c - Recv 调用获取空数据

Question

我正在学习使用 c 中的套接字。这是我的代码:

void work_with_client(int client_sock){
    char buff[10] = {0};

    while(1){
            kv_log_message("\tWork with client\n");
            int is_received = recv(client_sock, buff, 10, 0); 
            if(is_received < 0){ 
                    perror("Received failed");
            } else {
                    printf("RESPONSE: %s\n", buff);
            }   
            printf("RESPONSE %d\n", is_received);

            sleep(1);
    }   
}

当我通过 telnet 连接到该服务器并立即断开连接时，服务器打印以下行:

    Work with client
RESPONSE: 
RESPONSE 10
    Work with client
RESPONSE: 
RESPONSE 10
    Work with client
RESPONSE: 
RESPONSE 10
    Work with client
RESPONSE: 
RESPONSE 10
    Work with client
RESPONSE: 
RESPONSE 1
    Work with client
RESPONSE: 
RESPONSE 0
    Work with client

而且我不明白为什么前 4 个 recv 调用会获取完整大小的缓冲区数据(从客户端角度来看，我没有向套接字写入任何内容)。有什么建议么？附:在 Mac OS X Yosemite 上运行

更新:我在 Linux 上测试我的程序，在我的情况下，recv 调用总是返回 0，所以可能是 Mac OS X 上 telnet 的问题

Answer 1

当recv()返回0时，表示对方关闭了连接。

来自man recv :

RETURN VALUE

[...] The return value will be 0 when the peer has performed an orderly shutdown.

然后您可能想退出 while() 循环。

<小时/>

更新:

此外，代码还可能通过将非 0 终止的“字符串”传递给 printf() 来调用未定义的行为。

要解决此问题，请读取 buff 少一个 char，然后读取其大小并添加 0 终止符。

    while (1)
    {
        ssize_t is_received = recv(client_sock, buff, sizeof buff - 1, 0); 
        if (is_received < 0){ 
                perror("Received failed");
                break;
        } else if (is_received == 0) {
                printf("%s\n", "peer shutdown");
                break;
        }

        buff[is_received] = '\0';
        printf("RESPONSE: %s\n", buff);
   }