text: /*
   * Copyright © 2001-2010 Stéphane Raimbault <stephane.raimbault@gmail.com>
   *
   * This program is free software: you can redistribute it and/or modify
   * it under the terms of the GNU Lesser Public License as published by
   * the Free Software Foundation; either version 3 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 Lesser Public License for more details.
   *
   * You should have received a copy of the GNU Lesser Public License
   * along with this program.  If not, see <http://www.gnu.org/licenses/>.
   */
  
  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  #include <errno.h>
  #include <unistd.h>
  #include <signal.h>
  #include <sys/types.h>
  
  #if defined(_WIN32)
  # define OS_WIN32
  # include <winsock2.h>
  # include <ws2tcpip.h>
  # define SHUT_RDWR 2
  # define close closesocket
  #else
  # include <sys/socket.h>
  # include <sys/ioctl.h>
  
  #if defined(__OpenBSD__) || (defined(__FreeBSD__) && __FreeBSD__ < 5)
  # define OS_BSD
  # include <netinet/in_systm.h>
  #endif
  
  # include <netinet/in.h>
  # include <netinet/ip.h>
  # include <netinet/tcp.h>
  # include <arpa/inet.h>
  #endif
  
  #if !defined(MSG_NOSIGNAL)
  #define MSG_NOSIGNAL 0
  #endif
  
  #include "modbus_io/modbus-private.h"
  
  #include "modbus_io/modbus-tcp.h"
  #include "modbus_io/modbus-tcp-private.h"
  
  #ifdef OS_WIN32
  static int _modbus_tcp_init_win32(void)
  {
      // Initialise Win32 Socket API
      WORD wVersionRequested;
      WSADATA wsaData;
  
      wVersionRequested = MAKEWORD(2, 0);
      if (WSAStartup(wVersionRequested, &wsaData) != 0)
      {
          fprintf (stderr, "WSAStartup() returned error code %d\n",
                   GetLastError());
          errno = EIO;
          return -1;
      }
      return 0;
  }
  #endif
  
  static int _modbus_set_slave(modbus_t *ctx, int slave)
  {
      /* Broadcast address is 0 (MODBUS_BROADCAST_ADDRESS) */
      if (slave >= 0 && slave <= 247) {
          ctx->slave = slave;
      } else if (slave == MODBUS_TCP_SLAVE) {
          /* The special value MODBUS_TCP_SLAVE (0xFF) can be used in TCP mode to
           * restore the default value. */
          ctx->slave = slave;
      } else {
          errno = EINVAL;
          return -1;
      }
  
      return 0;
  }
  
  /* Builds a TCP request header */
  int _modbus_tcp_build_request_basis(modbus_t *ctx, int function,
                                      int addr, int nb,
                                      uint8_t *req)
  {
  
      /* Extract from MODBUS Messaging on TCP/IP Implementation Guide V1.0b
         (page 23/46):
         The transaction identifier is used to associate the future response
         with the request. So, at a time, on a TCP connection, this identifier
         must be unique. */
      static uint16_t t_id = 0;
  
      /* Transaction ID */
      if (t_id < UINT16_MAX)
          t_id++;
      else
          t_id = 0;
      req[0] = t_id >> 8;
      req[1] = t_id & 0x00ff;
  
      /* Protocol Modbus */
      req[2] = 0;
      req[3] = 0;
  
      /* Length will be defined later by set_req_length_tcp at offsets 4
         and 5 */
  
      req[6] = ctx->slave;
      req[7] = function;
      req[8] = addr >> 8;
      req[9] = addr & 0x00ff;
      req[10] = nb >> 8;
      req[11] = nb & 0x00ff;
  
      return _MODBUS_TCP_PRESET_REQ_LENGTH;
  }
  
  /* Builds a TCP response header */
  int _modbus_tcp_build_response_basis(sft_t *sft, uint8_t *rsp)
  {
      /* Extract from MODBUS Messaging on TCP/IP Implementation
         Guide V1.0b (page 23/46):
         The transaction identifier is used to associate the future
         response with the request. */
      rsp[0] = sft->t_id >> 8;
      rsp[1] = sft->t_id & 0x00ff;
  
      /* Protocol Modbus */
      rsp[2] = 0;
      rsp[3] = 0;
  
