Add jgvariant-ostree module.

Change-Id: Idf7bacad28d7cf65eb1ddd0994dcc2c2c2a7e18e

17 files changed, 628 insertions, 0 deletions

diff --git a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/ByteString.java b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/ByteString.java
new file mode 100644
index 0000000..1a85547
--- /dev/null
+++ b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/ByteString.java
@@ -0,0 +1,41 @@
+package eu.mulk.jgvariant.ostree;
+
+import eu.mulk.jgvariant.core.Decoder;
+import java.util.Arrays;
+import java.util.HexFormat;
+
+/**
+ * A wrapper for a {@code byte[]} that implements {@link #equals(Object)}, {@link #hashCode()}, and
+ * {@link #toString()} according to value semantics.
+ */
+public record ByteString(byte[] bytes) {
+
+  private static final Decoder<ByteString> DECODER = Decoder.ofByteArray().map(ByteString::new);
+
+  public static Decoder<ByteString> decoder() {
+    return DECODER;
+  }
+
+  @Override
+  public boolean equals(Object o) {
+    return (o instanceof ByteString byteString) && Arrays.equals(bytes, byteString.bytes);
+  }
+
+  @Override
+  public int hashCode() {
+    return Arrays.hashCode(bytes);
+  }
+
+  @Override
+  public String toString() {
+    return "ByteString{hex=\"%s\"}".formatted(hex());
+  }
+
+  public String hex() {
+    return HexFormat.of().formatHex(bytes);
+  }
+
+  public static ByteString ofHex(String hex) {
+    return new ByteString(HexFormat.of().parseHex(hex));
+  }
+}
diff --git a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Checksum.java b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Checksum.java
new file mode 100644
index 0000000..f77eb57
--- /dev/null
+++ b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Checksum.java
@@ -0,0 +1,24 @@
+package eu.mulk.jgvariant.ostree;
+
+import eu.mulk.jgvariant.core.Decoder;
+
+/**
+ * A wrapper for {@link ByteString} that refers to a content-addressed object in an OSTree
+ * repository.
+ */
+public record Checksum(ByteString bytes) {
+
+  private static final Decoder<Checksum> DECODER = ByteString.decoder().map(Checksum::new);
+
+  public static Decoder<Checksum> decoder() {
+    return DECODER;
+  }
+
+  public String hex() {
+    return bytes.hex();
+  }
+
+  public static Checksum ofHex(String hex) {
+    return new Checksum(ByteString.ofHex(hex));
+  }
+}
diff --git a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Commit.java b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Commit.java
new file mode 100644
index 0000000..43909ba
--- /dev/null
+++ b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Commit.java
@@ -0,0 +1,51 @@
+package eu.mulk.jgvariant.ostree;
+
+import eu.mulk.jgvariant.core.Decoder;
+import java.nio.ByteOrder;
+import java.nio.charset.StandardCharsets;
+import java.util.List;
+
+/**
+ * A commit in an OSTree repository.
+ *
+ * <p>Has an optional parent, a root directory, and various metadata.
+ *
+ * <p>Reference: {@code ostree-core.h#OSTREE_COMMIT_GVARIANT_STRING}
+ */
+public record Commit(
+    Metadata metadata,
+    Checksum parentChecksum,
+    List<RelatedObject> relatedObjects,
+    String subject,
+    String body,
+    long timestamp,
+    Checksum rootDirTreeChecksum,
+    Checksum rootDirMetaChecksum) {
+
+  public record RelatedObject(String ref, Checksum commitChecksum) {
+
+    private static final Decoder<RelatedObject> DECODER =
+        Decoder.ofStructure(
+            RelatedObject.class, Decoder.ofString(StandardCharsets.UTF_8), Checksum.decoder());
+
+    public static Decoder<RelatedObject> decoder() {
+      return DECODER;
+    }
+  }
+
+  private static final Decoder<Commit> DECODER =
+      Decoder.ofStructure(
+          Commit.class,
+          Metadata.decoder(),
+          Checksum.decoder(),
+          Decoder.ofArray(RelatedObject.decoder()),
+          Decoder.ofString(StandardCharsets.UTF_8),
+          Decoder.ofString(StandardCharsets.UTF_8),
+          Decoder.ofLong().withByteOrder(ByteOrder.BIG_ENDIAN),
+          Checksum.decoder(),
+          Checksum.decoder());
+
+  public static Decoder<Commit> decoder() {
+    return DECODER;
+  }
+}
diff --git a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaFallback.java b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaFallback.java
new file mode 100644
index 0000000..1b3cc0a
--- /dev/null
+++ b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaFallback.java
@@ -0,0 +1,25 @@
+package eu.mulk.jgvariant.ostree;
+
+import eu.mulk.jgvariant.core.Decoder;
+import java.nio.ByteOrder;
+
+/**
+ * A fallback entry in a {@link DeltaSuperblock}.
