Hermes

What is Hermes

Hermes is a scalable, GRPC based messaging service.

Technology Stack

Nats-Streaming
PostgreSQL
Redis

Terminology

• Channel: Channel is the basis of all communications in hermes, each user has it's own channel, each group is a channel, and each broadcast is a channel. Channels are basically NATS channels but they are persistant using a PostgreSQL database.
• Message: Messages are the data people send to each other, it could be a simple text message or a complex reply to another message maybe with a GIF.
• User: Users are the people :). Users are here to only know who has what permission but other than that, hermes is built entirely on the idea of channels and messages.

How Hermes Works

Hermes uses Nats-Streaming as pub/sub service and uses nats concept of channels as a way of communication between two users. Each new event will be published to a channel and the eventHandler specific to the event (there are only two event handlers) will deliver the event to the users using GRPC streaming.

Flow of new message

1. User creates a connection to hermes event buff with a valid JWT token.
2. Hermes subscribe user to user-discovery
   
3. User sends a new message to Hermes
   
4. Hermes finds target channel of the message (based on recipient, or if message itself has a channel)
5. Hermes makes sure that all members of target channel are subscribed to channel.
6. Hermes based on strategy and channel type decides whether to save the message or not.
7. Hermes sends message into channel (publishes message into nats).
8. other users that are subscribed to channel receive the message.

Installation

   git clone github.com/hermeschat/engine/
   cd hermes
   docker-compose up .

License

Hermes uses MIT license for more information read licence file.