Module-file format (DRAFT)
mr at sun.com
Fri Jan 15 14:11:06 PST 2010
Here's a first cut at a simple module-file format.
Jigsaw module-file format DRAFT
Mark Reinhold <mr at sun.com>
15 January 2010
- Optimized for streamed reading, from beginning to end. Random access
should not be required when reading a module file, though it can be
required when writing.
- Content-specific compression: Pack200+gzip/lzma for classes, bzip2 for
native code, etc.
- Independent of any specific installed-module format or target-filesystem
A module file has the following sections, in the order listed.
The first two sections are required:
- Header -- Magic number, format version, sizes
- module-info.class (never compressed, so as to be easily readable by tools)
These sections are optional:
- Classes (excluding module-info.class)
- Native libraries
- Native launchers
- Configuration (i.e., properties) files
The final section is required:
- Secure hash of the entire file (except for this section)
Module file header
u4 magic; // FileConstants.MAGIC
u2 type; // FileConstants.Type.MODULE_FILE
u2 major; // FileConstants.ModuleFile.MAJOR_VERSION
u2 minor; // FileConstants.ModuleFile.MINOR_VERSION
u4 csize; // Size of entire file, compressed
u4 usize; // Space required for uncompressed contents
// (upper bound; need not be exact)
All integers are in network byte order.
Each section has a header:
u2 type; // One of FileConstants.ModuleFile.SectionType
u2 compressor; // One of FileConstants.ModuleFile.Compressor
Compression is only relevant to section content; it never applies to the
headers defined here.
For sections that contain only one entity (i.e., module-info, classes, hash)
the section header is followed by a size pair, which is then followed by the
u4 csize; // Size of section content, compressed
u4 usize; // Size of section content, uncompressed
If a section contains named files (i.e., resources, native code, config) then
each file within that section has a header, which is then followed by the
u4 csize; // Size of file, compressed
u4 usize; // Size of file, uncompressed
u2 nameLength; // Length of file name
b* name; // File name, in UTF-8
File names may include directory separators, though they should not be used for
There is no mode field on files within a section. The module-installation code
must set the local mode appropriately; e.g., it must make native-code files
executable as appropriate.
A hash section has the content:
u2 type; // One of FileConstants.ModuleFile.HashType
u2 size; // Never compressed
- Signing: Should module files carry their own digital-signature information,
as jar files do today, or should such information be provided elsewhere?
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