stream: refine stream/iter backpressure and error handling#63697

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nodejs-github-bot merged 2 commits into from
Jun 17, 2026
Merged

stream: refine stream/iter backpressure and error handling #63697

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ff1188a
stream: refine the stream/iter backpressure
jasnell Jun 1, 2026
c29567e
stream: fixup error handling in stream/iter adapters
jasnell Jun 1, 2026
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2 changes: 1 addition & 1 deletion doc/api/stream_iter.md
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Original file line numberDiff line numberDiff line change
Expand Up@@ -1675,7 +1675,7 @@ Creates a classic [`stream.Writable`][] backed by a stream/iter Writer.

Each `_write()` / `_writev()` call attempts the Writer's synchronous method
first (`writeSync` / `writevSync`), falling back to the async method if the
sync path returns `false` or throws. Similarly, `_final()` tries `endSync()`
sync path returns `false`. Similarly, `_final()` tries `endSync()`
before `end()`. When the sync path succeeds, the callback is deferred via
`queueMicrotask` to preserve the async resolution contract.

Expand Down
67 changes: 16 additions & 51 deletions lib/internal/streams/iter/classic.js
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Original file line numberDiff line numberDiff line change
Expand Up@@ -57,7 +57,6 @@ const {
const {
toAsyncStreamable: kToAsyncStreamable,
kValidatedSource,
kSyncWriteAccepted,
drainableProtocol,
} = require('internal/streams/iter/types');

Expand DownExpand Up@@ -765,41 +764,11 @@ function toWritable(writer) {
const hasEndSync = hasEnd &&
typeof writer.endSync === 'function';
const hasFail = typeof writer.fail === 'function';
const hasSyncWriteAccepted =
typeof writer[kSyncWriteAccepted] === 'function';

function syncWriteAccepted() {
return hasSyncWriteAccepted && writer[kSyncWriteAccepted]();
}

function finishAfterSyncBackpressure(cb) {
let ondrain;
try {
if (typeof writer[drainableProtocol] === 'function') {
ondrain = writer[drainableProtocol]();
}
} catch (err) {
cb(err);
return;
}
if (ondrain !== null && ondrain !== undefined) {
PromisePrototypeThen(ondrain, (drained) => {
if (drained === false) {
cb(new ERR_INVALID_STATE.TypeError('Stream closed by consumer'));
return;
}
cb();
}, cb);
return;
}
queueMicrotask(cb);
}

// Try-sync-first pattern: attempt the synchronous method and fall back to the
// async method if it returns false without accepting the data, or if it
// throws. When the sync path succeeds, the callback is deferred via
// queueMicrotask to preserve the async resolution contract that Writable
// internals expect from _write/_writev/_final callbacks.
// async method if it returns false (data not accepted synchronously).
// When the sync path succeeds, the callback is deferred via queueMicrotask
// to preserve the async resolution contract that Writable internals expect
// from _write/_writev/_final callbacks.

function _write(chunk, encoding, cb) {
const bytes = typeof chunk === 'string' ?
Expand All@@ -810,13 +779,10 @@ function toWritable(writer) {
queueMicrotask(cb);
return;
}
if (syncWriteAccepted()) {
// The chunk was accepted; false only signaled backpressure.
finishAfterSyncBackpressure(cb);
return;
}
} catch {
// Sync path threw -- fall through to async.
// WriteSync returned false: not accepted, fall through to async.
} catch (err) {
Comment thread
jasnell marked this conversation as resolved.
cb(err);
return;
}
}
try {
Expand All@@ -839,13 +805,10 @@ function toWritable(writer) {
queueMicrotask(cb);
return;
}
if (syncWriteAccepted()) {
// The chunks were accepted; false only signaled backpressure.
finishAfterSyncBackpressure(cb);
return;
}
} catch {
// Sync path threw -- fall through to async.
// WritevSync returned false: not accepted, fall through to async.
} catch (err) {
cb(err);
return;
}
}
try {
Expand All@@ -867,8 +830,10 @@ function toWritable(writer) {
queueMicrotask(cb);
return;
}
} catch {
// Sync path threw -- fall through to async.
// Result < 0: can't end synchronously, fall through to async.
} catch (err) {
cb(err);
return;
}
}
try {
Expand Down
45 changes: 35 additions & 10 deletions lib/internal/streams/iter/consumers.js
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Original file line numberDiff line numberDiff line change
Expand Up@@ -480,6 +480,7 @@ function merge(...args) {
);
}

let primaryError;
try {
while (activeCount > 0 || ready.length > 0) {
signal?.throwIfAborted();
Expand All@@ -500,22 +501,46 @@ function merge(...args) {
});
}
}
} catch (err) {
primaryError = err;
} finally {
// Clean up: return all iterators
await SafePromiseAllReturnVoid(iterators, async (iterator) => {
if (iterator.return) {
try {
await iterator.return();
} catch {
// Ignore return errors
}
}
});
// Clean up: return all iterators. Cleanup errors are not
// swallowed - a broken iterator.return() (e.g., failing to
// release a resource) should be visible to the caller.
await cleanupIterators(iterators, primaryError);
}
},
};
}

async function cleanupIterators(iterators, primaryError) {
let cleanupError;
await SafePromiseAllReturnVoid(iterators, async (iterator) => {
if (iterator.return) {
try {
await iterator.return();
} catch (err) {
// Keep the first cleanup error encountered.
cleanupError ??= err;
}
}
});
if (cleanupError !== undefined) {
if (primaryError !== undefined) {
// Both a primary error and a cleanup error occurred.
// Wrap in SuppressedError so neither is lost:
// .error = primaryError, .suppressed = cleanupError.
// eslint-disable-next-line no-restricted-syntax
throw new SuppressedError(primaryError, cleanupError);
}
// No primary error - the cleanup error is the only error.
throw cleanupError;
}
if (primaryError !== undefined) {
throw primaryError;
}
}

module.exports = {
array,
arrayBuffer,
Expand Down
56 changes: 5 additions & 51 deletions lib/internal/streams/iter/pull.js
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Original file line numberDiff line numberDiff line change
Expand Up@@ -63,8 +63,6 @@ const {
} = require('internal/streams/iter/utils');

const {
drainableProtocol,
kSyncWriteAcceptedOnFalse,
kValidatedSource,
kValidatedTransform,
toAsyncStreamable,
Expand DownExpand Up@@ -863,18 +861,6 @@ async function* createAsyncPipeline(source, transforms, signal) {
}
}

/**
* Check if a false sync write result means accepted backpressure.
* @param {object} writer - The writer whose sync method returned.
* @param {*} result - The return value from writeSync() or writevSync().
* @returns {boolean}
*/
function isAcceptedSyncWriteBackpressure(writer, result) {
return result === false &&
writer[kSyncWriteAcceptedOnFalse] === true &&
writer.desiredSize === 0;
}

// =============================================================================
// Public API: pull() and pullSync()
// =============================================================================
Expand DownExpand Up@@ -968,9 +954,7 @@ function pipeToSync(source, ...args) {
break;
}
if (hasWritevSync && batch.length > 1) {
const result = writer.writevSync(batch);
if (result === false &&
!isAcceptedSyncWriteBackpressure(writer, result)) {
if (writer.writevSync(batch) === false) {
break;
}
for (let i = 0; i < batch.length; i++) {
Expand All@@ -979,9 +963,7 @@ function pipeToSync(source, ...args) {
} else {
for (let i = 0; i < batch.length; i++) {
const chunk = batch[i];
const result = writer.writeSync(chunk);
if (result === false &&
!isAcceptedSyncWriteBackpressure(writer, result)) {
if (writer.writeSync(chunk) === false) {
canContinue = false;
break;
}
Expand DownExpand Up@@ -1037,28 +1019,13 @@ async function pipeTo(source, ...args) {
const hasWritevSync = typeof writer.writevSync === 'function';
const hasEndSync = typeof writer.endSync === 'function';

function waitForSyncBackpressure() {
const ondrain = writer[drainableProtocol];
return ondrain?.call(writer);
}

async function writeBatchAfterAcceptedBackpressure(batch, startIndex) {
await waitForSyncBackpressure();
await writeBatchAsyncFallback(batch, startIndex);
}

// Async fallback for writeBatch when sync write fails partway through.
// Continues writing from batch[startIndex] using async write().
async function writeBatchAsyncFallback(batch, startIndex) {
for (let i = startIndex; i < batch.length; i++) {
const chunk = batch[i];
const result = hasWriteSync && writer.writeSync(chunk);
if (result) {
if (hasWriteSync && writer.writeSync(chunk)) {
// Sync retry succeeded
} else if (isAcceptedSyncWriteBackpressure(writer, result)) {
totalBytes += TypedArrayPrototypeGetByteLength(chunk);
await waitForSyncBackpressure();
continue;
} else {
const result = writer.write(
chunk, signal ? { __proto__: null, signal } : undefined);
Expand All@@ -1075,14 +1042,7 @@ async function pipeTo(source, ...args) {
// is required. Callers must check: const p = writeBatch(b); if (p) await p;
function writeBatch(batch) {
if (hasWritev && batch.length > 1) {
const result = hasWritevSync && writer.writevSync(batch);
if (!result) {
if (isAcceptedSyncWriteBackpressure(writer, result)) {
for (let i = 0; i < batch.length; i++) {
totalBytes += TypedArrayPrototypeGetByteLength(batch[i]);
}
return waitForSyncBackpressure();
}
if (!hasWritevSync || !writer.writevSync(batch)) {
const opts = signal ? { __proto__: null, signal } : undefined;
const writevResult = writer.writev(batch, opts);
if (writevResult === undefined) {
Expand All@@ -1104,14 +1064,8 @@ async function pipeTo(source, ...args) {
}
for (let i = 0; i < batch.length; i++) {
const chunk = batch[i];
const result = hasWriteSync && writer.writeSync(chunk);
if (!result) {
if (isAcceptedSyncWriteBackpressure(writer, result)) {
totalBytes += TypedArrayPrototypeGetByteLength(chunk);
return writeBatchAfterAcceptedBackpressure(batch, i + 1);
}
if (!hasWriteSync || !writer.writeSync(chunk)) {
// Sync path failed at index i - fall back to async for the rest.
// Count bytes for chunks already written synchronously (0..i-1).
return writeBatchAsyncFallback(batch, i);
}
totalBytes += TypedArrayPrototypeGetByteLength(chunk);
Expand Down
48 changes: 2 additions & 46 deletions lib/internal/streams/iter/push.js
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Original file line numberDiff line numberDiff line change
Expand Up@@ -33,8 +33,6 @@ const {

const {
drainableProtocol,
kSyncWriteAccepted,
kSyncWriteAcceptedOnFalse,
} = require('internal/streams/iter/types');

const {
Expand DownExpand Up@@ -369,19 +367,6 @@ class PushQueue {
this.#pendingEnd = pending;
}

/**
* Force-enqueue chunks into the slots buffer, bypassing capacity checks.
* Used by PushWriter.writeSync() for 'block' policy where the data is
* accepted but false is returned as a backpressure signal.
*/
forceEnqueue(chunks) {
this.#slots.push(chunks);
for (let i = 0; i < chunks.length; i++) {
this.#bytesWritten += TypedArrayPrototypeGetByteLength(chunks[i]);
}
this.#resolvePendingReads();
}

/**
* Wait for backpressure to clear (desiredSize > 0).
* @returns {Promise<void>}
Expand DownExpand Up@@ -563,16 +548,11 @@ class PushQueue {

class PushWriter {
#queue;
#syncWriteAccepted = false;

constructor(queue) {
this.#queue = queue;
}

[kSyncWriteAccepted]() {
return this.#syncWriteAccepted;
}

[drainableProtocol]() {
const desired = this.desiredSize;
if (desired === null) return null;
Expand All@@ -584,10 +564,6 @@ class PushWriter {
return this.#queue.desiredSize;
}

get [kSyncWriteAcceptedOnFalse]() {
return this.#queue.backpressurePolicy === 'block';
}

write(chunk, options) {
if (!options?.signal && this.#queue.canWriteSync()) {
const bytes = toUint8Array(chunk);
Expand All@@ -612,36 +588,16 @@ class PushWriter {
}

writeSync(chunk) {
this.#syncWriteAccepted = false;
const bytes = toUint8Array(chunk);
const result = this.#queue.writeSync([bytes]);
if (!result && this.#queue.backpressurePolicy === 'block' &&
this.#queue.desiredSize === 0) {
// Block policy: force-enqueue and return false as backpressure signal.
// Data IS accepted; false tells caller to slow down.
this.#queue.forceEnqueue([bytes]);
this.#syncWriteAccepted = true;
return false;
}
this.#syncWriteAccepted = result;
return result;
return this.#queue.writeSync([bytes]);
Comment thread
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}

writevSync(chunks) {
this.#syncWriteAccepted = false;
if (!ArrayIsArray(chunks)) {
throw new ERR_INVALID_ARG_TYPE('chunks', 'Array', chunks);
}
const bytes = convertChunks(chunks);
const result = this.#queue.writeSync(bytes);
if (!result && this.#queue.backpressurePolicy === 'block' &&
this.#queue.desiredSize === 0) {
this.#queue.forceEnqueue(bytes);
this.#syncWriteAccepted = true;
return false;
}
this.#syncWriteAccepted = result;
return result;
return this.#queue.writeSync(bytes);
}

end(options) {
Expand Down
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, 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Add copy buttons to all 
 blocks\n(function() {\n function addCopyButtons() {\n document.querySelectorAll('pre code').forEach(function(codeBlock) {\n if (codeBlock.parentElement.hasAttribute('data-copy-added')) return;\n codeBlock.parentElement.setAttribute('data-copy-added', 'true');\n \n var btn = document.createElement('button');\n btn.textContent = 'Copy';\n btn.style.cssText = 'position:absolute;top:4px;right:4px;padding:2px 8px;font-size:11px;background:#4ecdc4;border:none;border-radius:4px;color:#1a1a2e;cursor:pointer;opacity:0.7;transition:opacity 0.2s;';\n btn.onmouseover = function() { this.style.opacity = '1'; };\n btn.onmouseout = function() { this.style.opacity = '0.7'; };\n btn.onclick = function() {\n navigator.clipboard.writeText(codeBlock.textContent).then(function() {\n btn.textContent = 'Copied!';\n setTimeout(function() { btn.textContent = 'Copy'; }, 1500);\n });\n };\n codeBlock.parentElement.style.position = 'relative';\n codeBlock.parentElement.appendChild(btn);\n });\n }\n \n addCopyButtons();\n \n // Re-run on dynamic content\n var observer = new MutationObserver(addCopyButtons);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Add Copy Buttons to Code Blocks");
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})();
(function(){
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var __m = "github.com";
var __re = new RegExp('^' + "github\\.com" + '

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stream: refine stream/iter backpressure and error handling#63697

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 Merged

nodejs-github-bot
merged 2 commits into

from

Jun 17, 2026
 Merged


stream: refine stream/iter backpressure and error handling
#63697
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ff1188a

stream: refine the stream/iter backpressure


jasnell Jun 1, 2026
c29567e

stream: fixup error handling in stream/iter adapters


jasnell Jun 1, 2026

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2 changes: 1 addition & 1 deletion
doc/api/stream_iter.md

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -1675,7 +1675,7 @@ Creates a classic [`stream.Writable`][] backed by a stream/iter Writer.

