epan/dissectors/packet-mbtcp.c

   1 /* packet-mbtcp.c
   2  * Routines for Modbus/TCP and Modbus/UDP 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.modbus.org/
  10  *
  11  * for information on Modbus/TCP.
  12  *
  13  * $Id$
  14  *
  15  * Wireshark - Network traffic analyzer
  16  * By Gerald Combs <gerald@wireshark.org>
  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 PORT_MBTCP              502     /* Modbus/TCP and Modbus/UDP located on port 502 */
  47
  48 /* Modbus protocol function codes */
  49 #define READ_COILS              1
  50 #define READ_INPUT_DISCRETES    2
  51 #define READ_MULT_REGS          3
  52 #define READ_INPUT_REGS         4
  53 #define WRITE_COIL              5
  54 #define WRITE_SINGLE_REG        6
  55 #define READ_EXCEPT_STAT        7
  56 #define DIAGNOSTICS             8
  57 #define PROGRAM_484             9
  58 #define POLL_484                10
  59 #define GET_COMM_EVENT_CTRS     11
  60 #define GET_COMM_EVENT_LOG      12
  61 #define PROGRAM_584_984         13
  62 #define POLL_584_984            14
  63 #define FORCE_MULT_COILS        15
  64 #define WRITE_MULT_REGS         16
  65 #define REPORT_SLAVE_ID         17
  66 #define PROGRAM_884_U84         18
  67 #define RESET_COMM_LINK         19
  68 #define READ_GENL_REF           20
  69 #define WRITE_GENL_REF          21
  70 #define MASK_WRITE_REG          22
  71 #define READ_WRITE_REG          23
  72 #define READ_FIFO_QUEUE         24
  73 #define PROGRAM_CONCEPT         40
  74 #define ENCAP_INTERFACE_TRANSP  43
  75 #define FIRMWARE_REPLACE        125
  76 #define PROGRAM_584_984_2       126
  77 #define REPORT_LOCAL_ADDR_MB    127
  78
  79 /* Modbus protocol exception codes */
  80 #define ILLEGAL_FUNCTION        0x01
  81 #define ILLEGAL_ADDRESS         0x02
  82 #define ILLEGAL_VALUE           0x03
  83 #define ILLEGAL_RESPONSE        0x04
  84 #define ACKNOWLEDGE             0x05
  85 #define SLAVE_BUSY              0x06
  86 #define NEGATIVE_ACK            0x07
  87 #define MEMORY_ERR              0x08
  88 #define GATEWAY_UNAVAILABLE     0x0a
  89 #define GATEWAY_TRGT_FAIL       0x0b
  90
  91 /* return codes of function classifying packets as query/response */
  92 #define QUERY_PACKET            0
  93 #define RESPONSE_PACKET         1
  94 #define CANNOT_CLASSIFY         2
  95
  96 /* Modbus header */
  97 typedef struct _modbus_hdr {
  98         guint8  unit_id;        /* unit identifier (previously slave addr) */
  99         guint8  function_code;  /* Modbus function code */
 100 } modbus_hdr;
 101
 102 /* Modbus/TCP header, containing the Modbus header */
 103 typedef struct _mbtcp_hdr {
 104         guint16         transaction_id;         /* copied by svr, usually 0 */
 105         guint16         protocol_id;            /* always 0 */
 106         guint16         len;                    /* len of data that follows */
 107         modbus_hdr      mdbs_hdr;               /* mdbus hdr directly after mdbs/tcp hdr *
 108                                                  * in packet */
 109 } mbtcp_hdr;
 110
 111 /* Initialize the protocol and registered fields */
 112 static int proto_mbtcp = -1;
 113 static int hf_mbtcp_transid = -1;
 114 static int hf_mbtcp_protid = -1;
 115 static int hf_mbtcp_len = -1;
 116 static int hf_mbtcp_unitid = -1;
 117 static int hf_mbtcp_functioncode = -1;
 118 static int hf_modbus_reference = -1;
 119 static int hf_modbus_lreference = -1;
 120 static int hf_modbus_reftype = -1;
 121 static int hf_modbus_readref = -1;
 122 static int hf_modbus_writeref = -1;
 123 static int hf_modbus_wordcnt = -1;
 124 static int hf_modbus_readwordcnt = -1;
 125 static int hf_modbus_writewordcnt = -1;
 126 static int hf_modbus_bytecnt = -1;
 127 static int hf_modbus_lbytecnt = -1;
 128 static int hf_modbus_bitcnt = -1;
 129 static int hf_modbus_exceptioncode = -1;
 130 static int hf_modbus_andmask = -1;
 131 static int hf_modbus_ormask = -1;
 132
 133 /* Initialize the subtree pointers */
 134 static gint ett_mbtcp = -1;
 135 static gint ett_modbus_hdr = -1;
 136 static gint ett_group_hdr = -1;
 137
 138 static int
 139 classify_packet(packet_info *pinfo)
 140 {
 141         /* see if nature of packets can be derived from src/dst ports */
 142         /* if so, return as found */
 143         if (( pinfo->srcport == PORT_MBTCP ) && ( pinfo->destport != PORT_MBTCP ))
 144                 return RESPONSE_PACKET;
 145         if (( pinfo->srcport != PORT_MBTCP ) && ( pinfo->destport == PORT_MBTCP ))
 146                 return QUERY_PACKET;
 147
 148         /* else, cannot classify */
 149         return CANNOT_CLASSIFY;
 150 }
 151
 152 /* Translate function to string, as given on p6 of
