Add custom upload validator to allow_upload/3 options

lib/phoenix_component.ex

@@ -1216,13 +1216,15 @@ defmodule Phoenix.Component do
   * `:not_accepted` - The entry does not match the `:accept` MIME types
   * `:external_client_failure` - When external upload fails
   * `{:writer_failure, reason}` - When the custom writer fails with `reason`
+  * `reason` - When the custom validator fails with `reason`
 
   ## Examples
 
   ```elixir
   defp upload_error_to_string(:too_large), do: "The file is too large"
   defp upload_error_to_string(:not_accepted), do: "You have selected an unacceptable file type"
   defp upload_error_to_string(:external_client_failure), do: "Something went terribly wrong"
+  defp upload_error_to_string(:custom_validator_error), do: "Custom validation error"
   ```
 
   ```heex

lib/phoenix_live_view.ex

@@ -851,13 +851,26 @@ defmodule Phoenix.LiveView do
       temporary file for consumption. See the `Phoenix.LiveView.UploadWriter` docs
       for custom usage.
 
+    * `:validator` - An optional 1-arity function for performing custom validation
+      on each upload entry. The function receives the upload entry and must return
+      either `:ok` or `{:error, reason}`. When an error tuple is returned, the
+      entry is marked as failed and the error is exposed as `reason` via `upload_errors/2`.
+
   Raises when a previously allowed upload under the same name is still active.
 
   ## Examples
 
       allow_upload(socket, :avatar, accept: ~w(.jpg .jpeg), max_entries: 2)
       allow_upload(socket, :avatar, accept: :any)
 
+      allow_upload(socket, :avatar, validator: fn entry ->
+        if String.length(entry.client_name) > 100 do
+          {:error, :filename_too_long}
+        else
+          :ok
+        end
+      end)
+
   For consuming files automatically as they are uploaded, you can pair `auto_upload: true` with
   a custom progress function to consume the entries as they are completed. For example:
 

lib/phoenix_live_view/upload_config.ex

@@ -77,7 +77,8 @@ defmodule Phoenix.LiveView.UploadConfig do
              :errors,
              :auto_upload?,
              :progress_event,
-             :writer
+             :writer,
+             :validator
            ]}
 
   defstruct name: nil,
@@ -99,7 +100,8 @@ defmodule Phoenix.LiveView.UploadConfig do
             errors: [],
             auto_upload?: false,
             progress_event: nil,
-            writer: nil
+            writer: nil,
+            validator: nil
 
   @type t :: %__MODULE__{
           name: atom() | String.t(),
@@ -124,6 +126,7 @@ defmodule Phoenix.LiveView.UploadConfig do
           auto_upload?: boolean(),
           writer: (name :: atom() | String.t(), UploadEntry.t(), Phoenix.LiveView.Socket.t() ->
                      {module(), term()}),
+          validator: (UploadEntry.t() -> :ok | {:error, atom()}) | nil,
           progress_event:
             (name :: atom() | String.t(), UploadEntry.t(), Phoenix.LiveView.Socket.t() ->
                {:noreply, Phoenix.LiveView.Socket.t()})
@@ -294,6 +297,24 @@ defmodule Phoenix.LiveView.UploadConfig do
           fn _name, _entry, _socket -> {Phoenix.LiveView.UploadTmpFileWriter, []} end
       end
 
+    validator =
+      case Keyword.fetch(opts, :validator) do
+        {:ok, func} when is_function(func, 1) ->
+          func
+
+        {:ok, other} ->
+          raise ArgumentError, """
+          invalid :validator value provided to allow_upload.
+
+          Only a 1-arity anonymous function is supported. Got:
+
+          #{inspect(other)}
+          """
+
+        :error ->
+          fn _entry -> :ok end
+      end
+
     %UploadConfig{
       ref: random_ref,
       name: name,
@@ -309,6 +330,7 @@ defmodule Phoenix.LiveView.UploadConfig do
       chunk_timeout: chunk_timeout,
       progress_event: progress_event,
       writer: writer,
+      validator: validator,
       auto_upload?: Keyword.get(opts, :auto_upload, false),
       allowed?: true
     }
@@ -558,6 +580,7 @@ defmodule Phoenix.LiveView.UploadConfig do
     {:ok, entry}
     |> validate_max_file_size(conf)
     |> validate_accepted(conf)
+    |> call_validator(conf)
     |> case do
       {:ok, entry} ->
         {:ok, put_valid_entry(conf, entry)}
@@ -632,6 +655,15 @@ defmodule Phoenix.LiveView.UploadConfig do
     end
   end
 
+  defp call_validator({:ok, entry}, %UploadConfig{validator: validator_fun}) do
+    case validator_fun.(entry) do
+      {:error, reason} -> {:error, reason}
+      _ -> {:ok, entry}
+    end
+  end
+
+  defp call_validator({:error, _} = error, _conf), do: error
+
   defp recalculate_computed_fields(%UploadConfig{} = conf) do
     recalculate_errors(conf)
   end

test/phoenix_live_view/upload/channel_test.exs

@@ -179,14 +179,20 @@ defmodule Phoenix.LiveView.UploadChannelTest do
   end
 
   defp opts_for_allow_upload(opts) do
-    case Keyword.fetch(opts, :progress) do
