实现网络连通检测的五种方法

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方法一：

  • windows下调用icmp.dll库，实现ping连通检测，缺点是不能跨平台，受限于icmp.dll库：
// windows下调用icmp.dll库实现网络连通检测示例代码

#include <Winsock2.h>
#include <iphlpapi.h> 
#include <stdio.h>
   
#pragma comment(lib,"Iphlpapi.lib")
#pragma comment(lib,"Ws2_32.lib")
typedef HANDLE (WINAPI* ICMPCREATEFILE)(VOID);   
typedef BOOL (WINAPI* ICMPCLOSEHANDLE)(HANDLE);   
typedef DWORD (WINAPI* ICMPSENDECHO)(HANDLE, DWORD, LPVOID, WORD,PIP_OPTION_INFORMATION, LPVOID, DWORD, DWORD);    
                       
// 定义三个指针函数   
ICMPCREATEFILE pIcmpCreateFile;   
ICMPCLOSEHANDLE pIcmpCloseHandle;   
ICMPSENDECHO pIcmpSendEcho; 

// 函数功能：初始化ICMP函数：
BOOL InitIcmp()   
{   
    HINSTANCE hIcmp = LoadLibrary(TEXT("ICMP.DLL"));    // 需自行下载icmp.dll动态库
    if(hIcmp==NULL)
    {   
        return false; 
    }  
    pIcmpCreateFile = (ICMPCREATEFILE)GetProcAddress(hIcmp,"IcmpCreateFile");   
    pIcmpCloseHandle = (ICMPCLOSEHANDLE)GetProcAddress(hIcmp,"IcmpCloseHandle");   
    pIcmpSendEcho = (ICMPSENDECHO)GetProcAddress(hIcmp,"IcmpSendEcho");   
    if ((pIcmpCreateFile == NULL)||(pIcmpCloseHandle == NULL)||(pIcmpSendEcho == NULL))   
        return false;   
    return true;   
}

// 函数功能：判断是否能ping通IP
// 函数参数：IP地址或域名
BOOL ICMPPing(char* host) 
{   
    DWORD timeOut=1000;                                    // 设置超时   
    ULONG hAddr=inet_addr(host);                           // 如果是IP地址就直接转换   
    if(hAddr==INADDR_NONE)   
    {   
        hostent* hp=gethostbyname(host);                   // 如果是域名就用DNS解析出IP地址   
        if(hp)   
            memcpy(&hAddr,hp->h_addr_list,hp->h_length);   // IP地址   
        else
        {   
            return false;   
        }   
    }   
    HANDLE hIp=pIcmpCreateFile();   
    IP_OPTION_INFORMATION ipoi;   
    memset(&ipoi,0,sizeof(IP_OPTION_INFORMATION));   
    ipoi.Ttl =128;                  //Time-To-Live   
                    
    unsigned char pSend[36];                               // 发送包   
    memset(pSend,'E',32);   
                    
    int repSize=sizeof(ICMP_ECHO_REPLY)+32;   
    unsigned char pReply[100];                             // 接收包   
    ICMP_ECHO_REPLY* pEchoReply=(ICMP_ECHO_REPLY*)pReply;   
                    
    DWORD nPackets=pIcmpSendEcho(hIp,hAddr,pSend,32,&ipoi,pReply,repSize,timeOut);    // 发送ICMP数据报文   
                    
    if(pEchoReply->Status!=0)             // 超时，可能是主机禁用了ICMP 或者目标主机不存在  
    {   
        pIcmpCloseHandle(hIp);   
        return false;   
    }   
                    
    pIcmpCloseHandle(hIp);   
    return true;   
}
int main()
{
    InitIcmp();

    if (true == ICMPPing("127.0.0.1"))
    {
        printf("OK.
");
    }
    else
    {
        printf("NOT.
");
    }

    system("pause");

    return 0;
}

方法二：

  • 使用原始套接字，模拟实现ping程序以进行网络连通检测，可跨平台，缺点是在linux下使用原始套接字必须拥有超级用户权限：
// 模拟实现ping程序，跨平台检测网络连接

