feat: add unpack/2 to Protobuf.Any

lib/protobuf/any.ex

@@ -1,5 +1,4 @@
 defmodule Protobuf.Any do
-
   @moduledoc """
   Provides functions for working with the `google.protobuf.Any` type.
   """
@@ -28,6 +27,60 @@ defmodule Protobuf.Any do
     }
   end
 
+  @doc """
+  Unpacks a `Google.Protobuf.Any` message using a custom type provider.
+
+  The type provider module must implement the `Protobuf.Any.TypeProvider` behaviour,
+  which defines how to convert type URLs to their corresponding message modules.
+
+  ## Example
+
+      defmodule MyApp.AnyTypeProvider do
+        @behaviour Protobuf.Any.TypeProvider
+
+        def to_module("type.googleapis.com/google.protobuf.Duration"), do: {:ok, Google.Protobuf.Duration}
+        def to_module("type.googleapis.com/myapp.events.UserCreated"), do: {:ok, MyApp.Events.UserCreated}
+        def to_module("myapp.internal/myapp.events.OrderPlaced"), do: {:ok, MyApp.Events.OrderPlaced}
+        def to_module(_), do: {:error, "Unknown type_url"}
+      end
+
+      any = %Google.Protobuf.Any{
+        type_url: "type.googleapis.com/myapp.events.UserCreated",
+        value: <<...>>
+      }
+      Protobuf.Any.unpack(any, MyApp.AnyTypeProvider)
+      #=> {:ok, %MyApp.Events.UserCreated{...}}
+  """
+  @spec unpack(Google.Protobuf.Any.t(), module()) ::
+          {:ok, struct()} | {:error, reason :: any()}
+  def unpack(%Google.Protobuf.Any{type_url: type_url, value: value}, type_provider) do
+    with {:ok, module} <- resolve_module(type_provider, type_url) do
+      decode(module, value)
+    end
+  end
+
+  defp resolve_module(type_provider, type_url) do
+    case type_provider.to_module(type_url) do
+      {:ok, module} when is_atom(module) ->
+        {:ok, module}
+
+      {:ok, other} ->
+        {:error,
+         ArgumentError.exception(
+           "expected type provider to return an atom module, got: #{inspect(other)}"
+         )}
+
+      {:error, _} = error ->
+        error
+    end
+  end
+
+  defp decode(module, value) do
+    {:ok, module.decode(value)}
+  rescue
+    error -> {:error, error}
+  end
+
   @doc false
   @spec type_url_to_module(String.t()) :: module()
   def type_url_to_module(type_url) when is_binary(type_url) do

lib/protobuf/any/type_provider.ex

@@ -0,0 +1,32 @@
+defmodule Protobuf.Any.TypeProvider do
+  @moduledoc """
+  Behaviour for resolving type URLs to Protobuf message modules for `Google.Protobuf.Any`.
+
+  Implementations of this behaviour define how to convert a type URL to its corresponding module,
+  allowing customization of prefix handling and message routing.
+
+  ## Example
+
+      defmodule MyApp.AnyTypeProvider do
+        @behaviour Protobuf.Any.TypeProvider
+
+        def to_module("type.googleapis.com/google.protobuf.Duration"), do: {:ok, Google.Protobuf.Duration}
+        def to_module("type.googleapis.com/myapp.events.UserCreated"), do: {:ok, MyApp.Events.UserCreated}
+        def to_module("myapp.internal/myapp.events.OrderPlaced"), do: {:ok, MyApp.Events.OrderPlaced}
+        def to_module(_), do: {:error, "Unknown type_url"}
+      end
+
+  Then use it with `Protobuf.Any.unpack/2`:
+
+      Protobuf.Any.unpack(any_message, MyApp.AnyTypeProvider)
+      #=> {:ok, decoded_struct}
+  """
+
+  @doc """
+  Convert a type URL to its corresponding Protobuf message module.
+
+  Should return `{:ok, module}` if the type URL is recognized, or
+  `{:error, reason}` if it cannot be resolved.
+  """
+  @callback to_module(type_url :: String.t()) :: {:ok, module()} | {:error, reason :: any()}
+end