 153  * "Open Modbus/TCP Specification", release 1 by Andy Swales. */
 154 static const value_string function_code_vals[] = {
 155         { READ_COILS,                   "Read coils" },
 156         { READ_INPUT_DISCRETES,         "Read input discretes" },
 157         { READ_MULT_REGS,               "Read multiple registers" },
 158         { READ_INPUT_REGS,              "Read input registers" },
 159         { WRITE_COIL,                   "Write coil" },
 160         { WRITE_SINGLE_REG,             "Write single register" },
 161         { READ_EXCEPT_STAT,             "Read exception status" },
 162         { DIAGNOSTICS,                  "Diagnostics" },
 163         { PROGRAM_484,                  "Program (484)" },
 164         { POLL_484,                     "Poll (484)" },
 165         { GET_COMM_EVENT_CTRS,          "Get Comm. Event Counters" },
 166         { GET_COMM_EVENT_LOG,           "Get Comm. Event Log" },
 167         { PROGRAM_584_984,              "Program (584/984)" },
 168         { POLL_584_984,                 "Poll (584/984)" },
 169         { FORCE_MULT_COILS,             "Force Multiple Coils" },
 170         { WRITE_MULT_REGS,              "Write Multiple Registers" },
 171         { REPORT_SLAVE_ID,              "Report Slave ID" },
 172         { PROGRAM_884_U84,              "Program 884/u84" },
 173         { RESET_COMM_LINK,              "Reset Comm. Link (884/u84)" },
 174         { READ_GENL_REF,                "Read General Reference" },
 175         { WRITE_GENL_REF,               "Write General Reference" },
 176         { MASK_WRITE_REG,               "Mask Write Register" },
 177         { READ_WRITE_REG,               "Read Write Register" },
 178         { READ_FIFO_QUEUE,              "Read FIFO Queue" },
 179         { PROGRAM_CONCEPT,              "Program (ConCept)" },
 180         { ENCAP_INTERFACE_TRANSP,       "Encapsulated Interface Transport" },
 181         { FIRMWARE_REPLACE,             "Firmware replacement" },
 182         { PROGRAM_584_984_2,            "Program (584/984)" },
 183         { REPORT_LOCAL_ADDR_MB,         "Report local address (Modbus)" },
 184         { 0,                            NULL }
 185 };
 186
 187 static const value_string exception_code_vals[] = {
 188         { ILLEGAL_FUNCTION,     "Illegal function" },
 189         { ILLEGAL_ADDRESS,      "Illegal data address" },
 190         { ILLEGAL_VALUE,        "Illegal data value" },
 191         { ILLEGAL_RESPONSE,     "Illegal response length" },
 192         { ACKNOWLEDGE,          "Acknowledge" },
 193         { SLAVE_BUSY,           "Slave device busy" },
 194         { NEGATIVE_ACK,         "Negative acknowledge" },
 195         { MEMORY_ERR,           "Memory parity error" },
 196         { GATEWAY_UNAVAILABLE,  "Gateway path unavailable" },
 197         { GATEWAY_TRGT_FAIL,    "Gateway target device failed to respond" },
 198         { 0,                    NULL }
 199 };
 200
 201 /* Code to actually dissect the packets */
 202 static int
 203 dissect_mbtcp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
 204 {
 205 /* Set up structures needed to add the protocol subtree and manage it */
 206         mbtcp_hdr       mh;
 207         proto_item      *mi, *mf;
 208         proto_tree      *mbtcp_tree, *modbus_tree, *group_tree;
 209         int             offset, group_offset, packet_type;
 210         guint           i;
 211         gint            packet_len, payload_start, payload_len;
 212         const char      *func_string = "";
 213         const char      *pkt_type_str = "";
 214         const char      *err_str = "";
 215         guint32         byte_cnt, group_byte_cnt, group_word_cnt;
 216         guint32         packet_num;     /* num to uniquely identify different mbtcp
 217                                          * packets in one packet */
 218         guint8          exception_code;
 219         gboolean        exception_returned;
 220         guint8          fc;
 221
 222         mh.transaction_id = tvb_get_ntohs(tvb, 0);
 223         mh.protocol_id = tvb_get_ntohs(tvb, 2);
 224         mh.len = tvb_get_ntohs(tvb, 4);
 225         mh.mdbs_hdr.unit_id = tvb_get_guint8(tvb, 6);
 226         mh.mdbs_hdr.function_code = tvb_get_guint8(tvb, 7);
 227
 228
 229         /* check that it actually looks like Modbus/TCP */
 230         /* protocol id == 0 */
 231         if( mh.protocol_id != 0 ){
 232                 return 0;
 233         }
 234         /* length is at least 2 (unit_id + function_code) */
 235         if( mh.len < 2 ){
 236                 return 0;
 237         }
 238         /* function code is in the set 1-24, 40, 125-127.
