deferred-file-buffer.js

import { createHash } from 'crypto';
import fs from 'fs';
import { basename } from 'path';

/**
 * An abstraction for a buffered file suitable to be used
 * in tests (specially upload tests).
 *
 * Buffering and digesting are deffered until they are used.
 */
export class DeferredFileBuffer {
  constructor(path, metadata = {}) {
    Object.defineProperties(this, {
      _path: {
        value: path,
        enumerable: false,
        writable: false,
        configurable: false,
      },
      meta: {
        value: { path, filename: basename(path), ...metadata },
        enumerable: true,
        writable: false,
        configurable: false,
      },
      _buffer: {
        enumerable: false,
        writable: true,
        configurable: false,
      },
      _md5: {
        enumerable: false,
        writable: true,
        configurable: false,
      },
    });
  }

  /**
   * Buffers the file into memory and returns the buffered content.
   *
   * @returns Buffer
   */
  read() {
    if (Buffer.isBuffer(this._buffer)) return this._buffer;

    this._buffer = fs.readFileSync(this._path);

    return this._buffer;
  }

  /**
   * Returns the file buffer.
   *
   * @returns Buffer
   */
  get buffer() {
    return this.read();
  }

  /**
   * The file md5 digest.
   *
   * (Implies the buffering of the file)
   *
   * @returns string
   */
  get md5() {
    if (typeof this._md5 === 'string') return this._md5;

    this._md5 = createHash('md5').update(this.buffer).digest('hex');

    return this._md5;
  }

  /**
   * The file size in bytes.
   *
   * (Implies the buffering of the file)
   *
   * @returns number
   */
  get size() {
    return this.buffer.byteLength;
  }

  /**
   * Makes the buffered memory elegible to be freed.
   */
  free() {
    this._buffer = undefined;
  }
}