stream: reduce webstreams encoding and iteration overhead by mcollina · Pull Request #65414 · nodejs/node

mcollina · 2026-08-20T05:56:32Z

This PR is stacked on #65143 — please review the last two commits only.

Two independent optimizations for WHATWG streams:

TextEncoderStream: encode whole chunks natively. The encode-and-enqueue transform walked every code unit in JS, materializing a one-character string per index and building the output via string concatenation. The only state that crosses chunks is a trailing high (leading) surrogate, and TextEncoder.encode()'s USVString conversion already replaces interior lone surrogates with U+FFFD exactly like the spec loop. The transform now joins a pending high surrogate, holds back a new trailing one, and encodes the rest in a single native call. Verified byte-identical to the previous algorithm over 200k randomized surrogate-heavy chunk sequences, plus the full WPT encoding suite. The streaming decode path also stops allocating a { stream: true } options object per chunk.

ReadableStream.from(): drop the async pull machinery. The pull algorithm was an async function awaiting iterator.next() and then the value — an async frame, two await wrappers, and a controller-side reaction per chunk. It is now callback-style with per-stream cached reaction steps, delivering completion directly to the controller's cached pull reactions (the parked-algorithm-result contract from #65143). Thenable adoption is preserved, including the observable .then lookup on plain object values. The iterator's next method is now looked up once at setup, matching the spec's GetIteratorDirect.

Benchmark results (benchmark/compare.js --runs 10, new rows added since the suite covered neither path):

 confidence improvement accuracy (*) (**) (***)
webstreams/encoding-streams.js len=1024 kind='encode' n=100000 *** 546.04 % ±16.30% ±23.40% ±34.38%
webstreams/encoding-streams.js len=16 kind='encode' n=100000 *** 19.93 % ±4.31% ±5.96% ±8.26%
webstreams/from.js kind='sync' n=1000000 *** 27.39 % ±2.15% ±2.96% ±4.06%
webstreams/from.js kind='async' n=1000000 *** 23.30 % ±2.74% ±3.76% ±5.13%

All other webstreams rows (pipe-to ×9, pipe-through, read/read-buffered, async-iterator, tee, creation, js_transfer, decode) are unchanged. Full WPT streams + encoding suites and the parallel webstreams/whatwg test batches pass.

nodejs-github-bot · 2026-08-20T05:56:38Z

Review requested:

@nodejs/performance

XinGOfCloude18 · 2026-08-20T06:22:21Z

Review requested:
@nodejs/performance

codecov · 2026-08-20T07:42:04Z

Codecov Report

❌ Patch coverage is 41.83673% with 57 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.10%. Comparing base (9677349) to head (06951a7).
⚠️ Report is 83 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/internal/webstreams/readablestream.js	24.00%	57 Missing ⚠️

Additional details and impacted files

@@ Coverage Diff @@## main #65414 +/- ##
==========================================
- Coverage 90.12% 90.10% -0.02% 
==========================================
Files 752 751 -1 Lines 252317 252490 +173 Branches 47435 47464 +29 ==========================================
+ Hits 227401 227508 +107 - Misses 16209 16308 +99 + Partials 8707 8674 -33

Files with missing lines	Coverage Δ
lib/internal/webstreams/encoding.js	`100.00% <100.00%> (ø)`
lib/internal/webstreams/util.js	`96.48% <100.00%> (ø)`
lib/internal/webstreams/readablestream.js	`87.20% <24.00%> (-1.08%)`	⬇️

... and 47 files with indirect coverage changes

🚀 New features to boost your workflow:

❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

gurgunday

lgtm

The encode-and-enqueue transform walked the chunk code unit by code unit, materializing a single-character string per index and building the output with string concatenation. The only state that crosses chunks is a trailing high (leading) surrogate, and TextEncoder.encode's USVString conversion already replaces every interior lone surrogate with U+FFFD, which is exactly what the spec loop produces. Join a pending high surrogate with the incoming chunk, hold back a new trailing high surrogate, and encode the rest in a single native call. The streaming decode path also reuses a single options object instead of allocating { stream: true } per chunk. An encoding-streams benchmark is added since the suite had no TextEncoderStream/TextDecoderStream row. Encoding improves by ~546% with 1KB string chunks and ~20% with 16-character chunks; decode is unchanged. Signed-off-by: Matteo Collina <hello@matteocollina.com>

The pull algorithm was an async function that awaited iterator.next() and then the produced value, costing an async-function frame plus two await wrappers and a controller-side reaction per chunk. Rewrite it callback-style: the next() result is adopted exactly like the previous awaits (including the observable .then lookup on plain object values), the reaction steps are created once per stream, and completion is delivered straight to the controller's cached pull reactions using the parked-algorithm-result contract. The iterator's next method is also looked up once at setup, per the spec's GetIteratorDirect. A from benchmark is added since the suite had no ReadableStream.from row. Iterating a stream built from a sync generator improves by ~27% and from an async generator by ~23%; all other rows are unchanged. Signed-off-by: Matteo Collina <hello@matteocollina.com>

The parked-result sentinel is only ever compared by identity, so a Symbol describes its purpose better than an empty null-prototype object. Signed-off-by: Matteo Collina <hello@matteocollina.com>

nodejs-github-bot · 2026-08-22T20:56:04Z

CI: https://ci.nodejs.org/job/node-test-pull-request/76243/

nodejs-github-bot · 2026-08-23T17:06:00Z

CI: https://ci.nodejs.org/job/node-test-pull-request/76306/

nodejs-github-bot · 2026-08-23T17:06:20Z

CI: https://ci.nodejs.org/job/node-test-pull-request/76307/

nodejs-github-bot · 2026-08-24T18:17:13Z

Landed in f2c7f1b

The encode-and-enqueue transform walked the chunk code unit by code unit, materializing a single-character string per index and building the output with string concatenation. The only state that crosses chunks is a trailing high (leading) surrogate, and TextEncoder.encode's USVString conversion already replaces every interior lone surrogate with U+FFFD, which is exactly what the spec loop produces. Join a pending high surrogate with the incoming chunk, hold back a new trailing high surrogate, and encode the rest in a single native call. The streaming decode path also reuses a single options object instead of allocating { stream: true } per chunk. An encoding-streams benchmark is added since the suite had no TextEncoderStream/TextDecoderStream row. Encoding improves by ~546% with 1KB string chunks and ~20% with 16-character chunks; decode is unchanged. Signed-off-by: Matteo Collina <hello@matteocollina.com> PR-URL: #65414 Reviewed-By: Gürgün Dayıoğlu <hey@gurgun.day> Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com> Reviewed-By: Mattias Buelens <mattias@buelens.com>

mcollina · 2026-08-20T05:56:32Z

This PR is stacked on #65143 — please review the last two commits only.

