From 43bba8a449cf7a0c5e1698f8ee3b6b6c30cbe0fc Mon Sep 17 00:00:00 2001
From: Brendan Ball <brendan@nomanini.com>
Date: Thu, 16 Dec 2021 14:39:28 +0100
Subject: [PATCH 1/2] implement a configurable superivision tree

Currently Kadabra starts an application which is problematic
in some failure scenarios that can result in the entire BEAM node
being restarted.
Starting an application in a library doesn't put the library user in control.
This fixes it in a backwards compatible way by allowing the library user
to decide exactly how their application should behave when Kadabra
crashes.
---
 lib/application.ex           |  7 +------
 lib/connection_supervisor.ex | 24 ++++++++++++++++++++++++
 lib/kadabra.ex               | 17 ++++++++++++-----
 lib/supervisor.ex            | 36 ++++++++++++++++++++++++++++++++++++
 4 files changed, 73 insertions(+), 11 deletions(-)
 create mode 100644 lib/connection_supervisor.ex
 create mode 100644 lib/supervisor.ex

diff --git a/lib/application.ex b/lib/application.ex
index 6599e6a..2ea41d9 100644
--- a/lib/application.ex
+++ b/lib/application.ex
@@ -4,11 +4,6 @@ defmodule Kadabra.Application do
   use Application
 
   def start(_type, _args) do
-    children = [
-      {Registry, keys: :unique, name: Registry.Kadabra},
-      {Task.Supervisor, name: Kadabra.Tasks}
-    ]
-
-    Supervisor.start_link(children, strategy: :one_for_one, name: :kadabra)
+    Kadabra.Supervisor.start_link(name: :kadabra)
   end
 end
diff --git a/lib/connection_supervisor.ex b/lib/connection_supervisor.ex
new file mode 100644
index 0000000..7635a5e
--- /dev/null
+++ b/lib/connection_supervisor.ex
@@ -0,0 +1,24 @@
+defmodule Kadabra.ConnectionSupervisor do
+  @moduledoc false
+
+  use DynamicSupervisor
+
+  def start_link(args) do
+    instance_name = Keyword.fetch!(args, :instance_name)
+    DynamicSupervisor.start_link(__MODULE__, nil, name: name(instance_name))
+  end
+
+  @impl true
+  def init(_init_arg) do
+    DynamicSupervisor.init(strategy: :one_for_one)
+  end
+
+  def start_child(instance_name, opts) do
+    spec = {Kadabra.ConnectionPool, opts}
+    DynamicSupervisor.start_child(name(instance_name), spec)
+  end
+
+  defp name(instance_name) do
+    :"Kadabra.ConnectionSupervisor.#{instance_name}"
+  end
+end
diff --git a/lib/kadabra.ex b/lib/kadabra.ex
index 10b4558..f3e3ba2 100644
--- a/lib/kadabra.ex
+++ b/lib/kadabra.ex
@@ -92,6 +92,8 @@ defmodule Kadabra do
 
   @type uri :: charlist | String.t()
 
+  @type instance_name :: atom()
+
   @doc ~S"""
   Opens a new connection.
 
@@ -109,17 +111,22 @@ defmodule Kadabra do
   def open(uri, opts \\ [])
 
   def open(uri, opts) when is_binary(uri) do
+    open(:kadabra, uri, opts)
+  end
+
+  def open(uri, opts) when is_list(uri) do
+    uri |> to_string() |> open(opts)
+  end
+
+  @spec open(instance_name, uri, conn_opts) :: {:ok, pid} | {:error, term}
+  def open(instance_name, uri, opts) when is_binary(uri) do
     pool_opts = [
       uri: URI.parse(uri),
       pid: self(),
       opts: opts
     ]
 
-    Supervisor.start_child(:kadabra, {Kadabra.ConnectionPool, pool_opts})
-  end
-
-  def open(uri, opts) when is_list(uri) do
-    uri |> to_string() |> open(opts)
+    Kadabra.ConnectionSupervisor.start_child(instance_name, pool_opts)
   end
 
   @doc ~S"""
diff --git a/lib/supervisor.ex b/lib/supervisor.ex
new file mode 100644
index 0000000..cafff38
--- /dev/null
+++ b/lib/supervisor.ex
@@ -0,0 +1,36 @@
+defmodule Kadabra.Supervisor do
+  @moduledoc ~S"""
+  Supervisor to be used by the library user to add it to the desired supervision tree.
+  This allows the library user to be more in control of how failures are managed.
+  When using this, you probably don't want the Kadabra Application to be started.
+  You can accomplish this by specifying in your dependency:
+
+  ```elixir
+    {:kadabra, app: false}
+  ```
+
+  You can add this to your supervision tree with the following spec:
+
+  ```elixir
+  {Kadabra.Supervisor, name: :custom_kadabra_supervisor}
+  ```
+  """
+
+  use Supervisor
+
+  def start_link(args) do
+    name = Keyword.fetch!(args, :name)
+    Supervisor.start_link(__MODULE__, name, name: :"Kadabra.Supervisor.#{name}")
+  end
+
+  @impl true
+  def init(name) do
+    children = [
+      {Registry, keys: :unique, name: Registry.Kadabra},
+      {Task.Supervisor, name: Kadabra.Tasks},
+      {Kadabra.ConnectionSupervisor, instance_name: name}
+    ]
+
+    Supervisor.init(children, strategy: :one_for_one)
+  end
+end

From 779d323d8b046225068838fedfbea7b33d36204d Mon Sep 17 00:00:00 2001
From: Brendan Ball <brendan@nomanini.com>
Date: Tue, 11 Jan 2022 07:58:27 +0100
Subject: [PATCH 2/2] remove Application

It's not possible to include the Application in a release without
starting it automatically.
---
 lib/application.ex | 9 ---------
 mix.exs            | 3 +--
 2 files changed, 1 insertion(+), 11 deletions(-)
 delete mode 100644 lib/application.ex

diff --git a/lib/application.ex b/lib/application.ex
deleted file mode 100644
index 2ea41d9..0000000
--- a/lib/application.ex
+++ /dev/null
@@ -1,9 +0,0 @@
-defmodule Kadabra.Application do
-  @moduledoc false
-
-  use Application
-
-  def start(_type, _args) do
-    Kadabra.Supervisor.start_link(name: :kadabra)
-  end
-end
diff --git a/mix.exs b/mix.exs
index dbf7cb8..4f30c0b 100644
--- a/mix.exs
+++ b/mix.exs
@@ -31,8 +31,7 @@ defmodule Kadabra.Mixfile do
 
   def application do
     [
-      extra_applications: [:logger, :ssl],
-      mod: {Kadabra.Application, []}
+      extra_applications: [:logger, :ssl]
     ]
   end