stream: fix Writable.toWeb() desiredSize for non-object-mode

mcollina · aduh95 · commit f58c5bafcf9e · 2026-07-30T13:51:40.000+02:00
Writable.toWeb() used a plain { highWaterMark } as the queuing strategy for non-object-mode streams, which meant no size function was provided. The WritableStream defaulted to counting each chunk as size 1, so desiredSize was incorrect (e.g., a 3-byte Uint8Array was counted as size 1 instead of 3). Add a size() function to the strategy that mirrors how the Node.js stream computes chunk length: byteLength for typed arrays, length for strings/buffers, falling back to 1. Fixes: #56269 Signed-off-by: Matteo Collina <hello@matteocollina.com> PR-URL: #62986 Reviewed-By: René <contact.9a5d6388@renegade334.me.uk> Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
diff --git a/lib/internal/webstreams/adapters.js b/lib/internal/webstreams/adapters.js
@@ -179,7 +179,12 @@ function newWritableStreamFromStreamWritable(streamWritable, options = kEmptyObj
 const strategy =
 streamWritable.writableObjectMode ?
 new CountQueuingStrategy({ highWaterMark }) :
- { highWaterMark };
+ {
+ highWaterMark,
+ size(chunk) {
+ return chunk?.byteLength ?? chunk?.length ?? 1;
+ },
+ };
 
 let controller;
 let backpressurePromise;

-Original file line number
+Diff line change
 conststrategy=
 streamWritable.writableObjectMode ?
 newCountQueuingStrategy({ highWaterMark }) :
 -{ highWaterMark };
 +{
 + highWaterMark,
 +size(chunk){
 +returnchunk?.byteLength??chunk?.length??1;
 +},
 +};
 letcontroller;
 letbackpressurePromise;