fix(ext/web): Prevent TextDecoderStream resource leak on stream cancellation (#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 #13142

Co-authored-by: Bartek Iwańczuk <biwanczuk@gmail.com>

2 files changed, 12 insertions, 0 deletions

diff --git a/ext/web/06_streams.js b/ext/web/06_streams.js
index c5306ca9c..7ce045e68 100644
--- a/ext/web/06_streams.js
+++ b/ext/web/06_streams.js
@@ -6681,6 +6681,10 @@ webidl.converters.Transformer = webidl
       converter: webidl.converters.Function,
     },
     {
+      key: "cancel",
+      converter: webidl.converters.Function,
+    },
+    {
       key: "readableType",
       converter: webidl.converters.any,
     },
diff --git a/ext/web/08_text_encoding.js b/ext/web/08_text_encoding.js
index 45dbad538..5f8391e12 100644
--- a/ext/web/08_text_encoding.js
+++ b/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;
   }