# EredisSub
Wraps `eredis` and `eredis_sub` functionallity for Elixir usage.
- Publishes binary messages to Redis Pub/Sub channels.
- Subscribes to channels and calls a handler function when a message is received.
## Usage
### Publish
```elixir
EredisSub.publish("my_channel", "Hello, world!")
```
### Subscribe
Implement the behaviour to be called when a message is received:
```elixir
defmodule MyModule do
@behaviour EredisSub.Handler
@impl EredisSub.Handler
def handle_pubsub_message(message, metadata) do
# Do something...
end
end
```
Subscribe to a channel:
```elixir
metadata_example = %{subscribed_at: DateTime.utc_now()}
EredisSub.subscribe("my_channel", MyModule, metadata_example)
```
## Installation
```elixir
def deps do
[
{:eredis_sub, "~> 0.1.0"}
]
end
```
Add the following to your supervision tree on `application.ex`:
```elixir
children = [
EredisSub
]
```
Optional configuration can be passed to `eredis` and `eredis_sub`, check [their docs](https://hexdocs.pm/eredis/readme.html#connect-a-client-start_link-1):
```elixir
children = [
{EredisSub, [database: 2, username: "foo", password: "bar"]}
]
```
## Motivations
### Why not use `Phoenix.PubSub`?
Because multiple applications in many programming languages can use Redis Pub/Sub,
but they don't serialize their binary messages according to `Phoenix` schema.
### Why not use `eredis` directly?
That's also a great option. With `EredisSub` Elixir abstraction we intend to hide
Erlang specific knowledge, for example Erlang strings and OTP processes. We changed
the API to let clients subscribe a handler function to a Pub/Sub channel, similar
to how [`:telemetry`](https://hexdocs.pm/telemetry/readme.html) attaches handlers.
We sacrificed flexibility on client process architecture, for a simpler mental model.
If you need to handle message passing or a pool of processes, for example to handle
heavier loads, use `:eredis` directly.
