Thread: Socket Problem (with shell server)

Hi!
(firstly : sorry for my english, i posted my problem in a french forum but i diddn't found any answer )
So:
I have to make a shell in a server.
The client has to connect to the server, ask some tasks to the server, the server has to resolve the task and then give the result to the client.
The solution:
I redirected stdout and stderr to the client, then when the client ask someting to the server, the server use execvp and then the client read the stdout of the execvp.
The problem :
Some tasks (like chmod) doesn't have any output.
With those tasks, i have a big problem : The client waits a message from the server, but he receives nothing !
I can't post my code because it's for the school, but i can show some importants parts of it :
this is the main part of my client-Socket:

Code:

fgets(requete,250,stdin);
	while (strcmp(task,"exit\n" )){
	  write(sd,task,250);
	  read(sd,ligne,taille);
 printf(ligne);
fgets(task,250,stdin);
	}

server :

Code:

while(condition) {
i=0;
  tokens[i]=strtok(ligne," \n" );
  while (tokens[i] != NULL) tokens[++i]=strtok(NULL," \n" );
  if (fork()==0)
  {
  	fflush(stdout);
  	execvp(tokens[0],tokens);
  	fflush(stdout);
  	printf("invalid task\n" );
  	exit(1);
  }
  wait(0);
  read(h, ligne, strlen(ligne));
	  }
  }

with the others tasks (like "echo hello world" everything works fine).

Sorry again for my english, and thanks for helping

This is a problem that is generally solved in one of two ways: either by sending the size of the data followed by the data itself, or by sending the data followed by a terminating character or characters.

The downside to the first solution is that you have to know in advance how much data you have, and the downside to the second solution is that your data cannot contain the terminating character sequence without being escaped somehow.

Basically, you need to devise a simple protocol for the communication. It's up to you to figure out what makes sense for your application, assuming your assignment does not specify one.

Hi, fisrtly thank you for ur answers !

Originally Posted by cas

This is a problem that is generally solved in one of two ways: either by sending the size of the data followed by the data itself, or by sending the data followed by a terminating character or characters.

The downside to the first solution is that you have to know in advance how much data you have, and the downside to the second solution is that your data cannot contain the terminating character sequence without being escaped somehow.

Basically, you need to devise a simple protocol for the communication. It's up to you to figure out what makes sense for your application, assuming your assignment does not specify one.

I just redirect stdout of the server to the client, i can't sending the data followed by a terminating character :/ I don't know how to use one of those solutions with that :/

If you create a new (temporary) socket just to handle the stdout of the exec'ed program (use dup() to connect the socket fd to the stdout fd), then that temporary socket will close when the exec'ed program closes.

I have to use only 2 sockets

Thank u again for ur help