src,lib: support path in `v8.writeHeapSnapshot` output #58959

juanarbol · 2025-07-05T06:32:24Z

I'm a bit rusty with my C++. Any feedback will be more than valuable.

codecov · 2025-07-05T07:31:37Z

Codecov Report

❌ Patch coverage is 79.48718% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.51%. Comparing base (a65421a) to head (070a019).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
src/heap_utils.cc	72.41%	3 Missing and 5 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #58959      +/-   ##
==========================================
- Coverage   88.54%   88.51%   -0.03%     
==========================================
  Files         703      703              
  Lines      208545   208569      +24     
  Branches    40216    40240      +24     
==========================================
- Hits       184652   184625      -27     
- Misses      15905    15954      +49     
- Partials     7988     7990       +2

Files with missing lines	Coverage Δ
lib/v8.js	`99.04% <100.00%> (+0.01%)`	⬆️
src/node_internals.h	`83.01% <ø> (ø)`
src/heap_utils.cc	`79.54% <72.41%> (-0.60%)`	⬇️

... and 37 files with indirect coverage changes

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src/heap_utils.cc

test/sequential/test-write-heapsnapshot-options.js

jasnell

The BufferValue uses need to be cleaned up

juanarbol · 2025-07-18T23:08:16Z

@addaleax @jasnell @Renegade334 PTAL :-)

jasnell · 2025-07-19T16:22:27Z

src/heap_utils.cc

+  if (WriteSnapshot(env, final_filename.c_str(), options).IsNothing()) return;
+
+  args.GetReturnValue().Set(
+      String::NewFromUtf8(isolate, final_filename.c_str()).ToLocalChecked());


Unfortunately this is going to be a problem because it assumes the final_filename is utf8 encoded. Consider the following case:

const path = Buffer.from([0xe6]); // latin 1 character fs.mkdirSync(path); const res = v8.writeHeapSnapshot(undefined, { path }); fs.readfileSync(res); // fails! path doesn't exist

The reason fs.readfileSync would fail here is because the returned res will have interpreted the 0xe6 character incorrectly and will have replaced it with the unicode replacement char. The snapshot will have been written to disk correctly, but the returned path is wrong.

This likely needs to return the resulting path as a Buffer if the path was given as a Buffer and allow the API to accept an encoding option that optionally decodes the result as a string. But, that gets a bit awkward.

I love how picky this is, aaah, let me put the encoding option to make this a bit more consistent and leave utf8 as default encoding.

Nice catch, thanks! Anything else missing?

Nothing that sticks out, but I should have time to take another pass through by end of day monday

Hey James, I know its been a while; I've been quite busy lately, but now I have some bandwidth...

James, your snippet won't work.

node:fs:1326 const result = binding.mkdir( ^ Error: EILSEQ: illegal byte sequence, mkdir '�' at Object.mkdirSync (node:fs:1326:26) at Object.<anonymous> (/private/tmp/case.js:5:4) at Module._compile (node:internal/modules/cjs/loader:1759:14) at Object..js (node:internal/modules/cjs/loader:1890:10) at Module.load (node:internal/modules/cjs/loader:1480:32) at Module._load (node:internal/modules/cjs/loader:1299:12) at TracingChannel.traceSync (node:diagnostics_channel:328:14) at wrapModuleLoad (node:internal/modules/cjs/loader:245:24) at Module.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:154:5) at node:internal/main/run_main_module:33:47 { errno: -92, code: 'EILSEQ', syscall: 'mkdir', path: '�' }

I'm not able to create a latin1 folder in Node.js. I get the encoding requirements and stuff... but your snippet per se is not valid. What would you like me to do in this case? What should I consider adding in the test case?

juanarbol

I'm gonna use StringBytes::Encode but I would like to get my question answered before doing something

juanarbol · 2025-12-21T14:34:43Z

src/heap_utils.cc

+  if (WriteSnapshot(env, final_filename.c_str(), options).IsNothing()) return;
+
+  args.GetReturnValue().Set(
+      String::NewFromUtf8(isolate, final_filename.c_str()).ToLocalChecked());


Hey James, I know its been a while; I've been quite busy lately, but now I have some bandwidth...

