yauzl

What is yauzl?

The yauzl npm package is a library for unzipping ZIP files in Node.js. It provides a low-level interface for reading and extracting ZIP file contents, allowing developers to handle large files and read entries without decompressing the entire file to disk.

What are yauzl's main functionalities?

Opening a ZIP file

This code demonstrates how to open a ZIP file for reading. The 'lazyEntries' option allows reading entries one at a time.

const yauzl = require('yauzl');
yauzl.open('path/to/file.zip', {lazyEntries: true}, function(err, zipfile) {
  if (err) throw err;
  zipfile.readEntry();
});

Reading entries from a ZIP file

This code shows how to read entries from an open ZIP file. It handles directories and files differently, reading the next entry after each file is processed.

zipfile.on('entry', function(entry) {
  if (/\/.test(entry.fileName)) {
    // Directory file names end with '/'.
    zipfile.readEntry();
  } else {
    // File entry
    zipfile.openReadStream(entry, function(err, readStream) {
      if (err) throw err;
      // Handle the read stream, possibly piping it somewhere
      readStream.on('end', function() {
        zipfile.readEntry();
      });
    });
  }
});

Extracting a file entry

This code snippet demonstrates how to extract a file entry from a ZIP file. It creates a read stream for the entry and pipes it to a write stream.

zipfile.openReadStream(entry, function(err, readStream) {
  if (err) throw err;
  // Create a write stream to extract the file to
  var writeStream = fs.createWriteStream('output/path');
  readStream.pipe(writeStream);
});

Other packages similar to yauzl

adm-zip

adm-zip is a JavaScript implementation for zip data compression for NodeJS. It provides functionalities to read and write zip files, similar to yauzl, but also includes zip file creation which yauzl does not.

jszip

JSZip is a library for creating, reading, and editing .zip files with JavaScript, with a lovely and simple API. It works in both Node.js and browser environments, whereas yauzl is designed specifically for Node.js.

unzipper

unzipper is a decompression library for Node that supports streaming, promises, and piping for zip files. It is an alternative to yauzl with a slightly different API and additional features like parsing zip file contents without extraction.

README

yauzl

yet another unzip library for node.

Design principles:

• Follow the spec. Don't scan for local file headers. Read the central directory for file metadata.
• 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.

Usage

var yauzl = require("yauzl");
var fs = require('fs');

yauzl.open("path/to/file.zip", function(err, zipfile) {
  if (err) throw err;
  zipfile.readEntries(function(err, entries) {
    if (err) throw err;
    entries.forEach(function(entry) {
      zipfile.openReadStream(entry, function(err, readStream) {
        if (err) throw err;
        readStream.pipe(fs.createWriteStream(entry.fileName));
      });
    });
  });
});

API

The default for every callback parameter is:

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

open(path, [callback])

Calls fs.open(path, "r") and gives the fd and callback to fopen below.

fopen(fd, [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.

The callback is given the arguments (err, zipfile). An err is provided if the End of Central Directory Record Signature cannot be found in the file, which indicates that the fd is not a zip file. zipfile is an instance of ZipFile.

class ZipFile

The constructor for the class is not part of the public API. Use open or fopen instead.

close([callback])

Calls fs.close(fd, callback).

readEntries([callback])

callback gets (err, entries), where entries is an Array of Entry objects.

openReadStream(entry, [callback])

entry must be an Entry object from this ZipFile. callback gets (err, readStream), where readStream is a Readable Stream. If the entry is compressed (with a supported compression method), the read stream provides the decompressed data.

entriesRemaining()

Returns the number of entries in this ZipFile that have not yet been returned by readEntry.

readEntry([callback])

Most clients should use the readEntries function. readEntry and entriesRemaining provide low-level access for reading one entry at a time. This can be useful if the index were very large, and you wanted to start reading entries right away.

Calling this function directly sabotages the readEntries function. You must not call this function before any previous call to this function completes by calling its callback.

TODO: really? This API is super sketchy.

entryCount

Number. Total number of central directory records.

comment

Buffer. TODO: decode with cp473.

class Entry

Objects of this class represent Central Directory Records. Refer to the zip file specification for their type and meaning.

These fields are numbers:

• versionMadeBy
• versionNeededToExtract
• generalPurposeBitFlag
• compressionMethod
• lastModFileTime
• lastModFileDate
• crc32
• compressedSize
• uncompressedSize
• fileNameLength
• extraFieldLength
• fileCommentLength
• internalFileAttributes
• externalFileAttributes
• relativeOffsetOfLocalHeader

fileName

String. The bytes in the file are decoded with utf8 if generalPurposeBitFlag & 0x800, as per the spec. Otherwise, the file name is decoded with ascii, which is technically not correct. The correct default encoding is cp473.

extraFields

Array with each entry in the form {id: id, data: data}, where id is a Number and data is a Buffer. None of the extra fields are considered significant by this library.

comment

String decoded with the same charset as used for fileName.

Limitations

Default Charset Should Be CP437

Currently, the default charset is ascii, but it should be cp473.

No Multi-Disk Archive Support

This library does not support multi-disk zip files. This API was 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 or fopen 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

No Encryption Support

Currently, the presence of encryption is not even checked, and encrypted zip files will cause undefined behavior.

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. There may be conflicts between the Central Directory information and the Local File Header, but the Local File Header is always ignored.

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.

No Date/Time Conversion

The lastModFileTime and lastModFileDate fields of Entry objects probably need to be interpreted according to the zip file spec to make them useful. This library provides no support for this.

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.

No ZIP64 Support

A ZIP64 file will probably cause undefined behavior.

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.