Select() 在程序中实施错误，从服务器获取超时

Question

传奇中的第三个问题：How to correctly implement select to correctly get data from stdin and recv()。我建议阅读这个和它链接的另一个问题以了解情况。

基本上，我自己尝试实现了 select()。我的代码：

#include <iostream>
#include <sys/socket.h>
#include <sys/types.h>
#include <sys/select.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <cstring>
#include <stdlib.h>

using namespace std;

int main (int argc, char** argv) {
    if (argv[1] == NULL) {
        cout << "3[31mTARGET NOT SPECIFIED - TERMINATING...3[0m\n";
        return -1;
    }
    if (argv[2] == NULL) {
        cout << "3[31mPORT NOT SPECIFIED - TERMINATING...3[0m\n";
        return -2;
    }
    
    string target = argv[1];
    int port = atoi(argv[2]);

    cout << "GENERATING SOCKET...\n";
    int chatter = socket(AF_INET, SOCK_STREAM, 0);
    if (chatter == -1) {
        cout << "3[31mSOCKET GENERATION FAILURE - TERMINATING...3[0m\n";
        return -3;
    }
    cout << "3[32mSUCCESSFULLY GENERATED SOCKET3[0m\n";

    struct sockaddr_in hint;
    hint.sin_family = AF_INET;
    hint.sin_port   = htons(port);
    inet_pton(AF_INET, target.c_str(), &hint.sin_addr);

    struct timeval tv;
    tv.tv_usec = 0.0;
    tv.tv_sec = 5;
    int recval;

    cout << "CONNECTING TO " << target << " AT PORT " << port << "...\n";   
    int connection_status = connect(chatter, (sockaddr*)&hint, sizeof(hint));
    if (connection_status == -1) {
        cout << "3[31mCONNECTION FAILURE - TERMINATING...3[0m\n";
        return -4;
    }
    cout << "3[32mCONNECTED TO HOST3[0m\n";

    char buf[4096] = {0};
    string msg;
    while (true) {
        fd_set rfds;
        FD_ZERO(&rfds);
        FD_SET(chatter, &rfds);

        getline(cin, msg);
        msg+"\r\n";
        int sendmsg = send(chatter, msg.c_str(), msg.size()+1, 0);
        if (sendmsg == -1) {
            cout << "3[31mMESSAGE SENDING FAILURE - TERMINATING...3[0m\n";
            return -5;
        }

        recval = select(chatter + 1, &rfds, NULL, NULL, &tv);
        switch(recval) {
            case(0):
                cout << "3[31mTIMEOUT3[0m\n";
                break;
            case(-1):
                cout << "3[31mERROR3[0m\n";
                break;
            default:
                if (recv(chatter, buf, 4096, 0) < 0) {
                    cout << "3[31mFAILURE TO RECEIVE MESSAGE - TERMINATING...3[0m\n";
                    return -6;
                } else {
                    cout << recv(chatter, buf, 4096, 0) << "\n";
                    cout << buf << "\n";
                }
                break;
        }
    }

    close(chatter);

    return 0;
}

在 scanme.nmap.org 和我的 HTTP 服务器上尝试该程序时，我一直收到 TIMEOUT。我做错了什么？

此时，在解决了用户在第一个问题中指出的问题后，我知道我发送数据的方式没有问题。程序处理从 getline()/recv().

获取数据的方式存在问题

编辑：新的、改进的、工作代码感谢回答者

#include <iostream>
#include <sys/socket.h>
#include <sys/types.h>
#include <sys/select.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <cstring>
#include <stdlib.h>

using namespace std;

int main (int argc, char** argv) {
    if (argv[1] == NULL) {
        cout << "3[31mTARGET NOT SPECIFIED - TERMINATING...3[0m\n";
        return -1;
    }
    if (argv[2] == NULL) {
        cout << "3[31mPORT NOT SPECIFIED - TERMINATING...3[0m\n";
        return -2;
    }
    
    string target = argv[1];
    int port = atoi(argv[2]);

    cout << "GENERATING SOCKET...\n";
    int chatter = socket(AF_INET, SOCK_STREAM, 0);
    if (chatter == -1) {
        cout << "3[31mSOCKET GENERATION FAILURE - TERMINATING...3[0m\n";
        return -3;
    }
    cout << "3[32mSUCCESSFULLY GENERATED SOCKET3[0m\n";