 239          * Note that function code is only 7 bits.
 240          */
 241         fc=mh.mdbs_hdr.function_code&0x7f;
 242         if(!match_strval(fc, function_code_vals))
 243                 return 0;
 244
 245
 246         /* Make entries in Protocol column on summary display */
 247         if (check_col(pinfo->cinfo, COL_PROTOCOL))
 248                 col_set_str(pinfo->cinfo, COL_PROTOCOL, "Modbus/TCP");
 249
 250         if (check_col(pinfo->cinfo, COL_INFO))
 251                 col_clear(pinfo->cinfo, COL_INFO);
 252
 253
 254         /* Make entries in Info column on summary display */
 255         offset = 0;
 256
 257         if ( mh.mdbs_hdr.function_code & 0x80 ) {
 258                 exception_code = tvb_get_guint8(tvb, offset + sizeof(mbtcp_hdr));
 259                 mh.mdbs_hdr.function_code ^= 0x80;
 260                 exception_returned = TRUE;
 261         }
 262         else {
 263                 exception_code = 0;
 264                 exception_returned = FALSE;
 265         }
 266         func_string = val_to_str(mh.mdbs_hdr.function_code, function_code_vals,
 267             "Unknown function (%u)");
 268         if (check_col(pinfo->cinfo, COL_INFO))
 269         {
 270                 packet_type = classify_packet(pinfo);
 271                 switch ( packet_type ) {
 272                         case QUERY_PACKET :             pkt_type_str="query";
 273                                                                                                 break;
 274                         case RESPONSE_PACKET :  pkt_type_str="response";
 275                                                                                                 break;
 276                         case CANNOT_CLASSIFY :          err_str="Unable to classify as query or response.";
 277                                                                                 pkt_type_str="unknown";
 278                                                                                                 break;
 279                         default :
 280                                                                                                 break;
 281                 }
 282                 if ( exception_returned )
 283                         err_str="Exception returned ";
 284                 col_add_fstr(pinfo->cinfo, COL_INFO,
 285                                 "%8s [%2u pkt(s)]: trans: %5u; unit: %3u, func: %3u: %s. %s",
 286                                 pkt_type_str, 1, mh.transaction_id, (unsigned char) mh.mdbs_hdr.unit_id,
 287                                 (unsigned char) mh.mdbs_hdr.function_code, func_string, err_str);
 288         }
 289
 290         /* build up protocol tree and iterate over multiple packets */
 291         packet_num = 0;
 292         while (1) {
 293                 packet_type = classify_packet(pinfo);
 294                 packet_len = sizeof(mbtcp_hdr) - sizeof(modbus_hdr) + mh.len;
 295
 296                 /* if a tree exists, perform operations to add fields to it */
 297                 if (tree) {
 298                         mi = proto_tree_add_protocol_format(tree, proto_mbtcp, tvb, offset,
 299                                         packet_len, "Modbus/TCP");
 300                         mbtcp_tree = proto_item_add_subtree(mi, ett_mbtcp);
 301
 302                         /* Add items to protocol tree specific to Modbus/TCP */
 303                         proto_tree_add_uint(mbtcp_tree, hf_mbtcp_transid, tvb, offset, 2,
 304                                         mh.transaction_id);
 305                         proto_tree_add_uint(mbtcp_tree, hf_mbtcp_protid, tvb, offset + 2, 2,
 306                                         mh.protocol_id);
 307                         proto_tree_add_uint(mbtcp_tree, hf_mbtcp_len, tvb, offset + 4, 2,
 308                                         mh.len);
 309
 310                         proto_tree_add_uint(mbtcp_tree, hf_mbtcp_unitid, tvb, offset + 6, 1,
 311                                         mh.mdbs_hdr.unit_id);
 312
 313
 314                         /* Add items to protocol tree specific to Modbus generic */
 315                         mf = proto_tree_add_text(mbtcp_tree, tvb, offset + 7, mh.len - 1,
 316                                         "Modbus");
 317                         modbus_tree = proto_item_add_subtree(mf, ett_modbus_hdr);
 318                         mi = proto_tree_add_uint(modbus_tree, hf_mbtcp_functioncode, tvb, offset + 7, 1,
 319                                         mh.mdbs_hdr.function_code);
 320
 321                         /** detail payload as a function of exception/function code */
 322                         func_string = val_to_str(mh.mdbs_hdr.function_code,
 323                             function_code_vals, "Unknown function");
 324                         payload_start = offset + 8;
 325                         payload_len = mh.len - sizeof(modbus_hdr);
 326                         if (exception_returned) {
 327                                 proto_item_set_text(mi, "function %u:  %s.  Exception: %s",
 328                                                 mh.mdbs_hdr.function_code,
 329                                                 func_string,
 330                                                 val_to_str(exception_code,
 331                                                     exception_code_vals,
 332                                                     "Unknown exception code (%u)"));
 333                                 proto_tree_add_uint(modbus_tree, hf_modbus_exceptioncode, tvb, payload_start, 1,
