CODEWITHSUNDEEP
c++socketsnetwork-programming
Carlj901
Carlj901

Reputation: 1411

Server/client chat

The idea i'm having is that clients can connect to a chat room on a server and communicate with each other. In the chat room you should also be able to target another user and they should be able to talk with each other.

Now to the problem. I'm not sure which way is the easiest/best way to implement this. For the chat room I thought of when a user writes something, the message is sent to the server and the server then echoes that message to the other clients. Not sure what other options I have.

What i'm most confused about is how I can make only 2 clients talk to each other. Either the server act as a proxy and just forward the messages to the other client, this seem inefficient though. The only alternative to this I can think of is that the 2 clients establish a connection between each other. Which implementation is most common in order to achieve this?

I am using unix sockets with C++.

Upvotes: 1

Views: 954

Answers (2)

Matthew Hall
Matthew Hall

Reputation: 605

There are a few options for many-to-many chat and one-to-one chat. However, the only reasonably sane option for many-to-many chat is to do as you've said: send a message to the centralized server, the server relays the message to all other connected clients (or, in the same "room" / "channel").

For one-to-one chat, I recommend that you follow the same exact model: it's just a special case of the many-many chat relay in which the message is sent by the server, as a proxy, to only one other connected client. This is simple, and it hides every client's IP address from every other.

However, if the one-to-one communication were to become more voluminous than chat (e.g., a file transfer), direct one-to-one communication may be appropriate. In this case, the server should relay the initiation of a direct, peer-to-peer communication channel to the remote user, probably exchanging IP addresses upon setup, and the clients would then connect directly to each other for their special-purpose direct communication (while usually, though optionally, remaining connected to the server).

Thus, one-to-one communication is normally proxied by the server as in the general case of many-to-many, and the degree to which that practice is inefficient is superficial. Special purpose one-to-one communication (file transfers, VoIP, etc.) are done with direct client-to-client connections usually orchestrated at first by the server (i.e., to prepare each side for direct communication).

Implementation hint: the server is all TCP. Read about non-blocking sockets, the POSIX system call poll, and let the idea of message framing over TCP roll around in your head. You can then skip multithreading [and scalability] issues in the server code. The clients, besides speaking the same custom TCP protocol as your server, are up to you.

Upvotes: 1

Infinity
Infinity

Reputation: 75

Well you can implement a multi-threaded client/server. A single "server" relaying the messages is the right way to go(to preserve global ordering of messages). Also think about leader election algorithms(http://en.wikipedia.org/wiki/Bully_algorithm) for example in case your "server" goes down. Check out

Another way to do this would be to use signals and event-driven programming.

Upvotes: 1

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