test/protobuf/any_test.exs

@@ -19,6 +19,64 @@ defmodule Protobuf.AnyTest do
     end
   end
 
+  describe "unpack/2" do
+    test "unpacks a message from Any" do
+      message = %Google.Protobuf.Duration{seconds: 42}
+      any = Protobuf.Any.pack(message)
+
+      assert {:ok, unpacked} = Protobuf.Any.unpack(any, Protobuf.AnyTypeProviderSupport)
+      assert unpacked == message
+    end
+
+    test "returns error for unknown type_url" do
+      any = %Google.Protobuf.Any{
+        type_url: "custom.prefix/unknown.Type",
+        value: <<>>
+      }
+
+      assert {:error, "Unknown type_url"} =
+               Protobuf.Any.unpack(any, Protobuf.AnyTypeProviderSupport)
+    end
+
+    test "returns error for unmapped type_url" do
+      any = %Google.Protobuf.Any{
+        type_url: "type.googleapis.com/unknown.Message",
+        value: <<>>
+      }
+
+      assert {:error, "Unknown type_url"} =
+               Protobuf.Any.unpack(any, Protobuf.AnyTypeProviderSupport)
+    end
+
+    test "returns error when type provider returns a non-atom module" do
+      defmodule BadTypeProvider do
+        @behaviour Protobuf.Any.TypeProvider
+
+        def to_module(_type_url), do: {:ok, "not_an_atom"}
+      end
+
+      any = %Google.Protobuf.Any{
+        type_url: "type.googleapis.com/google.protobuf.Duration",
+        value: <<>>
+      }
+
+      assert {:error, %ArgumentError{message: message}} =
+               Protobuf.Any.unpack(any, BadTypeProvider)
+
+      assert message =~ "expected type provider to return an atom module"
+    end
+
+    test "returns error when decode fails" do
+      any = %Google.Protobuf.Any{
+        type_url: "type.googleapis.com/google.protobuf.Duration",
+        value: <<255, 255, 255>>
+      }
+
+      assert {:error, %Protobuf.DecodeError{}} =
+               Protobuf.Any.unpack(any, Protobuf.AnyTypeProviderSupport)
+    end
+  end
+
   describe "type_url_to_module/1" do
     test "returns the module for a valid type_url" do
       assert Protobuf.Any.type_url_to_module("type.googleapis.com/google.protobuf.Duration") ==

test/protobuf/protoc/cli_integration_test.exs

@@ -178,7 +178,8 @@ defmodule Protobuf.Protoc.CLIIntegrationTest do
       proto_path
     ])
 
-    assert [mod] = compile_file_and_clean_modules_on_exit("#{tmp_dir}/my_type/timestamp_wrapper.pb.ex")
+    assert [mod] =
+             compile_file_and_clean_modules_on_exit("#{tmp_dir}/my_type/timestamp_wrapper.pb.ex")
 
     assert mod == MyType.TimestampWrapper
     assert Map.fetch!(mod.__message_props__().field_props, 1).type == Google.Protobuf.Timestamp

test/support/any_type_provider.ex

@@ -0,0 +1,17 @@
+defmodule Protobuf.AnyTypeProviderSupport do
+  @moduledoc false
+
+  @behaviour Protobuf.Any.TypeProvider
+
+  @mappings %{
+    "type.googleapis.com/google.protobuf.Duration" => Google.Protobuf.Duration,
+    "type.googleapis.com/test.Request.SomeGroup" => My.Test.Request.SomeGroup
+  }
+
+  def to_module(type_url) do
+    case Map.fetch(@mappings, type_url) do
+      {:ok, module} -> {:ok, module}
+      :error -> {:error, "Unknown type_url"}
+    end
+  end
+end

test/test_helper.exs

@@ -36,13 +36,17 @@ defmodule Protobuf.TestHelpers do
           path = Path.join(dir, entry)
 
           cond do
-            entry == filename -> {:ok, path}
+            entry == filename ->
+              {:ok, path}
+
             File.dir?(path) ->
               case find_file_in_dir(path, filename) do
                 {:ok, found_path} -> {:ok, found_path}
                 :not_found -> nil
               end
-            true -> nil
+
+            true ->
+              nil
           end
         end)