# yauzl

yet another unzip library for node. For zipping, see
[yazl](https://github.com/thejoshwolfe/yazl).

Design principles:

 * Follow the spec.
   Don't scan for local file headers.
   Read the central directory for file metadata.
   (see [No Streaming Unzip API](#no-streaming-unzip-api)).
 * Don't block the JavaScript thread.
   Use and provide async APIs.
 * Keep memory usage under control.
   Don't attempt to buffer entire files in RAM at once.
 * Never crash (if used properly).
   Don't let malformed zip files bring down client applications who are trying to catch errors.
 * Catch unsafe file names.
   See `validateFileName()`.

## Usage

```js
var yauzl = require("yauzl");

yauzl.open("path/to/file.zip", {lazyEntries: true}, function(err, zipfile) {
  if (err) throw err;
  zipfile.readEntry();
  zipfile.on("entry", function(entry) {
    if (/\/$/.test(entry.fileName)) {
      // Directory file names end with '/'.
      // Note that entries for directories themselves are optional.
      // An entry's fileName implicitly requires its parent directories to exist.
      zipfile.readEntry();
    } else {
      // file entry
      zipfile.openReadStream(entry, function(err, readStream) {
        if (err) throw err;
        readStream.on("end", function() {
          zipfile.readEntry();
        });
        readStream.pipe(somewhere);
      });
    }
  });
});
```

See also `examples/` for more usage examples.

## API

The default for every optional `callback` parameter is:

```js
function defaultCallback(err) {
  if (err) throw err;
}
```

### open(path, [options], [callback])

Calls `fs.open(path, "r")` and reads the `fd` effectively the same as `fromFd()` would.

`options` may be omitted or `null`. The defaults are `{autoClose: true, lazyEntries: false, decodeStrings: true, validateEntrySizes: true, strictFileNames: false}`.

`autoClose` is effectively equivalent to:

```js
zipfile.once("end", function() {
  zipfile.close();
});
```

`lazyEntries` indicates that entries should be read only when `readEntry()` is called.
If `lazyEntries` is `false`, `entry` events will be emitted as fast as possible to allow `pipe()`ing
file data from all entries in parallel.
This is not recommended, as it can lead to out of control memory usage for zip files with many entries.
See [issue #22](https://github.com/thejoshwolfe/yauzl/issues/22).
If `lazyEntries` is `true`, an `entry` or `end` event will be emitted in response to each call to `readEntry()`.
This allows processing of one entry at a time, and will keep memory usage under control for zip files with many entries.

`decodeStrings` is the default and causes yauzl to decode strings with `CP437` or `UTF-8` as required by the spec.
The exact effects of turning this option off are:

* `zipfile.comment`, `entry.fileName`, and `entry.fileComment` will be `Buffer` objects instead of `String`s.
* Any Info-ZIP Unicode Path Extra Field will be ignored. See `extraFields`.
* Automatic file name validation will not be performed. See `validateFileName()`.

`validateEntrySizes` is the default and ensures that an entry's reported uncompressed size matches its actual uncompressed size.
This check happens as early as possible, which is either before emitting each `"entry"` event (for entries with no compression),
or during the `readStream` piping after calling `openReadStream()`.
See `openReadStream()` for more information on defending against zip bomb attacks.

When `strictFileNames` is `false` (the default) and `decodeStrings` is `true`,
all backslash (`\`) characters in each `entry.fileName` are replaced with forward slashes (`/`).
The spec forbids file names with backslashes,
but Microsoft's `System.IO.Compression.ZipFile` class in .NET versions 4.5.0 until 4.6.1
creates non-conformant zipfiles with backslashes in file names.
`strictFileNames` is `false` by default so that clients can read these
non-conformant zipfiles without knowing about this Microsoft-specific bug.
When `strictFileNames` is `true` and `decodeStrings` is `true`,
entries with backslashes in their file names will result in an error. See `validateFileName()`.
When `decodeStrings` is `false`, `strictFileNames` has no effect.

The `callback` is given the arguments `(err, zipfile)`.
An `err` is provided if the End of Central Directory Record cannot be found, or if its metadata appears malformed.
This kind of error usually indicates that this is not a zip file.
Otherwise, `zipfile` is an instance of `ZipFile`.

### fromFd(fd, [options], [callback])

Reads from the fd, which is presumed to be an open .zip file.
Note that random access is required by the zip file specification,
so the fd cannot be an open socket or any other fd that does not support random access.

`options` may be omitted or `null`. The defaults are `{autoClose: false, lazyEntries: false, decodeStrings: true, validateEntrySizes: true, strictFileNames: false}`.

See `open()` for the meaning of the options and callback.

### fromBuffer(buffer, [options], [callback])

Like `fromFd()`, but reads from a RAM buffer instead of an open file.
`buffer` is a `Buffer`.

If a `ZipFile` is acquired from this method,
it will never emit the `close` event,
and calling `close()` is not necessary.

`options` may be omitted or `null`. The defaults are `{lazyEntries: false, decodeStrings: true, validateEntrySizes: true, strictFileNames: false}`.

See `open()` for the meaning of the options and callback.
The `autoClose` option is ignored for this method.

### fromRandomAccessReader(reader, totalSize, [options], [callback])

This method of reading a zip file allows clients to implement their own back-end file system.
For example, a client might translate read calls into network requests.

The `reader` parameter must be of a type that is a subclass of
[RandomAccessReader](#class-randomaccessreader) that implements the required methods.
The `totalSize` is a Number and indicates the total file size of the zip file.

`options` may be omitted or `null`. The defaults are `{autoClose: true, lazyEntries: false, decodeStrings: true, validateEntrySizes: true, strictFileNames: false}`.

