c++ - cpp socket - TCP 传输(使用相同的端口发送和接收)

Question

我正在写一个套接字程序，一部分是先发送然后接收，一部分是接收然后发送。

程序是这样运行的:

ThreadA: Send to Port 8000-> close socket -> get myport (portA) that i send -> listen to my port(portA)

ThreadB: Listen port 8000 -> Get the port when receive (portA)-> close socket -> send pack to same port (port A)

std::thread ThreadA,ThreadB;
long share_port=8000;
char share_addr[INET_ADDRSTRLEN]="127.0.0.1";

void send_then_receive();
void receive_then_send();


void send_then_receive(){
    long myport = -1, receiver_port = share_port;
    SOCKET receive_then_send_A_Socket,receive_then_send_A_Socket_b,receive_then_send_B_Socket;

    //- Send to who i want
    struct sockaddr_in receive_then_send_B_Addr;
    receive_then_send_B_Addr.sin_family = AF_INET;
    inet_pton(AF_INET, share_addr, &receive_then_send_B_Addr.sin_addr.s_addr);
    receive_then_send_B_Addr.sin_port = htons((u_short)receiver_port);
    receive_then_send_B_Socket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    while (connect(receive_then_send_B_Socket, (struct sockaddr *)&receive_then_send_B_Addr, sizeof(sockaddr_in)) == SOCKET_ERROR){
        printf("\nConnect Fail in first response| Fail Code:%i\n", WSAGetLastError());
    }
    send(receive_then_send_B_Socket, "4321", 5, 0);
    printf("[1]The port I want to send to:%ld\n",receiver_port);

    //- Check My Port
    socklen_t checkport_adr_len = sizeof(receive_then_send_B_Addr);
    if (getsockname(receive_then_send_B_Socket, (struct sockaddr *)&receive_then_send_B_Addr, &checkport_adr_len) == 0){
        myport = ntohs(receive_then_send_B_Addr.sin_port);
        printf("[1]MyPort Check:%ld\n", myport);
    }
    close(receive_then_send_B_Socket);



    //- Then Recive
    sockaddr_in *receive_then_send_A_Addr = new sockaddr_in;
    receive_then_send_A_Addr->sin_family = AF_INET;
    receive_then_send_A_Addr->sin_addr.s_addr = INADDR_ANY;
    receive_then_send_A_Addr->sin_port = htons((u_short)myport);
    receive_then_send_A_Socket = socket(AF_INET, SOCK_STREAM, 0);
    bind(receive_then_send_A_Socket, (struct sockaddr *)receive_then_send_A_Addr, sizeof(struct sockaddr_in));
    listen(receive_then_send_A_Socket, 1);
    std::this_thread::sleep_for(std::chrono::milliseconds(1000));
    receive_then_send_A_Socket_b = accept(receive_then_send_A_Socket, 0, 0);
    char* buffer_A= new char[100];
    recv(receive_then_send_A_Socket_b, buffer_A, 100, 0);
    printf("[1]What I then receive: %s\n",buffer_A);

    close(receive_then_send_A_Socket);
    close(receive_then_send_A_Socket_b);


}
void receive_then_send(){
    long myport = -1, receiver_port = -1;
    SOCKET receive_then_send_A_Socket,receive_then_send_A_Socket_b,receive_then_send_B_Socket;

    //- First Recive
    sockaddr_in *receive_then_send_A_Addr = new sockaddr_in;
    receive_then_send_A_Addr->sin_family = AF_INET;
    receive_then_send_A_Addr->sin_addr.s_addr = INADDR_ANY;
    receive_then_send_A_Addr->sin_port = htons((u_short)share_port);
    receive_then_send_A_Socket = socket(AF_INET, SOCK_STREAM, 0);
    bind(receive_then_send_A_Socket, (struct sockaddr *)receive_then_send_A_Addr, sizeof(struct sockaddr_in));
    listen(receive_then_send_A_Socket, 1);
    receive_then_send_A_Socket_b = accept(receive_then_send_A_Socket, 0, 0);
    char* buffer_A= new char[100];
    recv(receive_then_send_A_Socket_b, buffer_A, 100, 0);
    printf("[2]What I first receive: %s\n",buffer_A);

    //- Check receiver Port
    struct sockaddr_storage receiver_addr;
    socklen_t receiver_addr_len = (socklen_t)sizeof receiver_addr;
    getpeername(receive_then_send_A_Socket_b, (struct sockaddr*)&receiver_addr, &receiver_addr_len);


    struct sockaddr_in *s = (struct sockaddr_in *)&receiver_addr;
    inet_ntop(AF_INET, &s->sin_addr, share_addr, sizeof share_addr);
    receiver_port = ntohs(s->sin_port); 
    printf("[2]The port I want to send to:%ld\n",receiver_port);
    close(receive_then_send_A_Socket);
    close(receive_then_send_A_Socket_b);

    //- Send Back to the port that sender send to me
    struct sockaddr_in receive_then_send_B_Addr;
    receive_then_send_B_Addr.sin_family = AF_INET;
    inet_pton(AF_INET, share_addr, &receive_then_send_B_Addr.sin_addr.s_addr);
    receive_then_send_B_Addr.sin_port = htons((u_short)receiver_port);
    receive_then_send_B_Socket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    while (connect(receive_then_send_B_Socket, (struct sockaddr *)&receive_then_send_B_Addr, sizeof(sockaddr_in)) == SOCKET_ERROR){
        printf("\nFail Code:%i\n", WSAGetLastError());
        break;
    }
    send(receive_then_send_B_Socket, "1234", 5, 0);
    close(receive_then_send_B_Socket);
    printf("[2]The port I want to send to:%ld\n",receiver_port);
}

int main(int argc, char *argv[])
{
    ThreadB = std::thread(receive_then_send);
    ThreadA = std::thread(send_then_receive);
    while(1);
    return 0;
}

但是，第一次传输很好用，第二次传输就不行了，怎么回事？？？

显示如下:

Connect Fail in first response| Fail Code:111

Connect Fail in first response| Fail Code:111 [1]The port I want to send to:8000 [1]MyPort Check:34004 [2]What I first receive: 4321 [2]The port I want to send to:34004

Fail Code:111

注意:我用的是Linux(二次传输不行)，但是修改成WinSock版本后一切正常。为什么会这样？

请注意，在绑定(bind)之前，我已经厌倦了 //将套接字上的 SO_REUSEADDR 设置为真 (1): int optval = 1; setsockopt(receive_then_send_A_Socket, SOL_SOCKET, SO_REUSEADDR, &optval, sizeof(int));

Answer 1

一个类轮答案:SO_REUSEADDR .

系统禁止在给定端口上重复使用 IP 地址，我记得，在它被释放后 60 秒内。除非设置了 SO_REUSEADDR 标志。

这是一个comprehensive answer on SO关于为什么以及如何设置这个选项标志。