+ *
+ * <p>Reference: {@code ostree-repo-static-delta-private.h#OSTREE_STATIC_DELTA_FALLBACK_FORMAT}
+ */
+public record DeltaFallback(
+    byte objectType, Checksum checksum, long compressedSize, long uncompressedSize) {
+
+  private static final Decoder<DeltaFallback> DECODER =
+      Decoder.ofStructure(
+          DeltaFallback.class,
+          Decoder.ofByte(),
+          Checksum.decoder(),
+          Decoder.ofLong().withByteOrder(ByteOrder.LITTLE_ENDIAN), // FIXME: non-canonical
+          Decoder.ofLong().withByteOrder(ByteOrder.LITTLE_ENDIAN)); // FIXME: non-canonical
+
+  public static Decoder<DeltaFallback> decoder() {
+    return DECODER;
+  }
+}
diff --git a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaMetaEntry.java b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaMetaEntry.java
new file mode 100644
index 0000000..39ada86
--- /dev/null
+++ b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaMetaEntry.java
@@ -0,0 +1,38 @@
+package eu.mulk.jgvariant.ostree;
+
+import eu.mulk.jgvariant.core.Decoder;
+import java.nio.ByteOrder;
+import java.util.List;
+
+/**
+ * An entry in a {@link DeltaSuperblock}.
+ *
+ * <p>Reference: {@code ostree-repo-static-delta-private.h#OSTREE_STATIC_DELTA_META_ENTRY_FORMAT}
+ */
+public record DeltaMetaEntry(
+    int version, Checksum checksum, long size, long usize, List<DeltaObject> objects) {
+
+  record DeltaObject(byte objectType, Checksum checksum) {
+
+    private static final Decoder<DeltaObject> DECODER =
+        Decoder.ofStructure(DeltaObject.class, Decoder.ofByte(), Checksum.decoder());
+
+    public static Decoder<DeltaObject> decoder() {
+      return DECODER;
+    }
+  }
+
+  private static final Decoder<DeltaMetaEntry> DECODER =
+      Decoder.ofStructure(
+          DeltaMetaEntry.class,
+          Decoder.ofInt().withByteOrder(ByteOrder.LITTLE_ENDIAN), // FIXME: non-canonical
+          Checksum.decoder(),
+          Decoder.ofLong().withByteOrder(ByteOrder.LITTLE_ENDIAN), // FIXME: non-canonical
+          Decoder.ofLong().withByteOrder(ByteOrder.LITTLE_ENDIAN), // FIXME: non-canonical
+          Decoder.ofByteArray().map(x -> List.of()) // FIXME
+          );
+
+  public static Decoder<DeltaMetaEntry> decoder() {
+    return DECODER;
+  }
+}
diff --git a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaPartPayload.java b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaPartPayload.java
new file mode 100644
index 0000000..c8c5fe7
--- /dev/null
+++ b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaPartPayload.java
@@ -0,0 +1,41 @@
+package eu.mulk.jgvariant.ostree;
+
+import eu.mulk.jgvariant.core.Decoder;
+import java.nio.ByteOrder;
+import java.util.List;
+
+/**
+ * Reference: {@code ostree-repo-static-delta-private.h#OSTREE_STATIC_DELTA_PART_PAYLOAD_FORMAT_V0}
+ */
+public record DeltaPartPayload(
+    List<FileMode> fileModes,
+    List<List<Xattr>> xattrs,
+    ByteString rawDataSource,
+    ByteString operations) {
+