Each `_write()` / `_writev()` call attempts the Writer's synchronous method
first (`writeSync` / `writevSync`), falling back to the async method if the
sync path returns `false` or throws. Similarly, `_final()` tries `endSync()`
sync path returns `false`. Similarly, `_final()` tries `endSync()`
before `end()`. When the sync path succeeds, the callback is deferred via
`queueMicrotask` to preserve the async resolution contract.

Expand Down

67 changes: 16 additions & 51 deletions
lib/internal/streams/iter/classic.js

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Original file line numberDiff line numberDiff line change
Expand Up@@ -57,7 +57,6 @@ const {
const {
 toAsyncStreamable: kToAsyncStreamable,
 kValidatedSource,
 kSyncWriteAccepted,
 drainableProtocol,
} = require('internal/streams/iter/types');

Expand DownExpand Up@@ -765,41 +764,11 @@ function toWritable(writer) {
 const hasEndSync = hasEnd &&
 typeof writer.endSync === 'function';
 const hasFail = typeof writer.fail === 'function';
 const hasSyncWriteAccepted =
 typeof writer[kSyncWriteAccepted] === 'function';

 function syncWriteAccepted() {
 return hasSyncWriteAccepted && writer[kSyncWriteAccepted]();
 }

 function finishAfterSyncBackpressure(cb) {
 let ondrain;
 try {
 if (typeof writer[drainableProtocol] === 'function') {
 ondrain = writer[drainableProtocol]();
 }
 } catch (err) {
 cb(err);
 return;
 }
 if (ondrain !== null && ondrain !== undefined) {
 PromisePrototypeThen(ondrain, (drained) => {
 if (drained === false) {
 cb(new ERR_INVALID_STATE.TypeError('Stream closed by consumer'));
 return;
 }
 cb();
 }, cb);
 return;
 }
 queueMicrotask(cb);
 }

 // Try-sync-first pattern: attempt the synchronous method and fall back to the
 // async method if it returns false without accepting the data, or if it
 // throws. When the sync path succeeds, the callback is deferred via
 // queueMicrotask to preserve the async resolution contract that Writable
 // internals expect from _write/_writev/_final callbacks.
 // async method if it returns false (data not accepted synchronously).
 // When the sync path succeeds, the callback is deferred via queueMicrotask
 // to preserve the async resolution contract that Writable internals expect
 // from _write/_writev/_final callbacks.

 function _write(chunk, encoding, cb) {
 const bytes = typeof chunk === 'string' ?
Expand All@@ -810,13 +779,10 @@ function toWritable(writer) {
 queueMicrotask(cb);
 return;
 }
 if (syncWriteAccepted()) {
 // The chunk was accepted; false only signaled backpressure.
 finishAfterSyncBackpressure(cb);
 return;
 }
 } catch {
 // Sync path threw -- fall through to async.
 // WriteSync returned false: not accepted, fall through to async.
 } catch (err) {
Comment thread
jasnell marked this conversation as resolved.

 cb(err);
 return;
 }
 }
 try {
Expand All@@ -839,13 +805,10 @@ function toWritable(writer) {
 queueMicrotask(cb);
 return;
 }
 if (syncWriteAccepted()) {
 // The chunks were accepted; false only signaled backpressure.
 finishAfterSyncBackpressure(cb);
 return;
 }
 } catch {
 // Sync path threw -- fall through to async.
 // WritevSync returned false: not accepted, fall through to async.
 } catch (err) {
 cb(err);
 return;
 }
 }
 try {
Expand All@@ -867,8 +830,10 @@ function toWritable(writer) {
 queueMicrotask(cb);
 return;
 }
 } catch {
 // Sync path threw -- fall through to async.
 // Result < 0: can't end synchronously, fall through to async.
 } catch (err) {
 cb(err);
 return;
 }
 }
 try {
Expand Down

45 changes: 35 additions & 10 deletions
lib/internal/streams/iter/consumers.js

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Original file line numberDiff line numberDiff line change
Expand Up@@ -480,6 +480,7 @@ function merge(...args) {
 );
 }

 let primaryError;
 try {
 while (activeCount > 0 || ready.length > 0) {
 signal?.throwIfAborted();
Expand All@@ -500,22 +501,46 @@ function merge(...args) {
 });
 }
 }
 } catch (err) {
 primaryError = err;
 } finally {
 // Clean up: return all iterators
 await SafePromiseAllReturnVoid(iterators, async (iterator) => {
 if (iterator.return) {
 try {
 await iterator.return();
 } catch {
 // Ignore return errors
 }
 }
 });
 // Clean up: return all iterators. Cleanup errors are not
 // swallowed - a broken iterator.return() (e.g., failing to
 // release a resource) should be visible to the caller.
 await cleanupIterators(iterators, primaryError);
 }
 },
 };
}

async function cleanupIterators(iterators, primaryError) {
 let cleanupError;
 await SafePromiseAllReturnVoid(iterators, async (iterator) => {
 if (iterator.return) {
 try {
 await iterator.return();
 } catch (err) {
 // Keep the first cleanup error encountered.
 cleanupError ??= err;
 }
 }
 });
 if (cleanupError !== undefined) {
 if (primaryError !== undefined) {
 // Both a primary error and a cleanup error occurred.
 // Wrap in SuppressedError so neither is lost:
 // .error = primaryError, .suppressed = cleanupError.
 // eslint-disable-next-line no-restricted-syntax
 throw new SuppressedError(primaryError, cleanupError);
 }
 // No primary error - the cleanup error is the only error.
 throw cleanupError;
 }
 if (primaryError !== undefined) {
 throw primaryError;
 }
}

module.exports = {
 array,
 arrayBuffer,
Expand Down

56 changes: 5 additions & 51 deletions
lib/internal/streams/iter/pull.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -63,8 +63,6 @@ const {
} = require('internal/streams/iter/utils');

const {
 drainableProtocol,
 kSyncWriteAcceptedOnFalse,
 kValidatedSource,
 kValidatedTransform,
 toAsyncStreamable,
Expand DownExpand Up@@ -863,18 +861,6 @@ async function* createAsyncPipeline(source, transforms, signal) {
 }
}

/**
 * Check if a false sync write result means accepted backpressure.
 * @param {object} writer - The writer whose sync method returned.
 * @param {*} result - The return value from writeSync() or writevSync().
 * @returns {boolean}
 */
function isAcceptedSyncWriteBackpressure(writer, result) {
 return result === false &&
 writer[kSyncWriteAcceptedOnFalse] === true &&
 writer.desiredSize === 0;
}

// =============================================================================
// Public API: pull() and pullSync()
// =============================================================================
Expand DownExpand Up@@ -968,9 +954,7 @@ function pipeToSync(source, ...args) {
 break;
 }
 if (hasWritevSync && batch.length > 1) {
 const result = writer.writevSync(batch);
 if (result === false &&
 !isAcceptedSyncWriteBackpressure(writer, result)) {
 if (writer.writevSync(batch) === false) {
 break;
 }
 for (let i = 0; i < batch.length; i++) {
Expand All@@ -979,9 +963,7 @@ function pipeToSync(source, ...args) {
 } else {
 for (let i = 0; i < batch.length; i++) {
 const chunk = batch[i];
 const result = writer.writeSync(chunk);
 if (result === false &&
 !isAcceptedSyncWriteBackpressure(writer, result)) {
 if (writer.writeSync(chunk) === false) {
 canContinue = false;
 break;
 }
Expand DownExpand Up@@ -1037,28 +1019,13 @@ async function pipeTo(source, ...args) {
 const hasWritevSync = typeof writer.writevSync === 'function';
 const hasEndSync = typeof writer.endSync === 'function';

 function waitForSyncBackpressure() {
 const ondrain = writer[drainableProtocol];
 return ondrain?.call(writer);
 }

 async function writeBatchAfterAcceptedBackpressure(batch, startIndex) {
 await waitForSyncBackpressure();
 await writeBatchAsyncFallback(batch, startIndex);
 }

 // Async fallback for writeBatch when sync write fails partway through.
 // Continues writing from batch[startIndex] using async write().
 async function writeBatchAsyncFallback(batch, startIndex) {
 for (let i = startIndex; i < batch.length; i++) {
 const chunk = batch[i];
 const result = hasWriteSync && writer.writeSync(chunk);
 if (result) {
 if (hasWriteSync && writer.writeSync(chunk)) {
 // Sync retry succeeded
 } else if (isAcceptedSyncWriteBackpressure(writer, result)) {
 totalBytes += TypedArrayPrototypeGetByteLength(chunk);
 await waitForSyncBackpressure();
 continue;
 } else {
 const result = writer.write(
 chunk, signal ? { __proto__: null, signal } : undefined);
Expand All@@ -1075,14 +1042,7 @@ async function pipeTo(source, ...args) {
 // is required. Callers must check: const p = writeBatch(b); if (p) await p;
 function writeBatch(batch) {
 if (hasWritev && batch.length > 1) {
 const result = hasWritevSync && writer.writevSync(batch);
 if (!result) {
 if (isAcceptedSyncWriteBackpressure(writer, result)) {
 for (let i = 0; i < batch.length; i++) {
 totalBytes += TypedArrayPrototypeGetByteLength(batch[i]);
 }
 return waitForSyncBackpressure();
 }
 if (!hasWritevSync || !writer.writevSync(batch)) {
 const opts = signal ? { __proto__: null, signal } : undefined;
 const writevResult = writer.writev(batch, opts);
 if (writevResult === undefined) {
Expand All@@ -1104,14 +1064,8 @@ async function pipeTo(source, ...args) {
 }
 for (let i = 0; i < batch.length; i++) {
 const chunk = batch[i];
 const result = hasWriteSync && writer.writeSync(chunk);
 if (!result) {
 if (isAcceptedSyncWriteBackpressure(writer, result)) {
 totalBytes += TypedArrayPrototypeGetByteLength(chunk);
 return writeBatchAfterAcceptedBackpressure(batch, i + 1);
 }
 if (!hasWriteSync || !writer.writeSync(chunk)) {
 // Sync path failed at index i - fall back to async for the rest.
 // Count bytes for chunks already written synchronously (0..i-1).
 return writeBatchAsyncFallback(batch, i);
 }
 totalBytes += TypedArrayPrototypeGetByteLength(chunk);
Expand Down

48 changes: 2 additions & 46 deletions
lib/internal/streams/iter/push.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -33,8 +33,6 @@ const {

const {
 drainableProtocol,
 kSyncWriteAccepted,
 kSyncWriteAcceptedOnFalse,
} = require('internal/streams/iter/types');

const {
Expand DownExpand Up@@ -369,19 +367,6 @@ class PushQueue {
 this.#pendingEnd = pending;
 }

 /**
 * Force-enqueue chunks into the slots buffer, bypassing capacity checks.
 * Used by PushWriter.writeSync() for 'block' policy where the data is
 * accepted but false is returned as a backpressure signal.
 */
 forceEnqueue(chunks) {
 this.#slots.push(chunks);
 for (let i = 0; i < chunks.length; i++) {
 this.#bytesWritten += TypedArrayPrototypeGetByteLength(chunks[i]);
 }
 this.#resolvePendingReads();
 }

 /**
 * Wait for backpressure to clear (desiredSize > 0).
 * @returns {Promise<void>}
Expand DownExpand Up@@ -563,16 +548,11 @@ class PushQueue {

class PushWriter {
 #queue;
 #syncWriteAccepted = false;

 constructor(queue) {
 this.#queue = queue;
 }

 [kSyncWriteAccepted]() {
 return this.#syncWriteAccepted;
 }

 [drainableProtocol]() {
 const desired = this.desiredSize;
 if (desired === null) return null;
Expand All@@ -584,10 +564,6 @@ class PushWriter {
 return this.#queue.desiredSize;
 }

 get [kSyncWriteAcceptedOnFalse]() {
 return this.#queue.backpressurePolicy === 'block';
 }

 write(chunk, options) {
 if (!options?.signal && this.#queue.canWriteSync()) {
 const bytes = toUint8Array(chunk);
Expand All@@ -612,36 +588,16 @@ class PushWriter {
 }

 writeSync(chunk) {
 this.#syncWriteAccepted = false;
 const bytes = toUint8Array(chunk);
 const result = this.#queue.writeSync([bytes]);
 if (!result && this.#queue.backpressurePolicy === 'block' &&
 this.#queue.desiredSize === 0) {
 // Block policy: force-enqueue and return false as backpressure signal.
 // Data IS accepted; false tells caller to slow down.
 this.#queue.forceEnqueue([bytes]);
 this.#syncWriteAccepted = true;
 return false;
 }
 this.#syncWriteAccepted = result;
 return result;
 return this.#queue.writeSync([bytes]);
Comment thread
jasnell marked this conversation as resolved.

 }

 writevSync(chunks) {
 this.#syncWriteAccepted = false;
 if (!ArrayIsArray(chunks)) {
 throw new ERR_INVALID_ARG_TYPE('chunks', 'Array', chunks);
 }
 const bytes = convertChunks(chunks);
 const result = this.#queue.writeSync(bytes);
 if (!result && this.#queue.backpressurePolicy === 'block' &&
 this.#queue.desiredSize === 0) {
 this.#queue.forceEnqueue(bytes);
 this.#syncWriteAccepted = true;
 return false;
 }
 this.#syncWriteAccepted = result;
 return result;
 return this.#queue.writeSync(bytes);
 }

 end(options) {
Expand Down
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Loading

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Force GitHub README to respect dark mode\n(function() {\n var style = document.createElement('style');\n style.textContent = '\n .markdown-body {\n color-scheme: dark light;\n }\n .markdown-body pre { background: #161b22 !important; }\n .markdown-body code { background: rgba(110, 118, 129, 0.4) !important; }\n .markdown-body table th, .markdown-body table td { border-color: #30363d !important; }\n .markdown-body img { background: #0d1117; }\n .markdown-body blockquote { border-left-color: #8b949e; }\n .markdown-body hr { border-color: #30363d; }\n ';\n document.head.appendChild(style);\n})();", "GitHub Dark Mode README Fix");
}
} catch(__e) { console.warn('[Userscript:GitHub Dark Mode README Fix]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

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Jun 17, 2026
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stream: refine stream/iter backpressure and error handling
#63697
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ff1188a

stream: refine the stream/iter backpressure


jasnell Jun 1, 2026
c29567e

stream: fixup error handling in stream/iter adapters


jasnell Jun 1, 2026

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2 changes: 1 addition & 1 deletion
doc/api/stream_iter.md

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -1675,7 +1675,7 @@ Creates a classic [`stream.Writable`][] backed by a stream/iter Writer.

