb", pcb != NULL);
00164   LWIP_ASSERT("tcp_create_segment: invalid pbuf", p != NULL);
00165 
00166   optlen = LWIP_TCP_OPT_LENGTH_SEGMENT(optflags, pcb);
00167 
00168   if ((seg = (struct tcp_seg *)memp_malloc(MEMP_TCP_SEG)) == NULL) {
00169     LWIP_DEBUGF(TCP_OUTPUT_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("tcp_create_segment: no memory.\n"));
00170     pbuf_free(p);
00171     return NULL;
00172   }
00173   seg->flags = optflags;
00174   seg->next = NULL;
00175   seg->p = p;
00176   LWIP_ASSERT("p->tot_len >= optlen", p->tot_len >= optlen);
00177   seg->len = p->tot_len - optlen;
00178 #if TCP_OVERSIZE_DBGCHECK
00179   seg->oversize_left = 0;
00180 #endif /* TCP_OVERSIZE_DBGCHECK */
00181 #if TCP_CHECKSUM_ON_COPY
00182   seg->chksum = 0;
00183   seg->chksum_swapped = 0;
00184   /* check optflags */
00185   LWIP_ASSERT("invalid optflags passed: TF_SEG_DATA_CHECKSUMMED",
00186               (optflags & TF_SEG_DATA_CHECKSUMMED) == 0);
00187 #endif /* TCP_CHECKSUM_ON_COPY */
00188 
00189   /* build TCP header */
00190   if (pbuf_add_header(p, TCP_HLEN)) {
00191     LWIP_DEBUGF(TCP_OUTPUT_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("tcp_create_segment: no room for TCP header in pbuf.\n"));
00192     TCP_STATS_INC(tcp.err);
00193     tcp_seg_free(seg);
00194     return NULL;
00195   }
00196   seg->tcphdr = (struct tcp_hdr *)seg->p->payload;
00197   seg->tcphdr->src = lwip_htons(pcb->local_port);
00198   seg->tcphdr->dest = lwip_htons(pcb->remote_port);
00199   seg->tcphdr->seqno = lwip_htonl(seqno);
00200   /* ackno is set in tcp_output */
00201   TCPH_HDRLEN_FLAGS_SET(seg->tcphdr, (5 + optlen / 4), hdrflags);
00202   /* wnd and chksum are set in tcp_output */
00203   seg->tcphdr->urgp = 0;
00204   return seg;
00205 }
00206 
00207 /**
00208  * Allocate a PBUF_RAM pbuf, perhaps with extra space at the end.
00209  *
00210  * This function is like pbuf_alloc(layer, length, PBUF_RAM) except
00211  * there may be extra bytes available at the end.
00212  *
00213  * Called by @ref tcp_write
00214  *
00215  * @param layer flag to define header size.
00216  * @param length size of the pbuf's payload.
00217  * @param max_length maximum usable size of payload+oversize.
00218  * @param oversize pointer to a u16_t that will receive the number of usable tail bytes.
00219  * @param pcb The TCP connection that will enqueue the pbuf.
00220  * @param apiflags API flags given to tcp_write.
00221  * @param first_seg true when this pbuf will be used in the first enqueued segment.
00222  */
00223 #if TCP_OVERSIZE
00224 static struct pbuf *
00225 tcp_pbuf_prealloc(pbuf_layer layer, u16_t length, u16_t max_length,
00226                   u16_t *oversize, const struct tcp_pcb *pcb, u8_t apiflags,
00227                   u8_t first_seg)
00228 {
00229   struct pbuf *p;
00230   u16_t alloc = length;
00231 
00232   LWIP_ASSERT("tcp_pbuf_prealloc: invalid oversize", oversize != NULL);
00233   LWIP_ASSERT("tcp_pbuf_prealloc: invalid pcb", pcb != NULL);
00234 
00235 #if LWIP_NETIF_TX_SINGLE_PBUF
00236   LWIP_UNUSED_ARG(max_length);
00237   LWIP_UNUSED_ARG(pcb);
00238   LWIP_UNUSED_ARG(apiflags);
00239   LWIP_UNUSED_ARG(first_seg);
00240   alloc = max_length;
00241 #else /* LWIP_NETIF_TX_SINGLE_PBUF */
00242   if (length < max_length) {
00243     /* Should we allocate an oversized pbuf, or just the minimum
00244      * length required? If tcp_write is going to be called again
00245      * before this segment is transmitted, we want the oversized
00246      * buffer. If the segment will be transmitted immediately, we can
00247      * save memory by allocating only length. We use a simple
00248      * heuristic based on the following information:
00249      *
00250      * Did the user set TCP_WRITE_FLAG_MORE?
00251      *
00252      * Will the Nagle algorithm defer transmission of this segment?
00253      */
00254     if ((apiflags & TCP_WRITE_FLAG_MORE) ||
00255         (!(pcb->flags & TF_NODELAY) &&
00256          (!first_seg ||
00257           pcb->unsent != NULL ||
00258           pcb->unacked != NULL))) {
00259       alloc = LWIP_MIN(max_length, LWIP_MEM_ALIGN_SIZE(TCP_OVERSIZE_CALC_LENGTH(length)));
00260     }
00261   }
00262 #endif /* LWIP_NETIF_TX_SINGLE_PBUF */
00263   p = pbuf_alloc(layer, alloc, PBUF_RAM);
00264   if (p == NULL) {
00265     return NULL;
00266   }
00267   LWIP_ASSERT("need unchained pbuf", p->next == NULL);
00268   *oversize = p->len - length;
00269   /* trim p->len to the currently used size */
00270   p->len = p->tot_len = length;
00271   return p;
00272 }
00273 #else /* TCP_OVERSIZE */
00274 #define tcp_pbuf_prealloc(layer, length, mx, os, pcb, api, fst) pbuf_alloc((layer), (length), PBUF_RAM)
00275 #endif /* TCP_OVERSIZE */
00276 
00277 #if TCP_CHECKSUM_ON_COPY
00278 /** Add a checksum of newly added data to the segment.
00279  *
00280  * Called by tcp_write and tcp_split_unsent_seg.
00281  */
00282 static void
00283 tcp_seg_add_chksum(u16_t chksum, u16_t len, u16_t *seg_chksum,
00284                    u8_t *seg_chksum_swapped)
00285 {
00286   u32_t helper;
00287   /* add chksum to old chksum and fold to u16_t */
00288   helper = chksum + *seg_chksum;
00289   chksum = FOLD_U32T(helper);
00290   if ((len & 1) != 0) {
00291     *seg_chksum_swapped = 1 - *seg_chksum_swapped;
00292     chksum = SWAP_BYTES_IN_WORD(chksum);
00293   }
00294   *seg_chksum = chksum;
00295 }
00296 #endif /* TCP_CHECKSUM_ON_COPY */
00297 
00298 /** Checks if tcp_write is allowed or not (checks state, snd_buf and snd_queuelen).
00299  *
00300  * @param pcb the tcp pcb to check for
00301  * @param len length of data to send (checked agains snd_buf)
00302  * @return ERR_OK if tcp_write is allowed to proceed, another err_t otherwise
00303  */
00304 static err_t
00305 tcp_write_checks(struct tcp_pcb *pcb, u16_t len)
00306 {
00307   LWIP_ASSERT("tcp_write_checks: invalid pcb", pcb != NULL);
00308 
00309   /* connection is in invalid state for data transmission? */
00310   if ((pcb->state != ESTABLISHED) &&
00311       (pcb->state != CLOSE_WAIT) &&
00312       (pcb->state != SYN_SENT) &&
00313       (pcb->state != SYN_RCVD)) {
00314     LWIP_DEBUGF(TCP_OUTPUT_DEBUG | LWIP_DBG_STATE | LWIP_DBG_LEVEL_SEVERE, ("tcp_write() called in invalid state\n"));
00315     return ERR_CONN;
00316   } else if (len == 0) {
00317     return ERR_OK;
00318   }
00319 
00320   /* fail on too much data */
00321   if (len > pcb->snd_buf) {
00322     LWIP_DEBUGF(TCP_OUTPUT_DEBUG | LWIP_DBG_LEVEL_SEVERE, ("tcp_write: too much data (len=%"U16_F" > snd_buf=%"TCPWNDSIZE_F")\n",
00323                 len, pcb->snd_buf));
00324     tcp_set_flags(pcb, TF_NAGLEMEMERR);
00325     return ERR_MEM;
00326   }
00327 
00328   LWIP_DEBUGF(TCP_QLEN_DEBUG, ("tcp_write: queuelen: %"TCPWNDSIZE_F"\n", (tcpwnd_size_t)pcb->snd_queuelen));
00329 
00330   /* If total number of pbufs on the unsent/unacked queues exceeds the
00331    * configured maximum, return an error */
00332   /* check for configured max queuelen and possible overflow */
00333   if (pcb->snd_queuelen >= LWIP_MIN(TCP_SND_QUEUELEN, (TCP_SNDQUEUELEN_OVERFLOW + 1))) {
00334     LWIP_DEBUGF(TCP_OUTPUT_DEBUG | LWIP_DBG_LEVEL_SEVERE, ("tcp_write: too long queue %"U16_F" (max %"U16_F")\n",
00335                 pcb->snd_queuelen, (u16_t)TCP_SND_QUEUELEN));
00336     TCP_STATS_INC(tcp.memerr);
00337     tcp_set_flags(pcb, TF_NAGLEMEMERR);
00338     return ERR_MEM;
00339   }
00340   if (pcb->snd_queuelen != 0) {
00341     LWIP_ASSERT("tcp_write: pbufs on queue => at least one queue non-empty",
00342                 pcb->unacked != NULL || pcb->unsent != NULL);
00343   } else {
00344     LWIP_ASSERT("tcp_write: no pbufs on queue => both queues empty",
00345                 pcb->unacked == NULL && pcb->unsent == NULL);
00346   }
00347   return ERR_OK;
00348 }
00349 
00350 /**
00351  * @ingroup tcp_raw
00352  * Write data for sending (but does not send it immediately).
00353  *
00354  * It waits in the expectation of more data being sent soon (as
00355  * it can send them more efficiently by combining them together).
00356  * To prompt the system to send data now, call tcp_output() after
00357  * calling tcp_write().
00358  * 
00359  * This function enqueues the data pointed to by the argument dataptr. The length of
00360  * the data is passed as the len parameter. The apiflags can be one or more of:
00361  * - TCP_WRITE_FLAG_COPY: indicates whether the new memory should be allocated
00362  *   for the data to be copied into. If this flag is not given, no new memory
00363  *   should be allocated and the data should only be referenced by pointer. This
00364  *   also means that the memory behind dataptr must not change until the data is
00365  *   ACKed by the remote host
00366  * - TCP_WRITE_FLAG_MORE: indicates that more data follows. If this is omitted,
00367  *   the PSH flag is set in the last segment created by this call to tcp_write.
00368  *   If this flag is given, the PSH flag is not set.
00369  *
00370  * The tcp_write() function will fail and return ERR_MEM if the length
00371  * of the data exceeds the current send buffer size or if the length of
00372  * the queue of outgoing segment is larger than the upper limit defined
00373  * in lwipopts.h. The number of bytes available in the output queue can
00374  * be retrieved with the tcp_sndbuf() function.
00375  *
00376  * The proper way to use this function is to call the function with at
00377  * most tcp_sndbuf() bytes of data. If the function returns ERR_MEM,
00378  * the application should wait until some of the currently enqueued
00379  * data has been successfully received by the other host and try again.
00380  *
00381  * @param pcb Protocol control block for the TCP connection to enqueue data for.
00382  * @param arg Pointer to the data to be enqueued for sending.
