src,lib: support path in v8.writeHeapSnapshot output

[juanarbol]

---

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

[codecov]

Codecov Report

Attention: Patch coverage is 78.78788% with 7 lines in your changes missing coverage. Please review.

Project coverage is 90.02%. Comparing base (cc856b3) to head (0055948).
Report is 61 commits behind head on main.

Files with missing lines	Patch %	Lines
src/heap_utils.cc	72.00%	3 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #58959      +/-   ##
==========================================
- Coverage   90.09%   90.02%   -0.07%     
==========================================
  Files         640      648       +8     
  Lines      188471   190963    +2492     
  Branches    36973    37433     +460     
==========================================
+ Hits       169802   171919    +2117     
- Misses      11382    11670     +288     
- Partials     7287     7374      +87     

Files with missing lines	Coverage Δ
lib/v8.js	99.38% <100.00%> (+<0.01%)	⬆️
src/node_internals.h	81.03% <ø> (ø)
src/heap_utils.cc	79.60% <72.00%> (-0.54%)	⬇️

... and 116 files with indirect coverage changes

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[jasnell]

The BufferValue uses need to be cleaned up

[juanarbol]

@addaleax @jasnell @Renegade334 PTAL :-)

[jasnell]

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.

[juanarbol]

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?

[jasnell]

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