+  private static final Decoder<DeltaPartPayload> DECODER =
+      Decoder.ofStructure(
+          DeltaPartPayload.class,
+          Decoder.ofArray(FileMode.decoder()),
+          Decoder.ofArray(Decoder.ofArray(Xattr.decoder())),
+          ByteString.decoder(),
+          ByteString.decoder());
+
+  public record FileMode(int uid, int gid, int mode) {
+
+    private static final Decoder<FileMode> DECODER =
+        Decoder.ofStructure(
+            FileMode.class,
+            Decoder.ofInt().withByteOrder(ByteOrder.LITTLE_ENDIAN),
+            Decoder.ofInt().withByteOrder(ByteOrder.LITTLE_ENDIAN),
+            Decoder.ofInt().withByteOrder(ByteOrder.LITTLE_ENDIAN));
+
+    public static Decoder<FileMode> decoder() {
+      return DECODER;
+    }
+  }
+
+  public static Decoder<DeltaPartPayload> decoder() {
+    return DECODER;
+  }
+}
diff --git a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaSuperblock.java b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaSuperblock.java
new file mode 100644
index 0000000..2b09645
--- /dev/null
+++ b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DeltaSuperblock.java
@@ -0,0 +1,43 @@
+package eu.mulk.jgvariant.ostree;
+
+import eu.mulk.jgvariant.core.Decoder;
+import java.nio.ByteOrder;
+import java.util.List;
+
+/** Reference: {@code ostree-repo-static-delta-private.h#OSTREE_STATIC_DELTA_SUPERBLOCK_FORMAT} */
+public record DeltaSuperblock(
+    Metadata metadata,
+    long timestamp,
+    Checksum fromChecksum,
+    Checksum toChecksum,
+    Commit commit,
+    List<DeltaName> dependencies,
+    List<DeltaMetaEntry> entries,
+    List<DeltaFallback> fallbacks) {
+
+  public record DeltaName(Checksum fromChecksum, Checksum toChecksum) {
+
+    private static final Decoder<DeltaName> DECODER =
+        Decoder.ofStructure(DeltaName.class, Checksum.decoder(), Checksum.decoder());
+
+    public static Decoder<DeltaName> decoder() {
+      return DECODER;
+    }
+  }
+
+  private static final Decoder<DeltaSuperblock> DECODER =
+      Decoder.ofStructure(
+          DeltaSuperblock.class,
+          Metadata.decoder(),
+          Decoder.ofLong().withByteOrder(ByteOrder.BIG_ENDIAN),
+          Checksum.decoder(),
+          Checksum.decoder(),
+          Commit.decoder(),
+          Decoder.ofByteArray().map(x -> List.of()), // FIXME
+          Decoder.ofArray(DeltaMetaEntry.decoder()),
+          Decoder.ofArray(DeltaFallback.decoder()));
+
+  public static Decoder<DeltaSuperblock> decoder() {
+    return DECODER;
+  }
+}
diff --git a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DirMeta.java b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DirMeta.java
new file mode 100644
index 0000000..3a9672d
--- /dev/null
+++ b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DirMeta.java
@@ -0,0 +1,25 @@
+package eu.mulk.jgvariant.ostree;
+
+import eu.mulk.jgvariant.core.Decoder;
+import java.nio.ByteOrder;
+import java.util.List;
+
+/**
+ * Permission bits and extended attributes for a directory.
