The application-manager uses a very simple package format: a standard UNIX gzip-compressed TAR archive. Metadata is embedded as normal files, but using the reserved name prefix
--PACKAGE-. Even though USTAR tar archives support a lot of features, the application-manager only supports standard files and directories with relative paths only (using
../ in a path is not allowed). Modes, except the owner's
x bit, are ignored.
This makes it very easy to write custom packagers as well as custom app-store server backends, since TAR archive handling is available as a utility library in any programming language.
Note: gzip is currently hardcoded, but since the (de)compression is done by libarchive, this could easily be replaced by bzip2 or xz compression. Both would lead to additional 3rd-party dependencies on Windows though.
These are the important files in a package:
|Exactly one YAML document that needs to be the first file in the package - see below for a format description. This file is used as format selector.|
|The manifest of the application. The packaging tool needs to make sure that this file is within the first 10 entries of the tar archive.|
|The icon of the application that is used in the app-store. Can also be used as the app's icon in the launcher menu on the device: see info.yaml. The packaging tool needs to make sure that this file is within the first 10 entries of the tar archive.|
|One or more YAML document(s) that need to be the last file(s) in the package - see below for a format description. If adding more than one footer (e.g. appending the store signature by the app-store server), an arbitrary string can be appended to the file name (e.g. |
In short, here is what is NOT allowed inside a package:
- You are not allowed to have file names that start with
- You are not allowed to have absolute paths
- You are not allowed to have
../in relative paths
- You are not allowed to have sym-links, hard-links, device files, sockets, etc.
- File modes except the owner's
xbit are ignored.
The Checksum Algorithm
All of package data, as well as important meta-data is protected by a SHA256 digest. This checksum has two purposes: it protects against transmission errors, and the package signing is done by encrypting this checksum.
The actual calculation of this checksum is done as follows:
- For every file that is not a
--PACKAGE-*meta-data file, the complete content is added to the digest. Afterwards the following UTF-8 encoded string is also added to the digest:
"F/<file size in bytes>/<file path>"(e.g. the file
foo/test.qmlwith a size of 250 bytes would generate
- For every directory, the following UTF-8 encoded string is added to the digst:
"D/0/<directory path>"(e.g. the directory
The generated digest is put into the
--PACKAGE-FOOTER-- as a 32-byte hex-encoded string.
The Signing Algorithm
The package format currently supports two signatures: a developer signature (generated by the developer before uploading to an appstore-server) and a store signature (generated by the appstore-server before the client actually downloads a package).
Both signatures are calculated the same way and are appended to the package's meta-data the same way: The binary digest is used as an input to create a detached PKCS7 signature. This PKCS7 signature is then BASE64 encoded and stored in
--PACKAGE-FOOTER-- - either in the
If you want to implement this signing algorithm yourself, then please look at these four existing implementations:
- C++ OpenSSL based in
- C++ WinCrypt based in
- C++ SecurityFramework based in
- Python m2crypt based in the appstore-server reference implementation.
This is an example of a minimal QML application package. The actual package can be created by tar'ing all these files up with
tar cvzf qmlapp.appkg ./--PACKAGE-HEADER-- info.yaml icon.png main.qml ./--PACKAGE-FOOTER--
%YAML 1.1 --- formatType: am-package-header formatVersion: 1 --- applicationId: com.pelagicore.minimal diskSpaceUsed: 1000
%YAML 1.1 --- formatType: am-application formatVersion: 1 --- id: 'com.pelagicore.minimal' icon: 'icon.png' name: en: 'Minimal App' code: 'main.qml' runtime: 'qml'
|a standard png image|
|your QML application|
%YAML 1.1 --- formatType: am-package-footer formatVersion: 1 --- # SHA256 digest in 32 char hex representation digest: '9df5635bb50e93846954c6377468c07835119e2835475ec90b3e9a9f7261cf27'
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