如何解决如何使用 select() 为套接字设置计时器？
我目前正在使用 Winsock2 来测试与多个本地 telnet 服务器的连接，但如果服务器连接失败，default Winsock client 将永远超时。
我从其他帖子中看到 select() 可以为连接部分设置超时，而 setsockopt() 和 timeval 可以使代码的接收部分超时，但我有也不知道如何实施。我从其他答案中复制/粘贴的代码片段对我来说似乎总是失败。
我将如何在默认客户端代码中使用这两个函数？或者，如果无法在默认客户端代码中使用这些函数，有人能给我一些有关如何正确使用这些函数的指示吗？
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdlib.h>
#include <stdio.h>
#include <ctime>
// Need to link with Ws2_32.lib,Mswsock.lib,and Advapi32.lib
#pragma comment (lib,"Ws2_32.lib")
#pragma comment (lib,"Mswsock.lib")
#pragma comment (lib,"AdvApi32.lib")
#define DEFAULT_BUFLEN 512
#define DEFAULT_PORT "23"
int __cdecl main(int argc,char** argv)
{
WSADATA wsaData;
SOCKET ConnectSocket = INVALID_SOCKET;
struct addrinfo* result = NULL,* ptr = NULL,hints;
const char* sendbuf = "this is a test";
char recvbuf[DEFAULT_BUFLEN];
int iResult;
int recvbuflen = DEFAULT_BUFLEN;
// Validate the parameters
if (argc != 2) {
printf("usage: %s server-name\n",argv[0]);
return 1;
}
// Initialize Winsock
iResult = WSAStartup(MAKEWORD(2,2),&wsaData);
if (iResult != 0) {
printf("WSAStartup Failed with error: %d\n",iResult);
return 1;
}
ZeroMemory(&hints,sizeof(hints));
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
hints.ai_protocol = IPPROTO_TCP;
/*
struct timeval timeout;
timeout.tv_sec = 10;
timeout.tv_usec = 0;
if (setsockopt(ConnectSocket,SOL_SOCKET,SO_RCVTIMEO,(char*)&timeout,sizeof(timeout)) < 0) {
printf("setsockopt Failed\n");
}
*/
// Resolve the server address and port
iResult = getaddrinfo(argv[1],DEFAULT_PORT,&hints,&result);
if (iResult != 0) {
printf("getaddrinfo Failed with error: %d\n",iResult);
WSACleanup();
return 1;
}
// Attempt to connect to an address until one succeeds
for (ptr = result; ptr != NULL; ptr = ptr->ai_next) {
// Create a SOCKET for connecting to server
ConnectSocket = socket(ptr->ai_family,ptr->ai_socktype,ptr->ai_protocol);
if (ConnectSocket == INVALID_SOCKET) {
printf("socket Failed with error: %ld\n",WSAGetLastError());
WSACleanup();
return 1;
}
// Connect to server.
iResult = connect(ConnectSocket,ptr->ai_addr,(int)ptr->ai_addrlen);
if (iResult == SOCKET_ERROR) {
closesocket(ConnectSocket);
ConnectSocket = INVALID_SOCKET;
continue;
}
break;
}
freeaddrinfo(result);
if (ConnectSocket == INVALID_SOCKET) {
printf("Unable to connect to server!\n");
WSACleanup();
return 1;
}
// Send an initial buffer
iResult = send(ConnectSocket,sendbuf,(int)strlen(sendbuf),0);
if (iResult == SOCKET_ERROR) {
printf("send Failed with error: %d\n",WSAGetLastError());
closesocket(ConnectSocket);
WSACleanup();
return 1;
}
printf("Bytes Sent: %ld\n",iResult);
// shutdown the connection since no more data will be sent
iResult = shutdown(ConnectSocket,SD_SEND);
if (iResult == SOCKET_ERROR) {
printf("shutdown Failed with error: %d\n",WSAGetLastError());
closesocket(ConnectSocket);
WSACleanup();
return 1;
}
// Receive until the peer closes the connection
do {
iResult = recv(ConnectSocket,recvbuf,recvbuflen,0);
if (iResult > 0)
printf("Bytes received: %d\n",iResult);
else if (iResult == 0)
printf("Connection closed\n");
else
printf("recv Failed with error: %d\n",WSAGetLastError());
} while (iResult > 0);
// cleanup
closesocket(ConnectSocket);
WSACleanup();
return 0;
}
解决方法
select() 可以设置连接部分的超时时间。
是的，但前提是你在调用 connect() 之前将套接字置于非阻塞模式，以便 connect() 立即退出，然后代码可以使用 select() 等待套接字连接操作完成时报告。但显示的代码并没有这样做。
setsockopt() 和 timeval 可以使代码的接收部分超时
是的，不过 select() 也可用于超时读取操作。只需先调用 select()，然后仅在 recv() 报告套接字可读（有待读取的数据）时调用 select()。
尝试这样的事情：
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdlib.h>
#include <stdio.h>
#include <ctime>
// Need to link with Ws2_32.lib,Mswsock.lib,and Advapi32.lib
#pragma comment (lib,"Ws2_32.lib")
#pragma comment (lib,"Mswsock.lib")
#pragma comment (lib,"AdvApi32.lib")
#define DEFAULT_BUFLEN 512
#define DEFAULT_PORT "23"
