我有一个问题，我需要在连接之前确定主机是否存在。此主机不能与函数gethostbyaddr()一起使用，因为它不是基于PC的，并且不返回主机信息。它仅基于IP。每当我尝试在IP地址上调用gethostbyaddr()时，WinSock都会返回 11004 （WSANODATA）。
在尝试连接之前是否有类似的功能（除ping之外）确定IP是否有效？
答案 0 :(得分：2)
如果您对目标主机有某种控制权，可以定期检查主机是否存在而不使用临时端口的一种方法是发送UDP数据报，并等待ICMP响应告诉您数据报被主持人拒绝。
您可以通过创建SOCK_DGRAM套接字，绑定到本地端口，并调用sendto（）发送到未侦听的已知远程端口来完成此操作。然后，您可以轮询并调用recvfrom（），如果您的主机收到ICMP响应，则应该给出错误。如果主机没有启动，那么您将无法获得响应。您可以使用相同的端口重用相同的套接字，以定期发送所需数量的数据报。
发送ICMP echo请求需要大多数系统的高权限，因此很难直接从您的代码中执行。
以下是一些示例代码，大致与我的描述相同：
struct sockaddr_in local_address;
struct sockaddr_in remote_address;
int sfd;
char * remote_host;
int s;
fd_set fds;
struct timeval timeout;
remote_host = argv[1];
sfd = socket(AF_INET, SOCK_DGRAM, 0);
if (sfd < 0) {
perror("socket");
}
memset(&local_address, 0, sizeof(struct sockaddr_in));
local_address.sin_family = AF_INET;
local_address.sin_addr.s_addr = INADDR_ANY;
local_address.sin_port = htons(6799);
s = bind(sfd,
(struct sockaddr*)&local_address,
sizeof(local_address));
if (s != 0) {
perror("bind");
exit(1);
}
memset(&remote_address, 0, sizeof(struct sockaddr_in));
remote_address.sin_family = AF_INET;
remote_address.sin_addr.s_addr = inet_addr(remote_host);
remote_address.sin_port = htons(6799);
s = sendto(sfd,
"MSG",
3,
0,
(struct sockaddr*)&remote_address,
sizeof(remote_address));
if (s != 3) {
perror("sento");
exit(1);
}
FD_ZERO(&fds);
FD_SET(sfd, &fds);
timeout.tv_sec = 5;
timeout.tv_usec = 0;
s = select(sfd + 1, &fds, 0, 0, &timeout);
if (s == 1) {
char buf[512];
printf("Got data, host is up\n");
s = recvfrom(sfd, &buf[0], 512, 0, 0, 0);
perror("recvfrom");
} else {
printf("Timeout, host is down\n");
}
答案 1 :(得分：1)
我通过使用内置的Windows API for PING解决了这个问题。我将gethostbyname()更改为inet_addr。
显示在此处：ICMP.DLL Method
<强> dllping.cpp
// Borland C++ 5.0: bcc32.cpp ping.cpp
// Visual C++ 5.0: cl ping.cpp wsock32.lib
//
// This sample program is hereby placed in the public domain.
#include <iostream.h>
#include <winsock.h>
#include <windowsx.h>
#include "icmpdefs.h"
int doit(int argc, char* argv[])
{
// Check for correct command-line args
if (argc < 2) {
cerr << "usage: ping <host>" << endl;
return 1;
}
// Load the ICMP.DLL
HINSTANCE hIcmp = LoadLibrary("ICMP.DLL");
if (hIcmp == 0) {
cerr << "Unable to locate ICMP.DLL!" << endl;
return 2;
}
// Look up an IP address for the given host name
struct hostent* phe;
if ((phe = gethostbyname(argv[1])) == 0) {
cerr << "Could not find IP address for " << argv[1] << endl;
return 3;
}
// Get handles to the functions inside ICMP.DLL that we'll need
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?
pfnHV pIcmpCreateFile;
pfnBH pIcmpCloseHandle;
pfnDHDPWPipPDD pIcmpSendEcho;
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;
}
// Open the ping service
HANDLE hIP = pIcmpCreateFile();
if (hIP == INVALID_HANDLE_VALUE) {
cerr << "Unable to open ping service." << endl;
return 5;
}
// Build ping packet
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);
// Send the ping packet
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;
}
// Shut down...
GlobalFree(pIpe);
FreeLibrary(hIcmp);
return 0;
}
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;
}
<强> icmpdefs.h
// Structures required to use functions in ICMP.DLL
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;
答案 2 :(得分：0)
在这里，您可以在C ++中找到short DNS resolver的来源。
答案 3 :(得分：0)
DNS查询不会帮助您确定框是否已启动（这似乎是您尝试做的事情）。
如果您可以在目标框上运行进程，则可以运行某种心跳服务，该服务将接受来自监控应用程序的TCP连接，并每2.5秒发送一次“我活着”消息。无法连接或缺少心跳会告诉您的监控应用程序存在问题。
或者（也许更直接），为什么不使用ICMP ping？
答案 4 :(得分：0)
如果您只允许一定数量的临时端口，请停止使用临时端口。将源套接字绑定到已知端口号，然后再使用它尝试连接到另一台机器。
或者，您没有说明为什么要避免ping。如果它只是在代码中执行它，您可以自己生成ICMP数据包并使用它。