00383  * @param len Data length in bytes
00384  * @param apiflags combination of following flags :
00385  * - TCP_WRITE_FLAG_COPY (0x01) data will be copied into memory belonging to the stack
00386  * - TCP_WRITE_FLAG_MORE (0x02) for TCP connection, PSH flag will not be set on last segment sent,
00387  * @return ERR_OK if enqueued, another err_t on error
00388  */
00389 err_t
00390 tcp_write(struct tcp_pcb *pcb, const void *arg, u16_t len, u8_t apiflags)
00391 {
00392   struct pbuf *concat_p = NULL;
00393   struct tcp_seg *last_unsent = NULL, *seg = NULL, *prev_seg = NULL, *queue = NULL;
00394   u16_t pos = 0; /* position in 'arg' data */
00395   u16_t queuelen;
00396   u8_t optlen;
00397   u8_t optflags = 0;
00398 #if TCP_OVERSIZE
00399   u16_t oversize = 0;
00400   u16_t oversize_used = 0;
00401 #if TCP_OVERSIZE_DBGCHECK
00402   u16_t oversize_add = 0;
00403 #endif /* TCP_OVERSIZE_DBGCHECK*/
00404 #endif /* TCP_OVERSIZE */
00405   u16_t extendlen = 0;
00406 #if TCP_CHECKSUM_ON_COPY
00407   u16_t concat_chksum = 0;
00408   u8_t concat_chksum_swapped = 0;
00409   u16_t concat_chksummed = 0;
00410 #endif /* TCP_CHECKSUM_ON_COPY */
00411   err_t err;
00412   u16_t mss_local;
00413 
00414   LWIP_ERROR("tcp_write: invalid pcb", pcb != NULL, return ERR_ARG);
00415 
00416   /* don't allocate segments bigger than half the maximum window we ever received */
00417   mss_local = LWIP_MIN(pcb->mss, TCPWND_MIN16(pcb->snd_wnd_max / 2));
00418   mss_local = mss_local ? mss_local : pcb->mss;
00419 
00420   LWIP_ASSERT_CORE_LOCKED();
00421 
00422 #if LWIP_NETIF_TX_SINGLE_PBUF
00423   /* Always copy to try to create single pbufs for TX */
00424   apiflags |= TCP_WRITE_FLAG_COPY;
00425 #endif /* LWIP_NETIF_TX_SINGLE_PBUF */
00426 
00427   LWIP_DEBUGF(TCP_OUTPUT_DEBUG, ("tcp_write(pcb=%p, data=%p, len=%"U16_F", apiflags=%"U16_F")\n",
00428                                  (void *)pcb, arg, len, (u16_t)apiflags));
00429   LWIP_ERROR("tcp_write: arg == NULL (programmer violates API)",
00430              arg != NULL, return ERR_ARG;);
00431 
00432   err = tcp_write_checks(pcb, len);
00433   if (err != ERR_OK) {
00434     return err;
00435   }
00436   queuelen = pcb->snd_queuelen;
00437 
00438 #if LWIP_TCP_TIMESTAMPS
00439   if ((pcb->flags & TF_TIMESTAMP)) {
00440     /* Make sure the timestamp option is only included in data segments if we
00441        agreed about it with the remote host. */
00442     optflags = TF_SEG_OPTS_TS;
00443     optlen = LWIP_TCP_OPT_LENGTH_SEGMENT(TF_SEG_OPTS_TS, pcb);
00444     /* ensure that segments can hold at least one data byte... */
00445     mss_local = LWIP_MAX(mss_local, LWIP_TCP_OPT_LEN_TS + 1);
00446   } else
00447 #endif /* LWIP_TCP_TIMESTAMPS */
00448   {
00449     optlen = LWIP_TCP_OPT_LENGTH_SEGMENT(0, pcb);
00450   }
00451 
00452 
00453   /*
00454    * TCP segmentation is done in three phases with increasing complexity:
00455    *
00456    * 1. Copy data directly into an oversized pbuf.
00457    * 2. Chain a new pbuf to the end of pcb->unsent.
00458    * 3. Create new segments.
00459    *
00460    * We may run out of memory at any point. In that case we must
00461    * return ERR_MEM and not change anything in pcb. Therefore, all
00462    * changes are recorded in local variables and committed at the end
00463    * of the function. Some pcb fields are maintained in local copies:
00464    *
00465    * queuelen = pcb->snd_queuelen
00466    * oversize = pcb->unsent_oversize
00467    *
00468    * These variables are set consistently by the phases:
00469    *
00470    * seg points to the last segment tampered with.
00471    *
00472    * pos records progress as data is segmented.
00473    */
00474 
00475   /* Find the tail of the unsent queue. */
00476   if (pcb->unsent != NULL) {
00477     u16_t space;
00478     u16_t unsent_optlen;
00479 
00480     /* @todo: this could be sped up by keeping last_unsent in the pcb */
00481     for (last_unsent = pcb->unsent; last_unsent->next != NULL;
00482          last_unsent = last_unsent->next);
00483 
00484     /* Usable space at the end of the last unsent segment */
00485     unsent_optlen = LWIP_TCP_OPT_LENGTH_SEGMENT(last_unsent->flags, pcb);
00486     LWIP_ASSERT("mss_local is too small", mss_local >= last_unsent->len + unsent_optlen);
00487     space = mss_local - (last_unsent->len + unsent_optlen);
00488 
00489     /*
00490      * Phase 1: Copy data directly into an oversized pbuf.
00491      *
00492      * The number of bytes copied is recorded in the oversize_used
00493      * variable. The actual copying is done at the bottom of the
00494      * function.
00495      */
00496 #if TCP_OVERSIZE
00497 #if TCP_OVERSIZE_DBGCHECK
00498     /* check that pcb->unsent_oversize matches last_unsent->oversize_left */
00499     LWIP_ASSERT("unsent_oversize mismatch (pcb vs. last_unsent)",
00500                 pcb->unsent_oversize == last_unsent->oversize_left);
00501 #endif /* TCP_OVERSIZE_DBGCHECK */
00502     oversize = pcb->unsent_oversize;
00503     if (oversize > 0) {
00504       LWIP_ASSERT("inconsistent oversize vs. space", oversize <= space);
00505       seg = last_unsent;
00506       oversize_used = LWIP_MIN(space, LWIP_MIN(oversize, len));
00507       pos += oversize_used;
00508       oversize -= oversize_used;
00509       space -= oversize_used;
00510     }
00511     /* now we are either finished or oversize is zero */
00512     LWIP_ASSERT("inconsistent oversize vs. len", (oversize == 0) || (pos == len));
00513 #endif /* TCP_OVERSIZE */
00514 
00515 #if !LWIP_NETIF_TX_SINGLE_PBUF
00516     /*
00517      * Phase 2: Chain a new pbuf to the end of pcb->unsent.
00518      *
00519      * As an exception when NOT copying the data, if the given data buffer
00520      * directly follows the last unsent data buffer in memory, extend the last
00521      * ROM pbuf reference to the buffer, thus saving a ROM pbuf allocation.
00522      *
00523      * We don't extend segments containing SYN/FIN flags or options
00524      * (len==0). The new pbuf is kept in concat_p and pbuf_cat'ed at
00525      * the end.
00526      *
00527      * This phase is skipped for LWIP_NETIF_TX_SINGLE_PBUF as we could only execute
00528      * it after rexmit puts a segment from unacked to unsent and at this point,
00529      * oversize info is lost.
00530      */
00531     if ((pos < len) && (space > 0) && (last_unsent->len > 0)) {
00532       u16_t seglen = LWIP_MIN(space, len - pos);
00533       seg = last_unsent;
00534 
00535       /* Create a pbuf with a copy or reference to seglen bytes. We
00536        * can use PBUF_RAW here since the data appears in the middle of
00537        * a segment. A header will never be prepended. */
00538       if (apiflags & TCP_WRITE_FLAG_COPY) {
00539         /* Data is copied */
00540         if ((concat_p = tcp_pbuf_prealloc(PBUF_RAW, seglen, space, &oversize, pcb, apiflags, 1)) == NULL) {
00541           LWIP_DEBUGF(TCP_OUTPUT_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
00542                       ("tcp_write : could not allocate memory for pbuf copy size %"U16_F"\n",
00543                        seglen));
00544           goto memerr;
00545         }
00546 #if TCP_OVERSIZE_DBGCHECK
00547         oversize_add = oversize;
00548 #endif /* TCP_OVERSIZE_DBGCHECK */
00549         TCP_DATA_COPY2(concat_p->payload, (const u8_t *)arg + pos, seglen, &concat_chksum, &concat_chksum_swapped);
00550 #if TCP_CHECKSUM_ON_COPY
00551         concat_chksummed += seglen;
00552 #endif /* TCP_CHECKSUM_ON_COPY */
00553         queuelen += pbuf_clen(concat_p);
00554       } else {
00555         /* Data is not copied */
00556         /* If the last unsent pbuf is of type PBUF_ROM, try to extend it. */
00557         struct pbuf *p;
00558         for (p = last_unsent->p; p->next != NULL; p = p->next);
00559         if (((p->type_internal & (PBUF_TYPE_FLAG_STRUCT_DATA_CONTIGUOUS | PBUF_TYPE_FLAG_DATA_VOLATILE)) == 0) &&
00560             (const u8_t *)p->payload + p->len == (const u8_t *)arg) {
00561           LWIP_ASSERT("tcp_write: ROM pbufs cannot be oversized", pos == 0);
00562           extendlen = seglen;
00563         } else {
00564           if ((concat_p = pbuf_alloc(PBUF_RAW, seglen, PBUF_ROM)) == NULL) {
00565             LWIP_DEBUGF(TCP_OUTPUT_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
00566                         ("tcp_write: could not allocate memory for zero-copy pbuf\n"));
00567             goto memerr;
00568           }
00569           /* reference the non-volatile payload data */
00570           ((struct pbuf_rom *)concat_p)->payload = (const u8_t *)arg + pos;
00571           queuelen += pbuf_clen(concat_p);
00572         }
00573 #if TCP_CHECKSUM_ON_COPY
00574         /* calculate the checksum of nocopy-data */
00575         tcp_seg_add_chksum(~inet_chksum((const u8_t *)arg + pos, seglen), seglen,
00576                            &concat_chksum, &concat_chksum_swapped);
00577         concat_chksummed += seglen;
00578 #endif /* TCP_CHECKSUM_ON_COPY */
00579       }
00580 
00581       pos += seglen;
00582     }
00583 #endif /* !LWIP_NETIF_TX_SINGLE_PBUF */
00584   } else {
00585 #if TCP_OVERSIZE
00586     LWIP_ASSERT("unsent_oversize mismatch (pcb->unsent is NULL)",
00587                 pcb->unsent_oversize == 0);
00588 #endif /* TCP_OVERSIZE */
00589   }
00590 
00591   /*
00592    * Phase 3: Create new segments.
00593    *
00594    * The new segments are chained together in the local 'queue'
00595    * variable, ready to be appended to pcb->unsent.
00596    */
00597   while (pos < len) {
00598     struct pbuf *p;
00599     u16_t left = len - pos;
00600     u16_t max_len = mss_local - optlen;
00601     u16_t seglen = LWIP_MIN(left, max_len);
00602 #if TCP_CHECKSUM_ON_COPY
00603     u16_t chksum = 0;
00604     u8_t chksum_swapped = 0;
00605 #endif /* TCP_CHECKSUM_ON_COPY */
00606 
00607     if (apiflags & TCP_WRITE_FLAG_COPY) {
00608       /* If copy is set, memory should be allocated and data copied
00609        * into pbuf */
00610       if ((p = tcp_pbuf_prealloc(PBUF_TRANSPORT, seglen + optlen, mss_local, &oversize, pcb, apiflags, queue == NULL)) == NULL) {
00611         LWIP_DEBUGF(TCP_OUTPUT_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("tcp_write : could not allocate memory for pbuf copy size %"U16_F"\n", seglen));
00612         goto memerr;
00613       }
00614       LWIP_ASSERT("tcp_write: check that first pbuf can hold the complete seglen",
00615                   (p->len >= seglen));
00616       TCP_DATA_COPY2((char *)p->payload + optlen, (const u8_t *)arg + pos, seglen, &chksum, &chksum_swapped);
00617     } else {
00618       /* Copy is not set: First allocate a pbuf for holding the data.
00619        * Since the referenced data is available at least until it is
00620        * sent out on the link (as it has to be ACKed by the remote
00621        * party) we can safely use PBUF_ROM instead of PBUF_REF here.
