fix(ext/web): Prevent TextDecoderStream resource leak on stream cance…

…llation (denoland#21074)

This PR uses the new `cancel` method of `TransformStream` to properly
clean up the internal `TextDecoder` used in `TextDecoderStream` if the
stream is cancelled.

Fixes denoland#13142

Co-authored-by: Bartek Iwańczuk <[email protected]>

cli/tests/unit/text_encoding_test.ts

@@ -319,3 +319,20 @@ Deno.test(function binaryEncode() {
  assertEquals(Array.from(bytes), decodeBinary(binaryString));
  }
 });
+
+Deno.test(
+ { permissions: { read: true } },
+ async function textDecoderStreamCleansUpOnCancel() {
+ const filename = "cli/tests/testdata/assets/hello.txt";
+ const file = await Deno.open(filename);
+ const readable = file.readable.pipeThrough(new TextDecoderStream());
+ const chunks = [];
+ for await (const chunk of readable) {
+ chunks.push(chunk);
+ // breaking out of the loop prevents normal shutdown at end of async iterator values and triggers the cancel method of the stream instead
+ break;
+ }
+ assertEquals(chunks.length, 1);
+ assertEquals(chunks[0].length, 12);
+ },
+);

ext/web/06_streams.js

@@ -6680,6 +6680,10 @@ webidl.converters.Transformer = webidl
  key: "flush",
  converter: webidl.converters.Function,
  },
+ {
+ key: "cancel",
+ converter: webidl.converters.Function,
+ },
  {
  key: "readableType",
  converter: webidl.converters.any,

ext/web/08_text_encoding.js

@@ -301,6 +301,14 @@ class TextDecoderStream {
  return PromiseReject(err);
  }
  },
+ cancel: (_reason) => {
+ try {
+ const _ = this.#decoder.decode();
+ return PromiseResolve();
+ } catch (err) {
+ return PromiseReject(err);
+ }
+ },
  });
  this[webidl.brand] = webidl.brand;
  }