/** * @file * * Transmission Control Protocol, incoming traffic * * The input processing functions of TCP. * * These functions are generally called in the order (ip_input() ->) tcp_input() -> * tcp_process() -> tcp_receive() (-> application). *  *//* * 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/def.h"#include "lwip/opt.h"#include "lwip/ip_addr.h"#include "lwip/netif.h"#include "lwip/mem.h"#include "lwip/memp.h"#include "lwip/inet.h"#include "lwip/tcp.h"#include "lwip/stats.h"#include "arch/perf.h"#if LWIP_TCP/* These variables are global to all functions involved in the input   processing of TCP segments. They are set by the tcp_input()   function. */static struct tcp_seg inseg;static struct tcp_hdr *tcphdr;static struct ip_hdr *iphdr;static u32_t seqno, ackno;static u8_t flags;static u16_t tcplen;static u8_t recv_flags;static struct pbuf *recv_data;struct tcp_pcb *tcp_input_pcb;/* Forward declarations. */static err_t tcp_process(struct tcp_pcb *pcb);static void tcp_receive(struct tcp_pcb *pcb);static void tcp_parseopt(struct tcp_pcb *pcb);static err_t tcp_listen_input(struct tcp_pcb_listen *pcb);static err_t tcp_timewait_input(struct tcp_pcb *pcb);/* tcp_input: * * The initial input processing of TCP. It verifies the TCP header, demultiplexes * the segment between the PCBs and passes it on to tcp_process(), which implements * the TCP finite state machine. This function is called by the IP layer (in * ip_input()). */voidtcp_input(struct pbuf *p, struct netif *inp){  struct tcp_pcb *pcb, *prev;  struct tcp_pcb_listen *lpcb;  u8_t hdrlen;  err_t err;  PERF_START;  TCP_STATS_INC(tcp.recv);  iphdr = p->payload;  tcphdr = (struct tcp_hdr *)((u8_t *)p->payload + IPH_HL(iphdr) * 4);#if TCP_INPUT_DEBUG  tcp_debug_print(tcphdr);#endif  /* remove header from payload */  if (pbuf_header(p, -((s16_t)(IPH_HL(iphdr) * 4))) || (p->tot_len < sizeof(struct tcp_hdr))) {    /* drop short packets */    LWIP_DEBUGF(TCP_INPUT_DEBUG, ("tcp_input: short packet (%"U16_F" bytes) discarded\n", p->tot_len));    TCP_STATS_INC(tcp.lenerr);    TCP_STATS_INC(tcp.drop);    pbuf_free(p);    return;  }  /* Don't even process incoming broadcasts/multicasts. */  if (ip_addr_isbroadcast(&(iphdr->dest), inp) ||      ip_addr_ismulticast(&(iphdr->dest))) {    pbuf_free(p);    return;  }#if CHECKSUM_CHECK_TCP  /* Verify TCP checksum. */  if (inet_chksum_pseudo(p, (struct ip_addr *)&(iphdr->src),      (struct ip_addr *)&(iphdr->dest),      IP_PROTO_TCP, p->tot_len) != 0) {      LWIP_DEBUGF(TCP_INPUT_DEBUG, ("tcp_input: packet discarded due to failing checksum 0x%04"X16_F"\n",        inet_chksum_pseudo(p, (struct ip_addr *)&(iphdr->src), (struct ip_addr *)&(iphdr->dest),      IP_PROTO_TCP, p->tot_len)));#if TCP_DEBUG    tcp_debug_print(tcphdr);#endif /* TCP_DEBUG */    TCP_STATS_INC(tcp.chkerr);    TCP_STATS_INC(tcp.drop);    pbuf_free(p);    return;  }#endif  /* Move the payload pointer in the pbuf so that it points to the     TCP data instead of the TCP header. */  hdrlen = TCPH_HDRLEN(tcphdr);  pbuf_header(p, -(hdrlen * 4));  /* Convert fields in TCP header to host byte order. */  tcphdr->src = ntohs(tcphdr->src);  tcphdr->dest = ntohs(tcphdr->dest);  seqno = tcphdr->seqno = ntohl(tcphdr->seqno);  ackno = tcphdr->ackno = ntohl(tcphdr->ackno);  tcphdr->wnd = ntohs(tcphdr->wnd);  flags = TCPH_FLAGS(tcphdr) & TCP_FLAGS;  tcplen = p->tot_len + ((flags & TCP_FIN || flags & TCP_SYN)? 