Unix/Linux Socket 服务器代码实例 - Socket编程

我们已经看过关于服务器socket创建的教程，为了使进程TCP服务器端需要执行以下步骤：

1. 创建一个socket使用socket() 系统调用.

2. 使用bind()系统调用套接字绑定到一个地址。对于互联网上的服务器套接字，地址包括主机的端口号。

3. 使用listen()系统调用连接监听。

4. accept() 系统调用形式接受连接。此调用通常会阻塞，直到有客户端与服务器连接。

5. 发送和接收数据，使用read() 和 write() 系统调用。

现在要把上面这些步骤的形式写成源代码。把这个代码写server.c文件并用gcc编译器编译。

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

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：

为了使服务器能够同时处理多个连接，我们在上面的代码进行以下更改：

1. 将accept语句和下面的代码在一个无限循环。

2. 建立连接后，调用fork()创建一个新的进程。

3. 子进程将关闭sockfd中致电doprocessing函数，通过新的套接字文件描述符作为参数。当两个进程已经完成了他们对话中表示由doprocessing()返回，这个过程简单地退出。

4. 父进程关闭newsockfd。因为所有这些代码是在一个无限循环，它接受语句将返回到等待下一个连接。

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

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);
    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 */
}

Here is the simple implementation of doprocessing function.

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);
    }
}