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Fix Packet::isCompleteLengthRTU to differentiate fix sized response p… #129

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merged 1 commit into from
Jan 25, 2023
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Fix Packet::isCompleteLengthRTU to differentiate fix sized response p… #129

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4 changes: 4 additions & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,10 @@ All notable changes to this project will be documented in this file.
The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).

# [3.1.1] - 2023-01-25

* Fixed `Packet::isCompleteLengthRTU()` to differentiate fix sized function code responses from variable sized responses.

# [3.1.0] - 2022-10-16

* Added `Packet::isCompleteLengthRTU()` to help checking if packet is complete RTU packet. Helps when receiving fragmented packets.
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38 changes: 29 additions & 9 deletions src/Utils/Packet.php
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Expand Up @@ -6,6 +6,7 @@

use ModbusTcpClient\Network\IOException;
use ModbusTcpClient\Packet\ErrorResponse;
use ModbusTcpClient\Packet\ModbusPacket;

final class Packet
{
Expand Down Expand Up @@ -39,8 +40,8 @@ public static function isCompleteLength(string|null $binaryData): bool
}

/**
* isCompleteLengthRTU checks if binary string is complete modbus RTU packet
* NB: this function works only for MODBUS RTU packets
* isCompleteLengthRTU checks if binary string is complete modbus RTU response packet
* NB: this function works only for MODBUS RTU response packets
*
* @param string|null $binaryData binary string to be checked
* @return bool true if data is actual error packet
Expand All @@ -52,17 +53,36 @@ public static function isCompleteLengthRTU(string|null $binaryData): bool
if ($length < 5) {
return false;
}
if ((ord($binaryData[1]) & ErrorResponse::EXCEPTION_BITMASK) > 0) { // seems to be error response
$functionCode = ord($binaryData[1]);
if (($functionCode & ErrorResponse::EXCEPTION_BITMASK) > 0) { // seems to be error response
return true;
}
// if it is not error response then 3rd byte contains data length in bytes
switch ($functionCode) {
case ModbusPacket::READ_COILS: //
case ModbusPacket::READ_INPUT_DISCRETES: //
case ModbusPacket::READ_HOLDING_REGISTERS: //
case ModbusPacket::READ_INPUT_REGISTERS: //
case ModbusPacket::READ_WRITE_MULTIPLE_REGISTERS: //
// if it is not error response then 3rd byte contains data length in bytes

// trailing 3 bytes are = unit id + function code + data length in bytes
// next is N bytes of data that should match 3rd byte value
// and 2 bytes for CRC
// so adding these number is what complete packet would be
$expectedLength = 3 + ord($binaryData[2]) + 2;
// trailing 3 bytes are = unit id (1) + function code (1) + data length in bytes (1) + (N)
// next is N bytes of data that should match 3rd byte value
$responseBytesLen = 3 + ord($binaryData[2]);
break;
case ModbusPacket::WRITE_SINGLE_COIL: // unit id (1) + function code (1) + start address (2) + coil data (2)
case ModbusPacket::WRITE_SINGLE_REGISTER: // unit id (1) + function code (1) + start address (2) + register data (2)
case ModbusPacket::WRITE_MULTIPLE_COILS: // unit id (1) + function code (1) + start address (2) + count of coils written (2)
case ModbusPacket::WRITE_MULTIPLE_REGISTERS: // unit id (1) + function code (1) + start address (2) + count of registers written (2)
$responseBytesLen = 6;
break;
case ModbusPacket::MASK_WRITE_REGISTER:
$responseBytesLen = 8; // unit id (1) + function code (1) + start address (2) + AND mask (2) + OR mask (2)
break;
default:
throw new IOException('can not determine complete length for unsupported modbus function code');
}

$expectedLength = $responseBytesLen + 2; // and 2 bytes for CRC
if ($length > $expectedLength) {
throw new IOException('packet length more bytes than expected');
}
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