perf: optimize parseHeaders

[tsctx]

Fixes #2491

benchmark

const { parseHeaders } = require("./undici/lib/core/util")
const benchmark = require("benchmark");

const suite = new benchmark.Suite();

const headers = Object.entries({
  "Content-Type": "application/json",
  Date: "Wed, 01 Nov 2023 00:00:00 GMT",
  "Powered-By": "NodeJS",
  "Content-Encoding": "gzip",
  "Set-Cookie": "__Secure-ID=123; Secure; Domain=example.com",
  "Content-Length": "150",
  Vary: "Accept-Encoding, Accept, X-Requested-With",
}).flat()

suite.add("parseHeaders", () => {
  parseHeaders(headers)
})
suite.on("cycle", function (event) {
  console.log(String(event.target));
});

// run async
new Promise((resolve) => setTimeout(resolve, 7000)).then(() =>
  suite.run({ async: true })
);

• main

parseHeaders x 754,545 ops/sec ±4.92% (73 runs sampled)

• this patch

parseHeaders x 1,718,324 ops/sec ±3.51% (85 runs sampled)

[codecov-commenter]

Codecov Report

Attention: 141 lines in your changes are missing coverage. Please review.

Comparison is base (e39a632) 85.54% compared to head (df412f5) 84.32%.
Report is 132 commits behind head on main.

Files	Patch %	Lines
lib/fetch/util.js	23.72%	45 Missing ⚠️
lib/fetch/index.js	49.39%	42 Missing ⚠️
lib/handler/RetryHandler.js	73.91%	30 Missing ⚠️
lib/compat/dispatcher-weakref.js	28.57%	5 Missing ⚠️
lib/fetch/headers.js	88.63%	5 Missing ⚠️
lib/api/readable.js	80.00%	4 Missing ⚠️
lib/client.js	92.10%	3 Missing ⚠️
lib/core/util.js	93.75%	2 Missing ⚠️
lib/fetch/request.js	90.47%	2 Missing ⚠️
lib/core/request.js	97.56%	1 Missing ⚠️
... and 2 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2492      +/-   ##
==========================================
- Coverage   85.54%   84.32%   -1.23%     
==========================================
  Files          76       78       +2     
  Lines        6858     7153     +295     
==========================================
+ Hits         5867     6032     +165     
- Misses        991     1121     +130     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[ronag]

Benchmark?

[tsctx]

@ronag added

[ronag]

Good job

[ronag]

Is a Map faster?

[tsctx]

@ronag

Is a Map faster?

Not much change.

parseHeaders x 1,707,785 ops/sec ±2.17% (84 runs sampled)

[ywave620]

@tsctx Thanks for this :)

[mcollina]

lgtm

Very good job!