In the hex dump, generate the offset at the beginning of each line in

[obnox/wireshark/wip.git] / packet-tcp.c

/* packet-tcp.c
 * Routines for TCP packet disassembly
 *
 * $Id: packet-tcp.c,v 1.144 2002/06/08 21:54:52 guy Exp $
 *
 * Ethereal - Network traffic analyzer
 * By Gerald Combs <gerald@ethereal.com>
 * Copyright 1998 Gerald Combs
 * 
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 */

#ifdef HAVE_CONFIG_H
# include "config.h"
#endif

#ifdef HAVE_SYS_TYPES_H
# include <sys/types.h>
#endif

#ifdef HAVE_NETINET_IN_H
# include <netinet/in.h>
#endif

#include <stdio.h>
#include <string.h>
#include <glib.h>
#include "in_cksum.h"

#ifdef NEED_SNPRINTF_H
# include "snprintf.h"
#endif

#include <epan/resolv.h>
#include "ipproto.h"
#include "follow.h"
#include "prefs.h"
#include "packet-tcp.h"
#include "packet-ip.h"
#include "packet-frame.h"
#include <epan/conversation.h>
#include <epan/strutil.h>
#include "reassemble.h"

/* Place TCP summary in proto tree */
static gboolean tcp_summary_in_tree = TRUE;

/*
 * Flag to control whether to check the TCP checksum.
 *
 * In at least some Solaris network traces, there are packets with bad
 * TCP checksums, but the traffic appears to indicate that the packets
 * *were* received; the packets were probably sent by the host on which
 * the capture was being done, on a network interface to which
 * checksumming was offloaded, so that DLPI supplied an un-checksummed
 * packet to the capture program but a checksummed packet got put onto
 * the wire.
 */
static gboolean tcp_check_checksum = TRUE;

extern FILE* data_out_file;

static int proto_tcp = -1;
static int hf_tcp_srcport = -1;
static int hf_tcp_dstport = -1;
static int hf_tcp_port = -1;
static int hf_tcp_seq = -1;
static int hf_tcp_nxtseq = -1;
static int hf_tcp_ack = -1;
static int hf_tcp_hdr_len = -1;
static int hf_tcp_flags = -1;
static int hf_tcp_flags_cwr = -1;
static int hf_tcp_flags_ecn = -1;
static int hf_tcp_flags_urg = -1;
static int hf_tcp_flags_ack = -1;
static int hf_tcp_flags_push = -1;
static int hf_tcp_flags_reset = -1;
static int hf_tcp_flags_syn = -1;
static int hf_tcp_flags_fin = -1;
static int hf_tcp_window_size = -1;
static int hf_tcp_checksum = -1;
static int hf_tcp_checksum_bad = -1;
static int hf_tcp_len = -1;
static int hf_tcp_urgent_pointer = -1;

static gint ett_tcp = -1;
static gint ett_tcp_flags = -1;
static gint ett_tcp_options = -1;
static gint ett_tcp_option_sack = -1;
static gint ett_tcp_segments = -1;

static dissector_table_t subdissector_table;
static heur_dissector_list_t heur_subdissector_list;
static dissector_handle_t data_handle;

/* TCP structs and definitions */

#define TH_FIN  0x01
#define TH_SYN  0x02
#define TH_RST  0x04
#define TH_PUSH 0x08
#define TH_ACK  0x10
#define TH_URG  0x20
#define TH_ECN  0x40
#define TH_CWR  0x80

/* Minimum TCP header length. */
#define TCPH_MIN_LEN    20

/*
 *      TCP option
 */
 
#define TCPOPT_NOP              1       /* Padding */
#define TCPOPT_EOL              0       /* End of options */
#define TCPOPT_MSS              2       /* Segment size negotiating */
#define TCPOPT_WINDOW           3       /* Window scaling */
#define TCPOPT_SACK_PERM        4       /* SACK Permitted */
#define TCPOPT_SACK             5       /* SACK Block */
#define TCPOPT_ECHO             6
#define TCPOPT_ECHOREPLY        7
#define TCPOPT_TIMESTAMP        8       /* Better RTT estimations/PAWS */
#define TCPOPT_CC               11
#define TCPOPT_CCNEW            12
#define TCPOPT_CCECHO           13
#define TCPOPT_MD5              19      /* RFC2385 */

/*
 *     TCP option lengths
 */

#define TCPOLEN_MSS            4
#define TCPOLEN_WINDOW         3
#define TCPOLEN_SACK_PERM      2
#define TCPOLEN_SACK_MIN       2
#define TCPOLEN_ECHO           6
#define TCPOLEN_ECHOREPLY      6
#define TCPOLEN_TIMESTAMP      10
#define TCPOLEN_CC             6
#define TCPOLEN_CCNEW          6
#define TCPOLEN_CCECHO         6
#define TCPOLEN_MD5            18



/* Desegmentation of TCP streams */
/* table to hold defragmented TCP streams */
static GHashTable *tcp_fragment_table = NULL;
static void
tcp_fragment_init(void)
{
        fragment_table_init(&tcp_fragment_table);
}

/* functions to trace tcp segments */
/* Enable desegmenting of TCP streams */
static gboolean tcp_desegment = FALSE;

static GHashTable *tcp_segment_table = NULL;
static GMemChunk *tcp_segment_key_chunk = NULL;
static int tcp_segment_init_count = 200;
static GMemChunk *tcp_segment_address_chunk = NULL;
static int tcp_segment_address_init_count = 500;

typedef struct _tcp_segment_key {
        /* for own bookkeeping inside packet-tcp.c */
        address *src;
        address *dst;
        guint32 seq;
        /* xxx */
        guint32 start_seq;
        guint32 tot_len;
        guint32 first_frame;
} tcp_segment_key;

static gboolean
free_all_segments(gpointer key_arg, gpointer value _U_, gpointer user_data _U_)
{
        tcp_segment_key *key = key_arg;

        if((key->src)&&(key->src->data)){
                g_free((gpointer)key->src->data);
                key->src->data=NULL;
        }

        if((key->dst)&&(key->dst->data)){
                g_free((gpointer)key->dst->data);
                key->dst->data=NULL;
        }

        return TRUE;
}

static guint
tcp_segment_hash(gconstpointer k)
{
        tcp_segment_key *key = (tcp_segment_key *)k;

        return key->seq;
}

static gint
tcp_segment_equal(gconstpointer k1, gconstpointer k2)
{
        tcp_segment_key *key1 = (tcp_segment_key *)k1;
        tcp_segment_key *key2 = (tcp_segment_key *)k2;

        return ( ( (key1->seq==key2->seq)
                 &&(ADDRESSES_EQUAL(key1->src, key2->src))
                 &&(ADDRESSES_EQUAL(key1->dst, key2->dst))
                 ) ? TRUE:FALSE);
}

static void
tcp_desegment_init(void)
{
        /*
         * Free this before freeing any memory chunks; those
         * chunks contain data we'll look at in "free_all_segments()".
         */
        if(tcp_segment_table){
                g_hash_table_foreach_remove(tcp_segment_table,
                        free_all_segments, NULL);
                g_hash_table_destroy(tcp_segment_table);
                tcp_segment_table = NULL;
        }

        if(tcp_segment_key_chunk){
                g_mem_chunk_destroy(tcp_segment_key_chunk);
                tcp_segment_key_chunk = NULL;
        }
        if(tcp_segment_address_chunk){
                g_mem_chunk_destroy(tcp_segment_address_chunk);
                tcp_segment_address_chunk = NULL;
        }