00622        */
00623       struct pbuf *p2;
00624 #if TCP_OVERSIZE
00625       LWIP_ASSERT("oversize == 0", oversize == 0);
00626 #endif /* TCP_OVERSIZE */
00627       if ((p2 = pbuf_alloc(PBUF_TRANSPORT, seglen, PBUF_ROM)) == NULL) {
00628         LWIP_DEBUGF(TCP_OUTPUT_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("tcp_write: could not allocate memory for zero-copy pbuf\n"));
00629         goto memerr;
00630       }
00631 #if TCP_CHECKSUM_ON_COPY
00632       /* calculate the checksum of nocopy-data */
00633       chksum = ~inet_chksum((const u8_t *)arg + pos, seglen);
00634       if (seglen & 1) {
00635         chksum_swapped = 1;
00636         chksum = SWAP_BYTES_IN_WORD(chksum);
00637       }
00638 #endif /* TCP_CHECKSUM_ON_COPY */
00639       /* reference the non-volatile payload data */
00640       ((struct pbuf_rom *)p2)->payload = (const u8_t *)arg + pos;
00641 
00642       /* Second, allocate a pbuf for the headers. */
00643       if ((p = pbuf_alloc(PBUF_TRANSPORT, optlen, PBUF_RAM)) == NULL) {
00644         /* If allocation fails, we have to deallocate the data pbuf as
00645          * well. */
00646         pbuf_free(p2);
00647         LWIP_DEBUGF(TCP_OUTPUT_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("tcp_write: could not allocate memory for header pbuf\n"));
00648         goto memerr;
00649       }
00650       /* Concatenate the headers and data pbufs together. */
00651       pbuf_cat(p/*header*/, p2/*data*/);
00652     }
00653 
00654     queuelen += pbuf_clen(p);
00655 
00656     /* Now that there are more segments queued, we check again if the
00657      * length of the queue exceeds the configured maximum or
00658      * overflows. */
00659     if (queuelen > LWIP_MIN(TCP_SND_QUEUELEN, TCP_SNDQUEUELEN_OVERFLOW)) {
00660       LWIP_DEBUGF(TCP_OUTPUT_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("tcp_write: queue too long %"U16_F" (%d)\n",
00661                   queuelen, (int)TCP_SND_QUEUELEN));
00662       pbuf_free(p);
00663       goto memerr;
00664     }
00665 
00666     if ((seg = tcp_create_segment(pcb, p, 0, pcb->snd_lbb + pos, optflags)) == NULL) {
00667       goto memerr;
00668     }
00669 #if TCP_OVERSIZE_DBGCHECK
00670     seg->oversize_left = oversize;
00671 #endif /* TCP_OVERSIZE_DBGCHECK */
00672 #if TCP_CHECKSUM_ON_COPY
00673     seg->chksum = chksum;
00674     seg->chksum_swapped = chksum_swapped;
00675     seg->flags |= TF_SEG_DATA_CHECKSUMMED;
00676 #endif /* TCP_CHECKSUM_ON_COPY */
00677 
00678     /* first segment of to-be-queued data? */
00679     if (queue == NULL) {
00680       queue = seg;
00681     } else {
00682       /* Attach the segment to the end of the queued segments */
00683       LWIP_ASSERT("prev_seg != NULL", prev_seg != NULL);
00684       prev_seg->next = seg;
00685     }
00686     /* remember last segment of to-be-queued data for next iteration */
00687     prev_seg = seg;
00688 
00689     LWIP_DEBUGF(TCP_OUTPUT_DEBUG | LWIP_DBG_TRACE, ("tcp_write: queueing %"U32_F":%"U32_F"\n",
00690                 lwip_ntohl(seg->tcphdr->seqno),
00691                 lwip_ntohl(seg->tcphdr->seqno) + TCP_TCPLEN(seg)));
00692 
00693     pos += seglen;
00694   }
00695 
00696   /*
00697    * All three segmentation phases were successful. We can commit the
00698    * transaction.
00699    */
00700 #if TCP_OVERSIZE_DBGCHECK
00701   if ((last_unsent != NULL) && (oversize_add != 0)) {
00702     last_unsent->oversize_left += oversize_add;
00703   }
00704 #endif /* TCP_OVERSIZE_DBGCHECK */
00705 
00706   /*
00707    * Phase 1: If data has been added to the preallocated tail of
00708    * last_unsent, we update the length fields of the pbuf chain.
00709    */
00710 #if TCP_OVERSIZE
00711   if (oversize_used > 0) {
00712     struct pbuf *p;
00713     /* Bump tot_len of whole chain, len of tail */
00714     for (p = last_unsent->p; p; p = p->next) {
00715       p->tot_len += oversize_used;
00716       if (p->next == NULL) {
00717         TCP_DATA_COPY((char *)p->payload + p->len, arg, oversize_used, last_unsent);
00718         p->len += oversize_used;
00719       }
00720     }
00721     last_unsent->len += oversize_used;
00722 #if TCP_OVERSIZE_DBGCHECK
00723     LWIP_ASSERT("last_unsent->oversize_left >= oversize_used",
00724                 last_unsent->oversize_left >= oversize_used);
00725     last_unsent->oversize_left -= oversize_used;
00726 #endif /* TCP_OVERSIZE_DBGCHECK */
00727   }
00728   pcb->unsent_oversize = oversize;
00729 #endif /* TCP_OVERSIZE */
00730 
00731   /*
00732    * Phase 2: concat_p can be concatenated onto last_unsent->p, unless we
00733    * determined that the last ROM pbuf can be extended to include the new data.
00734    */
00735   if (concat_p != NULL) {
00736     LWIP_ASSERT("tcp_write: cannot concatenate when pcb->unsent is empty",
00737                 (last_unsent != NULL));
00738     pbuf_cat(last_unsent->p, concat_p);
00739     last_unsent->len += concat_p->tot_len;
00740   } else if (extendlen > 0) {
00741     struct pbuf *p;
00742     LWIP_ASSERT("tcp_write: extension of reference requires reference",
00743                 last_unsent != NULL && last_unsent->p != NULL);
00744     for (p = last_unsent->p; p->next != NULL; p = p->next) {
00745       p->tot_len += extendlen;
00746     }
00747     p->tot_len += extendlen;
00748     p->len += extendlen;
00749     last_unsent->len += extendlen;
00750   }
00751 
00752 #if TCP_CHECKSUM_ON_COPY
00753   if (concat_chksummed) {
00754     LWIP_ASSERT("tcp_write: concat checksum needs concatenated data",
00755                 concat_p != NULL || extendlen > 0);
00756     /*if concat checksumm swapped - swap it back */
00757     if (concat_chksum_swapped) {
00758       concat_chksum = SWAP_BYTES_IN_WORD(concat_chksum);
00759     }
00760     tcp_seg_add_chksum(concat_chksum, concat_chksummed, &last_unsent->chksum,
00761                        &last_unsent->chksum_swapped);
00762     last_unsent->flags |= TF_SEG_DATA_CHECKSUMMED;
00763   }
00764 #endif /* TCP_CHECKSUM_ON_COPY */
00765 
00766   /*
00767    * Phase 3: Append queue to pcb->unsent. Queue may be NULL, but that
00768    * is harmless
00769    */
00770   if (last_unsent == NULL) {
00771     pcb->unsent = queue;
00772   } else {
00773     last_unsent->next = queue;
00774   }
00775 
00776   /*
00777    * Finally update the pcb state.
00778    */
00779   pcb->snd_lbb += len;
00780   pcb->snd_buf -= len;
00781   pcb->snd_queuelen = queuelen;
00782 
00783   LWIP_DEBUGF(TCP_QLEN_DEBUG, ("tcp_write: %"S16_F" (after enqueued)\n",
00784                                pcb->snd_queuelen));
00785   if (pcb->snd_queuelen != 0) {
00786     LWIP_ASSERT("tcp_write: valid queue length",
00787                 pcb->unacked != NULL || pcb->unsent != NULL);
00788   }
00789 
00790   /* Set the PSH flag in the last segment that we enqueued. */
00791   if (seg != NULL && seg->tcphdr != NULL && ((apiflags & TCP_WRITE_FLAG_MORE) == 0)) {
00792     TCPH_SET_FLAG(seg->tcphdr, TCP_PSH);
00793   }
00794 
00795   return ERR_OK;
00796 memerr:
00797   tcp_set_flags(pcb, TF_NAGLEMEMERR);
00798   TCP_STATS_INC(tcp.memerr);
00799 
00800   if (concat_p != NULL) {
00801     pbuf_free(concat_p);
00802   }
00803   if (queue != NULL) {
00804     tcp_segs_free(queue);
00805   }
00806   if (pcb->snd_queuelen != 0) {
00807     LWIP_ASSERT("tcp_write: valid queue length", pcb->unacked != NULL ||
00808                 pcb->unsent != NULL);
00809   }
00810   LWIP_DEBUGF(TCP_QLEN_DEBUG | LWIP_DBG_STATE, ("tcp_write: %"S16_F" (with mem err)\n", pcb->snd_queuelen));
00811   return ERR_MEM;
00812 }
00813 
00814 /**
00815  * Split segment on the head of the unsent queue.  If return is not
00816  * ERR_OK, existing head remains intact
00817  *
00818  * The split is accomplished by creating a new TCP segment and pbuf
00819  * which holds the remainder payload after the split.  The original
00820  * pbuf is trimmed to new length.  This allows splitting of read-only
00821  * pbufs
00822  *
00823  * @param pcb the tcp_pcb for which to split the unsent head
00824  * @param split the amount of payload to remain in the head
00825  */
00826 err_t
00827 tcp_split_unsent_seg(struct tcp_pcb *pcb, u16_t split)
00828 {
00829   struct tcp_seg *seg = NULL, *useg = NULL;
00830   struct pbuf *p = NULL;
00831   u8_t optlen;
00832   u8_t optflags;
00833   u8_t split_flags;
00834   u8_t remainder_flags;
00835   u16_t remainder;
00836   u16_t offset;
00837 #if TCP_CHECKSUM_ON_COPY
00838   u16_t chksum = 0;
00839   u8_t chksum_swapped = 0;
00840   struct pbuf *q;
00841 #endif /* TCP_CHECKSUM_ON_COPY */
00842 
00843   LWIP_ASSERT("tcp_split_unsent_seg: invalid pcb", pcb != NULL);
00844 
00845   useg = pcb->unsent;
00846   if (useg == NULL) {
00847     return ERR_MEM;
00848   }
00849 
00850   if (split == 0) {
00851     LWIP_ASSERT("Can't split segment into length 0", 0);
00852     return ERR_VAL;
00853   }
00854 
00855   if (useg->len <= split) {
00856     return ERR_OK;
00857   }
00858 
00859   LWIP_ASSERT("split <= mss", split <= pcb->mss);
00860   LWIP_ASSERT("useg->len > 0", useg->len > 0);
00861 
00862   /* We should check that we don't exceed TCP_SND_QUEUELEN but we need
00863    * to split this packet so we may actually exceed the max value by
00864    * one!