 334                                                 exception_code);
 335                         }
 336                         else {
 337                                 proto_item_set_text(mi, "function %u:  %s", mh.mdbs_hdr.function_code,
 338                                                 func_string);
 339                                 switch (mh.mdbs_hdr.function_code) {
 340
 341                                         case READ_COILS:
 342                                         case READ_INPUT_DISCRETES:
 343                                                 if (packet_type == QUERY_PACKET) {
 344                                                         proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, FALSE);
 345                                                         proto_tree_add_item(modbus_tree, hf_modbus_bitcnt, tvb, payload_start + 2, 2, FALSE);
 346                                                 }
 347                                                 else if (packet_type == RESPONSE_PACKET) {
 348                                                         byte_cnt = (guint32)tvb_get_guint8(tvb, payload_start);
 349                                                         proto_tree_add_uint(modbus_tree, hf_modbus_bytecnt, tvb, payload_start, 1, byte_cnt);
 350                                                         proto_tree_add_text(modbus_tree, tvb, payload_start + 1, byte_cnt, "Data");
 351                                                 }
 352                                                 break;
 353
 354                                         case READ_MULT_REGS:
 355                                         case READ_INPUT_REGS:
 356                                                 if (packet_type == QUERY_PACKET) {
 357                                                         proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, FALSE);
 358                                                         proto_tree_add_item(modbus_tree, hf_modbus_wordcnt, tvb, payload_start + 2, 2, FALSE);
 359                                                 }
 360                                                 else if (packet_type == RESPONSE_PACKET) {
 361                                                         byte_cnt = (guint32)tvb_get_guint8(tvb, payload_start);
 362                                                         proto_tree_add_uint(modbus_tree, hf_modbus_bytecnt, tvb, payload_start, 1, byte_cnt);
 363                                                         proto_tree_add_text(modbus_tree, tvb, payload_start + 1, byte_cnt, "Data");
 364                                                 }
 365                                                 break;
 366
 367                                         case WRITE_COIL:
 368                                                 if (packet_type == QUERY_PACKET) {
 369                                                         proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, FALSE);
 370                                                         proto_tree_add_text(modbus_tree, tvb, payload_start + 2, 1, "Data");
 371                                                         proto_tree_add_text(modbus_tree, tvb, payload_start + 3, 1, "Padding");
 372                                                 }
 373                                                 else if (packet_type == RESPONSE_PACKET) {
 374                                                         proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, FALSE);
 375                                                         proto_tree_add_text(modbus_tree, tvb, payload_start + 2, 1, "Data");
 376                                                         proto_tree_add_text(modbus_tree, tvb, payload_start + 3, 1, "Padding");
 377                                                 }
 378                                                 break;
 379
 380                                         case WRITE_SINGLE_REG:
 381                                                 if (packet_type == QUERY_PACKET) {
 382                                                         proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, FALSE);
 383                                                         proto_tree_add_text(modbus_tree, tvb, payload_start + 2, 2, "Data");
 384                                                 }
 385                                                 else if (packet_type == RESPONSE_PACKET) {
 386                                                         proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, FALSE);
 387                                                         proto_tree_add_text(modbus_tree, tvb, payload_start + 2, 2, "Data");
 388                                                 }
 389                                                 break;
 390
 391                                         case READ_EXCEPT_STAT:
 392                                                 if (packet_type == RESPONSE_PACKET)
 393                                                         proto_tree_add_text(modbus_tree, tvb, payload_start, 1, "Data");
 394                                                 break;
 395
 396                                         case FORCE_MULT_COILS:
 397                                                 if (packet_type == QUERY_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_bitcnt, tvb, payload_start + 2, 2, FALSE);
 400                                                         byte_cnt = (guint32)tvb_get_guint8(tvb, payload_start + 4);