int __cdecl main(int argc,char** argv)
{
WSADATA wsaData;
SOCKET ConnectSocket = INVALID_SOCKET;
struct addrinfo *result = NULL,*ptr = NULL,hints;
const char* sendbuf = "this is a test";
char recvbuf[DEFAULT_BUFLEN];
int iResult;
int recvbuflen = DEFAULT_BUFLEN;
// Validate the parameters
if (argc != 2) {
printf("usage: %s server-name\n",argv[0]);
return 1;
}
// Initialize Winsock
iResult = WSAStartup(MAKEWORD(2,2),&wsaData);
if (iResult != 0) {
printf("WSAStartup failed with error: %d\n",iResult);
return 1;
}
ZeroMemory(&hints,sizeof(hints));
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
hints.ai_protocol = IPPROTO_TCP;
// Resolve the server address and port
iResult = getaddrinfo(argv[1],DEFAULT_PORT,&hints,&result);
if (iResult != 0) {
printf("getaddrinfo failed with error: %d\n",iResult);
WSACleanup();
return 1;
}
// Attempt to connect to an address until one succeeds
for (ptr = result; ptr != NULL; ptr = ptr->ai_next) {
// Create a SOCKET for connecting to server
ConnectSocket = socket(ptr->ai_family,ptr->ai_socktype,ptr->ai_protocol);
if (ConnectSocket == INVALID_SOCKET) {
printf("socket failed with error: %ld\n",WSAGetLastError());
WSACleanup();
return 1;
}
// put the socket into non-blocking mode just for connect()
int iMode = 1;
iResult = ioctlsocket(ConnectSocket,FIONBIO,&iMode);
if (iResult == SOCKET_ERROR)
closesocket(ConnectSocket);
ConnectSocket = INVALID_SOCKET;
continue;
}
// Connect to server.
iResult = connect(ConnectSocket,ptr->ai_addr,(int)ptr->ai_addrlen);
if (iResult == SOCKET_ERROR) {
if (WSAGetLastError() != WSAEWOULDBLOCK) {
closesocket(ConnectSocket);
ConnectSocket = INVALID_SOCKET;
continue;
}
// wait for the connect to finish
fd_set fds;
FD_ZERO(&fds);
FD_SET(ConnectSocket,&fds);
struct timeval timeout;
timeout.tv_sec = 10;
timeout.tv_usec = 0;
iResult = select(0,NULL,&fds,&timeout);
if (iResult <= 0) {
closesocket(ConnectSocket);
ConnectSocket = INVALID_SOCKET;
continue;
}
}
// put the socket back into blocking mode
iMode = 0;
iResult = ioctlsocket(ConnectSocket,&iMode);
if (iResult == SOCKET_ERROR) {
closesocket(ConnectSocket);
ConnectSocket = INVALID_SOCKET;
continue;
}
break;
}
freeaddrinfo(result);
if (ConnectSocket == INVALID_SOCKET) {
printf("Unable to connect to server!\n");
WSACleanup();
return 1;
}
struct timeval timeout;
timeout.tv_sec = 10;
timeout.tv_usec = 0;
// set a read timeout
if (setsockopt(ConnectSocket,SOL_SOCKET,SO_RCVTIMEO,(char*)&timeout,sizeof(timeout)) == SOCKET_ERROR) {
printf("setsockopt failed\n");
}
// Send an initial buffer
iResult = send(ConnectSocket,sendbuf,(int)strlen(sendbuf),0);
if (iResult == SOCKET_ERROR) {
printf("send failed with error: %d\n",WSAGetLastError());
closesocket(ConnectSocket);
WSACleanup();
return 1;
}
printf("Bytes Sent: %ld\n",iResult);
// shutdown the connection since no more data will be sent
iResult = shutdown(ConnectSocket,SD_SEND);
if (iResult == SOCKET_ERROR) {
printf("shutdown failed with error: %d\n",WSAGetLastError());
closesocket(ConnectSocket);
WSACleanup();
return 1;
}
// Receive until the peer closes the connection
do {
/*
fd_set fds;
FD_ZERO(&fds);
FD_SET(ConnectSocket,&fds);
struct timeval timeout;
timeout.tv_sec = 10;
timeout.tv_usec = 0;
iResult = select(0,&timeout);
if (iResult <= 0) {
if (iResult == SOCKET_ERROR)
printf("select failed with error: %d\n",WSAGetLastError());
else
printf("select timed out\n");
break;
}
*/
iResult = recv(ConnectSocket,recvbuf,recvbuflen,0);
if (iResult > 0)
printf("Bytes received: %d\n",iResult);
else if (iResult == 0)
printf("Connection closed\n");
else if (WSAGetLastError() == WSAETIMEDOUT)
printf("recv timed out\n");
else
printf("recv failed with error: %d\n",WSAGetLastError());
} while (iResult > 0);
// cleanup
closesocket(ConnectSocket);
WSACleanup();
return 0;
}
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