[araujogui]

StreamBase::WriteString() created a String::ValueView twice, the first time in StringBytes::StorageSize() only to read the length. A ValueView flattens the string. So a string built by concatenation, like an HTTP response header, was copied to a new flat string on the V8 heap, then copied again into the write buffer. StreamBase::Writev() did the same for each string chunk.

Now StorageSize() reads the length from the string, and one-byte strings are copied with String::WriteOneByte(), which does not flatten. For UTF-8, the characters go to the last third of the buffer and are converted into the rest: a Latin-1 character takes at most two bytes. Two-byte strings, and UTF-8 strings whose buffer has no room for that, use StringBytes::Write() as before.

WriteString() and Writev() share this, so it covers every HTTP/1.1 response header, with a string body or a Buffer body, and TLS sockets too.

Flat strings written as UTF-8 pay one extra memcpy of at most 65535 bytes. Other StringBytes::Write() callers (fs, Buffer) are not changed.

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[codecov]

Codecov Report

❌ Patch coverage is 89.65517% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.70%. Comparing base (933cb11) to head (c8c2b24).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
src/string_bytes.cc	75.00%	2 Missing ⚠️
src/stream_base.cc	95.23%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #67435      +/-   ##
==========================================
+ Coverage   90.69%   90.70%   +0.01%     
==========================================
  Files         801      801              
  Lines      281875   281884       +9     
  Branches    54317    54323       +6     
==========================================
+ Hits       255652   255695      +43     
+ Misses      16348    16312      -36     
- Partials     9875     9877       +2     

Files with missing lines	Coverage Δ
src/stream_base.cc	76.27% <95.23%> (+0.14%)	⬆️
src/string_bytes.cc	75.57% <75.00%> (-0.18%)	⬇️

... and 35 files with indirect coverage changes

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[araujogui]

https://ci.nodejs.org/view/Node.js%20benchmark/job/benchmark-node-micro-benchmarks/1904/

benchmark/http/end-string.js

                                                                 confidence   improvement   accuracy (*)    (**)   (***)
http/end-string.js duration=5 c=50 len=4 benchmarker='wrk'                       +0.89 %   ±0.91%  ±1.21%  ±1.57%
http/end-string.js duration=5 c=50 len=64 benchmarker='wrk'      ***             +3.42 %   ±0.70%  ±0.93%  ±1.22%
http/end-string.js duration=5 c=50 len=1024 benchmarker='wrk'    ***             +5.66 %   ±0.64%  ±0.85%  ±1.11%
http/end-string.js duration=5 c=50 len=16384 benchmarker='wrk'                   -0.58 %   ±0.77%  ±1.03%  ±1.34%
http/end-string.js duration=5 c=50 len=102400 benchmarker='wrk'                  -0.12 %   ±0.44%  ±0.59%  ±0.76%

                                                                    -6.3%              0%              +6.3%
http/end-string.js duration=5 c=50 len=4 benchmarker='wrk'                           |▓▓░░░                +0.89% 
http/end-string.js duration=5 c=50 len=64 benchmarker='wrk'                          |██████████░░         +3.42% ***
http/end-string.js duration=5 c=50 len=1024 benchmarker='wrk'                        |█████████████████░░  +5.66% ***
http/end-string.js duration=5 c=50 len=16384 benchmarker='wrk'                   ░░▓▓|                     -0.58% 
http/end-string.js duration=5 c=50 len=102400 benchmarker='wrk'                    ░░|                     -0.12% 

Rates were scaled by 1000x into HdrHistogram (3 significant figures).
Use --scale to adjust precision if needed.

Be aware that when doing many comparisons the risk of a false-positive
result increases. In this case, there are 5 comparisons, you can thus
expect the following amount of false-positive results:
  0.25 false positives, when considering a   5% risk acceptance (*, **, ***),
  0.05 false positives, when considering a   1% risk acceptance (**, ***),
  0.01 false positives, when considering a 0.1% risk acceptance (***)

The stars above are per-benchmark and uncorrected. Adjusting for the size of
this comparison set (Holm-Bonferroni), 2 comparisons remain significant at 5%.