 401                                                         proto_tree_add_uint(modbus_tree, hf_modbus_bytecnt, tvb, payload_start + 4, 1,
 402                                                                         byte_cnt);
 403                                                         proto_tree_add_text(modbus_tree, tvb, payload_start + 5, byte_cnt, "Data");
 404                                                 }
 405                                                 else if (packet_type == RESPONSE_PACKET) {
 406                                                         proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, FALSE);
 407                                                         proto_tree_add_item(modbus_tree, hf_modbus_bitcnt, tvb, payload_start + 2, 2, FALSE);
 408                                                 }
 409                                                 break;
 410
 411                                         case WRITE_MULT_REGS:
 412                                                 if (packet_type == QUERY_PACKET) {
 413                                                         proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, FALSE);
 414                                                         proto_tree_add_item(modbus_tree, hf_modbus_wordcnt, tvb, payload_start + 2, 2, FALSE);
 415                                                         byte_cnt = (guint32)tvb_get_guint8(tvb, payload_start + 4);
 416                                                         proto_tree_add_uint(modbus_tree, hf_modbus_bytecnt, tvb, payload_start + 4, 1,
 417                                                                         byte_cnt);
 418                                                         proto_tree_add_text(modbus_tree, tvb, payload_start + 5, byte_cnt, "Data");
 419                                                 }
 420                                                 else if (packet_type == RESPONSE_PACKET) {
 421                                                         proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, FALSE);
 422                                                         proto_tree_add_item(modbus_tree, hf_modbus_wordcnt, tvb, payload_start + 2, 2, FALSE);
 423                                                 }
 424                                                 break;
 425
 426                                         case READ_GENL_REF:
 427                                                 if (packet_type == QUERY_PACKET) {
 428                                                         byte_cnt = (guint32)tvb_get_guint8(tvb, payload_start);
 429                                                         proto_tree_add_uint(modbus_tree, hf_modbus_bytecnt, tvb, payload_start, 1,
 430                                                                         byte_cnt);
 431
 432                                                         /* add subtrees to describe each group of packet */
 433                                                         group_offset = payload_start + 1;
 434                                                         for (i = 0; i < byte_cnt / 7; i++) {
 435                                                                 mi = proto_tree_add_text( modbus_tree, tvb, group_offset, 7,
 436                                                                                 "Group %u", i);
 437                                                                 group_tree = proto_item_add_subtree(mi, ett_group_hdr);
 438                                                                 proto_tree_add_item(group_tree, hf_modbus_reftype, tvb, group_offset, 1, FALSE);
 439                                                                 proto_tree_add_item(group_tree, hf_modbus_lreference, tvb, group_offset + 1, 4, FALSE);
 440                                                                 proto_tree_add_item(group_tree, hf_modbus_wordcnt, tvb, group_offset + 5, 2, FALSE);
 441                                                                 group_offset += 7;
 442                                                         }
 443                                                 }
 444                                                 else if (packet_type == RESPONSE_PACKET) {
 445                                                         byte_cnt = (guint32)tvb_get_guint8(tvb, payload_start);
 446                                                         proto_tree_add_uint(modbus_tree, hf_modbus_bytecnt, tvb, payload_start, 1,
 447                                                                         byte_cnt);
 448
 449                                                         /* add subtrees to describe each group of packet */
 450                                                         group_offset = payload_start + 1;
 451                                                         i = 0;
 452                                                         while (byte_cnt > 0) {
 453                                                                 group_byte_cnt = (guint32)tvb_get_guint8(tvb, group_offset);
 454                                                                 mi = proto_tree_add_text( modbus_tree, tvb, group_offset, group_byte_cnt + 1,
 455                                                                                 "Group %u", i);
 456                                                                 group_tree = proto_item_add_subtree(mi, ett_group_hdr);
 457                                                                 proto_tree_add_uint(group_tree, hf_modbus_bytecnt, tvb, group_offset, 1,
