epan/dissectors/packet-mbtcp.c

   1 /* packet-mbtcp.c
   2  * Routines for Modbus/TCP dissection
   3  * By Riaan Swart <rswart@cs.sun.ac.za>
   4  * Copyright 2001, Institute for Applied Computer Science
   5  *                                       University of Stellenbosch
   6  *
   7  * See
   8  *
   9  *      http://www.modicon.com/openmbus/
  10  *
  11  * for information on Modbus/TCP.
  12  *
  13  * $Id$
  14  *
  15  * Ethereal - Network traffic analyzer
  16  * By Gerald Combs <gerald@ethereal.com>
  17  * Copyright 1998 Gerald Combs
  18  *
  19  * This program is free software; you can redistribute it and/or
  20  * modify it under the terms of the GNU General Public License
  21  * as published by the Free Software Foundation; either version 2
  22  * of the License, or (at your option) any later version.
  23  *
  24  * This program is distributed in the hope that it will be useful,
  25  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  26  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  27  * GNU General Public License for more details.
  28  *
  29  * You should have received a copy of the GNU General Public License
  30  * along with this program; if not, write to the Free Software
  31  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  32  */
  33
  34 #ifdef HAVE_CONFIG_H
  35 # include "config.h"
  36 #endif
  37
  38 #include <stdio.h>
  39 #include <stdlib.h>
  40 #include <string.h>
  41
  42 #include <glib.h>
  43
  44 #include <epan/packet.h>
  45
  46 #define DEBUG
  47
  48 #define TCP_PORT_MBTCP          502     /* Modbus/TCP located on TCP port 502 */
  49
  50 /* Modbus protocol function codes */
  51 #define read_coils              1
  52 #define read_input_discretes    2
  53 #define read_mult_regs          3
  54 #define read_input_regs         4
  55 #define write_coil              5
  56 #define write_single_reg        6
  57 #define read_except_stat        7
  58 #define diagnostics             8
  59 #define program_484             9
  60 #define poll_484                10
  61 #define get_comm_event_ctrs     11
  62 #define get_comm_event_log      12
  63 #define program_584_984         13
  64 #define poll_584_984            14
  65 #define force_mult_coils        15
  66 #define write_mult_regs         16
  67 #define report_slave_id         17
  68 #define program_884_u84         18
  69 #define reset_comm_link         19
  70 #define read_genl_ref           20
  71 #define write_genl_ref          21
  72 #define mask_write_reg          22
  73 #define read_write_reg          23
  74 #define read_fifo_queue         24
  75 #define program_ConCept         40
  76 #define firmware_replace        125
  77 #define program_584_984_2       126
  78 #define report_local_addr_mb    127
  79
  80 /* Modbus protocol exception codes */
  81 #define illegal_function        0x01
  82 #define illegal_address         0x02
  83 #define illegal_value           0x03
  84 #define illegal_response        0x04
  85 #define acknowledge             0x05
  86 #define slave_busy              0x06
  87 #define negative_ack            0x07
  88 #define memory_err              0x08
  89 #define gateway_unavailable     0x0a
  90 #define gateway_trgt_fail       0x0b
  91
  92 /* return codes of function classifying packets as query/response */
  93 #define query_packet            0
  94 #define response_packet         1
  95 #define cannot_classify         2
  96
  97 /* Modbus header */
  98 typedef struct _modbus_hdr {
  99         guint8  unit_id;        /* unit identifier (previously slave addr) */
 100         guint8  function_code;  /* Modbus function code */
 101 } modbus_hdr;
 102
 103 /* Modbus/TCP header, containing the Modbus header */
 104 typedef struct _mbtcp_hdr {
 105         guint16         transaction_id;         /* copied by svr, usually 0 */
 106         guint16         protocol_id;            /* always 0 */
 107         guint16         len;                    /* len of data that follows */
 108         modbus_hdr      mdbs_hdr;               /* mdbus hdr directly after mdbs/tcp hdr *
 109                                                  * in packet */
 110 } mbtcp_hdr;
 111
 112 /* Initialize the protocol and registered fields */
 113 static int proto_mbtcp = -1;
 114 static int hf_mbtcp_transid = -1;
 115 static int hf_mbtcp_protid = -1;
 116 static int hf_mbtcp_len = -1;
 117 static int hf_mbtcp_unitid = -1;
 118 static int hf_mbtcp_functioncode = -1;
 119 static int hf_modbus_reference = -1;
 120 static int hf_modbus_lreference = -1;
 121 static int hf_modbus_reftype = -1;
 122 static int hf_modbus_readref = -1;
 123 static int hf_modbus_writeref = -1;
 124 static int hf_modbus_wordcnt = -1;
 125 static int hf_modbus_readwordcnt = -1;
 126 static int hf_modbus_writewordcnt = -1;
 127 static int hf_modbus_bytecnt = -1;
 128 static int hf_modbus_lbytecnt = -1;
 129 static int hf_modbus_bitcnt = -1;
 130 static int hf_modbus_exceptioncode = -1;
 131 static int hf_modbus_andmask = -1;
 132 static int hf_modbus_ormask = -1;
 133
 134 /* Initialize the subtree pointers */
 135 static gint ett_mbtcp = -1;
 136 static gint ett_modbus_hdr = -1;
 137 static gint ett_group_hdr = -1;
 138
 139 static int
 140 classify_packet(packet_info *pinfo)
 141 {
 142         /* see if nature of packets can be derived from src/dst ports */
 143         /* if so, return as found */
 144         if ( ( 502 == pinfo->srcport && 502 != pinfo->destport ) ||
