ffi: refresh cached string buffers on every call by trivikr · Pull Request #65051 · nodejs/node

trivikr · 2026-08-05T15:00:52Z

Native code can mutate temporary string storage during an FFI call. Rewrite cached buffers on every conversion so a later call with the same JavaScript string receives a fresh copy of its UTF-8 bytes.

Assisted-by: codex:gpt-5.6-sol

nodejs-github-bot · 2026-08-05T15:01:07Z

Review requested:

@nodejs/ffi

codecov · 2026-08-05T16:45:09Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.31%. Comparing base (a576f1c) to head (8ef6d08).
⚠️ Report is 51 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@## main #65051 +/- ##
=======================================
Coverage 90.30% 90.31% =======================================
Files 760 760 Lines 248526 248521 -5 Branches 46886 46896 +10 =======================================
+ Hits 224439 224445 +6 + Misses 15515 15502 -13 - Partials 8572 8574 +2

Files with missing lines	Coverage Δ
lib/internal/ffi/fast-api.js	`95.54% <ø> (+0.76%)`	⬆️

... and 28 files with indirect coverage changes

🚀 New features to boost your workflow:

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

mcollina

lgtm

trivikr · 2026-08-10T20:51:40Z

Converted to draft as test-ffi-fast-buffer is failing on ci.nodejs.org/job/node-test-commit-aix/64314

---duration_ms: 1355.201exitcode: 1severity: failstack: |- Test failure: 'fast FFI refreshes cached temporary string buffers' Location: test/ffi/test-ffi-fast-buffer.js:99:1 AssertionError [ERR_ASSERTION]: Expected values to be strictly equal: '' !== 'yello' at TestContext.<anonymous> (/home/iojs/build/workspace/node-test-commit-aix/nodes/aix72-power9/test/ffi/test-ffi-fast-buffer.js:108:12) at Test.runInAsyncScope (node:async_hooks:227:14) at Test.run (node:internal/test_runner/test:1397:25) at Test.processPendingSubtests (node:internal/test_runner/test:969:18) at Test.postRun (node:internal/test_runner/test:1537:19) at Test.run (node:internal/test_runner/test:1462:12) at process.processTicksAndRejections (node:internal/process/task_queues:104:5) at async Test.processPendingSubtests (node:internal/test_runner/test:969:7) { generatedMessage: true, code: 'ERR_ASSERTION', actual: '', expected: 'yello', operator: 'strictEqual', diff: 'simple' } (node:38469944) internal/test/binding: These APIs are for internal testing only. Do not use them. (Use `node --trace-warnings ...` to show where the warning was created) (node:38469944) ExperimentalWarning: FFI is an experimental feature and might change at any time...

trivikr · 2026-08-11T01:45:55Z

There was a bug in test.

AIX does not support Node’s PPC64 fast-call trampoline, so it exposes the test’s invalid assumption: the pointer returned by overwrite_string() points into temporary storage owned by Node’s generic FFI invocation. That storage is only valid during the native call. AIX frees/reuses the storage immediately, yielding ''.

Fast-path platforms retain the cached Buffer, so "yello" remains readable.

It was fixed in 89cc17f by observing the mutation during the native call instead of returning a pointer to temporary storage.

I'll re-request review after the CI is successful.

Native code can mutate temporary string storage during an FFI call. Rewrite cached buffers on every conversion so a later call with the same JavaScript string receives a fresh copy of its UTF-8 bytes. Signed-off-by: Kamat, Trivikram <16024985+trivikr@users.noreply.github.com> Assisted-by: codex:gpt-5.6-sol

trivikr · 2026-08-11T02:01:59Z

The ffi contract explicitly says JavaScript strings are copied to temporary NUL-terminated UTF-8 storage “for the duration of the call”

string values are copied to temporary NUL-terminated UTF-8 strings for the duration of the call.

The fast path happens to retain reusable buffers longer, but that is an implementation detail, not a lifetime guarantee.
The test should return the observed byte by value as done in 8ef6d08 and not the pointer.

nodejs-github-bot · 2026-08-11T03:46:48Z

CI: https://ci.nodejs.org/job/node-test-pull-request/75761/

trivikr · 2026-08-11T05:13:52Z

@mcollina @jasnell One of the tests was incorrect, and it surfaced in CI failures in AIX.
It's fixed now in 8ef6d08 and CI is successful.

Can you please provide your approval again?

nodejs-github-bot · 2026-08-14T01:54:43Z

Landed in 54ac460

Native code can mutate temporary string storage during an FFI call. Rewrite cached buffers on every conversion so a later call with the same JavaScript string receives a fresh copy of its UTF-8 bytes. Signed-off-by: Kamat, Trivikram <16024985+trivikr@users.noreply.github.com> Assisted-by: codex:gpt-5.6-sol PR-URL: #65051Fixes: #65050 Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com>

trivikr · 2026-08-05T15:00:52Z

Fixes: #65050

Native code can mutate temporary string storage during an FFI call. Rewrite cached buffers on every conversion so a later call with the same JavaScript string receives a fresh copy of its UTF-8 bytes.

