fix: replacement of existing NIF files

lib/rustler_precompiled.ex

@@ -732,8 +732,11 @@ defmodule RustlerPrecompiled do
     cached_tar_gz = Map.fetch!(metadata, :cached_tar_gz)
     cache_dir = Path.dirname(cached_tar_gz)
 
-    file_name = Map.fetch!(metadata, :file_name)
-    lib_file = Path.join(native_dir, file_name)
+    lib_file =
+      metadata
+      |> Map.fetch!(:file_name)
+      |> String.replace_suffix(".tar.gz", "")
+      |> then(&Path.join(native_dir, &1))
 
     base_url = config.base_url
     nif_module = config.module
@@ -745,11 +748,8 @@ defmodule RustlerPrecompiled do
     }
 
     if File.exists?(cached_tar_gz) do
-      # Remove existing NIF file so we don't have processes using it.
-      # See: https://github.com/rusterlium/rustler/blob/46494d261cbedd3c798f584459e42ab7ee6ea1f4/rustler_mix/lib/rustler/compiler.ex#L134
-      File.rm(lib_file)
-
       with :ok <- check_file_integrity(cached_tar_gz, nif_module),
+           :ok <- remove_existing_nif(lib_file),
            :ok <- :erl_tar.extract(cached_tar_gz, [:compressed, cwd: Path.dirname(lib_file)]) do
         Logger.debug("Copying NIF from cache and extracting to #{lib_file}")
         {:ok, result}
@@ -764,6 +764,7 @@ defmodule RustlerPrecompiled do
              with_retry(fn -> download_nif_artifact(tar_gz_url) end, config.max_retries),
            :ok <- File.write(cached_tar_gz, tar_gz),
            :ok <- check_file_integrity(cached_tar_gz, nif_module),
+           :ok <- remove_existing_nif(lib_file),
            :ok <-
              :erl_tar.extract({:binary, tar_gz}, [:compressed, cwd: Path.dirname(lib_file)]) do
         Logger.debug("NIF cached at #{cached_tar_gz} and extracted to #{lib_file}")
@@ -773,6 +774,15 @@ defmodule RustlerPrecompiled do
     end
   end
 
+  # Remove existing NIF file so we don't have processes using it.
+  # See: https://github.com/rusterlium/rustler/blob/46494d261cbedd3c798f584459e42ab7ee6ea1f4/rustler_mix/lib/rustler/compiler.ex#L134
+  defp remove_existing_nif(path) do
+    case File.rm(path) do
+      {:error, :enoent} -> :ok
+      result -> result
+    end
+  end
+
   defp checksum_map(nif_module) when is_atom(nif_module) do
     nif_module
     |> checksum_file()

test/rustler_precompiled_test.exs

@@ -517,6 +517,69 @@ defmodule RustlerPrecompiledTest do
       end)
     end
 
+    @tag :tmp_dir
+    test "safely replaces an open NIF file", %{
+      tmp_dir: tmp_dir,
+      checksum_sample: checksum_sample,
+      nif_fixtures_dir: nif_fixtures_dir
+    } do
+      bypass = Bypass.open()
+
+      in_tmp(tmp_dir, fn ->
+        File.write!("checksum-Elixir.RustlerPrecompilationExample.Native.exs", checksum_sample)
+
+        Bypass.expect_once(bypass, fn conn ->
+          file_name = List.last(conn.path_info)
+          file = File.read!(Path.join([nif_fixtures_dir, "precompiled_nifs", file_name]))
+
+          Plug.Conn.resp(conn, 200, file)
+        end)
+
+        capture_log(fn ->
+          config =
+            RustlerPrecompiled.Config.new(
+              otp_app: :rustler_precompiled,
+              module: RustlerPrecompilationExample.Native,
+              base_cache_dir: tmp_dir,
+              base_url: "http://localhost:#{bypass.port}/download",
+              version: "0.2.0",
+              crate: "example",
+              targets: @available_targets,
+              nif_versions: @default_nif_versions,
+              force_build: false
+            )
+
+          {:ok, metadata} = RustlerPrecompiled.build_metadata(config)
+          archive = Path.join([nif_fixtures_dir, "precompiled_nifs", metadata.file_name])
+          File.mkdir_p!(Path.dirname(metadata.cached_tar_gz))
+          File.cp!(archive, metadata.cached_tar_gz)
+
+          lib_file =
+            :rustler_precompiled
+            |> Application.app_dir("priv/native")
+            |> Path.join(Path.rootname(metadata.file_name, ".tar.gz"))
+
+          File.mkdir_p!(Path.dirname(lib_file))
+          File.write!(lib_file, "old NIF")
+
+          File.open!(lib_file, [:read, :binary], fn file ->
+            assert {:ok, _} = RustlerPrecompiled.download_or_reuse_nif_file(config, metadata)
+            assert IO.binread(file, :eof) == "old NIF"
+            refute File.read!(lib_file) == "old NIF"
+          end)
+
+          File.rm!(metadata.cached_tar_gz)
+          File.write!(lib_file, "old NIF")
+
+          File.open!(lib_file, [:read, :binary], fn file ->
+            assert {:ok, _} = RustlerPrecompiled.download_or_reuse_nif_file(config, metadata)
+            assert IO.binread(file, :eof) == "old NIF"
+            refute File.read!(lib_file) == "old NIF"
+          end)
+        end)
+      end)
+    end
+
     @tag :tmp_dir
     test "a project downloading precompiled NIFs with custom header", %{
       tmp_dir: tmp_dir,