Unix套接字-服务器示例

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📜 Unix套接字-服务器示例

📅 最后修改于: 2020-11-05 04:54:49 🧑 作者: Mango

要使进程成为TCP服务器，您需要执行以下步骤-

使用socket()系统调用创建一个套接字。
使用bind()系统调用将套接字绑定到一个地址。对于Internet上的服务器套接字，地址由主机上的端口号组成。
用listen()系统调用监听连接。
接受与accept()系统调用的连接。该调用通常会阻塞，直到客户端与服务器连接为止。
使用read()和write()系统调用发送和接收数据。

现在，让我们以源代码的形式来介绍这些步骤。将此代码放入文件server.c中，并使用gcc编译器进行编译。

#include 
#include 

#include 
#include 

#include 

int main( int argc, char *argv[] ) {
   int sockfd, newsockfd, portno, clilen;
   char buffer[256];
   struct sockaddr_in serv_addr, cli_addr;
   int  n;
   
   /* First call to socket() function */
   sockfd = socket(AF_INET, SOCK_STREAM, 0);
   
   if (sockfd < 0) {
      perror("ERROR opening socket");
      exit(1);
   }
   
   /* Initialize socket structure */
   bzero((char *) &serv_addr, sizeof(serv_addr));
   portno = 5001;
   
   serv_addr.sin_family = AF_INET;
   serv_addr.sin_addr.s_addr = INADDR_ANY;
   serv_addr.sin_port = htons(portno);
   
   /* Now bind the host address using bind() call.*/
   if (bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0) {
      perror("ERROR on binding");
      exit(1);
   }
      
   /* Now start listening for the clients, here process will
      * go in sleep mode and will wait for the incoming connection
   */
   
   listen(sockfd,5);
   clilen = sizeof(cli_addr);
   
   /* Accept actual connection from the client */
   newsockfd = accept(sockfd, (struct sockaddr *)&cli_addr, &clilen);
    
   if (newsockfd < 0) {
      perror("ERROR on accept");
      exit(1);
   }
   
   /* If connection is established then start communicating */
   bzero(buffer,256);
   n = read( newsockfd,buffer,255 );
   
   if (n < 0) {
      perror("ERROR reading from socket");
      exit(1);
   }
   
   printf("Here is the message: %s\n",buffer);
   
   /* Write a response to the client */
   n = write(newsockfd,"I got your message",18);
   
   if (n < 0) {
      perror("ERROR writing to socket");
      exit(1);
   }
      
   return 0;
}

处理多个连接

为了允许服务器处理多个同时连接，我们在上面的代码中进行了以下更改-

将accept语句和以下代码无限循环。
建立连接后，调用fork()创建一个新进程。
子进程将关闭sockfd并调用doprocessing函数，并将新的套接字文件描述符作为参数传递。当两个进程完成其对话时(如doprocessing()返回所示) ，该进程将简单退出。
父进程关闭newsockfd 。由于所有这些代码都处于无限循环中，因此它将返回到accept语句以等待下一个连接。

#include 
#include 

#include 
#include 

#include 

void doprocessing (int sock);

int main( int argc, char *argv[] ) {
   int sockfd, newsockfd, portno, clilen;
   char buffer[256];
   struct sockaddr_in serv_addr, cli_addr;
   int n, pid;
   
   /* First call to socket() function */
   sockfd = socket(AF_INET, SOCK_STREAM, 0);
   
   if (sockfd < 0) {
      perror("ERROR opening socket");
      exit(1);
   }
   
   /* Initialize socket structure */
   bzero((char *) &serv_addr, sizeof(serv_addr));
   portno = 5001;
   
   serv_addr.sin_family = AF_INET;
   serv_addr.sin_addr.s_addr = INADDR_ANY;
   serv_addr.sin_port = htons(portno);
   
   /* Now bind the host address using bind() call.*/
   if (bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0) {
      perror("ERROR on binding");
      exit(1);
   }
   
   /* Now start listening for the clients, here
      * process will go in sleep mode and will wait
      * for the incoming connection
   */
   
   listen(sockfd,5);
   clilen = sizeof(cli_addr);
   
   while (1) {
      newsockfd = accept(sockfd, (struct sockaddr *) &cli_addr, &clilen);
        
      if (newsockfd < 0) {
         perror("ERROR on accept");
         exit(1);
      }
      
      /* Create child process */
      pid = fork();
        
      if (pid < 0) {
         perror("ERROR on fork");
         exit(1);
      }
      
      if (pid == 0) {
         /* This is the client process */
         close(sockfd);
         doprocessing(newsockfd);
         exit(0);
      }
      else {
         close(newsockfd);
      }
        
   } /* end of while */
}

下面的代码序列显示了doprocessing函数的简单实现。

void doprocessing (int sock) {
   int n;
   char buffer[256];
   bzero(buffer,256);
   n = read(sock,buffer,255);
   
   if (n < 0) {
      perror("ERROR reading from socket");
      exit(1);
   }
   
   printf("Here is the message: %s\n",buffer);
   n = write(sock,"I got your message",18);
   
   if (n < 0) {
      perror("ERROR writing to socket");
      exit(1);
   }
    
}