+ *
+ * <p>Reference: {@code ostree-core.h#OSTREE_DIRMETA_GVARIANT_STRING}
+ */
+public record DirMeta(int uid, int gid, int mode, List<Xattr> xattrs) {
+
+  private static final Decoder<DirMeta> DECODER =
+      Decoder.ofStructure(
+          DirMeta.class,
+          Decoder.ofInt().withByteOrder(ByteOrder.BIG_ENDIAN),
+          Decoder.ofInt().withByteOrder(ByteOrder.BIG_ENDIAN),
+          Decoder.ofInt().withByteOrder(ByteOrder.BIG_ENDIAN),
+          Decoder.ofArray(Xattr.decoder()));
+
+  public static Decoder<DirMeta> decoder() {
+    return DECODER;
+  }
+}
diff --git a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DirTree.java b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DirTree.java
new file mode 100644
index 0000000..3a14abb
--- /dev/null
+++ b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/DirTree.java
@@ -0,0 +1,49 @@
+package eu.mulk.jgvariant.ostree;
+
+import eu.mulk.jgvariant.core.Decoder;
+import java.nio.charset.StandardCharsets;
+import java.util.List;
+
+/**
+ * Metadata describing files and directories of a file tree.
+ *
+ * <p>Referenced by {@link Commit#rootDirTreeChecksum()} and recursively by {@link
+ * Directory#treeChecksum()}.
+ *
+ * <p>Reference: {@code ostree-core.h#OSTREE_TREE_GVARIANT_STRING}
+ */
+public record DirTree(List<File> files, List<Directory> directories) {
+
+  public record File(String name, Checksum checksum) {
+
+    private static final Decoder<File> DECODER =
+        Decoder.ofStructure(
+            File.class, Decoder.ofString(StandardCharsets.UTF_8), Checksum.decoder());
+
+    public static Decoder<File> decoder() {
+      return DECODER;
+    }
+  }
+
+  public record Directory(String name, Checksum treeChecksum, Checksum dirChecksum) {
+
+    private static final Decoder<Directory> DECODER =
+        Decoder.ofStructure(
+            Directory.class,
+            Decoder.ofString(StandardCharsets.UTF_8),
+            Checksum.decoder(),
+            Checksum.decoder());
+
+    public static Decoder<Directory> decoder() {
+      return DECODER;
+    }
+  }
+
+  private static final Decoder<DirTree> DECODER =
+      Decoder.ofStructure(
+          DirTree.class, Decoder.ofArray(File.decoder()), Decoder.ofArray(Directory.decoder()));
+
+  public static Decoder<DirTree> decoder() {
+    return DECODER;
+  }
+}
diff --git a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/FileMeta.java b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/FileMeta.java
new file mode 100644
index 0000000..19e0677
--- /dev/null
+++ b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/FileMeta.java
@@ -0,0 +1,25 @@
+package eu.mulk.jgvariant.ostree;
+
+import eu.mulk.jgvariant.core.Decoder;
+import java.nio.ByteOrder;
+import java.util.List;
+
+/**
+ * Permission bits and extended attributes for a file.
+ *
+ * <p>Reference: {@code ostree-core.h#OSTREE_FILEMETA_GVARIANT_STRING}
+ */
+public record FileMeta(int uid, int gid, int mode, List<Xattr> xattrs) {
+
+  private static final Decoder<FileMeta> DECODER =
+      Decoder.ofStructure(
+          FileMeta.class,
+          Decoder.ofInt().withByteOrder(ByteOrder.BIG_ENDIAN),
+          Decoder.ofInt().withByteOrder(ByteOrder.BIG_ENDIAN),
+          Decoder.ofInt().withByteOrder(ByteOrder.BIG_ENDIAN),
+          Decoder.ofArray(Xattr.decoder()));
+
+  public static Decoder<FileMeta> decoder() {
+    return DECODER;
+  }
+}
diff --git a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Metadata.java b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Metadata.java
new file mode 100644
index 0000000..cf838d3
--- /dev/null
+++ b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Metadata.java
@@ -0,0 +1,33 @@
+package eu.mulk.jgvariant.ostree;
+
+import eu.mulk.jgvariant.core.Decoder;
+import eu.mulk.jgvariant.core.Variant;
+import java.nio.charset.StandardCharsets;
+import java.util.List;
+
+/**
+ * A wrapper for a list of metadata fields.
