Package Exports

asar
asar/lib/disk
asar/lib/disk.js
asar/lib/filesystem

This package does not declare an exports field, so the exports above have been automatically detected and optimized by JSPM instead. If any package subpath is missing, it is recommended to post an issue to the original package (asar) to support the "exports" field. If that is not possible, create a JSPM override to customize the exports field for this package.

Readme

asar - Atom-Shell Archive

Asar is a simple extensive archive format, it works like tar that concatenates all files together without compression, while having random access support.

Features

Support random access
Use JSON to store files' information
Very easy to write a parser

Command line utility

Install

$ npm install asar

Usage

$ asar --help

  Usage: asar [options] [command]

  Commands:

    pack|p <dir> <output>
       create asar archive

    list|l <archive>
       list files of asar archive

    extract-file|ef <archive> <filename>
       extract one file from archive


  Options:

    -h, --help     output usage information
    -V, --version  output the version number

Format

Asar uses Pickle to safely serialize binary value to file, there is also a node.js binding of Pickle class.

The format of asar is very flat:

| UInt32: header_size | String: header | Bytes: file1 | ... | Bytes: file42 |

The header_size and header are serialized with Pickle class, and header_size's Pickle object is 8 bytes.

The header is a JSON string, and the header_size is the size of header's Pickle object.

Structure of header is something like this:

{
   "files": {
      "tmp": {
         "files": {}
      },
      "usr" : {
         "files": {
           "bin": {
             "files": {
               "ls": {
                 "offset": "0",
                 "size": 100,
                 "executable": true
               },
               "cd": {
                 "offset": "100",
                 "size": 100,
                 "executable": true
               }
             }
           }
         }
      },
      "etc": {
         "files": {
           "hosts": {
             "offset": "200",
             "size": 32
           }
         }
      }
   }
}

offset and size records the information to read the file from archive, the offset starts from 0 so you have to manually add the size of header_size and header to the offset to get the real offset of the file.

offset is a UINT64 number represented in string, because there is no way to precisely represent UINT64 in JavaScript Number. size is a UINT32 number for the same reason, which indicates that we can not save a file larger than 4.2GB (though the archive itself doesn't have size limitation). We didn't store size in UINT64 because file size in Node.js is represented as Number and it is not safe to convert Number to UINT64.