See `open()` for the meaning of the options and callback.

### dosDateTimeToDate(date, time)

*Deprecated*. Since yauzl 3.2.0, it is highly recommended to call [`entry.getLastModDate()`](#getlastmoddateoptions)
instead of this function due to enhanced support for reading third-party extra fields.
If you ever have a use case for calling this function directly please
[open an issue against yauzl](https://github.com/thejoshwolfe/yauzl/issues/new)
requesting that this function be properly supported again.

This function only remains exported in order to maintain compatibility with older versions of yauzl.
It will be removed in yauzl 4.0.0 unless someone asks for it to remain supported.

### getFileNameLowLevel(generalPurposeBitFlag, fileNameBuffer, extraFields, strictFileNames)

If you are setting `decodeStrings` to `false`, then this function can be used to decode the file name yourself.
This function is effectively used internally by yauzl to populate the `entry.fileName` field when `decodeStrings` is `true`.

WARNING: This method of getting the file name bypasses the security checks in [`validateFileName()`](#validatefilename-filename).
You should call that function yourself to be sure to guard against malicious file paths.

`generalPurposeBitFlag` can be found on an [`Entry`](#class-entry) or [`LocalFileHeader`](#class-localfileheader).
Only General Purpose Bit 11 is used, and only when an Info-ZIP Unicode Path Extra Field cannot be found in `extraFields`.

`fileNameBuffer` is a `Buffer` representing the file name field of the entry.
This is `entry.fileNameRaw` or `localFileHeader.fileName`.

`extraFields` is the parsed extra fields array from `entry.extraFields` or `parseExtraFields()`.

`strictFileNames` is a boolean, the same as the option of the same name in `open()`.
When `false`, backslash characters (`\`) will be replaced with forward slash characters (`/`).

This function always returns a string, although it may not be a valid file name.
See `validateFileName()`.

### validateFileName(fileName)

Returns `null` or a `String` error message depending on the validity of `fileName`.
If `fileName` starts with `"/"` or `/[A-Za-z]:\//` or if it contains `".."` path segments or `"\\"`,
this function returns an error message appropriate for use like this:

```js
var errorMessage = yauzl.validateFileName(fileName);
if (errorMessage != null) throw new Error(errorMessage);
```

This function is automatically run for each entry, as long as `decodeStrings` is `true`.
See `open()`, `strictFileNames`, and `Event: "entry"` for more information.

### parseExtraFields(extraFieldBuffer)

This function is used internally by yauzl to compute [`entry.extraFields`](#extrafields).
It is exported in case you want to call it on [`localFileHeader.extraField`](#class-localfileheader).

`extraFieldBuffer` is a `Buffer`, such as `localFileHeader.extraField`.
Returns an `Array` with each item in the form `{id: id, data: data}`,
where `id` is a `Number` and `data` is a `Buffer`.
Throws an `Error` if the data encodes an item with a size that exceeds the bounds of the buffer.

You may want to surround calls to this function with `try { ... } catch (err) { ... }` to handle the error.

### Class: ZipFile

The constructor for the class is not part of the public API.
Use `open()`, `fromFd()`, `fromBuffer()`, or `fromRandomAccessReader()` instead.

#### Event: "entry"

Callback gets `(entry)`, which is an `Entry`.
See `open()` and `readEntry()` for when this event is emitted.

If `decodeStrings` is `true`, entries emitted via this event have already passed file name validation.
See `validateFileName()` and `open()` for more information.

If `validateEntrySizes` is `true` and this entry's `compressionMethod` is `0` (stored without compression),
this entry has already passed entry size validation.
See `open()` for more information.

#### Event: "end"

Emitted after the last `entry` event has been emitted.
See `open()` and `readEntry()` for more info on when this event is emitted.

#### Event: "close"

Emitted after the fd is actually closed.
This is after calling `close()` (or after the `end` event when `autoClose` is `true`),
and after all stream pipelines created from `openReadStream()` have finished reading data from the fd.

If this `ZipFile` was acquired from `fromRandomAccessReader()`,
the "fd" in the previous paragraph refers to the `RandomAccessReader` implemented by the client.

If this `ZipFile` was acquired from `fromBuffer()`, this event is never emitted.

#### Event: "error"

Emitted in the case of errors with reading the zip file.
(Note that other errors can be emitted from the streams created from `openReadStream()` as well.)
After this event has been emitted, no further `entry`, `end`, or `error` events will be emitted,
but the `close` event may still be emitted.

#### readEntry()

Causes this `ZipFile` to emit an `entry` or `end` event (or an `error` event).
This method must only be called when this `ZipFile` was created with the `lazyEntries` option set to `true` (see `open()`).
When this `ZipFile` was created with the `lazyEntries` option set to `true`,
`entry` and `end` events are only ever emitted in response to this method call.

The event that is emitted in response to this method will not be emitted until after this method has returned,
so it is safe to call this method before attaching event listeners.

After calling this method, calling this method again before the response event has been emitted will cause undefined behavior.
Calling this method after the `end` event has been emitted will cause undefined behavior.
Calling this method after calling `close()` will cause undefined behavior.

#### openReadStream(entry, [options], callback)

`entry` must be an `Entry` object from this `ZipFile`.
`callback` gets `(err, readStream)`, where `readStream` is a `Readable Stream` that provides the file data for this entry.
If this zipfile is already closed (see `close()`), the `callback` will receive an `err`.

