/* rlsd.c – a remote ls server – with paranoia
*/
#include
#include
#include
#include
#include
#include
#include
#include
#include
#define PORTNUM 15000 /* our remote ls server port */
#define HOSTLEN 256
#define oops(msg) { perror(msg) ; exit(1) ; }
void sanitize(char *str)
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);
}
}
void 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’;
}