Each `_write()` / `_writev()` call attempts the Writer's synchronous method
first (`writeSync` / `writevSync`), falling back to the async method if the
sync path returns `false` or throws. Similarly, `_final()` tries `endSync()`
sync path returns `false`. Similarly, `_final()` tries `endSync()`
before `end()`. When the sync path succeeds, the callback is deferred via
`queueMicrotask` to preserve the async resolution contract.

Expand Down

67 changes: 16 additions & 51 deletions
lib/internal/streams/iter/classic.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -57,7 +57,6 @@ const {
const {
 toAsyncStreamable: kToAsyncStreamable,
 kValidatedSource,
 kSyncWriteAccepted,
 drainableProtocol,
} = require('internal/streams/iter/types');

Expand DownExpand Up@@ -765,41 +764,11 @@ function toWritable(writer) {
 const hasEndSync = hasEnd &&
 typeof writer.endSync === 'function';
 const hasFail = typeof writer.fail === 'function';
 const hasSyncWriteAccepted =
 typeof writer[kSyncWriteAccepted] === 'function';

 function syncWriteAccepted() {
 return hasSyncWriteAccepted && writer[kSyncWriteAccepted]();
 }

 function finishAfterSyncBackpressure(cb) {
 let ondrain;
 try {
 if (typeof writer[drainableProtocol] === 'function') {
 ondrain = writer[drainableProtocol]();
 }
 } catch (err) {
 cb(err);
 return;
 }
 if (ondrain !== null && ondrain !== undefined) {
 PromisePrototypeThen(ondrain, (drained) => {
 if (drained === false) {
 cb(new ERR_INVALID_STATE.TypeError('Stream closed by consumer'));
 return;
 }
 cb();
 }, cb);
 return;
 }
 queueMicrotask(cb);
 }

 // Try-sync-first pattern: attempt the synchronous method and fall back to the
 // async method if it returns false without accepting the data, or if it
 // throws. When the sync path succeeds, the callback is deferred via
 // queueMicrotask to preserve the async resolution contract that Writable
 // internals expect from _write/_writev/_final callbacks.
 // async method if it returns false (data not accepted synchronously).
 // When the sync path succeeds, the callback is deferred via queueMicrotask
 // to preserve the async resolution contract that Writable internals expect
 // from _write/_writev/_final callbacks.

 function _write(chunk, encoding, cb) {
 const bytes = typeof chunk === 'string' ?
Expand All@@ -810,13 +779,10 @@ function toWritable(writer) {
 queueMicrotask(cb);
 return;
 }
 if (syncWriteAccepted()) {
 // The chunk was accepted; false only signaled backpressure.
 finishAfterSyncBackpressure(cb);
 return;
 }
 } catch {
 // Sync path threw -- fall through to async.
 // WriteSync returned false: not accepted, fall through to async.
 } catch (err) {
Comment thread
jasnell marked this conversation as resolved.

 cb(err);
 return;
 }
 }
 try {
Expand All@@ -839,13 +805,10 @@ function toWritable(writer) {
 queueMicrotask(cb);
 return;
 }
 if (syncWriteAccepted()) {
 // The chunks were accepted; false only signaled backpressure.
 finishAfterSyncBackpressure(cb);
 return;
 }
 } catch {
 // Sync path threw -- fall through to async.
 // WritevSync returned false: not accepted, fall through to async.
 } catch (err) {
 cb(err);
 return;
 }
 }
 try {
Expand All@@ -867,8 +830,10 @@ function toWritable(writer) {
 queueMicrotask(cb);
 return;
 }
 } catch {
 // Sync path threw -- fall through to async.
 // Result < 0: can't end synchronously, fall through to async.
 } catch (err) {
 cb(err);
 return;
 }
 }
 try {
Expand Down

45 changes: 35 additions & 10 deletions
lib/internal/streams/iter/consumers.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -480,6 +480,7 @@ function merge(...args) {
 );
 }

 let primaryError;
 try {
 while (activeCount > 0 || ready.length > 0) {
 signal?.throwIfAborted();
Expand All@@ -500,22 +501,46 @@ function merge(...args) {
 });
 }
 }
 } catch (err) {
 primaryError = err;
 } finally {
 // Clean up: return all iterators
 await SafePromiseAllReturnVoid(iterators, async (iterator) => {
 if (iterator.return) {
 try {
 await iterator.return();
 } catch {
 // Ignore return errors
 }
 }
 });
 // Clean up: return all iterators. Cleanup errors are not
 // swallowed - a broken iterator.return() (e.g., failing to
 // release a resource) should be visible to the caller.
 await cleanupIterators(iterators, primaryError);
 }
 },
 };
}

async function cleanupIterators(iterators, primaryError) {
 let cleanupError;
 await SafePromiseAllReturnVoid(iterators, async (iterator) => {
 if (iterator.return) {
 try {
 await iterator.return();
 } catch (err) {
 // Keep the first cleanup error encountered.
 cleanupError ??= err;
 }
 }
 });
 if (cleanupError !== undefined) {
 if (primaryError !== undefined) {
 // Both a primary error and a cleanup error occurred.
 // Wrap in SuppressedError so neither is lost:
 // .error = primaryError, .suppressed = cleanupError.
 // eslint-disable-next-line no-restricted-syntax
 throw new SuppressedError(primaryError, cleanupError);
 }
 // No primary error - the cleanup error is the only error.
 throw cleanupError;
 }
 if (primaryError !== undefined) {
 throw primaryError;
 }
}

module.exports = {
 array,
 arrayBuffer,
Expand Down

56 changes: 5 additions & 51 deletions
lib/internal/streams/iter/pull.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -63,8 +63,6 @@ const {
} = require('internal/streams/iter/utils');

const {
 drainableProtocol,
 kSyncWriteAcceptedOnFalse,
 kValidatedSource,
 kValidatedTransform,
 toAsyncStreamable,
Expand DownExpand Up@@ -863,18 +861,6 @@ async function* createAsyncPipeline(source, transforms, signal) {
 }
}

/**
 * Check if a false sync write result means accepted backpressure.
 * @param {object} writer - The writer whose sync method returned.
 * @param {*} result - The return value from writeSync() or writevSync().
 * @returns {boolean}
 */
function isAcceptedSyncWriteBackpressure(writer, result) {
 return result === false &&
 writer[kSyncWriteAcceptedOnFalse] === true &&
 writer.desiredSize === 0;
}

// =============================================================================
// Public API: pull() and pullSync()
// =============================================================================
Expand DownExpand Up@@ -968,9 +954,7 @@ function pipeToSync(source, ...args) {
 break;
 }
 if (hasWritevSync && batch.length > 1) {
 const result = writer.writevSync(batch);
 if (result === false &&
 !isAcceptedSyncWriteBackpressure(writer, result)) {
 if (writer.writevSync(batch) === false) {
 break;
 }
 for (let i = 0; i < batch.length; i++) {
Expand All@@ -979,9 +963,7 @@ function pipeToSync(source, ...args) {
 } else {
 for (let i = 0; i < batch.length; i++) {
 const chunk = batch[i];
 const result = writer.writeSync(chunk);
 if (result === false &&
 !isAcceptedSyncWriteBackpressure(writer, result)) {
 if (writer.writeSync(chunk) === false) {
 canContinue = false;
 break;
 }
Expand DownExpand Up@@ -1037,28 +1019,13 @@ async function pipeTo(source, ...args) {
 const hasWritevSync = typeof writer.writevSync === 'function';
 const hasEndSync = typeof writer.endSync === 'function';

 function waitForSyncBackpressure() {
 const ondrain = writer[drainableProtocol];
 return ondrain?.call(writer);
 }

 async function writeBatchAfterAcceptedBackpressure(batch, startIndex) {
 await waitForSyncBackpressure();
 await writeBatchAsyncFallback(batch, startIndex);
 }

 // Async fallback for writeBatch when sync write fails partway through.
 // Continues writing from batch[startIndex] using async write().
 async function writeBatchAsyncFallback(batch, startIndex) {
 for (let i = startIndex; i < batch.length; i++) {
 const chunk = batch[i];
 const result = hasWriteSync && writer.writeSync(chunk);
 if (result) {
 if (hasWriteSync && writer.writeSync(chunk)) {
 // Sync retry succeeded
 } else if (isAcceptedSyncWriteBackpressure(writer, result)) {
 totalBytes += TypedArrayPrototypeGetByteLength(chunk);
 await waitForSyncBackpressure();
 continue;
 } else {
 const result = writer.write(
 chunk, signal ? { __proto__: null, signal } : undefined);
Expand All@@ -1075,14 +1042,7 @@ async function pipeTo(source, ...args) {
 // is required. Callers must check: const p = writeBatch(b); if (p) await p;
 function writeBatch(batch) {
 if (hasWritev && batch.length > 1) {
 const result = hasWritevSync && writer.writevSync(batch);
 if (!result) {
 if (isAcceptedSyncWriteBackpressure(writer, result)) {
 for (let i = 0; i < batch.length; i++) {
 totalBytes += TypedArrayPrototypeGetByteLength(batch[i]);
 }
 return waitForSyncBackpressure();
 }
 if (!hasWritevSync || !writer.writevSync(batch)) {
 const opts = signal ? { __proto__: null, signal } : undefined;
 const writevResult = writer.writev(batch, opts);
 if (writevResult === undefined) {
Expand All@@ -1104,14 +1064,8 @@ async function pipeTo(source, ...args) {
 }
 for (let i = 0; i < batch.length; i++) {
 const chunk = batch[i];
 const result = hasWriteSync && writer.writeSync(chunk);
 if (!result) {
 if (isAcceptedSyncWriteBackpressure(writer, result)) {
 totalBytes += TypedArrayPrototypeGetByteLength(chunk);
 return writeBatchAfterAcceptedBackpressure(batch, i + 1);
 }
 if (!hasWriteSync || !writer.writeSync(chunk)) {
 // Sync path failed at index i - fall back to async for the rest.
 // Count bytes for chunks already written synchronously (0..i-1).
 return writeBatchAsyncFallback(batch, i);
 }
 totalBytes += TypedArrayPrototypeGetByteLength(chunk);
Expand Down

48 changes: 2 additions & 46 deletions
lib/internal/streams/iter/push.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -33,8 +33,6 @@ const {

const {
 drainableProtocol,
 kSyncWriteAccepted,
 kSyncWriteAcceptedOnFalse,
} = require('internal/streams/iter/types');

const {
Expand DownExpand Up@@ -369,19 +367,6 @@ class PushQueue {
 this.#pendingEnd = pending;
 }

 /**
 * Force-enqueue chunks into the slots buffer, bypassing capacity checks.
 * Used by PushWriter.writeSync() for 'block' policy where the data is
 * accepted but false is returned as a backpressure signal.
 */
 forceEnqueue(chunks) {
 this.#slots.push(chunks);
 for (let i = 0; i < chunks.length; i++) {
 this.#bytesWritten += TypedArrayPrototypeGetByteLength(chunks[i]);
 }
 this.#resolvePendingReads();
 }

 /**
 * Wait for backpressure to clear (desiredSize > 0).
 * @returns {Promise<void>}
Expand DownExpand Up@@ -563,16 +548,11 @@ class PushQueue {

class PushWriter {
 #queue;
 #syncWriteAccepted = false;

 constructor(queue) {
 this.#queue = queue;
 }

 [kSyncWriteAccepted]() {
 return this.#syncWriteAccepted;
 }

 [drainableProtocol]() {
 const desired = this.desiredSize;
 if (desired === null) return null;
Expand All@@ -584,10 +564,6 @@ class PushWriter {
 return this.#queue.desiredSize;
 }

 get [kSyncWriteAcceptedOnFalse]() {
 return this.#queue.backpressurePolicy === 'block';
 }

 write(chunk, options) {
 if (!options?.signal && this.#queue.canWriteSync()) {
 const bytes = toUint8Array(chunk);
Expand All@@ -612,36 +588,16 @@ class PushWriter {
 }

 writeSync(chunk) {
 this.#syncWriteAccepted = false;
 const bytes = toUint8Array(chunk);
 const result = this.#queue.writeSync([bytes]);
 if (!result && this.#queue.backpressurePolicy === 'block' &&
 this.#queue.desiredSize === 0) {
 // Block policy: force-enqueue and return false as backpressure signal.
 // Data IS accepted; false tells caller to slow down.
 this.#queue.forceEnqueue([bytes]);
 this.#syncWriteAccepted = true;
 return false;
 }
 this.#syncWriteAccepted = result;
 return result;
 return this.#queue.writeSync([bytes]);
Comment thread
jasnell marked this conversation as resolved.

 }

 writevSync(chunks) {
 this.#syncWriteAccepted = false;
 if (!ArrayIsArray(chunks)) {
 throw new ERR_INVALID_ARG_TYPE('chunks', 'Array', chunks);
 }
 const bytes = convertChunks(chunks);
 const result = this.#queue.writeSync(bytes);
 if (!result && this.#queue.backpressurePolicy === 'block' &&
 this.#queue.desiredSize === 0) {
 this.#queue.forceEnqueue(bytes);
 this.#syncWriteAccepted = true;
 return false;
 }
 this.#syncWriteAccepted = result;
 return result;
 return this.#queue.writeSync(bytes);
 }

 end(options) {
Expand Down
Loading
Loading

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Highlight search terms from Google/DuckDuckGo/Bing referrer\n(function() {\n var ref = document.referrer;\n var terms = [];\n \n if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) {\n var url = new URL(ref);\n var q = url.searchParams.get('q') || url.searchParams.get('p');\n if (q) {\n terms = q.split(/\\s+/).filter(function(t) { return t.length > 2; });\n }\n }\n \n if (terms.length === 0) return;\n \n var style = document.createElement('style');\n style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }';\n document.head.appendChild(style);\n \n function highlight(node) {\n if (node.nodeType === 3) { // text node\n var text = node.textContent;\n var found = false;\n terms.forEach(function(term) {\n var regex = new RegExp('(' + term.replace(/[.*+?^${}()|[\\]\\\\]/g, '\\\\') + ')', 'gi');\n if (regex.test(text)) {\n found = true;\n var frag = document.createDocumentFragment();\n var parts = text.split(regex);\n parts.forEach(function(part, i) {\n if (i % 2 === 0) {\n frag.appendChild(document.createTextNode(part));\n } else {\n var span = document.createElement('span');\n span.className = 'userscript-highlight';\n span.textContent = part;\n frag.appendChild(span);\n }\n });\n node.parentNode.replaceChild(frag, node);\n }\n });\n } else if (node.nodeType === 1 && node.childNodes) { // element\n var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT'];\n if (!skipTags.includes(node.tagName)) {\n Array.from(node.childNodes).forEach(highlight);\n }\n }\n }\n \n highlight(document.body);\n \n // Re-highlight on dynamic content\n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1 || node.nodeType === 3) highlight(node);\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Highlight Search Terms");
}
} catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

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stream: refine stream/iter backpressure and error handling#63697

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 Merged

nodejs-github-bot
merged 2 commits into

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Jun 17, 2026
 Merged


stream: refine stream/iter backpressure and error handling
#63697
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ff1188a

stream: refine the stream/iter backpressure


jasnell Jun 1, 2026
c29567e

stream: fixup error handling in stream/iter adapters


jasnell Jun 1, 2026

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2 changes: 1 addition & 1 deletion
doc/api/stream_iter.md

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -1675,7 +1675,7 @@ Creates a classic [`stream.Writable`][] backed by a stream/iter Writer.

