notepack.io/lib/DecodeKeyCache.js

A fast Node.js implementation of the latest MessagePack spec

const DEFAULT_MAX_SIZE = process.env.NOTEPACK_DECODE_KEY_CACHE_MAX_SIZE || 1024;
const DEFAULT_MAX_LENGTH = process.env.NOTEPACK_DECODE_KEY_CACHE_MAX_LENGTH || 16;

/**
 * Store the buffer-to-string values in a tree
 */
class DecodeKeyCache {
  constructor({ maxSize = DEFAULT_MAX_SIZE, maxLength = DEFAULT_MAX_LENGTH } = {}) {
    this.size = 0;
    this.maxSize = maxSize;
    this.maxLength = maxLength;
    this.cache = new Map();
    for (let i = 1; i <= this.maxLength; i++) {
      this.cache.set(i, new Map());
    }
  }

  get(buffer, offset, length) {
    if (length > this.maxLength) { return false; }
    let node = this.cache.get(length);
    for (let i = 0; i < length; i++) {
      const byte = buffer[offset + i];
      if (node.has(byte)) {
        node = node.get(byte);
      } else {
        return false;
      }
    }
    return node;
  }

  set(buffer, offset, length, value) {
    if (length > this.maxLength || this.size >= this.maxSize) { return; }
    this.size++;
    let node = this.cache.get(length);
    for (let i = 0; i < length; i++) {
      const byte = buffer[offset + i];
      if (i === length - 1) {
        node.set(byte, value);
      } else if (node.has(byte)) {
        node = node.get(byte);
      } else {
        const newNode = new Map();
        node.set(byte, newNode);
        node = newNode;
      }
    }
  }
}

module.exports = DecodeKeyCache;