【嵌入式】Libmodbus源码分析(五)-TCP相关函数分析-白红宇的个人博客

发布日期：2021-06-29 20:52:06 浏览次数：2 分类：技术文章

本文共 21023 字，大约阅读时间需要 70 分钟。

00. 目录

文章目录

01. modbus-tcp-private.h文件

modbus-tcp-private.h TCP模式私有数据类型声明和函数声明。

/* * Copyright © 2001-2011 Stéphane Raimbault 
   
     * * SPDX-License-Identifier: LGPL-2.1-or-later */#ifndef MODBUS_TCP_PRIVATE_H#define MODBUS_TCP_PRIVATE_H#define _MODBUS_TCP_HEADER_LENGTH      7#define _MODBUS_TCP_PRESET_REQ_LENGTH 12#define _MODBUS_TCP_PRESET_RSP_LENGTH  8#define _MODBUS_TCP_CHECKSUM_LENGTH    0/* In both structures, the transaction ID must be placed on first position   to have a quick access not dependent of the TCP backend */typedef struct _modbus_tcp {
       /* 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. This identifier is unique on each TCP connection. */    uint16_t t_id;    /* TCP port */ //端口    int port;    /* IP address */ //IP    char ip[16];} modbus_tcp_t;#define _MODBUS_TCP_PI_NODE_LENGTH    1025#define _MODBUS_TCP_PI_SERVICE_LENGTH   32typedef struct _modbus_tcp_pi {
       /* Transaction ID */    uint16_t t_id;    /* TCP port */    int port;    /* Node */    char node[_MODBUS_TCP_PI_NODE_LENGTH];    /* Service */    char service[_MODBUS_TCP_PI_SERVICE_LENGTH];} modbus_tcp_pi_t;#endif /* MODBUS_TCP_PRIVATE_H */

02. modbus-tcp.h文件

modbus-tcp.h TCP模式对外开放的类型声明和函数声明。

/* * Copyright © 2001-2010 Stéphane Raimbault 
   
     * * SPDX-License-Identifier: LGPL-2.1-or-later */#ifndef MODBUS_TCP_H#define MODBUS_TCP_H#include "modbus.h"MODBUS_BEGIN_DECLS#if defined(_WIN32) && !defined(__CYGWIN__)/* Win32 with MinGW, supplement to 
    
      */#include 
     
      #if !defined(ECONNRESET)#define ECONNRESET   WSAECONNRESET#endif#if !defined(ECONNREFUSED)#define ECONNREFUSED WSAECONNREFUSED#endif#if !defined(ETIMEDOUT)#define ETIMEDOUT    WSAETIMEDOUT#endif#if !defined(ENOPROTOOPT)#define ENOPROTOOPT  WSAENOPROTOOPT#endif#if !defined(EINPROGRESS)#define EINPROGRESS  WSAEINPROGRESS#endif#endif//默认端口#define MODBUS_TCP_DEFAULT_PORT   502#define MODBUS_TCP_SLAVE         0xFF/* Modbus_Application_Protocol_V1_1b.pdf Chapter 4 Section 1 Page 5 * TCP MODBUS ADU = 253 bytes + MBAP (7 bytes) = 260 bytes */#define MODBUS_TCP_MAX_ADU_LENGTH  260//创建modbus_t类型结构体MODBUS_API modbus_t* modbus_new_tcp(const char *ip_address, int port);//监听套接字MODBUS_API int modbus_tcp_listen(modbus_t *ctx, int nb_connection);//接受连接请求MODBUS_API int modbus_tcp_accept(modbus_t *ctx, int *s);MODBUS_API modbus_t* modbus_new_tcp_pi(const char *node, const char *service);MODBUS_API int modbus_tcp_pi_listen(modbus_t *ctx, int nb_connection);MODBUS_API int modbus_tcp_pi_accept(modbus_t *ctx, int *s);MODBUS_END_DECLS#endif /* MODBUS_TCP_H */

03. modbus-tcp.c文件

modbus-tcp.c 通信层实现，TCP模式下相关函数定义，主要包括TCP/IP网络的设置、连接、消息的发送和接收等等。封装了Linux平台和Windows平台相关网络协议层代码。