00865    */
00866   LWIP_DEBUGF(TCP_QLEN_DEBUG, ("tcp_enqueue: split_unsent_seg: %u\n", (unsigned int)pcb->snd_queuelen));
00867 
00868   optflags = useg->flags;
00869 #if TCP_CHECKSUM_ON_COPY
00870   /* Remove since checksum is not stored until after tcp_create_segment() */
00871   optflags &= ~TF_SEG_DATA_CHECKSUMMED;
00872 #endif /* TCP_CHECKSUM_ON_COPY */
00873   optlen = LWIP_TCP_OPT_LENGTH(optflags);
00874   remainder = useg->len - split;
00875 
00876   /* Create new pbuf for the remainder of the split */
00877   p = pbuf_alloc(PBUF_TRANSPORT, remainder + optlen, PBUF_RAM);
00878   if (p == NULL) {
00879     LWIP_DEBUGF(TCP_OUTPUT_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
00880                 ("tcp_split_unsent_seg: could not allocate memory for pbuf remainder %u\n", remainder));
00881     goto memerr;
00882   }
00883 
00884   /* Offset into the original pbuf is past TCP/IP headers, options, and split amount */
00885   offset = useg->p->tot_len - useg->len + split;
00886   /* Copy remainder into new pbuf, headers and options will not be filled out */
00887   if (pbuf_copy_partial(useg->p, (u8_t *)p->payload + optlen, remainder, offset ) != remainder) {
00888     LWIP_DEBUGF(TCP_OUTPUT_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
00889                 ("tcp_split_unsent_seg: could not copy pbuf remainder %u\n", remainder));
00890     goto memerr;
00891   }
00892 #if TCP_CHECKSUM_ON_COPY
00893   /* calculate the checksum on remainder data */
00894   tcp_seg_add_chksum(~inet_chksum((const u8_t *)p->payload + optlen, remainder), remainder,
00895                      &chksum, &chksum_swapped);
00896 #endif /* TCP_CHECKSUM_ON_COPY */
00897 
00898   /* Options are created when calling tcp_output() */
00899 
00900   /* Migrate flags from original segment */
00901   split_flags = TCPH_FLAGS(useg->tcphdr);
00902   remainder_flags = 0; /* ACK added in tcp_output() */
00903 
00904   if (split_flags & TCP_PSH) {
00905     split_flags &= ~TCP_PSH;
00906     remainder_flags |= TCP_PSH;
00907   }
00908   if (split_flags & TCP_FIN) {
00909     split_flags &= ~TCP_FIN;
00910     remainder_flags |= TCP_FIN;
00911   }
00912   /* SYN should be left on split, RST should not be present with data */
00913 
00914   seg = tcp_create_segment(pcb, p, remainder_flags, lwip_ntohl(useg->tcphdr->seqno) + split, optflags);
00915   if (seg == NULL) {
00916     LWIP_DEBUGF(TCP_OUTPUT_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
00917                 ("tcp_split_unsent_seg: could not create new TCP segment\n"));
00918     goto memerr;
00919   }
00920 
00921 #if TCP_CHECKSUM_ON_COPY
00922   seg->chksum = chksum;
00923   seg->chksum_swapped = chksum_swapped;
00924   seg->flags |= TF_SEG_DATA_CHECKSUMMED;
00925 #endif /* TCP_CHECKSUM_ON_COPY */
00926 
00927   /* Remove this segment from the queue since trimming it may free pbufs */
00928   pcb->snd_queuelen -= pbuf_clen(useg->p);
00929 
00930   /* Trim the original pbuf into our split size.  At this point our remainder segment must be setup
00931   successfully because we are modifying the original segment */
00932   pbuf_realloc(useg->p, useg->p->tot_len - remainder);
00933   useg->len -= remainder;
00934   TCPH_SET_FLAG(useg->tcphdr, split_flags);
00935 #if TCP_OVERSIZE_DBGCHECK
00936   /* By trimming, realloc may have actually shrunk the pbuf, so clear oversize_left */
00937   useg->oversize_left = 0;
00938 #endif /* TCP_OVERSIZE_DBGCHECK */
00939 
00940   /* Add back to the queue with new trimmed pbuf */
00941   pcb->snd_queuelen += pbuf_clen(useg->p);
00942 
00943 #if TCP_CHECKSUM_ON_COPY
00944   /* The checksum on the split segment is now incorrect. We need to re-run it over the split */
00945   useg->chksum = 0;
00946   useg->chksum_swapped = 0;
00947   q = useg->p;
00948   offset = q->tot_len - useg->len; /* Offset due to exposed headers */
00949 
00950   /* Advance to the pbuf where the offset ends */
00951   while (q != NULL && offset > q->len) {
00952     offset -= q->len;
00953     q = q->next;
00954   }
00955   LWIP_ASSERT("Found start of payload pbuf", q != NULL);
00956   /* Checksum the first payload pbuf accounting for offset, then other pbufs are all payload */
00957   for (; q != NULL; offset = 0, q = q->next) {
00958     tcp_seg_add_chksum(~inet_chksum((const u8_t *)q->payload + offset, q->len - offset), q->len - offset,
00959                        &useg->chksum, &useg->chksum_swapped);
00960   }
00961 #endif /* TCP_CHECKSUM_ON_COPY */
00962 
00963   /* Update number of segments on the queues. Note that length now may
00964    * exceed TCP_SND_QUEUELEN! We don't have to touch pcb->snd_buf
00965    * because the total amount of data is constant when packet is split */
00966   pcb->snd_queuelen += pbuf_clen(seg->p);
00967 
00968   /* Finally insert remainder into queue after split (which stays head) */
00969   seg->next = useg->next;
00970   useg->next = seg;
00971 
00972 #if TCP_OVERSIZE
00973   /* If remainder is last segment on the unsent, ensure we clear the oversize amount
00974    * because the remainder is always sized to the exact remaining amount */
00975   if (seg->next == NULL) {
00976     pcb->unsent_oversize = 0;
00977   }
00978 #endif /* TCP_OVERSIZE */
00979 
00980   return ERR_OK;
00981 memerr:
00982   TCP_STATS_INC(tcp.memerr);
00983 
00984   LWIP_ASSERT("seg == NULL", seg == NULL);
00985   if (p != NULL) {
00986     pbuf_free(p);
00987   }
00988 
00989   return ERR_MEM;
00990 }
00991 
00992 /**
00993  * Called by tcp_close() to send a segment including FIN flag but not data.
00994  * This FIN may be added to an existing segment or a new, otherwise empty
00995  * segment is enqueued.
00996  *
00997  * @param pcb the tcp_pcb over which to send a segment
00998  * @return ERR_OK if sent, another err_t otherwise
00999  */
01000 err_t
01001 tcp_send_fin(struct tcp_pcb *pcb)
01002 {
01003   LWIP_ASSERT("tcp_send_fin: invalid pcb", pcb != NULL);
01004 
01005   /* first, try to add the fin to the last unsent segment */
01006   if (pcb->unsent != NULL) {
01007     struct tcp_seg *last_unsent;
01008     for (last_unsent = pcb->unsent; last_unsent->next != NULL;
01009          last_unsent = last_unsent->next);
01010 
01011     if ((TCPH_FLAGS(last_unsent->tcphdr) & (TCP_SYN | TCP_FIN | TCP_RST)) == 0) {
01012       /* no SYN/FIN/RST flag in the header, we can add the FIN flag */
01013       TCPH_SET_FLAG(last_unsent->tcphdr, TCP_FIN);
01014       tcp_set_flags(pcb, TF_FIN);
01015       return ERR_OK;
01016     }
01017   }
01018   /* no data, no length, flags, copy=1, no optdata */
01019   return tcp_enqueue_flags(pcb, TCP_FIN);
01020 }
01021 
01022 /**
01023  * Enqueue SYN or FIN for transmission.
01024  *
01025  * Called by @ref tcp_connect, tcp_listen_input, and @ref tcp_close
01026  * (via @ref tcp_send_fin)
01027  *
01028  * @param pcb Protocol control block for the TCP connection.
01029  * @param flags TCP header flags to set in the outgoing segment.
01030  */
01031 err_t
01032 tcp_enqueue_flags(struct tcp_pcb *pcb, u8_t flags)
01033 {
01034   struct pbuf *p;
01035   struct tcp_seg *seg;
01036   u8_t optflags = 0;
01037   u8_t optlen = 0;
01038 
01039   LWIP_DEBUGF(TCP_QLEN_DEBUG, ("tcp_enqueue_flags: queuelen: %"U16_F"\n", (u16_t)pcb->snd_queuelen));
01040 
01041   LWIP_ASSERT("tcp_enqueue_flags: need either TCP_SYN or TCP_FIN in flags (programmer violates API)",
01042               (flags & (TCP_SYN | TCP_FIN)) != 0);
01043   LWIP_ASSERT("tcp_enqueue_flags: invalid pcb", pcb != NULL);
01044 
01045   /* No need to check pcb->snd_queuelen if only SYN or FIN are allowed! */
01046 
01047   /* Get options for this segment. This is a special case since this is the
01048      only place where a SYN can be sent. */
01049   if (flags & TCP_SYN) {
01050     optflags = TF_SEG_OPTS_MSS;
01051 #if LWIP_WND_SCALE
01052     if ((pcb->state != SYN_RCVD) || (pcb->flags & TF_WND_SCALE)) {
01053       /* In a <SYN,ACK> (sent in state SYN_RCVD), the window scale option may only
01054          be sent if we received a window scale option from the remote host. */
01055       optflags |= TF_SEG_OPTS_WND_SCALE;
01056     }
01057 #endif /* LWIP_WND_SCALE */
01058 #if LWIP_TCP_SACK_OUT
01059     if ((pcb->state != SYN_RCVD) || (pcb->flags & TF_SACK)) {
01060       /* In a <SYN,ACK> (sent in state SYN_RCVD), the SACK_PERM option may only
01061          be sent if we received a SACK_PERM option from the remote host. */
01062       optflags |= TF_SEG_OPTS_SACK_PERM;
01063     }
01064 #endif /* LWIP_TCP_SACK_OUT */
01065   }
01066 #if LWIP_TCP_TIMESTAMPS
01067   if ((pcb->flags & TF_TIMESTAMP) || ((flags & TCP_SYN) && (pcb->state != SYN_RCVD))) {
01068     /* Make sure the timestamp option is only included in data segments if we
01069        agreed about it with the remote host (and in active open SYN segments). */
01070     optflags |= TF_SEG_OPTS_TS;
01071   }
01072 #endif /* LWIP_TCP_TIMESTAMPS */
01073   optlen = LWIP_TCP_OPT_LENGTH_SEGMENT(optflags, pcb);
01074 
01075   /* Allocate pbuf with room for TCP header + options */
01076   if ((p = pbuf_alloc(PBUF_TRANSPORT, optlen, PBUF_RAM)) == NULL) {
01077     tcp_set_flags(pcb, TF_NAGLEMEMERR);
01078     TCP_STATS_INC(tcp.memerr);
01079     return ERR_MEM;
01080   }
01081   LWIP_ASSERT("tcp_enqueue_flags: check that first pbuf can hold optlen",
01082               (p->len >= optlen));
01083 
01084   /* Allocate memory for tcp_seg, and fill in fields. */
01085   if ((seg = tcp_create_segment(pcb, p, flags, pcb->snd_lbb, optflags)) == NULL) {
01086     tcp_set_flags(pcb, TF_NAGLEMEMERR);
01087     TCP_STATS_INC(tcp.memerr);
01088     return ERR_MEM;
01089   }
01090   LWIP_ASSERT("seg->tcphdr not aligned", ((mem_ptr_t)seg->tcphdr % LWIP_MIN(MEM_ALIGNMENT, 4)) == 0);
01091   LWIP_ASSERT("tcp_enqueue_flags: invalid segment length", seg->len == 0);
01092 
01093   LWIP_DEBUGF(TCP_OUTPUT_DEBUG | LWIP_DBG_TRACE,
01094               ("tcp_enqueue_flags: queueing %"U32_F":%"U32_F" (0x%"X16_F")\n",
01095                lwip_ntohl(seg->tcphdr->seqno),
01096                lwip_ntohl(seg->tcphdr->seqno) + TCP_TCPLEN(seg),
01097                (u16_t)flags));
01098 
01099   /* Now append seg to pcb->unsent queue */
01100   if (pcb->unsent == NULL) {
01101     pcb->unsent = seg;
01102   } else {
01103     struct tcp_seg *useg;
01104     for (useg = pcb->unsent; useg->next != NULL; useg = useg->next);
01105     useg->next = seg;
01106   }
01107 #if TCP_OVERSIZE
01108   /* The new unsent tail has no space */
01109   pcb->unsent_oversize = 0;
01110 #endif /* TCP_OVERSIZE */
01111 
01112   /* SYN and FIN bump the sequence number */
01113   if ((flags & TCP_SYN) || (flags & TCP_FIN)) {
01114     pcb->snd_lbb++;
01115     /* optlen does not influence snd_buf */
01116   }
01117   if (flags & TCP_FIN) {
01118     tcp_set_flags(pcb, TF_FIN);
01119   }
01120 
01121   /* update number of segments on the queues */
01122   pcb->snd_queuelen += pbuf_clen(seg->p);
01123   LWIP_DEBUGF(TCP_QLEN_DEBUG, ("tcp_enqueue_flags: %"S16_F" (after enqueued)\n", pcb->snd_queuelen));
01124   if (pcb->snd_queuelen != 0) {
01125     LWIP_ASSERT("tcp_enqueue_flags: invalid queue length",
01126                 pcb->unacked != NULL || pcb->unsent != NULL);
01127   }
01128 
01129   return ERR_OK;
01130 }
01131 
01132 #if LWIP_TCP_TIMESTAMPS
01133 /* Build a timestamp option (12 bytes long) at the specified options pointer)
01134  *
01135  * @param pcb tcp_pcb
01136  * @param opts option pointer where to store the timestamp option
01137  */
01138 static void
01139 tcp_build_timestamp_option(const struct tcp_pcb *pcb, u32_t *opts)
01140 {
01141   LWIP_ASSERT("tcp_build_timestamp_option: invalid pcb", pcb != NULL);
01142 
01143   /* Pad with two NOP options to make everything nicely aligned */
01144   opts[0] = PP_HTONL(0x0101080A);
01145   opts[1] = lwip_htonl(sys_now());
01146   opts[2] = lwip_htonl(pcb->ts_recent);
01147 }
01148 #endif
01149 
01150 #if LWIP_TCP_SACK_OUT
01151 /**
01152  * Calculates the number of SACK entries that should be generated.
01153  * It takes into account whether TF_SACK flag is set,
01154  * the number of SACK entries in tcp_pcb that are valid,
01155  * as well as the available options size.