        /* dont allocate any hash table or memory chunks unless the user
           really uses this option
        */
        if(!tcp_desegment){
                return;
        }

        tcp_segment_table = g_hash_table_new(tcp_segment_hash,
                tcp_segment_equal);

        tcp_segment_key_chunk = g_mem_chunk_new("tcp_segment_key_chunk",
                sizeof(tcp_segment_key),
                tcp_segment_init_count*sizeof(tcp_segment_key),
                G_ALLOC_ONLY);

        tcp_segment_address_chunk = g_mem_chunk_new("tcp_segment_address_chunk",
                sizeof(address),
                tcp_segment_address_init_count*sizeof(address),
                G_ALLOC_ONLY);
}

static void
desegment_tcp(tvbuff_t *tvb, packet_info *pinfo, int offset,
                guint32 seq, guint32 nxtseq,
                guint32 sport, guint32 dport,
                proto_tree *tree, proto_tree *tcp_tree)
{
        struct tcpinfo *tcpinfo = pinfo->private_data;
        fragment_data *ipfd_head;
        tcp_segment_key old_tsk, *tsk;
        gboolean must_desegment = FALSE;
        gboolean called_dissector = FALSE;
        int deseg_offset;
        guint32 deseg_seq;
        gint nbytes;

        /*
         * Initialize these to assume no desegmentation.
         * If that's not the case, these will be set appropriately
         * by the subdissector.
         */
        pinfo->desegment_offset = 0;
        pinfo->desegment_len = 0;

        /*
         * Initialize this to assume that this segment will just be
         * added to the middle of a desegmented chunk of data, so
         * that we should show it all as data.
         * If that's not the case, it will be set appropriately.
         */
        deseg_offset = offset;

        /* First we must check if this TCP segment should be desegmented.
           This is only to check if we should desegment this packet,
           so we dont spend time doing COPY_ADDRESS/g_free.
           We just "borrow" some address structures from pinfo instead. Cheaper.
        */
        old_tsk.src = &pinfo->src;
        old_tsk.dst = &pinfo->dst;
        old_tsk.seq = seq;
        tsk = g_hash_table_lookup(tcp_segment_table, &old_tsk);

        if(tsk){
                /* OK, this segment was found, which means it continues
                   a higher-level PDU. This means we must desegment it.
                   Add it to the defragmentation lists.
                */
                ipfd_head = fragment_add(tvb, offset, pinfo, tsk->start_seq,
                        tcp_fragment_table,
                        seq - tsk->start_seq,
                        nxtseq - seq,
                        (nxtseq < (tsk->start_seq + tsk->tot_len)) );

                if(!ipfd_head){
                        /* fragment_add() returned NULL, This means that 
                           desegmentation is not completed yet.
                           (its like defragmentation but we know we will
                            always add the segments in order).
                           XXX - no, we don't; there is no guarantee that
                           TCP segments are in order on the wire.

                           we must add next segment to our table so we will
                           find it later.
                        */
                        tcp_segment_key *new_tsk;

                        new_tsk = g_mem_chunk_alloc(tcp_segment_key_chunk);
                        memcpy(new_tsk, tsk, sizeof(tcp_segment_key));
                        new_tsk->seq=nxtseq;
                        g_hash_table_insert(tcp_segment_table,new_tsk,new_tsk);
                }
        } else {
                /* This segment was not found in our table, so it doesn't
                   contain a continuation of a higher-level PDU.
                   Call the normal subdissector.
                */
                decode_tcp_ports(tvb, offset, pinfo, tree, 
                                sport, dport);
                called_dissector = TRUE;

                /* Did the subdissector ask us to desegment some more data
                   before it could handle the packet? 
                   If so we have to create some structures in our table but
                   this is something we only do the first time we see this 
                   packet.
                */
                if(pinfo->desegment_len) {
                        if (!pinfo->fd->flags.visited)
                                must_desegment = TRUE;

                        /*
                         * Set "deseg_offset" to the offset in "tvb"
                         * of the first byte of data that the
                         * subdissector didn't process.
                         */
                        deseg_offset = offset + pinfo->desegment_offset;
                }

                /* Either no desegmentation is necessary, or this is
                   segment contains the beginning but not the end of
                   a higher-level PDU and thus isn't completely
                   desegmented.
                */
                ipfd_head = NULL;
        }

        /* is it completely desegmented? */
        if(ipfd_head){
                fragment_data *ipfd;
                proto_tree *st = NULL;
                proto_item *si = NULL;

                /*
                 * Yes, we think it is.
                 * We only call subdissector for the last segment.
                 * Note that the last segment may include more than what
                 * we needed.
                 */
                if(nxtseq >= (tsk->start_seq + tsk->tot_len)){
                        /*
                         * OK, this is the last segment.
                         * Let's call the subdissector with the desegmented
                         * data.
                         */
                        tvbuff_t *next_tvb;
                        int old_len;

                        /* create a new TVB structure for desegmented data */
                        next_tvb = tvb_new_real_data(ipfd_head->data,
                                        ipfd_head->datalen, ipfd_head->datalen);

                        /* add this tvb as a child to the original one */
                        tvb_set_child_real_data_tvbuff(tvb, next_tvb);

                        /* add desegmented data to the data source list */
                        add_new_data_source(pinfo, next_tvb, "Desegmented");

                        /*
                         * Supply the sequence number of the first of the
                         * reassembled bytes.
                         */
                        tcpinfo->seq = tsk->start_seq;

                        /* indicate that this is reassembled data */
                        tcpinfo->is_reassembled = TRUE;

                        /* call subdissector */
                        decode_tcp_ports(next_tvb, 0, pinfo, tree,
                                sport, dport);
                        called_dissector = TRUE;

                        /*
                         * OK, did the subdissector think it was completely
                         * desegmented, or does it think we need even more
                         * data?
                         */
                        old_len=(int)(tvb_reported_length(next_tvb)-tvb_reported_length_remaining(tvb, offset));
                        if(pinfo->desegment_len &&
                            pinfo->desegment_offset<=old_len){
                                tcp_segment_key *new_tsk;

                                /*
                                 * "desegment_len" isn't 0, so it needs more
                                 * data for something - and "desegment_offset"
                                 * is before "old_len", so it needs more data
                                 * to dissect the stuff we thought was
                                 * completely desegmented (as opposed to the
                                 * stuff at the beginning being completely
                                 * desegmented, but the stuff at the end
                                 * being a new higher-level PDU that also
                                 * needs desegmentation).
                                 */
                                fragment_set_partial_reassembly(pinfo,tsk->start_seq,tcp_fragment_table);
                                tsk->tot_len = tvb_reported_length(next_tvb) + pinfo->desegment_len;