Assisted-by: codex:gpt-5.6-sol

nodejs-github-bot · 2026-08-05T15:01:07Z

Review requested:

@nodejs/ffi

codecov · 2026-08-05T16:45:09Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.31%. Comparing base (a576f1c) to head (8ef6d08).
⚠️ Report is 51 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@## main #65051 +/- ##
=======================================
Coverage 90.30% 90.31% =======================================
Files 760 760 Lines 248526 248521 -5 Branches 46886 46896 +10 =======================================
+ Hits 224439 224445 +6 + Misses 15515 15502 -13 - Partials 8572 8574 +2

Files with missing lines	Coverage Δ
lib/internal/ffi/fast-api.js	`95.54% <ø> (+0.76%)`	⬆️

... and 28 files with indirect coverage changes

🚀 New features to boost your workflow:

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

mcollina

lgtm

trivikr · 2026-08-10T20:51:40Z

Converted to draft as test-ffi-fast-buffer is failing on ci.nodejs.org/job/node-test-commit-aix/64314

---duration_ms: 1355.201exitcode: 1severity: failstack: |- Test failure: 'fast FFI refreshes cached temporary string buffers' Location: test/ffi/test-ffi-fast-buffer.js:99:1 AssertionError [ERR_ASSERTION]: Expected values to be strictly equal: '' !== 'yello' at TestContext.<anonymous> (/home/iojs/build/workspace/node-test-commit-aix/nodes/aix72-power9/test/ffi/test-ffi-fast-buffer.js:108:12) at Test.runInAsyncScope (node:async_hooks:227:14) at Test.run (node:internal/test_runner/test:1397:25) at Test.processPendingSubtests (node:internal/test_runner/test:969:18) at Test.postRun (node:internal/test_runner/test:1537:19) at Test.run (node:internal/test_runner/test:1462:12) at process.processTicksAndRejections (node:internal/process/task_queues:104:5) at async Test.processPendingSubtests (node:internal/test_runner/test:969:7) { generatedMessage: true, code: 'ERR_ASSERTION', actual: '', expected: 'yello', operator: 'strictEqual', diff: 'simple' } (node:38469944) internal/test/binding: These APIs are for internal testing only. Do not use them. (Use `node --trace-warnings ...` to show where the warning was created) (node:38469944) ExperimentalWarning: FFI is an experimental feature and might change at any time...

trivikr · 2026-08-11T01:45:55Z

There was a bug in test.

AIX does not support Node’s PPC64 fast-call trampoline, so it exposes the test’s invalid assumption: the pointer returned by overwrite_string() points into temporary storage owned by Node’s generic FFI invocation. That storage is only valid during the native call. AIX frees/reuses the storage immediately, yielding ''.

Fast-path platforms retain the cached Buffer, so "yello" remains readable.

It was fixed in 89cc17f by observing the mutation during the native call instead of returning a pointer to temporary storage.

I'll re-request review after the CI is successful.

Native code can mutate temporary string storage during an FFI call. Rewrite cached buffers on every conversion so a later call with the same JavaScript string receives a fresh copy of its UTF-8 bytes. Signed-off-by: Kamat, Trivikram <16024985+trivikr@users.noreply.github.com> Assisted-by: codex:gpt-5.6-sol

trivikr · 2026-08-11T02:01:59Z

The ffi contract explicitly says JavaScript strings are copied to temporary NUL-terminated UTF-8 storage “for the duration of the call”

string values are copied to temporary NUL-terminated UTF-8 strings for the duration of the call.

The fast path happens to retain reusable buffers longer, but that is an implementation detail, not a lifetime guarantee.
The test should return the observed byte by value as done in 8ef6d08 and not the pointer.

nodejs-github-bot · 2026-08-11T03:46:48Z

CI: https://ci.nodejs.org/job/node-test-pull-request/75761/

trivikr · 2026-08-11T05:13:52Z

@mcollina @jasnell One of the tests was incorrect, and it surfaced in CI failures in AIX.
It's fixed now in 8ef6d08 and CI is successful.

Can you please provide your approval again?

nodejs-github-bot · 2026-08-14T01:54:43Z

Landed in 54ac460

Native code can mutate temporary string storage during an FFI call. Rewrite cached buffers on every conversion so a later call with the same JavaScript string receives a fresh copy of its UTF-8 bytes. Signed-off-by: Kamat, Trivikram <16024985+trivikr@users.noreply.github.com> Assisted-by: codex:gpt-5.6-sol PR-URL: #65051Fixes: #65050 Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com>

trivikr · 2026-08-05T15:00:52Z

Fixes: #65050

Native code can mutate temporary string storage during an FFI call. Rewrite cached buffers on every conversion so a later call with the same JavaScript string receives a fresh copy of its UTF-8 bytes.

