fix(ext/fs): truncate files when a ReadableStream is passed to writeF…

…ile (denoland#23330)

Closes denoland#19697. This fixes a bug where the writeFile API can create
partially-overwritten files which may lead to invalid / corrupt files or
data leakage. It also aligns the behavior of writing a ReadableStream
and writing a Uint8Array to the disk.

ext/fs/30_fs.js

@@ -926,6 +926,7 @@ async function writeFile(
  append: options.append ?? false,
  create: options.create ?? true,
  createNew: options.createNew ?? false,
+ truncate: !(options.append ?? false),
  write: true,
  });
  await data.pipeTo(file.writable, {

tests/unit/write_file_test.ts

@@ -425,3 +425,21 @@ Deno.test(
  assertEquals(Deno.readFileSync(filename), new Uint8Array([1, 2]));
  },
 );
+
+Deno.test(
+ { permissions: { read: true, write: true } },
+ async function overwriteFileWithStream() {
+ const filename = Deno.makeTempDirSync() + "/test.txt";
+ await Deno.writeFile(filename, new Uint8Array([1, 2, 3, 4]));
+
+ const stream = new ReadableStream({
+ pull(controller) {
+ controller.enqueue(new Uint8Array([1]));
+ controller.enqueue(new Uint8Array([2]));
+ controller.close();
+ },
+ });
+ await Deno.writeFile(filename, stream);
+ assertEquals(Deno.readFileSync(filename), new Uint8Array([1, 2]));
+ },
+);