      /* Length will be set later by send_msg (4 and 5) */
  
      /* The slave ID is copied from the indication */
      rsp[6] = sft->slave;
      rsp[7] = sft->function;
  
      return _MODBUS_TCP_PRESET_RSP_LENGTH;
  }
  
  
  int _modbus_tcp_prepare_response_tid(const uint8_t *req, int *req_length)
  {
      return (req[0] << 8) + req[1];
  }
  
  int _modbus_tcp_send_msg_pre(uint8_t *req, int req_length)
  {
      /* Substract the header length to the message length */
      int mbap_length = req_length - 6;
  
      req[4] = mbap_length >> 8;
      req[5] = mbap_length & 0x00FF;
  
      return req_length;
  }
  
  ssize_t _modbus_tcp_send(modbus_t *ctx, const uint8_t *req, int req_length)
  {
      /* MSG_NOSIGNAL
         Requests not to send SIGPIPE on errors on stream oriented
         sockets when the other end breaks the connection.  The EPIPE
         error is still returned. */
      return send(ctx->s, (const char*)req, req_length, MSG_NOSIGNAL);
  }
  
  ssize_t _modbus_tcp_recv(modbus_t *ctx, uint8_t *rsp, int rsp_length) {
      return recv(ctx->s, (char *)rsp, rsp_length, 0);
  }
  
  int _modbus_tcp_check_integrity(modbus_t *ctx, uint8_t *msg, const int msg_length)
  {
      return msg_length;
  }
  
  /* Establishes a modbus TCP connection with a Modbus server. */
  static int _modbus_tcp_connect(modbus_t *ctx)
  {
      int rc;
      int option;
      struct sockaddr_in addr;
      modbus_tcp_t *ctx_tcp = ctx->backend_data;
  
  #ifdef OS_WIN32
      if (_modbus_tcp_init_win32() == -1) {
          return -1;
      }
  #endif
  
      ctx->s = socket(PF_INET, SOCK_STREAM, 0);
      if (ctx->s == -1) {
          return -1;
      }
  
      /* Set the TCP no delay flag */
      /* SOL_TCP = IPPROTO_TCP */
      option = 1;
      rc = setsockopt(ctx->s, IPPROTO_TCP, TCP_NODELAY,
                      (const void *)&option, sizeof(int));
      if (rc == -1) {
          close(ctx->s);
          return -1;
      }
  
  #ifndef OS_WIN32
      /**
       * Cygwin defines IPTOS_LOWDELAY but can't handle that flag so it's
       * necessary to workaround that problem.
       **/
      /* Set the IP low delay option */
      option = IPTOS_LOWDELAY;
      rc = setsockopt(ctx->s, IPPROTO_IP, IP_TOS,
                      (const void *)&option, sizeof(int));
      if (rc == -1) {
          close(ctx->s);
          return -1;
      }
  #endif
  
      if (ctx->debug) {
          printf("Connecting to %s\n", ctx_tcp->ip);
      }
  
      addr.sin_family = AF_INET;
      addr.sin_port = htons(ctx_tcp->port);
      addr.sin_addr.s_addr = inet_addr(ctx_tcp->ip);
      rc = connect(ctx->s, (struct sockaddr *)&addr,
                   sizeof(struct sockaddr_in));
      if (rc == -1) {
          close(ctx->s);
          return -1;
      }
  
      return 0;
  }
  
  /* Closes the network connection and socket in TCP mode */
  void _modbus_tcp_close(modbus_t *ctx)
  {
      shutdown(ctx->s, SHUT_RDWR);
      close(ctx->s);
  }
  
  int _modbus_tcp_flush(modbus_t *ctx)
  {
      int rc;
  
      do {
          /* Extract the garbage from the socket */
          char devnull[MODBUS_TCP_MAX_ADU_LENGTH];
  #ifndef OS_WIN32
          rc = recv(ctx->s, devnull, MODBUS_TCP_MAX_ADU_LENGTH, MSG_DONTWAIT);
  #else
          /* On Win32, it's a bit more complicated to not wait */
          fd_set rfds;
          struct timeval tv;
  
          tv.tv_sec = 0;
          tv.tv_usec = 0;
          FD_ZERO(&rfds);
          FD_SET(ctx->s, &rfds);
          rc = select(ctx->s+1, &rfds, NULL, NULL, &tv);
          if (rc == -1) {
              return -1;
          }
  
          rc = recv(ctx->s, devnull, MODBUS_TCP_MAX_ADU_LENGTH, 0);
  #endif
          if (ctx->debug && rc != -1) {
              printf("\n%d bytes flushed\n", rc);
          }
      } while (rc > 0);
  
      return rc;
  }
  
  /* Listens for any request from one or many modbus masters in TCP */
  int modbus_tcp_listen(modbus_t *ctx, int nb_connection)
  {
      int new_socket;
      int yes;
      struct sockaddr_in addr;
      modbus_tcp_t *ctx_tcp = ctx->backend_data;
  
