linux TCP socket in a simple procedure (2)

   The program is a simple but complete tcp client / server instance. Implements connection establishment and the local customers and the server machine transmits a message to each other. After the connection is established, the client receives and prints out data sent from the server. Print out the server IP address of the client and the client sends data.

   Server program srv.c as follows:

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

#define PORT    1234
#define BACKLOG 1

int main()
{
        int listenfd,connectfd;
        struct sockaddr_in server;
        struct sockaddr_in client;
        int sin_size;

        if((listenfd=(socket(AF_INET,SOCK_STREAM,0)))==-1)
        {
                //handle exception
                perror("Creating socket failed");
                exit(1);
        }

        bzero(&server,sizeof(server));
        server.sin_family=AF_INET;
        server.sin_port=htons(PORT);
        server.sin_addr.s_addr=htonl(INADDR_ANY);

        /*Bind socket to address*/
        if(bind(listenfd,(struct sockaddr *)&server,sizeof(struct sockaddr))==-1)
        {
                perror("Bind error");
                exit(1);
        }

        /*Listen client's reqirement*/
        if(listen(listenfd,BACKLOG)==-1)
        {
                perror("listen failed");
                exit(1);
        }

        sin_size=sizeof(struct sockaddr_in);
        if((connectfd=accept(listenfd,(struct sockaddr *)&client,&sin_size))==-1)
        {
                perror("accept() error");
                exit(1);
        }


        //prints client's IP
        printf("You got a connection from %s\n",inet_ntoa(client.sin_addr));
        send(connectfd,"Welcome to my server.\n",22,0);

        close(connectfd);
        close(listenfd);

}

   The client program cli.c as follows:

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

#define PORT 1234
#define MAXDATASIZE 100

int main(int argc,char *argv[])
{
        int fd,numbytes;
        char buf[MAXDATASIZE];
        struct hostent *he;

        struct sockaddr_in server;

        if(argc!=2)
        {
                printf("Usage:%s<IP Address>",argv[0]);
                exit(1);
        }
        if((he=gethostbyname(argv[1]))==NULL)
        {
                perror("gethostbyname() error\n");
                exit(1);
        }

        if((fd=(socket(AF_INET,SOCK_STREAM,0)))==-1)
        {
                printf("socket() error");
                exit(1);
        }

        bzero(&server,sizeof(server));
        server.sin_family=AF_INET;
        server.sin_port=htons(PORT);
        server.sin_addr=*((struct in_addr*)he->h_addr);

        /*Connect to server and receive data from the server.*/

        if(connect(fd,(struct sockaddr *)&server,sizeof(struct sockaddr))==-1)
        {
                printf("connect() error\n");
                exit(1);
        }

        if((numbytes=recv(fd,buf,MAXDATASIZE,0))==-1)
        {
                printf("recv() error");
                exit(1);
        }
        buf[numbytes]='\0';
        printf("Server Message: %s\n",buf);

        close(fd);
}

   After compilation, first start the server program:

[root@mylinux 20160910]# ./srv

   And then start the client program:

[root@mylinux 20160910]# ./cli 127.0.0.1

  

   Operating results server:

[root@mylinux 20160910]# ./srv
You got a connection from 127.0.0.1

   The client's operating results:

[root@mylinux 20160910]# ./cli 127.0.0.1
Server Message: Welcome to my server.