Two independent optimizations for WHATWG streams:

TextEncoderStream: encode whole chunks natively. The encode-and-enqueue transform walked every code unit in JS, materializing a one-character string per index and building the output via string concatenation. The only state that crosses chunks is a trailing high (leading) surrogate, and TextEncoder.encode()'s USVString conversion already replaces interior lone surrogates with U+FFFD exactly like the spec loop. The transform now joins a pending high surrogate, holds back a new trailing one, and encodes the rest in a single native call. Verified byte-identical to the previous algorithm over 200k randomized surrogate-heavy chunk sequences, plus the full WPT encoding suite. The streaming decode path also stops allocating a { stream: true } options object per chunk.

ReadableStream.from(): drop the async pull machinery. The pull algorithm was an async function awaiting iterator.next() and then the value — an async frame, two await wrappers, and a controller-side reaction per chunk. It is now callback-style with per-stream cached reaction steps, delivering completion directly to the controller's cached pull reactions (the parked-algorithm-result contract from #65143). Thenable adoption is preserved, including the observable .then lookup on plain object values. The iterator's next method is now looked up once at setup, matching the spec's GetIteratorDirect.

Benchmark results (benchmark/compare.js --runs 10, new rows added since the suite covered neither path):

 confidence improvement accuracy (*) (**) (***)
webstreams/encoding-streams.js len=1024 kind='encode' n=100000 *** 546.04 % ±16.30% ±23.40% ±34.38%
webstreams/encoding-streams.js len=16 kind='encode' n=100000 *** 19.93 % ±4.31% ±5.96% ±8.26%
webstreams/from.js kind='sync' n=1000000 *** 27.39 % ±2.15% ±2.96% ±4.06%
webstreams/from.js kind='async' n=1000000 *** 23.30 % ±2.74% ±3.76% ±5.13%

All other webstreams rows (pipe-to ×9, pipe-through, read/read-buffered, async-iterator, tee, creation, js_transfer, decode) are unchanged. Full WPT streams + encoding suites and the parallel webstreams/whatwg test batches pass.

nodejs-github-bot · 2026-08-20T05:56:38Z

Review requested:

@nodejs/performance

XinGOfCloude18 · 2026-08-20T06:22:21Z

Review requested:
@nodejs/performance

codecov · 2026-08-20T07:42:04Z

Codecov Report

❌ Patch coverage is 41.83673% with 57 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.10%. Comparing base (9677349) to head (06951a7).
⚠️ Report is 83 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/internal/webstreams/readablestream.js	24.00%	57 Missing ⚠️

Additional details and impacted files

@@ Coverage Diff @@## main #65414 +/- ##
==========================================
- Coverage 90.12% 90.10% -0.02% 
==========================================
Files 752 751 -1 Lines 252317 252490 +173 Branches 47435 47464 +29 ==========================================
+ Hits 227401 227508 +107 - Misses 16209 16308 +99 + Partials 8707 8674 -33

Files with missing lines	Coverage Δ
lib/internal/webstreams/encoding.js	`100.00% <100.00%> (ø)`
lib/internal/webstreams/util.js	`96.48% <100.00%> (ø)`
lib/internal/webstreams/readablestream.js	`87.20% <24.00%> (-1.08%)`	⬇️

... and 47 files with indirect coverage changes

🚀 New features to boost your workflow:

❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

gurgunday

lgtm

The encode-and-enqueue transform walked the chunk code unit by code unit, materializing a single-character string per index and building the output with string concatenation. The only state that crosses chunks is a trailing high (leading) surrogate, and TextEncoder.encode's USVString conversion already replaces every interior lone surrogate with U+FFFD, which is exactly what the spec loop produces. Join a pending high surrogate with the incoming chunk, hold back a new trailing high surrogate, and encode the rest in a single native call. The streaming decode path also reuses a single options object instead of allocating { stream: true } per chunk. An encoding-streams benchmark is added since the suite had no TextEncoderStream/TextDecoderStream row. Encoding improves by ~546% with 1KB string chunks and ~20% with 16-character chunks; decode is unchanged. Signed-off-by: Matteo Collina <hello@matteocollina.com>

The pull algorithm was an async function that awaited iterator.next() and then the produced value, costing an async-function frame plus two await wrappers and a controller-side reaction per chunk. Rewrite it callback-style: the next() result is adopted exactly like the previous awaits (including the observable .then lookup on plain object values), the reaction steps are created once per stream, and completion is delivered straight to the controller's cached pull reactions using the parked-algorithm-result contract. The iterator's next method is also looked up once at setup, per the spec's GetIteratorDirect. A from benchmark is added since the suite had no ReadableStream.from row. Iterating a stream built from a sync generator improves by ~27% and from an async generator by ~23%; all other rows are unchanged. Signed-off-by: Matteo Collina <hello@matteocollina.com>

The parked-result sentinel is only ever compared by identity, so a Symbol describes its purpose better than an empty null-prototype object. Signed-off-by: Matteo Collina <hello@matteocollina.com>

nodejs-github-bot · 2026-08-22T20:56:04Z

CI: https://ci.nodejs.org/job/node-test-pull-request/76243/

nodejs-github-bot · 2026-08-23T17:06:00Z

CI: https://ci.nodejs.org/job/node-test-pull-request/76306/

nodejs-github-bot · 2026-08-23T17:06:20Z

CI: https://ci.nodejs.org/job/node-test-pull-request/76307/

nodejs-github-bot · 2026-08-24T18:17:13Z

Landed in f2c7f1b

The encode-and-enqueue transform walked the chunk code unit by code unit, materializing a single-character string per index and building the output with string concatenation. The only state that crosses chunks is a trailing high (leading) surrogate, and TextEncoder.encode's USVString conversion already replaces every interior lone surrogate with U+FFFD, which is exactly what the spec loop produces. Join a pending high surrogate with the incoming chunk, hold back a new trailing high surrogate, and encode the rest in a single native call. The streaming decode path also reuses a single options object instead of allocating { stream: true } per chunk. An encoding-streams benchmark is added since the suite had no TextEncoderStream/TextDecoderStream row. Encoding improves by ~546% with 1KB string chunks and ~20% with 16-character chunks; decode is unchanged. Signed-off-by: Matteo Collina <hello@matteocollina.com> PR-URL: #65414 Reviewed-By: Gürgün Dayıoğlu <hey@gurgun.day> Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com> Reviewed-By: Mattias Buelens <mattias@buelens.com>

mcollina · 2026-08-20T05:56:32Z

This PR is stacked on #65143 — please review the last two commits only.

