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[v14.x backport] fs: improve fsPromises readFile performance #37703

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[v14.x backport] fs: improve fsPromises readFile performance #37703

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50 changes: 36 additions & 14 deletions lib/internal/fs/promises.js
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Original file line number Diff line number Diff line change
Expand Up @@ -4,12 +4,12 @@
// See https://github.com/libuv/libuv/pull/1501.
const kIoMaxLength = 2 ** 31 - 1;

// Note: This is different from kReadFileBufferLength used for non-promisified
// fs.readFile.
const kReadFileMaxChunkSize = 2 ** 14;
const kReadFileBufferLength = 512 * 1024;
const kReadFileUnknownBufferLength = 64 * 1024;
const kWriteFileMaxChunkSize = 2 ** 14;

const {
ArrayPrototypePush,
Error,
MathMax,
MathMin,
Expand Down Expand Up @@ -272,21 +272,43 @@ async function readFileHandle(filehandle, options) {
if (size > kIoMaxLength)
throw new ERR_FS_FILE_TOO_LARGE(size);

const chunks = [];
const chunkSize = size === 0 ?
kReadFileMaxChunkSize :
MathMin(size, kReadFileMaxChunkSize);
let endOfFile = false;
let totalRead = 0;
const noSize = size === 0;
const buffers = [];
const fullBuffer = noSize ? undefined : Buffer.allocUnsafeSlow(size);
do {
const buf = Buffer.alloc(chunkSize);
const { bytesRead, buffer } =
await read(filehandle, buf, 0, chunkSize, -1);
endOfFile = bytesRead === 0;
if (bytesRead > 0)
chunks.push(buffer.slice(0, bytesRead));
let buffer;
let offset;
let length;
if (noSize) {
buffer = Buffer.allocUnsafeSlow(kReadFileUnknownBufferLength);
offset = 0;
length = kReadFileUnknownBufferLength;
} else {
buffer = fullBuffer;
offset = totalRead;
length = MathMin(size - totalRead, kReadFileBufferLength);
}

const bytesRead = (await binding.read(filehandle.fd, buffer, offset,
length, -1, kUsePromises)) || 0;
totalRead += bytesRead;
endOfFile = bytesRead === 0 || totalRead === size;
if (noSize && bytesRead > 0) {
const isBufferFull = bytesRead === kReadFileUnknownBufferLength;
const chunkBuffer = isBufferFull ? buffer : buffer.slice(0, bytesRead);
ArrayPrototypePush(buffers, chunkBuffer);
}
} while (!endOfFile);

const result = Buffer.concat(chunks);
let result;
if (size > 0) {
result = totalRead === size ? fullBuffer : fullBuffer.slice(0, totalRead);
} else {
result = buffers.length === 1 ? buffers[0] : Buffer.concat(buffers,
totalRead);
}

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