Assisted-by: codex:gpt-5.6-sol

nodejs-github-bot · 2026-08-05T15:01:07Z

Review requested:

@nodejs/ffi

codecov · 2026-08-05T16:45:09Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.31%. Comparing base (a576f1c) to head (8ef6d08).
⚠️ Report is 51 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@## main #65051 +/- ##
=======================================
Coverage 90.30% 90.31% =======================================
Files 760 760 Lines 248526 248521 -5 Branches 46886 46896 +10 =======================================
+ Hits 224439 224445 +6 + Misses 15515 15502 -13 - Partials 8572 8574 +2

Files with missing lines	Coverage Δ
lib/internal/ffi/fast-api.js	`95.54% <ø> (+0.76%)`	⬆️

... and 28 files with indirect coverage changes

🚀 New features to boost your workflow:

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

mcollina

lgtm

trivikr · 2026-08-10T20:51:40Z

Converted to draft as test-ffi-fast-buffer is failing on ci.nodejs.org/job/node-test-commit-aix/64314

---duration_ms: 1355.201exitcode: 1severity: failstack: |- Test failure: 'fast FFI refreshes cached temporary string buffers' Location: test/ffi/test-ffi-fast-buffer.js:99:1 AssertionError [ERR_ASSERTION]: Expected values to be strictly equal: '' !== 'yello' at TestContext.<anonymous> (/home/iojs/build/workspace/node-test-commit-aix/nodes/aix72-power9/test/ffi/test-ffi-fast-buffer.js:108:12) at Test.runInAsyncScope (node:async_hooks:227:14) at Test.run (node:internal/test_runner/test:1397:25) at Test.processPendingSubtests (node:internal/test_runner/test:969:18) at Test.postRun (node:internal/test_runner/test:1537:19) at Test.run (node:internal/test_runner/test:1462:12) at process.processTicksAndRejections (node:internal/process/task_queues:104:5) at async Test.processPendingSubtests (node:internal/test_runner/test:969:7) { generatedMessage: true, code: 'ERR_ASSERTION', actual: '', expected: 'yello', operator: 'strictEqual', diff: 'simple' } (node:38469944) internal/test/binding: These APIs are for internal testing only. Do not use them. (Use `node --trace-warnings ...` to show where the warning was created) (node:38469944) ExperimentalWarning: FFI is an experimental feature and might change at any time...

trivikr · 2026-08-11T01:45:55Z

There was a bug in test.

AIX does not support Node’s PPC64 fast-call trampoline, so it exposes the test’s invalid assumption: the pointer returned by overwrite_string() points into temporary storage owned by Node’s generic FFI invocation. That storage is only valid during the native call. AIX frees/reuses the storage immediately, yielding ''.

Fast-path platforms retain the cached Buffer, so "yello" remains readable.

It was fixed in 89cc17f by observing the mutation during the native call instead of returning a pointer to temporary storage.

I'll re-request review after the CI is successful.

Native code can mutate temporary string storage during an FFI call. Rewrite cached buffers on every conversion so a later call with the same JavaScript string receives a fresh copy of its UTF-8 bytes. Signed-off-by: Kamat, Trivikram <16024985+trivikr@users.noreply.github.com> Assisted-by: codex:gpt-5.6-sol

trivikr · 2026-08-11T02:01:59Z

The ffi contract explicitly says JavaScript strings are copied to temporary NUL-terminated UTF-8 storage “for the duration of the call”

string values are copied to temporary NUL-terminated UTF-8 strings for the duration of the call.

The fast path happens to retain reusable buffers longer, but that is an implementation detail, not a lifetime guarantee.
The test should return the observed byte by value as done in 8ef6d08 and not the pointer.

nodejs-github-bot · 2026-08-11T03:46:48Z

CI: https://ci.nodejs.org/job/node-test-pull-request/75761/

trivikr · 2026-08-11T05:13:52Z

@mcollina @jasnell One of the tests was incorrect, and it surfaced in CI failures in AIX.
It's fixed now in 8ef6d08 and CI is successful.

Can you please provide your approval again?

nodejs-github-bot · 2026-08-14T01:54:43Z

Landed in 54ac460

Native code can mutate temporary string storage during an FFI call. Rewrite cached buffers on every conversion so a later call with the same JavaScript string receives a fresh copy of its UTF-8 bytes. Signed-off-by: Kamat, Trivikram <16024985+trivikr@users.noreply.github.com> Assisted-by: codex:gpt-5.6-sol PR-URL: #65051Fixes: #65050 Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com>

trivikr · 2026-08-05T15:00:52Z

Fixes: #65050

Native code can mutate temporary string storage during an FFI call. Rewrite cached buffers on every conversion so a later call with the same JavaScript string receives a fresh copy of its UTF-8 bytes.