01156  *
01157  * @param pcb tcp_pcb
01158  * @param optlen the length of other TCP options (in bytes)
01159  * @return the number of SACK ranges that can be used
01160  */
01161 static u8_t
01162 tcp_get_num_sacks(const struct tcp_pcb *pcb, u8_t optlen)
01163 {
01164   u8_t num_sacks = 0;
01165 
01166   LWIP_ASSERT("tcp_get_num_sacks: invalid pcb", pcb != NULL);
01167 
01168   if (pcb->flags & TF_SACK) {
01169     u8_t i;
01170 
01171     /* The first SACK takes up 12 bytes (it includes SACK header and two NOP options),
01172        each additional one - 8 bytes. */
01173     optlen += 12;
01174 
01175     /* Max options size = 40, number of SACK array entries = LWIP_TCP_MAX_SACK_NUM */
01176     for (i = 0; (i < LWIP_TCP_MAX_SACK_NUM) && (optlen <= TCP_MAX_OPTION_BYTES) &&
01177          LWIP_TCP_SACK_VALID(pcb, i); ++i) {
01178       ++num_sacks;
01179       optlen += 8;
01180     }
01181   }
01182 
01183   return num_sacks;
01184 }
01185 
01186 /** Build a SACK option (12 or more bytes long) at the specified options pointer)
01187  *
01188  * @param pcb tcp_pcb
01189  * @param opts option pointer where to store the SACK option
01190  * @param num_sacks the number of SACKs to store
01191  */
01192 static void
01193 tcp_build_sack_option(const struct tcp_pcb *pcb, u32_t *opts, u8_t num_sacks)
01194 {
01195   u8_t i;
01196 
01197   LWIP_ASSERT("tcp_build_sack_option: invalid pcb", pcb != NULL);
01198   LWIP_ASSERT("tcp_build_sack_option: invalid opts", opts != NULL);
01199 
01200   /* Pad with two NOP options to make everything nicely aligned.
01201      We add the length (of just the SACK option, not the NOPs in front of it),
01202      which is 2B of header, plus 8B for each SACK. */
01203   *(opts++) = PP_HTONL(0x01010500 + 2 + num_sacks * 8);
01204 
01205   for (i = 0; i < num_sacks; ++i) {
01206     *(opts++) = lwip_htonl(pcb->rcv_sacks[i].left);
01207     *(opts++) = lwip_htonl(pcb->rcv_sacks[i].right);
01208   }
01209 }
01210 
01211 #endif
01212 
01213 #if LWIP_WND_SCALE
01214 /** Build a window scale option (3 bytes long) at the specified options pointer)
01215  *
01216  * @param opts option pointer where to store the window scale option
01217  */
01218 static void
01219 tcp_build_wnd_scale_option(u32_t *opts)
01220 {
01221   LWIP_ASSERT("tcp_build_wnd_scale_option: invalid opts", opts != NULL);
01222 
01223   /* Pad with one NOP option to make everything nicely aligned */
01224   opts[0] = PP_HTONL(0x01030300 | TCP_RCV_SCALE);
01225 }
01226 #endif
01227 
01228 /**
01229  * @ingroup tcp_raw
01230  * Find out what we can send and send it
01231  *
01232  * @param pcb Protocol control block for the TCP connection to send data
01233  * @return ERR_OK if data has been sent or nothing to send
01234  *         another err_t on error
01235  */
01236 err_t
01237 tcp_output(struct tcp_pcb *pcb)
01238 {
01239   struct tcp_seg *seg, *useg;
01240   u32_t wnd, snd_nxt;
01241   err_t err;
01242   struct netif *netif;
01243 #if TCP_CWND_DEBUG
01244   s16_t i = 0;
01245 #endif /* TCP_CWND_DEBUG */
01246 
01247   LWIP_ASSERT_CORE_LOCKED();
01248 
01249   LWIP_ASSERT("tcp_output: invalid pcb", pcb != NULL);
01250   /* pcb->state LISTEN not allowed here */
01251   LWIP_ASSERT("don't call tcp_output for listen-pcbs",
01252               pcb->state != LISTEN);
01253 
01254   /* First, check if we are invoked by the TCP input processing
01255      code. If so, we do not output anything. Instead, we rely on the
01256      input processing code to call us when input processing is done
01257      with. */
01258   if (tcp_input_pcb == pcb) {
01259     return ERR_OK;
01260   }
01261 
01262   wnd = LWIP_MIN(pcb->snd_wnd, pcb->cwnd);
01263 
01264   seg = pcb->unsent;
01265 
01266   if (seg == NULL) {
01267     LWIP_DEBUGF(TCP_OUTPUT_DEBUG, ("tcp_output: nothing to send (%p)\n",
01268                                    (void *)pcb->unsent));
01269     LWIP_DEBUGF(TCP_CWND_DEBUG, ("tcp_output: snd_wnd %"TCPWNDSIZE_F
01270                                  ", cwnd %"TCPWNDSIZE_F", wnd %"U32_F
01271                                  ", seg == NULL, ack %"U32_F"\n",
01272                                  pcb->snd_wnd, pcb->cwnd, wnd, pcb->lastack));
01273 
01274     /* If the TF_ACK_NOW flag is set and the ->unsent queue is empty, construct
01275      * an empty ACK segment and send it. */
01276     if (pcb->flags & TF_ACK_NOW) {
01277       return tcp_send_empty_ack(pcb);
01278     }
01279     /* nothing to send: shortcut out of here */
01280     goto output_done;
01281   } else {
01282     LWIP_DEBUGF(TCP_CWND_DEBUG,
01283                 ("tcp_output: snd_wnd %"TCPWNDSIZE_F", cwnd %"TCPWNDSIZE_F", wnd %"U32_F
01284                  ", effwnd %"U32_F", seq %"U32_F", ack %"U32_F"\n",
01285                  pcb->snd_wnd, pcb->cwnd, wnd,
01286                  lwip_ntohl(seg->tcphdr->seqno) - pcb->lastack + seg->len,
01287                  lwip_ntohl(seg->tcphdr->seqno), pcb->lastack));
01288   }
01289 
01290   netif = tcp_route(pcb, &pcb->local_ip, &pcb->remote_ip);
01291   if (netif == NULL) {
01292     return ERR_RTE;
01293   }
01294 
01295   /* If we don't have a local IP address, we get one from netif */
01296   if (ip_addr_isany(&pcb->local_ip)) {
01297     const ip_addr_t *local_ip = ip_netif_get_local_ip(netif, &pcb->remote_ip);
01298     if (local_ip == NULL) {
01299       return ERR_RTE;
01300     }
01301     ip_addr_copy(pcb->local_ip, *local_ip);
01302   }
01303 
01304   /* Handle the current segment not fitting within the window */
01305   if (lwip_ntohl(seg->tcphdr->seqno) - pcb->lastack + seg->len > wnd) {
01306     /* We need to start the persistent timer when the next unsent segment does not fit
01307      * within the remaining (could be 0) send window and RTO timer is not running (we
01308      * have no in-flight data). If window is still too small after persist timer fires,
01309      * then we split the segment. We don't consider the congestion window since a cwnd
01310      * smaller than 1 SMSS implies in-flight data
01311      */
01312     if (wnd == pcb->snd_wnd && pcb->unacked == NULL && pcb->persist_backoff == 0) {
01313       pcb->persist_cnt = 0;
01314       pcb->persist_backoff = 1;
01315       pcb->persist_probe = 0;
01316     }
01317     /* We need an ACK, but can't send data now, so send an empty ACK */
01318     if (pcb->flags & TF_ACK_NOW) {
01319       return tcp_send_empty_ack(pcb);
01320     }
01321     goto output_done;
01322   }
01323   /* Stop persist timer, above conditions are not active */
01324   pcb->persist_backoff = 0;
01325 
01326   /* useg should point to last segment on unacked queue */
01327   useg = pcb->unacked;
01328   if (useg != NULL) {
01329     for (; useg->next != NULL; useg = useg->next);
01330   }
01331   /* data available and window allows it to be sent? */
01332   while (seg != NULL &&
01333          lwip_ntohl(seg->tcphdr->seqno) - pcb->lastack + seg->len <= wnd) {
01334     LWIP_ASSERT("RST not expected here!",
01335                 (TCPH_FLAGS(seg->tcphdr) & TCP_RST) == 0);
01336     /* Stop sending if the nagle algorithm would prevent it
01337      * Don't stop:
01338      * - if tcp_write had a memory error before (prevent delayed ACK timeout) or
01339      * - if FIN was already enqueued for this PCB (SYN is always alone in a segment -
01340      *   either seg->next != NULL or pcb->unacked == NULL;
01341      *   RST is no sent using tcp_write/tcp_output.
01342      */
01343     if ((tcp_do_output_nagle(pcb) == 0) &&
01344         ((pcb->flags & (TF_NAGLEMEMERR | TF_FIN)) == 0)) {
01345       break;
01346     }
01347 #if TCP_CWND_DEBUG
01348     LWIP_DEBUGF(TCP_CWND_DEBUG, ("tcp_output: snd_wnd %"TCPWNDSIZE_F", cwnd %"TCPWNDSIZE_F", wnd %"U32_F", effwnd %"U32_F", seq %"U32_F", ack %"U32_F", i %"S16_F"\n",
01349                                  pcb->snd_wnd, pcb->cwnd, wnd,
01350                                  lwip_ntohl(seg->tcphdr->seqno) + seg->len -
01351                                  pcb->lastack,
01352                                  lwip_ntohl(seg->tcphdr->seqno), pcb->lastack, i));
01353     ++i;
01354 #endif /* TCP_CWND_DEBUG */
01355 
01356     if (pcb->state != SYN_SENT) {
01357       TCPH_SET_FLAG(seg->tcphdr, TCP_ACK);
01358     }
01359 
01360     err = tcp_output_segment(seg, pcb, netif);
01361     if (err != ERR_OK) {
01362       /* segment could not be sent, for whatever reason */
01363       tcp_set_flags(pcb, TF_NAGLEMEMERR);
01364       return err;
01365     }
01366 #if TCP_OVERSIZE_DBGCHECK
01367     seg->oversize_left = 0;
01368 #endif /* TCP_OVERSIZE_DBGCHECK */
01369     pcb->unsent = seg->next;
01370     if (pcb->state != SYN_SENT) {
01371       tcp_clear_flags(pcb, TF_ACK_DELAY | TF_ACK_NOW);
01372     }
01373     snd_nxt = lwip_ntohl(seg->tcphdr->seqno) + TCP_TCPLEN(seg);
01374     if (TCP_SEQ_LT(pcb->snd_nxt, snd_nxt)) {
01375       pcb->snd_nxt = snd_nxt;
01376     }
01377     /* put segment on unacknowledged list if length > 0 */
01378     if (TCP_TCPLEN(seg) > 0) {
01379       seg->next = NULL;
01380       /* unacked list is empty? */
01381       if (pcb->unacked == NULL) {
01382         pcb->unacked = seg;
01383         useg = seg;
01384         /* unacked list is not empty? */
01385       } else {
01386         /* In the case of fast retransmit, the packet should not go to the tail
01387          * of the unacked queue, but rather somewhere before it. We need to check for
01388          * this case. -STJ Jul 27, 2004 */
01389         if (TCP_SEQ_LT(lwip_ntohl(seg->tcphdr->seqno), lwip_ntohl(useg->tcphdr->seqno))) {
01390           /* add segment to before tail of unacked list, keeping the list sorted */
01391           struct tcp_seg **cur_seg = &(pcb->unacked);
01392           while (*cur_seg &&
01393                  TCP_SEQ_LT(lwip_ntohl((*cur_seg)->tcphdr->seqno), lwip_ntohl(seg->tcphdr->seqno))) {
01394             cur_seg = &((*cur_seg)->next );
01395           }
01396           seg->next = (*cur_seg);
01397           (*cur_seg) = seg;
01398         } else {
01399           /* add segment to tail of unacked list */
01400           useg->next = seg;
01401           useg = useg->next;
01402         }
01403       }
01404       /* do not queue empty segments on the unacked list */
01405     } else {
01406       tcp_seg_free(seg);
01407     }
01408     seg = pcb->unsent;
01409   }
01410 #if TCP_OVERSIZE
01411   if (pcb->unsent == NULL) {
01412     /* last unsent has been removed, reset unsent_oversize */
01413     pcb->unsent_oversize = 0;
01414   }
01415 #endif /* TCP_OVERSIZE */
01416 
01417 output_done:
01418   tcp_clear_flags(pcb, TF_NAGLEMEMERR);
01419   return ERR_OK;
01420 }
01421 
01422 /** Check if a segment's pbufs are used by someone else than TCP.