`options` may be omitted or `null`, and has the following defaults:

```js
{
  decodeFileData: true,
  start: 0,                  // actually the default is null, see below
  end: entry.compressedSize, // actually the default is null, see below
  decompress: null, // deprecated
  decrypt: null,    // deprecated
}
```

When `decodeFileData` is `true` (or `null` or omitted), yauzl will attempt to decode the file data using a zlib inflate transform when appropriate.
Setting `decodeFileData` to `false` will provide the bytes of the entry's contents exactly as-is in the archive.
When `compressionMethod` is `0` (stored with no compression) and the entry is not encrypted, `decodeFileData` has no effect.

If `canDecodeFileData()` returns `false`, then `decodeFileData` must be set to `false`, or else `callback` will receive an error.
It is up to the caller to make sense of any file data with encryption and/or an uncommon compression method.

The `start` (inclusive) and `end` (exclusive) options are byte offsets into this entry's file data,
and can be used to obtain part of an entry's file data rather than the whole thing.
When specifying `start` and/or `end`, it is recommended to unconditionally set `decodeFileData` to `false`.
If either `start` and/or `end` are specified and non-`null`, then either `decodeFileData` must be set to `false`,
or both `isEncrypted()` must return `false` and `compressionMethod` must be `0`.
Specifying `{start: 0, end: entry.compressedSize}` will result in the complete file.

For compatibility with versions of yauzl prior to 3.3.x, `start` and `end` can also be used
when the deprecated `decompress` and `decrypt` options are used appropriately.
This is no longer documented, but an archive of the documentation can be found here:
https://github.com/thejoshwolfe/yauzl/blob/c4695215b05c6adffda613b9051a2a85429b33fe/README.md#openreadstreamentry-options-callback

It's possible for the `readStream` provided to the `callback` to emit errors for several reasons.
For example, if zlib cannot decompress the data, the zlib error will be emitted from the `readStream`.
Two more error cases (when `validateEntrySizes` is `true`) are if the decompressed data has too many
or too few actual bytes compared to the reported byte count from the entry's `uncompressedSize` field.
yauzl notices this false information and emits an error from the `readStream`
after some number of bytes have already been piped through the stream.

This check allows clients to trust the `uncompressedSize` field in `Entry` objects.
Guarding against [zip bomb](http://en.wikipedia.org/wiki/Zip_bomb) attacks can be accomplished by
doing some heuristic checks on the size metadata and then watching out for the above errors.
Such heuristics are outside the scope of this library,
but enforcing the `uncompressedSize` is implemented here as a security feature.

It is possible to destroy the `readStream` before it has piped all of its data.
To do this, call `readStream.destroy()`.
You must `unpipe()` the `readStream` from any destination before calling `readStream.destroy()`.
If this zipfile was created using `fromRandomAccessReader()`, the `RandomAccessReader` implementation
must provide readable streams that implement a `._destroy()` method according to
https://nodejs.org/api/stream.html#writable_destroyerr-callback (see `randomAccessReader._readStreamForRange()`)
in order for calls to `readStream.destroy()` to work in this context.

#### readLocalFileHeader(entry, [options], callback)

This is a low-level function you probably don't need to call.
The intended use case is either preparing to call `openReadStreamLowLevel()`
or simply examining the content of the local file header out of curiosity or for debugging zip file structure issues.

`entry` is an entry obtained from `Event: "entry"`.
An `entry` in this library is a file's metadata from a Central Directory Header,
and this function gives the corresponding redundant data in a Local File Header.

`options` may be omitted or `null`, and has the following defaults:

```js
{
  minimal: false,
}
```

If `minimal` is `false` (or omitted or `null`), the callback receives a full [`LocalFileHeader`](#class-localfileheader).
If `minimal` is `true`, the callback receives an object with a single property and no prototype `{fileDataStart: fileDataStart}`.
For typical zipfile reading usecases, this field is the only one you need,
and yauzl internally effectively uses the `{minimal: true}` option as part of `openReadStream()`.

The `callback` receives `(err, localFileHeaderOrAnObjectWithJustOneFieldDependingOnTheMinimalOption)`,
where the type of the second parameter is described in the above discussion of the `minimal` option.

#### openReadStreamLowLevel(fileDataStart, compressedSize, relativeStart, relativeEnd, decompress, uncompressedSize, callback)

This is a low-level function available for advanced use cases. You probably want `openReadStream()` instead.

The intended use case for this function is calling `readEntry()` and `readLocalFileHeader()` with `{minimal: true}` first,
and then opening the read stream at a later time, possibly after closing and reopening the entire zipfile,
possibly even in a different process.
The parameters are all integers and booleans, which are friendly to serialization.

* `fileDataStart` - from `localFileHeader.fileDataStart`
* `compressedSize` - from `entry.compressedSize`
* `relativeStart` - the resolved value of `options.start` from `openReadStream()`. Must be a non-negative integer, not `null`. Typically `0` to start at the beginning of the data.
* `relativeEnd` - the resolved value of `options.end` from `openReadStream()`. Must be a non-negative integer, not `null`. Typically `entry.compressedSize` to include all the data.
* `decompress` - boolean indicating whether the data should be piped through a zlib inflate stream.
* `uncompressedSize` - from `entry.uncompressedSize`. Only used when `validateEntrySizes` is `true`. If `validateEntrySizes` is `false`, this value is ignored, but must still be present, not omitted, in the arguments; you have to give it some value, even if it's `null`.
* `callback` - receives `(err, readStream)`, the same as for `openReadStream()`

This low-level function does not read any metadata from the underlying storage before opening the read stream.
This is both a performance feature and a safety hazard.
None of the integer parameters are bounds checked.
None of the validation from `openReadStream()` with respect to compression and encryption is done here either.
Only the bounds checks from `validateEntrySizes` are done, because that is part of processing the stream data.