 145                  ( 502 != pinfo->srcport && 502 == pinfo->destport ) ) {
 146                 /* the slave is receiving queries on port 502 */
 147                 if ( 502 == pinfo->srcport )
 148                         return response_packet;
 149                 else if ( 502 == pinfo->destport )
 150                         return query_packet;
 151         }
 152         /* else, cannot classify */
 153         return cannot_classify;
 154 }
 155
 156 /* Translate function to string, as given on p6 of
 157  * "Open Modbus/TCP Specification", release 1 by Andy Swales. */
 158 static const value_string function_code_vals[] = {
 159         { read_coils,                   "Read coils" },
 160         { read_input_discretes,         "Read input discretes" },
 161         { read_mult_regs,               "Read multiple registers" },
 162         { read_input_regs,              "Read input registers" },
 163         { write_coil,                   "Write coil" },
 164         { write_single_reg,             "Write single register" },
 165         { read_except_stat,             "Read exception status" },
 166         { diagnostics,                  "Diagnostics" },
 167         { program_484,                  "Program (484)" },
 168         { poll_484,                     "Poll (484)" },
 169         { get_comm_event_ctrs,          "Get Comm. Event Counters" },
 170         { get_comm_event_log,           "Get Comm. Event Log" },
 171         { program_584_984,              "Program (584/984)" },
 172         { poll_584_984,                 "Poll (584/984)" },
 173         { force_mult_coils,             "Force Multiple Coils" },
 174         { write_mult_regs,              "Write Multiple Registers" },
 175         { report_slave_id,              "Report Slave ID" },
 176         { program_884_u84,              "Program 884/u84" },
 177         { reset_comm_link,              "Reset Comm. Link (884/u84)" },
 178         { read_genl_ref,                "Read General Reference" },
 179         { write_genl_ref,               "Write General Reference" },
 180         { mask_write_reg,               "Mask Write Register" },
 181         { read_write_reg,               "Read Write Register" },
 182         { read_fifo_queue,              "Read FIFO Queue" },
 183         { program_ConCept,              "Program (ConCept)" },
 184         { firmware_replace,             "Firmware replacement" },
 185         { program_584_984_2,            "Program (584/984)" },
 186         { report_local_addr_mb,         "Report local address (Modbus)" },
 187         { 0,                            NULL }
 188 };
 189
 190 static const value_string exception_code_vals[] = {
 191         { illegal_function,     "Illegal function" },
 192         { illegal_address,      "Illegal data address" },
 193         { illegal_value,        "Illegal data value" },
 194         { illegal_response,     "Illegal response length" },
 195         { acknowledge,          "Acknowledge" },
 196         { slave_busy,           "Slave device busy" },
 197         { negative_ack,         "Negative acknowledge" },
 198         { memory_err,           "Memory parity error" },
 199         { gateway_unavailable,  "Gateway path unavailable" },
 200         { gateway_trgt_fail,    "Gateway target device failed to respond" },
 201         { 0,                    NULL }
 202 };
 203
 204 /* Code to actually dissect the packets */
 205 static void
 206 dissect_mbtcp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
 207 {
 208 /* Set up structures needed to add the protocol subtree and manage it */
 209         mbtcp_hdr       mh;
 210         proto_item      *mi, *mf;
 211         proto_tree      *mbtcp_tree, *modbus_tree, *group_tree;
 212         int             offset, group_offset, packet_type;
 213         guint           i;
 214         gint            packet_len, payload_start, payload_len;
 215         char            *func_string = "", pkt_type_str[9] = "";
 216         char            err_str[100] = "";
 217         guint32         byte_cnt, group_byte_cnt, group_word_cnt;
 218         guint32         packet_num;     /* num to uniquely identify different mbtcp
 219                                          * packets in one TCP packet */
 220         guint8          exception_code;
 221         gboolean        exception_returned;
 222
 223 /* Make entries in Protocol column on summary display */
 224         if (check_col(pinfo->cinfo, COL_PROTOCOL))
 225                 col_set_str(pinfo->cinfo, COL_PROTOCOL, "Modbus/TCP");
 226
 227         if (check_col(pinfo->cinfo, COL_INFO))
 228                 col_clear(pinfo->cinfo, COL_INFO);
 229
 230 /* Make entries in Info column on summary display */
 231         offset = 0;
 232         tvb_memcpy(tvb, (guint8 *)&mh, offset, sizeof(mbtcp_hdr));
 233         mh.transaction_id                               =       g_ntohs(mh.transaction_id);
 234         mh.protocol_id                                  =       g_ntohs(mh.protocol_id);
 235         mh.len                                                  =       g_ntohs(mh.len);
 236         if ( mh.mdbs_hdr.function_code & 0x80 ) {
 237                 exception_code = tvb_get_guint8(tvb, offset + sizeof(mbtcp_hdr));
 238                 mh.mdbs_hdr.function_code ^= 0x80;
 239                 exception_returned = TRUE;
 240         }
 241         else {
 242                 exception_code = 0;
