msgpack-javascript/src/CachedKeyDecoder.ts at master · keybase/msgpack-javascript · GitHub

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import { utf8DecodeJs } from "./utils/utf8";

interface KeyCacheRecord {

readonly bytes: Uint8Array;

readonly value: string;

}

const DEFAULT_MAX_KEY_LENGTH = 16;

const DEFAULT_MAX_LENGTH_PER_KEY = 16;

export class CachedKeyDecoder {

private readonly caches: Array<Array<KeyCacheRecord>>;

constructor(readonly maxKeyLength = DEFAULT_MAX_KEY_LENGTH, readonly maxLengthPerKey = DEFAULT_MAX_LENGTH_PER_KEY) {

// avoid `new Array(N)` to create a non-sparse array for performance.

this.caches = [];

for (let i = 0; i < this.maxKeyLength; i++) {

this.caches.push([]);

}

public canBeCached(byteLength: number) {

return byteLength > 0 && byteLength <= this.maxKeyLength;

}

private get(bytes: Uint8Array, inputOffset: number, byteLength: number): string | null {

const records = this.caches[byteLength - 1];

const recordsLength = records.length;

FIND_CHUNK: for (let i = 0; i < recordsLength; i++) {

const record = records[i];

const recordBytes = record.bytes;

for (let j = 0; j < byteLength; j++) {

if (recordBytes[j] !== bytes[inputOffset + j]) {

continue FIND_CHUNK;

}

return record.value;

}

return null;

}

private store(bytes: Uint8Array, value: string) {

const records = this.caches[bytes.length - 1];

const record: KeyCacheRecord = { bytes, value };

if (records.length >= this.maxLengthPerKey) {

// `records` are full!

// Set `record` to a randomized position.

records[(Math.random() * records.length) | 0] = record;

} else {

records.push(record);

}

public decode(bytes: Uint8Array, inputOffset: number, byteLength: number): string {

const cachedValue = this.get(bytes, inputOffset, byteLength);

if (cachedValue) {

return cachedValue;

}

const value = utf8DecodeJs(bytes, inputOffset, byteLength);

// Ensure to copy a slice of bytes because the byte may be NodeJS Buffer and Buffer#slice() returns a reference to its internal ArrayBuffer.

const slicedCopyOfBytes = Uint8Array.prototype.slice.call(bytes, inputOffset, inputOffset + byteLength);

this.store(slicedCopyOfBytes, value);

return value;

}

msgpack-javascript/src/CachedKeyDecoder.ts at master · keybase/msgpack-javascript · GitHub

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