/* * Copyright © 2001-2013 Stéphane Raimbault 
   
     * * SPDX-License-Identifier: LGPL-2.1-or-later */#if defined(_WIN32)# define OS_WIN32/* ws2_32.dll has getaddrinfo and freeaddrinfo on Windows XP and later. * minwg32 headers check WINVER before allowing the use of these */# ifndef WINVER#   define WINVER 0x0501# endif#endif#include 
    
     #include 
     
      #include 
      
       #include 
       
        #ifndef _MSC_VER#include 
        
         #endif#include 
         
          #include 
          
           #if defined(_WIN32)/* Already set in modbus-tcp.h but it seems order matters in VS2005 */# include 
           
            # include 
            
             # define SHUT_RDWR 2# define close closesocket#else# include 
             
              # include 
              
               #if defined(__OpenBSD__) || (defined(__FreeBSD__) && __FreeBSD__ < 5)# define OS_BSD# include 
               
                #endif# include 
                
                 # include 
                 
                  # include 
                  
                   # include 
                   
                    # include 
                    
                     #endif#if !defined(MSG_NOSIGNAL)#define MSG_NOSIGNAL 0#endif#if defined(_AIX) && !defined(MSG_DONTWAIT)#define MSG_DONTWAIT MSG_NONBLOCK#endif#include "modbus-private.h"#include "modbus-tcp.h"#include "modbus-tcp-private.h"#ifdef OS_WIN32static int _modbus_tcp_init_win32(void){ /* Initialise Windows Socket API */ WSADATA wsaData; if (WSAStartup(MAKEWORD(2, 2), &wsaData) != 0) { fprintf(stderr, "WSAStartup() returned error code %d\n", (unsigned int)GetLastError()); errno = EIO; return -1; } return 0;}#endifstatic 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 */static int _modbus_tcp_build_request_basis(modbus_t *ctx, int function, int addr, int nb, uint8_t *req){ modbus_tcp_t *ctx_tcp = ctx->backend_data; /* Increase transaction ID */ if (ctx_tcp->t_id < UINT16_MAX) ctx_tcp->t_id++; else ctx_tcp->t_id = 0; req[0] = ctx_tcp->t_id >> 8; req[1] = ctx_tcp->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; //从设备ID req[7] = function; //功能码 req[8] = addr >> 8; //起始地址高位 req[9] = addr & 0x00ff; //起始地址低位 req[10] = nb >> 8; //数据高位 req[11] = nb & 0x00ff; //数据低位 return _MODBUS_TCP_PRESET_REQ_LENGTH;}/* Builds a TCP response header */static 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;}static int _modbus_tcp_prepare_response_tid(const uint8_t *req, int *req_length){ return (req[0] << 8) + req[1];}static int _modbus_tcp_send_msg_pre(uint8_t *req, int req_length){ /* Subtract 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;}static 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);}static int _modbus_tcp_receive(modbus_t *ctx, uint8_t *req) { return _modbus_receive_msg(ctx, req, MSG_INDICATION);}static ssize_t _modbus_tcp_recv(modbus_t *ctx, uint8_t *rsp, int rsp_length) { return recv(ctx->s, (char *)rsp, rsp_length, 0);}static int _modbus_tcp_check_integrity(modbus_t *ctx, uint8_t *msg, const int msg_length){ return msg_length;}static int _modbus_tcp_pre_check_confirmation(modbus_t *ctx, const uint8_t *req, const uint8_t *rsp, int rsp_length){ /* Check transaction ID */ if (req[0] != rsp[0] || req[1] != rsp[1]) { if (ctx->debug) { fprintf(stderr, "Invalid transaction ID received 0x%X (not 0x%X)\n", (rsp[0] << 8) + rsp[1], (req[0] << 8) + req[1]); } errno = EMBBADDATA; return -1; } /* Check protocol ID */ if (rsp[2] != 0x0 && rsp[3] != 0x0) { if (ctx->debug) { fprintf(stderr, "Invalid protocol ID received 0x%X (not 0x0)\n", (rsp[2] << 8) + rsp[3]); } errno = EMBBADDATA; return -1; } return 0;}static int _modbus_tcp_set_ipv4_options(int s){ int rc; int option; /* Set the TCP no delay flag */ /* SOL_TCP = IPPROTO_TCP */ option = 1; rc = setsockopt(s, IPPROTO_TCP, TCP_NODELAY, (const void *)&option, sizeof(int)); if (rc == -1) { return -1; } /* If the OS does not offer SOCK_NONBLOCK, fall back to setting FIONBIO to * make sockets non-blocking */ /* Do not care about the return value, this is optional */#if !defined(SOCK_NONBLOCK) && defined(FIONBIO)#ifdef OS_WIN32 { /* Setting FIONBIO expects an unsigned long according to MSDN */ u_long loption = 1; ioctlsocket(s, FIONBIO, &loption); }#else option = 1; ioctl(s, FIONBIO, &option);#endif#endif#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(s, IPPROTO_IP, IP_TOS, (const void *)&option, sizeof(int)); if (rc == -1) { return -1; }#endif return 0;}//连接到服务端static int _connect(int sockfd, const struct sockaddr *addr, socklen_t addrlen, const struct timeval *ro_tv){ int rc = connect(sockfd, addr, addrlen);#ifdef OS_WIN32 int wsaError = 0; if (rc == -1) { wsaError = WSAGetLastError(); } if (wsaError == WSAEWOULDBLOCK || wsaError == WSAEINPROGRESS) { #else if (rc == -1 && errno == EINPROGRESS) { #endif fd_set wset; int optval; socklen_t optlen = sizeof(optval); struct timeval tv = *ro_tv; /* Wait to be available in writing */ FD_ZERO(&wset); FD_SET(sockfd, &wset); rc = select(sockfd + 1, NULL, &wset, NULL, &tv); if (rc <= 0) { /* Timeout or fail */ return -1; } /* The connection is established if SO_ERROR and optval are set to 0 */ rc = getsockopt(sockfd, SOL_SOCKET, SO_ERROR, (void *)&optval, &optlen); if (rc == 0 && optval == 0) { return 0; } else { errno = ECONNREFUSED; return -1; } } return rc;}/* Establishes a modbus TCP connection with a Modbus server. */static int _modbus_tcp_connect(modbus_t *ctx){ int rc; /* Specialized version of sockaddr for Internet socket address (same size) */ struct sockaddr_in addr; modbus_tcp_t *ctx_tcp = ctx->backend_data; int flags = SOCK_STREAM;#ifdef OS_WIN32 if (_modbus_tcp_init_win32() == -1) { return -1; }#endif#ifdef SOCK_CLOEXEC flags |= SOCK_CLOEXEC;#endif#ifdef SOCK_NONBLOCK flags |= SOCK_NONBLOCK;#endif ctx->s = socket(PF_INET, flags, 0); if (ctx->s == -1) { return -1; } rc = _modbus_tcp_set_ipv4_options(ctx->s); if (rc == -1) { close(ctx->s); ctx->s = -1; return -1; } if (ctx->debug) { printf("Connecting to %s:%d\n", ctx_tcp->ip, ctx_tcp->port); } 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(addr), &ctx->response_timeout); if (rc == -1) { close(ctx->s); ctx->s = -1; return -1; } return 0;}/* Establishes a modbus TCP PI connection with a Modbus server. */static int _modbus_tcp_pi_connect(modbus_t *ctx){ int rc; struct addrinfo *ai_list; struct addrinfo *ai_ptr; struct addrinfo ai_hints; modbus_tcp_pi_t *ctx_tcp_pi = ctx->backend_data;#ifdef OS_WIN32 if (_modbus_tcp_init_win32() == -1) { return -1; }#endif memset(&ai_hints, 0, sizeof(ai_hints));#ifdef AI_ADDRCONFIG ai_hints.ai_flags |= AI_ADDRCONFIG;#endif ai_hints.ai_family = AF_UNSPEC; ai_hints.ai_socktype = SOCK_STREAM; ai_hints.ai_addr = NULL; ai_hints.ai_canonname = NULL; ai_hints.ai_next = NULL; ai_list = NULL; rc = getaddrinfo(ctx_tcp_pi->node, ctx_tcp_pi->service, &ai_hints, &ai_list); if (rc != 0) { if (ctx->debug) { fprintf(stderr, "Error returned by getaddrinfo: %s\n", gai_strerror(rc)); } errno = ECONNREFUSED; return -1; } for (ai_ptr = ai_list; ai_ptr != NULL; ai_ptr = ai_ptr->ai_next) { int flags = ai_ptr->ai_socktype; int s;#ifdef SOCK_CLOEXEC flags |= SOCK_CLOEXEC;#endif#ifdef SOCK_NONBLOCK flags |= SOCK_NONBLOCK;#endif s = socket(ai_ptr->ai_family, flags, ai_ptr->ai_protocol); if (s < 0) continue; if (ai_ptr->ai_family == AF_INET) _modbus_tcp_set_ipv4_options(s); if (ctx->debug) { printf("Connecting to [%s]:%s\n", ctx_tcp_pi->node, ctx_tcp_pi->service); } rc = _connect(s, ai_ptr->ai_addr, ai_ptr->ai_addrlen, &ctx->response_timeout); if (rc == -1) { close(s); continue; } ctx->s = s; break; } freeaddrinfo(ai_list); if (ctx->s < 0) { return -1; } return 0;}/* Closes the network connection and socket in TCP mode */static void _modbus_tcp_close(modbus_t *ctx){ if (ctx->s != -1) { shutdown(ctx->s, SHUT_RDWR); close(ctx->s); ctx->s = -1; }}static int _modbus_tcp_flush(modbus_t *ctx){ int rc; int rc_sum = 0; 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 rset; struct timeval tv; tv.tv_sec = 0; tv.tv_usec = 0; FD_ZERO(&rset); FD_SET(ctx->s, &rset); rc = select(ctx->s+1, &rset, NULL, NULL, &tv); if (rc == -1) { return -1; } if (rc == 1) { /* There is data to flush */ rc = recv(ctx->s, devnull, MODBUS_TCP_MAX_ADU_LENGTH, 0); }#endif if (rc > 0) { rc_sum += rc; } } while (rc == MODBUS_TCP_MAX_ADU_LENGTH); return rc_sum;}/* Listens for any request from one or many modbus masters in TCP */int modbus_tcp_listen(modbus_t *ctx, int nb_connection){ int new_s; int enable; int flags; struct sockaddr_in addr; modbus_tcp_t *ctx_tcp; if (ctx == NULL) { errno = EINVAL; return -1; } ctx_tcp = ctx->backend_data;#ifdef OS_WIN32 if (_modbus_tcp_init_win32() == -1) { return -1; }#endif flags = SOCK_STREAM;#ifdef SOCK_CLOEXEC flags |= SOCK_CLOEXEC;#endif new_s = socket(PF_INET, flags, IPPROTO_TCP); if (new_s == -1) { return -1; } enable = 1; if (setsockopt(new_s, SOL_SOCKET, SO_REUSEADDR, (char *)&enable, sizeof(enable)) == -1) { close(new_s); 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); if (ctx_tcp->ip[0] == '0') { /* Listen any addresses */ addr.sin_addr.s_addr = htonl(INADDR_ANY); } else { /* Listen only specified IP address */ addr.sin_addr.s_addr = inet_addr(ctx_tcp->ip); } if (bind(new_s, (struct sockaddr *)&addr, sizeof(addr)) == -1) { close(new_s); return -1; } if (listen(new_s, nb_connection) == -1) { close(new_s); return -1; } return new_s;}int modbus_tcp_pi_listen(modbus_t *ctx, int nb_connection){ int rc; struct addrinfo *ai_list; struct addrinfo *ai_ptr; struct addrinfo ai_hints; const