  #ifdef OS_WIN32
      if (_modbus_tcp_init_win32() == -1) {
          return -1;
      }
  #endif
  
      new_socket = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);
      if (new_socket == -1) {
          return -1;
      }
  
      yes = 1;
      if (setsockopt(new_socket, SOL_SOCKET, SO_REUSEADDR,
                     (char *) &yes, sizeof(yes)) == -1) {
          close(new_socket);
          return -1;
      }
  
      memset(&addr, 0, sizeof(addr));
      addr.sin_family = AF_INET;
      /* If the modbus port is < to 1024, we need the setuid root. */
      addr.sin_port = htons(ctx_tcp->port);
      addr.sin_addr.s_addr = INADDR_ANY;
      if (bind(new_socket, (struct sockaddr *)&addr, sizeof(addr)) == -1) {
          close(new_socket);
          return -1;
      }
  
      if (listen(new_socket, nb_connection) == -1) {
          close(new_socket);
          return -1;
      }
  
      return new_socket;
  }
  
  /* On success, the function return a non-negative integer that is a descriptor
     for the accepted socket. On error, -1 is returned, and errno is set
     appropriately. */
  int modbus_tcp_accept(modbus_t *ctx, int *socket)
  {
      struct sockaddr_in addr;
      socklen_t addrlen;
  
      addrlen = sizeof(struct sockaddr_in);
      ctx->s = accept(*socket, (struct sockaddr *)&addr, &addrlen);
      if (ctx->s == -1) {
          close(*socket);
          *socket = 0;
          return -1;
      }
  
      if (ctx->debug) {
          printf("The client %s is connected\n", inet_ntoa(addr.sin_addr));
      }
  
      return ctx->s;
  }
  
  int _modbus_tcp_select(modbus_t *ctx, fd_set *rfds, struct timeval *tv, int length_to_read)
  {
      int s_rc;
      while ((s_rc = select(ctx->s+1, rfds, NULL, NULL, tv)) == -1) {
          if (errno == EINTR) {
              if (ctx->debug) {
                  fprintf(stderr, "A non blocked signal was caught\n");
              }
              /* Necessary after an error */
              FD_ZERO(rfds);
              FD_SET(ctx->s, rfds);
          } else {
              _error_print(ctx, "select");
              if (ctx->error_recovery && (errno == EBADF)) {
                  modbus_close(ctx);
                  modbus_connect(ctx);
                  errno = EBADF;
                  return -1;
              } else {
                  return -1;
              }
          }
      }
  
      if (s_rc == 0) {
          errno = ETIMEDOUT;
          _error_print(ctx, "select");
          return -1;
      }
  
      return s_rc;
  }
  
  int _modbus_tcp_filter_request(modbus_t *ctx, int slave)
  {
      return 0;
  }
  
  const modbus_backend_t _modbus_tcp_backend = {
      _MODBUS_BACKEND_TYPE_TCP,
      _MODBUS_TCP_HEADER_LENGTH,
      _MODBUS_TCP_CHECKSUM_LENGTH,
      MODBUS_TCP_MAX_ADU_LENGTH,
      _modbus_set_slave,
      _modbus_tcp_build_request_basis,
      _modbus_tcp_build_response_basis,
      _modbus_tcp_prepare_response_tid,
      _modbus_tcp_send_msg_pre,
      _modbus_tcp_send,
      _modbus_tcp_recv,
      _modbus_tcp_check_integrity,
      _modbus_tcp_connect,
      _modbus_tcp_close,
      _modbus_tcp_flush,
      _modbus_tcp_select,
      _modbus_tcp_filter_request
  };
  
  
  /* Allocates and initializes the modbus_t structure for TCP.
     - ip : "192.168.0.5"
     - port : 1099
  
     Set the port to MODBUS_TCP_DEFAULT_PORT to use the default one
     (502). It's convenient to use a port number greater than or equal
     to 1024 because it's not necessary to be root to use this port
     number.
  */
  modbus_t* modbus_new_tcp(const char *ip, int port)
  {
      modbus_t *ctx;
      modbus_tcp_t *ctx_tcp;
  
  #if defined(OS_BSD)
      /* MSG_NOSIGNAL is unsupported on *BSD so we install an ignore
         handler for SIGPIPE. */
      struct sigaction sa;
  
      sa.sa_handler = SIG_IGN;
      if (sigaction(SIGPIPE, &sa, NULL) < 0) {
          /* The debug flag can't be set here... */
          fprintf(stderr, "Coud not install SIGPIPE handler.\n");
          return NULL;
      }
  #endif
  
      ctx = (modbus_t *) malloc(sizeof(modbus_t));
      _modbus_init_common(ctx);
  
      /* Could be changed after to reach a remote serial Modbus device */
      ctx->slave = MODBUS_TCP_SLAVE;
  
      ctx->backend = &(_modbus_tcp_backend);
  
      ctx->backend_data = (modbus_tcp_t *) malloc(sizeof(modbus_tcp_t));
      ctx_tcp = (modbus_tcp_t *)ctx->backend_data;
  
      strncpy(ctx_tcp->ip, ip, sizeof(char)*16);
      ctx_tcp->port = port;
  
      return ctx;
  }
  