/* packet-vssmonitoring.c
 * Routines for dissection of VSS Monitoring timestamp and portstamp
 *
 * Copyright VSS Monitoring 2011
 *
 * 20111205 - First edition by Sake Blok (sake.blok@SYN-bit.nl)
 *
 * Wireshark - Network traffic analyzer
 * By Gerald Combs <gerald@wireshark.org>
 * Copyright 1998 Gerald Combs
 *
 * SPDX-License-Identifier: GPL-2.0-or-later
 */

#include "config.h"

#include <epan/packet.h>
#include <epan/prefs.h>


#define VSS_NS_MASK     0x3fffffff
#define CLKSRC_SHIFT    30

#define CLKSRC_LOCAL    0
#define CLKSRC_NTP      1
#define CLKSRC_GPS      2
#define CLKSRC_PTP      3

static const value_string clksrc_vals[] = {
  { CLKSRC_LOCAL,       "Not Synced" },
  { CLKSRC_NTP,         "NTP" },
  { CLKSRC_GPS,         "GPS" },
  { CLKSRC_PTP,         "PTP" },
  { 0,                  NULL }
};

void proto_register_vssmonitoring(void);
void proto_reg_handoff_vssmonitoring(void);

static int proto_vssmonitoring = -1;

static int hf_vssmonitoring_time = -1;
static int hf_vssmonitoring_clksrc = -1;
static int hf_vssmonitoring_srcport = -1;

static gint ett_vssmonitoring = -1;

static int
dissect_vssmonitoring(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void *data _U_)
{
  proto_tree    *ti = NULL;
  proto_tree    *vssmonitoring_tree = NULL;
  guint         offset = 0;

  guint         trailer_len;
  nstime_t      vssmonitoring_time;
  guint8        vssmonitoring_clksrc = 0;
  guint16       vssmonitoring_srcport = 0;

  struct tm     *tmp;


  /* First get the length of the trailer */
  trailer_len = tvb_reported_length(tvb);

  /* The trailer length is a sum (of any combination) of:
   * timestamp (8 bytes)
   * port stamp (1 or 2 bytes)
   * fcs (4 bytes)
   *
   * The FCS is dissected by our caller, so we check for a trailer
   * with a length that includes one or more of a time stamp and
   * a 1-byte or 2-byte port stamp.
   *
   * See
   *
   *    https://web.archive.org/web/20160402091604/http://www.vssmonitoring.com/resources/feature-brief/Port-and-Time-Stamping.pdf
   *
   * (although that speaks of 2-byte port stamps as being for a "future
   * release").
   *
   * This means a trailer length must not be more than 14 bytes,
   * and:
   *
   *    must not be 3 modulo 3 (as it can't have both a 1-byte
   *    and a 2-byte port stamp);
   *
   *    if it's less than 8 bytes, must not be 0 modulo 3 (as
   *    it must have a 1-byte or 2-byte port stamp, given that
   *    it has no timestamp).
   */
  if ( trailer_len > 14 )
    return 0;

  /* ... and also a 1-byte port stamp can not co-exist with a 2-byte
   * portstamp
   */
  if ( (trailer_len & 3) == 3 )
    return 0;

  /* ... and if you have neither a time stamp nor a port stamp,
   * you don't have a trailer
   */
  if ( (trailer_len & 3) == 0 && trailer_len < 8 )
    return 0;

  /*
   * If we have a time stamp, check it for validity.
   *
   * Unfortunately, the port stamp can be zero, so this means that a
   * one-byte or two-byte all-zero trailer that's just padding can be
   * misinterpreted as a VSS monitoring trailer.
   */
  if ( trailer_len >= 8 ) {
    vssmonitoring_time.secs  = tvb_get_ntohl(tvb, offset);
    vssmonitoring_time.nsecs = tvb_get_ntohl(tvb, offset + 4);
    vssmonitoring_clksrc     = (guint8)(((guint32)vssmonitoring_time.nsecs) >> CLKSRC_SHIFT);
    vssmonitoring_time.nsecs &= VSS_NS_MASK;

      /* The timestamp will be based on the uptime until the TAP is completely booted,
       * this takes about 60s, but use 1 hour to be sure
       */

      /* Probably just null data to fill up a short frame.
       * FIXME: Should be made even stricter.
       */
      if (vssmonitoring_time.secs == 0)
        return 0;
      if (vssmonitoring_time.secs > 3600) {

