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util: make mime parsing faster - #66369

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@jasnell jasnell commented Sep 28, 2026

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Improve the implementation of util.MIMEType parsing to eliminate overhead. Modules like undici end up handrolling their mime parsing impls because util.MIMEType just had never been performance optimized. This update makes it about twice as fast as undici's handrolled version for typical inputs.

$ cd /home/dev/node && ./node benchmark/compare.js --old /tmp/opencode/mime/node-old --new ./out/Release/node --runs 10 --no-progress --analyze --csv /tmp/opencode/mime/compare.csv mime 2>&1 | tail -60
mime/mimetype-parse.js operation='essence' value='application/json' n=100000                                                                                                                      ***            +81.04 %   ±3.34%  ±4.63%  ±6.43%
mime/mimetype-parse.js operation='params.get' value='application/json' n=100000                                                                                                                   ***           +114.31 %   ±4.97%  ±7.03%  ±10.06%
mime/mimetype-parse.js operation='parse' value='text/html; charset=utf-8' n=100000                                                                                                                ***           +118.11 %   ±4.77%  ±6.66%  ±9.35%
mime/mimetype-parse.js operation='essence' value='text/html; charset=utf-8' n=100000                                                                                                              ***            +70.97 %   ±6.86%  ±9.54%  ±13.30%
mime/mimetype-parse.js operation='params.get' value='text/html; charset=utf-8' n=100000                                                                                                           ***           +139.05 %   ±4.51%  ±6.37%  ±9.11%
mime/mimetype-parse.js operation='parse' value='multipart/form-data; boundary=----WebKitFormBoundary7MA4YWxkTrZu0gW' n=100000                                                                     ***            +92.57 %   ±4.57%  ±6.40%  ±9.04%
mime/mimetype-parse.js operation='essence' value='multipart/form-data; boundary=----WebKitFormBoundary7MA4YWxkTrZu0gW' n=100000                                                                   ***            +73.89 %   ±18.69%  ±26.76%  ±39.13%
mime/mimetype-parse.js operation='params.get' value='multipart/form-data; boundary=----WebKitFormBoundary7MA4YWxkTrZu0gW' n=100000                                                                ***           +125.18 %   ±5.09%  ±7.20%  ±10.30%
mime/mimetype-parse.js operation='parse' value='text/plain; charset="utf-8"; foo="b\\"ar"; x=y' n=100000                                                                                          ***           +113.24 %   ±6.59%  ±9.26%  ±13.14%
mime/mimetype-parse.js operation='essence' value='text/plain; charset="utf-8"; foo="b\\"ar"; x=y' n=100000                                                                                        ***            +70.11 %   ±4.21%  ±5.84%  ±8.13%
mime/mimetype-parse.js operation='params.get' value='text/plain; charset="utf-8"; foo="b\\"ar"; x=y' n=100000                                                                                     ***           +179.52 %   ±6.07%  ±8.70%  ±12.74%
mime/mimetype-parse.js operation='parse' value='not a mime type' n=100000                                                                                                                         ***            +57.83 %   ±4.81%  ±6.78%  ±9.69%
mime/mimetype-parse.js operation='essence' value='not a mime type' n=100000                                                                                                                       ***            +59.27 %   ±4.64%  ±6.47%  ±9.09%
mime/mimetype-parse.js operation='params.get' value='not a mime type' n=100000                                                                                                                    ***            +57.58 %   ±4.10%  ±5.73%  ±8.05%
mime/mimetype-to-string.js value='application/ecmascript; ' n=100000                                                                                                                                              -8.77 %   ±15.56%  ±22.30%  ±32.67%
mime/mimetype-to-string.js value='text/html;charset=gbk' n=100000                                                                                                                                  **             +8.35 %   ±4.46%  ±6.13%  ±8.40%
mime/mimetype-to-string.js value='text/html;012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789=x;charset=gbk' n=100000      ***            +13.55 %   ±3.00%  ±4.17%  ±5.81%
mime/mimetype-to-string.js value='text/html;test=ÿ;charset=gbk' n=100000                                                                                                                          ***            +17.04 %   ±3.19%  ±4.38%  ±5.97%
mime/mimetype-to-string.js value='x/x;\n\r\t x=x\n\r\t ;x=y' n=100000                                                                                                                             ***            +15.31 %   ±3.41%  ±4.68%  ±6.38%

