SOCKET WITH FTP-->AN IMPLEMENTATION OF SOCKET WITH 1CLIENT & 1SERVER

/*iIN SERVER*/

/*AN IMPLEMENTATION OF FTP USING SOCKET*/

//FTP IS NOTHING BUT DEALING OF FILES ON INTERNET...THROUGH SOCKET...SOCKET IS LIKE A PIPE WHICH WE HAD STUDIED BEFORE IN SINGLE SYSTEM..

//NOW SOCKET WHOSE 1 END WILL ATTACH TO ANOTHER SOCKET ON INTERNET & ANOTHER END WITH SYSTEM OF CLIENT OR SERVER...

//BASICALLY THERE ARE TWO SOCKETS WHICH ARE COMMUNICATING EACH OTHER ...2 DIFFRENT SOCKETS OF 2 DIFFRENT SYSTEMS ,,,ARE DEALING WITH EACH OTHER...VIA NET...

//SERVER SOCKET IS HELPING TO CREATE || WE CAN SAY CREATING A EXACT COPY OF CLIENT SOCKET...ACCEPT CALL IS RETURNING US fd of CLIENT SOCKET ...THROUGH WHICH CLIENT SOCKET ..WHICH WILL ALSO RETURN FD OF CLIENT SOCKET ...SO BOTH CLIENT & SERVER ARE COMMUNICATING TO EACH OTHER BASICALLY WITH THE HELP OF CLIENT FD..

//IN SERVER WE ARE WRITTING IN CLIENT FD....& IN CLIENT WE ARE READING FROM SAME CLIENT FD....//

#include<stdio.h>

#include<stdlib.h>

#include<unistd.h>

#include<string.h>

#include<sys/socket.h>

#include<linux/in.h>

#include<fcntl.h>//FOR O_RDONLY MODE ...OR OPEN CALL OF SYSTEM

struct sockaddr_in ser_add,client_add;//declare the VARIABLES OF sockaddr_in structure defined in sys/socket.h

int main()

{

        char *usr,*page,*buff;//take 3 POINTERS & MALLOC THEM ..WITH WOULD BE USED FURTHER

        usr=malloc(30);

        printf("size of usr=%d\n",sizeof(usr));

        page=malloc(30);

        buff=malloc(243);

  int wfd,rfd,sfd,ret,fd;

        socklen_t len;

        ser_add.sin_family=AF_INET;//PUT ADDRESS FAMILY ..PORT NO..TO ENTER INTO OTHER SYSTEM.,..& IP ADDRESS TO SEARCH SYSTEM INTO NETWORK...INTO THIS VARIABLE...BCZ THESE MANY THINGS ARE DEMANDED AS ELEMENT OF struct sockaddr_in structure in sys/socket.h//////////

        ser_add.sin_port=htons(556);

        ser_add.sin_addr.s_addr=inet_addr("127.0.0.1");

        len=sizeof(struct sockaddr_in);

        sfd=socket(AF_INET,SOCK_STREAM,0);//socket system call is used to create a socket & it will return fd of server

        printf("sfd=%d\n",sfd);

        ret=bind(sfd,(struct sockaddr*)&ser_add,len);//SERVER SOCKET IS ALWAYS BINDED ...WITHOUT BINDING ...IT WILL NOT ALLOW THE CLIENT TO CONNECT.....struct sockaddr ..is padded with struct sockaddr_in...//

        if(ret==0)

                printf("binded\n");

        else

                printf("not binded\n");

        ret=listen(sfd,5);//listen call will decide ..how many max. no. of clients could wait for socket ...//

        if(ret==0)

                printf("listen successful\n");

        else

                printf("listen not succesful\n");

        fd=accept(sfd,(struct sockaddr*)&client_add,&len);//accept call DEMANDS socket fd,,,& RETURN CLIENT FD..

//2ND ARG IS EMPTY TILL NOW ...BUT WILL GET CLIENT_AAD AT RUN TIME ...&LEN WILL GET LENGHT OF THAT ADDRESS AT RUNTIME...

        printf("fd of client=%d\n",fd);

   ret=read(fd,usr,10);//SERVER WILL GET USERNAME THROGH FD RETURNED BY ACCEPT CALL...WHICH IS COPY OF CLIENT SOCKET

        printf("ret=%d\n",ret);

        printf("usr=%s\n",usr);

        if(strncmp(usr,"anubala",8) == 0)//COMPARE n NO. of characters OF USERNAME WITH actuall username..WHICH IS IN DATABASE OF SERVER

        {

        write(fd,"ENTER THE PASSWORD",19);//IF USERNAME IS MATCHED PROPERLY...THEN SEND THESE WORDS TO CLIENT..DEMAND THE PASSWORD

        }

        else

        {

        write(fd,"USERNAME NOT FOUND",20);//IF USERNAME IS NOT MATCHED ...THEN SEND THESE WORDS TO CLIENT

        return -1;

        }

        read(fd,usr,8);//SERVER WILL READ THAT PASSWORD

        if(strncmp(usr,"emblogic",8)==0)//& MATCH THAT PASSWORD WITH DATABASE OF SERVER...//

        write(fd,"PASSWORD IS ACCESSED",20);//IF PASSWORD IS MATCHED ....THEN  SEND THESE WORDS TO CLIENT INTO SAME FD THAT PASSWORD IS ACCESED

        else

        write(fd,"PASSWORD IS NOT ACCESSED",30);//OTHERWISE SEND THESE WORDS TO CLIENT THAT PASSWORD NOT ACCESSED