01423  * This can happen on retransmission if the pbuf of this segment is still
01424  * referenced by the netif driver due to deferred transmission.
01425  * This is the case (only!) if someone down the TX call path called
01426  * pbuf_ref() on one of the pbufs!
01427  *
01428  * @arg seg the tcp segment to check
01429  * @return 1 if ref != 1, 0 if ref == 1
01430  */
01431 static int
01432 tcp_output_segment_busy(const struct tcp_seg *seg)
01433 {
01434   LWIP_ASSERT("tcp_output_segment_busy: invalid seg", seg != NULL);
01435 
01436   /* We only need to check the first pbuf here:
01437      If a pbuf is queued for transmission, a driver calls pbuf_ref(),
01438      which only changes the ref count of the first pbuf */
01439   if (seg->p->ref != 1) {
01440     /* other reference found */
01441     return 1;
01442   }
01443   /* no other references found */
01444   return 0;
01445 }
01446 
01447 /**
01448  * Called by tcp_output() to actually send a TCP segment over IP.
01449  *
01450  * @param seg the tcp_seg to send
01451  * @param pcb the tcp_pcb for the TCP connection used to send the segment
01452  * @param netif the netif used to send the segment
01453  */
01454 static err_t
01455 tcp_output_segment(struct tcp_seg *seg, struct tcp_pcb *pcb, struct netif *netif)
01456 {
01457   err_t err;
01458   u16_t len;
01459   u32_t *opts;
01460 #if TCP_CHECKSUM_ON_COPY
01461   int seg_chksum_was_swapped = 0;
01462 #endif
01463 
01464   LWIP_ASSERT("tcp_output_segment: invalid seg", seg != NULL);
01465   LWIP_ASSERT("tcp_output_segment: invalid pcb", pcb != NULL);
01466   LWIP_ASSERT("tcp_output_segment: invalid netif", netif != NULL);
01467 
01468   if (tcp_output_segment_busy(seg)) {
01469     /* This should not happen: rexmit functions should have checked this.
01470        However, since this function modifies p->len, we must not continue in this case. */
01471     LWIP_DEBUGF(TCP_RTO_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("tcp_output_segment: segment busy\n"));
01472     return ERR_OK;
01473   }
01474 
01475   /* The TCP header has already been constructed, but the ackno and
01476    wnd fields remain. */
01477   seg->tcphdr->ackno = lwip_htonl(pcb->rcv_nxt);
01478 
01479   /* advertise our receive window size in this TCP segment */
01480 #if LWIP_WND_SCALE
01481   if (seg->flags & TF_SEG_OPTS_WND_SCALE) {
01482     /* The Window field in a SYN segment itself (the only type where we send
01483        the window scale option) is never scaled. */
01484     seg->tcphdr->wnd = lwip_htons(TCPWND_MIN16(pcb->rcv_ann_wnd));
01485   } else
01486 #endif /* LWIP_WND_SCALE */
01487   {
01488     seg->tcphdr->wnd = lwip_htons(TCPWND_MIN16(RCV_WND_SCALE(pcb, pcb->rcv_ann_wnd)));
01489   }
01490 
01491   pcb->rcv_ann_right_edge = pcb->rcv_nxt + pcb->rcv_ann_wnd;
01492 
01493   /* Add any requested options.  NB MSS option is only set on SYN
01494      packets, so ignore it here */
01495   /* cast through void* to get rid of alignment warnings */
01496   opts = (u32_t *)(void *)(seg->tcphdr + 1);
01497   if (seg->flags & TF_SEG_OPTS_MSS) {
01498     u16_t mss;
01499 #if TCP_CALCULATE_EFF_SEND_MSS
01500     mss = tcp_eff_send_mss_netif(TCP_MSS, netif, &pcb->remote_ip);
01501 #else /* TCP_CALCULATE_EFF_SEND_MSS */
01502     mss = TCP_MSS;
01503 #endif /* TCP_CALCULATE_EFF_SEND_MSS */
01504     *opts = TCP_BUILD_MSS_OPTION(mss);
01505     opts += 1;
01506   }
01507 #if LWIP_TCP_TIMESTAMPS
01508   pcb->ts_lastacksent = pcb->rcv_nxt;
01509 
01510   if (seg->flags & TF_SEG_OPTS_TS) {
01511     tcp_build_timestamp_option(pcb, opts);
01512     opts += 3;
01513   }
01514 #endif
01515 #if LWIP_WND_SCALE
01516   if (seg->flags & TF_SEG_OPTS_WND_SCALE) {
01517     tcp_build_wnd_scale_option(opts);
01518     opts += 1;
01519   }
01520 #endif
01521 #if LWIP_TCP_SACK_OUT
01522   if (seg->flags & TF_SEG_OPTS_SACK_PERM) {
01523     /* Pad with two NOP options to make everything nicely aligned
01524      * NOTE: When we send both timestamp and SACK_PERM options,
01525      * we could use the first two NOPs before the timestamp to store SACK_PERM option,
01526      * but that would complicate the code.
01527      */
01528     *(opts++) = PP_HTONL(0x01010402);
01529   }
01530 #endif
01531 
01532   /* Set retransmission timer running if it is not currently enabled
01533      This must be set before checking the route. */
01534   if (pcb->rtime < 0) {
01535     pcb->rtime = 0;
01536   }
01537 
01538   if (pcb->rttest == 0) {
01539     pcb->rttest = tcp_ticks;
01540     pcb->rtseq = lwip_ntohl(seg->tcphdr->seqno);
01541 
01542     LWIP_DEBUGF(TCP_RTO_DEBUG, ("tcp_output_segment: rtseq %"U32_F"\n", pcb->rtseq));
01543   }
01544   LWIP_DEBUGF(TCP_OUTPUT_DEBUG, ("tcp_output_segment: %"U32_F":%"U32_F"\n",
01545                                  lwip_htonl(seg->tcphdr->seqno), lwip_htonl(seg->tcphdr->seqno) +
01546                                  seg->len));
01547 
01548   len = (u16_t)((u8_t *)seg->tcphdr - (u8_t *)seg->p->payload);
01549   if (len == 0) {
01550     /** Exclude retransmitted segments from this count. */
01551     MIB2_STATS_INC(mib2.tcpoutsegs);
01552   }
01553 
01554   seg->p->len -= len;
01555   seg->p->tot_len -= len;
01556 
01557   seg->p->payload = seg->tcphdr;
01558 
01559   seg->tcphdr->chksum = 0;
01560 
01561 #ifdef LWIP_HOOK_TCP_OUT_ADD_TCPOPTS
01562   opts = LWIP_HOOK_TCP_OUT_ADD_TCPOPTS(seg->p, seg->tcphdr, pcb, opts);
01563 #endif
01564   LWIP_ASSERT("options not filled", (u8_t *)opts == ((u8_t *)(seg->tcphdr + 1)) + LWIP_TCP_OPT_LENGTH_SEGMENT(seg->flags, pcb));
01565 
01566 #if CHECKSUM_GEN_TCP
01567   IF__NETIF_CHECKSUM_ENABLED(netif, NETIF_CHECKSUM_GEN_TCP) {
01568 #if TCP_CHECKSUM_ON_COPY
01569     u32_t acc;
01570 #if TCP_CHECKSUM_ON_COPY_SANITY_CHECK
01571     u16_t chksum_slow = ip_chksum_pseudo(seg->p, IP_PROTO_TCP,
01572                                          seg->p->tot_len, &pcb->local_ip, &pcb->remote_ip);
01573 #endif /* TCP_CHECKSUM_ON_COPY_SANITY_CHECK */
01574     if ((seg->flags & TF_SEG_DATA_CHECKSUMMED) == 0) {
01575       LWIP_ASSERT("data included but not checksummed",
01576                   seg->p->tot_len == TCPH_HDRLEN_BYTES(seg->tcphdr));
01577     }
01578 
01579     /* rebuild TCP header checksum (TCP header changes for retransmissions!) */
01580     acc = ip_chksum_pseudo_partial(seg->p, IP_PROTO_TCP,
01581                                    seg->p->tot_len, TCPH_HDRLEN_BYTES(seg->tcphdr), &pcb->local_ip, &pcb->remote_ip);
01582     /* add payload checksum */
01583     if (seg->chksum_swapped) {
01584       seg_chksum_was_swapped = 1;
01585       seg->chksum = SWAP_BYTES_IN_WORD(seg->chksum);
01586       seg->chksum_swapped = 0;
01587     }
01588     acc = (u16_t)~acc + seg->chksum;
01589     seg->tcphdr->chksum = (u16_t)~FOLD_U32T(acc);
01590 #if TCP_CHECKSUM_ON_COPY_SANITY_CHECK
01591     if (chksum_slow != seg->tcphdr->chksum) {
01592       TCP_CHECKSUM_ON_COPY_SANITY_CHECK_FAIL(
01593         ("tcp_output_segment: calculated checksum is %"X16_F" instead of %"X16_F"\n",
01594          seg->tcphdr->chksum, chksum_slow));
01595       seg->tcphdr->chksum = chksum_slow;
01596     }
01597 #endif /* TCP_CHECKSUM_ON_COPY_SANITY_CHECK */
01598 #else /* TCP_CHECKSUM_ON_COPY */
01599     seg->tcphdr->chksum = ip_chksum_pseudo(seg->p, IP_PROTO_TCP,
01600                                            seg->p->tot_len, &pcb->local_ip, &pcb->remote_ip);
01601 #endif /* TCP_CHECKSUM_ON_COPY */
01602   }
01603 #endif /* CHECKSUM_GEN_TCP */
01604   TCP_STATS_INC(tcp.xmit);
01605 
01606   NETIF_SET_HINTS(netif, &(pcb->netif_hints));
01607   err = ip_output_if(seg->p, &pcb->local_ip, &pcb->remote_ip, pcb->ttl,
01608                      pcb->tos, IP_PROTO_TCP, netif);
01609   NETIF_RESET_HINTS(netif);
01610 
01611 #if TCP_CHECKSUM_ON_COPY
01612   if (seg_chksum_was_swapped) {
01613     /* if data is added to this segment later, chksum needs to be swapped,
01614        so restore this now */
01615     seg->chksum = SWAP_BYTES_IN_WORD(seg->chksum);
01616     seg->chksum_swapped = 1;
01617   }
01618 #endif
01619 
01620   return err;
01621 }
01622 
01623 /**
01624  * Requeue all unacked segments for retransmission
01625  *
01626  * Called by tcp_slowtmr() for slow retransmission.
01627  *
01628  * @param pcb the tcp_pcb for which to re-enqueue all unacked segments
01629  */
01630 err_t
01631 tcp_rexmit_rto_prepare(struct tcp_pcb *pcb)
01632 {
01633   struct tcp_seg *seg;
01634 
01635   LWIP_ASSERT("tcp_rexmit_rto_prepare: invalid pcb", pcb != NULL);
01636 
01637   if (pcb->unacked == NULL) {
01638     return ERR_VAL;
01639   }
01640 
01641   /* Move all unacked segments to the head of the unsent queue.
01642      However, give up if any of the unsent pbufs are still referenced by the
01643      netif driver due to deferred transmission. No point loading the link further
01644      if it is struggling to flush its buffered writes. */
01645   for (seg = pcb->unacked; seg->next != NULL; seg = seg->next) {
01646     if (tcp_output_segment_busy(seg)) {
01647       LWIP_DEBUGF(TCP_RTO_DEBUG, ("tcp_rexmit_rto: segment busy\n"));
01648       return ERR_VAL;
01649     }
01650   }
01651   if (tcp_output_segment_busy(seg)) {
01652     LWIP_DEBUGF(TCP_RTO_DEBUG, ("tcp_rexmit_rto: segment busy\n"));
01653     return ERR_VAL;
01654   }
01655   /* concatenate unsent queue after unacked queue */
01656   seg->next = pcb->unsent;
01657 #if TCP_OVERSIZE_DBGCHECK
01658   /* if last unsent changed, we need to update unsent_oversize */
01659   if (pcb->unsent == NULL) {
01660     pcb->unsent_oversize = seg->oversize_left;
01661   }
01662 #endif /* TCP_OVERSIZE_DBGCHECK */
01663   /* unsent queue is the concatenated queue (of unacked, unsent) */
01664   pcb->unsent = pcb->unacked;
01665   /* unacked queue is now empty */
01666   pcb->unacked = NULL;
01667 
01668   /* Mark RTO in-progress */
01669   tcp_set_flags(pcb, TF_RTO);
01670   /* Record the next byte following retransmit */
01671   pcb->rto_end = lwip_ntohl(seg->tcphdr->seqno) + TCP_TCPLEN(seg);
01672   /* Don't take any RTT measurements after retransmitting. */
01673   pcb->rttest = 0;
01674 
01675   return ERR_OK;
01676 }
01677 
01678 /**
01679  * Requeue all unacked segments for retransmission
01680  *
01681  * Called by tcp_slowtmr() for slow retransmission.
