client and server communicating - c

Question

Iam trying to run shell commands on a server and want them to be printed in the client shell..
that means when i type a command in the client shell that command should go to the server and execute inside the server and return the output back to the client
but the only problem iam, facing now is when i run commands like "Date,hostname etc" in the client programme it shows the expected output(Client -> server -> client). but when i run "ls" it shows only the first file in the folder..
as an example if i put five files in a folder it shows only the name of the first file in the folder
CLIENT program
#include <sys/socket.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <netdb.h>
#define PORT 1300
#define HOST "127.0.0.1"
#define MAXLINE 1024
main() {
register int s,len;
struct sockaddr_in pin;
struct hostent *hp;
char buff[MAXLINE + 1];
if ((hp=gethostbyname(HOST)) == 0) {
perror("gethostbyname");
exit(1);
}
bzero(&pin, sizeof(pin));
pin.sin_family = AF_INET;
pin.sin_addr.s_addr= ((struct in_addr *) (hp->h_addr)) -> s_addr;
pin.sin_port=htons(PORT);
if ((s=socket(AF_INET,SOCK_STREAM,0)) < 0) {
perror("client:socket");
exit(1);
}
if (connect(s,(struct sockaddr *) &pin,sizeof(pin)) < 0) {
perror("client:connect");
exit(1);
}
char out[20];
strcpy(out,"exit");
while(1){
bzero(buff,MAXLINE+1);
printf("Message> ");
scanf("%s",buff);
if(strcmp(out,buff) == 0){
exit(1);
}
send(s,buff,strlen(buff)+1, 0);
bzero(buff,MAXLINE+1);
read(s,buff,MAXLINE);
printf("Received>");
puts(buff);
}
close(s);
}
here's my SERVER program
#include <sys/socket.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <netdb.h>
#include <time.h>
#include<string.h>
#define PORT 1300
#define MAXLINE 4096
#define COMMAND_LEN 20
#define DATA_SIZE 1512
main() {
register int s,ns;
int len;
struct sockaddr_in sin,pin;
char buff[MAXLINE + 1];
time_t ticks;
struct tm * timeinfo;
FILE *pf;
char command[COMMAND_LEN];
char data[DATA_SIZE];
bzero(&sin, sizeof(sin));
sin.sin_family = AF_INET;
sin.sin_addr.s_addr= htonl(INADDR_ANY);
sin.sin_port=htons(PORT);
if ((s = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
perror("server: socket");
exit(1);
}
if (bind(s,(struct sockaddr *)&sin, sizeof(sin)) < 0) {
perror("server:bind");
exit(1);
}
if (listen(s,5) <0) {
perror("server: listen");
exit(1);
}
for(; ;) {
if ((ns = accept(s, (struct sockaddr *)&pin, &len)) < 0) {
perror("server: accept");
exit(1);
}
while(1){
bzero(buff,MAXLINE+1);
read(ns,buff,MAXLINE);
pf=popen(buff,"r");
if(!pf)
{
fprintf(stderr,"could not open for output. \n");
}
fgets(data,DATA_SIZE,pf);
send(ns,data,strlen(data)+1,0);
//puts(buff);
//send(ns,buff,strlen(buff)+1,0);
}
}
close(ns);
close(s);
}
i tried changing the buffer size but still the problem remains ...
this is how i changed the code segment in server side
bzero(buff,MAXLINE+1);
read(ns,buff,MAXLINE);
pf=popen(buff,"r");
if(!pf)
{
fprintf(stderr,"could not open for output. \n");
}
while(NULL!=fgets(data,DATA_SIZE,pf)){
send(ns,data,strlen(data)+1,0);
}
if(pclose(pf)!=0)
fprintf(stderr,"Error:failed to close command stream \n");
* data ='\0';
//puts(buff);
send(ns,data,1,0);
and in the client side i changed it as
the below code is just under the main method
int idone =0, ibytes;
char *p;
this part is in the client programme as shown
while(! idone)
{
ibytes = read (s,buff,MAXLINE);
for (p=buff;(ibytes--);p++)
{
if(! *p)
{idone=1;break;}
putc(*p,stdout);
}
now when i run the "ls" command it still shows only one file and now after doing the above change now it doesnt even run commands like "date ,hostname ..."

Answer 1

On the client side,
read(s,buff,MAXLINE);
Is not guaranteed to get all the data that the server sent. In fact it can return after returning 1 byte. You're going to have to add a header to your messages on the server side and then make sure you keep doing read until you receive the entire message.
Not to mention doing one fgets() on the server side means you only read one line from popen() and send that. You need to keep doing fgets() till EOF.
Not to mention that you never close pf with a pclose.
So, now in the comments you've tried to address point 2 & point 3. pclose is in the wrong place, but in addition, you still have the problem of point 1. You don't know how much to read on the client before the "results" are complete. So we have to make up a protocol.
So right now your code in the comments will send each line of ls back with a newline and a \0. Lets change that. Lets only send printable text until everything is done, then send a \0.
while ( NULL != fgets(data, DATA_SIZE,pf)) {
send( ns, data, strlen( data), 0) ; // not strlen() +1
}
if ( pclose( pf) != 0 ) { perror("Error") ; } // outside the while loop
* data= '\0' ;
send( ns, data, 1, 0 ) ; // send a null
Now the client can do read() all day long, and until it gets a \0 it knows there's more data. Beware of a few gotchas of course. You have to add \0 to your client side buffer before printing each message. And when you go looking for \0 in the message, you have to make sure you didn't find it passed the end of the number of bytes sent.
The key here is that you have to look at the return value of read() for how many bytes you actually got.
int idone= 0, ibytes ;
char * p;
while ( ! idone )
{
ibytes= read(s,buff,MAXLINE);
for ( p= buff ; ( ibytes -- ) ; p ++ )
{
if ( ! * p ) { idone= 1 ; break ; }
putchar( * p) ;
}
}