                                /*
                                 * Update tsk structure.
                                 * Can ask ->next->next because at least there's a hdr and one
                                 * entry in fragment_add()
                                 */
                                for(ipfd=ipfd_head->next; ipfd->next; ipfd=ipfd->next){
                                        old_tsk.seq = tsk->start_seq + ipfd->offset;
                                        new_tsk = g_hash_table_lookup(tcp_segment_table, &old_tsk);
                                        new_tsk->tot_len = tsk->tot_len;
                                }

                                /* this is the next segment in the sequence we want */
                                new_tsk = g_mem_chunk_alloc(tcp_segment_key_chunk);
                                memcpy(new_tsk, tsk, sizeof(tcp_segment_key));
                                new_tsk->seq = nxtseq;
                                g_hash_table_insert(tcp_segment_table,new_tsk,new_tsk);
                        } else {
                                /*
                                 * Show the stuff in this TCP segment as
                                 * just raw TCP segment data.
                                 */
                                nbytes =
                                    tvb_reported_length_remaining(tvb, offset);
                                proto_tree_add_text(tcp_tree, tvb, offset, -1,
                                    "TCP segment data (%u byte%s)", nbytes,
                                    plurality(nbytes, "", "s"));

                                /*
                                 * The subdissector thought it was completely
                                 * desegmented (although the stuff at the
                                 * end may, in turn, require desegmentation),
                                 * so we show a tree with all segments.
                                 */
                                si = proto_tree_add_text(tcp_tree, next_tvb,
                                                0, -1, "Segments");
                                st = proto_item_add_subtree(si, ett_tcp_segments);
                                for(ipfd=ipfd_head->next; ipfd; ipfd=ipfd->next){
                                        proto_tree_add_text(st, next_tvb,
                                        ipfd->offset, ipfd->len,
                                        "Frame:%u seq#:%u-%u [%u-%u]",
                                        ipfd->frame,
                                        tsk->start_seq + ipfd->offset,
                                        tsk->start_seq + ipfd->offset + ipfd->len-1,
                                        ipfd->offset,
                                        ipfd->offset + ipfd->len - 1);
                                }

                                /* Did the subdissector ask us to desegment
                                   some more data?  This means that the data
                                   at the beginning of this segment completed
                                   a higher-level PDU, but the data at the
                                   end of this segment started a higher-level
                                   PDU but didn't complete it.

                                   If so, we have to create some structures
                                   in our table, but this is something we
                                   only do the first time we see this packet.
                                */
                                if(pinfo->desegment_len) {
                                        if (!pinfo->fd->flags.visited)
                                                must_desegment = TRUE;

                                        /* The stuff we couldn't dissect
                                           must have come from this segment,
                                           so it's all in "tvb".

                                           "pinfo->desegment_offset" is
                                           relative to the beginning of
                                           "next_tvb"; we want an offset
                                           relative to the beginning of "tvb".

                                           First, compute the offset relative
                                           to the *end* of "next_tvb" - i.e.,
                                           the number of bytes before the end
                                           of "next_tvb" at which the
                                           subdissector stopped.  That's the
                                           length of "next_tvb" minus the
                                           offset, relative to the beginning
                                           of "next_tvb, at which the
                                           subdissector stopped.
                                        */
                                        deseg_offset =
                                            ipfd_head->datalen - pinfo->desegment_offset;

                                        /* "tvb" and "next_tvb" end at the
                                           same byte of data, so the offset
                                           relative to the end of "next_tvb"
                                           of the byte at which we stopped
                                           is also the offset relative to
                                           the end of "tvb" of the byte at
                                           which we stopped.

                                           Convert that back into an offset
                                           relative to the beginninng of
                                           "tvb", by taking the length of
                                           "tvb" and subtracting the offset
                                           relative to the end.
                                        */
                                        deseg_offset=tvb_reported_length(tvb) - deseg_offset;
                                }
                        }
                }
        }

        if (must_desegment) {
            tcp_segment_key *tsk, *new_tsk;

            /*
             * The sequence number at which the stuff to be desegmented
             * starts is the sequence number of the byte at an offset
             * of "deseg_offset" into "tvb".
             *
             * The sequence number of the byte at an offset of "offset"
             * is "seq", i.e. the starting sequence number of this
             * segment, so the sequence number of the byte at
             * "deseg_offset" is "seq + (deseg_offset - offset)".
             */
            deseg_seq = seq + (deseg_offset - offset);

            /*
             * XXX - how do we detect out-of-order transmissions?
             * We can't just check for "nxtseq" being greater than
             * "tsk->start_seq"; for now, we check for the difference
             * being less than a megabyte, but this is a really
             * gross hack - we really need to handle out-of-order
             * transmissions correctly.
             */
            if ((nxtseq - deseg_seq) <= 1024*1024) {
                /* OK, subdissector wants us to desegment
                   some data before it can process it. Add
                   what remains of this packet and set
                   up next packet/sequence number as well.

                   We must remember this segment
                */
                tsk = g_mem_chunk_alloc(tcp_segment_key_chunk);
                tsk->src = g_mem_chunk_alloc(tcp_segment_address_chunk);
                COPY_ADDRESS(tsk->src, &pinfo->src);
                tsk->dst = g_mem_chunk_alloc(tcp_segment_address_chunk);
                COPY_ADDRESS(tsk->dst, &pinfo->dst);
                tsk->seq = deseg_seq;
                tsk->start_seq = tsk->seq;
                tsk->tot_len = nxtseq - tsk->start_seq + pinfo->desegment_len;
                tsk->first_frame = pinfo->fd->num;
                g_hash_table_insert(tcp_segment_table, tsk, tsk);

                /* Add portion of segment unprocessed by the subdissector
                   to defragmentation lists */
                fragment_add(tvb, deseg_offset, pinfo, tsk->start_seq,
                    tcp_fragment_table,
                    tsk->seq - tsk->start_seq,
                    nxtseq - tsk->start_seq,
                    (nxtseq < tsk->start_seq + tsk->tot_len));

                /* this is the next segment in the sequence we want */
                new_tsk = g_mem_chunk_alloc(tcp_segment_key_chunk);
                memcpy(new_tsk, tsk, sizeof(tcp_segment_key));
                new_tsk->seq = nxtseq;
                g_hash_table_insert(tcp_segment_table,new_tsk,new_tsk);
            }
        }

        if (!called_dissector || pinfo->desegment_len != 0) {
                /*
                 * Either we didn't call the subdissector at all (i.e.,
                 * this is a segment that contains the middle of a
                 * higher-level PDU, but contains neither the beginning
                 * nor the end), or the subdissector couldn't dissect it
                 * all, as some data was missing (i.e., it set
                 * "pinfo->desegment_len" to the amount of additional
                 * data it needs).
                 */
                if (pinfo->desegment_offset == 0) {
                        /*
                         * It couldn't, in fact, dissect any of it (the
                         * first byte it couldn't dissect is at an offset
                         * of "pinfo->desegment_offset" from the beginning
                         * of the payload, and that's 0).
                         * Just mark this as TCP.
                         */
                        if (check_col(pinfo->cinfo, COL_PROTOCOL)){
                                col_set_str(pinfo->cinfo, COL_PROTOCOL, "TCP");
                        }
                        if (check_col(pinfo->cinfo, COL_INFO)){
                                col_set_str(pinfo->cinfo, COL_INFO, "[Desegmented TCP]");
                        }
                }