James, your snippet won't work.

node:fs:1326 const result = binding.mkdir( ^ Error: EILSEQ: illegal byte sequence, mkdir '�' at Object.mkdirSync (node:fs:1326:26) at Object.<anonymous> (/private/tmp/case.js:5:4) at Module._compile (node:internal/modules/cjs/loader:1759:14) at Object..js (node:internal/modules/cjs/loader:1890:10) at Module.load (node:internal/modules/cjs/loader:1480:32) at Module._load (node:internal/modules/cjs/loader:1299:12) at TracingChannel.traceSync (node:diagnostics_channel:328:14) at wrapModuleLoad (node:internal/modules/cjs/loader:245:24) at Module.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:154:5) at node:internal/main/run_main_module:33:47 { errno: -92, code: 'EILSEQ', syscall: 'mkdir', path: '�' }

I'm not able to create a latin1 folder in Node.js. I get the encoding requirements and stuff... but your snippet per se is not valid. What would you like me to do in this case? What should I consider adding in the test case?

juanarbol · 2025-12-21T14:48:06Z

@jasnell PTAL

juanarbol · 2025-12-21T19:54:50Z

Fixing linter and CI, sorry.

Fixes: nodejs#58857 Signed-off-by: Juan José Arboleda <soyjuanarbol@gmail.com>

Renegade334 · 2025-12-23T23:49:56Z

src/heap_utils.cc

+  if (StringBytes::Encode(isolate, final_filename.c_str(), encoding)
+          .ToLocal(&ret)) {
+    args.GetReturnValue().Set(ret);


The problem with the position of this StringBytes operation is that if it fails, the function call will throw but will still have had meaningful side-effects. It would probably be better to attempt the encoding before snapshotting.

Renegade334 · 2025-12-23T23:54:12Z

lib/v8.js

+  const encoding = options?.encoding || 'utf8';
+  return triggerHeapSnapshot(filename, optionArray, options?.path, encoding);


Nit: Defaulting this here shouldn't be necessary; ParseEncoding will fall back to the provided default if the value is undefined or not a string.

Suggested change

const encoding = options?.encoding || 'utf8';

return triggerHeapSnapshot(filename, optionArray, options?.path, encoding);

return triggerHeapSnapshot(filename, optionArray, options?.path, options?.encoding);

Renegade334 · 2025-12-23T23:56:00Z

lib/v8.js

    filename = getValidatedPath(filename);
  }
+
+  if (options?.path !== undefined) {


Nit: I believe the general convention for options validation is to check for any nullish value, unless null has a discrete meaning for that option.

Suggested change

if (options?.path !== undefined) {

if (options?.path != undefined) {

juanarbol requested a review from BridgeAR July 5, 2025 06:32

nodejs-github-bot added c++ Issues and PRs that require attention from people who are familiar with C++. needs-ci PRs that need a full CI run. labels Jul 5, 2025

juanarbol changed the title ~~Juan/filepath v8~~ src,lib: support path in v8.writeHeapSnapshot output Jul 5, 2025

juanarbol force-pushed the juan/filepath-v8 branch from dfc2f3a to 3ef78c4 Compare July 5, 2025 06:40

juanarbol added semver-minor PRs that contain new features and should be released in the next minor version. v8 module Issues and PRs related to the "v8" subsystem. labels Jul 6, 2025

addaleax reviewed Jul 7, 2025

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jasnell reviewed Jul 7, 2025

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juanarbol force-pushed the juan/filepath-v8 branch 2 times, most recently from b956356 to 0055948 Compare July 18, 2025 23:05

jasnell reviewed Jul 19, 2025

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juanarbol commented Dec 21, 2025

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juanarbol force-pushed the juan/filepath-v8 branch from 0055948 to ff92f3d Compare December 21, 2025 14:46

juanarbol force-pushed the juan/filepath-v8 branch from ff92f3d to 641975c Compare December 21, 2025 21:31

src,lib: support path and encoding in v8.writeHeapSnapshot output

070a019

Fixes: nodejs#58857 Signed-off-by: Juan José Arboleda <soyjuanarbol@gmail.com>

juanarbol force-pushed the juan/filepath-v8 branch from 641975c to 070a019 Compare December 21, 2025 21:35

Renegade334 reviewed Dec 24, 2025

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		const encoding = options?.encoding \|\| 'utf8';
		return triggerHeapSnapshot(filename, optionArray, options?.path, encoding);

	if (options?.path !== undefined) {
	if (options?.path != undefined) {

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src,lib: support path in v8.writeHeapSnapshot output #58959

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src,lib: support path in v8.writeHeapSnapshot output #58959

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src,lib: support path in `v8.writeHeapSnapshot` output #58959

src,lib: support path in `v8.writeHeapSnapshot` output #58959

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