php multiple keys for a single value

Question

Current Design

I'm making a chatting app where any 2 random users can talk.

On the server (in php), I have an array where I store the client pairs, and the key used to access these pairs is one of the client's IDs.

The reason I don't like this is I have to store the client pair in the array twice. I don't know which client is going to disconnect first, so I hash it twice, once for each client id.

In case this isn't clear yet, the process is: client A and B are chatting. Client B disconnects, so I access the pair with key B, figure out the other client's id is A, then unset both elements using keys A and B.

Question

Any better ideas ? It would be nice if 2 keys could be used to access the exact same element in an array, but I don't think that exists.

p.s.

(This client pair object may sound useless based on the description, but it also holds each client's corresponding socket which I can use to send messages to from the server when a disconnection occurs.)

How I'm picturing this with code:

/* The server receives a message from a client with id 1000 that he has left chat */

$client_pairs = array();  //map holding all client pairs currently chatting

connectClients( $client1, $client2 )
{
    $client_pairs[$client1 -> id] = array( $client1, $client2 );
    $client_pairs[$client2 -> id] = array( $client2, $client1 );
}

disconnectClient( $client_id )
{
    $client_pair = $this -> client_pairs[$client_id] 
    $client2 = $client_pair[1];

    unset( client_pairs[$client_id] );
    unset( client_pairs[$client2 -> id] );

    /*
       do stuff with the $client_pair
    */
}

You're question is rather broad, could you supply some code (pseudo) to describe how you achieve/don't achieve what you're trying to do? — Darren
– Darren, Commented Feb 17, 2015 at 1:24

user488187 · Accepted Answer · 2015-02-17 01:33:38Z

1

You could have two arrays: $users and $sessions. Let's say, for example, that you, have two users: client_id1 and client_id2. You could then:

$sessions[] = your session information, e.g. sockets, plus both client_ids
end($sessions);
$sessId = key($sessions);
$users[$cliend_id1] = $sessId;
$users[$cliend_id2] = $sessId;

When someone disconnects, use their ID as:

$sess = $sessions[$users[$id]];

$sess then should have everything you need.

answered Feb 17, 2015 at 1:33

user488187

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5 Comments

Kacy Over a year ago

I gave you an upvote for now. The only problem with this is this assumes a user is only involved in 1 session at a time. The worst case scenario is that a user could be logged in with 2 different devices, and thus, be in 2 sessions. But this did reinforce an idea I had earlier of just having the client send the session id to the server for whichever session he's disconnecting from. That way I could support any number of sessions.

user488187 Over a year ago

Use $users[$licent_id] = array(one or more session IDs).

Kacy Over a year ago

But how would you know which session the user is disconnecting from? It could any one of them within the array.

user488187 Over a year ago

I understand, you would need to get that at disconnect, but I was just suggesting how to track multiple session IDs for a single user if that was useful. As long as the session has both client_ids, you can always find out what you need.

Kacy Over a year ago

@bodbye Okay I'll just accept this since it was the (only) most useful answer. I'm going to generate a session id on the server side whenever 2 clients connect, send that to both clients (along w other info), then when a client disconnects, they'll send the server the session id they're disconnecting from. And for ungraceful disconnections( i.e. a phone shutting off ), I'll just remove them from all sessions they're involved in (using your suggestion). Thanks for bouncing ideas off with me (which kind of what I needed).

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