-      {:ok, progress} ->
-        Keyword.put(opts, :progress, fn _, entry, socket ->
-          apply(__MODULE__, progress, [entry, socket])
-        end)
+    opts =
+      case Keyword.fetch(opts, :progress) do
+        {:ok, progress} ->
+          Keyword.put(opts, :progress, fn _, entry, socket ->
+            apply(__MODULE__, progress, [entry, socket])
+          end)
+
+        :error ->
+          opts
+      end
 
-      :error ->
-        opts
+    case Keyword.fetch(opts, :validator_response) do
+      {:ok, response} -> Keyword.put(opts, :validator, fn _ -> response end)
+      :error -> opts
     end
   end
 
@@ -406,6 +412,25 @@ defmodule Phoenix.LiveView.UploadChannelTest do
         assert {:error, [[_ref, :too_large]]} = render_upload(avatar, "foo.jpeg")
       end
 
+      @tag allow: [
+             max_entries: 1,
+             chunk_size: 20,
+             accept: :any,
+             max_file_size: 100,
+             validator_response: {:error, :custom_validation_error}
+           ]
+      test "render_change error with validator failure upload", %{lv: lv} do
+        avatar = file_input(lv, "form", :avatar, [%{name: "foo.jpeg", content: "ok"}])
+
+        assert lv
+               |> form("form", user: %{})
+               |> render_change(avatar) =~
+                 "entry_error::custom_validation_error"
+
+        assert {:error, [[_ref, :custom_validation_error]]} =
+                 render_upload(avatar, "foo.jpeg")
+      end
+
       @tag allow: [max_entries: 1, chunk_size: 20, accept: :any, auto_upload: true]
       test "render_upload too many files with auto_upload", %{lv: lv} do
         avatar =

test/phoenix_live_view/upload/config_test.exs

@@ -153,6 +153,32 @@ defmodule Phoenix.LiveView.UploadConfigTest do
 
       assert %UploadConfig{max_file_size: 10_000_000} = socket.assigns.uploads.avatar
     end
+
+    test "raises when invalid :validator provided" do
+      assert_raise ArgumentError, ~r/invalid :validator value provided to allow_upload/, fn ->
+        LiveView.allow_upload(build_socket(), :avatar, accept: :any, validator: 0)
+      end
+
+      assert_raise ArgumentError, ~r/invalid :validator value provided to allow_upload/, fn ->
+        LiveView.allow_upload(build_socket(), :avatar, accept: :any, validator: "bad")
+      end
+
+      assert_raise ArgumentError, ~r/invalid :validator value provided to allow_upload/, fn ->
+        wrong_arity_fun = fn _, _ -> :ok end
+        LiveView.allow_upload(build_socket(), :avatar, accept: :any, validator: wrong_arity_fun)
+      end
+    end
+
+    test "supports optional :validator" do
+      socket =
+        LiveView.allow_upload(build_socket(), :avatar,
+          accept: :any,
+          validator: fn _ -> :ok end
+        )
+
+      %UploadConfig{validator: validator_fun} = socket.assigns.uploads.avatar
+      assert is_function(validator_fun, 1)
+    end
   end
 
   describe "disallow_upload/2" do

test/phoenix_live_view/upload/external_test.exs

@@ -45,6 +45,12 @@ defmodule Phoenix.LiveView.UploadExternalTest do
           opts
       end
 
+    opts =
+      case Keyword.fetch(opts, :validator_response) do
+        {:ok, response} -> Keyword.put(opts, :validator, fn _ -> response end)
+        :error -> opts
+      end
+
     {:ok, lv} = mount_lv(fn socket -> Phoenix.LiveView.allow_upload(socket, :avatar, opts) end)
 
     {:ok, lv: lv}
@@ -81,7 +87,13 @@ defmodule Phoenix.LiveView.UploadExternalTest do
     assert render_upload(avatar, "foo1.jpeg", 1) =~ "relative path:some/path/to/foo1.jpeg"
   end
 
-  @tag allow: [max_entries: 2, chunk_size: 20, accept: :any, external: :preflight]
+  @tag allow: [
+         max_entries: 2,
+         chunk_size: 20,
+         accept: :any,
+         external: :preflight,
+         validator_response: :ok
+       ]
   test "external upload invokes preflight per entry", %{lv: lv} do
     avatar =
       file_input(lv, "form", :avatar, [
@@ -165,6 +177,28 @@ defmodule Phoenix.LiveView.UploadExternalTest do
     assert {:error, :not_allowed} = render_upload(avatar, "foo2.jpeg", 1)
   end
 
+  @tag allow: [
+         max_entries: 1,
+         max_file_size: 100,
+         auto_upload: true,
+         accept: :any,
+         external: :preflight,
+         validator_response: {:error, :custom_validation_error}
+       ]
+  test "custom validator returns error", %{lv: lv} do
+    avatar = file_input(lv, "form", :avatar, [%{name: "foo.jpeg", content: "ok"}])
+
+    html =
+      lv
+      |> form("form", user: %{})
+      |> render_change(avatar)
+
+    assert html =~ "foo.jpeg:0%"
+
+    assert {:error, [[_, %{reason: :custom_validation_error}]]} =
+             render_upload(avatar, "foo.jpeg", 1)
+  end
+
   def bad_preflight(%LiveView.UploadEntry{} = _entry, socket), do: {:ok, %{}, socket}
 
   @tag allow: [max_entries: 1, chunk_size: 20, accept: :any, external: :bad_preflight]