                /*
                 * Show what's left in the packet as just raw TCP segment
                 * data.
                 * XXX - remember what protocol the last subdissector
                 * was, and report it as a continuation of that, instead?
                 */
                nbytes = tvb_reported_length_remaining(tvb, deseg_offset);
                proto_tree_add_text(tcp_tree, tvb, deseg_offset, -1,
                    "TCP segment data (%u byte%s)", nbytes,
                    plurality(nbytes, "", "s"));
        }
        pinfo->can_desegment=0;
        pinfo->desegment_offset = 0;
        pinfo->desegment_len = 0;
}

/*
 * Loop for dissecting PDUs within a TCP stream; assumes that a PDU
 * consists of a fixed-length chunk of data that contains enough information
 * to determine the length of the PDU, followed by rest of the PDU.
 *
 * The first three arguments are the arguments passed to the dissector
 * that calls this routine.
 *
 * "proto_desegment" is the dissector's flag controlling whether it should
 * desegment PDUs that cross TCP segment boundaries.
 *
 * "fixed_len" is the length of the fixed-length part of the PDU.
 *
 * "get_pdu_len()" is a routine called to get the length of the PDU from
 * the fixed-length part of the PDU; it's passed "tvb" and "offset".
 *
 * "dissect_pdu()" is the routine to dissect a PDU.
 */
void
tcp_dissect_pdus(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree,
                 gboolean proto_desegment, guint fixed_len,
                 guint (*get_pdu_len)(tvbuff_t *, int),
                 void (*dissect_pdu)(tvbuff_t *, packet_info *, proto_tree *))
{
  volatile int offset = 0;
  guint length_remaining;
  guint plen;
  guint length;
  tvbuff_t *next_tvb;

  while (tvb_reported_length_remaining(tvb, offset) != 0) {
    /*
     * We use "tvb_ensure_length_remaining()" to make sure there actually
     * *is* data remaining.  The protocol we're handling could conceivably
     * consists of a sequence of fixed-length PDUs, and therefore the
     * "get_pdu_len" routine might not actually fetch anything from
     * the tvbuff, and thus might not cause an exception to be thrown if
     * we've run past the end of the tvbuff.
     *
     * This means we're guaranteed that "length_remaining" is positive.
     */
    length_remaining = tvb_ensure_length_remaining(tvb, offset);

    /*
     * Can we do reassembly?
     */
    if (proto_desegment && pinfo->can_desegment) {
      /*
       * Yes - is the fixed-length part of the PDU split across segment
       * boundaries?
       */
      if (length_remaining < fixed_len) {
        /*
         * Yes.  Tell the TCP dissector where the data for this message
         * starts in the data it handed us, and how many more bytes we
         * need, and return.
         */
        pinfo->desegment_offset = offset;
        pinfo->desegment_len = fixed_len - length_remaining;
        return;
      }
    }

    /*
     * Get the length of the PDU.
     */
    plen = (*get_pdu_len)(tvb, offset);

    /*
     * Can we do reassembly?
     */
    if (proto_desegment && pinfo->can_desegment) {
      /*
       * Yes - is the PDU split across segment boundaries?
       */
      if (length_remaining < plen) {
        /*
         * Yes.  Tell the TCP dissector where the data for this message
         * starts in the data it handed us, and how many more bytes we
         * need, and return.
         */
        pinfo->desegment_offset = offset;
        pinfo->desegment_len = plen - length_remaining;
        return;
      }
    }

    /*
     * Construct a tvbuff containing the amount of the payload we have
     * available.  Make its reported length the amount of data in the PDU.
     *
     * XXX - if reassembly isn't enabled. the subdissector will throw a
     * BoundsError exception, rather than a ReportedBoundsError exception.
     * We really want a tvbuff where the length is "length", the reported
     * length is "plen", and the "if the snapshot length were infinite"
     * length is the minimum of the reported length of the tvbuff handed
     * to us and "plen", with a new type of exception thrown if the offset
     * is within the reported length but beyond that third length, with
     * that exception getting the "Unreassembled Packet" error.
     */
    if (plen < fixed_len) {
      /*
       * The PDU length from the fixed-length portion probably didn't
       * include the fixed-length portion's length, and was probably so
       * large that the total length overflowed.
       *
       * Report this as an error.
       */
      show_reported_bounds_error(tvb, pinfo, tree);
      return;
    }
    length = length_remaining;
    if (length > plen)
        length = plen;
    next_tvb = tvb_new_subset(tvb, offset, length, plen);

    /*
     * Dissect the PDU.
     *
     * Catch the ReportedBoundsError exception; if this particular message
     * happens to get a ReportedBoundsError exception, that doesn't mean
     * that we should stop dissecting PDUs within this frame or chunk of
     * reassembled data.
     *
     * If it gets a BoundsError, we can stop, as there's nothing more to
     * see, so we just re-throw it.
     */
    TRY {
      (*dissect_pdu)(next_tvb, pinfo, tree);
    }
    CATCH(BoundsError) {
      RETHROW;
    }
    CATCH(ReportedBoundsError) {
      show_reported_bounds_error(tvb, pinfo, tree);
    }
    ENDTRY;

    /*
     * Step to the next PDU.
     */
    offset += plen;
  }
}

static void
tcp_info_append_uint(packet_info *pinfo, const char *abbrev, guint32 val)
{
  if (check_col(pinfo->cinfo, COL_INFO))
    col_append_fstr(pinfo->cinfo, COL_INFO, " %s=%u", abbrev, val);
}

static void
dissect_tcpopt_maxseg(const ip_tcp_opt *optp, tvbuff_t *tvb,
    int offset, guint optlen, packet_info *pinfo, proto_tree *opt_tree)
{
  guint16 mss;

  mss = tvb_get_ntohs(tvb, offset + 2);
  proto_tree_add_text(opt_tree, tvb, offset,      optlen,
                        "%s: %u bytes", optp->name, mss);
  tcp_info_append_uint(pinfo, "MSS", mss);
}

static void
dissect_tcpopt_wscale(const ip_tcp_opt *optp, tvbuff_t *tvb,
    int offset, guint optlen, packet_info *pinfo, proto_tree *opt_tree)
{
  guint8 ws;

  ws = tvb_get_guint8(tvb, offset + 2);
  proto_tree_add_text(opt_tree, tvb, offset,      optlen,
                        "%s: %u bytes", optp->name, ws);
  tcp_info_append_uint(pinfo, "WS", ws);
}

static void
dissect_tcpopt_sack(const ip_tcp_opt *optp, tvbuff_t *tvb,
    int offset, guint optlen, packet_info *pinfo, proto_tree *opt_tree)
{
  proto_tree *field_tree = NULL;
  proto_item *tf;
  guint leftedge, rightedge;