    struct sockaddr_in hint;
    hint.sin_family = AF_INET;
    hint.sin_port   = htons(port);
    inet_pton(AF_INET, target.c_str(), &hint.sin_addr);

    int recval;

    cout << "CONNECTING TO " << target << " AT PORT " << port << "...\n";   
    int connection_status = connect(chatter, (sockaddr*)&hint, sizeof(hint));
    if (connection_status == -1) {
        cout << "3[31mCONNECTION FAILURE - TERMINATING...3[0m\n";
        return -4;
    }
    cout << "3[32mCONNECTED TO HOST3[0m\n";

    char buf[4096] = {0};
    string msg;
    while (true) {
        struct timeval tv;
        tv.tv_usec = 0.0;
        tv.tv_sec = 5;

        fd_set rfds;
        FD_ZERO(&rfds);
        FD_SET(chatter, &rfds);

        getline(cin, msg);
        msg += "\r\n";
        const char *pMsg = msg.c_str();
        size_t msgSize = msg.size();
        do {
            int numSent = send(chatter, pMsg, msgSize, 0);
            if (numSent == -1) {
                cout << "3[31mMESSAGE SENDING FAILURE - TERMINATING...3[0m\n";
                close(chatter);
                return -5;
            }
            pMsg += numSent;
            msgSize -= numSent;
        } while (msgSize > 0);

        recval = select(chatter + 1, &rfds, NULL, NULL, &tv);
        switch(recval) {
            case(0):
                cout << "3[31mTIMEOUT3[0m\n";
                break;
            case(-1):
                cout << "3[31mERROR3[0m\n";
                break;
            default:
                int numRead = recv(chatter, buf, 4096, 0);
                if (numRead < 0) {
                    cout << "3[31mFAILURE TO RECEIVE MESSAGE - TERMINATING...3[0m\n";
                    close(chatter);
                    return -6;
                }
                else if (numRead == 0) {
                    cout << "3[31mDISCONNECTED - TERMINATING...3[0m\n";
                    close(chatter);
                    break;
                } else {
                    cout << numRead << "\n";
                    cout.write(buf, numRead);
                    cout << "\n";
                }
                break;
        }
    }

    close(chatter);

    return 0;
}

Answer 1

在某些平台上，select() 会更改传递的 timeval 以指示剩余时间。所以这很可能是你超时错误的原因，因为你只设置了一次 timeval 并且它最终会下降到 0。你需要在每次调用 [=13= 时重置你的 tv 变量]，所以将它移到 while 循环中。

此外，您有 2 次调用 recv()，而您应该只使用 1 次调用。您忽略了第一个 recv() 接收到的字节，如果服务器恰好发送少于 4096 个字节，那么 next 调用将不会留下任何数据select()检测，除非连接断开。

改变这个：

if (recv(chatter, buf, 4096, 0) < 0) {
    cout << "3[31mFAILURE TO RECEIVE MESSAGE - TERMINATING...3[0m\n";
    return -6;
} else {
    cout << recv(chatter, buf, 4096, 0) << "\n";
    cout << buf << "\n";
}

为此：

int numRead = recv(chatter, buf, 4096, 0);
if (numRead < 0) {
    cout << "3[31mFAILURE TO RECEIVE MESSAGE - TERMINATING...3[0m\n";
    return -6;
}
else if (numRead == 0) {
    cout << "3[32mHOST DISCONNECTED3[0m\n";
    break;
} else {
    cout << numRead << "\n";
    cout.write(buf, numRead);
    cout << "\n";
}

此外，msg+"\r\n"; 是空操作，您可能打算改用 msg += "\r\n";。

并且，调用 send() 时不应包含 msg 的空终止符。而且您没有考虑 send() 可能无法 一次性发送全部数据的可能性。您需要在循环中调用 send()，例如：

const char *pMsg = msg.c_str();
size_t msgSize = msg.size();

do {
    int numSent = send(chatter, pMsg, msgSize, 0);
    if (numSent == -1) {
        cout << "3[31mMESSAGE SENDING FAILURE - TERMINATING...3[0m\n";
        return -5;
    }
    pMsg += numSent;
    msgSize -= numSent;
}
while (msgSize > 0);

Select() 在程序中实施错误，从服务器获取超时

Select() implemented wrong in program, getting timeouts from server

c++

sockets

linux

select

file-descriptor