#### close()

Causes all future calls to `openReadStream()` to fail,
and closes the fd, if any, after all streams created by `openReadStream()` have emitted their `end` events.

If the `autoClose` option is set to `true` (see `open()`),
this function will be called automatically effectively in response to this object's `end` event.

If the `lazyEntries` option is set to `false` (see `open()`) and this object's `end` event has not been emitted yet,
this function causes undefined behavior.
If the `lazyEntries` option is set to `true`,
you can call this function instead of calling `readEntry()` to abort reading the entries of a zipfile.

It is safe to call this function multiple times; after the first call, successive calls have no effect.
This includes situations where the `autoClose` option effectively calls this function for you.

If `close()` is never called, then the zipfile is "kept open".
For zipfiles created with `fromFd()`, this will leave the `fd` open, which may be desirable.
For zipfiles created with `open()`, this will leave the underlying `fd` open, thereby "leaking" it, which is probably undesirable.
For zipfiles created with `fromRandomAccessReader()`, the reader's `close()` method will never be called.
For zipfiles created with `fromBuffer()`, the `close()` function has no effect on resource usage.

Regardless of how this `ZipFile` was created, there are no resources other than those listed above that require cleanup from this function.
This means it may be desirable to never call `close()` in some usecases.

#### isOpen

`Boolean`. `true` until `close()` is called; then it's `false`.

#### entryCount

`Number`. Total number of central directory records.

#### comment

`String`. Always decoded with `CP437` per the spec.

If `decodeStrings` is `false` (see `open()`), this field is the undecoded `Buffer` instead of a decoded `String`.

### Class: Entry

Objects of this class represent Central Directory Records.
Refer to the zipfile specification for more details about these fields.

These fields are of type `Number`:

 * `versionMadeBy`
 * `versionNeededToExtract`
 * `generalPurposeBitFlag`
 * `compressionMethod`
 * `lastModFileTime` (MS-DOS format, see [`getLastModDate()`](#getlastmoddateoptions))
 * `lastModFileDate` (MS-DOS format, see [`getLastModDate()`](#getlastmoddateoptions))
 * `crc32`
 * `compressedSize`
 * `uncompressedSize`
 * `fileNameLength` (in bytes)
 * `extraFieldLength` (in bytes)
 * `fileCommentLength` (in bytes)
 * `internalFileAttributes`
 * `externalFileAttributes`
 * `relativeOffsetOfLocalHeader`

These fields are of type `Buffer`, and represent variable-length bytes before being processed:
 * `fileNameRaw`
 * `extraFieldRaw`
 * `fileCommentRaw`

There are additional fields described below: `fileName`, `extraFields`, `fileComment`.
These are the processed versions of the `*Raw` fields listed above. See their own sections below.
(Note the inconsistency in pluralization of "field" vs "fields" in `extraField`, `extraFields`, and `extraFieldRaw`.
Sorry about that.)

The `new Entry()` constructor is available for clients to call, but it's usually not useful.
The constructor takes no parameters and does nothing; no fields will exist.

#### fileName

`String`.
Following the spec, the bytes for the file name are decoded with
`UTF-8` if `generalPurposeBitFlag & 0x800`, otherwise with `CP437`.
Alternatively, this field may be populated from the Info-ZIP Unicode Path Extra Field
(see `extraFields`).

This field is automatically validated by `validateFileName()` before yauzl emits an "entry" event.
If this field would contain unsafe characters, yauzl emits an error instead of an entry.

If `decodeStrings` is `false` (see `open()`), this field is the undecoded `Buffer` instead of a decoded `String`.
Therefore, `generalPurposeBitFlag` and any Info-ZIP Unicode Path Extra Field are ignored.
Furthermore, no automatic file name validation is performed for this file name.

#### extraFields

`Array` with each item in the form `{id: id, data: data}`,
where `id` is a `Number` and `data` is a `Buffer`.

This library looks for and reads the ZIP64 Extended Information Extra Field (0x0001)
in order to support ZIP64 format zip files.

This library also looks for and reads the Info-ZIP Unicode Path Extra Field (0x7075)
in order to support some zipfiles that use it instead of General Purpose Bit 11
to convey `UTF-8` file names.
When the field is identified and verified to be reliable (see the zipfile spec),
the file name in this field is stored in the `fileName` property,
and the file name in the central directory record for this entry is ignored.
Note that when `decodeStrings` is false, all Info-ZIP Unicode Path Extra Fields are ignored.

See also [`getLastModDate()`](#getlastmoddateoptions) for additional extra fields that are recognized by this library.

#### fileComment

`String` decoded with the charset indicated by `generalPurposeBitFlag & 0x800` as with the `fileName`.
(The Info-ZIP Unicode Path Extra Field has no effect on the charset used for this field.)

If `decodeStrings` is `false` (see `open()`), this field is the undecoded `Buffer` instead of a decoded `String`.

Prior to yauzl version 2.7.0, this field was erroneously documented as `comment` instead of `fileComment`.
For compatibility with any code that uses the field name `comment`,
yauzl creates an alias field named `comment` which is identical to `fileComment`.

#### getLastModDate([options])

Returns the modification time of the file as a JavaScript `Date` object.
The timezone situation is a mess due to both ZIP issues and JavaScript issues; read on to learn more.

