Clone yauzl for patching

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Clone yauzl for patching

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This module does not have any useful function in itself. It is purely designed to help with creating modules that modify yauzl unzipping library in some way.
yauzl-promise and yauzl-crc, for example, use this module internally.
When monkey-patching a module, it is good practice to clone the original module first so as not to alter the result of calling require('yauzl') somewhere else in your application (perhaps inside a dependency).
This module provides some helper methods for creating cloned versions of yauzl for later modification.


.clone( yauzl [, options ] )

Options are as follows (defaults shown):
  clone: true,
  subclassZipFile: false,
  subclassEntry: false,
  eventsIntercept: false


Clones the yauzl object. Equivalent to Object.assign({}, yauzl).
const yauzl = require('yauzl');
const yauzlClone = require('yauzlClone');

const clone = yauzlClone(yauzl);


Creates a subclass of yauzl.ZipFile. The prototype of yauzl.ZipFile can then be altered without affecting the original.
This option also monkey patches the access methods (.open(), .fromFd(), .fromBuffer(), .testFromRandomAccessReader()) to callback with instances of this ZipFile subclass.


Creates a subclass of yauzl.Entry (same idea as subclassZipFile).
This option also monkey-patches the access methods in order to intercept emitted 'entry' events and modify the emitted values to instances of the Entry subclass. events-intercept module is used internally for event interception.


Adds events-intercept methods to ZipFile prototype. This option is automatically set to true if subclassEntry option is true.

.patch( yauzl, methodName, wrapper )

Patches an access method. wrapper is called with the original method original and should return the replacement method. This API is identical to shimmer.
const yauzl = require('yauzl');
const yauzlClone = require('yauzlClone');

yauzlClone.patch( yauzl, 'fromRandomAccessReader', function(original) {
  return function(reader, totalSize, options, callback) {
    original(reader, totalSize, options, function(err, zipFile) {
      if (err) return callback(err);
      // Do something to zipFile
      callback(null, zipFile);

This method also does a couple of other useful things:
  1. Arguments passed into the patched method are conformed to standard form
i.e. if no options are provided in the original call, an empty options object is created. There is no need to check for whether the 2nd or 3rd argument is the callback.
  1. Always 4 arguments passed in to the patched method
.open(), .fromFd() and .fromBuffer() take 3 arguments, .fromRandomAccessReader() takes 4.
To allow patching all methods simply using the same wrapper function, the patched method will be called for .open(), .fromFd() and .fromBuffer() with an extra empty argument. original should also be called with an extra argument.
yauzlClone.patch( yauzl, 'open', function(original) {
  return function(path, unused, options, callback) {
    // NB Notice `unused` argument above
    original(reader, null, options, function(err, zipFile) {
      if (err) return callback(err);
      // Do something to zipFile
      callback(null, zipFile);

.patchAll( yauzl, wrapper )

Convenience method to patch all 4 access methods at once.
yauzlClone.patchAll( yauzl, wrapper );

// ...is equivalent to:
yauzlClone.patch( yauzl, 'open', wrapper );
yauzlClone.patch( yauzl, 'fromFd', wrapper );
yauzlClone.patch( yauzl, 'fromBuffer', wrapper );
yauzlClone.patch( yauzl, 'fromRandomAccessReader', wrapper );


Use npm test to run the tests. Use npm run cover to check coverage.


See changelog.md


If you discover a bug, please raise an issue on Github. https://github.com/overlookmotel/yauzl-clone/issues


Pull requests are very welcome. Please:
  • ensure all tests pass before submitting PR
  • add an entry to changelog
  • add tests for new features
  • document new functionality/API additions in README