Assisted-by: codex:gpt-5.6-sol

nodejs-github-bot · 2026-08-05T15:01:07Z

Review requested:

@nodejs/ffi

codecov · 2026-08-05T16:45:09Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.31%. Comparing base (a576f1c) to head (8ef6d08).
⚠️ Report is 51 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@## main #65051 +/- ##
=======================================
Coverage 90.30% 90.31% =======================================
Files 760 760 Lines 248526 248521 -5 Branches 46886 46896 +10 =======================================
+ Hits 224439 224445 +6 + Misses 15515 15502 -13 - Partials 8572 8574 +2

Files with missing lines	Coverage Δ
lib/internal/ffi/fast-api.js	`95.54% <ø> (+0.76%)`	⬆️

... and 28 files with indirect coverage changes

🚀 New features to boost your workflow:

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

mcollina

lgtm

trivikr · 2026-08-10T20:51:40Z

Converted to draft as test-ffi-fast-buffer is failing on ci.nodejs.org/job/node-test-commit-aix/64314

---duration_ms: 1355.201exitcode: 1severity: failstack: |- Test failure: 'fast FFI refreshes cached temporary string buffers' Location: test/ffi/test-ffi-fast-buffer.js:99:1 AssertionError [ERR_ASSERTION]: Expected values to be strictly equal: '' !== 'yello' at TestContext.<anonymous> (/home/iojs/build/workspace/node-test-commit-aix/nodes/aix72-power9/test/ffi/test-ffi-fast-buffer.js:108:12) at Test.runInAsyncScope (node:async_hooks:227:14) at Test.run (node:internal/test_runner/test:1397:25) at Test.processPendingSubtests (node:internal/test_runner/test:969:18) at Test.postRun (node:internal/test_runner/test:1537:19) at Test.run (node:internal/test_runner/test:1462:12) at process.processTicksAndRejections (node:internal/process/task_queues:104:5) at async Test.processPendingSubtests (node:internal/test_runner/test:969:7) { generatedMessage: true, code: 'ERR_ASSERTION', actual: '', expected: 'yello', operator: 'strictEqual', diff: 'simple' } (node:38469944) internal/test/binding: These APIs are for internal testing only. Do not use them. (Use `node --trace-warnings ...` to show where the warning was created) (node:38469944) ExperimentalWarning: FFI is an experimental feature and might change at any time...

trivikr · 2026-08-11T01:45:55Z

There was a bug in test.

AIX does not support Node’s PPC64 fast-call trampoline, so it exposes the test’s invalid assumption: the pointer returned by overwrite_string() points into temporary storage owned by Node’s generic FFI invocation. That storage is only valid during the native call. AIX frees/reuses the storage immediately, yielding ''.

Fast-path platforms retain the cached Buffer, so "yello" remains readable.

It was fixed in 89cc17f by observing the mutation during the native call instead of returning a pointer to temporary storage.

I'll re-request review after the CI is successful.

Native code can mutate temporary string storage during an FFI call. Rewrite cached buffers on every conversion so a later call with the same JavaScript string receives a fresh copy of its UTF-8 bytes. Signed-off-by: Kamat, Trivikram <16024985+trivikr@users.noreply.github.com> Assisted-by: codex:gpt-5.6-sol

trivikr · 2026-08-11T02:01:59Z

The ffi contract explicitly says JavaScript strings are copied to temporary NUL-terminated UTF-8 storage “for the duration of the call”

string values are copied to temporary NUL-terminated UTF-8 strings for the duration of the call.

The fast path happens to retain reusable buffers longer, but that is an implementation detail, not a lifetime guarantee.
The test should return the observed byte by value as done in 8ef6d08 and not the pointer.

nodejs-github-bot · 2026-08-11T03:46:48Z

CI: https://ci.nodejs.org/job/node-test-pull-request/75761/

trivikr · 2026-08-11T05:13:52Z

@mcollina @jasnell One of the tests was incorrect, and it surfaced in CI failures in AIX.
It's fixed now in 8ef6d08 and CI is successful.

Can you please provide your approval again?

nodejs-github-bot · 2026-08-14T01:54:43Z

Landed in 54ac460

Native code can mutate temporary string storage during an FFI call. Rewrite cached buffers on every conversion so a later call with the same JavaScript string receives a fresh copy of its UTF-8 bytes. Signed-off-by: Kamat, Trivikram <16024985+trivikr@users.noreply.github.com> Assisted-by: codex:gpt-5.6-sol PR-URL: #65051Fixes: #65050 Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com>

trivikr · 2026-08-05T15:00:52Z

Fixes: #65050

Native code can mutate temporary string storage during an FFI call. Rewrite cached buffers on every conversion so a later call with the same JavaScript string receives a fresh copy of its UTF-8 bytes.