Due to the zip file specification having lackluster support for specifying timestamps natively,
there are several third-party extensions that add better support in the `extraFields`.
yauzl supports these encodings:

1. Info-ZIP "universal timestamp" extended field (`0x5455` aka `"UT"`): signed 32-bit seconds since `1970-01-01 00:00:00Z`, which supports the years 1901-2038 (partially inclusive) with 1-second precision. The value is timezone agnostic, i.e. always UTC.
2. NTFS extended field (`0x000a`): 64-bit signed 100-nanoseconds since `1601-01-01 00:00:00Z`, which supports the approximate years 20,000BCE-20,000CE with precision rounded to 1-millisecond (due to the JavaScript `Date` type). The value is timezone agnostic, i.e. always UTC.
3. DOS `lastModFileDate` and `lastModFileTime`: supports the years 1980-2108 (inclusive) with 2-second precision. Timezone is interpreted either as the local timezone or UTC depending on the `timezone` option documented below.

If both the Info-ZIP "universal timestamp" and NTFS extended fields are found, yauzl uses one of them, but which one is unspecified.
If neither are found, yauzl falls back to the built-in DOS `lastModFileDate` and `lastModFileTime`.
Every possible bit pattern of every encoding can be represented by a JavaScript `Date` object,
meaning this function cannot fail (barring parameter validation), and will never return an `Invalid Date` object.

`options` may be omitted or `null`, and has the following defaults:

```js
{
  timezone: "local", // or "UTC"
  forceDosFormat: false,
}
```

Set `forceDosFormat` to `true` (and do not set `timezone`) to enable pre-yauzl 3.2.0 behavior
where the Info-ZIP "universal timestamp" and NTFS extended fields are ignored.

The `timezone` option is only used in the DOS fallback.
If `timezone` is `"local"` (or omitted or `null`), the `lastModFileDate` and `lastModFileTime` are interpreted in the system's current timezone (using `new Date(year, ...)`).
If `timezone` is `"UTC"`, the interpretation is in UTC+00:00 (using `new Date(Date.UTC(year, ...))`).

The JavaScript `Date` object, has several inherent limitations surrounding timezones.
There is an ECMAScript proposal to add better timezone support to JavaScript called the `Temporal` API.
Last I checked, it was at stage 4. https://github.com/tc39/proposal-temporal
Once that new API is available and stable, better timezone handling should be possible here somehow.
If you notice that the new API has become widely available, please open a feature request against this library to add support for it.

#### canDecodeFileData()

Returns `true` if and only if the metadata for this entry specifies an encoding that yauzl can automatically decode as part of `openReadStream()`.
This considers compression method and encryption.
Only compression methods `0` (stored with no compression) and `8` (deflated) are supported,
and neither traditional encryption nor strong encryption is supported.

See also `openReadStream()`.

#### isEncrypted()

Note that "Strong Encryption" is not supported, and will result in an `"error"` event emitted from the `ZipFile`.

This method is effectively implemented as `return (this.generalPurposeBitFlag & 0x1) !== 0`.
yauzl provides no functionality to decrypt file data.

#### isCompressed()

*DEPRECATED*: use `canDecodeFileData()` instead, and/or manually check `compressionMethod`.
This method is effectively implemented as `return this.compressionMethod === 8`,
which misleadingly returns `false` for entries that are compressed using a compression method other than `8`.
This implementation is maintained for backward compatibility with yauzl versions prior to 3.3.x.

### Class: LocalFileHeader

This is a trivial class that has no methods and only the following properties.
The constructor is available to call, but it doesn't do anything.
See `readLocalFileHeader()`.

See the zipfile spec for what these fields mean.

 * `fileDataStart` - `Number`: inferred from `fileNameLength`, `extraFieldLength`, and this struct's position in the zipfile.
 * `versionNeededToExtract` - `Number`
 * `generalPurposeBitFlag` - `Number`
 * `compressionMethod` - `Number`
 * `lastModFileTime` - `Number`
 * `lastModFileDate` - `Number`
 * `crc32` - `Number`
 * `compressedSize` - `Number`
 * `uncompressedSize` - `Number`
 * `fileNameLength` - `Number`
 * `extraFieldLength` - `Number`
 * `fileName` - `Buffer`
 * `extraField` - `Buffer`

Note that unlike `Class: Entry`, the `fileName` and `extraField` are completely unprocessed.
This notably lacks Unicode and ZIP64 handling as well as any kind of safety validation on the file name.
See also [`parseExtraFields()`](#parseextrafields-extrafieldbuffer).

Also note that if your object is missing some of these fields,
make sure to read the docs on the `minimal` option in `readLocalFileHeader()`.

### Class: RandomAccessReader

This class is meant to be subclassed by clients and instantiated for the `fromRandomAccessReader()` function.

An example implementation can be found in `test/test.js`.

#### randomAccessReader._readStreamForRange(start, end)

Subclasses *must* implement this method.

`start` and `end` are Numbers and indicate byte offsets from the start of the file.
`end` is exclusive, so `_readStreamForRange(0x1000, 0x2000)` would indicate to read `0x1000` bytes.
`end - start` will always be at least `1`.

This method should return a readable stream which will be `pipe()`ed into another stream.
It is expected that the readable stream will provide data in several chunks if necessary.
If the readable stream provides too many or too few bytes, an error will be emitted.
(Note that `validateEntrySizes` has no effect on this check,
because this is a low-level API that should behave correctly regardless of the contents of the file.)
Any errors emitted on the readable stream will be handled and re-emitted on the client-visible stream
(returned from `zipfile.openReadStream()`) or provided as the `err` argument to the appropriate callback
(for example, for `fromRandomAccessReader()`).

If you call `readStream.destroy()` on streams you get from `openReadStream()`,
the returned stream *must* implement a method `._destroy()` according to https://nodejs.org/api/stream.html#writable_destroyerr-callback .
If you never call `readStream.destroy()`, then streams returned from this method do not need to implement a method `._destroy()`.
`._destroy()` should abort any streaming that is in progress and clean up any associated resources.
`._destroy()` will only be called after the stream has been `unpipe()`d from its destination.

