modbus_server.cpp

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#include "modbus_server.h"
#include "esphome/core/application.h"
#include "esphome/core/log.h"
 
namespace esphome::modbus_server {
using modbus::ModbusFunctionCode;
using modbus::ModbusExceptionCode;
 
static const char *const TAG = "modbus_server";
 
void ModbusServer::on_modbus_read_registers(uint8_t function_code, uint16_t start_address,
                                            uint16_t number_of_registers) {
  ESP_LOGV(TAG,
           "Received read holding/input registers for device 0x%X. FC: 0x%X. Start address: 0x%X. Number of registers: "
           "0x%X.",
           this->address_, function_code, start_address, number_of_registers);
 
  if (number_of_registers == 0 || number_of_registers > modbus::MAX_NUM_OF_REGISTERS_TO_READ) {
    ESP_LOGW(TAG, "Invalid number of registers %d. Sending exception response.", number_of_registers);
    this->send_error(function_code, ModbusExceptionCode::ILLEGAL_DATA_ADDRESS);
    return;
  }
 
  std::vector<uint16_t> sixteen_bit_response;
  for (uint16_t current_address = start_address; current_address < start_address + number_of_registers;) {
    bool found = false;
    for (auto *server_register : this->server_registers_) {
      if (server_register->address == current_address) {
        if (!server_register->read_lambda) {
          break;
        }
        int64_t value = server_register->read_lambda();
        ESP_LOGV(TAG, "Matched register. Address: 0x%02X. Value type: %zu. Register count: %u. Value: %s.",
                 server_register->address, static_cast<size_t>(server_register->value_type),
                 server_register->register_count, server_register->format_value(value).c_str());
 
        std::vector<uint16_t> payload;
        payload.reserve(server_register->register_count * 2);
        modbus::helpers::number_to_payload(payload, value, server_register->value_type);
        sixteen_bit_response.insert(sixteen_bit_response.end(), payload.cbegin(), payload.cend());
        current_address += server_register->register_count;
        found = true;
        break;
      }
    }
 
    if (!found) {
      if (this->server_courtesy_response_.enabled &&
          (current_address <= this->server_courtesy_response_.register_last_address)) {
        ESP_LOGV(TAG,
                 "Could not match any register to address 0x%02X, but default allowed. "
                 "Returning default value: %d.",
                 current_address, this->server_courtesy_response_.register_value);
        sixteen_bit_response.push_back(this->server_courtesy_response_.register_value);
        current_address += 1;  // Just increment by 1, as the default response is a single register
      } else {
        ESP_LOGW(TAG,
                 "Could not match any register to address 0x%02X and default not allowed. Sending exception response.",
                 current_address);
        this->send_error(function_code, ModbusExceptionCode::ILLEGAL_DATA_ADDRESS);
        return;
      }
    }
  }
 
  std::vector<uint8_t> response;
  for (auto v : sixteen_bit_response) {
    auto decoded_value = decode_value(v);
    response.push_back(decoded_value[0]);
    response.push_back(decoded_value[1]);
  }
 
  this->send(function_code, start_address, number_of_registers, response.size(), response.data());
}
 
void ModbusServer::on_modbus_write_registers(uint8_t function_code, const std::vector<uint8_t> &data) {
  uint16_t number_of_registers;
  uint16_t payload_offset;
 
