网络编程初探

第一个例子很简单，单服务器单客户端。出自csapp，稍微做了一丁点改变。

建立链接后，客户端向服务器发送字符串，并把字符串显示在终端；服务器接受到字符串后，显示长度，并将字符串显示在终端。客户端如果遇到ctrl＋c或ctrl＋d意外中止，可以重新连接服务器。

客户端代码：

/*    echoClient.c
*    Author: toyxia
*/

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

int writen( int fd, char * usrbuf, int n )
{
    char * buf = usrbuf;
    int nleft = n;
    int nwritten;
    while( nleft > 0 )
    {
        if( (nwritten = write(fd, buf, n)) <= 0 )
        {
            if( errno == EINTR )
            {
                nwritten = 0;
            }
            else return -1;
        }
        nleft-=nwritten;
        buf+=nwritten;
    }
    return n;
}


int main( int argc, char ** argv )
{

    /*Defenition*/
    int clientfd;
    struct hostent * hep;
    struct sockaddr_in serverAddr;
    int echoPort=3333;
    char buf[100];
    int readChar=0;

    if( argc != 2 )
    {
        printf( "Usage: %s hostname\n ",argv[0]);
        return -1;
    }

    /*create socket */
    if( (clientfd = socket(AF_INET, SOCK_STREAM, 0 )) < 0 )
    {
        perror( "socket error\n" );
        return -1;
    }

    /* create host entry */
    if( ( hep = gethostbyname(argv[1]) ) == NULL )
    {
        perror( "gethostname error\n" );
        return -1;
    }

    /* set clientAddr */
    bzero( ( char* )&serverAddr, sizeof(serverAddr) );
    serverAddr.sin_family = AF_INET;
    serverAddr.sin_port = htons(echoPort);
    serverAddr.sin_addr = *( (struct in_addr *)hep->h_addr );

    /* connect to server */
    if( ( connect( clientfd, (struct sockaddr *)&serverAddr, sizeof(serverAddr) ) ) < 0 )
    {
        perror("connect error\n");
        return -1;
    }

    /* read from stdio, and write to server */
    while( (readChar = read(STDIN_FILENO, buf, 33)) != 0 )
    {
        printf("read %d char from stdio ", readChar);
        if( writen( clientfd, buf,readChar ) == -1 )
        {
            perror("write error\n");
        }

        buf[ readChar ] = '\0';
        printf( "client echo: %s", buf );
    }

    close( clientfd );
    return 0;

}

服务器端：

/*    echoServer.c
*    Author: toyxia
*/

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netdb.h>
#include <netinet/in.h>
#include <sys/types.h>
#include <strings.h>
#include <arpa/inet.h>

#define BACKLOG 5

int main( int argc, char ** argv )
{
    /* Definition */

    int serverfd, confd;
    struct hostent * hep;
    struct sockaddr_in serverAddr, clientAddr;
    int echoPort = 3333;
    int readChar=0;
    char buf[100];
    int addLen;

    /*create socket*/
    if( (serverfd = socket(AF_INET, SOCK_STREAM,0)) < 0 )
    {
        perror("create socket error\n");
        return -1;
    }

    /* create host entry */
    bzero( (char *)&serverAddr, sizeof(serverAddr) );
    serverAddr.sin_family = AF_INET;
    serverAddr.sin_addr.s_addr = htonl(INADDR_ANY);
    serverAddr.sin_port = htons(echoPort);

    /*binding the socket*/
    if( ( bind( serverfd, (struct sockaddr *)&serverAddr, sizeof(serverAddr) ) ) < 0 )
    {
        perror( "binding socket error\n" );
        return -1;
    }

    /* listen the socket */
    if( listen( serverfd,BACKLOG ) == -1 )
    {
        perror( "lister error\n" );
        return -1;
    }

    /* accept the request */
    while(1)
    {
        /* get the connectino ip */
        addLen= sizeof(serverAddr);
        confd = accept( serverfd, (struct sockaddr *)&clientAddr, &addLen);
        printf( "got connection from %s\n",inet_ntoa(clientAddr.sin_addr) );

        /* read the message from client */
        while( 1 )
        {
            if( ( readChar = read(confd,buf,100) ) == -1 )
            {

                perror("read error\n");
                return -1;
            }
            else if( readChar == 0 )
            {
                perror( "EOF, detach\n" );
                break;
            }

            printf("read %d char from client\n", readChar-1);
            buf[readChar] = '\0';
            printf("server echo: %s", buf);

        }

        close(confd);
    }

    close(serverfd);
}