Longhouse

A user presence service.

Prerequisites

• nvm
• Redis v3.0.2

Install

# Assumes Redis is already running locally on port 6379
git clone [email protected]:usecanvas/longhouse.git
cd longhouse
nvm install
nvm use
npm run bootstrap
npm run dev

Use

Longhouse tracks user presence as soon as they connect. To connect to space in Longhouse, open a WebSocket connection to a URL like:

wss://longhouse.example.com/[email protected]

After joining, the client will quickly receive a message with the current clients connected to the space:

{
  "id": "123",
  "clients": [
    { "id": "123", "identity": "[email protected]", "spaceID": "space_uuid", "joinedAt": "2015-06-05T21:09:26.480Z" },
    { "id": "456", "identity": "[email protected]", "spaceID": "space_uuid", "joinedAt": "2015-06-05T21:09:28.493Z" }
  ]
}

Reconnecting

In the event of a disconnection by Longhouse, a client can attempt to reconnect with a former "id". This ensures that as long as their old presence lease has not expired, they will not appear to have left and re-joined the room.

This is useful in handling sudden process restarts.

wss://longhouse.example.com/[email protected]&id=123

Actions

ping

Sending this action will renew the client's presence lease.

This is currently the only action that should be sent to Longhouse. It needs to be sent less frequently than the value of $PRESENCE_TTL (in milliseconds).

{"action": "ping"}

Remote Events

When relevant events happen on remote clients, Longhouse will send a message to each client connected to the space where the event occurred.

remote join

A client has joined the space.

{
  "event": "remote join",
  "client": { "id": "456", "identity": "[email protected]", "spaceID": "space_uuid", "joinedAt": "2015-06-05T21:09:28.493Z" }
}

remote leave

A client has left the space (either by expiration or closing their connection).

{
  "event": "remote leave",
  "client": { "id": "456", "identity": "[email protected]", "spaceID": "space_uuid", "joinedAt": "2015-06-05T21:09:28.493Z" }
}

Configuration (environvment variables)

• $PRESENCE_TTL The time (in ms) after which client presence will automatically expire
• $REDIS_URL The URL to a Redis server that supports keyspace notifications
• $REDISCLOUD_URL A URL pointing to a RedisCloud server that will override $REDIS_URL if it exists

Errors

When an error occurs that is relevant to the client, an error message will be sent in this format:

{ "error": "Error message" }

An error may or may not result in Longhouse terminating the socket connection.

How does it work?

Longhouse is extremely simple. When a user joins, it sets a key in Redis with the format longhouse/spaces/${spaceID}/${clientUUID}/${userIdentity}/${joinedAt} with a value of the user identity.

These keys have a default expire time of 60 seconds.

In order to determine who is present in a given space, Longhouse just gets every key that matches the pattern longhouse/spaces/${spaceID}.*. The user identity for each present user is in the key itself, and the values are only used for testing purposes.

Testing

The unit tests can be run with npm test. A Redis server must be running, but be aware that the tests will call FLUSHDB after every test.

Another useful tool for testing is wscat:

npm i -g wscat

Then, one can connect to Longhouse using wscat once they've started the server:

# Terminal 1
wscat -c ws://localhost:5000/[email protected]
>
  < {"clients": [
      { "id": "123", "identity": "[email protected]", "spaceID": "space-id", "joinedAt": "2015-06-05T21:09:26.480Z" }
    ]

# Terminal 2
wscat -c ws://localhost:5000/[email protected]
>
  < {"clients": [
      { "id": "123", "identity": "[email protected]", "spaceID": "space-id", "joinedAt": "2015-06-05T21:09:26.480Z" },
      { "id": "456", "identity": "[email protected]", "spaceID": "space-id", "joinedAt": "2015-06-05T21:09:28.493Z" }
    ]