README.md

# PonyExpress

## Securely extend a Phoenix PubSub over SSL

PonyExpress creates two-way authenticated SSL connections over the WAN which
are intended to unidirectionally extend a PubSub over the internet.  PubSub
broadcasts are forwarded from Server to Client.

The use case is when you have a trusted pair of nodes (for example a backend
and a BFF) that could use live-updating pubsub propagation.  These might be
located in distinct layer-2 networks, for example, a BFF in the cloud which
services an on-premises backend.  Or you may be wanting security in-depth with
end-to-end encryption in your layer-2 network to mitigate damage from a
potential network intrusion event.  For whatever reason either case, if full
erlang distribution is not right for you, this is a low-footprint way of
propagating those `Phoenix.PubSub` messages (without writing a full
`Phoenix.Channel` client).

On the server side:

```elixir
iex> Phoenix.PubSub.PG2.start_link(:source, [])
iex> PonyExpress.Daemon.start_link(
       pubsub_server: SourcePubSub,
       port: <port>,
       tls_opts: [
         cacertfile: <ca_certfile>
         certfile: <certfile>
         keyfile: <keyfile>
       ])
```

On the client side:

```elixir
iex> Phoenix.PubSub.PG2.start_link(:dest, [])
iex> PonyExpress.Client.start_link(
       server: <server IP>,
       port: port,
       topic: "my_topic",
       pubsub_server: DestPubSub,
       tls_opts: [
         cacertfile: <ca_certfile>
         certfile: <certfile>
         keyfile: <keyfile>
       ])
iex> Phoenix.PubSub.subscribe(:dest, "my_topic")
```

Then you can send a message on the server side:

```elixir
iex> Phoenix.PubSub.broadcast(:source, "my_topic", "my_message")
```

And it will appear on the client side:

```elixir
iex> flush()
"my_message"
:ok
```

Consult the documentation for more comprehensive OTP-compliant strategies for
using this library.

## Installation

If [available in Hex](https://hex.pm/docs/publish), the package can be installed
by adding `pony_express` to your list of dependencies in `mix.exs`:

```elixir
def deps do
  [
    {:pony_express, "~> 0.4.1"}
  ]
end
```

Documentation can be generated with [ExDoc](https://github.com/elixir-lang/ex_doc)
and published on [HexDocs](https://hexdocs.pm). Once published, the docs can
be found at [https://hexdocs.pm/pony_express](https://hexdocs.pm/pony_express).

## Testing

PonyExpress creates a series of testing keys in `/tmp/.pony-express-test/<32-byte-slug>`.
These keys are deleted if the test suite is successful and left for examination
if the test suite is not.