char *node; const char *service; int new_s; modbus_tcp_pi_t *ctx_tcp_pi; if (ctx == NULL) { errno = EINVAL; return -1; } ctx_tcp_pi = ctx->backend_data;#ifdef OS_WIN32 if (_modbus_tcp_init_win32() == -1) { return -1; }#endif if (ctx_tcp_pi->node[0] == 0) { node = NULL; /* == any */ } else { node = ctx_tcp_pi->node; } if (ctx_tcp_pi->service[0] == 0) { service = "502"; } else { service = ctx_tcp_pi->service; } memset(&ai_hints, 0, sizeof (ai_hints)); /* If node is not NULL, than the AI_PASSIVE flag is ignored. */ ai_hints.ai_flags |= AI_PASSIVE;#ifdef AI_ADDRCONFIG ai_hints.ai_flags |= AI_ADDRCONFIG;#endif ai_hints.ai_family = AF_UNSPEC; ai_hints.ai_socktype = SOCK_STREAM; ai_hints.ai_addr = NULL; ai_hints.ai_canonname = NULL; ai_hints.ai_next = NULL; ai_list = NULL; rc = getaddrinfo(node, service, &ai_hints, &ai_list); if (rc != 0) { if (ctx->debug) { fprintf(stderr, "Error returned by getaddrinfo: %s\n", gai_strerror(rc)); } errno = ECONNREFUSED; return -1; } new_s = -1; for (ai_ptr = ai_list; ai_ptr != NULL; ai_ptr = ai_ptr->ai_next) { int flags = ai_ptr->ai_socktype; int s;#ifdef SOCK_CLOEXEC flags |= SOCK_CLOEXEC;#endif s = socket(ai_ptr->ai_family, flags, ai_ptr->ai_protocol); if (s < 0) { if (ctx->debug) { perror("socket"); } continue; } else { int enable = 1; rc = setsockopt(s, SOL_SOCKET, SO_REUSEADDR, (void *)&enable, sizeof (enable)); if (rc != 0) { close(s); if (ctx->debug) { perror("setsockopt"); } continue; } } rc = bind(s, ai_ptr->ai_addr, ai_ptr->ai_addrlen); if (rc != 0) { close(s); if (ctx->debug) { perror("bind"); } continue; } rc = listen(s, nb_connection); if (rc != 0) { close(s); if (ctx->debug) { perror("listen"); } continue; } new_s = s; break; } freeaddrinfo(ai_list); if (new_s < 0) { return -1; } return new_s;}int modbus_tcp_accept(modbus_t *ctx, int *s){ struct sockaddr_in addr; socklen_t addrlen; if (ctx == NULL) { errno = EINVAL; return -1; } addrlen = sizeof(addr);#ifdef HAVE_ACCEPT4 /* Inherit socket flags and use accept4 call */ ctx->s = accept4(*s, (struct sockaddr *)&addr, &addrlen, SOCK_CLOEXEC);#else ctx->s = accept(*s, (struct sockaddr *)&addr, &addrlen);#endif if (ctx->s == -1) { return -1; } if (ctx->debug) { printf("The client connection from %s is accepted\n", inet_ntoa(addr.sin_addr)); } return ctx->s;}int modbus_tcp_pi_accept(modbus_t *ctx, int *s){ struct sockaddr_storage addr; socklen_t addrlen; if (ctx == NULL) { errno = EINVAL; return -1; } addrlen = sizeof(addr);#ifdef HAVE_ACCEPT4 /* Inherit socket flags and use accept4 call */ ctx->s = accept4(*s, (struct sockaddr *)&addr, &addrlen, SOCK_CLOEXEC);#else ctx->s = accept(*s, (struct sockaddr *)&addr, &addrlen);#endif if (ctx->s == -1) { return -1; } if (ctx->debug) { printf("The client connection is accepted.