  tf = proto_tree_add_text(opt_tree, tvb, offset,      optlen, "%s:", optp->name);
  offset += 2;  /* skip past type and length */
  optlen -= 2;  /* subtract size of type and length */
  while (optlen > 0) {
    if (field_tree == NULL) {
      /* Haven't yet made a subtree out of this option.  Do so. */
      field_tree = proto_item_add_subtree(tf, *optp->subtree_index);
    }
    if (optlen < 4) {
      proto_tree_add_text(field_tree, tvb, offset,      optlen,
        "(suboption would go past end of option)");
      break;
    }
    leftedge = tvb_get_ntohl(tvb, offset);
    optlen -= 4;
    if (optlen < 4) {
      proto_tree_add_text(field_tree, tvb, offset,      optlen,
        "(suboption would go past end of option)");
      break;
    }
    /* XXX - check whether it goes past end of packet */
    rightedge = tvb_get_ntohl(tvb, offset + 4);
    optlen -= 4;
    proto_tree_add_text(field_tree, tvb, offset,      8,
        "left edge = %u, right edge = %u", leftedge, rightedge);
    tcp_info_append_uint(pinfo, "SLE", leftedge);
    tcp_info_append_uint(pinfo, "SRE", rightedge);
    offset += 8;
  }
}

static void
dissect_tcpopt_echo(const ip_tcp_opt *optp, tvbuff_t *tvb,
    int offset, guint optlen, packet_info *pinfo, proto_tree *opt_tree)
{
  guint32 echo;

  echo = tvb_get_ntohl(tvb, offset + 2);
  proto_tree_add_text(opt_tree, tvb, offset,      optlen,
                        "%s: %u", optp->name, echo);
  tcp_info_append_uint(pinfo, "ECHO", echo);
}

static void
dissect_tcpopt_timestamp(const ip_tcp_opt *optp, tvbuff_t *tvb,
    int offset, guint optlen, packet_info *pinfo, proto_tree *opt_tree)
{
  guint32 tsv, tser;

  tsv = tvb_get_ntohl(tvb, offset + 2);
  tser = tvb_get_ntohl(tvb, offset + 6);
  proto_tree_add_text(opt_tree, tvb, offset,      optlen,
    "%s: tsval %u, tsecr %u", optp->name, tsv, tser);
  tcp_info_append_uint(pinfo, "TSV", tsv);
  tcp_info_append_uint(pinfo, "TSER", tser);
}

static void
dissect_tcpopt_cc(const ip_tcp_opt *optp, tvbuff_t *tvb,
    int offset, guint optlen, packet_info *pinfo, proto_tree *opt_tree)
{
  guint32 cc;

  cc = tvb_get_ntohl(tvb, offset + 2);
  proto_tree_add_text(opt_tree, tvb, offset,      optlen,
                        "%s: %u", optp->name, cc);
  tcp_info_append_uint(pinfo, "CC", cc);
}

static const ip_tcp_opt tcpopts[] = {
  {
    TCPOPT_EOL,
    "EOL",
    NULL,
    NO_LENGTH,
    0,
    NULL,
  },
  {
    TCPOPT_NOP,
    "NOP",
    NULL,
    NO_LENGTH,
    0,
    NULL,
  },
  {
    TCPOPT_MSS,
    "Maximum segment size",
    NULL,
    FIXED_LENGTH,
    TCPOLEN_MSS,
    dissect_tcpopt_maxseg
  },
  {
    TCPOPT_WINDOW,
    "Window scale",
    NULL,
    FIXED_LENGTH,
    TCPOLEN_WINDOW,
    dissect_tcpopt_wscale
  },
  {
    TCPOPT_SACK_PERM,
    "SACK permitted",
    NULL,
    FIXED_LENGTH,
    TCPOLEN_SACK_PERM,
    NULL,
  },
  {
    TCPOPT_SACK,
    "SACK",
    &ett_tcp_option_sack,
    VARIABLE_LENGTH,
    TCPOLEN_SACK_MIN,
    dissect_tcpopt_sack
  },
  {
    TCPOPT_ECHO,
    "Echo",
    NULL,
    FIXED_LENGTH,
    TCPOLEN_ECHO,
    dissect_tcpopt_echo
  },
  {
    TCPOPT_ECHOREPLY,
    "Echo reply",
    NULL,
    FIXED_LENGTH,
    TCPOLEN_ECHOREPLY,
    dissect_tcpopt_echo
  },
  {
    TCPOPT_TIMESTAMP,
    "Time stamp",
    NULL,
    FIXED_LENGTH,
    TCPOLEN_TIMESTAMP,
    dissect_tcpopt_timestamp
  },
  {
    TCPOPT_CC,
    "CC",
    NULL,
    FIXED_LENGTH,
    TCPOLEN_CC,
    dissect_tcpopt_cc
  },
  {
    TCPOPT_CCNEW,
    "CC.NEW",
    NULL,
    FIXED_LENGTH,
    TCPOLEN_CCNEW,
    dissect_tcpopt_cc
  },
  {
    TCPOPT_CCECHO,
    "CC.ECHO",
    NULL,
    FIXED_LENGTH,
    TCPOLEN_CCECHO,
    dissect_tcpopt_cc
  },
  {
    TCPOPT_MD5,
    "TCP MD5 signature",
    NULL,
    FIXED_LENGTH,
    TCPOLEN_MD5,
    NULL
  }
};

#define N_TCP_OPTS      (sizeof tcpopts / sizeof tcpopts[0])

/* TCP flags flag */
static const true_false_string flags_set_truth = {
  "Set",
  "Not set"
};


/* Determine if there is a sub-dissector and call it.  This has been */
/* separated into a stand alone routine to other protocol dissectors */
/* can call to it, ie. socks    */

void
decode_tcp_ports(tvbuff_t *tvb, int offset, packet_info *pinfo,
        proto_tree *tree, int src_port, int dst_port)
{
  tvbuff_t *next_tvb;
  int low_port, high_port;

  next_tvb = tvb_new_subset(tvb, offset, -1, -1);

/* determine if this packet is part of a conversation and call dissector */
/* for the conversation if available */

  if (try_conversation_dissector(&pinfo->src, &pinfo->dst, PT_TCP,
                src_port, dst_port, next_tvb, pinfo, tree))
    return;

  /* Do lookups with the subdissector table.
     We try the port number with the lower value first, followed by the
     port number with the higher value.  This means that, for packets
     where a dissector is registered for *both* port numbers:

        1) we pick the same dissector for traffic going in both directions;

        2) we prefer the port number that's more likely to be the right
           one (as that prefers well-known ports to reserved ports);

     although there is, of course, no guarantee that any such strategy
     will always pick the right port number.

