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fs: improve promises.readFile performance #37127

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addaleax wants to merge 3 commits into from
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fs: improve promises.readFile performance #37127

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69c87cc
fs: only use Buffer.concat in promises.readFile when necessary
addaleax Jan 29, 2021
5ce769e
fs: read full size if known in promises.readFile
addaleax Jan 29, 2021
759440f
fixup! fs: read full size if known in promises.readFile
addaleax Jan 29, 2021
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13 changes: 7 additions & 6 deletions lib/internal/fs/promises.js
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Original file line number Diff line number Diff line change
Expand Up @@ -315,23 +315,24 @@ async function readFileHandle(filehandle, options) {
throw new ERR_FS_FILE_TOO_LARGE(size);

const chunks = [];
const chunkSize = size === 0 ?
kReadFileMaxChunkSize :
MathMin(size, kReadFileMaxChunkSize);
let isFirstChunk = true;
const firstChunkSize = size === 0 ? kReadFileMaxChunkSize : size;
const chunkSize = MathMin(firstChunkSize, kReadFileMaxChunkSize);
let endOfFile = false;
do {
if (signal?.aborted) {
throw lazyDOMException('The operation was aborted', 'AbortError');
}
const buf = Buffer.alloc(chunkSize);
const buf = Buffer.alloc(isFirstChunk ? firstChunkSize : chunkSize);
const { bytesRead, buffer } =
await read(filehandle, buf, 0, chunkSize, -1);
await read(filehandle, buf, 0, buf.length, -1);
endOfFile = bytesRead === 0;
if (bytesRead > 0)
ArrayPrototypePush(chunks, buffer.slice(0, bytesRead));
isFirstChunk = false;
} while (!endOfFile);

const result = Buffer.concat(chunks);
const result = chunks.length === 1 ? chunks[0] : Buffer.concat(chunks);

return options.encoding ? result.toString(options.encoding) : result;
}
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