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perf(content-type parser): faster string collector #1894

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Jan 29, 2023
Merged

perf(content-type parser): faster string collector #1894

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39 changes: 29 additions & 10 deletions lib/fetch/dataURL.js
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Original file line number Diff line number Diff line change
Expand Up @@ -31,8 +31,8 @@ function dataURLProcessor (dataURL) {
// 5. Let mimeType be the result of collecting a
// sequence of code points that are not equal
// to U+002C (,), given position.
let mimeType = collectASequenceOfCodePoints(
(char) => char !== ',',
let mimeType = collectASequenceOfCodePointsFast(
',',
input,
position
)
Expand Down Expand Up @@ -145,6 +145,25 @@ function collectASequenceOfCodePoints (condition, input, position) {
return result
}

/**
* A faster collectASequenceOfCodePoints that only works when comparing a single character.
* @param {string} char
* @param {string} input
* @param {{ position: number }} position
*/
function collectASequenceOfCodePointsFast (char, input, position) {
const idx = input.indexOf(char, position.position)
const start = position.position

if (idx === -1) {
position.position = input.length
return input.slice(start)
}

position.position = idx
return input.slice(start, position.position)
}

// https://url.spec.whatwg.org/#string-percent-decode
/** @param {string} input */
function stringPercentDecode (input) {
Expand Down Expand Up @@ -214,8 +233,8 @@ function parseMIMEType (input) {
// 3. Let type be the result of collecting a sequence
// of code points that are not U+002F (/) from
// input, given position.
const type = collectASequenceOfCodePoints(
(char) => char !== '/',
const type = collectASequenceOfCodePointsFast(
'/',
input,
position
)
Expand All @@ -239,8 +258,8 @@ function parseMIMEType (input) {
// 7. Let subtype be the result of collecting a sequence of
// code points that are not U+003B (;) from input, given
// position.
let subtype = collectASequenceOfCodePoints(
(char) => char !== ';',
let subtype = collectASequenceOfCodePointsFast(
';',
input,
position
)
Expand Down Expand Up @@ -324,8 +343,8 @@ function parseMIMEType (input) {

// 2. Collect a sequence of code points that are not
// U+003B (;) from input, given position.
collectASequenceOfCodePoints(
(char) => char !== ';',
collectASequenceOfCodePointsFast(
';',
input,
position
)
Expand All @@ -335,8 +354,8 @@ function parseMIMEType (input) {
// 1. Set parameterValue to the result of collecting
// a sequence of code points that are not U+003B (;)
// from input, given position.
parameterValue = collectASequenceOfCodePoints(
(char) => char !== ';',
parameterValue = collectASequenceOfCodePointsFast(
';',
input,
position
)
Expand Down