Assisted-by: codex:gpt-5.6-sol

nodejs-github-bot · 2026-08-05T15:01:07Z

Review requested:

@nodejs/ffi

codecov · 2026-08-05T16:45:09Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.31%. Comparing base (a576f1c) to head (8ef6d08).
⚠️ Report is 51 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@## main #65051 +/- ##
=======================================
Coverage 90.30% 90.31% =======================================
Files 760 760 Lines 248526 248521 -5 Branches 46886 46896 +10 =======================================
+ Hits 224439 224445 +6 + Misses 15515 15502 -13 - Partials 8572 8574 +2

Files with missing lines	Coverage Δ
lib/internal/ffi/fast-api.js	`95.54% <ø> (+0.76%)`	⬆️

... and 28 files with indirect coverage changes

🚀 New features to boost your workflow:

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

mcollina

lgtm

trivikr · 2026-08-10T20:51:40Z

Converted to draft as test-ffi-fast-buffer is failing on ci.nodejs.org/job/node-test-commit-aix/64314

---duration_ms: 1355.201exitcode: 1severity: failstack: |- Test failure: 'fast FFI refreshes cached temporary string buffers' Location: test/ffi/test-ffi-fast-buffer.js:99:1 AssertionError [ERR_ASSERTION]: Expected values to be strictly equal: '' !== 'yello' at TestContext.<anonymous> (/home/iojs/build/workspace/node-test-commit-aix/nodes/aix72-power9/test/ffi/test-ffi-fast-buffer.js:108:12) at Test.runInAsyncScope (node:async_hooks:227:14) at Test.run (node:internal/test_runner/test:1397:25) at Test.processPendingSubtests (node:internal/test_runner/test:969:18) at Test.postRun (node:internal/test_runner/test:1537:19) at Test.run (node:internal/test_runner/test:1462:12) at process.processTicksAndRejections (node:internal/process/task_queues:104:5) at async Test.processPendingSubtests (node:internal/test_runner/test:969:7) { generatedMessage: true, code: 'ERR_ASSERTION', actual: '', expected: 'yello', operator: 'strictEqual', diff: 'simple' } (node:38469944) internal/test/binding: These APIs are for internal testing only. Do not use them. (Use `node --trace-warnings ...` to show where the warning was created) (node:38469944) ExperimentalWarning: FFI is an experimental feature and might change at any time...

trivikr · 2026-08-11T01:45:55Z

There was a bug in test.

AIX does not support Node’s PPC64 fast-call trampoline, so it exposes the test’s invalid assumption: the pointer returned by overwrite_string() points into temporary storage owned by Node’s generic FFI invocation. That storage is only valid during the native call. AIX frees/reuses the storage immediately, yielding ''.

Fast-path platforms retain the cached Buffer, so "yello" remains readable.

It was fixed in 89cc17f by observing the mutation during the native call instead of returning a pointer to temporary storage.

I'll re-request review after the CI is successful.

Native code can mutate temporary string storage during an FFI call. Rewrite cached buffers on every conversion so a later call with the same JavaScript string receives a fresh copy of its UTF-8 bytes. Signed-off-by: Kamat, Trivikram <16024985+trivikr@users.noreply.github.com> Assisted-by: codex:gpt-5.6-sol

trivikr · 2026-08-11T02:01:59Z

The ffi contract explicitly says JavaScript strings are copied to temporary NUL-terminated UTF-8 storage “for the duration of the call”

string values are copied to temporary NUL-terminated UTF-8 strings for the duration of the call.

The fast path happens to retain reusable buffers longer, but that is an implementation detail, not a lifetime guarantee.
The test should return the observed byte by value as done in 8ef6d08 and not the pointer.

nodejs-github-bot · 2026-08-11T03:46:48Z

CI: https://ci.nodejs.org/job/node-test-pull-request/75761/

trivikr · 2026-08-11T05:13:52Z

@mcollina @jasnell One of the tests was incorrect, and it surfaced in CI failures in AIX.
It's fixed now in 8ef6d08 and CI is successful.

Can you please provide your approval again?

nodejs-github-bot · 2026-08-14T01:54:43Z

Landed in 54ac460

Native code can mutate temporary string storage during an FFI call. Rewrite cached buffers on every conversion so a later call with the same JavaScript string receives a fresh copy of its UTF-8 bytes. Signed-off-by: Kamat, Trivikram <16024985+trivikr@users.noreply.github.com> Assisted-by: codex:gpt-5.6-sol PR-URL: #65051Fixes: #65050 Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com>

trivikr · 2026-08-05T15:00:52Z

Fixes: #65050

Native code can mutate temporary string storage during an FFI call. Rewrite cached buffers on every conversion so a later call with the same JavaScript string receives a fresh copy of its UTF-8 bytes.

Assisted-by: codex:gpt-5.6-sol

nodejs-github-bot · 2026-08-05T15:01:07Z

Review requested:

@nodejs/ffi

codecov · 2026-08-05T16:45:09Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.31%. Comparing base (a576f1c) to head (8ef6d08).
⚠️ Report is 51 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@## main #65051 +/- ##
=======================================
Coverage 90.30% 90.31% =======================================
Files 760 760 Lines 248526 248521 -5 Branches 46886 46896 +10 =======================================
+ Hits 224439 224445 +6 + Misses 15515 15502 -13 - Partials 8572 8574 +2

Files with missing lines	Coverage Δ
lib/internal/ffi/fast-api.js	`95.54% <ø> (+0.76%)`	⬆️

... and 28 files with indirect coverage changes

🚀 New features to boost your workflow:

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

mcollina

lgtm

trivikr · 2026-08-10T20:51:40Z

Converted to draft as test-ffi-fast-buffer is failing on ci.nodejs.org/job/node-test-commit-aix/64314