#ifdef _WIN32
#include <WinSock2.h>
#pragma comment(lib, "WS2_32")

struct WindowsSocketLibInit
{
    WindowsSocketLibInit()
    {
        WSADATA wsaData;
        WORD sockVersion = MAKEWORD(2, 2);
        WSAStartup(sockVersion, &wsaData);
    }
    ~WindowsSocketLibInit()
    {
        WSACleanup();
    }
} INITSOCKETGLOBALVARIABLE;
#else
#include <unistd.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <arpa/inet.h>
#include <ctime>
#include <cstdlib>
#include <cstdint>
#include <cstring>
#endif

#include <string>
#include <limits>

unsigned short getChecksum(unsigned short *buff, unsigned size);

bool ping(std::string ip)
{
    static unsigned INDEX = 0;
    const unsigned IP_HEADER_LENGTH = 20;
    const unsigned FILL_LENGTH = 32;

    struct IcmpHdr
    {
        unsigned char icmpType;
        unsigned char icmpCode;
        unsigned short icmpChecksum;
        unsigned short icmpId;
        unsigned short icmpSequence;
    };

    int socketFd = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);

    int timeoutTick = 200;
    setsockopt(socketFd, SOL_SOCKET, SO_RCVTIMEO, (char *)&timeoutTick, sizeof(timeoutTick));

    sockaddr_in des = {AF_INET, htons(0)};
    des.sin_addr.s_addr = inet_addr(ip.c_str());

    char buff[sizeof(IcmpHdr) + FILL_LENGTH] = {0};
    IcmpHdr *pIcmpHdr = (IcmpHdr *)(buff);

    unsigned short id = std::rand() % (std::numeric_limits<unsigned short>::max)();

    pIcmpHdr->icmpType = 8;
    std::cout << "---" << pIcmpHdr->icmpType << std::endl;
    pIcmpHdr->icmpCode = 0;
    pIcmpHdr->icmpId = id;
    pIcmpHdr->icmpSequence = INDEX++;
    std::memcpy(&buff[sizeof(IcmpHdr)], "TestTest", sizeof("TestTest"));
    pIcmpHdr->icmpChecksum = getChecksum((unsigned short *)buff, sizeof(buff));

    if (-1 == sendto(socketFd, buff, sizeof(buff), 0, (sockaddr *)&des, sizeof(des)))
    {
        return false;
    }

    char recv[1 << 10];
    int ret = recvfrom(socketFd, recv, sizeof(recv), 0, NULL, NULL);
    if (-1 == ret || ret < IP_HEADER_LENGTH + sizeof(IcmpHdr))
    {
        return false;
    }
    IcmpHdr *pRecv = (IcmpHdr *)(recv + IP_HEADER_LENGTH);

    return !(pRecv->icmpType != 0 || pRecv->icmpId != id);
}

unsigned short getChecksum(unsigned short *buff, unsigned size)
{
    unsigned long ret = 0;
    for (unsigned i = 0; i < size; i += sizeof(unsigned short))
    {
        ret += *buff++;
    }
    if (size & 1)
    {
        ret += *(unsigned char *)buff;
    }
    ret = (ret >> 16) + (ret & 0xFFFF);
    ret += ret >> 16;

    return (unsigned short)~ret;
}

方法三：

  • 使用非阻塞connect函数和select定时相结合来检测网络连通，可跨平台，以下为windows下实现代码：
// 使用非阻塞connect和select定时检测解决connect失败时阻塞时间过长的问题

#include <stdio.h>  
#include <winsock2.h>  
#pragma comment(lib, "ws2_32.lib")  
  
int main()  
{  
    // 网络初始化  
    WORD wVersionRequested;  
    WSADATA wsaData;  
    wVersionRequested = MAKEWORD(2, 2);  
    WSAStartup( wVersionRequested, &wsaData );  

    // 创建客户端socket(默认为是阻塞socket)  
    SOCKET sockClient = socket(AF_INET, SOCK_STREAM, 0);  