Each `_write()` / `_writev()` call attempts the Writer's synchronous method
first (`writeSync` / `writevSync`), falling back to the async method if the
sync path returns `false` or throws. Similarly, `_final()` tries `endSync()`
sync path returns `false`. Similarly, `_final()` tries `endSync()`
before `end()`. When the sync path succeeds, the callback is deferred via
`queueMicrotask` to preserve the async resolution contract.

Expand Down

67 changes: 16 additions & 51 deletions
lib/internal/streams/iter/classic.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -57,7 +57,6 @@ const {
const {
 toAsyncStreamable: kToAsyncStreamable,
 kValidatedSource,
 kSyncWriteAccepted,
 drainableProtocol,
} = require('internal/streams/iter/types');

Expand DownExpand Up@@ -765,41 +764,11 @@ function toWritable(writer) {
 const hasEndSync = hasEnd &&
 typeof writer.endSync === 'function';
 const hasFail = typeof writer.fail === 'function';
 const hasSyncWriteAccepted =
 typeof writer[kSyncWriteAccepted] === 'function';

 function syncWriteAccepted() {
 return hasSyncWriteAccepted && writer[kSyncWriteAccepted]();
 }

 function finishAfterSyncBackpressure(cb) {
 let ondrain;
 try {
 if (typeof writer[drainableProtocol] === 'function') {
 ondrain = writer[drainableProtocol]();
 }
 } catch (err) {
 cb(err);
 return;
 }
 if (ondrain !== null && ondrain !== undefined) {
 PromisePrototypeThen(ondrain, (drained) => {
 if (drained === false) {
 cb(new ERR_INVALID_STATE.TypeError('Stream closed by consumer'));
 return;
 }
 cb();
 }, cb);
 return;
 }
 queueMicrotask(cb);
 }

 // Try-sync-first pattern: attempt the synchronous method and fall back to the
 // async method if it returns false without accepting the data, or if it
 // throws. When the sync path succeeds, the callback is deferred via
 // queueMicrotask to preserve the async resolution contract that Writable
 // internals expect from _write/_writev/_final callbacks.
 // async method if it returns false (data not accepted synchronously).
 // When the sync path succeeds, the callback is deferred via queueMicrotask
 // to preserve the async resolution contract that Writable internals expect
 // from _write/_writev/_final callbacks.

 function _write(chunk, encoding, cb) {
 const bytes = typeof chunk === 'string' ?
Expand All@@ -810,13 +779,10 @@ function toWritable(writer) {
 queueMicrotask(cb);
 return;
 }
 if (syncWriteAccepted()) {
 // The chunk was accepted; false only signaled backpressure.
 finishAfterSyncBackpressure(cb);
 return;
 }
 } catch {
 // Sync path threw -- fall through to async.
 // WriteSync returned false: not accepted, fall through to async.
 } catch (err) {
Comment thread
jasnell marked this conversation as resolved.

 cb(err);
 return;
 }
 }
 try {
Expand All@@ -839,13 +805,10 @@ function toWritable(writer) {
 queueMicrotask(cb);
 return;
 }
 if (syncWriteAccepted()) {
 // The chunks were accepted; false only signaled backpressure.
 finishAfterSyncBackpressure(cb);
 return;
 }
 } catch {
 // Sync path threw -- fall through to async.
 // WritevSync returned false: not accepted, fall through to async.
 } catch (err) {
 cb(err);
 return;
 }
 }
 try {
Expand All@@ -867,8 +830,10 @@ function toWritable(writer) {
 queueMicrotask(cb);
 return;
 }
 } catch {
 // Sync path threw -- fall through to async.
 // Result < 0: can't end synchronously, fall through to async.
 } catch (err) {
 cb(err);
 return;
 }
 }
 try {
Expand Down

45 changes: 35 additions & 10 deletions
lib/internal/streams/iter/consumers.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -480,6 +480,7 @@ function merge(...args) {
 );
 }

 let primaryError;
 try {
 while (activeCount > 0 || ready.length > 0) {
 signal?.throwIfAborted();
Expand All@@ -500,22 +501,46 @@ function merge(...args) {
 });
 }
 }
 } catch (err) {
 primaryError = err;
 } finally {
 // Clean up: return all iterators
 await SafePromiseAllReturnVoid(iterators, async (iterator) => {
 if (iterator.return) {
 try {
 await iterator.return();
 } catch {
 // Ignore return errors
 }
 }
 });
 // Clean up: return all iterators. Cleanup errors are not
 // swallowed - a broken iterator.return() (e.g., failing to
 // release a resource) should be visible to the caller.
 await cleanupIterators(iterators, primaryError);
 }
 },
 };
}

async function cleanupIterators(iterators, primaryError) {
 let cleanupError;
 await SafePromiseAllReturnVoid(iterators, async (iterator) => {
 if (iterator.return) {
 try {
 await iterator.return();
 } catch (err) {
 // Keep the first cleanup error encountered.
 cleanupError ??= err;
 }
 }
 });
 if (cleanupError !== undefined) {
 if (primaryError !== undefined) {
 // Both a primary error and a cleanup error occurred.
 // Wrap in SuppressedError so neither is lost:
 // .error = primaryError, .suppressed = cleanupError.
 // eslint-disable-next-line no-restricted-syntax
 throw new SuppressedError(primaryError, cleanupError);
 }
 // No primary error - the cleanup error is the only error.
 throw cleanupError;
 }
 if (primaryError !== undefined) {
 throw primaryError;
 }
}

module.exports = {
 array,
 arrayBuffer,
Expand Down

56 changes: 5 additions & 51 deletions
lib/internal/streams/iter/pull.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -63,8 +63,6 @@ const {
} = require('internal/streams/iter/utils');

const {
 drainableProtocol,
 kSyncWriteAcceptedOnFalse,
 kValidatedSource,
 kValidatedTransform,
 toAsyncStreamable,
Expand DownExpand Up@@ -863,18 +861,6 @@ async function* createAsyncPipeline(source, transforms, signal) {
 }
}

/**
 * Check if a false sync write result means accepted backpressure.
 * @param {object} writer - The writer whose sync method returned.
 * @param {*} result - The return value from writeSync() or writevSync().
 * @returns {boolean}
 */
function isAcceptedSyncWriteBackpressure(writer, result) {
 return result === false &&
 writer[kSyncWriteAcceptedOnFalse] === true &&
 writer.desiredSize === 0;
}

// =============================================================================
// Public API: pull() and pullSync()
// =============================================================================
Expand DownExpand Up@@ -968,9 +954,7 @@ function pipeToSync(source, ...args) {
 break;
 }
 if (hasWritevSync && batch.length > 1) {
 const result = writer.writevSync(batch);
 if (result === false &&
 !isAcceptedSyncWriteBackpressure(writer, result)) {
 if (writer.writevSync(batch) === false) {
 break;
 }
 for (let i = 0; i < batch.length; i++) {
Expand All@@ -979,9 +963,7 @@ function pipeToSync(source, ...args) {
 } else {
 for (let i = 0; i < batch.length; i++) {
 const chunk = batch[i];
 const result = writer.writeSync(chunk);
 if (result === false &&
 !isAcceptedSyncWriteBackpressure(writer, result)) {
 if (writer.writeSync(chunk) === false) {
 canContinue = false;
 break;
 }
Expand DownExpand Up@@ -1037,28 +1019,13 @@ async function pipeTo(source, ...args) {
 const hasWritevSync = typeof writer.writevSync === 'function';
 const hasEndSync = typeof writer.endSync === 'function';

 function waitForSyncBackpressure() {
 const ondrain = writer[drainableProtocol];
 return ondrain?.call(writer);
 }

 async function writeBatchAfterAcceptedBackpressure(batch, startIndex) {
 await waitForSyncBackpressure();
 await writeBatchAsyncFallback(batch, startIndex);
 }

 // Async fallback for writeBatch when sync write fails partway through.
 // Continues writing from batch[startIndex] using async write().
 async function writeBatchAsyncFallback(batch, startIndex) {
 for (let i = startIndex; i < batch.length; i++) {
 const chunk = batch[i];
 const result = hasWriteSync && writer.writeSync(chunk);
 if (result) {
 if (hasWriteSync && writer.writeSync(chunk)) {
 // Sync retry succeeded
 } else if (isAcceptedSyncWriteBackpressure(writer, result)) {
 totalBytes += TypedArrayPrototypeGetByteLength(chunk);
 await waitForSyncBackpressure();
 continue;
 } else {
 const result = writer.write(
 chunk, signal ? { __proto__: null, signal } : undefined);
Expand All@@ -1075,14 +1042,7 @@ async function pipeTo(source, ...args) {
 // is required. Callers must check: const p = writeBatch(b); if (p) await p;
 function writeBatch(batch) {
 if (hasWritev && batch.length > 1) {
 const result = hasWritevSync && writer.writevSync(batch);
 if (!result) {
 if (isAcceptedSyncWriteBackpressure(writer, result)) {
 for (let i = 0; i < batch.length; i++) {
 totalBytes += TypedArrayPrototypeGetByteLength(batch[i]);
 }
 return waitForSyncBackpressure();
 }
 if (!hasWritevSync || !writer.writevSync(batch)) {
 const opts = signal ? { __proto__: null, signal } : undefined;
 const writevResult = writer.writev(batch, opts);
 if (writevResult === undefined) {
Expand All@@ -1104,14 +1064,8 @@ async function pipeTo(source, ...args) {
 }
 for (let i = 0; i < batch.length; i++) {
 const chunk = batch[i];
 const result = hasWriteSync && writer.writeSync(chunk);
 if (!result) {
 if (isAcceptedSyncWriteBackpressure(writer, result)) {
 totalBytes += TypedArrayPrototypeGetByteLength(chunk);
 return writeBatchAfterAcceptedBackpressure(batch, i + 1);
 }
 if (!hasWriteSync || !writer.writeSync(chunk)) {
 // Sync path failed at index i - fall back to async for the rest.
 // Count bytes for chunks already written synchronously (0..i-1).
 return writeBatchAsyncFallback(batch, i);
 }
 totalBytes += TypedArrayPrototypeGetByteLength(chunk);
Expand Down

48 changes: 2 additions & 46 deletions
lib/internal/streams/iter/push.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -33,8 +33,6 @@ const {

const {
 drainableProtocol,
 kSyncWriteAccepted,
 kSyncWriteAcceptedOnFalse,
} = require('internal/streams/iter/types');

const {
Expand DownExpand Up@@ -369,19 +367,6 @@ class PushQueue {
 this.#pendingEnd = pending;
 }

 /**
 * Force-enqueue chunks into the slots buffer, bypassing capacity checks.
 * Used by PushWriter.writeSync() for 'block' policy where the data is
 * accepted but false is returned as a backpressure signal.
 */
 forceEnqueue(chunks) {
 this.#slots.push(chunks);
 for (let i = 0; i < chunks.length; i++) {
 this.#bytesWritten += TypedArrayPrototypeGetByteLength(chunks[i]);
 }
 this.#resolvePendingReads();
 }

 /**
 * Wait for backpressure to clear (desiredSize > 0).
 * @returns {Promise<void>}
Expand DownExpand Up@@ -563,16 +548,11 @@ class PushQueue {

class PushWriter {
 #queue;
 #syncWriteAccepted = false;

 constructor(queue) {
 this.#queue = queue;
 }

 [kSyncWriteAccepted]() {
 return this.#syncWriteAccepted;
 }

 [drainableProtocol]() {
 const desired = this.desiredSize;
 if (desired === null) return null;
Expand All@@ -584,10 +564,6 @@ class PushWriter {
 return this.#queue.desiredSize;
 }

 get [kSyncWriteAcceptedOnFalse]() {
 return this.#queue.backpressurePolicy === 'block';
 }

 write(chunk, options) {
 if (!options?.signal && this.#queue.canWriteSync()) {
 const bytes = toUint8Array(chunk);
Expand All@@ -612,36 +588,16 @@ class PushWriter {
 }

 writeSync(chunk) {
 this.#syncWriteAccepted = false;
 const bytes = toUint8Array(chunk);
 const result = this.#queue.writeSync([bytes]);
 if (!result && this.#queue.backpressurePolicy === 'block' &&
 this.#queue.desiredSize === 0) {
 // Block policy: force-enqueue and return false as backpressure signal.
 // Data IS accepted; false tells caller to slow down.
 this.#queue.forceEnqueue([bytes]);
 this.#syncWriteAccepted = true;
 return false;
 }
 this.#syncWriteAccepted = result;
 return result;
 return this.#queue.writeSync([bytes]);
Comment thread
jasnell marked this conversation as resolved.

 }

 writevSync(chunks) {
 this.#syncWriteAccepted = false;
 if (!ArrayIsArray(chunks)) {
 throw new ERR_INVALID_ARG_TYPE('chunks', 'Array', chunks);
 }
 const bytes = convertChunks(chunks);
 const result = this.#queue.writeSync(bytes);
 if (!result && this.#queue.backpressurePolicy === 'block' &&
 this.#queue.desiredSize === 0) {
 this.#queue.forceEnqueue(bytes);
 this.#syncWriteAccepted = true;
 return false;
 }
 this.#syncWriteAccepted = result;
 return result;
 return this.#queue.writeSync(bytes);
 }

 end(options) {
Expand Down
Loading
Loading

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Strip utm_, fbclid, gclid, etc. from all links on page\n(function() {\n var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',\n 'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',\n 'ref', 'ref_src', 'source', 'medium', 'campaign'];\n \n function cleanUrl(url) {\n try {\n var u = new URL(url, window.location.origin);\n var changed = false;\n trackingParams.forEach(function(p) {\n if (u.searchParams.has(p)) {\n u.searchParams.delete(p);\n changed = true;\n }\n });\n return changed ? u.toString() : url;\n } catch (e) {\n return url;\n }\n }\n \n function cleanLinks() {\n document.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n \n cleanLinks();\n \n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1) {\n if (node.tagName === 'A') cleanLinks();\n node.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Remove Tracking Parameters from Links");
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '

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stream: refine stream/iter backpressure and error handling#63697

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merged 2 commits into

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Jun 17, 2026
 Merged


stream: refine stream/iter backpressure and error handling
#63697
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ff1188a

stream: refine the stream/iter backpressure


jasnell Jun 1, 2026
c29567e

stream: fixup error handling in stream/iter adapters


jasnell Jun 1, 2026

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2 changes: 1 addition & 1 deletion
doc/api/stream_iter.md

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -1675,7 +1675,7 @@ Creates a classic [`stream.Writable`][] backed by a stream/iter Writer.