Note that the stream returned from this method might not be the same object that is provided by `openReadStream()`.
The stream returned from this method might be `pipe()`d through one or more filter streams (for example, a zlib inflate stream).

#### randomAccessReader.read(buffer, offset, length, position, callback)

Subclasses may implement this method.
The default implementation uses `createReadStream()` to fill the `buffer`.

This method should behave like `fs.read()`.

#### randomAccessReader.close(callback)

Subclasses may implement this method.
The default implementation is effectively `setImmediate(callback);`.

`callback` takes parameters `(err)`.

This method is called once the all streams returned from `_readStreamForRange()` have ended,
and no more `_readStreamForRange()` or `read()` requests will be issued to this object.

## How to Avoid Crashing

When a malformed zipfile is encountered, the default behavior is to crash (throw an exception).
If you want to handle errors more gracefully than this,
be sure to do the following:

 * Provide `callback` parameters where they are allowed, and check the `err` parameter.
 * Attach a listener for the `error` event on any `ZipFile` object you get from `open()`, `fromFd()`, `fromBuffer()`, or `fromRandomAccessReader()`.
 * Attach a listener for the `error` event on any stream you get from `openReadStream()`.

Minor version updates to yauzl will not add any additional requirements to this list.

## Limitations

The automated tests for this project run on node versions 12 and up. Older versions of node are not supported.

### Files corrupted by the Mac Archive Utility are not my problem

For a lengthy discussion, see [issue #69](https://github.com/thejoshwolfe/yauzl/issues/69).
In summary, the Mac Archive Utility is buggy when creating large zip files,
and this library does not make any effort to work around the bugs.
This library will attempt to interpret the zip file data at face value,
which may result in errors, or even silently incomplete data.
If this bothers you, that's good! Please complain to Apple. :)
I have accepted that this library will simply not support that nonsense.

### No Streaming Unzip API

Due to the design of the .zip file format, it's impossible to interpret a .zip file from start to finish
(such as from a readable stream) without sacrificing correctness.
The Central Directory, which is the authority on the contents of the .zip file, is at the end of a .zip file, not the beginning.
A streaming API would need to either buffer the entire .zip file to get to the Central Directory before interpreting anything
(defeating the purpose of a streaming interface), or rely on the Local File Headers which are interspersed through the .zip file.
However, the Local File Headers are explicitly denounced in the spec as being unreliable copies of the Central Directory,
so trusting them would be a violation of the spec.

Any library that offers a streaming unzip API must make one of the above two compromises,
which makes the library either dishonest or nonconformant (usually the latter).
This library insists on correctness and adherence to the spec, and so does not offer a streaming API.

Here is a way to create a spec-conformant .zip file using the `zip` command line program (Info-ZIP)
available in most unix-like environments, that is (nearly) impossible to parse correctly with a streaming parser:

```
$ echo -ne '\x50\x4b\x07\x08\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00' > file.txt
$ zip -q0 - file.txt | cat > out.zip
```

This .zip file contains a single file entry that uses General Purpose Bit 3,
which means the Local File Header doesn't know the size of the file.
Any streaming parser that encounters this situation will either immediately fail,
or attempt to search for the Data Descriptor after the file's contents.
The file's contents is a sequence of 16-bytes crafted to exactly mimic a valid Data Descriptor for an empty file,
which will fool any parser that gets this far into thinking that the file is empty rather than containing 16-bytes.
What follows the file's real contents is the file's real Data Descriptor,
which will likely cause some kind of signature mismatch error for a streaming parser (if one hasn't occurred already).

By using General Purpose Bit 3 (and compression method 0),
it's possible to create arbitrarily ambiguous .zip files that
distract parsers with file contents that contain apparently valid .zip file metadata.

### Limited ZIP64 Support

For ZIP64, only zip files smaller than `8PiB` are supported,
not the full `16EiB` range that a 64-bit integer should be able to index.
This is due to the JavaScript Number type being an IEEE 754 double precision float.

The Node.js `fs` module probably has this same limitation.

### ZIP64 Extensible Data Sector Is Ignored

The spec does not allow zip file creators to put arbitrary data here,
but rather reserves its use for PKWARE and mentions something about Z390.
This doesn't seem useful to expose in this library, so it is ignored.

### No Multi-Disk Archive Support

This library does not support multi-disk zip files.
The multi-disk fields in the zipfile spec were intended for a zip file to span multiple floppy disks,
which probably never happens now.
If the "number of this disk" field in the End of Central Directory Record is not `0`,
the `open()`, `fromFd()`, `fromBuffer()`, or `fromRandomAccessReader()` `callback` will receive an `err`.
By extension the following zip file fields are ignored by this library and not provided to clients:

 * Disk where central directory starts
 * Number of central directory records on this disk
 * Disk number where file starts

### Limited Encryption Handling

You can detect when a file entry is encrypted with "Traditional Encryption" via `generalPurposeBitFlag`,
but yauzl will not help you decrypt it.
See the `openReadStream()` option `decodeFileData`.

If a zip file contains file entries encrypted with "Strong Encryption", yauzl emits an error.

If the central directory is encrypted or compressed, yauzl emits an error.

### Local File Headers Are Ignored

Many unzip libraries mistakenly read the Local File Header data in zip files.
This data is officially defined to be redundant with the Central Directory information,
and is not to be trusted.
Aside from checking the signature, yauzl ignores the content of the Local File Header.

