Make Odoo GenServer more resilient

i.e. do not crash if Odoo is not available or configuration not set

lib/recycledcloud/odoo.ex

@@ -0,0 +1,110 @@
+defmodule RecycledCloud.Odoo do
+  use GenServer
+  require Logger
+
+  @common_endpoint "/xmlrpc/2/common"
+  @object_endpoint "/xmlrpc/2/object"
+
+  # Odoo 14.0 API is documented at https://www.odoo.com/documentation/14.0/webservices/odoo.html
+
+  defp get_odoo_config(key) do
+    Application.get_env(:recycledcloud, :odoo, [])  |> Keyword.get(key)
+  end
+
+  defp post!(call, endpoint) do
+    url = get_odoo_config(:server) <> endpoint
+    opts = [proxy_auth: {get_odoo_config(:user), get_odoo_config(:secret)}]
+    headers = []
+    body = call |> XMLRPC.encode!
+
+    response = HTTPoison.post!(url, body, headers, opts).body |> XMLRPC.decode!
+    case response do
+      %{fault_code: _, fault_string: err} -> {:error, err}
+      %{param: result} -> {:ok, result}
+    end
+  end
+
+  defp authenticate do
+    auth_params = [
+      get_odoo_config(:database),
+      get_odoo_config(:user),
+      get_odoo_config(:secret),
+      nil
+    ]
+
+    auth_response = %XMLRPC.MethodCall{method_name: "authenticate", params: auth_params}
+                    |> post!(@common_endpoint)
+    case auth_response do
+      {:ok, false} -> {:error, "Could not authenticate against Odoo."}
+      {:ok, uid} -> {:ok, uid}
+      {:error, err} -> {:error, err}
+    end
+  end
+
+  defp check_odoo_config(key) do
+    case get_odoo_config(key) do
+      nil ->
+        Logger.warn("Odoo #{key} configuration is missing.")
+        false
+      _value -> true
+    end
+  end
+
+  def start_link(_) do
+    GenServer.start_link(__MODULE__, :ok, name: __MODULE__)
+  end
+
+  def init(:ok) do
+    # Make sure Odoo configuration is defined.
+    conf_ok? = for key <- [:server, :database, :user, :secret], reduce: true do
+      acc -> acc && check_odoo_config(key)
+    end
+
+    if conf_ok? do
+      case authenticate() do
+        {:ok, uid} ->
+        # Print Odoo version on console (not quite useful...).
+          version_call = %XMLRPC.MethodCall{method_name: "version", params: []} |> post!(@common_endpoint)
+          {:ok, %{"server_version" => version}} = version_call
+          Logger.info("Successfuly authenticated against Odoo #{version} at #{get_odoo_config(:server)}")
+
+          {:ok, uid}
+        {:error, err} ->
+          Logger.warning("Failed to authenticate against Odoo: #{inspect(err)}")
+
+          # We do not fail here since we do not want to hinder the application's
+          # main supervisor if Odoo is down.
+          {:ok, nil}
+      end
+    else
+        Logger.warning("Failed to authenticate against Odoo: missing configuration!")
+
+        {:ok, nil}
+    end
+  end
+
+  def handle_call({method, params}, _from, uid) do
+    case uid do
+      # uid is nil if start_link's init/1 call failed.
+      # ... we try to authenticate once again!
+      nil ->
+        case init(:ok) do
+          {:ok, new_uid} -> handle_call({method, params}, nil, new_uid)
+          err -> {:reply, err, nil}
+        end
+      _ ->
+        call = %XMLRPC.MethodCall{
+          method_name: method,
+          params: [get_odoo_config(:database), uid, get_odoo_config(:secret) | params]
+        }
+        result = call |> post!(@object_endpoint)
+
+        {:reply, result, uid}
+    end
+  end
+
+  def query(params), do: execute_kw(params)
+  defp execute_kw(params) do
+    GenServer.call(__MODULE__, {"execute_kw", params})
+  end
+end