 243                 exception_returned = FALSE;
 244         }
 245         func_string = val_to_str(mh.mdbs_hdr.function_code, function_code_vals,
 246             "Unknown function (%u)");
 247         if (check_col(pinfo->cinfo, COL_INFO))
 248         {
 249                 packet_type = classify_packet(pinfo);
 250                 switch ( packet_type ) {
 251                         case query_packet :             strcpy(pkt_type_str, "query");
 252                                                                                                 break;
 253                         case response_packet :  strcpy(pkt_type_str, "response");
 254                                                                                                 break;
 255                         case cannot_classify :          strcpy(err_str, "Unable to classify as query or response.");
 256                                                                                 strcpy(pkt_type_str, "unknown");
 257                                                                                                 break;
 258                         default :
 259                                                                                                 break;
 260                 }
 261                 if ( exception_returned )
 262                         strcpy(err_str, "Exception returned ");
 263                 col_add_fstr(pinfo->cinfo, COL_INFO,
 264                                 "%8s [%2u pkt(s)]: trans: %5u; unit: %3u, func: %3u: %s. %s",
 265                                 pkt_type_str, 1, mh.transaction_id, (unsigned char) mh.mdbs_hdr.unit_id,
 266                                 (unsigned char) mh.mdbs_hdr.function_code, func_string, err_str);
 267         }
 268
 269         /* build up protocol tree and iterate over multiple packets */
 270         packet_num = 0;
 271         while (1) {
 272                 packet_type = classify_packet(pinfo);
 273                 packet_len = sizeof(mbtcp_hdr) - sizeof(modbus_hdr) + mh.len;
 274
 275                 /* if a tree exists, perform operations to add fields to it */
 276                 if (tree) {
 277                         mi = proto_tree_add_protocol_format(tree, proto_mbtcp, tvb, offset,
 278                                         packet_len, "Modbus/TCP");
 279                         mbtcp_tree = proto_item_add_subtree(mi, ett_mbtcp);
 280
 281                         /* Add items to protocol tree specific to Modbus/TCP Modbus/TCP */
 282                         proto_tree_add_uint(mbtcp_tree, hf_mbtcp_transid, tvb, offset, 2,
 283                                         mh.transaction_id);
 284                         proto_tree_add_uint(mbtcp_tree, hf_mbtcp_protid, tvb, offset + 2, 2,
 285                                         mh.protocol_id);
 286                         proto_tree_add_uint(mbtcp_tree, hf_mbtcp_len, tvb, offset + 4, 2,
 287                                         mh.len);
 288
 289                         /* Add items to protocol tree specific to Modbus generic */
 290                         mf = proto_tree_add_text(mbtcp_tree, tvb, offset + 6, mh.len,
 291                                         "Modbus");
 292                         modbus_tree = proto_item_add_subtree(mf, ett_modbus_hdr);
 293                         proto_tree_add_uint(modbus_tree, hf_mbtcp_unitid, tvb, offset + 6, 1,
 294                                         mh.mdbs_hdr.unit_id);
 295                         mi = proto_tree_add_uint(modbus_tree, hf_mbtcp_functioncode, tvb, offset + 7, 1,
 296                                         mh.mdbs_hdr.function_code);
 297
 298                         /** detail payload as a function of exception/function code */
 299                         func_string = val_to_str(mh.mdbs_hdr.function_code,
 300                             function_code_vals, "Unknown function");
 301                         payload_start = offset + 8;
 302                         payload_len = mh.len - sizeof(modbus_hdr);
 303                         if (exception_returned) {
 304                                 proto_item_set_text(mi, "function %u:  %s.  Exception: %s",
 305                                                 mh.mdbs_hdr.function_code,
 306                                                 func_string,
 307                                                 val_to_str(exception_code,
 308                                                     exception_code_vals,
 309                                                     "Unknown exception code (%u)"));
 310                                 proto_tree_add_uint(modbus_tree, hf_modbus_exceptioncode, tvb, payload_start, 1,
 311                                                 exception_code);
 312                         }
 313                         else {
 314                                 proto_item_set_text(mi, "function %u:  %s", mh.mdbs_hdr.function_code,
 315                                                 func_string);
 316                                 switch (mh.mdbs_hdr.function_code) {
 317
 318                                         case read_coils:
 319                                         case read_input_discretes:
 320                                                 if (packet_type == query_packet) {
 321                                                         proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, FALSE);
