yazl

yet another zip library for node

Design principles:

• 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.
• Catch unsafe filenames entries. addFile() throws an error if its file name starts with "/" or /[A-Za-z]:\// or if it contains ".." path segments or "\\" (per the spec).

Usage

var yazl = require("yazl");

var zipfile = new yazl.ZipFile();
zipfile.addFile("file1.txt", "file1.txt");
// (add only files, not directories)
zipfile.addFile("path/to/file.txt", "path/in/zipfile.txt");
zipfile.end();
zipfile.outputStream.pipe(fs.createWriteStream("output.zip")).on("finish", function() {
  console.log("done");
});

API

Class: ZipFile

new ZipFile()

No parameters. Nothing can go wrong.

addFile(realPath, metadataPath)

Adds a file from the file system at realPath into the zipfile as metadataPath. Typically metadataPath would be calculated as path.relative(root, realPath). Unzip programs would extract the file from the zipfile as metadataPath. realPath is not stored in the zipfile.

The path should be a regular file, not a directory or symlink, etc. The mtime and unix permission bits are stored in the file (in the fields "last mod file time", "last mod file date", and "external file attributes"). yazl does not store group and user ids in the zip file (note that Info-Zip does do this in the field "extra fields".).

Internally, fs.open() is called immediately in the addFile function, and the fd obtained is later used for getting stats and file data. So theoretically, clients could delete the file from the file system immediately after calling this function, and yazl would be able to function without any trouble.

end()

Indicates that no more files will be added via addFile(). Some time after calling this function, outputStream will be ended.

outputStream

A readable stream that will produce the contents of the zip file. It is typical to pipe this stream to a writable stream created from fs.createWriteStream().

Internally, large amounts of file data are piped to outputStream using pipe(), which means throttling happens appropriately when this stream is piped to a slow destination.

Data becomes available in this stream soon after calling addFile() for the first time. Clients can call pipe() on this stream immediately after getting a new ZipFile instance. It is not necessary to add all files and call end() before calling pipe() on this stream.

dateToDosDateTime(jsDate)

jsDate is a Date instance. Returns {date: date, time: time}, where date and time are unsigned 16-bit integers.

Output Structure

The Zip File Spec leaves a lot of flexibility up to the zip file creator. This section explains and justifies yazl's interpretation and decisions regarding this flexibility.

This section is probably not useful to yazl clients, but may be interesting to unzip implementors and zip file enthusiasts.

Disk Numbers

All values related to disk numbers are 0, because yazl has no multi-disk archive support.

Version Made By

Always 0x031e. This is the value reported by a Linux build of Info-Zip. Instead of experimenting with different values of this field to see how different unzip clients would behave, yazl mimics Info-Zip, which should work everywhere.

Note that the top byte means "UNIX" and has implications in the External File Attributes.

Version Needed to Extract

Always 0x0014. Without this value, Info-Zip, and possibly other unzip implementations, refuse to acknowledge General Purpose Bit 8, which enables utf8 filename encoding.

General Purpose Bit Flag

Bit 8 is always set. Filenames are always encoded in utf8, even if the result is indistinguishable from ascii.

Bit 3 is set in the Local File Header. To support both a streaming input and streaming output api, it is impossible to know the crc32 before processing the file data. File Descriptors are given after each file data with this information, as per the spec. But remember a complete metadata listing is still always available in the central directory record, so if unzip implementations are relying on that, like they should, none of this paragraph will matter anyway.

All other bits are unset.

Internal File Attributes

Always 0. The "apparently an ASCII or text file" bit is always unset meaning "apparently binary". This kind of determination is outside the scope of yazl, and is probably not significant in any modern unzip implementation.

External File Attributes

Always stats.mode << 16. This is apparently the convention for "version made by" = 0x03xx (UNIX).