linux 的tcp 服务器端、客户端事例

linux 的tcp 服务器端、客户端例子

TCP编程的服务器端一般步骤是：

1、创建一个socket，用函数socket()；
2、设置socket属性，用函数setsockopt(); * 可选
3、绑定IP地址、端口等信息到socket上，用函数bind();
4、开启监听，用函数listen()；
5、接收客户端上来的连接，用函数accept()；
6、收发数据，用函数send()和recv()，或者read()和write();
7、关闭网络连接；
8、关闭监听；
TCP编程的客户端一般步骤是：

1、创建一个socket，用函数socket()；
2、设置socket属性，用函数setsockopt();* 可选
3、绑定IP地址、端口等信息到socket上，用函数bind();* 可选
4、设置要连接的对方的IP地址和端口等属性；
5、连接服务器，用函数connect()；
6、收发数据，用函数send()和recv()，或者read()和write();
7、关闭网络连接；

Tcp的多用户连接:

#include<stdio.h>
#include <string.h>
#include <unistd.h>
#include <ctype.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <errno.h>
#include <stdlib.h>
#include <signal.h>

#define MAXLINE 800
int port = 8000;

int main(void)
{
    struct sockaddr_insin;
    struct sockaddr_in pin;
    int listen_fd;
    int conn_fd;
    int sock_fd;
    int nready;
    int maxi;
    int max;
    int client[FD_SETSIZE];
    int address_size = sizeof(pin);
    char buf[MAXLINE];
    char str[INET_ADDRSTRLEN];
    int i;
    int len;
    int n;
    int ret;

    bzero(&sin,sizeof(sin));
    sin.sin_family= AF_INET;
    sin.sin_addr.s_addr= INADDR_ANY;
    sin.sin_port= htons(port);

    signal(SIGPIPE,SIG_IGN);
    signal(SIGCHLD,SIG_IGN);

    listen_fd = socket(AF_INET,SOCK_STREAM, 0);
    if (-1== listen_fd)
    {
        perror("call to socket");
        exit(1);
    }
    n = bind(listen_fd,(struct sockaddr *)&sin,sizeof(sin));
    if (-1== n)
    {
        perror("call to bind");
        exit(1);
    }
    n = listen(listen_fd, 20);
    if (-1== n)
    {
        perror("call to listen");
        exit(1);
    }
    printf("Accepting connections...\n");

    while(1)
    {
        conn_fd = accept(listen_fd,(struct sockaddr *)&pin,&address_size);

        n = fork();
        if (-1== n){
            perror("call to fork");
            exit(1);
        }

        else if(0 == n)
        {
            close(listen_fd);
            while(1)
            {
                memset(buf,'\0',MAXLINE);
readagain:
                ret = read(conn_fd,buf,MAXLINE);
                printf("I read %d Byte!\n",ret);

                if (-1 == ret){
                    if (errno == EINTR){
                        goto readagain;
                    }else{
                        perror("call to read");
                        exit(1);
                    }
                } else if (0== ret){
                    printf("the other side has been closed.\n");
                    break;
                }


                printf("you ip is %s at port %d:%s\n",
                     inet_ntop(AF_INET,&pin.sin_addr,str,sizeof(str)),
                     ntohs(pin.sin_port),buf);

                len = strlen(buf);
                for (i = 0; i< len; i++)
                {
                    buf[i]= toupper(buf[i]);
                }

writeagain:
                ret = write(conn_fd, buf, len+1);
                printf("I write %d Byte!\n",ret);

                if (-1 == ret){
                    if (errno == EINTR){
                        goto writeagain;
                    } else {
                        perror("call to write!");
                        break;
                    }
                }
            }// end while


            ret = close(conn_fd);
            if (-1== ret){
                perror("call close");
                return -1;
            }
            exit(0);
        }
    }
    return 0;
}

     若读操作和写操作还没有开始,就被信号中断，此时对read和write的调用也返回-1,并且errno置为EINTR.对于这种情况，应该再次调用read和write。因为socket此时仍然是完好的。一个处理方法为：     readagain:         n = read(socket_fd, buf ,MAXLEN);         if (-1 == ret){
            if (errno == EINTR){
               goto readagain;
            }else{
               perror("call to read");
               exit(1);
            }
         } else if (0 == ret){
              printf("the other side has been closed.\n");
              break;
         } 　　此外，如果read的返回为0,表明已经读到文件末尾，对于网络socket,则表明已经主动关闭了连接。对于close，最好还是检查一下。因为close是可能是不成功的。如write不返回往往不代表确实写成功(为提高性能的"后写"技术导致的)，如果写出错，调用close时会返回一个错误，如果不检查这个值，就会漏掉这个错误。(摘自akae培训教材) TCP的客户端： 

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

#define MAXLINE 80
int port = 8000;

int main(int argc,char *argv[])
{
  struct sockaddr_in pin;
  int sock_fd;
  char buf[MAXLINE];
  char str[MAXLINE];
  int n;


  signal(SIGPIPE,SIG_IGN);

  bzero(&pin,sizeof(pin));
  pin.sin_family =AF_INET;
  inet_pton(AF_INET,"192.168.2.222",&pin.sin_addr);
  pin.sin_port =htons(port);
  
  sock_fd = socket(AF_INET,SOCK_STREAM, 0);
  n=connect(sock_fd,(void *)&pin,sizeof(pin));
  if (-1== n)
  {
     perror("call connect");
     exit(1);
  }
  while(NULL!= fgets(str,MAXLINE,stdin))
  {
    write(sock_fd, str,strlen(str)+1);
    n=read(sock_fd, buf, MAXLINE);
    if (0 == n)
      printf("the othere side has been closed.\n");
    else
      printf("receive from server:%s\n",buf);
  }
  close(sock_fd);
  return 0;
}

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