 322                                                         proto_tree_add_item(modbus_tree, hf_modbus_bitcnt, tvb, payload_start + 2, 2, FALSE);
 323                                                 }
 324                                                 else if (packet_type == response_packet) {
 325                                                         byte_cnt = (guint32)tvb_get_guint8(tvb, payload_start);
 326                                                         proto_tree_add_uint(modbus_tree, hf_modbus_bytecnt, tvb, payload_start, 1, byte_cnt);
 327                                                         proto_tree_add_text(modbus_tree, tvb, payload_start + 1, byte_cnt, "Data");
 328                                                 }
 329                                                 break;
 330
 331                                         case read_mult_regs:
 332                                         case read_input_regs:
 333                                                 if (packet_type == query_packet) {
 334                                                         proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, FALSE);
 335                                                         proto_tree_add_item(modbus_tree, hf_modbus_wordcnt, tvb, payload_start + 2, 2, FALSE);
 336                                                 }
 337                                                 else if (packet_type == response_packet) {
 338                                                         byte_cnt = (guint32)tvb_get_guint8(tvb, payload_start);
 339                                                         proto_tree_add_uint(modbus_tree, hf_modbus_bytecnt, tvb, payload_start, 1, byte_cnt);
 340                                                         proto_tree_add_text(modbus_tree, tvb, payload_start + 1, byte_cnt, "Data");
 341                                                 }
 342                                                 break;
 343
 344                                         case write_coil:
 345                                                 if (packet_type == query_packet) {
 346                                                         proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, FALSE);
 347                                                         proto_tree_add_text(modbus_tree, tvb, payload_start + 2, 1, "Data");
 348                                                         proto_tree_add_text(modbus_tree, tvb, payload_start + 3, 1, "Padding");
 349                                                 }
 350                                                 else if (packet_type == response_packet) {
 351                                                         proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, FALSE);
 352                                                         proto_tree_add_text(modbus_tree, tvb, payload_start + 2, 1, "Data");
 353                                                         proto_tree_add_text(modbus_tree, tvb, payload_start + 3, 1, "Padding");
 354                                                 }
 355                                                 break;
 356
 357                                         case write_single_reg:
 358                                                 if (packet_type == query_packet) {
 359                                                         proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, FALSE);
 360                                                         proto_tree_add_text(modbus_tree, tvb, payload_start + 2, 2, "Data");
 361                                                 }
 362                                                 else if (packet_type == response_packet) {
 363                                                         proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, FALSE);
 364                                                         proto_tree_add_text(modbus_tree, tvb, payload_start + 2, 2, "Data");
 365                                                 }
 366                                                 break;
 367
 368                                         case read_except_stat:
 369                                                 if (packet_type == response_packet)
 370                                                         proto_tree_add_text(modbus_tree, tvb, payload_start, 1, "Data");
 371                                                 break;
 372
 373                                         case force_mult_coils:
 374                                                 if (packet_type == query_packet) {
 375                                                         proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, FALSE);
 376                                                         proto_tree_add_item(modbus_tree, hf_modbus_bitcnt, tvb, payload_start + 2, 2, FALSE);
 377                                                         byte_cnt = (guint32)tvb_get_guint8(tvb, payload_start + 4);
 378                                                         proto_tree_add_uint(modbus_tree, hf_modbus_bytecnt, tvb, payload_start + 4, 1,
 379                                                                         byte_cnt);
 380                                                         proto_tree_add_text(modbus_tree, tvb, payload_start + 5, byte_cnt, "Data");
 381                                                 }
 382                                                 else if (packet_type == response_packet) {
