IP Networking

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

void error(char *msg)
{
    perror(msg);
    exit(0);
}

int main(int argc, char *argv[])
{
    int sockfd, portno, n,*choice;

    struct sockaddr_in serv_addr;
    struct hostent *server;

    char buffer[256];
    if (argc < 3) {
       fprintf(stderr,"usage %s hostname port\n", argv[0]);
       exit(0);
    }
    portno = atoi(argv[2]);
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0) 
        error("ERROR opening socket");
    server = gethostbyname(argv[1]);
    if (server == NULL) {
        fprintf(stderr,"ERROR, no such host\n");
        exit(0);
 }
    bzero((char *) &serv_addr, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    bcopy((char *)server->h_addr, 
         (char *)&serv_addr.sin_addr.s_addr,
         server->h_length);
    serv_addr.sin_port = htons(portno);
    if (connect(sockfd,(struct sockaddr *)&serv_addr,sizeof(serv_addr)) < 0) 
        error("ERROR connecting");
bzero(buffer,256);// clears buffer
    n = read(sockfd,buffer,255);//reading
    if (n < 0) 
         error("ERROR readin from socket");
printf("%s", buffer);
 
    fgets(buffer,255,stdin);

//scanf("%d",choice);//readin mesg from terminal
    n = write(sockfd,buffer,255);//writes
    if (n < 0) 
         error("ERROR writing to socket");

if(*buffer == 'r'){
printf("enter user name :  ");

bzero(buffer,256);
fgets(buffer,255,stdin);//readin mesg from terminal
    n = write(sockfd,buffer,strlen(buffer));//writes
    if (n < 0) 
         error("ERROR writing to socket");
n = read(sockfd,buffer,255);//reading
    if (n < 0) 
         error("ERROR readin from socket");
printf("%s\n",buffer);// printing
bzero(buffer,256);

}

if(*buffer == 'l')//login
{
printf("enter your user name: ");

bzero(buffer,256);
fgets(buffer,255,stdin);//readin mesg from terminal
    n = write(sockfd,buffer,strlen(buffer));//writes
    if (n < 0) 
         error("ERROR writing to socket");
printf("\n enter your password");
bzero(buffer,256);
fgets(buffer,256,stdin);//readin mesg from terminal
    n = write(sockfd,buffer,strlen(buffer));//writes
n = read(sockfd,buffer,255);//reading
    if (n < 0) 
         error("ERROR readin from socket");
printf("%s\n",buffer);// printing

}
    while(1)
{
    printf("type  message: ");
    bzero(buffer,256);

    fgets(buffer,255,stdin);//readin mesg from terminal
    n = write(sockfd,buffer,strlen(buffer));//writes
    if (n < 0) 
         error("ERROR writing to socket");
    bzero(buffer,256);// clears buffer
    n = read(sockfd,buffer,255);//reading
    if (n < 0) 
         error("ERROR reading from socket");
    printf("%s\n",buffer);// printing
}
    return 0;
}

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

void readwrite(int, int, int); /* function prototype */
void error(char *msg)
{
    perror(msg);
    exit(1);
}

int main(int argc, char *argv[])
{
     int sockfd, newsockfd, portno, clilen, pid;
     struct sockaddr_in serv_addr, cli_addr;

     if (argc < 2) {
         fprintf(stderr,"ERROR, no port provided\n");
         exit(1);
     }
     sockfd = socket(AF_INET, SOCK_STREAM, 0);
     if (sockfd < 0) 
        error("ERROR opening socket");
     bzero((char *) &serv_addr, sizeof(serv_addr));
     portno = atoi(argv[1]);
     serv_addr.sin_family = AF_INET;
     serv_addr.sin_addr.s_addr = INADDR_ANY;
     serv_addr.sin_port = htons(portno);
     if (bind(sockfd, (struct sockaddr *) &serv_addr,
              sizeof(serv_addr)) < 0) 
              error("ERROR on binding");
     listen(sockfd,5);
     clilen = sizeof(cli_addr);

     while (1) {
         newsockfd = accept(sockfd, 
               (struct sockaddr *) &cli_addr, &clilen);
         if (newsockfd < 0) 
             error("ERROR on accept");
         pid = fork();
         if (pid < 0)
             error("ERROR on fork");
         if (pid == 0)  {
             close(sockfd);
              int x,y,x1,y1,i=0,n,choice;
              char buffer[256],ex[256];
               FILE *fp;
           printf("Incoming connection from %s - sending welcome\n", inet_ntoa(cli_addr));
          n = write(newsockfd," welcome \n - select one \n r for registration \n l for login",145);
             if (n < 0) error("ERROR writin to socket");
 
 bzero(buffer,256);
                n = read(newsockfd,buffer,255);
               if (n < 0) error("ERROR reading from socket");

if(*buffer == 'r')
{
   
// n = write(newsockfd," welcome \n - please Enter a user name:",45);
            // if (n < 0) error("ERROR writing to socket");
             bzero(buffer,256);
                n = read(newsockfd,buffer,255);
               if (n < 0) error("ERROR reading from socket");
             fp=fopen(buffer,"a+");
             fwrite(buffer,1,strlen(buffer),fp);
n = write(newsockfd,"\n your user name is your password:",45);
             if (n < 0) error("ERROR writing to socket");
                            
              fclose(fp);
exit(0);

             
}
if(*buffer == 'l')
{
   char key[256];

bzero(buffer,256);
                n = read(newsockfd,buffer,255);
               if (n < 0) error("ERROR reading from socket");
       
  fp=fopen(buffer,"r");

  if(fp=='\0')
{
  n = write(newsockfd,"\n No user exist:",45);
             if (n < 0) error("ERROR writing to socket");
 // n = write(newsockfd,"\n please register :",45);
           //  if (n < 0) error("ERROR writing to socket");
}
else
{


bzero(buffer,256);
 n = read(newsockfd,buffer,255);
               

fscanf(fp,"%s",key);

if(strcmp(buffer,key)!=0)
{
n = write(newsockfd,"\nunsucessful login:",45);
            // if (n < 0) error("ERROR writing to socket");
break;
}

   
    n = write(newsockfd,"\n loged:",45);
             if (n < 0) 
          error("ERROR writing to socket");


              
}

}
         
  
              srand((unsigned)time(3));
              x=rand()%4;
              y=rand()%4;
             
             readwrite(newsockfd,x,y);
             exit(0);
         }
         else close(newsockfd);
     } /* end of while */
     return 0; /* we never get here */
}


void readwrite(int sock,int x ,int y)
{
   int n;
   char buffer[256];
   
  printf("x=%d y=%d",x,y);
    while(1){
   bzero(buffer,256);
   n = read(sock,buffer,255);
   if (n < 0) error("ERROR reading from socket");
   printf("Client: %s\n",buffer);
   n = write(sock,"Server :msg reached",25);
   if (n < 0) error("ERROR writing to socket");
}
 
}