客户端在 2-3 次成功连接后停止与服务器的连接。 c 中的套接字编程

Question

我正在尝试使用 c 中的套接字编程来编写简单的客户端-服务器程序。当我先执行服务器然后执行客户端时，该程序工作正常，但在成功执行两到三次后，客户端停止连接到服务器。如果我在一段时间后执行程序，这将再次开始工作。

客户端代码:

#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <string.h>

int main(){
    int clientSocket,len;
    char buffer[1024];
    struct sockaddr_in sadd;

    clientSocket = socket(PF_INET, SOCK_STREAM, 0);

    sadd.sin_family = AF_INET;
    sadd.sin_port = htons(12345);
    sadd.sin_addr.s_addr = inet_addr("127.0.0.1");
    memset(sadd.sin_zero, '\0', sizeof sadd.sin_zero);  

    len = sizeof sadd;
    while(connect(clientSocket, (struct sockaddr *) &sadd, len) == -1) {
        sleep(1);
        printf("trying again..\n");
    }

    read(clientSocket, buffer, sizeof(buffer));
    printf("Data received: %s",buffer);  

    return 0;
}

服务器代码:

#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <string.h>

int main(){
    int defSock, newSock, len;
    char buffer[1024];
    struct sockaddr_in sadd, cadd;


    socklen_t addr_size;

    defSock = socket(PF_INET, SOCK_STREAM, 0);

    sadd.sin_family = AF_INET;
    sadd.sin_port = htons(12345);
    sadd.sin_addr.s_addr = INADDR_ANY;  

    bind(defSock, (struct sockaddr *) &sadd, sizeof(sadd));

    if(listen(defSock,5)==0)
        printf("Listening\n");
    else
        printf("Error\n");

    len = sizeof(cadd);

    newSock = accept(defSock, (struct sockaddr *) &cadd, &len);
    strcpy(buffer,"Hello World\n");
    int n = write(newSock,buffer,sizeof(buffer));

    close(newSock);

    return 0;
}

在终端中多次执行客户端:

[kj@localhost Downloads]$ gcc client.c -o client
client.c: In function ‘main’:
client.c:16:25: warning: implicit declaration of function ‘inet_addr’ [-Wimplicit-function-declaration]
  sadd.sin_addr.s_addr = inet_addr("127.0.0.1");
                         ^
client.c:21:3: warning: implicit declaration of function ‘sleep’ [-Wimplicit-function-declaration]
   sleep(1);
   ^
client.c:25:2: warning: implicit declaration of function ‘read’ [-Wimplicit-function-declaration]
  read(clientSocket, buffer, sizeof(buffer));
  ^
[kj@localhost Downloads]$ ./client 
Data received: Hello World
[kj@localhost Downloads]$ ./client 
trying again..
trying again..
trying again..
trying again..
trying again..
trying again..
trying again..
trying again..
trying again..
^C
[kj@localhost Downloads]$ ./client 
trying again..
trying again..
trying again..
^C
[kj@localhost Downloads]$ ./client 
trying again..
trying again..
trying again..
trying again..
^C
[kj@localhost Downloads]$ 

在另一个终端上同时执行服务器:

[kj@localhost Downloads]$ gcc server.c -o server
server.c: In function ‘main’:
server.c:31:10: warning: implicit declaration of function ‘write’ [-Wimplicit-function-declaration]
  int n = write(newSock,buffer,sizeof(buffer));
          ^
server.c:33:2: warning: implicit declaration of function ‘close’ [-Wimplicit-function-declaration]
  close(newSock);
  ^
[kj@localhost Downloads]$ ./server 
Listening
[kj@localhost Downloads]$ ./server 
Listening
^C
[kj@localhost Downloads]$ ./server 
Listening
^C
[kj@localhost Downloads]$ ./server 
Listening
^C
[kj@localhost Downloads]$ 

Answer 1

使用SO_REUSEADDR隐藏了另一个问题:

您的服务器只能为一个客户端提供服务，并且在为一个客户端提供服务后不会完全关闭其监听套接字。

要纠正此问题，您应该在服务器中添加一个 while 循环，以允许多个客户端连接。

在您的代码中，我添加了:

• 一个 while 循环在第一个客户端连接后不停止，
• 一次测试/perror，用于在出现错误时停止服务器，
• 对监听套接字进行一次关闭以干净退出。

这是代码:

/* include */

int main(){

    /* init */

    if(listen(defSock,5)==0)
        printf("Listening\n");
    else
        printf("Error\n");

    len = sizeof(cadd);

    // while they're no error
    while (1)
    {
        // wait for new connection
        newSock = accept(defSock, (struct sockaddr *) &cadd, &len);

        // test if client connection succeded
        if (-1 == newSock)
        {
            // something went wrong: kill the server
            perror("accept()");
            break
        }
        else        
        {
            // say hello
            static const char hello[] = "Hello, world!\n";
            int n = write(newSock, hello, sizeof hello - 1); /* -1 to exclude the final '\0' char */
            if (n < 0)
                perror("write");
            close(newSock);
        }
    }

    // And close the server listening socket
    close(defSock);

    return 0;
}