Each `_write()` / `_writev()` call attempts the Writer's synchronous method
first (`writeSync` / `writevSync`), falling back to the async method if the
sync path returns `false` or throws. Similarly, `_final()` tries `endSync()`
sync path returns `false`. Similarly, `_final()` tries `endSync()`
before `end()`. When the sync path succeeds, the callback is deferred via
`queueMicrotask` to preserve the async resolution contract.

Expand Down

67 changes: 16 additions & 51 deletions
lib/internal/streams/iter/classic.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -57,7 +57,6 @@ const {
const {
 toAsyncStreamable: kToAsyncStreamable,
 kValidatedSource,
 kSyncWriteAccepted,
 drainableProtocol,
} = require('internal/streams/iter/types');

Expand DownExpand Up@@ -765,41 +764,11 @@ function toWritable(writer) {
 const hasEndSync = hasEnd &&
 typeof writer.endSync === 'function';
 const hasFail = typeof writer.fail === 'function';
 const hasSyncWriteAccepted =
 typeof writer[kSyncWriteAccepted] === 'function';

 function syncWriteAccepted() {
 return hasSyncWriteAccepted && writer[kSyncWriteAccepted]();
 }

 function finishAfterSyncBackpressure(cb) {
 let ondrain;
 try {
 if (typeof writer[drainableProtocol] === 'function') {
 ondrain = writer[drainableProtocol]();
 }
 } catch (err) {
 cb(err);
 return;
 }
 if (ondrain !== null && ondrain !== undefined) {
 PromisePrototypeThen(ondrain, (drained) => {
 if (drained === false) {
 cb(new ERR_INVALID_STATE.TypeError('Stream closed by consumer'));
 return;
 }
 cb();
 }, cb);
 return;
 }
 queueMicrotask(cb);
 }

 // Try-sync-first pattern: attempt the synchronous method and fall back to the
 // async method if it returns false without accepting the data, or if it
 // throws. When the sync path succeeds, the callback is deferred via
 // queueMicrotask to preserve the async resolution contract that Writable
 // internals expect from _write/_writev/_final callbacks.
 // async method if it returns false (data not accepted synchronously).
 // When the sync path succeeds, the callback is deferred via queueMicrotask
 // to preserve the async resolution contract that Writable internals expect
 // from _write/_writev/_final callbacks.

 function _write(chunk, encoding, cb) {
 const bytes = typeof chunk === 'string' ?
Expand All@@ -810,13 +779,10 @@ function toWritable(writer) {
 queueMicrotask(cb);
 return;
 }
 if (syncWriteAccepted()) {
 // The chunk was accepted; false only signaled backpressure.
 finishAfterSyncBackpressure(cb);
 return;
 }
 } catch {
 // Sync path threw -- fall through to async.
 // WriteSync returned false: not accepted, fall through to async.
 } catch (err) {
Comment thread
jasnell marked this conversation as resolved.

 cb(err);
 return;
 }
 }
 try {
Expand All@@ -839,13 +805,10 @@ function toWritable(writer) {
 queueMicrotask(cb);
 return;
 }
 if (syncWriteAccepted()) {
 // The chunks were accepted; false only signaled backpressure.
 finishAfterSyncBackpressure(cb);
 return;
 }
 } catch {
 // Sync path threw -- fall through to async.
 // WritevSync returned false: not accepted, fall through to async.
 } catch (err) {
 cb(err);
 return;
 }
 }
 try {
Expand All@@ -867,8 +830,10 @@ function toWritable(writer) {
 queueMicrotask(cb);
 return;
 }
 } catch {
 // Sync path threw -- fall through to async.
 // Result < 0: can't end synchronously, fall through to async.
 } catch (err) {
 cb(err);
 return;
 }
 }
 try {
Expand Down

45 changes: 35 additions & 10 deletions
lib/internal/streams/iter/consumers.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -480,6 +480,7 @@ function merge(...args) {
 );
 }

 let primaryError;
 try {
 while (activeCount > 0 || ready.length > 0) {
 signal?.throwIfAborted();
Expand All@@ -500,22 +501,46 @@ function merge(...args) {
 });
 }
 }
 } catch (err) {
 primaryError = err;
 } finally {
 // Clean up: return all iterators
 await SafePromiseAllReturnVoid(iterators, async (iterator) => {
 if (iterator.return) {
 try {
 await iterator.return();
 } catch {
 // Ignore return errors
 }
 }
 });
 // Clean up: return all iterators. Cleanup errors are not
 // swallowed - a broken iterator.return() (e.g., failing to
 // release a resource) should be visible to the caller.
 await cleanupIterators(iterators, primaryError);
 }
 },
 };
}

async function cleanupIterators(iterators, primaryError) {
 let cleanupError;
 await SafePromiseAllReturnVoid(iterators, async (iterator) => {
 if (iterator.return) {
 try {
 await iterator.return();
 } catch (err) {
 // Keep the first cleanup error encountered.
 cleanupError ??= err;
 }
 }
 });
 if (cleanupError !== undefined) {
 if (primaryError !== undefined) {
 // Both a primary error and a cleanup error occurred.
 // Wrap in SuppressedError so neither is lost:
 // .error = primaryError, .suppressed = cleanupError.
 // eslint-disable-next-line no-restricted-syntax
 throw new SuppressedError(primaryError, cleanupError);
 }
 // No primary error - the cleanup error is the only error.
 throw cleanupError;
 }
 if (primaryError !== undefined) {
 throw primaryError;
 }
}

module.exports = {
 array,
 arrayBuffer,
Expand Down

56 changes: 5 additions & 51 deletions
lib/internal/streams/iter/pull.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -63,8 +63,6 @@ const {
} = require('internal/streams/iter/utils');

const {
 drainableProtocol,
 kSyncWriteAcceptedOnFalse,
 kValidatedSource,
 kValidatedTransform,
 toAsyncStreamable,
Expand DownExpand Up@@ -863,18 +861,6 @@ async function* createAsyncPipeline(source, transforms, signal) {
 }
}

/**
 * Check if a false sync write result means accepted backpressure.
 * @param {object} writer - The writer whose sync method returned.
 * @param {*} result - The return value from writeSync() or writevSync().
 * @returns {boolean}
 */
function isAcceptedSyncWriteBackpressure(writer, result) {
 return result === false &&
 writer[kSyncWriteAcceptedOnFalse] === true &&
 writer.desiredSize === 0;
}

// =============================================================================
// Public API: pull() and pullSync()
// =============================================================================
Expand DownExpand Up@@ -968,9 +954,7 @@ function pipeToSync(source, ...args) {
 break;
 }
 if (hasWritevSync && batch.length > 1) {
 const result = writer.writevSync(batch);
 if (result === false &&
 !isAcceptedSyncWriteBackpressure(writer, result)) {
 if (writer.writevSync(batch) === false) {
 break;
 }
 for (let i = 0; i < batch.length; i++) {
Expand All@@ -979,9 +963,7 @@ function pipeToSync(source, ...args) {
 } else {
 for (let i = 0; i < batch.length; i++) {
 const chunk = batch[i];
 const result = writer.writeSync(chunk);
 if (result === false &&
 !isAcceptedSyncWriteBackpressure(writer, result)) {
 if (writer.writeSync(chunk) === false) {
 canContinue = false;
 break;
 }
Expand DownExpand Up@@ -1037,28 +1019,13 @@ async function pipeTo(source, ...args) {
 const hasWritevSync = typeof writer.writevSync === 'function';
 const hasEndSync = typeof writer.endSync === 'function';

 function waitForSyncBackpressure() {
 const ondrain = writer[drainableProtocol];
 return ondrain?.call(writer);
 }

 async function writeBatchAfterAcceptedBackpressure(batch, startIndex) {
 await waitForSyncBackpressure();
 await writeBatchAsyncFallback(batch, startIndex);
 }

 // Async fallback for writeBatch when sync write fails partway through.
 // Continues writing from batch[startIndex] using async write().
 async function writeBatchAsyncFallback(batch, startIndex) {
 for (let i = startIndex; i < batch.length; i++) {
 const chunk = batch[i];
 const result = hasWriteSync && writer.writeSync(chunk);
 if (result) {
 if (hasWriteSync && writer.writeSync(chunk)) {
 // Sync retry succeeded
 } else if (isAcceptedSyncWriteBackpressure(writer, result)) {
 totalBytes += TypedArrayPrototypeGetByteLength(chunk);
 await waitForSyncBackpressure();
 continue;
 } else {
 const result = writer.write(
 chunk, signal ? { __proto__: null, signal } : undefined);
Expand All@@ -1075,14 +1042,7 @@ async function pipeTo(source, ...args) {
 // is required. Callers must check: const p = writeBatch(b); if (p) await p;
 function writeBatch(batch) {
 if (hasWritev && batch.length > 1) {
 const result = hasWritevSync && writer.writevSync(batch);
 if (!result) {
 if (isAcceptedSyncWriteBackpressure(writer, result)) {
 for (let i = 0; i < batch.length; i++) {
 totalBytes += TypedArrayPrototypeGetByteLength(batch[i]);
 }
 return waitForSyncBackpressure();
 }
 if (!hasWritevSync || !writer.writevSync(batch)) {
 const opts = signal ? { __proto__: null, signal } : undefined;
 const writevResult = writer.writev(batch, opts);
 if (writevResult === undefined) {
Expand All@@ -1104,14 +1064,8 @@ async function pipeTo(source, ...args) {
 }
 for (let i = 0; i < batch.length; i++) {
 const chunk = batch[i];
 const result = hasWriteSync && writer.writeSync(chunk);
 if (!result) {
 if (isAcceptedSyncWriteBackpressure(writer, result)) {
 totalBytes += TypedArrayPrototypeGetByteLength(chunk);
 return writeBatchAfterAcceptedBackpressure(batch, i + 1);
 }
 if (!hasWriteSync || !writer.writeSync(chunk)) {
 // Sync path failed at index i - fall back to async for the rest.
 // Count bytes for chunks already written synchronously (0..i-1).
 return writeBatchAsyncFallback(batch, i);
 }
 totalBytes += TypedArrayPrototypeGetByteLength(chunk);
Expand Down

48 changes: 2 additions & 46 deletions
lib/internal/streams/iter/push.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -33,8 +33,6 @@ const {

const {
 drainableProtocol,
 kSyncWriteAccepted,
 kSyncWriteAcceptedOnFalse,
} = require('internal/streams/iter/types');

const {
Expand DownExpand Up@@ -369,19 +367,6 @@ class PushQueue {
 this.#pendingEnd = pending;
 }

 /**
 * Force-enqueue chunks into the slots buffer, bypassing capacity checks.
 * Used by PushWriter.writeSync() for 'block' policy where the data is
 * accepted but false is returned as a backpressure signal.
 */
 forceEnqueue(chunks) {
 this.#slots.push(chunks);
 for (let i = 0; i < chunks.length; i++) {
 this.#bytesWritten += TypedArrayPrototypeGetByteLength(chunks[i]);
 }
 this.#resolvePendingReads();
 }

 /**
 * Wait for backpressure to clear (desiredSize > 0).
 * @returns {Promise<void>}
Expand DownExpand Up@@ -563,16 +548,11 @@ class PushQueue {

class PushWriter {
 #queue;
 #syncWriteAccepted = false;

 constructor(queue) {
 this.#queue = queue;
 }

 [kSyncWriteAccepted]() {
 return this.#syncWriteAccepted;
 }

 [drainableProtocol]() {
 const desired = this.desiredSize;
 if (desired === null) return null;
Expand All@@ -584,10 +564,6 @@ class PushWriter {
 return this.#queue.desiredSize;
 }

 get [kSyncWriteAcceptedOnFalse]() {
 return this.#queue.backpressurePolicy === 'block';
 }

 write(chunk, options) {
 if (!options?.signal && this.#queue.canWriteSync()) {
 const bytes = toUint8Array(chunk);
Expand All@@ -612,36 +588,16 @@ class PushWriter {
 }

 writeSync(chunk) {
 this.#syncWriteAccepted = false;
 const bytes = toUint8Array(chunk);
 const result = this.#queue.writeSync([bytes]);
 if (!result && this.#queue.backpressurePolicy === 'block' &&
 this.#queue.desiredSize === 0) {
 // Block policy: force-enqueue and return false as backpressure signal.
 // Data IS accepted; false tells caller to slow down.
 this.#queue.forceEnqueue([bytes]);
 this.#syncWriteAccepted = true;
 return false;
 }
 this.#syncWriteAccepted = result;
 return result;
 return this.#queue.writeSync([bytes]);
Comment thread
jasnell marked this conversation as resolved.

 }

 writevSync(chunks) {
 this.#syncWriteAccepted = false;
 if (!ArrayIsArray(chunks)) {
 throw new ERR_INVALID_ARG_TYPE('chunks', 'Array', chunks);
 }
 const bytes = convertChunks(chunks);
 const result = this.#queue.writeSync(bytes);
 if (!result && this.#queue.backpressurePolicy === 'block' &&
 this.#queue.desiredSize === 0) {
 this.#queue.forceEnqueue(bytes);
 this.#syncWriteAccepted = true;
 return false;
 }
 this.#syncWriteAccepted = result;
 return result;
 return this.#queue.writeSync(bytes);
 }

 end(options) {
Expand Down
Loading
Loading

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Auto-enable theater mode on YouTube\n(function() {\n function tryTheater() {\n var btn = document.querySelector('button[aria-label=\"Theater mode\"], ytd-player #player button[title=\"Theater mode\"]');\n if (btn && !btn.classList.contains('activated')) {\n btn.click();\n }\n }\n \n // Try immediately\n tryTheater();\n \n // Try after navigation (SPA)\n var lastUrl = location.href;\n setInterval(function() {\n if (location.href !== lastUrl) {\n lastUrl = location.href;\n setTimeout(tryTheater, 500);\n }\n }, 1000);\n \n // Also try on player load\n var observer = new MutationObserver(tryTheater);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "YouTube Theater Mode Default");
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
stream: refine stream/iter backpressure and error handling#63697

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Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

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privacy statement. We’ll occasionally send you account related emails.

