/* packet-discard.c

 * Routines for Discard Protocol dissection

 *

 * Discard specs taken from RFC 863

 * https://tools.ietf.org/html/rfc863

 *

 * Inspiration from packet-chargen.c and packet-data.

 *

 * 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>

#include <wsutil/wsgcrypt.h>

#include <wsutil/to_str.h>

#define DISCARD_PORT_UDP 9

#define DISCARD_PORT_TCP 9

void proto_register_discard(void);

void proto_reg_handoff_discard(void);

static int proto_discard;

static int hf_discard_data;

static int hf_discard_text;

static int hf_discard_md5_hash;

static int hf_discard_len;

static bool show_as_text;

static bool generate_md5_hash;

static int ett_discard;

dissector_handle_t discard_handle;

dissector_handle_t wol_handle;

/* dissect_discard - dissects discard packet data

 * tvb - tvbuff for packet data (IN)

 * pinfo - packet info

 * proto_tree - resolved protocol tree

 */

static int

dissect_discard(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* dissector_data _U_)

{

  proto_tree* discard_tree;

  proto_item* ti;

  uint32_t len;

  uint32_t cap_len;

  col_set_str(pinfo->cinfo, COL_PROTOCOL, "DISCARD");

  if (show_as_text) {

    col_set_str(pinfo->cinfo, COL_INFO, "Discard: ");

  } else {

    col_set_str(pinfo->cinfo, COL_INFO, "Discard");

  }

  ti = proto_tree_add_item(tree, proto_discard, tvb, 0, -1, ENC_NA);

  discard_tree = proto_item_add_subtree(ti, ett_discard);

  len = tvb_reported_length(tvb);

  cap_len = tvb_captured_length(tvb);

  proto_tree_add_item(discard_tree, hf_discard_data, tvb, 0, -1, ENC_NA);

  if (show_as_text) {

    char *display_str;

    proto_tree_add_item_ret_display_string(discard_tree, hf_discard_text, tvb, 0, -1, ENC_ASCII, pinfo->pool, &display_str);

    col_append_str(pinfo->cinfo, COL_INFO, display_str);

  }

  if (generate_md5_hash) {

    const uint8_t *cp;

    uint8_t       digest[HASH_MD5_LENGTH];

    const char   *digest_string;

    cp = tvb_get_ptr(tvb, 0, cap_len);

    gcry_md_hash_buffer(GCRY_MD_MD5, digest, cp, cap_len);

    digest_string = bytes_to_str_punct(pinfo->pool, digest, HASH_MD5_LENGTH, '\0');

    ti = proto_tree_add_string(discard_tree, hf_discard_md5_hash, tvb, 0, 0, digest_string);

    proto_item_set_generated(ti);

  }

  ti = proto_tree_add_uint(discard_tree, hf_discard_len, tvb, 0, 0, len);

  proto_item_set_generated(ti);

  if(len > cap_len) {

    /*

     * Trigger _ws.short, e.g. [Packet size limited during capture: DISCARD truncated]

     */

    tvb_get_ptr(tvb, 0, len);

  }

  return cap_len;

}

static int

dissect_discard_udp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data)

{

  /* Wake On Lan is commonly used over UDP port 9 and has strong heuristics,

   * whereas the discard dissector never rejects a packet, so try WOL first.

   * Unfortunately "discard" still ends up in frame.protocols this way.

   */

  if (wol_handle && call_dissector_only(wol_handle, tvb, pinfo, tree, data)) {

    return tvb_captured_length(tvb);

  }

  return dissect_discard(tvb, pinfo, tree, data);

}

void

proto_register_discard(void)

{

  static hf_register_info hf[] = {

    { &hf_discard_data, {

      "Data", "discard.data",

      FT_BYTES, BASE_NONE, NULL, 0,

      NULL, HFILL }

    },

    { &hf_discard_text, {

      "Text", "discard.text",

      FT_STRING, BASE_NONE, NULL, 0,

      NULL, HFILL }

    },

    { &hf_discard_md5_hash, {

      "Payload MD5 hash", "discard.md5_hash",

      FT_STRING, BASE_NONE, NULL, 0,

      NULL, HFILL }

    },

    { &hf_discard_len, {

      "Reported Length", "discard.len",

      FT_UINT32, BASE_DEC, NULL, 0,

      NULL, HFILL }

    },

  };

  static int *ett[] = {

    &ett_discard,

  };

  module_t *module_data;

  proto_discard = proto_register_protocol("Discard Protocol", "DISCARD", "discard");

  proto_register_field_array(proto_discard, hf, array_length(hf));

  proto_register_subtree_array(ett, array_length(ett));

  module_data = prefs_register_protocol(proto_discard, NULL);

  prefs_register_bool_preference(module_data,

    "show_as_text",

    "Show data as text",

    "Show data as text in the Packet Details pane",

    &show_as_text);

  prefs_register_bool_preference(module_data,

    "md5_hash",

    "Generate MD5 hash",

    "Whether or not MD5 hashes should be generated and shown for each payload.",

    &generate_md5_hash);

  discard_handle = register_dissector("discard", dissect_discard, proto_discard);

}

void

proto_reg_handoff_discard(void)

{

  dissector_add_uint_with_preference("udp.port", DISCARD_PORT_UDP, create_dissector_handle(dissect_discard_udp, proto_discard));

  dissector_add_uint_with_preference("tcp.port", DISCARD_PORT_TCP, discard_handle);

  wol_handle = find_dissector_add_dependency("wol", proto_discard);

}

/*

 * Editor modelines  -  https://www.wireshark.org/tools/modelines.html

 *

 * Local variables:

 * c-basic-offset: 8

 * tab-width: 8

 * indent-tabs-mode: t

 * End:

 *

 * vi: set shiftwidth=8 tabstop=8 noexpandtab:

 * :indentSize=8:tabSize=8:noTabs=false:

 */