                                                                                                                                                                                                     -185.6%            0%            +185.6%
mime/mimetype-instantiation.js value='application/ecmascript; ' n=100000                                                                                                                                              |████████░            +86.21% ***
mime/mimetype-instantiation.js value='text/html;charset=gbk' n=100000                                                                                                                                                 |████████████░░       +124.07% ***
mime/mimetype-instantiation.js value='text/html;012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789=x;charset=gbk' n=100000                      |███████████░         +113.17% ***
mime/mimetype-instantiation.js value='text/html;test=ÿ;charset=gbk' n=100000                                                                                                                                          |████████████░        +117.66% ***
mime/mimetype-instantiation.js value='x/x;\n\r\t x=x\n\r\t ;x=y' n=100000                                                                                                                                             |██████████████       +137.13% ***
mime/mimetype-parse.js operation='parse' value='application/json' n=100000                                                                                                                                            |██████████░          +104.81% ***
mime/mimetype-parse.js operation='essence' value='application/json' n=100000                                                                                                                                          |████████             +81.04% ***
mime/mimetype-parse.js operation='params.get' value='application/json' n=100000                                                                                                                                       |███████████░         +114.31% ***
mime/mimetype-parse.js operation='parse' value='text/html; charset=utf-8' n=100000                                                                                                                                    |████████████         +118.11% ***
mime/mimetype-parse.js operation='essence' value='text/html; charset=utf-8' n=100000                                                                                                                                  |███████              +70.97% ***
mime/mimetype-parse.js operation='params.get' value='text/html; charset=utf-8' n=100000                                                                                                                               |██████████████       +139.05% ***
mime/mimetype-parse.js operation='parse' value='multipart/form-data; boundary=----WebKitFormBoundary7MA4YWxkTrZu0gW' n=100000                                                                                         |█████████            +92.57% ***
mime/mimetype-parse.js operation='essence' value='multipart/form-data; boundary=----WebKitFormBoundary7MA4YWxkTrZu0gW' n=100000                                                                                       |███████░░            +73.89% ***
mime/mimetype-parse.js operation='params.get' value='multipart/form-data; boundary=----WebKitFormBoundary7MA4YWxkTrZu0gW' n=100000                                                                                    |████████████░        +125.18% ***
mime/mimetype-parse.js operation='parse' value='text/plain; charset="utf-8"; foo="b\\"ar"; x=y' n=100000                                                                                                              |███████████░         +113.24% ***
mime/mimetype-parse.js operation='essence' value='text/plain; charset="utf-8"; foo="b\\"ar"; x=y' n=100000                                                                                                            |███████              +70.11% ***
mime/mimetype-parse.js operation='params.get' value='text/plain; charset="utf-8"; foo="b\\"ar"; x=y' n=100000                                                                                                         |██████████████████░  +179.52% ***
mime/mimetype-parse.js operation='parse' value='not a mime type' n=100000                                                                                                                                             |█████░               +57.83% ***
mime/mimetype-parse.js operation='essence' value='not a mime type' n=100000                                                                                                                                           |█████░               +59.27% ***
mime/mimetype-parse.js operation='params.get' value='not a mime type' n=100000                                                                                                                                        |█████░               +57.58% ***
mime/mimetype-to-string.js value='application/ecmascript; ' n=100000                                                                                                                                               ░░▓|                     -8.77% 
mime/mimetype-to-string.js value='text/html;charset=gbk' n=100000                                                                                                                                                     |                     +8.35% **
mime/mimetype-to-string.js value='text/html;012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789=x;charset=gbk' n=100000                          |░                    +13.55% ***
mime/mimetype-to-string.js value='text/html;test=ÿ;charset=gbk' n=100000                                                                                                                                              |█                    +17.04% ***
mime/mimetype-to-string.js value='x/x;\n\r\t x=x\n\r\t ;x=y' n=100000                                                                                                                                                 |█                    +15.31% ***

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 25 comparisons, you can thus
expect the following amount of false-positive results:
  1.25 false positives, when considering a   5% risk acceptance (*, **, ***),
  0.25 false positives, when considering a   1% risk acceptance (**, ***),
  0.03 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), 24 comparisons remain significant at 5%.
--max-regression uses the corrected values.

Signed-off-by: James M Snell <jasnell@gmail.com>
Assisted-by: Opencode
@jasnell
jasnell requested review from mcollina and ronag September 28, 2026 05:22
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Review requested:

  • @nodejs/performance

@nodejs-github-bot nodejs-github-bot added the needs-ci PRs that need a full CI run. label Sep 28, 2026
@codecov

codecov Bot commented Sep 28, 2026

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.36%. Comparing base (cd908df) to head (cf37283).
⚠️ Report is 15 commits behind head on main.

Additional details and impacted files
@@            Coverage Diff             @@
##             main   #66369      +/-   ##
==========================================
- Coverage   90.37%   90.36%   -0.02%     
==========================================
  Files         792      792              
  Lines      275324   275526     +202     
  Branches    52764    52824      +60     
==========================================
+ Hits       248828   248982     +154     
- Misses      16918    16973      +55     
+ Partials     9578     9571       -7     
Files with missing lines Coverage Δ
lib/internal/mime.js 100.00% <100.00%> (ø)

... and 45 files with indirect coverage changes

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