在一台服务器上接收多个客户端数据包

Question

我有 3 个应用程序，一台服务器，2 个客户端。我正在尝试对此进行编程，以便我可以从我的客户端向服务器发送登录请求，并请求查看有关另一个客户端的信息。

问题：我对所有 3 个应用程序使用相同的 ip 和端口号（全部在我的计算机上的 3 个 Visual Studio 应用程序上完成），否则我认为它无法连接到服务器。这样可以吗？

当我尝试在服务器的 while 循环之外使用侦听和接受时，它适用于一个客户端，但不适用于另一个客户端。当我尝试将监听和接受放在 while 循环中时，它适用于两个客户端，但不会响应多个接受。我的问题是什么？

服务器

struct Users {

int message;
char userName[50];
char ipAddress[50];
int PortNumber;
bool online;

};

int main () {

//Create users
Users client[2];

client[0].PortNumber = 20000;
client[0].online = false;
sprintf(&client[0].userName[0], "Albert");
sprintf(&client[0].ipAddress[0], "127.0.0.1");

client[1].PortNumber = 20000;
client[1].online = false;
sprintf(&client[1].userName[0], "Monique");
sprintf(&client[1].ipAddress[0], "127.0.0.1");


//Set up all the connection stuff
struct sockaddr_in SvrAddr;
SOCKET WelcomeSocket, ConnectionSocket;
int PortNumber = 20000;
int result;
char IPAddress[] = "127.0.0.1";
char RxBuffer[128];
char TxBuffer[128];


WORD wVersionRequested; 
WSADATA wsaData; 

wVersionRequested = MAKEWORD(2,2); //For Server 


if(WSAStartup(wVersionRequested, &wsaData) != 0) 
    return -1;


//Setting up the welcome socket
WelcomeSocket = socket(AF_INET, SOCK_STREAM, 0);

//Setting up the sockaddr svraddr structure
SvrAddr.sin_family = AF_INET;
SvrAddr.sin_addr.s_addr = inet_addr(IPAddress);
SvrAddr.sin_port = htons(PortNumber);


//Bind
bind(WelcomeSocket, (sockaddr*)&SvrAddr, sizeof(SvrAddr));

//listening
//listen(WelcomeSocket, 5);

//temp users
Users temp;
//ConnectionSocket = accept(WelcomeSocket, NULL, NULL);
ConnectionSocket = SOCKET_ERROR;

//while loop for the connection 
while (1) {

    listen(WelcomeSocket, 5);

    if ((ConnectionSocket = accept(WelcomeSocket, NULL, NULL)) == SOCKET_ERROR)
    {
        return -1;
    }

    else {

    int n = recv(ConnectionSocket, RxBuffer, sizeof(RxBuffer), 0);

    if (n == 0)
        break;


    memcpy(&temp, RxBuffer, sizeof(struct Users));

    //cout << temp.message << temp.userName << endl << endl;

    //check which message type is being sent
    switch(temp.message) {

    //if message type 1
    case 1 :
        for (int i = 0; i < 2; i++) {

            //if receieved username matches with any username in the database
            if (strcmp(temp.userName, client[i].userName) == 0) {

                //assign the recieved users information to the matched one in database
                strcpy(client[i].userName, temp.userName);
                client[i].online = true;
                client[i].message = 2;

                cout << "Username: " << client[i].userName << endl << "Online status: " << client[i].online << endl << endl;

                //send the acknowledgement packet
                send(ConnectionSocket, (char *)&client[i], sizeof(struct Users), 0);
                //closesocket(ConnectionSocket);
            }

        }
        break;

    //if message type 3
    case 3 :

        cout << "User being searched for: " << temp.userName << endl << endl;
        for (int i = 0; i < 2; i++) {

            //if receieved username matches with any username in the database
            if (strcmp(temp.userName, client[i].userName) == 0) {
                client[i].message = 4;
                //send the acknowledgement packet
                send(ConnectionSocket, (char *)&client[i], sizeof(struct Users), 0);
                //closesocket(ConnectionSocket);
            }

        }
        break;

    default :
        break;

    }

}

}

closesocket(ConnectionSocket);
WSACleanup();
}

客户端（两者相同）

struct Users {

int message;
char userName[50];
char ipAddress[50];
int PortNumber;
bool online;

