c - C套接字中需要多个连接

Question

我编写了以下代码作为连接两个程序的中间代码。在两个不同的系统上运行一个服务器程序和一个客户端程序。此代码有望充当这两个程序之间的中间层。

#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>

//Connect with program on server side
char * serv_con(char app_data[50])
{
int sock, bytes_recieved;  
char send_data[1024];
char *recv_data = malloc(1024);
struct hostent *host;
struct sockaddr_in server_addr;  
host = gethostbyname("10.47.3.249");
if ((sock = socket(AF_INET, SOCK_STREAM, 0)) == -1)
{

    perror("Socket");
    exit(1);

}
server_addr.sin_family = AF_INET;     
server_addr.sin_port = htons(3128);   
server_addr.sin_addr = *((struct in_addr *)host->h_addr);
bzero(&(server_addr.sin_zero),8); 
if (connect(sock, (struct sockaddr *)&server_addr, sizeof(struct sockaddr)) == -1) 
{

    perror("Connect");
    exit(1);

}
bytes_recieved=recv(sock,recv_data,1024,0);
recv_data[bytes_recieved] = '\0';
send(sock, app_data, 50, 0);
return recv_data;
//close(sock);

}


//Connect with client app
char * cli_con(char ser_data[50])
{
int sock, connected, bytes_recieved , true = 1;  
char send_data [1024];
char *recv_data = malloc(1024);       
struct sockaddr_in server_addr,client_addr;    
int sin_size;
if ((sock = socket(AF_INET, SOCK_STREAM, 0)) == -1)
{

    perror("Socket");
    exit(1);

}
if (setsockopt(sock,SOL_SOCKET,SO_REUSEADDR,&true,sizeof(int)) == -1)
{

    perror("Setsockopt");
    exit(1);

}
server_addr.sin_family = AF_INET;         
server_addr.sin_port = htons(5000);     
server_addr.sin_addr.s_addr = INADDR_ANY; 
bzero(&(server_addr.sin_zero),8); 
if (bind(sock, (struct sockaddr *)&server_addr, sizeof(struct sockaddr)) == -1)
{

    perror("Unable to bind1");
    exit(1);

}
if (listen(sock, 5) == -1)
{

    perror("Listen");
    exit(1);

}
sin_size = sizeof(struct sockaddr_in);
connected = accept(sock, (struct sockaddr *)&client_addr,&sin_size1);
printf("\n I got a connection from (%s , %d)",inet_ntoa(client_addr.sin_addr),ntohs(client_addr.sin_port));
bytes_recieved = recv(connected,recv_data,1024,0);
recv_data[bytes_recieved] = '\0';   
send(connected, ser_data,50, 0);
//close(sock);

}


int main()
{

char *ser_data, *app_data;
int pid = fork();
while(1)
{

    if(pid == 0)
        app_data = serv_con(ser_data);

    else
        ser_data = cli_con(app_data);

}

}

在客户端应用程序运行之前，它工作正常。但是一旦客户端应用程序运行，代码就会退出并给出错误:

Unable to bind: Address already in use
I got a connection from (192.168.0.3 , 45691)

我应该在代码中做些什么修改来纠正这个错误？我在 Linux 上工作。提前致谢。

编辑:我删除了 close(sock) 中的注释，并在函数 cli_con 中添加了 close(connect)。客户端代码如下:

int sock, bytes_recieved;  
char send_data[1024],recv_data[1024];
struct hostent *host;
struct sockaddr_in server_addr;  
host = gethostbyname("192.168.0.2");
if ((sock = socket(AF_INET, SOCK_STREAM, 0)) == -1)
{
    perror("Socket");
    exit(1);
}
server_addr.sin_family = AF_INET;     
server_addr.sin_port = htons(5555);   
server_addr.sin_addr = *((struct in_addr *)host->h_addr);
bzero(&(server_addr.sin_zero),8); 
if (connect(sock, (struct sockaddr *)&server_addr,
sizeof(struct sockaddr)) == -1) 
{
    perror("Connect");
    exit(1);
}
while(1)
{
    //necessary codes
    if (connect(sock, (struct sockaddr *)&server_addr, sizeof(struct sockaddr)) == -1) 
    {
        close(sock);
        goto connct;
    }
}

但是现在运行，第一个程序没有退出，甚至没有打印

I got a connection from (192.168.0.3 , 45691)

但只是继续运行而不打印任何消息。但另一方面，客户端退出显示错误:

Connect: Connection reset by peer

我现在该怎么办？

Answer 1

当客户端断开连接时，您创建一个新的服务器套接字并将其绑定(bind)到同一端口。如果服务器端套接字未关闭，则端口仍在使用中，因此 bind 失败。

通常，套接字程序的服务器端有一个围绕accept 的循环，以允许它处理来自许多客户端的连接。这样 bind 和 listen 只被调用一次。

while (connected = accept(sock, (struct sockaddr *)&client_addr,&sin_size1)) {
    printf("\n I got a connection from (%s , %d)",inet_ntoa(client_addr.sin_addr),ntohs(client_addr.sin_port));
    bytes_recieved = recv(connected,recv_data,1024,0);
    recv_data[bytes_recieved] = '\0';   
    send(connected, ser_data,50, 0);
    close(connected);
}