---duration_ms: 1355.201exitcode: 1severity: failstack: |- Test failure: 'fast FFI refreshes cached temporary string buffers' Location: test/ffi/test-ffi-fast-buffer.js:99:1 AssertionError [ERR_ASSERTION]: Expected values to be strictly equal: '' !== 'yello' at TestContext.<anonymous> (/home/iojs/build/workspace/node-test-commit-aix/nodes/aix72-power9/test/ffi/test-ffi-fast-buffer.js:108:12) at Test.runInAsyncScope (node:async_hooks:227:14) at Test.run (node:internal/test_runner/test:1397:25) at Test.processPendingSubtests (node:internal/test_runner/test:969:18) at Test.postRun (node:internal/test_runner/test:1537:19) at Test.run (node:internal/test_runner/test:1462:12) at process.processTicksAndRejections (node:internal/process/task_queues:104:5) at async Test.processPendingSubtests (node:internal/test_runner/test:969:7) { generatedMessage: true, code: 'ERR_ASSERTION', actual: '', expected: 'yello', operator: 'strictEqual', diff: 'simple' } (node:38469944) internal/test/binding: These APIs are for internal testing only. Do not use them. (Use `node --trace-warnings ...` to show where the warning was created) (node:38469944) ExperimentalWarning: FFI is an experimental feature and might change at any time...

trivikr · 2026-08-11T01:45:55Z

There was a bug in test.

AIX does not support Node’s PPC64 fast-call trampoline, so it exposes the test’s invalid assumption: the pointer returned by overwrite_string() points into temporary storage owned by Node’s generic FFI invocation. That storage is only valid during the native call. AIX frees/reuses the storage immediately, yielding ''.

Fast-path platforms retain the cached Buffer, so "yello" remains readable.

It was fixed in 89cc17f by observing the mutation during the native call instead of returning a pointer to temporary storage.

I'll re-request review after the CI is successful.

Native code can mutate temporary string storage during an FFI call. Rewrite cached buffers on every conversion so a later call with the same JavaScript string receives a fresh copy of its UTF-8 bytes. Signed-off-by: Kamat, Trivikram <16024985+trivikr@users.noreply.github.com> Assisted-by: codex:gpt-5.6-sol

trivikr · 2026-08-11T02:01:59Z

The ffi contract explicitly says JavaScript strings are copied to temporary NUL-terminated UTF-8 storage “for the duration of the call”

string values are copied to temporary NUL-terminated UTF-8 strings for the duration of the call.

The fast path happens to retain reusable buffers longer, but that is an implementation detail, not a lifetime guarantee.
The test should return the observed byte by value as done in 8ef6d08 and not the pointer.

nodejs-github-bot · 2026-08-11T03:46:48Z

CI: https://ci.nodejs.org/job/node-test-pull-request/75761/

trivikr · 2026-08-11T05:13:52Z

@mcollina @jasnell One of the tests was incorrect, and it surfaced in CI failures in AIX.
It's fixed now in 8ef6d08 and CI is successful.

Can you please provide your approval again?

nodejs-github-bot · 2026-08-14T01:54:43Z

Landed in 54ac460

Native code can mutate temporary string storage during an FFI call. Rewrite cached buffers on every conversion so a later call with the same JavaScript string receives a fresh copy of its UTF-8 bytes. Signed-off-by: Kamat, Trivikram <16024985+trivikr@users.noreply.github.com> Assisted-by: codex:gpt-5.6-sol PR-URL: #65051Fixes: #65050 Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com>

trivikr · 2026-08-05T15:00:52Z

Fixes: #65050

Native code can mutate temporary string storage during an FFI call. Rewrite cached buffers on every conversion so a later call with the same JavaScript string receives a fresh copy of its UTF-8 bytes.

Assisted-by: codex:gpt-5.6-sol

nodejs-github-bot · 2026-08-05T15:01:07Z

Review requested:

@nodejs/ffi

codecov · 2026-08-05T16:45:09Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.31%. Comparing base (a576f1c) to head (8ef6d08).
⚠️ Report is 51 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@## main #65051 +/- ##
=======================================
Coverage 90.30% 90.31% =======================================
Files 760 760 Lines 248526 248521 -5 Branches 46886 46896 +10 =======================================
+ Hits 224439 224445 +6 + Misses 15515 15502 -13 - Partials 8572 8574 +2

Files with missing lines	Coverage Δ
lib/internal/ffi/fast-api.js	`95.54% <ø> (+0.76%)`	⬆️

... and 28 files with indirect coverage changes

🚀 New features to boost your workflow:

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

mcollina

lgtm

trivikr · 2026-08-10T20:51:40Z

Converted to draft as test-ffi-fast-buffer is failing on ci.nodejs.org/job/node-test-commit-aix/64314