     XXX - we ignore port numbers of 0, as some dissectors use a port
     number of 0 to disable the port. */
  if (src_port > dst_port) {
    low_port = dst_port;
    high_port = src_port;
  } else {
    low_port = src_port;
    high_port = dst_port;
  }
  if (low_port != 0 &&
      dissector_try_port(subdissector_table, low_port, next_tvb, pinfo, tree))
    return;
  if (high_port != 0 &&
      dissector_try_port(subdissector_table, high_port, next_tvb, pinfo, tree))
    return;

  /* do lookup with the heuristic subdissector table */
  if (dissector_try_heuristic(heur_subdissector_list, next_tvb, pinfo, tree))
    return;

  /* Oh, well, we don't know this; dissect it as data. */
  call_dissector(data_handle,next_tvb, pinfo, tree);
}


static void
dissect_tcp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
{
  guint16 th_sport;
  guint16 th_dport;
  guint32 th_seq;
  guint32 th_ack;
  guint8  th_off_x2; /* combines th_off and th_x2 */
  guint8  th_flags;
  guint16 th_win;
  guint16 th_sum;
  guint16 th_urp;
  proto_tree *tcp_tree = NULL, *field_tree = NULL;
  proto_item *ti = NULL, *tf;
  int        offset = 0;
  gchar      flags[64] = "<None>";
  gchar     *fstr[] = {"FIN", "SYN", "RST", "PSH", "ACK", "URG", "ECN", "CWR" };
  gint       fpos = 0, i;
  guint      bpos;
  guint      hlen;
  guint      optlen;
  guint32    seglen;
  guint32    nxtseq;
  guint      len;
  guint      reported_len;
  vec_t      cksum_vec[4];
  guint32    phdr[2];
  guint16    computed_cksum;
  guint      length_remaining;
  gboolean   desegment_ok;
  struct tcpinfo tcpinfo;
  gboolean   save_fragmented;

  if (check_col(pinfo->cinfo, COL_PROTOCOL))
    col_set_str(pinfo->cinfo, COL_PROTOCOL, "TCP");

  /* Clear out the Info column. */
  if (check_col(pinfo->cinfo, COL_INFO))
    col_clear(pinfo->cinfo, COL_INFO);

  th_sport = tvb_get_ntohs(tvb, offset);
  th_dport = tvb_get_ntohs(tvb, offset + 2);
  if (check_col(pinfo->cinfo, COL_INFO)) {
    col_append_fstr(pinfo->cinfo, COL_INFO, "%s > %s",
      get_tcp_port(th_sport), get_tcp_port(th_dport));
  }
  
  if (tree) {
    if (tcp_summary_in_tree) {
            ti = proto_tree_add_protocol_format(tree, proto_tcp, tvb, 0, -1,
                "Transmission Control Protocol, Src Port: %s (%u), Dst Port: %s (%u)",
                get_tcp_port(th_sport), th_sport,
                get_tcp_port(th_dport), th_dport);
    }
    else {
            ti = proto_tree_add_item(tree, proto_tcp, tvb, 0, -1, FALSE);
    }
    tcp_tree = proto_item_add_subtree(ti, ett_tcp);
    proto_tree_add_uint_format(tcp_tree, hf_tcp_srcport, tvb, offset, 2, th_sport,
        "Source port: %s (%u)", get_tcp_port(th_sport), th_sport);
    proto_tree_add_uint_format(tcp_tree, hf_tcp_dstport, tvb, offset + 2, 2, th_dport,
        "Destination port: %s (%u)", get_tcp_port(th_dport), th_dport);
    proto_tree_add_uint_hidden(tcp_tree, hf_tcp_port, tvb, offset, 2, th_sport);
    proto_tree_add_uint_hidden(tcp_tree, hf_tcp_port, tvb, offset + 2, 2, th_dport);
  }

  th_seq = tvb_get_ntohl(tvb, offset + 4);
  th_ack = tvb_get_ntohl(tvb, offset + 8);
  th_off_x2 = tvb_get_guint8(tvb, offset + 12);
  th_flags = tvb_get_guint8(tvb, offset + 13);
  th_win = tvb_get_ntohs(tvb, offset + 14);
  
  if (check_col(pinfo->cinfo, COL_INFO) || tree) {  
    for (i = 0; i < 8; i++) {
      bpos = 1 << i;
      if (th_flags & bpos) {
        if (fpos) {
          strcpy(&flags[fpos], ", ");
          fpos += 2;
        }
        strcpy(&flags[fpos], fstr[i]);
        fpos += 3;
      }
    }
    flags[fpos] = '\0';
  }

  if (check_col(pinfo->cinfo, COL_INFO)) {
    col_append_fstr(pinfo->cinfo, COL_INFO, " [%s] Seq=%u Ack=%u Win=%u",
      flags, th_seq, th_ack, th_win);
  }

  if (tree) {
    if (tcp_summary_in_tree)
      proto_item_append_text(ti, ", Seq: %u", th_seq);
    proto_tree_add_uint(tcp_tree, hf_tcp_seq, tvb, offset + 4, 4, th_seq);
  }

  hlen = hi_nibble(th_off_x2) * 4;  /* TCP header length, in bytes */

  if (hlen < TCPH_MIN_LEN) {
    /* Give up at this point; we put the source and destination port in
       the tree, before fetching the header length, so that they'll
       show up if this is in the failing packet in an ICMP error packet,
       but it's now time to give up if the header length is bogus. */
    if (check_col(pinfo->cinfo, COL_INFO))
      col_append_fstr(pinfo->cinfo, COL_INFO, ", bogus TCP header length (%u, must be at least %u)",
        hlen, TCPH_MIN_LEN);
    if (tree) {
      proto_tree_add_uint_format(tcp_tree, hf_tcp_hdr_len, tvb, offset + 12, 1, hlen,
       "Header length: %u bytes (bogus, must be at least %u)", hlen,
       TCPH_MIN_LEN);
    }
    return;
  }

  reported_len = tvb_reported_length(tvb);
  len = tvb_length(tvb);

  /* Compute the length of data in this segment. */
  seglen = reported_len - hlen;

  if (tree) { /* Add the seglen as an invisible field */

    proto_tree_add_uint_hidden(ti, hf_tcp_len, tvb, offset, 4, seglen);

  }

  /* Compute the sequence number of next octet after this segment. */
  nxtseq = th_seq + seglen;

  if (tree) {
    if (tcp_summary_in_tree)
      proto_item_append_text(ti, ", Ack: %u, Len: %u", th_ack, seglen);
    proto_item_set_len(ti, hlen);
    if (nxtseq != th_seq)
      proto_tree_add_uint(tcp_tree, hf_tcp_nxtseq, tvb, offset, 0, nxtseq);
    if (th_flags & TH_ACK)
      proto_tree_add_uint(tcp_tree, hf_tcp_ack, tvb, offset + 8, 4, th_ack);
    proto_tree_add_uint_format(tcp_tree, hf_tcp_hdr_len, tvb, offset + 12, 1, hlen,
        "Header length: %u bytes", hlen);
    tf = proto_tree_add_uint_format(tcp_tree, hf_tcp_flags, tvb, offset + 13, 1,
        th_flags, "Flags: 0x%04x (%s)", th_flags, flags);
    field_tree = proto_item_add_subtree(tf, ett_tcp_flags);
    proto_tree_add_boolean(field_tree, hf_tcp_flags_cwr, tvb, offset + 13, 1, th_flags);
    proto_tree_add_boolean(field_tree, hf_tcp_flags_ecn, tvb, offset + 13, 1, th_flags);
    proto_tree_add_boolean(field_tree, hf_tcp_flags_urg, tvb, offset + 13, 1, th_flags);
    proto_tree_add_boolean(field_tree, hf_tcp_flags_ack, tvb, offset + 13, 1, th_flags);
    proto_tree_add_boolean(field_tree, hf_tcp_flags_push, tvb, offset + 13, 1, th_flags);
    proto_tree_add_boolean(field_tree, hf_tcp_flags_reset, tvb, offset + 13, 1, th_flags);
    proto_tree_add_boolean(field_tree, hf_tcp_flags_syn, tvb, offset + 13, 1, th_flags);
    proto_tree_add_boolean(field_tree, hf_tcp_flags_fin, tvb, offset + 13, 1, th_flags);
    proto_tree_add_uint(tcp_tree, hf_tcp_window_size, tvb, offset + 14, 2, th_win);
  }