1: 0);  /* Demultiplex an incoming segment. First, we check if it is destined     for an active connection. */  prev = NULL;    for(pcb = tcp_active_pcbs; pcb != NULL; pcb = pcb->next) {    if (pcb->remote_port == tcphdr->src &&       pcb->local_port == tcphdr->dest &&       ip_addr_cmp(&(pcb->remote_ip), &(iphdr->src)) &&       ip_addr_cmp(&(pcb->local_ip), &(iphdr->dest))) {      /* Move this PCB to the front of the list so that subsequent   lookups will be faster (we exploit locality in TCP segment   arrivals). */      if (prev != NULL) {  prev->next = pcb->next;  pcb->next = tcp_active_pcbs;  tcp_active_pcbs = pcb;      }            break;    }    prev = pcb;  }  if (pcb == NULL) {    /* If it did not go to an active connection, we check the connections       in the TIME-WAIT state. */    for(pcb = tcp_tw_pcbs; pcb != NULL; pcb = pcb->next) {            if (pcb->remote_port == tcphdr->src &&   pcb->local_port == tcphdr->dest &&   ip_addr_cmp(&(pcb->remote_ip), &(iphdr->src)) &&         ip_addr_cmp(&(pcb->local_ip), &(iphdr->dest))) {  /* We don't really care enough to move this PCB to the front     of the list since we are not very likely to receive that     many segments for connections in TIME-WAIT. */  tcp_timewait_input(pcb);  pbuf_free(p);  return;      }    }  /* Finally, if we still did not get a match, we check all PCBs that     are LISTENing for incoming connections. */    prev = NULL;    for(lpcb = tcp_listen_pcbs.listen_pcbs; lpcb != NULL; lpcb = lpcb->next) {      if ((ip_addr_isany(&(lpcb->local_ip)) ||    ip_addr_cmp(&(lpcb->local_ip), &(iphdr->dest))) &&   lpcb->local_port == tcphdr->dest) {  /* Move this PCB to the front of the list so that subsequent     lookups will be faster (we exploit locality in TCP segment     arrivals). */  if (prev != NULL) {    ((struct tcp_pcb_listen *)prev)->next = lpcb->next;          /* our successor is the remainder of the listening list */    lpcb->next = tcp_listen_pcbs.listen_pcbs;          /* put this listening pcb at the head of the listening list */    tcp_listen_pcbs.listen_pcbs = lpcb;  }    tcp_listen_input(lpcb);  pbuf_free(p);  return;      }      prev = (struct tcp_pcb *)lpcb;    }  }  if (pcb != NULL) {    /* The incoming segment belongs to a connection. */    /* Set up a tcp_seg structure. */    inseg.next = NULL;    inseg.len = p->tot_len;    inseg.dataptr = p->payload;    inseg.p = p;    inseg.tcphdr = tcphdr;    recv_data = NULL;    recv_flags = 0;    tcp_input_pcb = pcb;    err = tcp_process(pcb);    tcp_input_pcb = NULL;    /* A return value of ERR_ABRT means that tcp_abort() was called       and that the pcb has been freed. If so, we don't do anything. */    if (err != ERR_ABRT) {      if (recv_flags & TF_RESET) {  /* TF_RESET means that the connection was reset by the other     end. We then call the error callback to inform the     application that the connection is dead before we     deallocate the PCB. */  TCP_EVENT_ERR(pcb->errf, pcb->callback_arg, ERR_RST);  tcp_pcb_remove(&tcp_active_pcbs, pcb);  memp_free(MEMP_TCP_PCB, pcb);      } else if (recv_flags & TF_CLOSED) {  /* The connection has been closed and we will deallocate the     PCB. */  tcp_pcb_remove(&tcp_active_pcbs, pcb);  memp_free(MEMP_TCP_PCB, pcb);      } else {  err = ERR_OK;  /* If the application has registered a "sent" function to be     called when new send buffer space is available, we call it     now. */  if (pcb->acked > 0) {    TCP_EVENT_SENT(pcb, pcb->acked, err);  }  if (recv_data != NULL) {    /* Notify application that data has been received. */    TCP_EVENT_RECV(pcb, recv_data, ERR_OK, err);  }  /* If a FIN segment was received, we call the callback     