嵌入式Libmodbus源码分析-TCP相关函数分析
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00. 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 <stephane.raimbault@gmail.com>
*
* 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 32
typedef 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 <stephane.raimbault@gmail.com>
*
* 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 <errno.h> */
#include <winsock2.h>
#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 <stephane.raimbault@gmail.com>
*
* 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 <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#ifndef _MSC_VER
#include <unistd.h>
#endif
#include <signal.h>
#include <sys/types.h>
#if defined(_WIN32)
/* Already set in modbus-tcp.h but it seems order matters in VS2005 */
# 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>
# include <netdb.h>
#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_WIN32
static 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;
}
#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 */
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
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