 383                                                         proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, FALSE);
 384                                                         proto_tree_add_item(modbus_tree, hf_modbus_bitcnt, tvb, payload_start + 2, 2, FALSE);
 385                                                 }
 386                                                 break;
 387
 388                                         case write_mult_regs:
 389                                                 if (packet_type == query_packet) {
 390                                                         proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, FALSE);
 391                                                         proto_tree_add_item(modbus_tree, hf_modbus_wordcnt, tvb, payload_start + 2, 2, FALSE);
 392                                                         byte_cnt = (guint32)tvb_get_guint8(tvb, payload_start + 4);
 393                                                         proto_tree_add_uint(modbus_tree, hf_modbus_bytecnt, tvb, payload_start + 4, 1,
 394                                                                         byte_cnt);
 395                                                         proto_tree_add_text(modbus_tree, tvb, payload_start + 5, byte_cnt, "Data");
 396                                                 }
 397                                                 else if (packet_type == response_packet) {
 398                                                         proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, FALSE);
 399                                                         proto_tree_add_item(modbus_tree, hf_modbus_wordcnt, tvb, payload_start + 2, 2, FALSE);
 400                                                 }
 401                                                 break;
 402
 403                                         case read_genl_ref:
 404                                                 if (packet_type == query_packet) {
 405                                                         byte_cnt = (guint32)tvb_get_guint8(tvb, payload_start);
 406                                                         proto_tree_add_uint(modbus_tree, hf_modbus_bytecnt, tvb, payload_start, 1,
 407                                                                         byte_cnt);
 408
 409                                                         /* add subtrees to describe each group of packet */
 410                                                         group_offset = payload_start + 1;
 411                                                         for (i = 0; i < byte_cnt / 7; i++) {
 412                                                                 mi = proto_tree_add_text( modbus_tree, tvb, group_offset, 7,
 413                                                                                 "Group %u", i);
 414                                                                 group_tree = proto_item_add_subtree(mi, ett_group_hdr);
 415                                                                 proto_tree_add_item(group_tree, hf_modbus_reftype, tvb, group_offset, 1, FALSE);
 416                                                                 proto_tree_add_item(group_tree, hf_modbus_lreference, tvb, group_offset + 1, 4, FALSE);
 417                                                                 proto_tree_add_item(group_tree, hf_modbus_wordcnt, tvb, group_offset + 5, 2, FALSE);
 418                                                                 group_offset += 7;
 419                                                         }
 420                                                 }
 421                                                 else if (packet_type == response_packet) {
 422                                                         byte_cnt = (guint32)tvb_get_guint8(tvb, payload_start);
 423                                                         proto_tree_add_uint(modbus_tree, hf_modbus_bytecnt, tvb, payload_start, 1,
 424                                                                         byte_cnt);
 425
 426                                                         /* add subtrees to describe each group of packet */
 427                                                         group_offset = payload_start + 1;
 428                                                         i = 0;
 429                                                         while (byte_cnt > 0) {
 430                                                                 group_byte_cnt = (guint32)tvb_get_guint8(tvb, group_offset);
 431                                                                 mi = proto_tree_add_text( modbus_tree, tvb, group_offset, group_byte_cnt + 1,
 432                                                                                 "Group %u", i);
 433                                                                 group_tree = proto_item_add_subtree(mi, ett_group_hdr);
 434                                                                 proto_tree_add_uint(group_tree, hf_modbus_bytecnt, tvb, group_offset, 1,
 435                                                                                 group_byte_cnt);
 436                                                                 proto_tree_add_item(group_tree, hf_modbus_reftype, tvb, group_offset + 1, 1, FALSE);