01682  *
01683  * @param pcb the tcp_pcb for which to re-enqueue all unacked segments
01684  */
01685 void
01686 tcp_rexmit_rto_commit(struct tcp_pcb *pcb)
01687 {
01688   LWIP_ASSERT("tcp_rexmit_rto_commit: invalid pcb", pcb != NULL);
01689 
01690   /* increment number of retransmissions */
01691   if (pcb->nrtx < 0xFF) {
01692     ++pcb->nrtx;
01693   }
01694   /* Do the actual retransmission */
01695   tcp_output(pcb);
01696 }
01697 
01698 /**
01699  * Requeue all unacked segments for retransmission
01700  *
01701  * Called by tcp_process() only, tcp_slowtmr() needs to do some things between
01702  * "prepare" and "commit".
01703  *
01704  * @param pcb the tcp_pcb for which to re-enqueue all unacked segments
01705  */
01706 void
01707 tcp_rexmit_rto(struct tcp_pcb *pcb)
01708 {
01709   LWIP_ASSERT("tcp_rexmit_rto: invalid pcb", pcb != NULL);
01710 
01711   if (tcp_rexmit_rto_prepare(pcb) == ERR_OK) {
01712     tcp_rexmit_rto_commit(pcb);
01713   }
01714 }
01715 
01716 /**
01717  * Requeue the first unacked segment for retransmission
01718  *
01719  * Called by tcp_receive() for fast retransmit.
01720  *
01721  * @param pcb the tcp_pcb for which to retransmit the first unacked segment
01722  */
01723 err_t
01724 tcp_rexmit(struct tcp_pcb *pcb)
01725 {
01726   struct tcp_seg *seg;
01727   struct tcp_seg **cur_seg;
01728 
01729   LWIP_ASSERT("tcp_rexmit: invalid pcb", pcb != NULL);
01730 
01731   if (pcb->unacked == NULL) {
01732     return ERR_VAL;
01733   }
01734 
01735   seg = pcb->unacked;
01736 
01737   /* Give up if the segment is still referenced by the netif driver
01738      due to deferred transmission. */
01739   if (tcp_output_segment_busy(seg)) {
01740     LWIP_DEBUGF(TCP_RTO_DEBUG, ("tcp_rexmit busy\n"));
01741     return ERR_VAL;
01742   }
01743 
01744   /* Move the first unacked segment to the unsent queue */
01745   /* Keep the unsent queue sorted. */
01746   pcb->unacked = seg->next;
01747 
01748   cur_seg = &(pcb->unsent);
01749   while (*cur_seg &&
01750          TCP_SEQ_LT(lwip_ntohl((*cur_seg)->tcphdr->seqno), lwip_ntohl(seg->tcphdr->seqno))) {
01751     cur_seg = &((*cur_seg)->next );
01752   }
01753   seg->next = *cur_seg;
01754   *cur_seg = seg;
01755 #if TCP_OVERSIZE
01756   if (seg->next == NULL) {
01757     /* the retransmitted segment is last in unsent, so reset unsent_oversize */
01758     pcb->unsent_oversize = 0;
01759   }
01760 #endif /* TCP_OVERSIZE */
01761 
01762   if (pcb->nrtx < 0xFF) {
01763     ++pcb->nrtx;
01764   }
01765 
01766   /* Don't take any rtt measurements after retransmitting. */
01767   pcb->rttest = 0;
01768 
01769   /* Do the actual retransmission. */
01770   MIB2_STATS_INC(mib2.tcpretranssegs);
01771   /* No need to call tcp_output: we are always called from tcp_input()
01772      and thus tcp_output directly returns. */
01773   return ERR_OK;
01774 }
01775 
01776 
01777 /**
01778  * Handle retransmission after three dupacks received
01779  *
01780  * @param pcb the tcp_pcb for which to retransmit the first unacked segment
01781  */
01782 void
01783 tcp_rexmit_fast(struct tcp_pcb *pcb)
01784 {
01785   LWIP_ASSERT("tcp_rexmit_fast: invalid pcb", pcb != NULL);
01786 
01787   if (pcb->unacked != NULL && !(pcb->flags & TF_INFR)) {
01788     /* This is fast retransmit. Retransmit the first unacked segment. */
01789     LWIP_DEBUGF(TCP_FR_DEBUG,
01790                 ("tcp_receive: dupacks %"U16_F" (%"U32_F
01791                  "), fast retransmit %"U32_F"\n",
01792                  (u16_t)pcb->dupacks, pcb->lastack,
01793                  lwip_ntohl(pcb->unacked->tcphdr->seqno)));
01794     if (tcp_rexmit(pcb) == ERR_OK) {
01795       /* Set ssthresh to half of the minimum of the current
01796        * cwnd and the advertised window */
01797       pcb->ssthresh = LWIP_MIN(pcb->cwnd, pcb->snd_wnd) / 2;
01798 
01799       /* The minimum value for ssthresh should be 2 MSS */
01800       if (pcb->ssthresh < (2U * pcb->mss)) {
01801         LWIP_DEBUGF(TCP_FR_DEBUG,
01802                     ("tcp_receive: The minimum value for ssthresh %"TCPWNDSIZE_F
01803                      " should be min 2 mss %"U16_F"...\n",
01804                      pcb->ssthresh, (u16_t)(2 * pcb->mss)));
01805         pcb->ssthresh = 2 * pcb->mss;
01806       }
01807 
01808       pcb->cwnd = pcb->ssthresh + 3 * pcb->mss;
01809       tcp_set_flags(pcb, TF_INFR);
01810 
01811       /* Reset the retransmission timer to prevent immediate rto retransmissions */
01812       pcb->rtime = 0;
01813     }
01814   }
01815 }
01816 
01817 static struct pbuf *
01818 tcp_output_alloc_header_common(u32_t ackno, u16_t optlen, u16_t datalen,
01819                         u32_t seqno_be /* already in network byte order */,
01820                         u16_t src_port, u16_t dst_port, u8_t flags, u16_t wnd)
01821 {
01822   struct tcp_hdr *tcphdr;
01823   struct pbuf *p;
01824 
01825   p = pbuf_alloc(PBUF_IP, TCP_HLEN + optlen + datalen, PBUF_RAM);
01826   if (p != NULL) {
01827     LWIP_ASSERT("check that first pbuf can hold struct tcp_hdr",
01828                 (p->len >= TCP_HLEN + optlen));
01829     tcphdr = (struct tcp_hdr *)p->payload;
01830     tcphdr->src = lwip_htons(src_port);
01831     tcphdr->dest = lwip_htons(dst_port);
01832     tcphdr->seqno = seqno_be;
01833     tcphdr->ackno = lwip_htonl(ackno);
01834     TCPH_HDRLEN_FLAGS_SET(tcphdr, (5 + optlen / 4), flags);
01835     tcphdr->wnd = lwip_htons(wnd);
01836     tcphdr->chksum = 0;
01837     tcphdr->urgp = 0;
01838   }
01839   return p;
01840 }
01841 
01842 /** Allocate a pbuf and create a tcphdr at p->payload, used for output
01843  * functions other than the default tcp_output -> tcp_output_segment
01844  * (e.g. tcp_send_empty_ack, etc.)
01845  *
01846  * @param pcb tcp pcb for which to send a packet (used to initialize tcp_hdr)
01847  * @param optlen length of header-options
01848  * @param datalen length of tcp data to reserve in pbuf
01849  * @param seqno_be seqno in network byte order (big-endian)
01850  * @return pbuf with p->payload being the tcp_hdr
01851  */
01852 static struct pbuf *
01853 tcp_output_alloc_header(struct tcp_pcb *pcb, u16_t optlen, u16_t datalen,
01854                         u32_t seqno_be /* already in network byte order */)
01855 {
01856   struct pbuf *p;
01857 
01858   LWIP_ASSERT("tcp_output_alloc_header: invalid pcb", pcb != NULL);
01859 
01860   p = tcp_output_alloc_header_common(pcb->rcv_nxt, optlen, datalen,
01861     seqno_be, pcb->local_port, pcb->remote_port, TCP_ACK,
01862     TCPWND_MIN16(RCV_WND_SCALE(pcb, pcb->rcv_ann_wnd)));
01863   if (p != NULL) {
01864     /* If we're sending a packet, update the announced right window edge */
01865     pcb->rcv_ann_right_edge = pcb->rcv_nxt + pcb->rcv_ann_wnd;
01866   }
01867   return p;
01868 }
01869 
01870 /* Fill in options for control segments */
01871 static void
01872 tcp_output_fill_options(const struct tcp_pcb *pcb, struct pbuf *p, u8_t optflags, u8_t num_sacks)
01873 {
01874   struct tcp_hdr *tcphdr;
01875   u32_t *opts;
01876   u16_t sacks_len = 0;
01877 
01878   LWIP_ASSERT("tcp_output_fill_options: invalid pbuf", p != NULL);
01879 
01880   tcphdr = (struct tcp_hdr *)p->payload;
01881   opts = (u32_t *)(void *)(tcphdr + 1);
01882 
01883   /* NB. MSS and window scale options are only sent on SYNs, so ignore them here */
01884 
01885 #if LWIP_TCP_TIMESTAMPS
01886   if (optflags & TF_SEG_OPTS_TS) {
01887     tcp_build_timestamp_option(pcb, opts);
01888     opts += 3;
01889   }
01890 #endif
01891 
01892 #if LWIP_TCP_SACK_OUT
01893   if (pcb && (num_sacks > 0)) {
01894     tcp_build_sack_option(pcb, opts, num_sacks);
01895     /* 1 word for SACKs header (including 2xNOP), and 2 words for each SACK */
01896     sacks_len = 1 + num_sacks * 2;
01897     opts += sacks_len;
01898   }
01899 #else
01900   LWIP_UNUSED_ARG(num_sacks);
01901 #endif
01902 
01903 #ifdef LWIP_HOOK_TCP_OUT_ADD_TCPOPTS
01904   opts = LWIP_HOOK_TCP_OUT_ADD_TCPOPTS(p, tcphdr, pcb, opts);
01905 #endif
01906 
01907   LWIP_UNUSED_ARG(pcb);
01908   LWIP_UNUSED_ARG(sacks_len);
01909   LWIP_ASSERT("options not filled", (u8_t *)opts == ((u8_t *)(tcphdr + 1)) + sacks_len * 4 + LWIP_TCP_OPT_LENGTH_SEGMENT(optflags, pcb));
01910   LWIP_UNUSED_ARG(optflags); /* for LWIP_NOASSERT */
01911   LWIP_UNUSED_ARG(opts); /* for LWIP_NOASSERT */
01912 }
01913 
01914 /** Output a control segment pbuf to IP.
01915  *
01916  * Called from tcp_rst, tcp_send_empty_ack, tcp_keepalive and tcp_zero_window_probe,
01917  * this function combines selecting a netif for transmission, generating the tcp
01918  * header checksum and calling ip_output_if while handling netif hints and stats.
01919  */
01920 static err_t
01921 tcp_output_control_segment(const struct tcp_pcb *pcb, struct pbuf *p,
01922                            const ip_addr_t *src, const ip_addr_t *dst)
01923 {
01924   err_t err;
01925   struct netif *netif;
01926 
01927   LWIP_ASSERT("tcp_output_control_segment: invalid pbuf", p != NULL);
01928 
01929   netif = tcp_route(pcb, src, dst);
01930   if (netif == NULL) {
01931     err = ERR_RTE;
01932   } else {
01933     u8_t ttl, tos;
01934 #if CHECKSUM_GEN_TCP
01935     IF__NETIF_CHECKSUM_ENABLED(netif, NETIF_CHECKSUM_GEN_TCP) {
01936       struct tcp_hdr *tcphdr = (struct tcp_hdr *)p->payload;
01937       tcphdr->chksum = ip_chksum_pseudo(p, IP_PROTO_TCP, p->tot_len,
01938                                         src, dst);
01939     }
01940 #endif
01941     if (pcb != NULL) {
01942       NETIF_SET_HINTS(netif, LWIP_CONST_CAST(struct netif_hint*, &(pcb->netif_hints)));
01943       ttl = pcb->ttl;
01944       tos = pcb->tos;
01945     } else {
01946       /* Send output with hardcoded TTL/HL since we have no access to the pcb */
01947       ttl = TCP_TTL;
01948       tos = 0;
01949     }
01950     TCP_STATS_INC(tcp.xmit);
01951     err = ip_output_if(p, src, dst, ttl, tos, IP_PROTO_TCP, netif);
01952     NETIF_RESET_HINTS(netif);
01953   }
01954   pbuf_free(p);
01955   return err;
01956 }
01957 
01958 /**
01959  * Send a TCP RESET packet (empty segment with RST flag set) either to
01960  * abort a connection or to show that there is no matching local connection
01961  * for a received segment.