        /* Check whether the timestamp in the PCAP header and the VSS-Monitoring
         * differ less than 30 days, otherwise, this might not be a VSS-Monitoring
         * timestamp
         */
        if ( vssmonitoring_time.secs > pinfo->abs_ts.secs ) {
          if ( vssmonitoring_time.secs - pinfo->abs_ts.secs > 2592000 ) /* 30 days */
            return 0;
        } else {
          if ( pinfo->abs_ts.secs - vssmonitoring_time.secs > 2592000 ) /* 30 days */
            return 0;
        }
      }

      /* The nanoseconds field should be less than 1000000000
       */
      if ( vssmonitoring_time.nsecs >= 1000000000 )
        return 0;
  }

  /* All systems are go, lets dissect the VSS-Monitoring trailer */
  if (tree) {
    ti = proto_tree_add_item(tree, proto_vssmonitoring,
             tvb, 0, (trailer_len & 0xb), ENC_NA);
    vssmonitoring_tree = proto_item_add_subtree(ti, ett_vssmonitoring);
  }

  /* Do we have a timestamp? */
  if ( trailer_len >= 8 ) {
    if (tree) {
      proto_tree_add_time(vssmonitoring_tree, hf_vssmonitoring_time, tvb, offset, 8, &vssmonitoring_time);
      proto_tree_add_uint(vssmonitoring_tree, hf_vssmonitoring_clksrc, tvb, offset + 4, 1, vssmonitoring_clksrc);

      tmp = localtime(&vssmonitoring_time.secs);
      if (tmp)
        proto_item_append_text(ti, ", Timestamp: %02d:%02d:%02d.%09ld",
            tmp->tm_hour, tmp->tm_min, tmp->tm_sec,(long)vssmonitoring_time.nsecs);
      else
        proto_item_append_text(ti, ", Timestamp: <Not representable>");
    }
    offset += 8;
  }

  /* Do we have a portstamp? */
  if ( trailer_len & 3) {
    if ( trailer_len & 1) {
      vssmonitoring_srcport = (guint16)tvb_get_guint8(tvb, offset);
      if (tree)
        proto_tree_add_item(vssmonitoring_tree, hf_vssmonitoring_srcport, tvb, offset, 1, ENC_BIG_ENDIAN);
      offset++;
    } else if ( trailer_len & 2) {
      vssmonitoring_srcport = tvb_get_ntohs(tvb, offset);
      if (tree)
        proto_tree_add_item(vssmonitoring_tree, hf_vssmonitoring_srcport, tvb, offset, 2, ENC_BIG_ENDIAN);
      offset += 2;
    }
    if (tree)
      proto_item_append_text(ti, ", Source Port: %d", vssmonitoring_srcport);
  }

  return offset;
}

void
proto_register_vssmonitoring(void)
{
  static hf_register_info hf[] = {
    { &hf_vssmonitoring_time, {
        "Time Stamp", "vssmonitoring.time",
        FT_ABSOLUTE_TIME, ABSOLUTE_TIME_LOCAL, NULL, 0x0,
        "VSS Monitoring Time Stamp", HFILL }},

    { &hf_vssmonitoring_clksrc, {
        "Clock Source", "vssmonitoring.clksrc",
        FT_UINT8, BASE_DEC, VALS(clksrc_vals), 0x0,
        "VSS Monitoring Clock Source", HFILL }},

    { &hf_vssmonitoring_srcport, {
        "Src Port", "vssmonitoring.srcport",
        FT_UINT16, BASE_DEC, NULL, 0x0,
        "VSS Monitoring Source Port", HFILL }}
  };

  static gint *ett[] = {
    &ett_vssmonitoring
  };

  module_t *vssmonitoring_module;

  proto_vssmonitoring = proto_register_protocol("VSS Monitoring Ethernet trailer", "VSS Monitoring", "vssmonitoring");
  proto_register_field_array(proto_vssmonitoring, hf, array_length(hf));
  proto_register_subtree_array(ett, array_length(ett));

  vssmonitoring_module = prefs_register_protocol(proto_vssmonitoring, NULL);

  prefs_register_obsolete_preference(vssmonitoring_module, "use_heuristics");
}

void
proto_reg_handoff_vssmonitoring(void)
{
  heur_dissector_add("eth.trailer", dissect_vssmonitoring, "VSS Monitoring ethernet trailer", "vssmonitoring_eth", proto_vssmonitoring, HEURISTIC_ENABLE);
}

/*
 * Editor modelines  -  https://www.wireshark.org/tools/modelines.html
 *
 * Local Variables:
 * c-basic-offset: 2
 * tab-width: 8
 * indent-tabs-mode: nil
 * End:
 *
 * ex: set shiftwidth=2 tabstop=8 expandtab:
 * :indentSize=2:tabSize=8:noTabs=true:
 */
