Add Ethers.Utils.find_and_decode/2 function (#156)

Author: alisinabh

CHANGELOG.md

@@ -6,6 +6,7 @@
 
 - Move and export abi decode functionality to `Ethers.TxData` module
 - Export `Ethers.TxData.to_map/2` in docs
+- Add `Ethers.Event.find_and_decode/2` function
 
 ## v0.5.4 (2024-10-22)
 

lib/ethers/contract.ex

@@ -119,18 +119,20 @@ defmodule Ethers.Contract do
 
     events_mod_name = Module.concat(module, EventFilters)
 
-    events =
-      function_selectors_with_meta
-      |> Enum.filter(&(&1.type == :event))
-      |> Enum.map(&impl(&1, module, impl_opts))
+    events = Enum.filter(function_selectors_with_meta, &(&1.type == :event))
+
+    events_impl = Enum.map(events, &impl(&1, module, impl_opts))
+    event_selectors = Enum.flat_map(events, & &1.selectors)
 
     events_module_ast =
       quote context: module do
         defmodule unquote(events_mod_name) do
           @moduledoc "Events for `#{Macro.to_string(unquote(module))}`"
 
           defdelegate __default_address__, to: unquote(module)
-          unquote(events)
+          unquote(events_impl)
+
+          def __events__, do: unquote(Macro.escape(event_selectors))
         end
       end
 

lib/ethers/event.ex

@@ -92,4 +92,29 @@ defmodule Ethers.Event do
       transaction_index: transaction_index
     }
   end
+
+  @doc """
+  Given a log entry and an EventFilters module (e.g. `Ethers.Contracts.ERC20.EventFilters`)
+  will find a matching event filter in the given module and decodes the log using the event selector.
+  """
+  @spec find_and_decode(map(), module()) :: {:ok, t()} | {:error, :not_found}
+  def find_and_decode(log, event_filters_module) do
+    [topic | _] = Map.fetch!(log, "topics")
+
+    topic_raw = Utils.hex_decode!(topic)
+
+    selector =
+      Enum.find(
+        event_filters_module.__events__(),
+        fn %ABI.FunctionSelector{method_id: method_id} -> method_id == topic_raw end
+      )
+
+    case selector do
+      nil ->
+        {:error, :not_found}
+
+      %ABI.FunctionSelector{} ->
+        {:ok, decode(log, selector)}
+    end
+  end
 end

test/ethers/event_test.exs

@@ -3,39 +3,67 @@ defmodule Ethers.EventTest do
   alias Ethers.Event
   doctest Event
 
-  test "decode log with no data returns empty list" do
-    selector = %ABI.FunctionSelector{
-      function: "Approval",
-      method_id: <<140, 91, 225, 229>>,
-      type: :event,
-      inputs_indexed: [true, true, false],
-      state_mutability: nil,
-      input_names: ["owner", "spender", "value"],
-      types: [:address, :address, {:uint, 256}],
-      returns: [uint: 256]
-    }
+  describe "decode/2" do
+    test "decode log with no data returns empty list" do
+      selector = %ABI.FunctionSelector{
+        function: "Approval",
+        method_id: <<140, 91, 225, 229>>,
+        type: :event,
+        inputs_indexed: [true, true, true],
+        state_mutability: nil,
+        input_names: ["owner", "spender", "value"],
+        types: [:address, :address, {:uint, 256}],
+        returns: [uint: 256]
+      }
 
-    assert %Ethers.Event{data: []} =
-             Event.decode(
-               %{
-                 "address" => "0xaa107ccfe230a29c345fd97bc6eb9bd2fccd0750",
-                 "blockHash" =>
-                   "0xe8885761ec559c5e267c48f44b4b12e4169f7d3a116f5e8f43314147722f0d83",
-                 "blockNumber" => "0x1138b39",
-                 "data" => "0x",
-                 "logIndex" => "0x1a1",
-                 "removed" => false,
-                 "topics" => [
-                   "0x8c5be1e5ebec7d5bd14f71427d1e84f3dd0314c0f7b2291e5b200ac8c7c3b925",
-                   "0x00000000000000000000000023c5d7a16cf2e14a00f1c81be9443259f3cbc4ce",
-                   "0x0000000000000000000000000000000000000000000000000000000000000000",
-                   "0x0000000000000000000000000000000000000000000000000000000000000ef7"
-                 ],
-                 "transactionHash" =>
-                   "0xf6e06e4f3fbd67088e8278843e55862957537760c63bae7b682a0e39da75b45d",
-                 "transactionIndex" => "0x83"
-               },
-               selector
-             )
+      assert %Ethers.Event{data: []} =
+               Event.decode(
+                 %{
+                   "address" => "0xaa107ccfe230a29c345fd97bc6eb9bd2fccd0750",
+                   "blockHash" =>
+                     "0xe8885761ec559c5e267c48f44b4b12e4169f7d3a116f5e8f43314147722f0d83",
+                   "blockNumber" => "0x1138b39",
+                   "data" => "0x",
+                   "logIndex" => "0x1a1",
+                   "removed" => false,
+                   "topics" => [
+                     "0x8c5be1e5ebec7d5bd14f71427d1e84f3dd0314c0f7b2291e5b200ac8c7c3b925",
+                     "0x00000000000000000000000023c5d7a16cf2e14a00f1c81be9443259f3cbc4ce",
+                     "0x0000000000000000000000000000000000000000000000000000000000000000",
+                     "0x0000000000000000000000000000000000000000000000000000000000000ef7"
+                   ],
+                   "transactionHash" =>
+                     "0xf6e06e4f3fbd67088e8278843e55862957537760c63bae7b682a0e39da75b45d",
+                   "transactionIndex" => "0x83"
+                 },
+                 selector
+               )
+    end
+  end
+
+  describe "find_and_decode/2" do
+    test "finds correct selector and decodes log" do
+      assert {:ok, %Ethers.Event{data: [3831]}} =
+               Event.find_and_decode(
+                 %{
+                   "address" => "0xaa107ccfe230a29c345fd97bc6eb9bd2fccd0750",
+                   "blockHash" =>
+                     "0xe8885761ec559c5e267c48f44b4b12e4169f7d3a116f5e8f43314147722f0d83",
+                   "blockNumber" => "0x1138b39",
+                   "data" => "0x0000000000000000000000000000000000000000000000000000000000000ef7",
+                   "logIndex" => "0x1a1",
+                   "removed" => false,
+                   "topics" => [
+                     "0x8c5be1e5ebec7d5bd14f71427d1e84f3dd0314c0f7b2291e5b200ac8c7c3b925",
+                     "0x00000000000000000000000023c5d7a16cf2e14a00f1c81be9443259f3cbc4ce",
+                     "0x0000000000000000000000000000000000000000000000000000000000000000"
+                   ],
+                   "transactionHash" =>
+                     "0xf6e06e4f3fbd67088e8278843e55862957537760c63bae7b682a0e39da75b45d",
+                   "transactionIndex" => "0x83"
+                 },
+                 Ethers.Contracts.ERC20.EventFilters
+               )
+    end
   end
 end