};


int main () {

struct sockaddr_in SvrAddr;
SOCKET ClientSocket;
int PortNumber = 20000;
char IPAddress[] = "127.0.0.1";
//char message[] = "Hello this is the client.";
char RxBuffer[128];

WORD wVersionRequested; 
WSADATA wsaData; 

wVersionRequested = MAKEWORD(2,3); //For Client 

if(WSAStartup(wVersionRequested, &wsaData) != 0) 
    return -1; 


ClientSocket = socket(AF_INET, SOCK_STREAM, 0);

SvrAddr.sin_family = AF_INET;
SvrAddr.sin_addr.s_addr = inet_addr(IPAddress);
SvrAddr.sin_port = htons(PortNumber);

connect(ClientSocket, (sockaddr*)&SvrAddr, sizeof(SvrAddr));



//cout << "Name: ";
//cin >> login;

//Send request to login
int log;
char * name = new char[128];
char * request = new char[128];
Users client;
Users talkto;


do {

    cout << "To login press (1) to end press (2). ";
    cin >> log;
    flushall();

    if (log == 1) {

        cout << "Username : ";
        cin.getline(name, 128, '\n');
        cout << endl;
        flushall();

        //Set client login info
        strcpy(client.userName, name);
        client.message = 1;



        send(ClientSocket, (char *)&client, sizeof(struct Users), 0);


        //Recieve acknowledgement
        recv(ClientSocket, RxBuffer, sizeof(RxBuffer), 0);
        //create temp users
        Users temp;

        memcpy(&temp, RxBuffer, sizeof(struct Users));

        //If logged in and received a message of type 2 (acknowledgement)
        if (temp.message == 2) {

            cout << "You have logged in." << endl << endl;

            cout << "Enter user to request user information: ";
            cin.getline(talkto.userName, 128, '\n');
            flushall();
            cout << endl;

            talkto.message = 3;

            //send request for user information packet
            send(ClientSocket, (char *)&talkto, sizeof(struct Users), 0);

            recv(ClientSocket, RxBuffer, sizeof(RxBuffer), 0);

            memcpy(&temp, RxBuffer, sizeof(struct Users));

            //if message received is of type 4 (acknowledgement of user request info)
            if (temp.message == 4) {

                cout << "Requested User: " << temp.userName << endl << "Online status: " << temp.online << endl << endl;
            }
        }

        //cout << temp.userName << endl << temp.online << endl << temp.message;
    } 

} while (log != 2);


closesocket(ClientSocket);


WSACleanup();



} 

Answer 1

您不要在循环内使用listen()。只有accept()。此外，您不使用nonblocking socket，但这是您的偏好。另一件事，每次完成accept 时，都必须使用closesocket。此外，您的recv() 必须在循环中处理，因为与发送不同，它可能会在接收到所有数据之前返回。

你的服务器基本结构：

struct sockaddr_in inAddr; //incoming address. Use it to distinguise between incoming clients
struct sockaddr_in address;
unsigned int inLen;
int recvMsgSize;
unsigned short port = 20000;
Socket socket_handle, acceptSocket;

socket_handle = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
if(socket_handle == INVALID_SOCKET){
    //error
}

memset(&address, 0, sizeof(address));
address.sin_family = AF_INET;
address.sin_addr.s_addr = htonl(INADDR_ANY); //All incoming addresses
address.sin_port = htons(port); //port must be unsigned short not int!
if(bind(socket_handle, (struct sockaddr *)&address, sizeof(address)) < 0){
    //error
}

if(listen(socket_handle, MAXPENDING) < 0){
    //error
}

while(true){
    acceptSocket = accept(socket_handle, (struct sockaddr *) &inAddr, &inLen));
    if(acceptSocket == INVALID_SOCKET){
        //error
    }

    while(true){
        recvMsgSize = recv(acceptSocket, received_data, strlen(received_data), 0);
        if(recvMsgSize < 0){/*error*/}
        else if(recvMsgSize == 0){break;}
        else{/*receive your data*/}
    }

    (do other stuff...)
    closesocket(acceptSocket);
}

closesocket(socket_handle);
WSACleanup();

变态