Already on GitHub?
Sign in
to your account

 Merged

nodejs-github-bot
merged 2 commits into

from

Jun 17, 2026
 Merged


stream: refine stream/iter backpressure and error handling
#63697
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ff1188a

stream: refine the stream/iter backpressure


jasnell Jun 1, 2026
c29567e

stream: fixup error handling in stream/iter adapters


jasnell Jun 1, 2026

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2 changes: 1 addition & 1 deletion
doc/api/stream_iter.md

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -1675,7 +1675,7 @@ Creates a classic [`stream.Writable`][] backed by a stream/iter Writer.

Each `_write()` / `_writev()` call attempts the Writer's synchronous method
first (`writeSync` / `writevSync`), falling back to the async method if the
sync path returns `false` or throws. Similarly, `_final()` tries `endSync()`
sync path returns `false`. Similarly, `_final()` tries `endSync()`
before `end()`. When the sync path succeeds, the callback is deferred via
`queueMicrotask` to preserve the async resolution contract.

Expand Down

67 changes: 16 additions & 51 deletions
lib/internal/streams/iter/classic.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -57,7 +57,6 @@ const {
const {
 toAsyncStreamable: kToAsyncStreamable,
 kValidatedSource,
 kSyncWriteAccepted,
 drainableProtocol,
} = require('internal/streams/iter/types');

Expand DownExpand Up@@ -765,41 +764,11 @@ function toWritable(writer) {
 const hasEndSync = hasEnd &&
 typeof writer.endSync === 'function';
 const hasFail = typeof writer.fail === 'function';
 const hasSyncWriteAccepted =
 typeof writer[kSyncWriteAccepted] === 'function';

 function syncWriteAccepted() {
 return hasSyncWriteAccepted && writer[kSyncWriteAccepted]();
 }

 function finishAfterSyncBackpressure(cb) {
 let ondrain;
 try {
 if (typeof writer[drainableProtocol] === 'function') {
 ondrain = writer[drainableProtocol]();
 }
 } catch (err) {
 cb(err);
 return;
 }
 if (ondrain !== null && ondrain !== undefined) {
 PromisePrototypeThen(ondrain, (drained) => {
 if (drained === false) {
 cb(new ERR_INVALID_STATE.TypeError('Stream closed by consumer'));
 return;
 }
 cb();
 }, cb);
 return;
 }
 queueMicrotask(cb);
 }

 // Try-sync-first pattern: attempt the synchronous method and fall back to the
 // async method if it returns false without accepting the data, or if it
 // throws. When the sync path succeeds, the callback is deferred via
 // queueMicrotask to preserve the async resolution contract that Writable
 // internals expect from _write/_writev/_final callbacks.
 // async method if it returns false (data not accepted synchronously).
 // When the sync path succeeds, the callback is deferred via queueMicrotask
 // to preserve the async resolution contract that Writable internals expect
 // from _write/_writev/_final callbacks.

 function _write(chunk, encoding, cb) {
 const bytes = typeof chunk === 'string' ?
Expand All@@ -810,13 +779,10 @@ function toWritable(writer) {
 queueMicrotask(cb);
 return;
 }
 if (syncWriteAccepted()) {
 // The chunk was accepted; false only signaled backpressure.
 finishAfterSyncBackpressure(cb);
 return;
 }
 } catch {
 // Sync path threw -- fall through to async.
 // WriteSync returned false: not accepted, fall through to async.
 } catch (err) {
Comment thread
jasnell marked this conversation as resolved.

 cb(err);
 return;
 }
 }
 try {
Expand All@@ -839,13 +805,10 @@ function toWritable(writer) {
 queueMicrotask(cb);
 return;
 }
 if (syncWriteAccepted()) {
 // The chunks were accepted; false only signaled backpressure.
 finishAfterSyncBackpressure(cb);
 return;
 }
 } catch {
 // Sync path threw -- fall through to async.
 // WritevSync returned false: not accepted, fall through to async.
 } catch (err) {
 cb(err);
 return;
 }
 }
 try {
Expand All@@ -867,8 +830,10 @@ function toWritable(writer) {
 queueMicrotask(cb);
 return;
 }
 } catch {
 // Sync path threw -- fall through to async.
 // Result < 0: can't end synchronously, fall through to async.
 } catch (err) {
 cb(err);
 return;
 }
 }
 try {
Expand Down

45 changes: 35 additions & 10 deletions
lib/internal/streams/iter/consumers.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -480,6 +480,7 @@ function merge(...args) {
 );
 }

 let primaryError;
 try {
 while (activeCount > 0 || ready.length > 0) {
 signal?.throwIfAborted();
Expand All@@ -500,22 +501,46 @@ function merge(...args) {
 });
 }
 }
 } catch (err) {
 primaryError = err;
 } finally {
 // Clean up: return all iterators
 await SafePromiseAllReturnVoid(iterators, async (iterator) => {
 if (iterator.return) {
 try {
 await iterator.return();
 } catch {
 // Ignore return errors
 }
 }
 });
 // Clean up: return all iterators. Cleanup errors are not
 // swallowed - a broken iterator.return() (e.g., failing to
 // release a resource) should be visible to the caller.
 await cleanupIterators(iterators, primaryError);
 }
 },
 };
}

async function cleanupIterators(iterators, primaryError) {
 let cleanupError;
 await SafePromiseAllReturnVoid(iterators, async (iterator) => {
 if (iterator.return) {
 try {
 await iterator.return();
 } catch (err) {
 // Keep the first cleanup error encountered.
 cleanupError ??= err;
 }
 }
 });
 if (cleanupError !== undefined) {
 if (primaryError !== undefined) {
 // Both a primary error and a cleanup error occurred.
 // Wrap in SuppressedError so neither is lost:
 // .error = primaryError, .suppressed = cleanupError.
 // eslint-disable-next-line no-restricted-syntax
 throw new SuppressedError(primaryError, cleanupError);
 }
 // No primary error - the cleanup error is the only error.
 throw cleanupError;
 }
 if (primaryError !== undefined) {
 throw primaryError;
 }
}

module.exports = {
 array,
 arrayBuffer,
Expand Down

56 changes: 5 additions & 51 deletions
lib/internal/streams/iter/pull.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -63,8 +63,6 @@ const {
} = require('internal/streams/iter/utils');

const {
 drainableProtocol,
 kSyncWriteAcceptedOnFalse,
 kValidatedSource,
 kValidatedTransform,
 toAsyncStreamable,
Expand DownExpand Up@@ -863,18 +861,6 @@ async function* createAsyncPipeline(source, transforms, signal) {
 }
}

/**
 * Check if a false sync write result means accepted backpressure.
 * @param {object} writer - The writer whose sync method returned.
 * @param {*} result - The return value from writeSync() or writevSync().
 * @returns {boolean}
 */
function isAcceptedSyncWriteBackpressure(writer, result) {
 return result === false &&
 writer[kSyncWriteAcceptedOnFalse] === true &&
 writer.desiredSize === 0;
}

// =============================================================================
// Public API: pull() and pullSync()
// =============================================================================
Expand DownExpand Up@@ -968,9 +954,7 @@ function pipeToSync(source, ...args) {
 break;
 }
 if (hasWritevSync && batch.length > 1) {
 const result = writer.writevSync(batch);
 if (result === false &&
 !isAcceptedSyncWriteBackpressure(writer, result)) {
 if (writer.writevSync(batch) === false) {
 break;
 }
 for (let i = 0; i < batch.length; i++) {
Expand All@@ -979,9 +963,7 @@ function pipeToSync(source, ...args) {
 } else {
 for (let i = 0; i < batch.length; i++) {
 const chunk = batch[i];
 const result = writer.writeSync(chunk);
 if (result === false &&
 !isAcceptedSyncWriteBackpressure(writer, result)) {
 if (writer.writeSync(chunk) === false) {
 canContinue = false;
 break;
 }
Expand DownExpand Up@@ -1037,28 +1019,13 @@ async function pipeTo(source, ...args) {
 const hasWritevSync = typeof writer.writevSync === 'function';
 const hasEndSync = typeof writer.endSync === 'function';

 function waitForSyncBackpressure() {
 const ondrain = writer[drainableProtocol];
 return ondrain?.call(writer);
 }

 async function writeBatchAfterAcceptedBackpressure(batch, startIndex) {
 await waitForSyncBackpressure();
 await writeBatchAsyncFallback(batch, startIndex);
 }

 // Async fallback for writeBatch when sync write fails partway through.
 // Continues writing from batch[startIndex] using async write().
 async function writeBatchAsyncFallback(batch, startIndex) {
 for (let i = startIndex; i < batch.length; i++) {
 const chunk = batch[i];
 const result = hasWriteSync && writer.writeSync(chunk);
 if (result) {
 if (hasWriteSync && writer.writeSync(chunk)) {
 // Sync retry succeeded
 } else if (isAcceptedSyncWriteBackpressure(writer, result)) {
 totalBytes += TypedArrayPrototypeGetByteLength(chunk);
 await waitForSyncBackpressure();
 continue;
 } else {
 const result = writer.write(
 chunk, signal ? { __proto__: null, signal } : undefined);
Expand All@@ -1075,14 +1042,7 @@ async function pipeTo(source, ...args) {
 // is required. Callers must check: const p = writeBatch(b); if (p) await p;
 function writeBatch(batch) {
 if (hasWritev && batch.length > 1) {
 const result = hasWritevSync && writer.writevSync(batch);
 if (!result) {
 if (isAcceptedSyncWriteBackpressure(writer, result)) {
 for (let i = 0; i < batch.length; i++) {
 totalBytes += TypedArrayPrototypeGetByteLength(batch[i]);
 }
 return waitForSyncBackpressure();
 }
 if (!hasWritevSync || !writer.writevSync(batch)) {
 const opts = signal ? { __proto__: null, signal } : undefined;
 const writevResult = writer.writev(batch, opts);
 if (writevResult === undefined) {
Expand All@@ -1104,14 +1064,8 @@ async function pipeTo(source, ...args) {
 }
 for (let i = 0; i < batch.length; i++) {
 const chunk = batch[i];
 const result = hasWriteSync && writer.writeSync(chunk);
 if (!result) {
 if (isAcceptedSyncWriteBackpressure(writer, result)) {
 totalBytes += TypedArrayPrototypeGetByteLength(chunk);
 return writeBatchAfterAcceptedBackpressure(batch, i + 1);
 }
 if (!hasWriteSync || !writer.writeSync(chunk)) {
 // Sync path failed at index i - fall back to async for the rest.
 // Count bytes for chunks already written synchronously (0..i-1).
 return writeBatchAsyncFallback(batch, i);
 }
 totalBytes += TypedArrayPrototypeGetByteLength(chunk);
Expand Down

48 changes: 2 additions & 46 deletions
lib/internal/streams/iter/push.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -33,8 +33,6 @@ const {

const {
 drainableProtocol,
 kSyncWriteAccepted,
 kSyncWriteAcceptedOnFalse,
} = require('internal/streams/iter/types');

const {
Expand DownExpand Up@@ -369,19 +367,6 @@ class PushQueue {
 this.#pendingEnd = pending;
 }

 /**
 * Force-enqueue chunks into the slots buffer, bypassing capacity checks.
 * Used by PushWriter.writeSync() for 'block' policy where the data is
 * accepted but false is returned as a backpressure signal.
 */
 forceEnqueue(chunks) {
 this.#slots.push(chunks);
 for (let i = 0; i < chunks.length; i++) {
 this.#bytesWritten += TypedArrayPrototypeGetByteLength(chunks[i]);
 }
 this.#resolvePendingReads();
 }

 /**
 * Wait for backpressure to clear (desiredSize > 0).
 * @returns {Promise<void>}
Expand DownExpand Up@@ -563,16 +548,11 @@ class PushQueue {

class PushWriter {
 #queue;
 #syncWriteAccepted = false;

 constructor(queue) {
 this.#queue = queue;
 }

 [kSyncWriteAccepted]() {
 return this.#syncWriteAccepted;
 }

 [drainableProtocol]() {
 const desired = this.desiredSize;
 if (desired === null) return null;
Expand All@@ -584,10 +564,6 @@ class PushWriter {
 return this.#queue.desiredSize;
 }

 get [kSyncWriteAcceptedOnFalse]() {
 return this.#queue.backpressurePolicy === 'block';
 }

 write(chunk, options) {
 if (!options?.signal && this.#queue.canWriteSync()) {
 const bytes = toUint8Array(chunk);
Expand All@@ -612,36 +588,16 @@ class PushWriter {
 }

 writeSync(chunk) {
 this.#syncWriteAccepted = false;
 const bytes = toUint8Array(chunk);
 const result = this.#queue.writeSync([bytes]);
 if (!result && this.#queue.backpressurePolicy === 'block' &&
 this.#queue.desiredSize === 0) {
 // Block policy: force-enqueue and return false as backpressure signal.
 // Data IS accepted; false tells caller to slow down.
 this.#queue.forceEnqueue([bytes]);
 this.#syncWriteAccepted = true;
 return false;
 }
 this.#syncWriteAccepted = result;
 return result;
 return this.#queue.writeSync([bytes]);
Comment thread
jasnell marked this conversation as resolved.

 }

 writevSync(chunks) {
 this.#syncWriteAccepted = false;
 if (!ArrayIsArray(chunks)) {
 throw new ERR_INVALID_ARG_TYPE('chunks', 'Array', chunks);
 }
 const bytes = convertChunks(chunks);
 const result = this.#queue.writeSync(bytes);
 if (!result && this.#queue.backpressurePolicy === 'block' &&
 this.#queue.desiredSize === 0) {
 this.#queue.forceEnqueue(bytes);
 this.#syncWriteAccepted = true;
 return false;
 }
 this.#syncWriteAccepted = result;
 return result;
 return this.#queue.writeSync(bytes);
 }

 end(options) {
Expand Down
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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Remove or un-stick sticky/fixed headers that block content\n(function() {\n function unstick() {\n document.querySelectorAll('header, nav, [role=\"banner\"], .header, .navbar, .sticky, .fixed-top, [style*=\"position: fixed\"], [style*=\"position:sticky\"]').forEach(function(el) {\n if (el.style.position === 'fixed' || el.style.position === 'sticky' || \n getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {\n el.style.position = 'static';\n el.style.top = 'auto';\n el.style.zIndex = 'auto';\n }\n });\n }\n \n unstick();\n \n var observer = new MutationObserver(unstick);\n observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });\n})();", "Kill Sticky Headers");
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

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Jun 17, 2026
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stream: refine stream/iter backpressure and error handling
#63697
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ff1188a

stream: refine the stream/iter backpressure


jasnell Jun 1, 2026
c29567e

stream: fixup error handling in stream/iter adapters


jasnell Jun 1, 2026

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2 changes: 1 addition & 1 deletion
doc/api/stream_iter.md

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -1675,7 +1675,7 @@ Creates a classic [`stream.Writable`][] backed by a stream/iter Writer.

