require explicitly specifying node name in subscription pubsub (#607)

modify pubsub behaviour to include `node_name/0` callback

CHANGELOG.md

@@ -11,3 +11,4 @@ Alpha 0 note: 1.5.0 alpha is safe to use on existing schemas. However, there are
 - Feature: SDL support
 - Feature: Schema decorators
 - Breaking Change: `default_value: DateTime.utc_now()` will have its time set at compile time. IE: DON'T DO THIS. It only worked by accident before anyway, and now it no longer works, which is correct.
+- Breaking change: added `node_name/0` callback to `Absinthe.Subscription.PubSub` behaviour. To retain old behaviour, implement this callback to return `Kernel.node/0`.

lib/absinthe/subscription/proxy.ex

@@ -4,7 +4,8 @@ defmodule Absinthe.Subscription.Proxy do
   use GenServer
 
   defstruct [
-    :pubsub
+    :pubsub,
+    :node
   ]
 
   alias Absinthe.Subscription
@@ -16,11 +17,12 @@ defmodule Absinthe.Subscription.Proxy do
   def topic(shard), do: "__absinthe__:proxy:#{shard}"
 
   def init({pubsub, shard}) do
+    node_name = pubsub.node_name()
     :ok = pubsub.subscribe(topic(shard))
-    {:ok, %__MODULE__{pubsub: pubsub}}
+    {:ok, %__MODULE__{pubsub: pubsub, node: node_name}}
   end
 
-  def handle_info(%{node: src_node}, state) when src_node == node() do
+  def handle_info(%{node: src_node}, %{node: node} = state) when src_node == node do
     {:noreply, state}
   end
 

lib/absinthe/subscription/pubsub.ex

@@ -22,8 +22,19 @@ defmodule Absinthe.Subscription.Pubsub do
   @callback subscribe(topic :: binary) :: term
 
   @doc """
-  An Absinthe.Subscription.Pubsub system may extend across multiple nodes in a 
-  cluster. Processes need only subscribe to the pubsub process that 
+  An Absinthe.Subscription.Pubsub system may extend across multiple nodes
+  connected by some mechanism. Regardless of this mechanism, all nodes should
+  have unique names.
+
+  Absinthe invokes `node_name` function to get current node's name. If you
+  are running inside erlang cluster, you can use `Kernel.node/0` as a node
+  name.
+  """
+  @callback node_name() :: binary
+
+  @doc """
+  An Absinthe.Subscription.Pubsub system may extend across multiple nodes.
+  Processes need only subscribe to the pubsub process that
   is running on their own node.
 
   However, mutations can happen on any node in the custer and must to be 
@@ -38,7 +49,7 @@ defmodule Absinthe.Subscription.Pubsub do
   The message broadcast should be a map that contains, at least
 
       %{
-          node: node_id,        # probably from Kernel.node/0
+          node: node_name,      # should be equal to `node_name/0`
           mutation_result: …,   # from arguments
           subscribed_fields: …  # from arguments
 

test/absinthe/execution/subscription_test.exs

@@ -10,6 +10,10 @@ defmodule Absinthe.Execution.SubscriptionTest do
       Registry.start_link(keys: :unique, name: __MODULE__)
     end
 
+    def node_name() do
+      node()
+    end
+
     def subscribe(topic) do
       Registry.register(__MODULE__, topic, [])
       :ok