### No CRC-32 Checking

This library provides the `crc32` field of `Entry` objects read from the Central Directory.
However, this field is not used for anything in this library.

### versionNeededToExtract Is Ignored

The field `versionNeededToExtract` is ignored,
because this library doesn't support the complete zip file spec at any version,

### No Support For Obscure Compression Methods

Regarding the `compressionMethod` field of `Entry` objects,
only method `0` (stored with no compression)
and method `8` (deflated) are supported.
Any of the other 15 official methods will cause the `openReadStream()` `callback` to receive an `err`.

### Data Descriptors Are Ignored

There may or may not be Data Descriptor sections in a zip file.
This library provides no support for finding or interpreting them.

### Archive Extra Data Record Is Ignored

There may or may not be an Archive Extra Data Record section in a zip file.
This library provides no support for finding or interpreting it.

### No Language Encoding Flag Support

Zip files officially support charset encodings other than CP437 and UTF-8,
but the zip file spec does not specify how it works.
This library makes no attempt to interpret the Language Encoding Flag.

### How Ambiguities Are Handled

The zip file specification has several ambiguities inherent in its design. Yikes!

* The `.ZIP file comment` must not contain the `end of central dir signature` bytes `50 4b 05 06`. This corresponds to the text `"PK☺☻"` in CP437. While this is allowed by the specification, yauzl will hopefully reject this situation with an "Invalid comment length" error. However, in some situations unpredictable incorrect behavior will ensue, which will probably manifest in either an invalid signature error or some kind of bounds check error, such as "Unexpected EOF".
* In non-ZIP64 files, the last central directory header must not have the bytes `50 4b 06 07` (`"PK♠•"` in CP437) exactly 20 bytes from its end, which might be in the `file name`, the `extra field`, or the `file comment`. The presence of these bytes indicates that this is a ZIP64 file.

## Change History

 * 3.3.2
   * Vendor and simplify `buffer-crc` dependency and prefer `zlib.crc32()` when available. [issue #172](https://github.com/thejoshwolfe/yauzl/issues/172) [pull #173](https://github.com/thejoshwolfe/yauzl/pull/173)
   * Fixed typo in error handling for obscure IO errors. Raised in [issue #174](https://github.com/thejoshwolfe/yauzl/issues/174).
 * 3.3.1
   * Fixed bugs related to interrupting streams with `destroy()` and with async iteration on read streams. [issue #169](https://github.com/thejoshwolfe/yauzl/issues/169) [pull #170](https://github.com/thejoshwolfe/yauzl/pull/170)
 * 3.3.0
   * Added `entry.canDecodeFileData()` and option `decodeFileData` for `entry.openReadStream()`, and marked as deprecated `isCompressed()` and options `decompress` and `decrypt`. [issue #80](https://github.com/thejoshwolfe/yauzl/issues/80) [pull #81](https://github.com/thejoshwolfe/yauzl/pull/81) [pull #82](https://github.com/thejoshwolfe/yauzl/pull/82) [issue #166](https://github.com/thejoshwolfe/yauzl/issues/166)
 * 3.2.1
   * Fix crash when reading certain corrupted NTFS timestamp extra fields. Thanks to CodeAnt AI Code Reviewer ( https://www.codeant.ai/ai-code-review ) for finding the bug.
 * 3.2.0
   * Added support for reading third-party extensions for timestamps: Info-ZIP "universal timestamp" extra field and NTFS extra field. [pull #160](https://github.com/thejoshwolfe/yauzl/pull/160)
   * `entry.getLastModDate()` takes options `forceDosFormat` to revert the above change, and `timezone` to allow UTC interpretation of DOS timestamps.
   * Documented `dosDateTimeToDate()` as now deprecated.
 * 3.1.3
   * Fixed a crash when using `fromBuffer()` to read corrupt zip files that specify out of bounds file offsets. [issue #156](https://github.com/thejoshwolfe/yauzl/pull/156)
   * Enahnced the test suite to run the error tests through `fromBuffer()` and `fromRandomAccessReader()` in addition to `open()`, which would have caught the above.
 * 3.1.2
   * Fixed handling non-64 bit entries (similar to the version 3.1.1 fix) that actually have exactly 0xffffffff values in the fields. This fixes erroneous "expected zip64 extended information extra field" errors. [issue #109](https://github.com/thejoshwolfe/yauzl/pull/109)
 * 3.1.1
   * Fixed handling non-64 bit files that actually have exactly 0xffff or 0xffffffff values in End of Central Directory Record. This fixes erroneous "invalid zip64 end of central directory locator signature" errors. [issue #108](https://github.com/thejoshwolfe/yauzl/pull/108)
   * Fixed handling of 64-bit zip files that put 0xffff or 0xffffffff in every field overridden in the Zip64 end of central directory record even if the value would have fit without overflow. In particular, this fixes an incorrect "multi-disk zip files are not supported" error. [pull #118](https://github.com/thejoshwolfe/yauzl/pull/118)
 * 3.1.0
   * Added `readLocalFileHeader()` and `Class: LocalFileHeader`.
   * Added `openReadStreamLowLevel()`.
   * Added `getFileNameLowLevel()` and `parseExtraFields()`.
     Added fields to `Class: Entry`: `fileNameRaw`, `extraFieldRaw`, `fileCommentRaw`.
   * Added `examples/compareCentralAndLocalHeaders.js` that demonstrate many of these low level APIs.
   * Noted dropped support of node versions before 12 in the `"engines"` field of `package.json`.
   * Fixed a crash when calling `openReadStream()` with an explicitly `null` options parameter (as opposed to omitted).
 * 3.0.0
   * BREAKING CHANGE: implementations of [RandomAccessReader](#class-randomaccessreader) that implement a `destroy` method must instead implement `_destroy` in accordance with the node standard https://nodejs.org/api/stream.html#writable_destroyerr-callback (note the error and callback parameters). If you continue to override `destory` instead, some error handling may be subtly broken. Additionally, this is required for async iterators to work correctly in some versions of node. [issue #110](https://github.com/thejoshwolfe/yauzl/issues/110)
   * BREAKING CHANGE: Drop support for node versions older than 12.
   * Maintenance: Fix buffer deprecation warning by bundling `fd-slicer` with a 1-line change, rather than depending on it. [issue #114](https://github.com/thejoshwolfe/yauzl/issues/114)
   * Maintenance: Upgrade `bl` dependency; add `package-lock.json`; drop deprecated istanbul dependency. This resolves all security warnings for this project. [pull #125](https://github.com/thejoshwolfe/yauzl/pull/125)
   * Maintenance: Replace broken Travis CI with GitHub Actions. [pull #148](https://github.com/thejoshwolfe/yauzl/pull/148)
   * Maintenance: Fixed a long-standing issue in the test suite where a premature exit would incorrectly signal success.
   * Officially gave up on supporting Mac Archive Utility corruption in order to rescue my motivation for this project. [issue #69](https://github.com/thejoshwolfe/yauzl/issues/69)