 437                                                                 proto_tree_add_text(group_tree, tvb, group_offset + 2, group_byte_cnt - 1, "Data");
 438                                                                 group_offset += (group_byte_cnt + 1);
 439                                                                 byte_cnt -= (group_byte_cnt + 1);
 440                                                                 i++;
 441                                                         }
 442                                                 }
 443                                                 break;
 444
 445                                         case write_genl_ref:
 446                                                 if ((packet_type == query_packet) || (packet_type == response_packet)) {
 447                                                         byte_cnt = (guint32)tvb_get_guint8(tvb, payload_start);
 448                                                         proto_tree_add_uint(modbus_tree, hf_modbus_bytecnt, tvb, payload_start, 1,
 449                                                                         byte_cnt);
 450
 451                                                         /* add subtrees to describe each group of packet */
 452                                                         group_offset = payload_start + 1;
 453                                                         i = 0;
 454                                                         while (byte_cnt > 0) {
 455                                                                 group_word_cnt = tvb_get_ntohs(tvb, group_offset + 5);
 456                                                                 group_byte_cnt = (2 * group_word_cnt) + 7;
 457                                                                 mi = proto_tree_add_text( modbus_tree, tvb, group_offset,
 458                                                                                 group_byte_cnt, "Group %u", i);
 459                                                                 group_tree = proto_item_add_subtree(mi, ett_group_hdr);
 460                                                                 proto_tree_add_item(group_tree, hf_modbus_reftype, tvb, group_offset, 1, FALSE);
 461                                                                 proto_tree_add_item(group_tree, hf_modbus_lreference, tvb, group_offset + 1, 4, FALSE);
 462                                                                 proto_tree_add_uint(group_tree, hf_modbus_wordcnt, tvb, group_offset + 5, 2,
 463                                                                                 group_word_cnt);
 464                                                                 proto_tree_add_text(group_tree, tvb, group_offset + 7, group_byte_cnt - 7, "Data");
 465                                                                 group_offset += group_byte_cnt;
 466                                                                 byte_cnt -= group_byte_cnt;
 467                                                                 i++;
 468                                                         }
 469                                                 }
 470                                                 break;
 471
 472                                         case mask_write_reg:
 473                                                 if ((packet_type == query_packet) || (packet_type == response_packet)) {
 474                                                         proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, FALSE);
 475                                                         proto_tree_add_item(modbus_tree, hf_modbus_andmask, tvb, payload_start + 2, 2, FALSE);
 476                                                         proto_tree_add_item(modbus_tree, hf_modbus_ormask, tvb, payload_start + 4, 2, FALSE);
 477                                                 }
 478                                                 break;
 479
 480                                         case read_write_reg:
 481                                                 if (packet_type == query_packet) {
 482                                                         proto_tree_add_item(modbus_tree, hf_modbus_readref, tvb, payload_start, 2, FALSE);
 483                                                         proto_tree_add_item(modbus_tree, hf_modbus_readwordcnt, tvb, payload_start + 2, 2, FALSE);
 484                                                         proto_tree_add_item(modbus_tree, hf_modbus_writeref, tvb, payload_start + 4, 2, FALSE);
 485                                                         proto_tree_add_item(modbus_tree, hf_modbus_writewordcnt, tvb, payload_start + 6, 2, FALSE);
 486                                                         byte_cnt = (guint32)tvb_get_guint8(tvb, payload_start + 8);
 487                                                         proto_tree_add_uint(modbus_tree, hf_modbus_bytecnt, tvb, payload_start + 8, 1,
 488                                                                         byte_cnt);
 489                                                         proto_tree_add_text(modbus_tree, tvb, payload_start + 9, byte_cnt, "Data");
 490                                                 }
 491                                                 else if (packet_type == response_packet) {
 492                                                         byte_cnt = (guint32)tvb_get_guint8(tvb, payload_start);