Two independent optimizations for WHATWG streams:

TextEncoderStream: encode whole chunks natively. The encode-and-enqueue transform walked every code unit in JS, materializing a one-character string per index and building the output via string concatenation. The only state that crosses chunks is a trailing high (leading) surrogate, and TextEncoder.encode()'s USVString conversion already replaces interior lone surrogates with U+FFFD exactly like the spec loop. The transform now joins a pending high surrogate, holds back a new trailing one, and encodes the rest in a single native call. Verified byte-identical to the previous algorithm over 200k randomized surrogate-heavy chunk sequences, plus the full WPT encoding suite. The streaming decode path also stops allocating a { stream: true } options object per chunk.

ReadableStream.from(): drop the async pull machinery. The pull algorithm was an async function awaiting iterator.next() and then the value — an async frame, two await wrappers, and a controller-side reaction per chunk. It is now callback-style with per-stream cached reaction steps, delivering completion directly to the controller's cached pull reactions (the parked-algorithm-result contract from #65143). Thenable adoption is preserved, including the observable .then lookup on plain object values. The iterator's next method is now looked up once at setup, matching the spec's GetIteratorDirect.

Benchmark results (benchmark/compare.js --runs 10, new rows added since the suite covered neither path):

 confidence improvement accuracy (*) (**) (***)
webstreams/encoding-streams.js len=1024 kind='encode' n=100000 *** 546.04 % ±16.30% ±23.40% ±34.38%
webstreams/encoding-streams.js len=16 kind='encode' n=100000 *** 19.93 % ±4.31% ±5.96% ±8.26%
webstreams/from.js kind='sync' n=1000000 *** 27.39 % ±2.15% ±2.96% ±4.06%
webstreams/from.js kind='async' n=1000000 *** 23.30 % ±2.74% ±3.76% ±5.13%

All other webstreams rows (pipe-to ×9, pipe-through, read/read-buffered, async-iterator, tee, creation, js_transfer, decode) are unchanged. Full WPT streams + encoding suites and the parallel webstreams/whatwg test batches pass.

nodejs-github-bot · 2026-08-20T05:56:38Z

Review requested:

@nodejs/performance

XinGOfCloude18 · 2026-08-20T06:22:21Z

Review requested:
@nodejs/performance

codecov · 2026-08-20T07:42:04Z

Codecov Report

❌ Patch coverage is 41.83673% with 57 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.10%. Comparing base (9677349) to head (06951a7).
⚠️ Report is 83 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/internal/webstreams/readablestream.js	24.00%	57 Missing ⚠️

Additional details and impacted files

@@ Coverage Diff @@## main #65414 +/- ##
==========================================
- Coverage 90.12% 90.10% -0.02% 
==========================================
Files 752 751 -1 Lines 252317 252490 +173 Branches 47435 47464 +29 ==========================================
+ Hits 227401 227508 +107 - Misses 16209 16308 +99 + Partials 8707 8674 -33

Files with missing lines	Coverage Δ
lib/internal/webstreams/encoding.js	`100.00% <100.00%> (ø)`
lib/internal/webstreams/util.js	`96.48% <100.00%> (ø)`
lib/internal/webstreams/readablestream.js	`87.20% <24.00%> (-1.08%)`	⬇️

... and 47 files with indirect coverage changes

🚀 New features to boost your workflow:

❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

gurgunday

lgtm

The encode-and-enqueue transform walked the chunk code unit by code unit, materializing a single-character string per index and building the output with string concatenation. The only state that crosses chunks is a trailing high (leading) surrogate, and TextEncoder.encode's USVString conversion already replaces every interior lone surrogate with U+FFFD, which is exactly what the spec loop produces. Join a pending high surrogate with the incoming chunk, hold back a new trailing high surrogate, and encode the rest in a single native call. The streaming decode path also reuses a single options object instead of allocating { stream: true } per chunk. An encoding-streams benchmark is added since the suite had no TextEncoderStream/TextDecoderStream row. Encoding improves by ~546% with 1KB string chunks and ~20% with 16-character chunks; decode is unchanged. Signed-off-by: Matteo Collina <hello@matteocollina.com>

The pull algorithm was an async function that awaited iterator.next() and then the produced value, costing an async-function frame plus two await wrappers and a controller-side reaction per chunk. Rewrite it callback-style: the next() result is adopted exactly like the previous awaits (including the observable .then lookup on plain object values), the reaction steps are created once per stream, and completion is delivered straight to the controller's cached pull reactions using the parked-algorithm-result contract. The iterator's next method is also looked up once at setup, per the spec's GetIteratorDirect. A from benchmark is added since the suite had no ReadableStream.from row. Iterating a stream built from a sync generator improves by ~27% and from an async generator by ~23%; all other rows are unchanged. Signed-off-by: Matteo Collina <hello@matteocollina.com>

The parked-result sentinel is only ever compared by identity, so a Symbol describes its purpose better than an empty null-prototype object. Signed-off-by: Matteo Collina <hello@matteocollina.com>

nodejs-github-bot · 2026-08-22T20:56:04Z

CI: https://ci.nodejs.org/job/node-test-pull-request/76243/

nodejs-github-bot · 2026-08-23T17:06:00Z

CI: https://ci.nodejs.org/job/node-test-pull-request/76306/

nodejs-github-bot · 2026-08-23T17:06:20Z

CI: https://ci.nodejs.org/job/node-test-pull-request/76307/

nodejs-github-bot · 2026-08-24T18:17:13Z

Landed in f2c7f1b

The encode-and-enqueue transform walked the chunk code unit by code unit, materializing a single-character string per index and building the output with string concatenation. The only state that crosses chunks is a trailing high (leading) surrogate, and TextEncoder.encode's USVString conversion already replaces every interior lone surrogate with U+FFFD, which is exactly what the spec loop produces. Join a pending high surrogate with the incoming chunk, hold back a new trailing high surrogate, and encode the rest in a single native call. The streaming decode path also reuses a single options object instead of allocating { stream: true } per chunk. An encoding-streams benchmark is added since the suite had no TextEncoderStream/TextDecoderStream row. Encoding improves by ~546% with 1KB string chunks and ~20% with 16-character chunks; decode is unchanged. Signed-off-by: Matteo Collina <hello@matteocollina.com> PR-URL: #65414 Reviewed-By: Gürgün Dayıoğlu <hey@gurgun.day> Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com> Reviewed-By: Mattias Buelens <mattias@buelens.com>

mcollina · 2026-08-20T05:56:32Z

This PR is stacked on #65143 — please review the last two commits only.