 458                                                                                 group_byte_cnt);
 459                                                                 proto_tree_add_item(group_tree, hf_modbus_reftype, tvb, group_offset + 1, 1, FALSE);
 460                                                                 proto_tree_add_text(group_tree, tvb, group_offset + 2, group_byte_cnt - 1, "Data");
 461                                                                 group_offset += (group_byte_cnt + 1);
 462                                                                 byte_cnt -= (group_byte_cnt + 1);
 463                                                                 i++;
 464                                                         }
 465                                                 }
 466                                                 break;
 467
 468                                         case WRITE_GENL_REF:
 469                                                 if ((packet_type == QUERY_PACKET) || (packet_type == RESPONSE_PACKET)) {
 470                                                         byte_cnt = (guint32)tvb_get_guint8(tvb, payload_start);
 471                                                         proto_tree_add_uint(modbus_tree, hf_modbus_bytecnt, tvb, payload_start, 1,
 472                                                                         byte_cnt);
 473
 474                                                         /* add subtrees to describe each group of packet */
 475                                                         group_offset = payload_start + 1;
 476                                                         i = 0;
 477                                                         while (byte_cnt > 0) {
 478                                                                 group_word_cnt = tvb_get_ntohs(tvb, group_offset + 5);
 479                                                                 group_byte_cnt = (2 * group_word_cnt) + 7;
 480                                                                 mi = proto_tree_add_text( modbus_tree, tvb, group_offset,
 481                                                                                 group_byte_cnt, "Group %u", i);
 482                                                                 group_tree = proto_item_add_subtree(mi, ett_group_hdr);
 483                                                                 proto_tree_add_item(group_tree, hf_modbus_reftype, tvb, group_offset, 1, FALSE);
 484                                                                 proto_tree_add_item(group_tree, hf_modbus_lreference, tvb, group_offset + 1, 4, FALSE);
 485                                                                 proto_tree_add_uint(group_tree, hf_modbus_wordcnt, tvb, group_offset + 5, 2,
 486                                                                                 group_word_cnt);
 487                                                                 proto_tree_add_text(group_tree, tvb, group_offset + 7, group_byte_cnt - 7, "Data");
 488                                                                 group_offset += group_byte_cnt;
 489                                                                 byte_cnt -= group_byte_cnt;
 490                                                                 i++;
 491                                                         }
 492                                                 }
 493                                                 break;
 494
 495                                         case MASK_WRITE_REG:
 496                                                 if ((packet_type == QUERY_PACKET) || (packet_type == RESPONSE_PACKET)) {
 497                                                         proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, FALSE);
 498                                                         proto_tree_add_item(modbus_tree, hf_modbus_andmask, tvb, payload_start + 2, 2, FALSE);
 499                                                         proto_tree_add_item(modbus_tree, hf_modbus_ormask, tvb, payload_start + 4, 2, FALSE);
 500                                                 }
 501                                                 break;
 502
 503                                         case READ_WRITE_REG:
 504                                                 if (packet_type == QUERY_PACKET) {
 505                                                         proto_tree_add_item(modbus_tree, hf_modbus_readref, tvb, payload_start, 2, FALSE);
 506                                                         proto_tree_add_item(modbus_tree, hf_modbus_readwordcnt, tvb, payload_start + 2, 2, FALSE);
 507                                                         proto_tree_add_item(modbus_tree, hf_modbus_writeref, tvb, payload_start + 4, 2, FALSE);
 508                                                         proto_tree_add_item(modbus_tree, hf_modbus_writewordcnt, tvb, payload_start + 6, 2, FALSE);
 509                                                         byte_cnt = (guint32)tvb_get_guint8(tvb, payload_start + 8);
 510                                                         proto_tree_add_uint(modbus_tree, hf_modbus_bytecnt, tvb, payload_start + 8, 1,
 511                                                                         byte_cnt);
 512                                                         proto_tree_add_text(modbus_tree, tvb, payload_start + 9, byte_cnt, "Data");
 513                                                 }
 514                                                 else if (packet_type == RESPONSE_PACKET) {
