PING 在网络探测中的应用

     最近在做P2P方面的软件项目，发现一个问题：如果用户不注意的情况下使用防火墙禁止软件访问网络，那么软件基本不能正常工作，并且用户对此毫不知情。因此我们希望能够实现一种检查机制，如果发现网络连接失败，那么弹出对话框提示用户可能是防火墙设置的原因。问题是实际情况下既有可能是防火墙的原因也有可能就是用户没有联网。因此我们必须能够识别这两种情况，防止错误的提示。测试了两款防火墙软件后，发现即使在应用程序被禁止访问网络的情况下，使用PING仍然能够正常地工作（不熟悉防火墙的原理），所以萌生了在网络异常的情况下采用PING来探测用户的网络是否真的可用：如果软件无法正常地访问网络而PING能够正常工作，那么有可能就是防火墙的问题。

     Windows自带了一套PING的API，放在ICMP.DLL中。下面给出一个使用ICMP.DLL进行编程的例子，该代码是从一位名为MarkG的家伙的GUI程序中取出来的，转自网上某位仁兄的blog，我这算是转帖。

 

#include <iostream.h>
#include <winsock.h>
#include <windowsx.h>
#include "icmpdefs.h"

 

==================ping的实现部分==================
int doit(int argc, char* argv[])
{

//[bugfree] 建议将这个argc和argv的处理拿到main函数中
    // 检查命令行参数
    if (argc < 2) {
        cerr << "usage: ping <host>" << endl;
        return 1;
    }
    
    // 装载ICMP.DLL连接库
    HINSTANCE hIcmp = LoadLibrary("ICMP.DLL");
    if (hIcmp == 0) {
        cerr << "Unable to locate ICMP.DLL!" << endl;
        return 2;
    }

    // 查找给定机器的IP地址信息
    struct hostent* phe;
    if ((phe = gethostbyname(argv[1])) == 0) {
        cerr << "Could not find IP address for " << argv[1] << endl;
        return 3;
    }

    // 定义函数三个指针类型
    typedef HANDLE (WINAPI* pfnHV)(VOID);
    typedef BOOL (WINAPI* pfnBH)(HANDLE);
    typedef DWORD (WINAPI* pfnDHDPWPipPDD)(HANDLE, DWORD, LPVOID, WORD,
            PIP_OPTION_INFORMATION, LPVOID, DWORD, DWORD); // evil, no?

    //定义三个指针函数
    pfnHV pIcmpCreateFile;
    pfnBH pIcmpCloseHandle;
    pfnDHDPWPipPDD pIcmpSendEcho;
    
    //从ICMP.DLL中得到函数入口地址
    pIcmpCreateFile = (pfnHV)GetProcAddress(hIcmp, "IcmpCreateFile");
    pIcmpCloseHandle = (pfnBH)GetProcAddress(hIcmp, "IcmpCloseHandle");
    pIcmpSendEcho = (pfnDHDPWPipPDD)GetProcAddress(hIcmp, "IcmpSendEcho");
    if ((pIcmpCreateFile == 0) || (pIcmpCloseHandle == 0) || (pIcmpSendEcho == 0))

{
        cerr << "Failed to get proc addr for function." << endl;
        return 4;
    }

    // 打开ping服务
    HANDLE hIP = pIcmpCreateFile();
    if (hIP == INVALID_HANDLE_VALUE) {
        cerr << "Unable to open ping service." << endl;
        return 5;
    }
   
    // 构造ping数据包
    char acPingBuffer[64];
    memset(acPingBuffer, '/xAA', sizeof(acPingBuffer));
    PIP_ECHO_REPLY pIpe = (PIP_ECHO_REPLY)GlobalAlloc( GMEM_FIXED | GMEM_ZEROINIT,
            sizeof(IP_ECHO_REPLY) + sizeof(acPingBuffer)); 
    if (pIpe == 0)

{
        cerr << "Failed to allocate global ping packet buffer." << endl;
        return 6;
    }
    pIpe->Data = acPingBuffer;
    pIpe->DataSize = sizeof(acPingBuffer);     

    // 发送ping数据包
    DWORD dwStatus = pIcmpSendEcho(hIP, *((DWORD*)phe->h_addr_list[0]), 
            acPingBuffer, sizeof(acPingBuffer), NULL, pIpe, 
            sizeof(IP_ECHO_REPLY) + sizeof(acPingBuffer), 5000);
    if (dwStatus != 0) {
        cout << "Addr: " <<
                int(LOBYTE(LOWORD(pIpe->Address))) << "." <<
                int(HIBYTE(LOWORD(pIpe->Address))) << "." <<
                int(LOBYTE(HIWORD(pIpe->Address))) << "." <<
                int(HIBYTE(HIWORD(pIpe->Address))) << ", " <<
                "RTT: " << int(pIpe->RoundTripTime) << "ms, " <<
                "TTL: " << int(pIpe->Options.Ttl) << endl;
    }else

{
        cerr << "Error obtaining info from ping packet." << endl;
    }

    // 关闭,回收资源
    GlobalFree(pIpe);
    FreeLibrary(hIcmp);
    return 0;
}

==================主函数==================
int main(int argc, char* argv[])
{
WSAData wsaData;
    if (WSAStartup(MAKEWORD(1, 1), &wsaData) != 0)

{
        return 255;
    }

    int retval = doit(argc, argv);

    WSACleanup();
    return retval;
}

 

 

==================头文件==================
icmpdefs.h
//ICMP.DLL 函数中需要的结构

typedef struct {
unsigned char Ttl;                         // Time To Live
unsigned char Tos;                         // Type Of Service
    unsigned char Flags;                       // IP header flags
    unsigned char OptionsSize;                 // Size in bytes of options data
    unsigned char *OptionsData;                // Pointer to options data
} IP_OPTION_INFORMATION, * PIP_OPTION_INFORMATION;

typedef struct {
    DWORD Address;                             // Replying address
    unsigned long Status;                     // Reply status
    unsigned long RoundTripTime;              // RTT in milliseconds
    unsigned short DataSize;                   // Echo data size
    unsigned short Reserved;                   // Reserved for system use
    void *Data;                                // Pointer to the echo data
    IP_OPTION_INFORMATION Options;             // Reply options
} IP_ECHO_REPLY, * PIP_ECHO_REPLY;

 

     该代码会返回PING消息的结果，如果PING操作失败那么pIcmpSendEcho函数返回为0，否则可以得到RTT和TTL的信息。我们在代码中借此来判断主机的网络是否是正常的。