Two independent optimizations for WHATWG streams:

TextEncoderStream: encode whole chunks natively. The encode-and-enqueue transform walked every code unit in JS, materializing a one-character string per index and building the output via string concatenation. The only state that crosses chunks is a trailing high (leading) surrogate, and TextEncoder.encode()'s USVString conversion already replaces interior lone surrogates with U+FFFD exactly like the spec loop. The transform now joins a pending high surrogate, holds back a new trailing one, and encodes the rest in a single native call. Verified byte-identical to the previous algorithm over 200k randomized surrogate-heavy chunk sequences, plus the full WPT encoding suite. The streaming decode path also stops allocating a { stream: true } options object per chunk.

ReadableStream.from(): drop the async pull machinery. The pull algorithm was an async function awaiting iterator.next() and then the value — an async frame, two await wrappers, and a controller-side reaction per chunk. It is now callback-style with per-stream cached reaction steps, delivering completion directly to the controller's cached pull reactions (the parked-algorithm-result contract from #65143). Thenable adoption is preserved, including the observable .then lookup on plain object values. The iterator's next method is now looked up once at setup, matching the spec's GetIteratorDirect.

Benchmark results (benchmark/compare.js --runs 10, new rows added since the suite covered neither path):

 confidence improvement accuracy (*) (**) (***)
webstreams/encoding-streams.js len=1024 kind='encode' n=100000 *** 546.04 % ±16.30% ±23.40% ±34.38%
webstreams/encoding-streams.js len=16 kind='encode' n=100000 *** 19.93 % ±4.31% ±5.96% ±8.26%
webstreams/from.js kind='sync' n=1000000 *** 27.39 % ±2.15% ±2.96% ±4.06%
webstreams/from.js kind='async' n=1000000 *** 23.30 % ±2.74% ±3.76% ±5.13%

All other webstreams rows (pipe-to ×9, pipe-through, read/read-buffered, async-iterator, tee, creation, js_transfer, decode) are unchanged. Full WPT streams + encoding suites and the parallel webstreams/whatwg test batches pass.

nodejs-github-bot · 2026-08-20T05:56:38Z

Review requested:

@nodejs/performance

XinGOfCloude18 · 2026-08-20T06:22:21Z

Review requested:
@nodejs/performance

codecov · 2026-08-20T07:42:04Z

Codecov Report

❌ Patch coverage is 41.83673% with 57 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.10%. Comparing base (9677349) to head (06951a7).
⚠️ Report is 83 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/internal/webstreams/readablestream.js	24.00%	57 Missing ⚠️

Additional details and impacted files

@@ Coverage Diff @@## main #65414 +/- ##
==========================================
- Coverage 90.12% 90.10% -0.02% 
==========================================
Files 752 751 -1 Lines 252317 252490 +173 Branches 47435 47464 +29 ==========================================
+ Hits 227401 227508 +107 - Misses 16209 16308 +99 + Partials 8707 8674 -33

Files with missing lines	Coverage Δ
lib/internal/webstreams/encoding.js	`100.00% <100.00%> (ø)`
lib/internal/webstreams/util.js	`96.48% <100.00%> (ø)`
lib/internal/webstreams/readablestream.js	`87.20% <24.00%> (-1.08%)`	⬇️

... and 47 files with indirect coverage changes

🚀 New features to boost your workflow:

❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

gurgunday

lgtm

The encode-and-enqueue transform walked the chunk code unit by code unit, materializing a single-character string per index and building the output with string concatenation. The only state that crosses chunks is a trailing high (leading) surrogate, and TextEncoder.encode's USVString conversion already replaces every interior lone surrogate with U+FFFD, which is exactly what the spec loop produces. Join a pending high surrogate with the incoming chunk, hold back a new trailing high surrogate, and encode the rest in a single native call. The streaming decode path also reuses a single options object instead of allocating { stream: true } per chunk. An encoding-streams benchmark is added since the suite had no TextEncoderStream/TextDecoderStream row. Encoding improves by ~546% with 1KB string chunks and ~20% with 16-character chunks; decode is unchanged. Signed-off-by: Matteo Collina <hello@matteocollina.com>

The pull algorithm was an async function that awaited iterator.next() and then the produced value, costing an async-function frame plus two await wrappers and a controller-side reaction per chunk. Rewrite it callback-style: the next() result is adopted exactly like the previous awaits (including the observable .then lookup on plain object values), the reaction steps are created once per stream, and completion is delivered straight to the controller's cached pull reactions using the parked-algorithm-result contract. The iterator's next method is also looked up once at setup, per the spec's GetIteratorDirect. A from benchmark is added since the suite had no ReadableStream.from row. Iterating a stream built from a sync generator improves by ~27% and from an async generator by ~23%; all other rows are unchanged. Signed-off-by: Matteo Collina <hello@matteocollina.com>

The parked-result sentinel is only ever compared by identity, so a Symbol describes its purpose better than an empty null-prototype object. Signed-off-by: Matteo Collina <hello@matteocollina.com>

nodejs-github-bot · 2026-08-22T20:56:04Z

CI: https://ci.nodejs.org/job/node-test-pull-request/76243/

nodejs-github-bot · 2026-08-23T17:06:00Z

CI: https://ci.nodejs.org/job/node-test-pull-request/76306/

nodejs-github-bot · 2026-08-23T17:06:20Z

CI: https://ci.nodejs.org/job/node-test-pull-request/76307/

nodejs-github-bot · 2026-08-24T18:17:13Z

Landed in f2c7f1b

The encode-and-enqueue transform walked the chunk code unit by code unit, materializing a single-character string per index and building the output with string concatenation. The only state that crosses chunks is a trailing high (leading) surrogate, and TextEncoder.encode's USVString conversion already replaces every interior lone surrogate with U+FFFD, which is exactly what the spec loop produces. Join a pending high surrogate with the incoming chunk, hold back a new trailing high surrogate, and encode the rest in a single native call. The streaming decode path also reuses a single options object instead of allocating { stream: true } per chunk. An encoding-streams benchmark is added since the suite had no TextEncoderStream/TextDecoderStream row. Encoding improves by ~546% with 1KB string chunks and ~20% with 16-character chunks; decode is unchanged. Signed-off-by: Matteo Collina <hello@matteocollina.com> PR-URL: #65414 Reviewed-By: Gürgün Dayıoğlu <hey@gurgun.day> Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com> Reviewed-By: Mattias Buelens <mattias@buelens.com>

mcollina · 2026-08-20T05:56:32Z

This PR is stacked on #65143 — please review the last two commits only.

Two independent optimizations for WHATWG streams:

TextEncoderStream: encode whole chunks natively. The encode-and-enqueue transform walked every code unit in JS, materializing a one-character string per index and building the output via string concatenation. The only state that crosses chunks is a trailing high (leading) surrogate, and TextEncoder.encode()'s USVString conversion already replaces interior lone surrogates with U+FFFD exactly like the spec loop. The transform now joins a pending high surrogate, holds back a new trailing one, and encodes the rest in a single native call. Verified byte-identical to the previous algorithm over 200k randomized surrogate-heavy chunk sequences, plus the full WPT encoding suite. The streaming decode path also stops allocating a { stream: true } options object per chunk.

