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Fix detection of 'Write Multiple Registers' and 'Write Multiple Coils' function message 'direction' 

Also did some refactoring of existing code to make it more readable for the various existing function code types.

** Commit amendment to not use depreciated tvb_length() function.

Change-Id: Ia4c9f3514968c2a7bebc404ca9185cf8d814dfca
Reviewed-on: https://code.wireshark.org/review/8301
Reviewed-by: Anders Broman <a.broman58@gmail.com>
This commit is contained in:
cbontje 2015-05-05 14:26:21 -06:00 committed by Anders Broman
parent c3c4d42d86
commit 7771ed2faa
1 changed files with 43 additions and 15 deletions
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58
epan/dissectors/packet-mbtcp.c
View File

@ -211,6 +211,11 @@ classify_mbtcp_packet(packet_info *pinfo)
static int
classify_mbrtu_packet(packet_info *pinfo, tvbuff_t *tvb)
{
guint8 func, len;
func = tvb_get_guint8(tvb, 1);
len = tvb_reported_length(tvb);
/* see if nature of packets can be derived from src/dst ports */
/* if so, return as found */
if (( pinfo->srcport == global_mbus_rtu_port ) && ( pinfo->destport != global_mbus_rtu_port ))
@ -221,29 +226,52 @@ classify_mbrtu_packet(packet_info *pinfo, tvbuff_t *tvb)
/* Special case for serial-captured packets that don't have an Ethernet header */
/* Dig into these a little deeper to try to guess the message type */
if (!pinfo->srcport) {
/* If length is 8, this is either a query or very short response */
if (tvb_length(tvb) == 8) {
/* Only possible to get a response message of 8 bytes with Discrete or Coils */
if ((tvb_get_guint8(tvb, 1) == READ_COILS) || (tvb_get_guint8(tvb, 1) == READ_DISCRETE_INPUTS)) {
/* If this is, in fact, a response then the data byte count will be 3 */
/* This will correctly identify all messages except for those that are discrete or coil polls */
/* where the base address range happens to have 0x03 in the upper 16-bit address register */
if (tvb_get_guint8(tvb, 2) == 3) {
switch (func) {
case READ_COILS:
case READ_DISCRETE_INPUTS:
/* Only possible to get a response message of 8 bytes with Discrete or Coils */
if (len == 8) {
/* If this is, in fact, a response then the data byte count will be 3 */
/* This will correctly identify all messages except for those that are discrete or coil polls */
/* where the base address range happens to have 0x03 in the upper 16-bit address register */
if (tvb_get_guint8(tvb, 2) == 3) {
return RESPONSE_PACKET;
}
else {
return QUERY_PACKET;
}
}
break;
case READ_HOLDING_REGS:
case READ_INPUT_REGS:
case WRITE_SINGLE_COIL:
case WRITE_SINGLE_REG:
if (len == 8) {
return QUERY_PACKET;
}
else {
return RESPONSE_PACKET;
}
break;
case WRITE_MULT_REGS:
case WRITE_MULT_COILS:
if (len == 8) {
return RESPONSE_PACKET;
}
else {
return QUERY_PACKET;
}
}
else {
return QUERY_PACKET;
}
}
else {
return RESPONSE_PACKET;
break;
default:
return CANNOT_CLASSIFY;
break;
}
}
/* else, cannot classify */
return CANNOT_CLASSIFY;
}