Hash function to debug absolute paths sent to the update chunk hash method in webpack.

HashFunction.ts

import * as crypto from 'crypto';
import * as fs from 'fs';
import * as path from 'path';

/**
 * Interface for Webpack's hashFunction
 */
export interface IHashFunction {
  update: (data: string | Buffer, encoding: string) => IHashFunction;
  digest: (encoding: string) => string | Buffer;
  new (algorithm: string): IHashFunction;
}

/**
 * Webpack hashFunction based on md5
 * with debugging.
 */
export function HashFunction(algorithm: string): IHashFunction {
  const _algorithm: string = algorithm ? algorithm : 'md5';
  this._hashFunction = crypto.createHash(_algorithm);
  // This dynamically creates the absolute path to our project's root directy, which is 
  // 4 levels up from where we keep this file.
  // You could just manually set _absolutePath, e.g. to "Users/sally/workspace/myproject"
  const numberOfNestedDirs = 4;
  this._absolutePath = path.join(...__dirname.split(path.sep).slice(0, -numberOfNestedDirs));
  if (path.sep === '/') {
    // Add back leading '/' in *nix fs.
    this._absolutePath = '/' + this._absolutePath;
  }
  const logPath: string = path.join(this._absolutePath, 'abs_path_errors.log');
  this._logFile = fs.createWriteStream(logPath, {flags: 'a+'});

  this.update = (data: string | Buffer, encoding: string): IHashFunction => {
    if (data.indexOf(this._absolutePath) !== -1) {
      this._logFile.write(
        'Absolute Path Detected: ' + data.slice(0, 2000) + '\n\n'
      );
      debugger; // tslint:disable-line:no-debugger
    } else {
      this._hashFunction.update(data, encoding);
    }
    return this;
  };

  this.digest = (encoding: string): string => {
    return this._hashFunction.digest('hex').substring(0, 16);
  };

  return this;
}