 515                                                         byte_cnt = (guint32)tvb_get_guint8(tvb, payload_start);
 516                                                         proto_tree_add_uint(modbus_tree, hf_modbus_bytecnt, tvb, payload_start, 1,
 517                                                                         byte_cnt);
 518                                                         proto_tree_add_text(modbus_tree, tvb, payload_start + 1, byte_cnt, "Data");
 519                                                 }
 520                                                 break;
 521
 522                                         case READ_FIFO_QUEUE:
 523                                                 if (packet_type == QUERY_PACKET)
 524                                                         proto_tree_add_item(modbus_tree, hf_modbus_reference, tvb, payload_start, 2, FALSE);
 525                                                 else if (packet_type == RESPONSE_PACKET) {
 526                                                         byte_cnt = (guint32)tvb_get_ntohs(tvb, payload_start);
 527                                                         proto_tree_add_uint(modbus_tree, hf_modbus_lbytecnt, tvb, payload_start, 2,
 528                                                                         byte_cnt);
 529                                                         proto_tree_add_item(modbus_tree, hf_modbus_wordcnt, tvb, payload_start + 2, 2, FALSE);
 530                                                         proto_tree_add_text(modbus_tree, tvb, payload_start + 4, byte_cnt - 2, "Data");
 531                                                 }
 532                                                 break;
 533
 534                                         case DIAGNOSTICS:
 535                                         case PROGRAM_484:
 536                                         case POLL_484:
 537                                         case GET_COMM_EVENT_CTRS:
 538                                         case GET_COMM_EVENT_LOG:
 539                                         case PROGRAM_584_984:
 540                                         case POLL_584_984:
 541                                         case REPORT_SLAVE_ID:
 542                                         case PROGRAM_884_U84:
 543                                         case RESET_COMM_LINK:
 544                                         case PROGRAM_CONCEPT:
 545                                         case FIRMWARE_REPLACE:
 546                                         case PROGRAM_584_984_2:
 547                                         case REPORT_LOCAL_ADDR_MB:
 548                                                 /* these function codes are not part of the Modbus/TCP specification */
 549                                         default:
 550                                                 if (payload_len > 0)
 551                                                         proto_tree_add_text(modbus_tree, tvb, payload_start, payload_len, "Data");
 552                                                 break;
 553                                 }
 554                         }
 555                 }
 556
 557                 /* move onto next packet (if there) */
 558                 offset += packet_len;
 559                 packet_num++;
 560                 if (tvb_reported_length_remaining(tvb, offset) > 0) {
 561
 562                         /* load header structure for next packet */
 563                         mh.transaction_id = tvb_get_ntohs(tvb, offset+0);
 564                         mh.protocol_id = tvb_get_ntohs(tvb, offset+2);
 565                         mh.len = tvb_get_ntohs(tvb, offset+4);
 566                         mh.mdbs_hdr.unit_id = tvb_get_guint8(tvb, offset+6);
 567                         mh.mdbs_hdr.function_code = tvb_get_guint8(tvb, offset+7);
 568
 569
 570                         if ( mh.mdbs_hdr.function_code & 0x80 ) {
 571                                 exception_code = tvb_get_guint8(tvb, offset + sizeof(mbtcp_hdr));
 572                                 mh.mdbs_hdr.function_code ^= 0x80;
 573                                 exception_returned = TRUE;
 574                         } else
 575                                 exception_returned = FALSE;
 576                 }
 577                 else
 578                         break;
 579         }
 580
 581         return tvb_length(tvb);
 582 }
 583
 584
 585 /* Register the protocol with Wireshark */
 586
 587 void
 588 proto_register_modbus(void)
 589 {
 590
 591 /* Setup list of header fields  See Section 1.6.1 for details*/
 592         static hf_register_info hf[] = {
 593                 /* Modbus/TCP header fields */
 594                 { &hf_mbtcp_transid,
 595                         { "transaction identifier",                     "modbus_tcp.trans_id",
 596                         FT_UINT16, BASE_DEC, NULL, 0x0,
 597                         NULL, HFILL }
 598                 },
 599                 { &hf_mbtcp_protid,
 600                         { "protocol identifier",                        "modbus_tcp.prot_id",
 601                         FT_UINT16, BASE_DEC, NULL, 0x0,
 602                         NULL, HFILL }
 603                 },
 604                 { &hf_mbtcp_len,
 605                         { "length",                                                     "modbus_tcp.len",
 606                         FT_UINT16, BASE_DEC, NULL, 0x0,
 607                         NULL, HFILL }
 608                 },