Each `_write()` / `_writev()` call attempts the Writer's synchronous method
first (`writeSync` / `writevSync`), falling back to the async method if the
sync path returns `false` or throws. Similarly, `_final()` tries `endSync()`
sync path returns `false`. Similarly, `_final()` tries `endSync()`
before `end()`. When the sync path succeeds, the callback is deferred via
`queueMicrotask` to preserve the async resolution contract.

Expand Down

67 changes: 16 additions & 51 deletions
lib/internal/streams/iter/classic.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -57,7 +57,6 @@ const {
const {
 toAsyncStreamable: kToAsyncStreamable,
 kValidatedSource,
 kSyncWriteAccepted,
 drainableProtocol,
} = require('internal/streams/iter/types');

Expand DownExpand Up@@ -765,41 +764,11 @@ function toWritable(writer) {
 const hasEndSync = hasEnd &&
 typeof writer.endSync === 'function';
 const hasFail = typeof writer.fail === 'function';
 const hasSyncWriteAccepted =
 typeof writer[kSyncWriteAccepted] === 'function';

 function syncWriteAccepted() {
 return hasSyncWriteAccepted && writer[kSyncWriteAccepted]();
 }

 function finishAfterSyncBackpressure(cb) {
 let ondrain;
 try {
 if (typeof writer[drainableProtocol] === 'function') {
 ondrain = writer[drainableProtocol]();
 }
 } catch (err) {
 cb(err);
 return;
 }
 if (ondrain !== null && ondrain !== undefined) {
 PromisePrototypeThen(ondrain, (drained) => {
 if (drained === false) {
 cb(new ERR_INVALID_STATE.TypeError('Stream closed by consumer'));
 return;
 }
 cb();
 }, cb);
 return;
 }
 queueMicrotask(cb);
 }

 // Try-sync-first pattern: attempt the synchronous method and fall back to the
 // async method if it returns false without accepting the data, or if it
 // throws. When the sync path succeeds, the callback is deferred via
 // queueMicrotask to preserve the async resolution contract that Writable
 // internals expect from _write/_writev/_final callbacks.
 // async method if it returns false (data not accepted synchronously).
 // When the sync path succeeds, the callback is deferred via queueMicrotask
 // to preserve the async resolution contract that Writable internals expect
 // from _write/_writev/_final callbacks.

 function _write(chunk, encoding, cb) {
 const bytes = typeof chunk === 'string' ?
Expand All@@ -810,13 +779,10 @@ function toWritable(writer) {
 queueMicrotask(cb);
 return;
 }
 if (syncWriteAccepted()) {
 // The chunk was accepted; false only signaled backpressure.
 finishAfterSyncBackpressure(cb);
 return;
 }
 } catch {
 // Sync path threw -- fall through to async.
 // WriteSync returned false: not accepted, fall through to async.
 } catch (err) {
Comment thread
jasnell marked this conversation as resolved.

 cb(err);
 return;
 }
 }
 try {
Expand All@@ -839,13 +805,10 @@ function toWritable(writer) {
 queueMicrotask(cb);
 return;
 }
 if (syncWriteAccepted()) {
 // The chunks were accepted; false only signaled backpressure.
 finishAfterSyncBackpressure(cb);
 return;
 }
 } catch {
 // Sync path threw -- fall through to async.
 // WritevSync returned false: not accepted, fall through to async.
 } catch (err) {
 cb(err);
 return;
 }
 }
 try {
Expand All@@ -867,8 +830,10 @@ function toWritable(writer) {
 queueMicrotask(cb);
 return;
 }
 } catch {
 // Sync path threw -- fall through to async.
 // Result < 0: can't end synchronously, fall through to async.
 } catch (err) {
 cb(err);
 return;
 }
 }
 try {
Expand Down

45 changes: 35 additions & 10 deletions
lib/internal/streams/iter/consumers.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -480,6 +480,7 @@ function merge(...args) {
 );
 }

 let primaryError;
 try {
 while (activeCount > 0 || ready.length > 0) {
 signal?.throwIfAborted();
Expand All@@ -500,22 +501,46 @@ function merge(...args) {
 });
 }
 }
 } catch (err) {
 primaryError = err;
 } finally {
 // Clean up: return all iterators
 await SafePromiseAllReturnVoid(iterators, async (iterator) => {
 if (iterator.return) {
 try {
 await iterator.return();
 } catch {
 // Ignore return errors
 }
 }
 });
 // Clean up: return all iterators. Cleanup errors are not
 // swallowed - a broken iterator.return() (e.g., failing to
 // release a resource) should be visible to the caller.
 await cleanupIterators(iterators, primaryError);
 }
 },
 };
}

async function cleanupIterators(iterators, primaryError) {
 let cleanupError;
 await SafePromiseAllReturnVoid(iterators, async (iterator) => {
 if (iterator.return) {
 try {
 await iterator.return();
 } catch (err) {
 // Keep the first cleanup error encountered.
 cleanupError ??= err;
 }
 }
 });
 if (cleanupError !== undefined) {
 if (primaryError !== undefined) {
 // Both a primary error and a cleanup error occurred.
 // Wrap in SuppressedError so neither is lost:
 // .error = primaryError, .suppressed = cleanupError.
 // eslint-disable-next-line no-restricted-syntax
 throw new SuppressedError(primaryError, cleanupError);
 }
 // No primary error - the cleanup error is the only error.
 throw cleanupError;
 }
 if (primaryError !== undefined) {
 throw primaryError;
 }
}

module.exports = {
 array,
 arrayBuffer,
Expand Down

56 changes: 5 additions & 51 deletions
lib/internal/streams/iter/pull.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -63,8 +63,6 @@ const {
} = require('internal/streams/iter/utils');

const {
 drainableProtocol,
 kSyncWriteAcceptedOnFalse,
 kValidatedSource,
 kValidatedTransform,
 toAsyncStreamable,
Expand DownExpand Up@@ -863,18 +861,6 @@ async function* createAsyncPipeline(source, transforms, signal) {
 }
}

/**
 * Check if a false sync write result means accepted backpressure.
 * @param {object} writer - The writer whose sync method returned.
 * @param {*} result - The return value from writeSync() or writevSync().
 * @returns {boolean}
 */
function isAcceptedSyncWriteBackpressure(writer, result) {
 return result === false &&
 writer[kSyncWriteAcceptedOnFalse] === true &&
 writer.desiredSize === 0;
}

// =============================================================================
// Public API: pull() and pullSync()
// =============================================================================
Expand DownExpand Up@@ -968,9 +954,7 @@ function pipeToSync(source, ...args) {
 break;
 }
 if (hasWritevSync && batch.length > 1) {
 const result = writer.writevSync(batch);
 if (result === false &&
 !isAcceptedSyncWriteBackpressure(writer, result)) {
 if (writer.writevSync(batch) === false) {
 break;
 }
 for (let i = 0; i < batch.length; i++) {
Expand All@@ -979,9 +963,7 @@ function pipeToSync(source, ...args) {
 } else {
 for (let i = 0; i < batch.length; i++) {
 const chunk = batch[i];
 const result = writer.writeSync(chunk);
 if (result === false &&
 !isAcceptedSyncWriteBackpressure(writer, result)) {
 if (writer.writeSync(chunk) === false) {
 canContinue = false;
 break;
 }
Expand DownExpand Up@@ -1037,28 +1019,13 @@ async function pipeTo(source, ...args) {
 const hasWritevSync = typeof writer.writevSync === 'function';
 const hasEndSync = typeof writer.endSync === 'function';

 function waitForSyncBackpressure() {
 const ondrain = writer[drainableProtocol];
 return ondrain?.call(writer);
 }

 async function writeBatchAfterAcceptedBackpressure(batch, startIndex) {
 await waitForSyncBackpressure();
 await writeBatchAsyncFallback(batch, startIndex);
 }

 // Async fallback for writeBatch when sync write fails partway through.
 // Continues writing from batch[startIndex] using async write().
 async function writeBatchAsyncFallback(batch, startIndex) {
 for (let i = startIndex; i < batch.length; i++) {
 const chunk = batch[i];
 const result = hasWriteSync && writer.writeSync(chunk);
 if (result) {
 if (hasWriteSync && writer.writeSync(chunk)) {
 // Sync retry succeeded
 } else if (isAcceptedSyncWriteBackpressure(writer, result)) {
 totalBytes += TypedArrayPrototypeGetByteLength(chunk);
 await waitForSyncBackpressure();
 continue;
 } else {
 const result = writer.write(
 chunk, signal ? { __proto__: null, signal } : undefined);
Expand All@@ -1075,14 +1042,7 @@ async function pipeTo(source, ...args) {
 // is required. Callers must check: const p = writeBatch(b); if (p) await p;
 function writeBatch(batch) {
 if (hasWritev && batch.length > 1) {
 const result = hasWritevSync && writer.writevSync(batch);
 if (!result) {
 if (isAcceptedSyncWriteBackpressure(writer, result)) {
 for (let i = 0; i < batch.length; i++) {
 totalBytes += TypedArrayPrototypeGetByteLength(batch[i]);
 }
 return waitForSyncBackpressure();
 }
 if (!hasWritevSync || !writer.writevSync(batch)) {
 const opts = signal ? { __proto__: null, signal } : undefined;
 const writevResult = writer.writev(batch, opts);
 if (writevResult === undefined) {
Expand All@@ -1104,14 +1064,8 @@ async function pipeTo(source, ...args) {
 }
 for (let i = 0; i < batch.length; i++) {
 const chunk = batch[i];
 const result = hasWriteSync && writer.writeSync(chunk);
 if (!result) {
 if (isAcceptedSyncWriteBackpressure(writer, result)) {
 totalBytes += TypedArrayPrototypeGetByteLength(chunk);
 return writeBatchAfterAcceptedBackpressure(batch, i + 1);
 }
 if (!hasWriteSync || !writer.writeSync(chunk)) {
 // Sync path failed at index i - fall back to async for the rest.
 // Count bytes for chunks already written synchronously (0..i-1).
 return writeBatchAsyncFallback(batch, i);
 }
 totalBytes += TypedArrayPrototypeGetByteLength(chunk);
Expand Down

48 changes: 2 additions & 46 deletions
lib/internal/streams/iter/push.js

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -33,8 +33,6 @@ const {

const {
 drainableProtocol,
 kSyncWriteAccepted,
 kSyncWriteAcceptedOnFalse,
} = require('internal/streams/iter/types');

const {
Expand DownExpand Up@@ -369,19 +367,6 @@ class PushQueue {
 this.#pendingEnd = pending;
 }

 /**
 * Force-enqueue chunks into the slots buffer, bypassing capacity checks.
 * Used by PushWriter.writeSync() for 'block' policy where the data is
 * accepted but false is returned as a backpressure signal.
 */
 forceEnqueue(chunks) {
 this.#slots.push(chunks);
 for (let i = 0; i < chunks.length; i++) {
 this.#bytesWritten += TypedArrayPrototypeGetByteLength(chunks[i]);
 }
 this.#resolvePendingReads();
 }

 /**
 * Wait for backpressure to clear (desiredSize > 0).
 * @returns {Promise<void>}
Expand DownExpand Up@@ -563,16 +548,11 @@ class PushQueue {

class PushWriter {
 #queue;
 #syncWriteAccepted = false;

 constructor(queue) {
 this.#queue = queue;
 }

 [kSyncWriteAccepted]() {
 return this.#syncWriteAccepted;
 }

 [drainableProtocol]() {
 const desired = this.desiredSize;
 if (desired === null) return null;
Expand All@@ -584,10 +564,6 @@ class PushWriter {
 return this.#queue.desiredSize;
 }

 get [kSyncWriteAcceptedOnFalse]() {
 return this.#queue.backpressurePolicy === 'block';
 }

 write(chunk, options) {
 if (!options?.signal && this.#queue.canWriteSync()) {
 const bytes = toUint8Array(chunk);
Expand All@@ -612,36 +588,16 @@ class PushWriter {
 }

 writeSync(chunk) {
 this.#syncWriteAccepted = false;
 const bytes = toUint8Array(chunk);
 const result = this.#queue.writeSync([bytes]);
 if (!result && this.#queue.backpressurePolicy === 'block' &&
 this.#queue.desiredSize === 0) {
 // Block policy: force-enqueue and return false as backpressure signal.
 // Data IS accepted; false tells caller to slow down.
 this.#queue.forceEnqueue([bytes]);
 this.#syncWriteAccepted = true;
 return false;
 }
 this.#syncWriteAccepted = result;
 return result;
 return this.#queue.writeSync([bytes]);
Comment thread
jasnell marked this conversation as resolved.

 }

 writevSync(chunks) {
 this.#syncWriteAccepted = false;
 if (!ArrayIsArray(chunks)) {
 throw new ERR_INVALID_ARG_TYPE('chunks', 'Array', chunks);
 }
 const bytes = convertChunks(chunks);
 const result = this.#queue.writeSync(bytes);
 if (!result && this.#queue.backpressurePolicy === 'block' &&
 this.#queue.desiredSize === 0) {
 this.#queue.forceEnqueue(bytes);
 this.#syncWriteAccepted = true;
 return false;
 }
 this.#syncWriteAccepted = result;
 return result;
 return this.#queue.writeSync(bytes);
 }

 end(options) {
Expand Down
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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Universal Dark Mode - works on any site\n(function() {\n var enabled = true;\n \n function applyDarkMode() {\n if (!enabled) return;\n \n // Create style element if it doesn't exist\n var style = document.getElementById('universal-dark-mode-style');\n if (!style) {\n style = document.createElement('style');\n style.id = 'universal-dark-mode-style';\n document.head.appendChild(style);\n }\n \n // Dark mode CSS - inverts colors but preserves images/video\n style.textContent = '\n /* Invert everything except media */\n html {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #1a1a2e !important;\n }\n \n /* Restore images, videos, iframes, canvas */\n img, video, iframe, canvas, svg, picture, [style*=\"background-image\"] {\n filter: invert(1) hue-rotate(180deg) !important;\n }\n \n /* Preserve specific elements that should not be inverted */\n .no-dark-mode, .no-dark-mode *,\n [data-theme=\"light\"], [data-theme=\"light\"],\n .ace_editor, .ace_editor *,\n .CodeMirror, .CodeMirror *,\n .monaco-editor, .monaco-editor *,\n .markdown-body pre, .markdown-body pre *,\n .highlight, .highlight *,\n pre code, pre code * {\n filter: none !important;\n }\n \n /* Fix common UI elements */\n .modal, .popup, .dropdown-menu, .tooltip, .popover {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #2d2d44 !important;\n border-color: #444 !important;\n }\n \n /* Scrollbars */\n ::-webkit-scrollbar { background: #1a1a2e !important; }\n ::-webkit-scrollbar-thumb { background: #444 !important; }\n ::-webkit-scrollbar-thumb:hover { background: #555 !important; }\n \n /* Selection */\n ::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ';\n }\n \n function removeDarkMode() {\n var style = document.getElementById('universal-dark-mode-style');\n if (style) style.remove();\n }\n \n // Toggle with Alt+Shift+D\n document.addEventListener('keydown', function(e) {\n if (e.altKey && e.shiftKey && e.key === 'D') {\n e.preventDefault();\n enabled = !enabled;\n if (enabled) {\n applyDarkMode();\n console.log('[Universal Dark Mode] Enabled');\n } else {\n removeDarkMode();\n console.log('[Universal Dark Mode] Disabled');\n }\n }\n });\n \n // Apply on load\n applyDarkMode();\n \n // Re-apply on dynamic content\n var observer = new MutationObserver(function(mutations) {\n if (enabled && !document.getElementById('universal-dark-mode-style')) {\n applyDarkMode();\n }\n });\n observer.observe(document.head, { childList: true });\n \n console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');\n})();", "Universal Dark Mode");
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();

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Jun 17, 2026
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stream: refine stream/iter backpressure and error handling
#63697
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ff1188a

stream: refine the stream/iter backpressure


jasnell Jun 1, 2026
c29567e

stream: fixup error handling in stream/iter adapters


jasnell Jun 1, 2026

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2 changes: 1 addition & 1 deletion
doc/api/stream_iter.md

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Original file line numberDiff line numberDiff line change
Expand Up@@ -1675,7 +1675,7 @@ Creates a classic [`stream.Writable`][] backed by a stream/iter Writer.