ReadableStream.from(): drop the async pull machinery. The pull algorithm was an async function awaiting iterator.next() and then the value — an async frame, two await wrappers, and a controller-side reaction per chunk. It is now callback-style with per-stream cached reaction steps, delivering completion directly to the controller's cached pull reactions (the parked-algorithm-result contract from #65143). Thenable adoption is preserved, including the observable .then lookup on plain object values. The iterator's next method is now looked up once at setup, matching the spec's GetIteratorDirect.

Benchmark results (benchmark/compare.js --runs 10, new rows added since the suite covered neither path):

 confidence improvement accuracy (*) (**) (***)
webstreams/encoding-streams.js len=1024 kind='encode' n=100000 *** 546.04 % ±16.30% ±23.40% ±34.38%
webstreams/encoding-streams.js len=16 kind='encode' n=100000 *** 19.93 % ±4.31% ±5.96% ±8.26%
webstreams/from.js kind='sync' n=1000000 *** 27.39 % ±2.15% ±2.96% ±4.06%
webstreams/from.js kind='async' n=1000000 *** 23.30 % ±2.74% ±3.76% ±5.13%

All other webstreams rows (pipe-to ×9, pipe-through, read/read-buffered, async-iterator, tee, creation, js_transfer, decode) are unchanged. Full WPT streams + encoding suites and the parallel webstreams/whatwg test batches pass.

nodejs-github-bot · 2026-08-20T05:56:38Z

Review requested:

@nodejs/performance

XinGOfCloude18 · 2026-08-20T06:22:21Z

Review requested:
@nodejs/performance

codecov · 2026-08-20T07:42:04Z

Codecov Report

❌ Patch coverage is 41.83673% with 57 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.10%. Comparing base (9677349) to head (06951a7).
⚠️ Report is 83 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/internal/webstreams/readablestream.js	24.00%	57 Missing ⚠️

Additional details and impacted files

@@ Coverage Diff @@## main #65414 +/- ##
==========================================
- Coverage 90.12% 90.10% -0.02% 
==========================================
Files 752 751 -1 Lines 252317 252490 +173 Branches 47435 47464 +29 ==========================================
+ Hits 227401 227508 +107 - Misses 16209 16308 +99 + Partials 8707 8674 -33

Files with missing lines	Coverage Δ
lib/internal/webstreams/encoding.js	`100.00% <100.00%> (ø)`
lib/internal/webstreams/util.js	`96.48% <100.00%> (ø)`
lib/internal/webstreams/readablestream.js	`87.20% <24.00%> (-1.08%)`	⬇️

... and 47 files with indirect coverage changes

🚀 New features to boost your workflow:

❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

gurgunday

lgtm

The encode-and-enqueue transform walked the chunk code unit by code unit, materializing a single-character string per index and building the output with string concatenation. The only state that crosses chunks is a trailing high (leading) surrogate, and TextEncoder.encode's USVString conversion already replaces every interior lone surrogate with U+FFFD, which is exactly what the spec loop produces. Join a pending high surrogate with the incoming chunk, hold back a new trailing high surrogate, and encode the rest in a single native call. The streaming decode path also reuses a single options object instead of allocating { stream: true } per chunk. An encoding-streams benchmark is added since the suite had no TextEncoderStream/TextDecoderStream row. Encoding improves by ~546% with 1KB string chunks and ~20% with 16-character chunks; decode is unchanged. Signed-off-by: Matteo Collina <hello@matteocollina.com>

The pull algorithm was an async function that awaited iterator.next() and then the produced value, costing an async-function frame plus two await wrappers and a controller-side reaction per chunk. Rewrite it callback-style: the next() result is adopted exactly like the previous awaits (including the observable .then lookup on plain object values), the reaction steps are created once per stream, and completion is delivered straight to the controller's cached pull reactions using the parked-algorithm-result contract. The iterator's next method is also looked up once at setup, per the spec's GetIteratorDirect. A from benchmark is added since the suite had no ReadableStream.from row. Iterating a stream built from a sync generator improves by ~27% and from an async generator by ~23%; all other rows are unchanged. Signed-off-by: Matteo Collina <hello@matteocollina.com>

The parked-result sentinel is only ever compared by identity, so a Symbol describes its purpose better than an empty null-prototype object. Signed-off-by: Matteo Collina <hello@matteocollina.com>

nodejs-github-bot · 2026-08-22T20:56:04Z

CI: https://ci.nodejs.org/job/node-test-pull-request/76243/

nodejs-github-bot · 2026-08-23T17:06:00Z

CI: https://ci.nodejs.org/job/node-test-pull-request/76306/

nodejs-github-bot · 2026-08-23T17:06:20Z

CI: https://ci.nodejs.org/job/node-test-pull-request/76307/

nodejs-github-bot · 2026-08-24T18:17:13Z

Landed in f2c7f1b

The encode-and-enqueue transform walked the chunk code unit by code unit, materializing a single-character string per index and building the output with string concatenation. The only state that crosses chunks is a trailing high (leading) surrogate, and TextEncoder.encode's USVString conversion already replaces every interior lone surrogate with U+FFFD, which is exactly what the spec loop produces. Join a pending high surrogate with the incoming chunk, hold back a new trailing high surrogate, and encode the rest in a single native call. The streaming decode path also reuses a single options object instead of allocating { stream: true } per chunk. An encoding-streams benchmark is added since the suite had no TextEncoderStream/TextDecoderStream row. Encoding improves by ~546% with 1KB string chunks and ~20% with 16-character chunks; decode is unchanged. Signed-off-by: Matteo Collina <hello@matteocollina.com> PR-URL: #65414 Reviewed-By: Gürgün Dayıoğlu <hey@gurgun.day> Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com> Reviewed-By: Mattias Buelens <mattias@buelens.com>

mcollina · 2026-08-20T05:56:32Z

This PR is stacked on #65143 — please review the last two commits only.

Two independent optimizations for WHATWG streams:

TextEncoderStream: encode whole chunks natively. The encode-and-enqueue transform walked every code unit in JS, materializing a one-character string per index and building the output via string concatenation. The only state that crosses chunks is a trailing high (leading) surrogate, and TextEncoder.encode()'s USVString conversion already replaces interior lone surrogates with U+FFFD exactly like the spec loop. The transform now joins a pending high surrogate, holds back a new trailing one, and encodes the rest in a single native call. Verified byte-identical to the previous algorithm over 200k randomized surrogate-heavy chunk sequences, plus the full WPT encoding suite. The streaming decode path also stops allocating a { stream: true } options object per chunk.

