modbus_client_transport.c

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/**
 * @file modbus_client_transport.c
 * @brief Transport protocol abstraction layer
 *
 * @section License
 *
 * SPDX-License-Identifier: GPL-2.0-or-later
 *
 * Copyright (C) 2010-2026 Oryx Embedded SARL. All rights reserved.
 *
 * This file is part of CycloneTCP Open.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 *
 * @author Oryx Embedded SARL (www.oryx-embedded.com)
 * @version 2.6.0
 **/
 
//Switch to the appropriate trace level
#define TRACE_LEVEL MODBUS_TRACE_LEVEL
 
//Dependencies
#include "core/net.h"
#include "modbus/modbus_client.h"
#include "modbus/modbus_client_transport.h"
#include "debug.h"
 
//Check TCP/IP stack configuration
#if (MODBUS_CLIENT_SUPPORT == ENABLED)
 
 
/**
 * @brief Open network connection
 * @param[in] context Pointer to the Modbus/TCP client context
 * @return Error code
 **/
 
error_t modbusClientOpenConnection(ModbusClientContext *context)
{
   error_t error;
 
   //Open a TCP socket
   context->socket = socketOpenEx(context->netContext, SOCKET_TYPE_STREAM,
      SOCKET_IP_PROTO_TCP);
   //Failed to open socket?
   if(context->socket == NULL)
      return ERROR_OPEN_FAILED;
 
   //Associate the socket with the relevant interface
   error = socketBindToInterface(context->socket, context->interface);
   //Any error to report?
   if(error)
      return error;
 
   //Set timeout
   error = socketSetTimeout(context->socket, context->timeout);
   //Any error to report?
   if(error)
      return error;
 
#if (MODBUS_CLIENT_TLS_SUPPORT == ENABLED)
   //TLS-secured connection?
   if(context->tlsInitCallback != NULL)
   {
      //Allocate TLS context
      context->tlsContext = tlsInit();
      //Failed to allocate TLS context?
      if(context->tlsContext == NULL)
         return ERROR_OPEN_FAILED;
 
      //Devices must provide TLS v1.2 or better
      error = tlsSetVersion(context->tlsContext, TLS_VERSION_1_2,
         TLS_VERSION_1_3);
      //Any error to report?
      if(error)
         return error;
 
      //Select client operation mode
      error = tlsSetConnectionEnd(context->tlsContext,
         TLS_CONNECTION_END_CLIENT);
      //Any error to report?
      if(error)
         return error;
 
      //Bind TLS to the relevant socket
      error = tlsSetSocket(context->tlsContext, context->socket);
      //Any error to report?
      if(error)
         return error;
 
      //Set TX and RX buffer size
      error = tlsSetBufferSize(context->tlsContext,
         MODBUS_CLIENT_TLS_TX_BUFFER_SIZE, MODBUS_CLIENT_TLS_RX_BUFFER_SIZE);
      //Any error to report?
      if(error)
         return error;
 
      //Restore TLS session
      error = tlsRestoreSessionState(context->tlsContext, &context->tlsSession);
      //Any error to report?
      if(error)
         return error;
 
      //Perform TLS related initialization
      error = context->tlsInitCallback(context, context->tlsContext);
      //Any error to report?
      if(error)
         return error;
   }
#endif
 
   //Successful processing
   return NO_ERROR;
}
 
 
/**
 * @brief Establish network connection
 * @param[in] context Pointer to the Modbus/TCP client context
 * @param[in] serverIpAddr IP address of the Modbus/TCP server to connect to
 * @param[in] serverPort TCP port number that will be used to establish the
 *   connection
 * @return Error code
 **/
 
error_t modbusClientEstablishConnection(ModbusClientContext *context,
   const IpAddr *serverIpAddr, uint16_t serverPort)
{
   error_t error;
 
   //Establish TCP connection
   error = socketConnect(context->socket, serverIpAddr, serverPort);
   //Any error to report?
   if(error)
      return error;
 
