Skip to content

Latest commit

 

History

History
72 lines (56 loc) · 2.16 KB

readme.md

File metadata and controls

72 lines (56 loc) · 2.16 KB
Raw

Project

This document describes how this project works.

Note: This is all subject to change

Idea

The idea of this project is quite similar to the idea of a realtime chat application.

  1. User A performs an action (sends a message).
  2. User B receives a notification about the action (receives the message).

Event flow

Whenever a user subscribes to realtime notifications, it creates a queue in NATS and the relay opens a stream back to the browser.

sequenceDiagram
autonumber
actor Alice
actor Bob
participant Relay
participant Redis
participant PocketBase
participant Nats


Alice      ->>  PocketBase : Authenticate
Bob        ->>  PocketBase : Authenticate
Bob        ->>+ Relay      : Sends msg to "channel1"
Relay      ->>+ PocketBase : Verify Token
PocketBase ->>- Relay      : OK
Relay      ->>  Redis      : Cache message in Redis
Relay      ->>- Nats       : Publish msg to "channel1"
Note       over Nats       : Since there are no subscribers the msg is dropped
Alice      ->>+ Relay      : Subscribe to "channel1"
Relay      ->>+ PocketBase : Verify Token
PocketBase ->>- Relay      : OK
Relay      ->>+ Redis      : Get "channel1" history from last timestamp
Redis      ->>- Relay      : Bob's message
Relay      ->>  Alice      : Bob's message arrives at Alice
Relay      ->>- Nats       : Subscribe to "channel1"
Relay      ->>  Alice      : Open server stream

loop Server Stream
    Nats  -->+ Relay : Subscribe
    Bob   ->>  Relay : New message
    Relay ->>  Redis : Cache
    Relay ->>  Nats  : Publish
    Nats  -->> Relay : Msg
    Note  over Relay : Nats -> gRPC
    Relay -->> Alice : gRPC server stream
    Relay ->>- Nats  : Ack msg
end
Loading

Data

The message payload has the following structure

channelid: the NATS queue ID is the same as a channel
userid: where the message came from
text: the actual message
ts: timestamp in Unix Nano seconds

The relay creates a hardcoded group called events and each user that presses the subscribe button is the subject on that group. So for user bob the queue is named events.bob.

Anyone can subscribe to that queue but since it's a queue only one instance will pick up the latest message.