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<!--
SPDX-FileCopyrightText: © 2021 Matthias Andreas Benkard <code@mail.matthias.benkard.de>
SPDX-License-Identifier: GFDL-1.3-or-later
-->
# GVariant for Java
This library provides a [GVariant][] parser in pure Java.
## Overview
`jgvariant-core` provides `Decoder<T>`, which read a given type of
GVariant-encoded value from a [ByteBuffer][]. The class also contains
factory methods to acquire those instances.
The various subclasses of `Decoder` together implement the [GVariant
serialization][] specification.
`jgvariant-ostree` provides instances of `Decoder<T>` for various
[GVariant][] types used in [OSTree][] repositories.
## Example
To parse a [GVariant][] value of type `"a(si)"`, which is an array of
pairs of [String][] and `int`, you can use the following code:
record ExampleRecord(String s, int i) {}
var decoder =
Decoder.ofArray(
Decoder.ofStructure(
ExampleRecord.class,
Decoder.ofString(StandardCharsets.UTF_8),
Decoder.ofInt().withByteOrder(ByteOrder.LITTLE_ENDIAN)));
byte[] bytes = ...;
List<ExampleRecord> example = decoder.decode(ByteBuffer.wrap(bytes));
## Command line tool
The `jgvariant-tool` module contains a tool called `jgvariant` that can
be used to manipulate [GVariant][]-formatted files from the command line.
Its primary purpose is to enable the scripting of [OSTree][] repository
management tasks.
### Usage examples
#### Dumping the contents of an [OSTree][] summary file
$ jgvariant ostree summary read ./jgvariant-ostree/src/test/resources/ostree/summary
Output:
{
"entries": [
{
"ref": "mulkos/1.x/amd64",
"value": {
"checksum": "66ff167ff35ce87daac817447a9490a262ee75f095f017716a6eb1a9d9eb3350",
"metadata": {
"fields": {
"ostree.commit.timestamp": 1640537170
}
},
"size": 214
}
}
],
"metadata": {
"fields": {
"ostree.summary.last-modified": 1640537300,
"ostree.summary.tombstone-commits": false,
"ostree.static-deltas": {
"3d3b3329dca38871f29aeda1bf5854d76c707fa269759a899d0985c91815fe6f-66ff167ff35ce87daac817447a9490a262ee75f095f017716a6eb1a9d9eb3350": "03738040e28e7662e9c9d2599c530ea974e642c9f87e6c00cbaa39a0cdac8d44",
"31c8835d5c9d2c6687a50091c85142d1b2d853ff416a9fb81b4ee30754510d52": "f481144629474bd88c106e45ac405ebd75b324b0655af1aec14b31786ae1fd61",
"31c8835d5c9d2c6687a50091c85142d1b2d853ff416a9fb81b4ee30754510d52-3d3b3329dca38871f29aeda1bf5854d76c707fa269759a899d0985c91815fe6f": "2c6a07bc1cf4d7ce7d00f82d7d2d6d156fd0e31d476851b46dc2306b181b064a"
},
"ostree.summary.mode": "bare",
"ostree.summary.indexed-deltas": true
}
}
}
#### Adding a static delta to an [OSTree][] summary file
Superblock checksum `0...`, between commits `3...` and `6...`:
$ jgvariant ostree summary add-static-delta ./jgvariant-ostree/src/test/resources/ostree/summary 03738040e28e7662e9c9d2599c530ea974e642c9f87e6c00cbaa39a0cdac8d44 66ff167ff35ce87daac817447a9490a262ee75f095f017716a6eb1a9d9eb3350 3d3b3329dca38871f29aeda1bf5854d76c707fa269759a899d0985c91815fe6f
Superblock checksum `f...`, between the empty commit and `3...`:
$ jgvariant ostree summary add-static-delta ./jgvariant-ostree/src/test/resources/ostree/summary f481144629474bd88c106e45ac405ebd75b324b0655af1aec14b31786ae1fd61 31c8835d5c9d2c6687a50091c85142d1b2d853ff416a9fb81b4ee30754510d52
Checksums can be given in either hex (64 digits) or a variant of Base64 (43
digits) where `/` is replaced by `_`. The latter format is used to identify
the start and end commits of deltas as part of folder names below `deltas/` in
the OSTree repository itself.
### Building the tool
You can build the tool either as a shaded JAR or as a native executable.
To build and run a shaded JAR:
$ mvn package -pl jgvariant-tool -am -Pshade
$ java -jar jgvariant-tool/target/jgvariant-tool-*.jar ...
To build and run a native executable:
$ mvn package -pl jgvariant-tool -am -Pnative
$ ./jgvariant-tool/target/jgvariant ...
You can also run the tool directly with Maven using the `exec` profile:
$ mvn verify -pl jgvariant-tool -am -Pexec -Dexec.args="..."
## Library installation
### Usage with Maven
<project>
...
<dependencyManagement>
...
<dependencies>
<dependency>
<groupId>eu.mulk.jgvariant</groupId>
<artifactId>jgvariant-bom</artifactId>
<version>0.1.10</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
...
</dependencyManagement>
<dependencies>
...
<dependency>
<groupId>eu.mulk.jgvariant</groupId>
<artifactId>jgvariant-core</artifactId>
</dependency>
<dependency>
<groupId>eu.mulk.jgvariant</groupId>
<artifactId>jgvariant-ostree</artifactId>
</dependency>
...
</dependencies>
...
</project>
### Usage with Gradle
dependencies {
...
implementation(platform("eu.mulk.jgvariant:jgvariant-bom:0.1.10")
implementation("eu.mulk.jgvariant:jgvariant-core")
implementation("eu.mulk.jgvariant:jgvariant-ostree")
...
}
[ByteBuffer]: https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/nio/ByteBuffer.html
[GVariant]: https://docs.gtk.org/glib/struct.Variant.html
[GVariant serialization]: https://people.gnome.org/~desrt/gvariant-serialisation.pdf
[OSTree]: https://ostreedev.github.io/ostree/
[String]: https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/String.html
|