---duration_ms: 1355.201exitcode: 1severity: failstack: |- Test failure: 'fast FFI refreshes cached temporary string buffers' Location: test/ffi/test-ffi-fast-buffer.js:99:1 AssertionError [ERR_ASSERTION]: Expected values to be strictly equal: '' !== 'yello' at TestContext.<anonymous> (/home/iojs/build/workspace/node-test-commit-aix/nodes/aix72-power9/test/ffi/test-ffi-fast-buffer.js:108:12) at Test.runInAsyncScope (node:async_hooks:227:14) at Test.run (node:internal/test_runner/test:1397:25) at Test.processPendingSubtests (node:internal/test_runner/test:969:18) at Test.postRun (node:internal/test_runner/test:1537:19) at Test.run (node:internal/test_runner/test:1462:12) at process.processTicksAndRejections (node:internal/process/task_queues:104:5) at async Test.processPendingSubtests (node:internal/test_runner/test:969:7) { generatedMessage: true, code: 'ERR_ASSERTION', actual: '', expected: 'yello', operator: 'strictEqual', diff: 'simple' } (node:38469944) internal/test/binding: These APIs are for internal testing only. Do not use them. (Use `node --trace-warnings ...` to show where the warning was created) (node:38469944) ExperimentalWarning: FFI is an experimental feature and might change at any time...

trivikr · 2026-08-11T01:45:55Z

There was a bug in test.

AIX does not support Node’s PPC64 fast-call trampoline, so it exposes the test’s invalid assumption: the pointer returned by overwrite_string() points into temporary storage owned by Node’s generic FFI invocation. That storage is only valid during the native call. AIX frees/reuses the storage immediately, yielding ''.

Fast-path platforms retain the cached Buffer, so "yello" remains readable.

It was fixed in 89cc17f by observing the mutation during the native call instead of returning a pointer to temporary storage.

I'll re-request review after the CI is successful.

Native code can mutate temporary string storage during an FFI call. Rewrite cached buffers on every conversion so a later call with the same JavaScript string receives a fresh copy of its UTF-8 bytes. Signed-off-by: Kamat, Trivikram <16024985+trivikr@users.noreply.github.com> Assisted-by: codex:gpt-5.6-sol

trivikr · 2026-08-11T02:01:59Z

The ffi contract explicitly says JavaScript strings are copied to temporary NUL-terminated UTF-8 storage “for the duration of the call”

string values are copied to temporary NUL-terminated UTF-8 strings for the duration of the call.

The fast path happens to retain reusable buffers longer, but that is an implementation detail, not a lifetime guarantee.
The test should return the observed byte by value as done in 8ef6d08 and not the pointer.

nodejs-github-bot · 2026-08-11T03:46:48Z

CI: https://ci.nodejs.org/job/node-test-pull-request/75761/

trivikr · 2026-08-11T05:13:52Z

@mcollina @jasnell One of the tests was incorrect, and it surfaced in CI failures in AIX.
It's fixed now in 8ef6d08 and CI is successful.

Can you please provide your approval again?

nodejs-github-bot · 2026-08-14T01:54:43Z

Landed in 54ac460

Native code can mutate temporary string storage during an FFI call. Rewrite cached buffers on every conversion so a later call with the same JavaScript string receives a fresh copy of its UTF-8 bytes. Signed-off-by: Kamat, Trivikram <16024985+trivikr@users.noreply.github.com> Assisted-by: codex:gpt-5.6-sol PR-URL: #65051Fixes: #65050 Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com>

trivikr · 2026-08-05T15:00:52Z

Fixes: #65050

Native code can mutate temporary string storage during an FFI call. Rewrite cached buffers on every conversion so a later call with the same JavaScript string receives a fresh copy of its UTF-8 bytes.

Assisted-by: codex:gpt-5.6-sol

nodejs-github-bot · 2026-08-05T15:01:07Z

Review requested:

@nodejs/ffi

codecov · 2026-08-05T16:45:09Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.31%. Comparing base (a576f1c) to head (8ef6d08).
⚠️ Report is 51 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@## main #65051 +/- ##
=======================================
Coverage 90.30% 90.31% =======================================
Files 760 760 Lines 248526 248521 -5 Branches 46886 46896 +10 =======================================
+ Hits 224439 224445 +6 + Misses 15515 15502 -13 - Partials 8572 8574 +2

Files with missing lines	Coverage Δ
lib/internal/ffi/fast-api.js	`95.54% <ø> (+0.76%)`	⬆️

... and 28 files with indirect coverage changes

🚀 New features to boost your workflow:

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

mcollina

lgtm

trivikr · 2026-08-10T20:51:40Z

Converted to draft as test-ffi-fast-buffer is failing on ci.nodejs.org/job/node-test-commit-aix/64314