  /* Supply the sequence number of the first byte. */
  tcpinfo.seq = th_seq;

  /* Assume we'll pass un-reassembled data to subdissectors. */
  tcpinfo.is_reassembled = FALSE;

  pinfo->private_data = &tcpinfo;

  /*
   * Assume, initially, that we can't desegment.
   */
  pinfo->can_desegment = 0;

  th_sum = tvb_get_ntohs(tvb, offset + 16);
  if (!pinfo->fragmented && len >= reported_len) {
    /* The packet isn't part of an un-reassembled fragmented datagram
       and isn't truncated.  This means we have all the data, and thus
       can checksum it and, unless it's being returned in an error
       packet, are willing to allow subdissectors to request reassembly
       on it. */
  
    if (tcp_check_checksum) {
      /* We haven't turned checksum checking off; checksum it. */

      /* Set up the fields of the pseudo-header. */
      cksum_vec[0].ptr = pinfo->src.data;
      cksum_vec[0].len = pinfo->src.len;
      cksum_vec[1].ptr = pinfo->dst.data;
      cksum_vec[1].len = pinfo->dst.len;
      cksum_vec[2].ptr = (const guint8 *)&phdr;
      switch (pinfo->src.type) {

      case AT_IPv4:
        phdr[0] = htonl((IP_PROTO_TCP<<16) + reported_len);
        cksum_vec[2].len = 4;
        break;

      case AT_IPv6:
        phdr[0] = htonl(reported_len);
        phdr[1] = htonl(IP_PROTO_TCP);
        cksum_vec[2].len = 8;
        break;

      default:
        /* TCP runs only atop IPv4 and IPv6.... */
        g_assert_not_reached();
        break;
      }
      cksum_vec[3].ptr = tvb_get_ptr(tvb, offset, len);
      cksum_vec[3].len = reported_len;
      computed_cksum = in_cksum(&cksum_vec[0], 4);
      if (computed_cksum == 0) {
        proto_tree_add_uint_format(tcp_tree, hf_tcp_checksum, tvb,
          offset + 16, 2, th_sum, "Checksum: 0x%04x (correct)", th_sum);

        /* Checksum is valid, so we're willing to desegment it. */
        desegment_ok = TRUE;
      } else {
        proto_tree_add_boolean_hidden(tcp_tree, hf_tcp_checksum_bad, tvb,
           offset + 16, 2, TRUE);
        proto_tree_add_uint_format(tcp_tree, hf_tcp_checksum, tvb,
           offset + 16, 2, th_sum,
           "Checksum: 0x%04x (incorrect, should be 0x%04x)", th_sum,
           in_cksum_shouldbe(th_sum, computed_cksum));

        /* Checksum is invalid, so we're not willing to desegment it. */
        desegment_ok = FALSE;
      }
    } else {
      proto_tree_add_uint_format(tcp_tree, hf_tcp_checksum, tvb,
         offset + 16, 2, th_sum, "Checksum: 0x%04x", th_sum);

      /* We didn't check the checksum, and don't care if it's valid,
         so we're willing to desegment it. */
      desegment_ok = TRUE;
    }
  } else {
    /* We don't have all the packet data, so we can't checksum it... */
    proto_tree_add_uint_format(tcp_tree, hf_tcp_checksum, tvb,
       offset + 16, 2, th_sum, "Checksum: 0x%04x", th_sum);

    /* ...and aren't willing to desegment it. */
    desegment_ok = FALSE;
  }

  if (desegment_ok) {
    /* We're willing to desegment this.  Is desegmentation enabled? */
    if (tcp_desegment) {
      /* Yes - is this segment being returned in an error packet? */
      if (!pinfo->in_error_pkt) {
        /* No - indicate that we will desegment.
           We do NOT want to desegment segments returned in error
           packets, as they're not part of a TCP connection. */
        pinfo->can_desegment = 2;
      }
    }
  }

  if (th_flags & TH_URG) {
    th_urp = tvb_get_ntohs(tvb, offset + 18);
    /* Export the urgent pointer, for the benefit of protocols such as
       rlogin. */
    tcpinfo.urgent = TRUE;
    tcpinfo.urgent_pointer = th_urp;
    if (check_col(pinfo->cinfo, COL_INFO))
      col_append_fstr(pinfo->cinfo, COL_INFO, " Urg=%u", th_urp);
    if (tcp_tree != NULL)
      proto_tree_add_uint(tcp_tree, hf_tcp_urgent_pointer, tvb, offset + 18, 2, th_urp);
  } else
    tcpinfo.urgent = FALSE;

  if (check_col(pinfo->cinfo, COL_INFO))
    col_append_fstr(pinfo->cinfo, COL_INFO, " Len=%u", seglen);

  /* Decode TCP options, if any. */
  if (tree && hlen > TCPH_MIN_LEN) {
    /* There's more than just the fixed-length header.  Decode the
       options. */
    optlen = hlen - TCPH_MIN_LEN; /* length of options, in bytes */
    tf = proto_tree_add_text(tcp_tree, tvb, offset +  20, optlen,
      "Options: (%u bytes)", optlen);
    field_tree = proto_item_add_subtree(tf, ett_tcp_options);
    dissect_ip_tcp_options(tvb, offset + 20, optlen,
      tcpopts, N_TCP_OPTS, TCPOPT_EOL, pinfo, field_tree);
  }

  /* Skip over header + options */
  offset += hlen;

  pinfo->ptype = PT_TCP;
  pinfo->srcport = th_sport;
  pinfo->destport = th_dport;
  