    // 设置为非阻塞的socket  
    int iMode = 1;  
    ioctlsocket(sockClient, FIONBIO, (u_long FAR*)&iMode);   
        
    // 定义服务端  
    SOCKADDR_IN addrSrv;  
    addrSrv.sin_addr.S_un.S_addr = inet_addr("192.168.26.67");  
    addrSrv.sin_family = AF_INET;  
    addrSrv.sin_port = htons(31800);  

    // 超时时间  
    struct timeval tm;  
    tm.tv_sec  = 0;  
    tm.tv_usec = 5000;  
    int ret = -1;  

    // 尝试去连接服务端  
    if (-1 != connect(sockClient, (SOCKADDR*)&addrSrv, sizeof(SOCKADDR)))  
    {  
        ret = 1; // 连接成功  
    }  
    else  
    {  
        fd_set set;  
        FD_ZERO(&set);  
        FD_SET(sockClient, &set);  

        if (select(-1, NULL, &set, NULL, &tm) <= 0)  
        {  
            ret = -1; // 有错误(select错误或者超时)  
        }  
        else  
        {  
            int error = -1;  
            int optLen = sizeof(int);  
            getsockopt(sockClient, SOL_SOCKET, SO_ERROR, (char*)&error, &optLen);   

            // 之所以下面的程序不写成三目运算符的形式， 是为了更直观， 便于注释  
            if (0 != error)  
            {  
                ret = -1; // 有错误  
            }  
            else  
            {  
                ret = 1;  // 无错误  
            }  
        }  
    }  

    // 设回为阻塞socket  
    iMode = 0;  
    ioctlsocket(sockClient, FIONBIO, (u_long FAR*)&iMode); //设置为阻塞模式  

    // connect状态  
    if (-1 == ret) {
        printf("error
");
    } else if (1 == ret) {
        printf("success");
    }
    //printf("ret is %d
", ret);  

    // 发送数据到服务端测试以下  
    if(1 == ret)  
    {  
        send(sockClient, "hello world", strlen("hello world") + 1, 0);  
    }  

    // 释放网络连接  
    closesocket(sockClient);  
    WSACleanup();  
    
    getchar();
  
    return 0;  
}

方法四：

  • 使用setsockopt函数设定socket连接、接收和发送的响应时间，可以通过connect之前设定SO_SNDTIMO来达到控制连接超时的目的：
// 自行添加相应头文件

int main(int argc, char *argv[])
{
    int fd;

    struct sockaddr_in addr;

    struct timeval timeo = {3, 0};

    socklen_t len = sizeof(timeo);

    fd = socket(AF_INET, SOCK_STREAM, 0);  
    if (argc == 4)  
        timeo.tv_sec = atoi(argv[3]);  

    setsockopt(fd, SOL_SOCKET, SO_SNDTIMEO, &timeo, len);  
    addr.sin_family = AF_INET;  
    addr.sin_addr.s_addr = inet_addr(argv[1]);  
    addr.sin_port = htons(atoi(argv[2]));  

    if (connect(fd, (struct sockaddr*)&addr, sizeof(addr)) == -1) {  
        if (errno == EINPROGRESS) {  
            fprintf(stderr, "timeout/n");  
            return -1;  
        }         
        perror("connect");  
        return 0;  
    }         
    printf("connected/n");  

    return 0;
}

方法五：

  • linux下直接调用执行ping子程序以实现检测网络连通功能：
// 自行添加相应代码文件

int go_ping(char *svrip)
{
    int i = 0;
    while(i < 3)
    {
        pid_t pid;
        if ((pid = vfork()) < 0) 
        {
            printf("vfork error");
            exit(1);
        } 
        else if (pid == 0) 
        {
            if ( execlp("ping", "ping","-c 1",svrip, (char*)0) < 0)
            {
                printf("execlp error
");
                exit(1);
            }
        }

        int stat;
        waitpid(pid, &stat, 0);

        if (stat == 0)
        {
            return 0;
        }
        sleep(3);
        i++;
    }
    return -1;
}

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