#if (MODBUS_CLIENT_TLS_SUPPORT == ENABLED)
   //TLS-secured connection?
   if(context->tlsContext != NULL)
   {
      //Establish TLS connection
      error = tlsConnect(context->tlsContext);
      //Any error to report?
      if(error)
         return error;
 
      //Save TLS session
      error = tlsSaveSessionState(context->tlsContext, &context->tlsSession);
      //Any error to report?
      if(error)
         return error;
   }
#endif
 
   //Successful processing
   return NO_ERROR;
}
 
 
/**
 * @brief Shutdown network connection
 * @param[in] context Pointer to the Modbus/TCP client context
 * @return Error code
 **/
 
error_t modbusClientShutdownConnection(ModbusClientContext *context)
{
   error_t error;
 
   //Initialize status code
   error = NO_ERROR;
 
#if (MODBUS_CLIENT_TLS_SUPPORT == ENABLED)
   //Valid TLS context?
   if(context->tlsContext != NULL)
   {
      //Shutdown TLS session
      error = tlsShutdown(context->tlsContext);
   }
#endif
 
   //Check status code
   if(!error)
   {
      //Valid TCP socket?
      if(context->socket != NULL)
      {
         //Shutdown TCP connection
         error = socketShutdown(context->socket, SOCKET_SD_BOTH);
      }
   }
 
   //Return status code
   return error;
}
 
 
/**
 * @brief Close network connection
 * @param[in] context Pointer to the Modbus/TCP client context
 **/
 
void modbusClientCloseConnection(ModbusClientContext *context)
{
#if (MODBUS_CLIENT_TLS_SUPPORT == ENABLED)
   //Release TLS context
   if(context->tlsContext != NULL)
   {
      tlsFree(context->tlsContext);
      context->tlsContext = NULL;
   }
#endif
 
   //Close TCP connection
   if(context->socket != NULL)
   {
      socketClose(context->socket);
      context->socket = NULL;
   }
}
 
 
/**
 * @brief Send data using the relevant transport protocol
 * @param[in] context Pointer to the Modbus/TCP client context
 * @param[in] data Pointer to a buffer containing the data to be transmitted
 * @param[in] length Number of bytes to be transmitted
 * @param[out] written Actual number of bytes written (optional parameter)
 * @param[in] flags Set of flags that influences the behavior of this function
 * @return Error code
 **/
 
error_t modbusClientSendData(ModbusClientContext *context, const void *data,
   size_t length, size_t *written, uint_t flags)
{
   error_t error;
 
#if (MODBUS_CLIENT_TLS_SUPPORT == ENABLED)
   //TLS-secured connection?
   if(context->tlsContext != NULL)
   {
      //Send TLS-encrypted data
      error = tlsWrite(context->tlsContext, data, length, written, flags);
   }
   else
#endif
   {
      //Transmit data
      error = socketSend(context->socket, data, length, written, flags);
   }
 
   //Return status code
   return error;
}
 
 
/**
 * @brief Receive data using the relevant transport protocol
 * @param[in] context Pointer to the Modbus/TCP client context
 * @param[out] data Buffer into which received data will be placed
 * @param[in] size Maximum number of bytes that can be received
 * @param[out] received Number of bytes that have been received
 * @param[in] flags Set of flags that influences the behavior of this function
 * @return Error code
 **/
 
error_t modbusClientReceiveData(ModbusClientContext *context, void *data,
   size_t size, size_t *received, uint_t flags)
{
   error_t error;
 
#if (MODBUS_CLIENT_TLS_SUPPORT == ENABLED)
   //TLS-secured connection?
   if(context->tlsContext != NULL)
   {
      //Receive TLS-encrypted data
      error = tlsRead(context->tlsContext, data, size, received, flags);
   }
   else
#endif
   {
      //Receive data
      error = socketReceive(context->socket, data, size, received, flags);
   }
 
   //Return status code
   return error;
}
 
#endif