ReadableStream.from(): drop the async pull machinery. The pull algorithm was an async function awaiting iterator.next() and then the value — an async frame, two await wrappers, and a controller-side reaction per chunk. It is now callback-style with per-stream cached reaction steps, delivering completion directly to the controller's cached pull reactions (the parked-algorithm-result contract from #65143). Thenable adoption is preserved, including the observable .then lookup on plain object values. The iterator's next method is now looked up once at setup, matching the spec's GetIteratorDirect.

Benchmark results (benchmark/compare.js --runs 10, new rows added since the suite covered neither path):

 confidence improvement accuracy (*) (**) (***)
webstreams/encoding-streams.js len=1024 kind='encode' n=100000 *** 546.04 % ±16.30% ±23.40% ±34.38%
webstreams/encoding-streams.js len=16 kind='encode' n=100000 *** 19.93 % ±4.31% ±5.96% ±8.26%
webstreams/from.js kind='sync' n=1000000 *** 27.39 % ±2.15% ±2.96% ±4.06%
webstreams/from.js kind='async' n=1000000 *** 23.30 % ±2.74% ±3.76% ±5.13%

All other webstreams rows (pipe-to ×9, pipe-through, read/read-buffered, async-iterator, tee, creation, js_transfer, decode) are unchanged. Full WPT streams + encoding suites and the parallel webstreams/whatwg test batches pass.

nodejs-github-bot · 2026-08-20T05:56:38Z

Review requested:

@nodejs/performance

XinGOfCloude18 · 2026-08-20T06:22:21Z

Review requested:
@nodejs/performance

codecov · 2026-08-20T07:42:04Z

Codecov Report

❌ Patch coverage is 41.83673% with 57 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.10%. Comparing base (9677349) to head (06951a7).
⚠️ Report is 83 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/internal/webstreams/readablestream.js	24.00%	57 Missing ⚠️

Additional details and impacted files

@@ Coverage Diff @@## main #65414 +/- ##
==========================================
- Coverage 90.12% 90.10% -0.02% 
==========================================
Files 752 751 -1 Lines 252317 252490 +173 Branches 47435 47464 +29 ==========================================
+ Hits 227401 227508 +107 - Misses 16209 16308 +99 + Partials 8707 8674 -33

Files with missing lines	Coverage Δ
lib/internal/webstreams/encoding.js	`100.00% <100.00%> (ø)`
lib/internal/webstreams/util.js	`96.48% <100.00%> (ø)`
lib/internal/webstreams/readablestream.js	`87.20% <24.00%> (-1.08%)`	⬇️

... and 47 files with indirect coverage changes

🚀 New features to boost your workflow:

❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

gurgunday

lgtm

The encode-and-enqueue transform walked the chunk code unit by code unit, materializing a single-character string per index and building the output with string concatenation. The only state that crosses chunks is a trailing high (leading) surrogate, and TextEncoder.encode's USVString conversion already replaces every interior lone surrogate with U+FFFD, which is exactly what the spec loop produces. Join a pending high surrogate with the incoming chunk, hold back a new trailing high surrogate, and encode the rest in a single native call. The streaming decode path also reuses a single options object instead of allocating { stream: true } per chunk. An encoding-streams benchmark is added since the suite had no TextEncoderStream/TextDecoderStream row. Encoding improves by ~546% with 1KB string chunks and ~20% with 16-character chunks; decode is unchanged. Signed-off-by: Matteo Collina <hello@matteocollina.com>

The pull algorithm was an async function that awaited iterator.next() and then the produced value, costing an async-function frame plus two await wrappers and a controller-side reaction per chunk. Rewrite it callback-style: the next() result is adopted exactly like the previous awaits (including the observable .then lookup on plain object values), the reaction steps are created once per stream, and completion is delivered straight to the controller's cached pull reactions using the parked-algorithm-result contract. The iterator's next method is also looked up once at setup, per the spec's GetIteratorDirect. A from benchmark is added since the suite had no ReadableStream.from row. Iterating a stream built from a sync generator improves by ~27% and from an async generator by ~23%; all other rows are unchanged. Signed-off-by: Matteo Collina <hello@matteocollina.com>

The parked-result sentinel is only ever compared by identity, so a Symbol describes its purpose better than an empty null-prototype object. Signed-off-by: Matteo Collina <hello@matteocollina.com>

nodejs-github-bot · 2026-08-22T20:56:04Z

CI: https://ci.nodejs.org/job/node-test-pull-request/76243/

nodejs-github-bot · 2026-08-23T17:06:00Z

CI: https://ci.nodejs.org/job/node-test-pull-request/76306/

nodejs-github-bot · 2026-08-23T17:06:20Z

CI: https://ci.nodejs.org/job/node-test-pull-request/76307/

nodejs-github-bot · 2026-08-24T18:17:13Z

Landed in f2c7f1b

The encode-and-enqueue transform walked the chunk code unit by code unit, materializing a single-character string per index and building the output with string concatenation. The only state that crosses chunks is a trailing high (leading) surrogate, and TextEncoder.encode's USVString conversion already replaces every interior lone surrogate with U+FFFD, which is exactly what the spec loop produces. Join a pending high surrogate with the incoming chunk, hold back a new trailing high surrogate, and encode the rest in a single native call. The streaming decode path also reuses a single options object instead of allocating { stream: true } per chunk. An encoding-streams benchmark is added since the suite had no TextEncoderStream/TextDecoderStream row. Encoding improves by ~546% with 1KB string chunks and ~20% with 16-character chunks; decode is unchanged. Signed-off-by: Matteo Collina <hello@matteocollina.com> PR-URL: #65414 Reviewed-By: Gürgün Dayıoğlu <hey@gurgun.day> Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com> Reviewed-By: Mattias Buelens <mattias@buelens.com>

mcollina · 2026-08-20T05:56:32Z

This PR is stacked on #65143 — please review the last two commits only.

Two independent optimizations for WHATWG streams:

TextEncoderStream: encode whole chunks natively. The encode-and-enqueue transform walked every code unit in JS, materializing a one-character string per index and building the output via string concatenation. The only state that crosses chunks is a trailing high (leading) surrogate, and TextEncoder.encode()'s USVString conversion already replaces interior lone surrogates with U+FFFD exactly like the spec loop. The transform now joins a pending high surrogate, holds back a new trailing one, and encodes the rest in a single native call. Verified byte-identical to the previous algorithm over 200k randomized surrogate-heavy chunk sequences, plus the full WPT encoding suite. The streaming decode path also stops allocating a { stream: true } options object per chunk.