 493                                                         proto_tree_add_uint(modbus_tree, hf_modbus_bytecnt, tvb, payload_start, 1,
 494                                                                         byte_cnt);
 495                                                         proto_tree_add_text(modbus_tree, tvb, payload_start + 1, byte_cnt, "Data");
 496                                                 }
 497                                                 break;
 498
 499                                         case read_fifo_queue:
 500                                                 if (packet_type == query_packet)
 501                                                         proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, FALSE);
 502                                                 else if (packet_type == response_packet) {
 503                                                         byte_cnt = (guint32)tvb_get_ntohs(tvb, payload_start);
 504                                                         proto_tree_add_uint(modbus_tree, hf_modbus_lbytecnt, tvb, payload_start, 2,
 505                                                                         byte_cnt);
 506                                                         proto_tree_add_item(modbus_tree, hf_modbus_wordcnt, tvb, payload_start + 2, 2, FALSE);
 507                                                         proto_tree_add_text(modbus_tree, tvb, payload_start + 4, byte_cnt - 2, "Data");
 508                                                 }
 509                                                 break;
 510
 511                                         case diagnostics:
 512                                         case program_484:
 513                                         case poll_484:
 514                                         case get_comm_event_ctrs:
 515                                         case get_comm_event_log:
 516                                         case program_584_984:
 517                                         case poll_584_984:
 518                                         case report_slave_id:
 519                                         case program_884_u84:
 520                                         case reset_comm_link:
 521                                         case program_ConCept:
 522                                         case firmware_replace:
 523                                         case program_584_984_2:
 524                                         case report_local_addr_mb:
 525                                                 /* these function codes are not part of the Modbus/TCP specification */
 526                                         default:
 527                                                 if (payload_len > 0)
 528                                                         proto_tree_add_text(modbus_tree, tvb, payload_start, payload_len, "Data");
 529                                                 break;
 530                                 }
 531                         }
 532                 }
 533
 534                 /* move onto next packet (if there) */
 535                 offset += packet_len;
 536                 packet_num++;
 537                 if (tvb_reported_length_remaining(tvb, offset) > 0) {
 538
 539                         /* load header structure for next packet */
 540                         tvb_memcpy(tvb, (guint8 *)&mh, offset, sizeof(mbtcp_hdr));
 541                         mh.transaction_id                               =       g_ntohs(mh.transaction_id);
 542                         mh.protocol_id                                  =       g_ntohs(mh.protocol_id);
 543                         mh.len                                                  =       g_ntohs(mh.len);
 544
 545                         if ( mh.mdbs_hdr.function_code & 0x80 ) {
 546                                 exception_code = tvb_get_guint8(tvb, offset + sizeof(mbtcp_hdr));
 547                                 mh.mdbs_hdr.function_code ^= 0x80;
 548                                 exception_returned = TRUE;
 549                         } else
 550                                 exception_returned = FALSE;
 551                 }
 552                 else
 553                         break;
 554         }
 555 }
 556
 557
 558 /* Register the protocol with Ethereal */
 559
 560 void
 561 proto_register_modbus(void)
 562 {
 563
 564 /* Setup list of header fields  See Section 1.6.1 for details*/
 565         static hf_register_info hf[] = {
 566                 /* Modbus/TCP header fields */
 567                 { &hf_mbtcp_transid,
 568                         { "transaction identifier",                     "modbus_tcp.trans_id",
 569                         FT_UINT16, BASE_DEC, NULL, 0x0,
 570                         "", HFILL }
 571                 },
 572                 { &hf_mbtcp_protid,
 573                         { "protocol identifier",                        "modbus_tcp.prot_id",
 574                         FT_UINT16, BASE_DEC, NULL, 0x0,
 575                         "", HFILL }
 576                 },
 577                 { &hf_mbtcp_len,
 578                         { "length",                                                     "modbus_tcp.len",
 579                         FT_UINT16, BASE_DEC, NULL, 0x0,
 580                         "", HFILL }
 581                 },
 582                 /* Modbus header fields */