Each `_write()` / `_writev()` call attempts the Writer's synchronous method
first (`writeSync` / `writevSync`), falling back to the async method if the
sync path returns `false` or throws. Similarly, `_final()` tries `endSync()`
sync path returns `false`. Similarly, `_final()` tries `endSync()`
before `end()`. When the sync path succeeds, the callback is deferred via
`queueMicrotask` to preserve the async resolution contract.

Expand Down

67 changes: 16 additions & 51 deletions
lib/internal/streams/iter/classic.js

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -57,7 +57,6 @@ const {
const {
 toAsyncStreamable: kToAsyncStreamable,
 kValidatedSource,
 kSyncWriteAccepted,
 drainableProtocol,
} = require('internal/streams/iter/types');

Expand DownExpand Up@@ -765,41 +764,11 @@ function toWritable(writer) {
 const hasEndSync = hasEnd &&
 typeof writer.endSync === 'function';
 const hasFail = typeof writer.fail === 'function';
 const hasSyncWriteAccepted =
 typeof writer[kSyncWriteAccepted] === 'function';

 function syncWriteAccepted() {
 return hasSyncWriteAccepted && writer[kSyncWriteAccepted]();
 }

 function finishAfterSyncBackpressure(cb) {
 let ondrain;
 try {
 if (typeof writer[drainableProtocol] === 'function') {
 ondrain = writer[drainableProtocol]();
 }
 } catch (err) {
 cb(err);
 return;
 }
 if (ondrain !== null && ondrain !== undefined) {
 PromisePrototypeThen(ondrain, (drained) => {
 if (drained === false) {
 cb(new ERR_INVALID_STATE.TypeError('Stream closed by consumer'));
 return;
 }
 cb();
 }, cb);
 return;
 }
 queueMicrotask(cb);
 }

 // Try-sync-first pattern: attempt the synchronous method and fall back to the
 // async method if it returns false without accepting the data, or if it
 // throws. When the sync path succeeds, the callback is deferred via
 // queueMicrotask to preserve the async resolution contract that Writable
 // internals expect from _write/_writev/_final callbacks.
 // async method if it returns false (data not accepted synchronously).
 // When the sync path succeeds, the callback is deferred via queueMicrotask
 // to preserve the async resolution contract that Writable internals expect
 // from _write/_writev/_final callbacks.

 function _write(chunk, encoding, cb) {
 const bytes = typeof chunk === 'string' ?
Expand All@@ -810,13 +779,10 @@ function toWritable(writer) {
 queueMicrotask(cb);
 return;
 }
 if (syncWriteAccepted()) {
 // The chunk was accepted; false only signaled backpressure.
 finishAfterSyncBackpressure(cb);
 return;
 }
 } catch {
 // Sync path threw -- fall through to async.
 // WriteSync returned false: not accepted, fall through to async.
 } catch (err) {
Comment thread
jasnell marked this conversation as resolved.

 cb(err);
 return;
 }
 }
 try {
Expand All@@ -839,13 +805,10 @@ function toWritable(writer) {
 queueMicrotask(cb);
 return;
 }
 if (syncWriteAccepted()) {
 // The chunks were accepted; false only signaled backpressure.
 finishAfterSyncBackpressure(cb);
 return;
 }
 } catch {
 // Sync path threw -- fall through to async.
 // WritevSync returned false: not accepted, fall through to async.
 } catch (err) {
 cb(err);
 return;
 }
 }
 try {
Expand All@@ -867,8 +830,10 @@ function toWritable(writer) {
 queueMicrotask(cb);
 return;
 }
 } catch {
 // Sync path threw -- fall through to async.
 // Result < 0: can't end synchronously, fall through to async.
 } catch (err) {
 cb(err);
 return;
 }
 }
 try {
Expand Down

45 changes: 35 additions & 10 deletions
lib/internal/streams/iter/consumers.js

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Original file line numberDiff line numberDiff line change
Expand Up@@ -480,6 +480,7 @@ function merge(...args) {
 );
 }

 let primaryError;
 try {
 while (activeCount > 0 || ready.length > 0) {
 signal?.throwIfAborted();
Expand All@@ -500,22 +501,46 @@ function merge(...args) {
 });
 }
 }
 } catch (err) {
 primaryError = err;
 } finally {
 // Clean up: return all iterators
 await SafePromiseAllReturnVoid(iterators, async (iterator) => {
 if (iterator.return) {
 try {
 await iterator.return();
 } catch {
 // Ignore return errors
 }
 }
 });
 // Clean up: return all iterators. Cleanup errors are not
 // swallowed - a broken iterator.return() (e.g., failing to
 // release a resource) should be visible to the caller.
 await cleanupIterators(iterators, primaryError);
 }
 },
 };
}

async function cleanupIterators(iterators, primaryError) {
 let cleanupError;
 await SafePromiseAllReturnVoid(iterators, async (iterator) => {
 if (iterator.return) {
 try {
 await iterator.return();
 } catch (err) {
 // Keep the first cleanup error encountered.
 cleanupError ??= err;
 }
 }
 });
 if (cleanupError !== undefined) {
 if (primaryError !== undefined) {
 // Both a primary error and a cleanup error occurred.
 // Wrap in SuppressedError so neither is lost:
 // .error = primaryError, .suppressed = cleanupError.
 // eslint-disable-next-line no-restricted-syntax
 throw new SuppressedError(primaryError, cleanupError);
 }
 // No primary error - the cleanup error is the only error.
 throw cleanupError;
 }
 if (primaryError !== undefined) {
 throw primaryError;
 }
}

module.exports = {
 array,
 arrayBuffer,
Expand Down

56 changes: 5 additions & 51 deletions
lib/internal/streams/iter/pull.js

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Original file line numberDiff line numberDiff line change
Expand Up@@ -63,8 +63,6 @@ const {
} = require('internal/streams/iter/utils');

const {
 drainableProtocol,
 kSyncWriteAcceptedOnFalse,
 kValidatedSource,
 kValidatedTransform,
 toAsyncStreamable,
Expand DownExpand Up@@ -863,18 +861,6 @@ async function* createAsyncPipeline(source, transforms, signal) {
 }
}

/**
 * Check if a false sync write result means accepted backpressure.
 * @param {object} writer - The writer whose sync method returned.
 * @param {*} result - The return value from writeSync() or writevSync().
 * @returns {boolean}
 */
function isAcceptedSyncWriteBackpressure(writer, result) {
 return result === false &&
 writer[kSyncWriteAcceptedOnFalse] === true &&
 writer.desiredSize === 0;
}

// =============================================================================
// Public API: pull() and pullSync()
// =============================================================================
Expand DownExpand Up@@ -968,9 +954,7 @@ function pipeToSync(source, ...args) {
 break;
 }
 if (hasWritevSync && batch.length > 1) {
 const result = writer.writevSync(batch);
 if (result === false &&
 !isAcceptedSyncWriteBackpressure(writer, result)) {
 if (writer.writevSync(batch) === false) {
 break;
 }
 for (let i = 0; i < batch.length; i++) {
Expand All@@ -979,9 +963,7 @@ function pipeToSync(source, ...args) {
 } else {
 for (let i = 0; i < batch.length; i++) {
 const chunk = batch[i];
 const result = writer.writeSync(chunk);
 if (result === false &&
 !isAcceptedSyncWriteBackpressure(writer, result)) {
 if (writer.writeSync(chunk) === false) {
 canContinue = false;
 break;
 }
Expand DownExpand Up@@ -1037,28 +1019,13 @@ async function pipeTo(source, ...args) {
 const hasWritevSync = typeof writer.writevSync === 'function';
 const hasEndSync = typeof writer.endSync === 'function';

 function waitForSyncBackpressure() {
 const ondrain = writer[drainableProtocol];
 return ondrain?.call(writer);
 }

 async function writeBatchAfterAcceptedBackpressure(batch, startIndex) {
 await waitForSyncBackpressure();
 await writeBatchAsyncFallback(batch, startIndex);
 }

 // Async fallback for writeBatch when sync write fails partway through.
 // Continues writing from batch[startIndex] using async write().
 async function writeBatchAsyncFallback(batch, startIndex) {
 for (let i = startIndex; i < batch.length; i++) {
 const chunk = batch[i];
 const result = hasWriteSync && writer.writeSync(chunk);
 if (result) {
 if (hasWriteSync && writer.writeSync(chunk)) {
 // Sync retry succeeded
 } else if (isAcceptedSyncWriteBackpressure(writer, result)) {
 totalBytes += TypedArrayPrototypeGetByteLength(chunk);
 await waitForSyncBackpressure();
 continue;
 } else {
 const result = writer.write(
 chunk, signal ? { __proto__: null, signal } : undefined);
Expand All@@ -1075,14 +1042,7 @@ async function pipeTo(source, ...args) {
 // is required. Callers must check: const p = writeBatch(b); if (p) await p;
 function writeBatch(batch) {
 if (hasWritev && batch.length > 1) {
 const result = hasWritevSync && writer.writevSync(batch);
 if (!result) {
 if (isAcceptedSyncWriteBackpressure(writer, result)) {
 for (let i = 0; i < batch.length; i++) {
 totalBytes += TypedArrayPrototypeGetByteLength(batch[i]);
 }
 return waitForSyncBackpressure();
 }
 if (!hasWritevSync || !writer.writevSync(batch)) {
 const opts = signal ? { __proto__: null, signal } : undefined;
 const writevResult = writer.writev(batch, opts);
 if (writevResult === undefined) {
Expand All@@ -1104,14 +1064,8 @@ async function pipeTo(source, ...args) {
 }
 for (let i = 0; i < batch.length; i++) {
 const chunk = batch[i];
 const result = hasWriteSync && writer.writeSync(chunk);
 if (!result) {
 if (isAcceptedSyncWriteBackpressure(writer, result)) {
 totalBytes += TypedArrayPrototypeGetByteLength(chunk);
 return writeBatchAfterAcceptedBackpressure(batch, i + 1);
 }
 if (!hasWriteSync || !writer.writeSync(chunk)) {
 // Sync path failed at index i - fall back to async for the rest.
 // Count bytes for chunks already written synchronously (0..i-1).
 return writeBatchAsyncFallback(batch, i);
 }
 totalBytes += TypedArrayPrototypeGetByteLength(chunk);
Expand Down

48 changes: 2 additions & 46 deletions
lib/internal/streams/iter/push.js

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Original file line numberDiff line numberDiff line change
Expand Up@@ -33,8 +33,6 @@ const {

const {
 drainableProtocol,
 kSyncWriteAccepted,
 kSyncWriteAcceptedOnFalse,
} = require('internal/streams/iter/types');

const {
Expand DownExpand Up@@ -369,19 +367,6 @@ class PushQueue {
 this.#pendingEnd = pending;
 }

 /**
 * Force-enqueue chunks into the slots buffer, bypassing capacity checks.
 * Used by PushWriter.writeSync() for 'block' policy where the data is
 * accepted but false is returned as a backpressure signal.
 */
 forceEnqueue(chunks) {
 this.#slots.push(chunks);
 for (let i = 0; i < chunks.length; i++) {
 this.#bytesWritten += TypedArrayPrototypeGetByteLength(chunks[i]);
 }
 this.#resolvePendingReads();
 }

 /**
 * Wait for backpressure to clear (desiredSize > 0).
 * @returns {Promise<void>}
Expand DownExpand Up@@ -563,16 +548,11 @@ class PushQueue {

class PushWriter {
 #queue;
 #syncWriteAccepted = false;

 constructor(queue) {
 this.#queue = queue;
 }

 [kSyncWriteAccepted]() {
 return this.#syncWriteAccepted;
 }

 [drainableProtocol]() {
 const desired = this.desiredSize;
 if (desired === null) return null;
Expand All@@ -584,10 +564,6 @@ class PushWriter {
 return this.#queue.desiredSize;
 }

 get [kSyncWriteAcceptedOnFalse]() {
 return this.#queue.backpressurePolicy === 'block';
 }

 write(chunk, options) {
 if (!options?.signal && this.#queue.canWriteSync()) {
 const bytes = toUint8Array(chunk);
Expand All@@ -612,36 +588,16 @@ class PushWriter {
 }

 writeSync(chunk) {
 this.#syncWriteAccepted = false;
 const bytes = toUint8Array(chunk);
 const result = this.#queue.writeSync([bytes]);
 if (!result && this.#queue.backpressurePolicy === 'block' &&
 this.#queue.desiredSize === 0) {
 // Block policy: force-enqueue and return false as backpressure signal.
 // Data IS accepted; false tells caller to slow down.
 this.#queue.forceEnqueue([bytes]);
 this.#syncWriteAccepted = true;
 return false;
 }
 this.#syncWriteAccepted = result;
 return result;
 return this.#queue.writeSync([bytes]);
Comment thread
jasnell marked this conversation as resolved.

 }

 writevSync(chunks) {
 this.#syncWriteAccepted = false;
 if (!ArrayIsArray(chunks)) {
 throw new ERR_INVALID_ARG_TYPE('chunks', 'Array', chunks);
 }
 const bytes = convertChunks(chunks);
 const result = this.#queue.writeSync(bytes);
 if (!result && this.#queue.backpressurePolicy === 'block' &&
 this.#queue.desiredSize === 0) {
 this.#queue.forceEnqueue(bytes);
 this.#syncWriteAccepted = true;
 return false;
 }
 this.#syncWriteAccepted = result;
 return result;
 return this.#queue.writeSync(bytes);
 }

 end(options) {
Expand Down
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