Is it acceptable to use resource ids as an array key?

sneakyimp

I have a loop that accepts socket connections from clients. Each socket is a resource much like a file pointer is a resource or a database connection is a resource. I'm wondering if I can create an array to track my connected clients that uses the socket resource id as a key.

Currently, my code doesn't do that. As you can see here, I loop through my entire array of numerically-indexed clients every time sockets need reading and check to see if each of those clients is in the $sockets_to_read array.

		while (true) { 

		/* specify which sockets need listening...should include
		 all connected client sockets *and* the main listening socket */
		$this->sockets_to_read = array();
		$this->sockets_to_read[0] = $this->main_listening_socket;
		foreach ($this->clients as $client) {
			if ($client['socket_id'] != NULL)
				$this->sockets_to_read[] = $client['socket_id'];
		}

		/* Set up a blocking call to socket_select()...this call alters
		   the $sockets_to_xxxx arrays so that they indicate which sockets
		   need attention */
		$num_changed_sockets = socket_select($this->sockets_to_read, $this->sockets_to_write, $this->sockets_to_except, $this->socket_select_timeout);


		/* loop through all our clients and deal with those whose socket_ids
		   show up in the $this->sockets_to_read array */
		foreach($this->clients as $client_key => $client) {

			if (in_array($client['socket_id'] , $this->sockets_to_read)) {
				$incoming_socket_data = socket_read($client['socket_id'], $this->socket_read_length, PHP_BINARY_READ);
				// blah blah blah
			}

			// blah blah blah

		}
	}

I know this is really inefficient because I might have 40 connected clients and only 1 socket that needs reading, but I was worried about just doing something like

$new_client_resource = socket_accept($this->main_listening_socket); // echo $new_client_resource and it says something like "Resource #1"
$client = array();
$client['username'] = 'foo';
$client['rank'] = 'Admiral';
$this->clients[$new_client_resource] = $client; // warning!  weirdness here.  Is this an associative array?  numeric?  This looks weird to me.

I have a feeling that I could use the socket resource id as an array index and it would work but am wondering if that might cause weird problems that I can't foresee...like if a client disconnects and a new client connects and acquires a previously used resource id.

Any sage advice would be much appreciated.

NogDog

Other than the fact that it feels not quite right to me, I don't know of any technical reason you can't do it. My one concern would be what happens if that resource is closed for some reason by another piece of code. Does that screw up the array or not?

sneakyimp

I agree that it doesn't sound quite right. The issue of uniqueness is what's really bugging me. When a socket closes, its associated element in the array is [man]unset[/man]. If a new socket opens later with that same resource id, I don't imagine there would be any conflict.

It just doesn't feel right though 🙁

NogDog

Some food for thought:

From the Arrays page:

A key may be either an integer or a string.

I would therefore assume that the resource is being converted to a string when used as an array key.

From the Strings page:

Resources are always converted to strings with the structure "Resource id #1", where 1 is the unique number assigned to the resource by PHP at runtime. Do not rely upon this structure; it is subject to change. To get a resource's type, use the get_resource_type() function.

Therefore, I'd be in favor of finding some other structure that did not depend upon a resource id for an array key, even if it seems to work.

sneakyimp

I think it's worth noting that I don't expect these arrays to go into any kind of persistent data structure. Even so, that warning seems to really discourage use of resources-converted-to-strings stuff. I was considering something like this:

$new_client_resource = socket_accept($this->main_listening_socket); // echo $new_client_resource and it says something like "Resource #1"
$client = array();
$client['username'] = 'foo';
$client['rank'] = 'Admiral';
$new_key = md5($new_client_resource);
$this->clients[$new_key] = $client;

Now I'm not so sure.

What I'm really tring to get at here is the best way to associate some data with a particular socket. For instance, if some client connects and [man]socket_accept[/man] sets a socket resource pointer in $this->sockets_to_read then I want to prompt that client for a username and then remember the username as being associated with that particular socket connection.

I currently do this by maintaining a numerically indexed array in $this->clients. This results in some nested loop stuff which looks inherently inefficient. If a given socket sends an incoming message, and I want to know the username associated with that socket, I have to loop through $this->clients until I find the $client where $client['socket_resource'] == $socket_speaking.

See what I mean? If you can think of any good/cool way to associate data with a socket, I'd appreciate knowing about it.