 583                 { &hf_mbtcp_unitid,
 584                         { "unit identifier",                    "modbus_tcp.unit_id",
 585                         FT_UINT8, BASE_DEC, NULL, 0x0,
 586                         "", HFILL }
 587                 },
 588                 { &hf_mbtcp_functioncode,
 589                         { "function code",                      "modbus_tcp.func_code",
 590                         FT_UINT8, BASE_DEC, VALS(function_code_vals), 0x0,
 591                         "", HFILL }
 592                 },
 593                 { &hf_modbus_reference,
 594                         { "reference number",                   "modbus_tcp.reference_num",
 595                         FT_UINT16, BASE_DEC, NULL, 0x0,
 596                         "", HFILL }
 597                 },
 598                 { &hf_modbus_lreference,
 599                         { "reference number (32 bit)",          "modbus_tcp.reference_num_32",
 600                         FT_UINT32, BASE_DEC, NULL, 0x0,
 601                         "", HFILL }
 602                 },
 603                 { &hf_modbus_reftype,
 604                         { "reference type",                             "modbus_tcp.reference_type",
 605                         FT_UINT8, BASE_DEC, NULL, 0x0,
 606                         "", HFILL }
 607                 },
 608                 { &hf_modbus_readref,
 609                         { "read reference number",              "modbus_tcp.read_reference_num",
 610                         FT_UINT16, BASE_DEC, NULL, 0x0,
 611                         "", HFILL }
 612                 },
 613                 { &hf_modbus_writeref,
 614                         { "write reference number",             "modbus_tcp.write_reference_num",
 615                         FT_UINT16, BASE_DEC, NULL, 0x0,
 616                         "", HFILL }
 617                 },
 618                 { &hf_modbus_wordcnt,
 619                         { "word count",                                 "modbus_tcp.word_cnt",
 620                         FT_UINT16, BASE_DEC, NULL, 0x0,
 621                         "", HFILL }
 622                 },
 623                 { &hf_modbus_readwordcnt,
 624                         { "read word count",                            "modbus_tcp.read_word_cnt",
 625                         FT_UINT16, BASE_DEC, NULL, 0x0,
 626                         "", HFILL }
 627                 },
 628                 { &hf_modbus_writewordcnt,
 629                         { "write word count",                   "modbus_tcp.write_word_cnt",
 630                         FT_UINT16, BASE_DEC, NULL, 0x0,
 631                         "", HFILL }
 632                 },
 633                 { &hf_modbus_bitcnt,
 634                         { "bit count",                                  "modbus_tcp.bit_cnt",
 635                         FT_UINT16, BASE_DEC, NULL, 0x0,
 636                         "", HFILL }
 637                 },
 638                 { &hf_modbus_bytecnt,
 639                         { "byte count",                                 "modbus_tcp.byte_cnt",
 640                         FT_UINT8, BASE_DEC, NULL, 0x0,
 641                         "", HFILL }
 642                 },
 643                 { &hf_modbus_lbytecnt,
 644                         { "byte count (16-bit)",                        "modbus_tcp.byte_cnt_16",
 645                         FT_UINT8, BASE_DEC, NULL, 0x0,
 646                         "", HFILL }
 647                 },
 648                 { &hf_modbus_exceptioncode,
 649                         { "exception code",                     "modbus_tcp.exception_code",
 650                         FT_UINT8, BASE_DEC, VALS(exception_code_vals), 0x0,
 651                         "", HFILL }
 652                 },
 653                 { &hf_modbus_andmask,
 654                         { "AND mask",                                   "modbus_tcp.and_mask",
 655                         FT_UINT16, BASE_HEX, NULL, 0x0,
 656                         "", HFILL }
 657                 },
 658                 { &hf_modbus_ormask,
 659                         { "OR mask",                                    "modbus_tcp.or_mask",
 660                         FT_UINT16, BASE_HEX, NULL, 0x0,
 661                         "", HFILL }
 662                 }
 663         };
 664
 665         /* Setup protocol subtree array */
 666         static gint *ett[] = {
 667                 &ett_mbtcp,
 668                 &ett_modbus_hdr,
 669                 &ett_group_hdr
 670         };
 671
 672         /* Register the protocol name and description */
 673         proto_mbtcp = proto_register_protocol("Modbus/TCP", "Modbus/TCP", "mbtcp");
 674
 675         /* Required function calls to register the header fields and subtrees used */
 676         proto_register_field_array(proto_mbtcp, hf, array_length(hf));
 677         proto_register_subtree_array(ett, array_length(ett));
 678 }
 679
 680
 681 /* If this dissector uses sub-dissector registration add a registration routine.
 682    This format is required because a script is used to find these routines and
 683    create the code that calls these routines.
 684  */
 685 void
 686 proto_reg_handoff_mbtcp(void)
 687 {
 688         dissector_handle_t mbtcp_handle;
 689
 690         mbtcp_handle = create_dissector_handle(dissect_mbtcp, proto_mbtcp);
 691         dissector_add("tcp.port", TCP_PORT_MBTCP, mbtcp_handle);
 692 }