ReadableStream.from(): drop the async pull machinery. The pull algorithm was an async function awaiting iterator.next() and then the value — an async frame, two await wrappers, and a controller-side reaction per chunk. It is now callback-style with per-stream cached reaction steps, delivering completion directly to the controller's cached pull reactions (the parked-algorithm-result contract from #65143). Thenable adoption is preserved, including the observable .then lookup on plain object values. The iterator's next method is now looked up once at setup, matching the spec's GetIteratorDirect.

Benchmark results (benchmark/compare.js --runs 10, new rows added since the suite covered neither path):

 confidence improvement accuracy (*) (**) (***)
webstreams/encoding-streams.js len=1024 kind='encode' n=100000 *** 546.04 % ±16.30% ±23.40% ±34.38%
webstreams/encoding-streams.js len=16 kind='encode' n=100000 *** 19.93 % ±4.31% ±5.96% ±8.26%
webstreams/from.js kind='sync' n=1000000 *** 27.39 % ±2.15% ±2.96% ±4.06%
webstreams/from.js kind='async' n=1000000 *** 23.30 % ±2.74% ±3.76% ±5.13%

All other webstreams rows (pipe-to ×9, pipe-through, read/read-buffered, async-iterator, tee, creation, js_transfer, decode) are unchanged. Full WPT streams + encoding suites and the parallel webstreams/whatwg test batches pass.

nodejs-github-bot · 2026-08-20T05:56:38Z

Review requested:

@nodejs/performance

XinGOfCloude18 · 2026-08-20T06:22:21Z

Review requested:
@nodejs/performance

codecov · 2026-08-20T07:42:04Z

Codecov Report

❌ Patch coverage is 41.83673% with 57 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.10%. Comparing base (9677349) to head (06951a7).
⚠️ Report is 83 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/internal/webstreams/readablestream.js	24.00%	57 Missing ⚠️

Additional details and impacted files

@@ Coverage Diff @@## main #65414 +/- ##
==========================================
- Coverage 90.12% 90.10% -0.02% 
==========================================
Files 752 751 -1 Lines 252317 252490 +173 Branches 47435 47464 +29 ==========================================
+ Hits 227401 227508 +107 - Misses 16209 16308 +99 + Partials 8707 8674 -33

Files with missing lines	Coverage Δ
lib/internal/webstreams/encoding.js	`100.00% <100.00%> (ø)`
lib/internal/webstreams/util.js	`96.48% <100.00%> (ø)`
lib/internal/webstreams/readablestream.js	`87.20% <24.00%> (-1.08%)`	⬇️

... and 47 files with indirect coverage changes

🚀 New features to boost your workflow:

❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

gurgunday

lgtm

The encode-and-enqueue transform walked the chunk code unit by code unit, materializing a single-character string per index and building the output with string concatenation. The only state that crosses chunks is a trailing high (leading) surrogate, and TextEncoder.encode's USVString conversion already replaces every interior lone surrogate with U+FFFD, which is exactly what the spec loop produces. Join a pending high surrogate with the incoming chunk, hold back a new trailing high surrogate, and encode the rest in a single native call. The streaming decode path also reuses a single options object instead of allocating { stream: true } per chunk. An encoding-streams benchmark is added since the suite had no TextEncoderStream/TextDecoderStream row. Encoding improves by ~546% with 1KB string chunks and ~20% with 16-character chunks; decode is unchanged. Signed-off-by: Matteo Collina <hello@matteocollina.com>

The pull algorithm was an async function that awaited iterator.next() and then the produced value, costing an async-function frame plus two await wrappers and a controller-side reaction per chunk. Rewrite it callback-style: the next() result is adopted exactly like the previous awaits (including the observable .then lookup on plain object values), the reaction steps are created once per stream, and completion is delivered straight to the controller's cached pull reactions using the parked-algorithm-result contract. The iterator's next method is also looked up once at setup, per the spec's GetIteratorDirect. A from benchmark is added since the suite had no ReadableStream.from row. Iterating a stream built from a sync generator improves by ~27% and from an async generator by ~23%; all other rows are unchanged. Signed-off-by: Matteo Collina <hello@matteocollina.com>

The parked-result sentinel is only ever compared by identity, so a Symbol describes its purpose better than an empty null-prototype object. Signed-off-by: Matteo Collina <hello@matteocollina.com>

nodejs-github-bot · 2026-08-22T20:56:04Z

CI: https://ci.nodejs.org/job/node-test-pull-request/76243/

nodejs-github-bot · 2026-08-23T17:06:00Z

CI: https://ci.nodejs.org/job/node-test-pull-request/76306/

nodejs-github-bot · 2026-08-23T17:06:20Z

CI: https://ci.nodejs.org/job/node-test-pull-request/76307/

nodejs-github-bot · 2026-08-24T18:17:13Z

Landed in f2c7f1b

The encode-and-enqueue transform walked the chunk code unit by code unit, materializing a single-character string per index and building the output with string concatenation. The only state that crosses chunks is a trailing high (leading) surrogate, and TextEncoder.encode's USVString conversion already replaces every interior lone surrogate with U+FFFD, which is exactly what the spec loop produces. Join a pending high surrogate with the incoming chunk, hold back a new trailing high surrogate, and encode the rest in a single native call. The streaming decode path also reuses a single options object instead of allocating { stream: true } per chunk. An encoding-streams benchmark is added since the suite had no TextEncoderStream/TextDecoderStream row. Encoding improves by ~546% with 1KB string chunks and ~20% with 16-character chunks; decode is unchanged. Signed-off-by: Matteo Collina <hello@matteocollina.com> PR-URL: #65414 Reviewed-By: Gürgün Dayıoğlu <hey@gurgun.day> Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com> Reviewed-By: Mattias Buelens <mattias@buelens.com>

mcollina · 2026-08-20T05:56:32Z

This PR is stacked on #65143 — please review the last two commits only.

Two independent optimizations for WHATWG streams:

TextEncoderStream: encode whole chunks natively. The encode-and-enqueue transform walked every code unit in JS, materializing a one-character string per index and building the output via string concatenation. The only state that crosses chunks is a trailing high (leading) surrogate, and TextEncoder.encode()'s USVString conversion already replaces interior lone surrogates with U+FFFD exactly like the spec loop. The transform now joins a pending high surrogate, holds back a new trailing one, and encodes the rest in a single native call. Verified byte-identical to the previous algorithm over 200k randomized surrogate-heavy chunk sequences, plus the full WPT encoding suite. The streaming decode path also stops allocating a { stream: true } options object per chunk.

ReadableStream.from(): drop the async pull machinery. The pull algorithm was an async function awaiting iterator.next() and then the value — an async frame, two await wrappers, and a controller-side reaction per chunk. It is now callback-style with per-stream cached reaction steps, delivering completion directly to the controller's cached pull reactions (the parked-algorithm-result contract from #65143). Thenable adoption is preserved, including the observable .then lookup on plain object values. The iterator's next method is now looked up once at setup, matching the spec's GetIteratorDirect.

