Multiple chat rooms - Is using ports the only way ? What if there are hundreds of rooms?_问答_开发者

Need some direction on this. I'm writing a chat room browser-application, however there is a subtle difference.

These are collaboration chats where one person types and the other person can see live ever keystroke entered by the other person as they type.

Also the the chat space is not a single line but a textarea space, like the one here (SO) to enter a question.

All keystrokes including tabs/spaces/enter should be visible live to the other person. And only one person can type at one time (I guess locking should be trivial)

I haven't written a multiple chatroom application. A simple client/server where both are communicatiing over a port is something I've written.

So here are the questions

1.) How is a multiple chatroom application written ? Is it also port based ?

2.) Showing the other persons eve开发者_高级运维ry keystroke as they type is I guess possible through ajax. Is there any other mechanism available ?

Note : I'm going to use a python framework (web2py) but I don't think framework would matter here.

Any suggestions are welcome, thanks !

The Wikipedia entry for Comet (programming) has a pretty good overview of different approaches you can take on the client (assuming that your client's a web browser), and those approaches suggest the proper design for the server (assuming that the server's a web server).

One thing that's not mentioned on that page, but that you're almost certainly going to want to think about, is buffering input on the client. I don't think it's premature optimization to consider that a multi-user application in which every user's keystroke hits the server is going to scale poorly. I'd consider having user keystrokes go into a client-side buffer, and only sending them to the server when the user hasn't typed anything for 500 milliseconds or so.

You absolutely don't want to use ports for this. That's putting application-layer information in the transport layer, and it pushes application-level concerns (the application's going to create a new chat room) into transport-level concerns (a new port needs to be opened on the firewall).

Besides, a port's just a 16-bit field in the packet header. You can do the same thing in the design of your application's messages: put a room ID and a user ID at the start of each message, and have the server sort it all out.

The thing that strikes me as a pain about this is figuring out, when a client requests an update, what should be sent. The naive solution is to retain a buffer for each user in a room, and maintain an index into each (other) user's buffer as part of the user state; that way, when user A requests an update, the server can send down everything that users B, C, and D have typed since A's last request. This raises all kind of issues about memory usage and persistence that don't have obvious simple solutions

The right answers to the problems I've discussed here are going to depend on your requirements. Make sure those requirements are defined in great detail. You don't want to find yourself asking questions like "should I batch together keystrokes?" while you're building this thing.

You could try doing something like IRC, where the current "room" is sent from the client to the server "before" the text (/PRIVMSG #room-name Hello World), delimited by a space. For example, you could send ROOMNAME Sample text from the browser to the server.

Using AJAX would be the most reasonable option. I've never used web2py, but I'm guessing you could just use JSON to parse the data between the browser and the server, if you wanted to be fancy.