\n"); } return ctx->s;}static int _modbus_tcp_select(modbus_t *ctx, fd_set *rset, struct timeval *tv, int length_to_read){ int s_rc; while ((s_rc = select(ctx->s+1, rset, 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(rset); FD_SET(ctx->s, rset); } else { return -1; } } if (s_rc == 0) { errno = ETIMEDOUT; return -1; } return s_rc;}static void _modbus_tcp_free(modbus_t *ctx) { free(ctx->backend_data); free(ctx);}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_receive, _modbus_tcp_recv, _modbus_tcp_check_integrity, _modbus_tcp_pre_check_confirmation, _modbus_tcp_connect, _modbus_tcp_close, _modbus_tcp_flush, _modbus_tcp_select, _modbus_tcp_free};const modbus_backend_t _modbus_tcp_pi_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_receive, _modbus_tcp_recv, _modbus_tcp_check_integrity, _modbus_tcp_pre_check_confirmation, _modbus_tcp_pi_connect, _modbus_tcp_close, _modbus_tcp_flush, _modbus_tcp_select, _modbus_tcp_free};modbus_t* modbus_new_tcp(const char *ip, int port){ modbus_t *ctx; modbus_tcp_t *ctx_tcp; size_t dest_size; size_t ret_size;#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, "Could not install SIGPIPE handler.\n"); return NULL; }#endif ctx = (modbus_t *)malloc(sizeof(modbus_t)); if (ctx == NULL) { return NULL; } _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)); if (ctx->backend_data == NULL) { modbus_free(ctx); errno = ENOMEM; return NULL; } ctx_tcp = (modbus_tcp_t *)ctx->backend_data; if (ip != NULL) { dest_size = sizeof(char) * 16; ret_size = strlcpy(ctx_tcp->ip, ip, dest_size); if (ret_size == 0) { fprintf(stderr, "The IP string is empty\n"); modbus_free(ctx); errno = EINVAL; return NULL; } if (ret_size >= dest_size) { fprintf(stderr, "The IP string has been truncated\n"); modbus_free(ctx); errno = EINVAL; return NULL; } } else { ctx_tcp->ip[0] = '0'; } ctx_tcp->port = port; ctx_tcp->t_id = 0; return ctx;}modbus_t* modbus_new_tcp_pi(const char *node, const char *service){ modbus_t *ctx; modbus_tcp_pi_t *ctx_tcp_pi; size_t dest_size; size_t ret_size; ctx = (modbus_t *)malloc(sizeof(modbus_t)); if (ctx == NULL) { return NULL; } _modbus_init_common(ctx); /* Could be changed after to reach a remote serial Modbus device */ ctx->slave = MODBUS_TCP_SLAVE; ctx->backend = &_modbus_tcp_pi_backend; ctx->backend_data = (modbus_tcp_pi_t *)malloc(sizeof(modbus_tcp_pi_t)); if (ctx->backend_data == NULL) { modbus_free(ctx); errno = ENOMEM; return NULL; } ctx_tcp_pi = (modbus_tcp_pi_t *)ctx->backend_data; if (node == NULL) { /* The node argument can be empty to indicate any hosts */ ctx_tcp_pi->node[0] = 0; } else { dest_size = sizeof(char) * _MODBUS_TCP_PI_NODE_LENGTH; ret_size = strlcpy(ctx_tcp_pi->node, node, dest_size); if (ret_size == 0) { fprintf(stderr, "The node string is empty\n"); modbus_free(ctx); errno = EINVAL; return NULL; } if (ret_size >= dest_size) { fprintf(stderr, "The node string has been truncated\n"); modbus_free(ctx); errno = EINVAL; return NULL; } } if (service != NULL) { dest_size = sizeof(char) * _MODBUS_TCP_PI_SERVICE_LENGTH; ret_size = strlcpy(ctx_tcp_pi->service, service, dest_size); } else { /* Empty service is not allowed, error caught below. */ ret_size = 0; } if (ret_size == 0) { fprintf(stderr, "The service string is empty\n"); modbus_free(ctx); errno = EINVAL; return NULL; } if (ret_size >= dest_size) { fprintf(stderr, "The service string has been truncated\n"); modbus_free(ctx); errno = EINVAL; return NULL; } ctx_tcp_pi->t_id = 0; return ctx;}

04. 预留

05. 附录

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喝酒易醉，品茶养心，人生如梦，品茶悟道，何以解忧？唯有杜康！

-- 愿君每日到此一游！