 * 2.10.0
   * Added support for non-conformant zipfiles created by Microsoft, and added option `strictFileNames` to disable the workaround. [issue #66](https://github.com/thejoshwolfe/yauzl/issues/66), [issue #88](https://github.com/thejoshwolfe/yauzl/issues/88)
 * 2.9.2
   * Removed `tools/hexdump-zip.js` and `tools/hex2bin.js`. Those tools are now located here: [thejoshwolfe/hexdump-zip](https://github.com/thejoshwolfe/hexdump-zip) and [thejoshwolfe/hex2bin](https://github.com/thejoshwolfe/hex2bin)
   * Worked around performance problem with zlib when using `fromBuffer()` and `readStream.destroy()` for large compressed files. [issue #87](https://github.com/thejoshwolfe/yauzl/issues/87)
 * 2.9.1
   * Removed `console.log()` accidentally introduced in 2.9.0. [issue #64](https://github.com/thejoshwolfe/yauzl/issues/64)
 * 2.9.0
   * Throw an exception if `readEntry()` is called without `lazyEntries:true`. Previously this caused undefined behavior. [issue #63](https://github.com/thejoshwolfe/yauzl/issues/63)
 * 2.8.0
   * Added option `validateEntrySizes`. [issue #53](https://github.com/thejoshwolfe/yauzl/issues/53)
   * Added `examples/promises.js`
   * Added ability to read raw file data via `decompress` and `decrypt` options. [issue #11](https://github.com/thejoshwolfe/yauzl/issues/11), [issue #38](https://github.com/thejoshwolfe/yauzl/issues/38), [pull #39](https://github.com/thejoshwolfe/yauzl/pull/39)
   * Added `start` and `end` options to `openReadStream()`. [issue #38](https://github.com/thejoshwolfe/yauzl/issues/38)
 * 2.7.0
   * Added option `decodeStrings`. [issue #42](https://github.com/thejoshwolfe/yauzl/issues/42)
   * Fixed documentation for `entry.fileComment` and added compatibility alias. [issue #47](https://github.com/thejoshwolfe/yauzl/issues/47)
 * 2.6.0
   * Support Info-ZIP Unicode Path Extra Field, used by WinRAR for Chinese file names. [issue #33](https://github.com/thejoshwolfe/yauzl/issues/33)
 * 2.5.0
   * Ignore malformed Extra Field that is common in Android .apk files. [issue #31](https://github.com/thejoshwolfe/yauzl/issues/31)
 * 2.4.3
   * Fix crash when parsing malformed Extra Field buffers. [issue #31](https://github.com/thejoshwolfe/yauzl/issues/31)
 * 2.4.2
   * Remove .npmignore and .travis.yml from npm package.
 * 2.4.1
   * Fix error handling.
 * 2.4.0
   * Add ZIP64 support. [issue #6](https://github.com/thejoshwolfe/yauzl/issues/6)
   * Add `lazyEntries` option. [issue #22](https://github.com/thejoshwolfe/yauzl/issues/22)
   * Add `readStream.destroy()` method. [issue #26](https://github.com/thejoshwolfe/yauzl/issues/26)
   * Add `fromRandomAccessReader()`. [issue #14](https://github.com/thejoshwolfe/yauzl/issues/14)
   * Add `examples/unzip.js`.
 * 2.3.1
   * Documentation updates.
 * 2.3.0
   * Check that `uncompressedSize` is correct, or else emit an error. [issue #13](https://github.com/thejoshwolfe/yauzl/issues/13)
 * 2.2.1
   * Update dependencies.
 * 2.2.0
   * Update dependencies.
 * 2.1.0
   * Remove dependency on `iconv`.
 * 2.0.3
   * Fix crash when trying to read a 0-byte file.
 * 2.0.2
   * Fix event behavior after errors.
 * 2.0.1
   * Fix bug with using `iconv`.
 * 2.0.0
   * Initial release.

## Development

One of the trickiest things in development is crafting test cases located in `test/{success,failure}/`.
These are zip files that have been specifically generated or design to test certain conditions in this library.
I recommend using [hexdump-zip](https://github.com/thejoshwolfe/hexdump-zip) to examine the structure of a zipfile.

For making new error cases, I typically start by copying `test/success/linux-info-zip.zip`, and then editing a few bytes with a hex editor.
