tcp通信

TCP通信，理解都在注释里，看着敲敲。

TCP的三次握手可以看http://www.cnblogs.com/leezhxing/p/4524176.html可以看出listen()函数阶段完成的三次握手,accept()时三次握手已经完成。

关于listen函数的backlog参数可以看：http://blog.chinaunix.net/uid-24782829-id-3456109.html

tcp_client.c

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>  /* struct hostent 需要 */

#define PORT 4321  /* server端口 */
#define MAXSIZE 100

int main(int argc, char *argv[])
{
    int sockfd;    //socket文件描述符
    int num;       //用于存储接收和发送的字节数
    char buf[MAXSIZE];    //用于recv的接收字符数组
    struct hostent *he;    //通过域名获取IP
    struct sockaddr_in server; //存储server的socket信息
   
   /* 例如： ./tcp_client.out 127.0.0.1 */
    if (argc != 2)
    {
        printf("Usage: %s <IP Address>
",argv[0]);
        exit(1);
    }
   
    if((he=gethostbyname(argv[1]))==NULL)
    {
        printf("gethostbyname() error
");
        exit(1);
    }
   
   //建立socket
    if((sockfd=socket(AF_INET,SOCK_STREAM, 0))==-1)
    {
        printf("socket() error
");
        exit(1);
    }

    //server端的socket信息
    bzero(&server,sizeof(server)); //先清空server
    server.sin_family = AF_INET;
    server.sin_port = htons(PORT); //转为网络字节序
    server.sin_addr = *((struct in_addr *)he->h_addr); //看udp的client的解释

    if(connect(sockfd, (struct sockaddr *)&server, sizeof(server))==-1)
    {
        printf("connect() error
");
        exit(1);
    }
    
    char str[] = "hello
";

    //send成功返回发送的字节数,失败返回-1
    if((num=send(sockfd,str,sizeof(str),0))==-1){
        printf("send() error
");
        exit(1);
    }

    //recv成功返回接收的字节数,失败返回-1
    if((num=recv(sockfd,buf,MAXSIZE,0))==-1)
    {
        printf("recv() error
");
        exit(1);
    }
    buf[num-1]='';
    printf("server message: %s
",buf);
    close(sockfd);
    return 0;
}

tcp_server.c

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

#define PORT 4321  //占用端口
#define BACKLOG 1 //定义侦听队列长度  
#define MAXSIZE 1024

int main(int argc, char *argv[])
{
    char buf[MAXSIZE]; //recv()接收用字符数组
    int listenfd, connectfd;  
    struct sockaddr_in server; 
    struct sockaddr_in client; 
    socklen_t addrlen; //存储struct sockaddr_in的长度

    //建立TCP SOCKET
    if ((listenfd = socket(AF_INET, SOCK_STREAM, 0)) == -1)
    {
        /* handle exception */
        perror("socket() error. Failed to initiate a socket");
        exit(1);
    }
 
    //填充socket信息
    bzero(&server, sizeof(server));
    server.sin_family = AF_INET;
    server.sin_port = htons(PORT);
    server.sin_addr.s_addr = htonl(INADDR_ANY); //接收任意连接

    //bind
    if(bind(listenfd, (struct sockaddr *)&server, sizeof(server)) == -1)
    {
        /* handle exception */
        perror("Bind() error.");
        exit(1);
    }
   
   //listen
    if(listen(listenfd, BACKLOG) == -1)
    {
        perror("listen() error. 
");
        exit(1);
    }

    addrlen = sizeof(client);  //等同于sizeof(struct sockaddr_in)
    while(1){
        /*
         * accept函数返回一个新的sockfd,之后的操作都会在这个fd上进行
         * 系统会把远端端的socket信息都存储在client上
         * addrlen是地址
         */
        if((connectfd=accept(listenfd,(struct sockaddr *)&client, &addrlen))==-1)
          {
            perror("accept() error. 
");
            exit(1);
          }

        struct timeval tv;
        gettimeofday(&tv, NULL); //获取微妙级时间,具体看手册
        printf("client's ip %s, port %d at time %ld.%ld
",inet_ntoa(client.sin_addr),htons(client.sin_port), tv.tv_sec,tv.tv_usec);
       
        int iret=-1; //初始化接收字节的长度
        while(1)
        {
            iret = recv(connectfd, buf, MAXSIZE, 0);
            if(iret>0){
                printf("%s
", buf);
            }else{
                close(connectfd);
                break;
            }

            //发送接收到的信息给client
            send(connectfd, buf, iret, 0); 
        }
    }
    close(listenfd); 
    return 0;
}