 609                 /* Modbus header fields */
 610                 { &hf_mbtcp_unitid,
 611                         { "unit identifier",                    "modbus_tcp.unit_id",
 612                         FT_UINT8, BASE_DEC, NULL, 0x0,
 613                         NULL, HFILL }
 614                 },
 615                 { &hf_mbtcp_functioncode,
 616                         { "function code",                      "modbus_tcp.func_code",
 617                         FT_UINT8, BASE_DEC, VALS(function_code_vals), 0x0,
 618                         NULL, HFILL }
 619                 },
 620                 { &hf_modbus_reference,
 621                         { "reference number",                   "modbus_tcp.reference_num",
 622                         FT_UINT16, BASE_DEC, NULL, 0x0,
 623                         NULL, HFILL }
 624                 },
 625                 { &hf_modbus_lreference,
 626                         { "reference number (32 bit)",          "modbus_tcp.reference_num_32",
 627                         FT_UINT32, BASE_DEC, NULL, 0x0,
 628                         NULL, HFILL }
 629                 },
 630                 { &hf_modbus_reftype,
 631                         { "reference type",                             "modbus_tcp.reference_type",
 632                         FT_UINT8, BASE_DEC, NULL, 0x0,
 633                         NULL, HFILL }
 634                 },
 635                 { &hf_modbus_readref,
 636                         { "read reference number",              "modbus_tcp.read_reference_num",
 637                         FT_UINT16, BASE_DEC, NULL, 0x0,
 638                         NULL, HFILL }
 639                 },
 640                 { &hf_modbus_writeref,
 641                         { "write reference number",             "modbus_tcp.write_reference_num",
 642                         FT_UINT16, BASE_DEC, NULL, 0x0,
 643                         NULL, HFILL }
 644                 },
 645                 { &hf_modbus_wordcnt,
 646                         { "word count",                                 "modbus_tcp.word_cnt",
 647                         FT_UINT16, BASE_DEC, NULL, 0x0,
 648                         NULL, HFILL }
 649                 },
 650                 { &hf_modbus_readwordcnt,
 651                         { "read word count",                            "modbus_tcp.read_word_cnt",
 652                         FT_UINT16, BASE_DEC, NULL, 0x0,
 653                         NULL, HFILL }
 654                 },
 655                 { &hf_modbus_writewordcnt,
 656                         { "write word count",                   "modbus_tcp.write_word_cnt",
 657                         FT_UINT16, BASE_DEC, NULL, 0x0,
 658                         NULL, HFILL }
 659                 },
 660                 { &hf_modbus_bitcnt,
 661                         { "bit count",                                  "modbus_tcp.bit_cnt",
 662                         FT_UINT16, BASE_DEC, NULL, 0x0,
 663                         NULL, HFILL }
 664                 },
 665                 { &hf_modbus_bytecnt,
 666                         { "byte count",                                 "modbus_tcp.byte_cnt",
 667                         FT_UINT8, BASE_DEC, NULL, 0x0,
 668                         NULL, HFILL }
 669                 },
 670                 { &hf_modbus_lbytecnt,
 671                         { "byte count (16-bit)",                        "modbus_tcp.byte_cnt_16",
 672                         FT_UINT8, BASE_DEC, NULL, 0x0,
 673                         NULL, HFILL }
 674                 },
 675                 { &hf_modbus_exceptioncode,
 676                         { "exception code",                     "modbus_tcp.exception_code",
 677                         FT_UINT8, BASE_DEC, VALS(exception_code_vals), 0x0,
 678                         NULL, HFILL }
 679                 },
 680                 { &hf_modbus_andmask,
 681                         { "AND mask",                                   "modbus_tcp.and_mask",
 682                         FT_UINT16, BASE_HEX, NULL, 0x0,
 683                         NULL, HFILL }
 684                 },
 685                 { &hf_modbus_ormask,
 686                         { "OR mask",                                    "modbus_tcp.or_mask",
 687                         FT_UINT16, BASE_HEX, NULL, 0x0,
 688                         NULL, HFILL }
 689                 }
 690         };
 691
 692         /* Setup protocol subtree array */
 693         static gint *ett[] = {
 694                 &ett_mbtcp,
 695                 &ett_modbus_hdr,
 696                 &ett_group_hdr
 697         };
 698
 699         /* Register the protocol name and description */
 700         proto_mbtcp = proto_register_protocol("Modbus/TCP", "Modbus/TCP", "mbtcp");
 701
 702         /* Required function calls to register the header fields and subtrees used */
 703         proto_register_field_array(proto_mbtcp, hf, array_length(hf));
 704         proto_register_subtree_array(ett, array_length(ett));
 705 }
 706
 707
 708 /* If this dissector uses sub-dissector registration add a registration routine.
 709    This format is required because a script is used to find these routines and
 710    create the code that calls these routines.
 711  */
 712 void
 713 proto_reg_handoff_mbtcp(void)
 714 {
 715         dissector_handle_t mbtcp_handle;
 716
 717         mbtcp_handle = new_create_dissector_handle(dissect_mbtcp, proto_mbtcp);
 718         dissector_add("tcp.port", PORT_MBTCP, mbtcp_handle);
 719         dissector_add("udp.port", PORT_MBTCP, mbtcp_handle);
 720 }