bs-socket

Simple bindings to socket.io.

To build everything run npm run build and to run the demo run npm run run and go to localhost:3000 on two tabs. You can send messages back and forth!

Documentation

Everything lives under the namespace BsSocket. To create a server/client/namespace, use Server.Make, Client.Make and Namespace.Make respectively. These functors take a module that contains 2 things: a type called clientToServer and a type called serverToClient, which define the type of the message that the client will send to the server and vice versa.

For example:

module Messages = {
  type username = string;
  type clientToServer =
  | Login(username);
  type serverToClient =
  | LoginSuccessful(username, bool);
};
module MyServer = BsSocket.Server.Make(Messages);
let io = MyServer.create();

A common pattern is to use the same message type for clientToServer and serverToClient in the following way:

module Messages = {
  type t = ...;
  type clientToServer = t;
  type serverToClient = t;
};

See example/ folder for full usage.

The API differs a bit from socket.io's API to be more idiomatic in Reason. Generally, e.g. JavaScript's socket.emit("bla", 10) becomes Server.emit(socket, Bla(10)) in Reason.

Conceptual difference between socket.io and bs-socket.io

Whereas in socket.io, emitting a message requires a string as the first argument as a way to tag what type of message you're sending, in bs-socket.io, the intended usage is that there is only one type of message and therefore there is no string tag required. This is so that the function that handles messages from the other side of the socket, i.e. MyClient.on and MyServer.on, can leverage Reason's exhaustive pattern matching on variant types, which can help ensure that they are handling all potential message variants that they could possibly be sent.

As a concrete example, the following socket.io and bs-socket.io pseudo-code would be analogous to each other.

Socket.io:

// client
socket.emit('login', { username: 'user2157' });
socket.emit('chat message', 'hello');

// server
socket.on('login', msg => ...);
socket.on('chat message', msg => ...);

Bs-socket.io:

// client
MyClient.emit(client, Login("user2157"));
MyClient.emit(client, ChatMessage("hello"));

// server
MyServer.Socket.on(socket, msg =>
  switch(msg) {
  | Login(username) => ...
  | ChatMessage(msg) => ...
  );

If you later extended the type of clientToServer to have another case, i.e.

type username = string;
type clientToServer =
  | Login(username)
  | ChatMessage(string)
  | Logout(username);

Then the previous implementation of MyServer.on would no longer compile with the reason that you haven't handled the Logout variant of the clientToServer type.

Couple Gotchas

There are a couple differences between the JS API and this one. We'll refer to the supposed module you've created from the Server.Make functor as MyServer. Same for Namespace and Client.

• MyServer.emit is different from MyServer.Socket.emit. The former emits to all connected peers while the latter emits to the given peer.
• Instead of io.sockets there is MyNamespace.default(io) which does the same thing.
• Instead of io.of there is MyNamespace.of_(io) which does the same thing. (of is a Reason keyword)
• All functions that are overloaded have different names depending on what you're passing. There's MyServer.create but also MyServer.createWithHttp (see example) among others.