  /* Check the packet length to see if there's more data
     (it could be an ACK-only packet) */
  length_remaining = tvb_length_remaining(tvb, offset);

  if( data_out_file ) {
    reassemble_tcp( th_seq,             /* sequence number */
        seglen,                         /* data length */
        tvb_get_ptr(tvb, offset, length_remaining),     /* data */
        length_remaining,               /* captured data length */
        ( th_flags & TH_SYN ),          /* is syn set? */
        &pinfo->net_src,
        &pinfo->net_dst,
        pinfo->srcport,
        pinfo->destport);
  }

  if (length_remaining != 0) {
    if (th_flags & TH_RST) {
      /*
       * RFC1122 says:
       *
       *        4.2.2.12  RST Segment: RFC-793 Section 3.4
       *
       *          A TCP SHOULD allow a received RST segment to include data.
       *
       *          DISCUSSION
       *               It has been suggested that a RST segment could contain
       *               ASCII text that encoded and explained the cause of the
       *               RST.  No standard has yet been established for such
       *               data.
       *
       * so for segments with RST we just display the data as text.
       */
      proto_tree_add_text(tcp_tree, tvb, offset, length_remaining,
                            "Reset cause: %s",
                            tvb_format_text(tvb, offset, length_remaining));
    } else {
      /* Can we desegment this segment? */
      if (pinfo->can_desegment) {
        /* Yes. */
        desegment_tcp(tvb, pinfo, offset, th_seq, nxtseq, th_sport, th_dport, tree, tcp_tree);
      } else {
        /* No - just call the subdissector.
           Mark this as fragmented, so if somebody throws an exception,
           we don't report it as a malformed frame. */
        save_fragmented = pinfo->fragmented;
        pinfo->fragmented = TRUE;
        decode_tcp_ports(tvb, offset, pinfo, tree, th_sport, th_dport);
        pinfo->fragmented = save_fragmented;
      }
    }
  }
}

void
proto_register_tcp(void)
{
        static hf_register_info hf[] = {

                { &hf_tcp_srcport,
                { "Source Port",                "tcp.srcport", FT_UINT16, BASE_DEC, NULL, 0x0,
                        "", HFILL }},

                { &hf_tcp_dstport,
                { "Destination Port",           "tcp.dstport", FT_UINT16, BASE_DEC, NULL, 0x0,
                        "", HFILL }},

                { &hf_tcp_port,
                { "Source or Destination Port", "tcp.port", FT_UINT16, BASE_DEC, NULL, 0x0,
                        "", HFILL }},

                { &hf_tcp_seq,
                { "Sequence number",            "tcp.seq", FT_UINT32, BASE_DEC, NULL, 0x0,
                        "", HFILL }},

                { &hf_tcp_nxtseq,
                { "Next sequence number",       "tcp.nxtseq", FT_UINT32, BASE_DEC, NULL, 0x0,
                        "", HFILL }},

                { &hf_tcp_ack,
                { "Acknowledgement number",     "tcp.ack", FT_UINT32, BASE_DEC, NULL, 0x0,
                        "", HFILL }},

                { &hf_tcp_hdr_len,
                { "Header Length",              "tcp.hdr_len", FT_UINT8, BASE_DEC, NULL, 0x0,
                        "", HFILL }},

                { &hf_tcp_flags,
                { "Flags",                      "tcp.flags", FT_UINT8, BASE_HEX, NULL, 0x0,
                        "", HFILL }},

                { &hf_tcp_flags_cwr,
                { "Congestion Window Reduced (CWR)",                    "tcp.flags.cwr", FT_BOOLEAN, 8, TFS(&flags_set_truth), TH_CWR,
                        "", HFILL }},

                { &hf_tcp_flags_ecn,
                { "ECN-Echo",                   "tcp.flags.ecn", FT_BOOLEAN, 8, TFS(&flags_set_truth), TH_ECN,
                        "", HFILL }},

                { &hf_tcp_flags_urg,
                { "Urgent",                     "tcp.flags.urg", FT_BOOLEAN, 8, TFS(&flags_set_truth), TH_URG,
                        "", HFILL }},

                { &hf_tcp_flags_ack,
                { "Acknowledgment",             "tcp.flags.ack", FT_BOOLEAN, 8, TFS(&flags_set_truth), TH_ACK,
                        "", HFILL }},

                { &hf_tcp_flags_push,
                { "Push",                       "tcp.flags.push", FT_BOOLEAN, 8, TFS(&flags_set_truth), TH_PUSH,
                        "", HFILL }},

                { &hf_tcp_flags_reset,
                { "Reset",                      "tcp.flags.reset", FT_BOOLEAN, 8, TFS(&flags_set_truth), TH_RST,
                        "", HFILL }},

                { &hf_tcp_flags_syn,
                { "Syn",                        "tcp.flags.syn", FT_BOOLEAN, 8, TFS(&flags_set_truth), TH_SYN,
                        "", HFILL }},

                { &hf_tcp_flags_fin,
                { "Fin",                        "tcp.flags.fin", FT_BOOLEAN, 8, TFS(&flags_set_truth), TH_FIN,
                        "", HFILL }},

                { &hf_tcp_window_size,
                { "Window size",                "tcp.window_size", FT_UINT16, BASE_DEC, NULL, 0x0,
                        "", HFILL }},

                { &hf_tcp_checksum,
                { "Checksum",                   "tcp.checksum", FT_UINT16, BASE_HEX, NULL, 0x0,
                        "", HFILL }},

                { &hf_tcp_checksum_bad,
                { "Bad Checksum",               "tcp.checksum_bad", FT_BOOLEAN, BASE_NONE, NULL, 0x0,
                        "", HFILL }},

                { &hf_tcp_len,
                  { "TCP Segment Len",            "tcp.len", FT_UINT32, BASE_DEC, NULL, 0x0, 
                    "", HFILL}},

                { &hf_tcp_urgent_pointer,
                { "Urgent pointer",             "tcp.urgent_pointer", FT_UINT16, BASE_DEC, NULL, 0x0,
                        "", HFILL }},
        };
        static gint *ett[] = {
                &ett_tcp,
                &ett_tcp_flags,
                &ett_tcp_options,
                &ett_tcp_option_sack,
                &ett_tcp_segments,
        };
        module_t *tcp_module;

        proto_tcp = proto_register_protocol("Transmission Control Protocol",
            "TCP", "tcp");
        proto_register_field_array(proto_tcp, hf, array_length(hf));
        proto_register_subtree_array(ett, array_length(ett));

        /* subdissector code */
        subdissector_table = register_dissector_table("tcp.port",
            "TCP port", FT_UINT16, BASE_DEC);
        register_heur_dissector_list("tcp", &heur_subdissector_list);

        /* Register configuration preferences */
        tcp_module = prefs_register_protocol(proto_tcp, NULL);
        prefs_register_bool_preference(tcp_module, "tcp_summary_in_tree",
            "Show TCP summary in protocol tree",
"Whether the TCP summary line should be shown in the protocol tree",
            &tcp_summary_in_tree);
        prefs_register_bool_preference(tcp_module, "check_checksum",
            "Check the validity of the TCP checksum when possible",
"Whether to check the validity of the TCP checksum",
            &tcp_check_checksum);
        prefs_register_bool_preference(tcp_module, "desegment_tcp_streams",
            "Allow subdissector to desegment TCP streams",
"Whether subdissector can request TCP streams to be desegmented",
            &tcp_desegment);

        register_init_routine(tcp_desegment_init);
        register_init_routine(tcp_fragment_init);
}

void
proto_reg_handoff_tcp(void)
{
        dissector_handle_t tcp_handle;

        tcp_handle = create_dissector_handle(dissect_tcp, proto_tcp);
        dissector_add("ip.proto", IP_PROTO_TCP, tcp_handle);
        data_handle = find_dissector("data");
}