function with a NULL buffer to indicate EOF. */  if (recv_flags & TF_GOT_FIN) {    TCP_EVENT_RECV(pcb, NULL, ERR_OK, err);  }  /* If there were no errors, we try to send something out. */  if (err == ERR_OK) {    tcp_output(pcb);  }      }    }    /* We deallocate the incoming pbuf. If it was buffered by the       application, the application should have called pbuf_ref() to       increase the reference counter in the pbuf. If so, the buffer       isn't actually deallocated by the call to pbuf_free(), only the       reference count is decreased. */    if (inseg.p != NULL) pbuf_free(inseg.p);        } else {    /* If no matching PCB was found, send a TCP RST (reset) to the       sender. */        if (!(TCPH_FLAGS(tcphdr) & TCP_RST)) {      TCP_STATS_INC(tcp.proterr);      TCP_STATS_INC(tcp.drop);      tcp_rst(ackno, seqno + tcplen,        &(iphdr->dest), &(iphdr->src),        tcphdr->dest, tcphdr->src);    }    pbuf_free(p);  }}/* tcp_listen_input(): * * Called by tcp_input() when a segment arrives for a listening * connection. */static err_ttcp_listen_input(struct tcp_pcb_listen *pcb){  struct tcp_pcb *npcb;  u32_t optdata;  /* In the LISTEN state, we check for incoming SYN segments,     creates a new PCB, and responds with a SYN|ACK. */  if (flags & TCP_ACK) {    /* For incoming segments with the ACK flag set, respond with a       RST. */    LWIP_DEBUGF(TCP_RST_DEBUG, ("tcp_listen_input: ACK in LISTEN, sending reset\n"));    tcp_rst(ackno + 1, seqno + tcplen,      &(iphdr->dest), &(iphdr->src),      tcphdr->dest, tcphdr->src);  } else if (flags & TCP_SYN) {    LWIP_DEBUGF(TCP_DEBUG, ("TCP connection request %"U16_F" -> %"U16_F".\n", tcphdr->src, tcphdr->dest));    npcb = tcp_alloc(pcb->prio);    /* If a new PCB could not be created (probably due to lack of memory),       we don't do anything, but rely on the sender will retransmit the       SYN at a time when we have more memory available. */    if (npcb == NULL) {      LWIP_DEBUGF(TCP_DEBUG, ("tcp_listen_input: could not allocate PCB\n"));      TCP_STATS_INC(tcp.memerr);      return ERR_MEM;    }    /* Set up the new PCB. */    ip_addr_set(&(npcb->local_ip), &(iphdr->dest));    npcb->local_port = pcb->local_port;    ip_addr_set(&(npcb->remote_ip), &(iphdr->src));    npcb->remote_port = tcphdr->src;    npcb->state = SYN_RCVD;    npcb->rcv_nxt = seqno + 1;    npcb->snd_wnd = tcphdr->wnd;    npcb->ssthresh = npcb->snd_wnd;    npcb->snd_wl1 = seqno - 1;/* initialise to seqno-1 to force window update */    npcb->callback_arg = pcb->callback_arg;#if LWIP_CALLBACK_API    npcb->accept = pcb->accept;#endif /* LWIP_CALLBACK_API */    /* inherit socket options */    npcb->so_options = pcb->so_options & (SOF_DEBUG|SOF_DONTROUTE|SOF_KEEPALIVE|SOF_OOBINLINE|SOF_LINGER);    /* Register the new PCB so that we can begin receiving segments       for it. */    TCP_REG(&tcp_active_pcbs, npcb);    /* Parse any options in the SYN. */    tcp_parseopt(npcb);    /* Build an MSS option. */    optdata = htonl(((u32_t)2 << 24) |        ((u32_t)4 << 16) |        (((u32_t)npcb->mss / 256) << 8) |        (npcb->mss & 255));    /* Send a SYN|ACK together with the MSS option. */    tcp_enqueue(npcb, NULL, 0, TCP_SYN | TCP_ACK, 0, (u8_t *)&optdata, 4);    return tcp_output(npcb);  }  return ERR_OK;}/* tcp_timewait_input(): * * Called by tcp_input() when a segment arrives for a connection in * TIME_WAIT. */static err_ttcp_timewait_input(struct tcp_pcb *pcb){  if (TCP_SEQ_GT(seqno + tcplen, pcb->rcv_nxt)) {    pcb->rcv_nxt = seqno + tcplen;  }  if (tcplen > 0) {