01962  *
01963  * Called by tcp_abort() (to abort a local connection), tcp_input() (if no
01964  * matching local pcb was found), tcp_listen_input() (if incoming segment
01965  * has ACK flag set) and tcp_process() (received segment in the wrong state)
01966  *
01967  * Since a RST segment is in most cases not sent for an active connection,
01968  * tcp_rst() has a number of arguments that are taken from a tcp_pcb for
01969  * most other segment output functions.
01970  *
01971  * @param pcb TCP pcb (may be NULL if no pcb is available)
01972  * @param seqno the sequence number to use for the outgoing segment
01973  * @param ackno the acknowledge number to use for the outgoing segment
01974  * @param local_ip the local IP address to send the segment from
01975  * @param remote_ip the remote IP address to send the segment to
01976  * @param local_port the local TCP port to send the segment from
01977  * @param remote_port the remote TCP port to send the segment to
01978  */
01979 void
01980 tcp_rst(const struct tcp_pcb *pcb, u32_t seqno, u32_t ackno,
01981         const ip_addr_t *local_ip, const ip_addr_t *remote_ip,
01982         u16_t local_port, u16_t remote_port)
01983 {
01984   struct pbuf *p;
01985   u16_t wnd;
01986   u8_t optlen;
01987 
01988   LWIP_ASSERT("tcp_rst: invalid local_ip", local_ip != NULL);
01989   LWIP_ASSERT("tcp_rst: invalid remote_ip", remote_ip != NULL);
01990 
01991   optlen = LWIP_TCP_OPT_LENGTH_SEGMENT(0, pcb);
01992 
01993 #if LWIP_WND_SCALE
01994   wnd = PP_HTONS(((TCP_WND >> TCP_RCV_SCALE) & 0xFFFF));
01995 #else
01996   wnd = PP_HTONS(TCP_WND);
01997 #endif
01998 
01999   p = tcp_output_alloc_header_common(ackno, optlen, 0, lwip_htonl(seqno), local_port,
02000     remote_port, TCP_RST | TCP_ACK, wnd);
02001   if (p == NULL) {
02002     LWIP_DEBUGF(TCP_DEBUG, ("tcp_rst: could not allocate memory for pbuf\n"));
02003     return;
02004   }
02005   tcp_output_fill_options(pcb, p, 0, optlen);
02006 
02007   MIB2_STATS_INC(mib2.tcpoutrsts);
02008 
02009   tcp_output_control_segment(pcb, p, local_ip, remote_ip);
02010   LWIP_DEBUGF(TCP_RST_DEBUG, ("tcp_rst: seqno %"U32_F" ackno %"U32_F".\n", seqno, ackno));
02011 }
02012 
02013 /**
02014  * Send an ACK without data.
02015  *
02016  * @param pcb Protocol control block for the TCP connection to send the ACK
02017  */
02018 err_t
02019 tcp_send_empty_ack(struct tcp_pcb *pcb)
02020 {
02021   err_t err;
02022   struct pbuf *p;
02023   u8_t optlen, optflags = 0;
02024   u8_t num_sacks = 0;
02025 
02026   LWIP_ASSERT("tcp_send_empty_ack: invalid pcb", pcb != NULL);
02027 
02028 #if LWIP_TCP_TIMESTAMPS
02029   if (pcb->flags & TF_TIMESTAMP) {
02030     optflags = TF_SEG_OPTS_TS;
02031   }
02032 #endif
02033   optlen = LWIP_TCP_OPT_LENGTH_SEGMENT(optflags, pcb);
02034 
02035 #if LWIP_TCP_SACK_OUT
02036   /* For now, SACKs are only sent with empty ACKs */
02037   if ((num_sacks = tcp_get_num_sacks(pcb, optlen)) > 0) {
02038     optlen += 4 + num_sacks * 8; /* 4 bytes for header (including 2*NOP), plus 8B for each SACK */
02039   }
02040 #endif
02041 
02042   p = tcp_output_alloc_header(pcb, optlen, 0, lwip_htonl(pcb->snd_nxt));
02043   if (p == NULL) {
02044     /* let tcp_fasttmr retry sending this ACK */
02045     tcp_set_flags(pcb, TF_ACK_DELAY | TF_ACK_NOW);
02046     LWIP_DEBUGF(TCP_OUTPUT_DEBUG, ("tcp_output: (ACK) could not allocate pbuf\n"));
02047     return ERR_BUF;
02048   }
02049   tcp_output_fill_options(pcb, p, optflags, num_sacks);
02050 
02051 #if LWIP_TCP_TIMESTAMPS
02052   pcb->ts_lastacksent = pcb->rcv_nxt;
02053 #endif
02054 
02055   LWIP_DEBUGF(TCP_OUTPUT_DEBUG,
02056               ("tcp_output: sending ACK for %"U32_F"\n", pcb->rcv_nxt));
02057   err = tcp_output_control_segment(pcb, p, &pcb->local_ip, &pcb->remote_ip);
02058   if (err != ERR_OK) {
02059     /* let tcp_fasttmr retry sending this ACK */
02060     tcp_set_flags(pcb, TF_ACK_DELAY | TF_ACK_NOW);
02061   } else {
02062     /* remove ACK flags from the PCB, as we sent an empty ACK now */
02063     tcp_clear_flags(pcb, TF_ACK_DELAY | TF_ACK_NOW);
02064   }
02065 
02066   return err;
02067 }
02068 
02069 /**
02070  * Send keepalive packets to keep a connection active although
02071  * no data is sent over it.
02072  *
02073  * Called by tcp_slowtmr()
02074  *
02075  * @param pcb the tcp_pcb for which to send a keepalive packet
02076  */
02077 err_t
02078 tcp_keepalive(struct tcp_pcb *pcb)
02079 {
02080   err_t err;
02081   struct pbuf *p;
02082   u8_t optlen = LWIP_TCP_OPT_LENGTH_SEGMENT(0, pcb);
02083 
02084   LWIP_ASSERT("tcp_keepalive: invalid pcb", pcb != NULL);
02085 
02086   LWIP_DEBUGF(TCP_DEBUG, ("tcp_keepalive: sending KEEPALIVE probe to "));
02087   ip_addr_debug_print_val(TCP_DEBUG, pcb->remote_ip);
02088   LWIP_DEBUGF(TCP_DEBUG, ("\n"));
02089 
02090   LWIP_DEBUGF(TCP_DEBUG, ("tcp_keepalive: tcp_ticks %"U32_F"   pcb->tmr %"U32_F" pcb->keep_cnt_sent %"U16_F"\n",
02091                           tcp_ticks, pcb->tmr, (u16_t)pcb->keep_cnt_sent));
02092 
02093   p = tcp_output_alloc_header(pcb, optlen, 0, lwip_htonl(pcb->snd_nxt - 1));
02094   if (p == NULL) {
02095     LWIP_DEBUGF(TCP_DEBUG,
02096                 ("tcp_keepalive: could not allocate memory for pbuf\n"));
02097     return ERR_MEM;
02098   }
02099   tcp_output_fill_options(pcb, p, 0, optlen);
02100   err = tcp_output_control_segment(pcb, p, &pcb->local_ip, &pcb->remote_ip);
02101 
02102   LWIP_DEBUGF(TCP_DEBUG, ("tcp_keepalive: seqno %"U32_F" ackno %"U32_F" err %d.\n",
02103                           pcb->snd_nxt - 1, pcb->rcv_nxt, (int)err));
02104   return err;
02105 }
02106 
02107 /**
02108  * Send persist timer zero-window probes to keep a connection active
02109  * when a window update is lost.
02110  *
02111  * Called by tcp_slowtmr()
02112  *
02113  * @param pcb the tcp_pcb for which to send a zero-window probe packet
02114  */
02115 err_t
02116 tcp_zero_window_probe(struct tcp_pcb *pcb)
02117 {
02118   err_t err;
02119   struct pbuf *p;
02120   struct tcp_hdr *tcphdr;
02121   struct tcp_seg *seg;
02122   u16_t len;
02123   u8_t is_fin;
02124   u32_t snd_nxt;
02125   u8_t optlen = LWIP_TCP_OPT_LENGTH_SEGMENT(0, pcb);
02126 
02127   LWIP_ASSERT("tcp_zero_window_probe: invalid pcb", pcb != NULL);
02128 
02129   LWIP_DEBUGF(TCP_DEBUG, ("tcp_zero_window_probe: sending ZERO WINDOW probe to "));
02130   ip_addr_debug_print_val(TCP_DEBUG, pcb->remote_ip);
02131   LWIP_DEBUGF(TCP_DEBUG, ("\n"));
02132 
02133   LWIP_DEBUGF(TCP_DEBUG,
02134               ("tcp_zero_window_probe: tcp_ticks %"U32_F
02135                "   pcb->tmr %"U32_F" pcb->keep_cnt_sent %"U16_F"\n",
02136                tcp_ticks, pcb->tmr, (u16_t)pcb->keep_cnt_sent));
02137 
02138   /* Only consider unsent, persist timer should be off when there is data in-flight */
02139   seg = pcb->unsent;
02140   if (seg == NULL) {
02141     /* Not expected, persist timer should be off when the send buffer is empty */
02142     return ERR_OK;
02143   }
02144 
02145   /* increment probe count. NOTE: we record probe even if it fails
02146      to actually transmit due to an error. This ensures memory exhaustion/
02147      routing problem doesn't leave a zero-window pcb as an indefinite zombie.
02148      RTO mechanism has similar behavior, see pcb->nrtx */
02149   if (pcb->persist_probe < 0xFF) {
02150     ++pcb->persist_probe;
02151   }
02152 
02153   is_fin = ((TCPH_FLAGS(seg->tcphdr) & TCP_FIN) != 0) && (seg->len == 0);
02154   /* we want to send one seqno: either FIN or data (no options) */
02155   len = is_fin ? 0 : 1;
02156 
02157   p = tcp_output_alloc_header(pcb, optlen, len, seg->tcphdr->seqno);
02158   if (p == NULL) {
02159     LWIP_DEBUGF(TCP_DEBUG, ("tcp_zero_window_probe: no memory for pbuf\n"));
02160     return ERR_MEM;
02161   }
02162   tcphdr = (struct tcp_hdr *)p->payload;
02163 
02164   if (is_fin) {
02165     /* FIN segment, no data */
02166     TCPH_FLAGS_SET(tcphdr, TCP_ACK | TCP_FIN);
02167   } else {
02168     /* Data segment, copy in one byte from the head of the unacked queue */
02169     char *d = ((char *)p->payload + TCP_HLEN);
02170     /* Depending on whether the segment has already been sent (unacked) or not
02171        (unsent), seg->p->payload points to the IP header or TCP header.
02172        Ensure we copy the first TCP data byte: */
02173     pbuf_copy_partial(seg->p, d, 1, seg->p->tot_len - seg->len);
02174   }
02175 
02176   /* The byte may be acknowledged without the window being opened. */
02177   snd_nxt = lwip_ntohl(seg->tcphdr->seqno) + 1;
02178   if (TCP_SEQ_LT(pcb->snd_nxt, snd_nxt)) {
02179     pcb->snd_nxt = snd_nxt;
02180   }
02181   tcp_output_fill_options(pcb, p, 0, optlen);
02182 
02183   err = tcp_output_control_segment(pcb, p, &pcb->local_ip, &pcb->remote_ip);
02184 
02185   LWIP_DEBUGF(TCP_DEBUG, ("tcp_zero_window_probe: seqno %"U32_F
02186                           " ackno %"U32_F" err %d.\n",
02187                           pcb->snd_nxt - 1, pcb->rcv_nxt, (int)err));
02188   return err;
02189 }
02190 #endif /* LWIP_TCP */