---duration_ms: 1355.201exitcode: 1severity: failstack: |- Test failure: 'fast FFI refreshes cached temporary string buffers' Location: test/ffi/test-ffi-fast-buffer.js:99:1 AssertionError [ERR_ASSERTION]: Expected values to be strictly equal: '' !== 'yello' at TestContext.<anonymous> (/home/iojs/build/workspace/node-test-commit-aix/nodes/aix72-power9/test/ffi/test-ffi-fast-buffer.js:108:12) at Test.runInAsyncScope (node:async_hooks:227:14) at Test.run (node:internal/test_runner/test:1397:25) at Test.processPendingSubtests (node:internal/test_runner/test:969:18) at Test.postRun (node:internal/test_runner/test:1537:19) at Test.run (node:internal/test_runner/test:1462:12) at process.processTicksAndRejections (node:internal/process/task_queues:104:5) at async Test.processPendingSubtests (node:internal/test_runner/test:969:7) { generatedMessage: true, code: 'ERR_ASSERTION', actual: '', expected: 'yello', operator: 'strictEqual', diff: 'simple' } (node:38469944) internal/test/binding: These APIs are for internal testing only. Do not use them. (Use `node --trace-warnings ...` to show where the warning was created) (node:38469944) ExperimentalWarning: FFI is an experimental feature and might change at any time...

trivikr · 2026-08-11T01:45:55Z

There was a bug in test.

AIX does not support Node’s PPC64 fast-call trampoline, so it exposes the test’s invalid assumption: the pointer returned by overwrite_string() points into temporary storage owned by Node’s generic FFI invocation. That storage is only valid during the native call. AIX frees/reuses the storage immediately, yielding ''.

Fast-path platforms retain the cached Buffer, so "yello" remains readable.

It was fixed in 89cc17f by observing the mutation during the native call instead of returning a pointer to temporary storage.

I'll re-request review after the CI is successful.

Native code can mutate temporary string storage during an FFI call. Rewrite cached buffers on every conversion so a later call with the same JavaScript string receives a fresh copy of its UTF-8 bytes. Signed-off-by: Kamat, Trivikram <16024985+trivikr@users.noreply.github.com> Assisted-by: codex:gpt-5.6-sol

trivikr · 2026-08-11T02:01:59Z

The ffi contract explicitly says JavaScript strings are copied to temporary NUL-terminated UTF-8 storage “for the duration of the call”

string values are copied to temporary NUL-terminated UTF-8 strings for the duration of the call.

The fast path happens to retain reusable buffers longer, but that is an implementation detail, not a lifetime guarantee.
The test should return the observed byte by value as done in 8ef6d08 and not the pointer.

nodejs-github-bot · 2026-08-11T03:46:48Z

CI: https://ci.nodejs.org/job/node-test-pull-request/75761/

trivikr · 2026-08-11T05:13:52Z

@mcollina @jasnell One of the tests was incorrect, and it surfaced in CI failures in AIX.
It's fixed now in 8ef6d08 and CI is successful.

Can you please provide your approval again?

nodejs-github-bot · 2026-08-14T01:54:43Z

Landed in 54ac460

Native code can mutate temporary string storage during an FFI call. Rewrite cached buffers on every conversion so a later call with the same JavaScript string receives a fresh copy of its UTF-8 bytes. Signed-off-by: Kamat, Trivikram <16024985+trivikr@users.noreply.github.com> Assisted-by: codex:gpt-5.6-sol PR-URL: #65051Fixes: #65050 Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com>

nodejs-github-bot added ffi Issues and PRs related to experimental Foreign Function Interface support. needs-ci PRs that need a full CI run. labels Aug 5, 2026

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trivikr force-pushed the ffi-temp-string-buffer-reuse branch from a88fe4c to 8f76513Compare August 9, 2026 23:22

mcollina approved these changes Aug 10, 2026
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trivikr added request-ci Add this label to start a Jenkins CI on a PR. needs-ci PRs that need a full CI run. and removed needs-ci PRs that need a full CI run. request-ci Add this label to start a Jenkins CI on a PR. labels Aug 10, 2026

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trivikr marked this pull request as draft August 10, 2026 20:51

trivikr marked this pull request as ready for review August 11, 2026 01:43

trivikr force-pushed the ffi-temp-string-buffer-reuse branch from 89cc17f to d225103Compare August 11, 2026 01:46

trivikr removed the author ready PRs with CI started, the required approvals, and no outstanding review comments. label Aug 11, 2026

fixup! test: avoid dangling FFI string pointer
8ef6d08

trivikr force-pushed the ffi-temp-string-buffer-reuse branch from d225103 to 8ef6d08Compare August 11, 2026 01:52

trivikr mentioned this pull request Aug 11, 2026
ffi reuses mutated temporary string buffer without restoring its contents #65050
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trivikr requested review from ShogunPanda and jasnell August 12, 2026 15:35

jasnell approved these changes Aug 14, 2026
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trivikr added commit-queue-squash PRs the Commit Queue should land as one squashed commit. commit-queue PRs queued for automated landing through the Commit Queue. labels Aug 14, 2026

nodejs-github-bot merged commit 54ac460 into nodejs:mainAug 14, 2026
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nodejs-github-bot removed the commit-queue PRs queued for automated landing through the Commit Queue. label Aug 14, 2026

trivikr deleted the ffi-temp-string-buffer-reuse branch August 16, 2026 16:01

github-actionsBot mentioned this pull request Aug 25, 2026
2026-08-26, Version 26.8.0 (Current) #65551
Merged