  if (function_code == ModbusFunctionCode::WRITE_MULTIPLE_REGISTERS) {
    if (data.size() < 5) {
      ESP_LOGW(TAG, "Write multiple registers data too short (%zu bytes)", data.size());
      this->send_error(function_code, ModbusExceptionCode::ILLEGAL_DATA_VALUE);
      return;
    }
    number_of_registers = uint16_t(data[3]) | (uint16_t(data[2]) << 8);
    if (number_of_registers == 0 || number_of_registers > modbus::MAX_NUM_OF_REGISTERS_TO_WRITE) {
      ESP_LOGW(TAG, "Invalid number of registers %d. Sending exception response.", number_of_registers);
      this->send_error(function_code, ModbusExceptionCode::ILLEGAL_DATA_VALUE);
      return;
    }
    uint16_t payload_size = data[4];
    if (payload_size != number_of_registers * 2) {
      ESP_LOGW(TAG, "Payload size of %d bytes is not 2 times the number of registers (%d). Sending exception response.",
               payload_size, number_of_registers);
      this->send_error(function_code, ModbusExceptionCode::ILLEGAL_DATA_VALUE);
      return;
    }
    if (data.size() < 5 + payload_size) {
      ESP_LOGW(TAG, "Write multiple registers payload truncated (%zu bytes, expected %u)", data.size(),
               5 + payload_size);
      this->send_error(function_code, ModbusExceptionCode::ILLEGAL_DATA_VALUE);
      return;
    }
    payload_offset = 5;
  } else if (function_code == ModbusFunctionCode::WRITE_SINGLE_REGISTER) {
    if (data.size() < 4) {
      ESP_LOGW(TAG, "Write single register data too short (%zu bytes)", data.size());
      this->send_error(function_code, ModbusExceptionCode::ILLEGAL_DATA_VALUE);
      return;
    }
    number_of_registers = 1;
    payload_offset = 2;
  } else {
    ESP_LOGW(TAG, "Invalid function code 0x%X. Sending exception response.", function_code);
    this->send_error(function_code, ModbusExceptionCode::ILLEGAL_FUNCTION);
    return;
  }
 
  uint16_t start_address = uint16_t(data[1]) | (uint16_t(data[0]) << 8);
  ESP_LOGD(TAG,
           "Received write holding registers for device 0x%X. FC: 0x%X. Start address: 0x%X. Number of registers: "
           "0x%X.",
           this->address_, function_code, start_address, number_of_registers);
 
  auto for_each_register = [this, start_address, number_of_registers, payload_offset](
                               const std::function<bool(ServerRegister *, uint16_t offset)> &callback) -> bool {
    uint16_t offset = payload_offset;
    for (uint16_t current_address = start_address; current_address < start_address + number_of_registers;) {
      bool ok = false;
      for (auto *server_register : this->server_registers_) {
        if (server_register->address == current_address) {
          ok = callback(server_register, offset);
          current_address += server_register->register_count;
          offset += server_register->register_count * sizeof(uint16_t);
          break;
        }
      }
 
      if (!ok) {
        return false;
      }
    }
    return true;
  };
 
  // check all registers are writable before writing to any of them:
  if (!for_each_register([](ServerRegister *server_register, uint16_t offset) -> bool {
        return server_register->write_lambda != nullptr;
      })) {
    this->send_error(function_code, ModbusExceptionCode::ILLEGAL_FUNCTION);
    return;
  }
 
  // Actually write to the registers:
  if (!for_each_register([&data](ServerRegister *server_register, uint16_t offset) {
        int64_t number = modbus::helpers::payload_to_number(data, server_register->value_type, offset, 0xFFFFFFFF);
        return server_register->write_lambda(number);
      })) {
    this->send_error(function_code, ModbusExceptionCode::SERVICE_DEVICE_FAILURE);
    return;
  }
 
  std::vector<uint8_t> response;
  response.reserve(6);
  response.push_back(this->address_);
  response.push_back(function_code);
  response.insert(response.end(), data.begin(), data.begin() + 4);
  this->send_raw(response);
}
 
void ModbusServer::dump_config() {
  ESP_LOGCONFIG(TAG,
                "ModbusServer:\n"
                "  Address: 0x%02X\n"
                "  Server Courtesy Response:\n"
                "    Enabled: %s\n"
                "    Register Last Address: 0x%02X\n"
                "    Register Value: %" PRIu16,
                this->address_, this->server_courtesy_response_.enabled ? "true" : "false",
                this->server_courtesy_response_.register_last_address, this->server_courtesy_response_.register_value);
 
#if ESPHOME_LOG_LEVEL >= ESPHOME_LOG_LEVEL_VERBOSE
  ESP_LOGCONFIG(TAG, "server registers");
  for (auto &r : this->server_registers_) {
    ESP_LOGCONFIG(TAG, "  Address=0x%02X value_type=%u register_count=%u", r->address,
                  static_cast<uint8_t>(r->value_type), r->register_count);
  }
#endif
}
 
}  // namespace esphome::modbus_server