Only query for coin balance when channel connected

Normally, it is good idea to only query the database once no matter the
number of sockets for a channel, but most addresses don't have listeners,
so it is cheaper to not query unless the channel is in use.

If we start to see popular addresses, con_cache can be used to only do
the query once across all connected sockets for the same address.

Co-authored-by: Chris McCord <chris@chrismccord.com>

apps/block_scout_web/lib/block_scout_web/channels/address_channel.ex

@@ -5,13 +5,14 @@ defmodule BlockScoutWeb.AddressChannel do
   use BlockScoutWeb, :channel
 
   alias BlockScoutWeb.{AddressCoinBalanceView, AddressView, InternalTransactionView, TransactionView}
+  alias Explorer.Chain
   alias Explorer.Chain.Hash
   alias Phoenix.View
 
   intercept(["balance_update", "coin_balance", "count", "internal_transaction", "transaction"])
 
-  def join("addresses:" <> _address_hash, _params, socket) do
+  def join("addresses:" <> address_hash, _params, socket) do
-    {:ok, %{}, socket}
+    {:ok, %{}, assign(socket, :address_hash, address_hash)}
   end
 
   def handle_out(
@@ -63,7 +64,9 @@ defmodule BlockScoutWeb.AddressChannel do
 
   def handle_out("transaction", data, socket), do: handle_transaction(data, socket, "transaction")
 
-  def handle_out("coin_balance", %{coin_balance: coin_balance}, socket) do
+  def handle_out("coin_balance", %{block_number: block_number}, socket) do
+    coin_balance = Chain.get_coin_balance(socket.assigns.address_hash, block_number)
+
     Gettext.put_locale(BlockScoutWeb.Gettext, socket.assigns.locale)
 
     rendered_coin_balance =

apps/block_scout_web/lib/block_scout_web/notifier.ex

@@ -95,10 +95,8 @@ defmodule BlockScoutWeb.Notifier do
   def handle_event(_), do: nil
 
   defp broadcast_address_coin_balance(%{address_hash: address_hash, block_number: block_number}) do
-    coin_balance = Chain.get_coin_balance(address_hash, block_number)
-
     Endpoint.broadcast("addresses:#{address_hash}", "coin_balance", %{
-      coin_balance: coin_balance
+      block_number: block_number
     })
   end