Benchmark results (benchmark/compare.js --runs 10, new rows added since the suite covered neither path):

 confidence improvement accuracy (*) (**) (***)
webstreams/encoding-streams.js len=1024 kind='encode' n=100000 *** 546.04 % ±16.30% ±23.40% ±34.38%
webstreams/encoding-streams.js len=16 kind='encode' n=100000 *** 19.93 % ±4.31% ±5.96% ±8.26%
webstreams/from.js kind='sync' n=1000000 *** 27.39 % ±2.15% ±2.96% ±4.06%
webstreams/from.js kind='async' n=1000000 *** 23.30 % ±2.74% ±3.76% ±5.13%

All other webstreams rows (pipe-to ×9, pipe-through, read/read-buffered, async-iterator, tee, creation, js_transfer, decode) are unchanged. Full WPT streams + encoding suites and the parallel webstreams/whatwg test batches pass.

nodejs-github-bot · 2026-08-20T05:56:38Z

Review requested:

@nodejs/performance

XinGOfCloude18 · 2026-08-20T06:22:21Z

Review requested:
@nodejs/performance

codecov · 2026-08-20T07:42:04Z

Codecov Report

❌ Patch coverage is 41.83673% with 57 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.10%. Comparing base (9677349) to head (06951a7).
⚠️ Report is 83 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/internal/webstreams/readablestream.js	24.00%	57 Missing ⚠️

Additional details and impacted files

@@ Coverage Diff @@## main #65414 +/- ##
==========================================
- Coverage 90.12% 90.10% -0.02% 
==========================================
Files 752 751 -1 Lines 252317 252490 +173 Branches 47435 47464 +29 ==========================================
+ Hits 227401 227508 +107 - Misses 16209 16308 +99 + Partials 8707 8674 -33

Files with missing lines	Coverage Δ
lib/internal/webstreams/encoding.js	`100.00% <100.00%> (ø)`
lib/internal/webstreams/util.js	`96.48% <100.00%> (ø)`
lib/internal/webstreams/readablestream.js	`87.20% <24.00%> (-1.08%)`	⬇️

... and 47 files with indirect coverage changes

🚀 New features to boost your workflow:

❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

gurgunday

lgtm

The encode-and-enqueue transform walked the chunk code unit by code unit, materializing a single-character string per index and building the output with string concatenation. The only state that crosses chunks is a trailing high (leading) surrogate, and TextEncoder.encode's USVString conversion already replaces every interior lone surrogate with U+FFFD, which is exactly what the spec loop produces. Join a pending high surrogate with the incoming chunk, hold back a new trailing high surrogate, and encode the rest in a single native call. The streaming decode path also reuses a single options object instead of allocating { stream: true } per chunk. An encoding-streams benchmark is added since the suite had no TextEncoderStream/TextDecoderStream row. Encoding improves by ~546% with 1KB string chunks and ~20% with 16-character chunks; decode is unchanged. Signed-off-by: Matteo Collina <hello@matteocollina.com>

The pull algorithm was an async function that awaited iterator.next() and then the produced value, costing an async-function frame plus two await wrappers and a controller-side reaction per chunk. Rewrite it callback-style: the next() result is adopted exactly like the previous awaits (including the observable .then lookup on plain object values), the reaction steps are created once per stream, and completion is delivered straight to the controller's cached pull reactions using the parked-algorithm-result contract. The iterator's next method is also looked up once at setup, per the spec's GetIteratorDirect. A from benchmark is added since the suite had no ReadableStream.from row. Iterating a stream built from a sync generator improves by ~27% and from an async generator by ~23%; all other rows are unchanged. Signed-off-by: Matteo Collina <hello@matteocollina.com>

The parked-result sentinel is only ever compared by identity, so a Symbol describes its purpose better than an empty null-prototype object. Signed-off-by: Matteo Collina <hello@matteocollina.com>

nodejs-github-bot · 2026-08-22T20:56:04Z

CI: https://ci.nodejs.org/job/node-test-pull-request/76243/

nodejs-github-bot · 2026-08-23T17:06:00Z

CI: https://ci.nodejs.org/job/node-test-pull-request/76306/

nodejs-github-bot · 2026-08-23T17:06:20Z

CI: https://ci.nodejs.org/job/node-test-pull-request/76307/

nodejs-github-bot · 2026-08-24T18:17:13Z

Landed in f2c7f1b

The encode-and-enqueue transform walked the chunk code unit by code unit, materializing a single-character string per index and building the output with string concatenation. The only state that crosses chunks is a trailing high (leading) surrogate, and TextEncoder.encode's USVString conversion already replaces every interior lone surrogate with U+FFFD, which is exactly what the spec loop produces. Join a pending high surrogate with the incoming chunk, hold back a new trailing high surrogate, and encode the rest in a single native call. The streaming decode path also reuses a single options object instead of allocating { stream: true } per chunk. An encoding-streams benchmark is added since the suite had no TextEncoderStream/TextDecoderStream row. Encoding improves by ~546% with 1KB string chunks and ~20% with 16-character chunks; decode is unchanged. Signed-off-by: Matteo Collina <hello@matteocollina.com> PR-URL: #65414 Reviewed-By: Gürgün Dayıoğlu <hey@gurgun.day> Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com> Reviewed-By: Mattias Buelens <mattias@buelens.com>

nodejs-github-bot added needs-ci PRs that need a full CI run. web streams Issues and PRs related to the Web Streams API. labels Aug 20, 2026

jasnell reviewed Aug 20, 2026
View reviewed changes

Comment threadlib/internal/webstreams/util.js Outdated

mcollina force-pushed the webstream-perf-round14 branch 2 times, most recently from fde1b0b to 4a02249Compare August 20, 2026 17:29

gurgunday approved these changes Aug 20, 2026
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mcollina added 2 commits August 21, 2026 03:02

mcollina force-pushed the webstream-perf-round14 branch from 4a02249 to c8e5339Compare August 21, 2026 01:08

anonrig approved these changes Aug 21, 2026
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stream: use a Symbol for kParkedAlgorithmResult
06951a7
The parked-result sentinel is only ever compared by identity, so a Symbol describes its purpose better than an empty null-prototype object. Signed-off-by: Matteo Collina <hello@matteocollina.com>

anonrig approved these changes Aug 22, 2026
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jasnell requested a review from MattiasBuelens August 22, 2026 23:47

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nodejs-github-bot merged commit f2c7f1b into nodejs:mainAug 24, 2026
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github-actionsBot mentioned this pull request Aug 25, 2026
2026-08-26, Version 26.8.0 (Current) #65551
Merged