/* rlsd.c - a remote ls server - with paranoia
 */

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

#define   PORTNUM  15000   /* our remote ls server port */
#define   HOSTLEN  256
#define   oops(msg)      { perror(msg) ; exit(1) ; }

int main(int ac, char *av[])
{
	struct  sockaddr_in   saddr;   /* build our address here */
	struct	hostent		*hp;   /* this is part of our    */
	char	hostname[HOSTLEN];     /* address 	         */
	int	sock_id,sock_fd;       /* line id, file desc     */
	FILE	*sock_fpi, *sock_fpo;  /* streams for in and out */
	FILE	*pipe_fp;	       /* use popen to run ls    */
	char    dirname[BUFSIZ];       /* from client            */
	char    command[BUFSIZ];       /* for popen()            */
	int	dirlen, c;

      /** Step 1: ask kernel for a socket **/

	sock_id = socket( PF_INET, SOCK_STREAM, 0 );    /* get a socket */
	if ( sock_id == -1 ) 
		oops( "socket" );

      /** Step 2: bind address to socket.  Address is host,port **/

	bzero( (void *)&saddr, sizeof(saddr) ); /* clear out struct     */
	gethostname( hostname, HOSTLEN );       /* where am I ?         */
	hp = gethostbyname( hostname );         /* get info about host  */
	bcopy( (void *)hp->h_addr, (void *)&saddr.sin_addr, hp->h_length);
	saddr.sin_port = htons(PORTNUM);        /* fill in socket port  */
	saddr.sin_family = AF_INET ;            /* fill in addr family  */
	if ( bind(sock_id, (struct sockaddr *)&saddr, sizeof(saddr)) != 0 )
	       oops( "bind" );

      /** Step 3: allow incoming calls with Qsize=1 on socket **/

	if ( listen(sock_id, 1) != 0 ) 
		oops( "listen" );

      /*
       * main loop: accept(), write(), close()
       */

	while ( 1 ){
	       sock_fd = accept(sock_id, NULL, NULL); /* wait for call */
	       if ( sock_fd == -1 )
		       oops("accept");       

	       /* open reading direction as buffered stream */
	       if( (sock_fpi = fdopen(sock_fd,"r")) == NULL )
		       oops("fdopen reading");

	       if ( fgets(dirname, BUFSIZ-5, sock_fpi) == NULL )
		       oops("reading dirname");
	       sanitize(dirname);

	       /* open writing direction as buffered stream */
	       if ( (sock_fpo = fdopen(sock_fd,"w")) == NULL )
		       oops("fdopen writing");

	       sprintf(command,"ls %s", dirname);
	       if ( (pipe_fp = popen(command, "r")) == NULL )
		       oops("popen");
	      
	       /* transfer data from ls to socket */
	       while( (c = getc(pipe_fp)) != EOF )
		       putc(c, sock_fpo);
	       pclose(pipe_fp);
	       fclose(sock_fpo);
	       fclose(sock_fpi);
       }
}

sanitize(char *str)
/*
 * it would be very bad if someone passed us an dirname like
 * "; rm *"  and we naively created a command  "ls ; rm *"
 *
 * so..we remove everything but slashes and alphanumerics
 * There are nicer solutions, see exercises
 */
{
	char *src, *dest;

	for ( src = dest = str ; *src ; src++ )
		if ( *src == '/' || isalnum(*src) )
			*dest++ = *src;
	*dest = '\0';
}