为什么socket recv会在while循环中不断接收数据，即使我没有从发件人发送任何数据 [英] why socket recv keeps receiving data in a while loop, even if I don't send any data from sender

问题描述

问题: 1.为什么即使我不从发送方发送任何数据，socket recv仍会在while循环中继续接收数据?不是recv()的阻塞函数，我以为它会阻塞直到tcp接收到一些数据为止； 2.为什么numbytes = 0?

Questions: 1. why socket recv keeps receiving data in a while loop, even if I don't send any data from sender? isn't recv() a blocking function, I thought it blocks until tcp receives some data; 2. why numbytes = 0 ?

下面是代码，我只发布了recv()和send()的代码，我认为代码的其他部分都可以正常工作，但是如果您需要所有代码进行调试，请告诉我，我将发布它们，谢谢！

Below is the code, I just post the code of recv() and send(), I think other parts of the code works fine, but if you need all code to debug, please let me know I'll post them, Thanks!

 while(1) { //client receiving code
        if ((numbytes = recv(sockfd, buf, MAXDATASIZE, 0)) == -1)
            perror("recv");
        }
        buf[numbytes] = '\0'; 
        printf("numbytes is %d\n", numbytes);   
        printf("client: received '%s'\n", buf); 
    }


while(1) { //server sending code
        char str[100];
        sin_size = sizeof their_addr;
        new_fd = accept(sockfd, (struct sockaddr *)&their_addr, &sin_size);

        if (new_fd == -1) {
            perror("accept");
            continue;
        }

        inet_ntop(their_addr.ss_family, get_in_addr((struct sockaddr *)&their_addr), s, sizeof s);
        printf("server: got connection from %s\n", s);

        while(1) {
            printf( "Enter a value :");
            scanf("%s", str);
            if (send(new_fd, str, 50, 0) == -1)
            perror("send");
        }
    }

以下是结果的屏幕截图: 在服务器终端上输入

Below is the screenshot of the result: Input on the server terminal

Enter a value :123456

客户终端上的输出

numbytes is 0
client: received '12345'
numbytes is 0
client: received '6'
numbytes is 0
client: received ''
numbytes is 0
client: received ''
numbytes is 0
client: received ''
numbytes is 0
client: received ''
numbytes is 0
client: received ''
numbytes is 0
client: received ''
numbytes is 0
client: received ''
numbytes is 0
client: received ''

推荐答案

因为您忽略了recv()返回零的可能性，这意味着对等方已经关闭了连接，这意味着您也必须这样做，并停止阅读.

Because you're ignoring the possibility of a zero return from recv(), which means the peer has closed the connection, which means you must do so too, and stop reading.

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