+ *
+ * <p>Reference: (embedded in other data types)
+ */
+public record Metadata(List<Field> fields) {
+
+  /** A metadata field with a key and a value. */
+  public record Field(String key, Variant value) {
+
+    private static final Decoder<Field> DECODER =
+        Decoder.ofStructure(
+            Field.class, Decoder.ofString(StandardCharsets.UTF_8), Decoder.ofVariant());
+
+    public static Decoder<Field> decoder() {
+      return DECODER;
+    }
+  }
+
+  private static final Decoder<Metadata> DECODER =
+      Decoder.ofArray(Field.decoder()).map(Metadata::new);
+
+  public static Decoder<Metadata> decoder() {
+    return DECODER;
+  }
+}
diff --git a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/SignedDelta.java b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/SignedDelta.java
new file mode 100644
index 0000000..2fc5c25
--- /dev/null
+++ b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/SignedDelta.java
@@ -0,0 +1,38 @@
+package eu.mulk.jgvariant.ostree;
+
+import eu.mulk.jgvariant.core.Decoder;
+import eu.mulk.jgvariant.core.Variant;
+import java.nio.ByteOrder;
+import java.nio.charset.StandardCharsets;
+import java.util.List;
+
+/**
+ * A {@link DeltaSuperblock} signed with some sort of key.
+ *
+ * <p>Reference: {@code ostree-repo-static-delta-private.h#OSTREE_STATIC_DELTA_SIGNED_FORMAT}
+ */
+public record SignedDelta(
+    long magicNumber, ByteString superblock, List<SignedDelta.Signature> signatures) {
+
+  /** A cryptographic signature. */
+  public record Signature(String key, Variant data) {
+    private static final Decoder<Signature> DECODER =
+        Decoder.ofStructure(
+            Signature.class, Decoder.ofString(StandardCharsets.US_ASCII), Decoder.ofVariant());
+
+    public static Decoder<Signature> decoder() {
+      return DECODER;
+    }
+  }
+
+  private static final Decoder<SignedDelta> DECODER =
+      Decoder.ofStructure(
+          SignedDelta.class,
+          Decoder.ofLong().withByteOrder(ByteOrder.BIG_ENDIAN),
+          ByteString.decoder(),
+          Decoder.ofArray(Signature.decoder()));
+
+  public static Decoder<SignedDelta> decoder() {
+    return DECODER;
+  }
+}
diff --git a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Summary.java b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Summary.java
new file mode 100644
index 0000000..8f4ddf6
--- /dev/null
+++ b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Summary.java
@@ -0,0 +1,47 @@
+package eu.mulk.jgvariant.ostree;
+
+import eu.mulk.jgvariant.core.Decoder;
+import java.nio.ByteOrder;
+import java.nio.charset.StandardCharsets;
+import java.util.List;
+
+/**
+ * The summary file of an OSTree repository.
+ *
+ * <p>Stored as a file named {@code summary} in the OSTree repository root.
+ *
+ * <p>Reference: {@code ostree-core.h#OSTREE_SUMMARY_GVARIANT_STRING}
+ */
+public record Summary(List<Entry> entries, Metadata metadata) {
+
+  public record Entry(String ref, Value value) {
+
+    public record Value(long size, Checksum checksum, Metadata metadata) {
+
+      private static final Decoder<Value> DECODER =
+          Decoder.ofStructure(
+              Value.class,
+              Decoder.ofLong().withByteOrder(ByteOrder.LITTLE_ENDIAN),
+              Checksum.decoder(),
+              Metadata.decoder());
+
+      public static Decoder<Value> decoder() {
+        return DECODER;
+      }
+    }
+
+    private static final Decoder<Entry> DECODER =
+        Decoder.ofStructure(Entry.class, Decoder.ofString(StandardCharsets.UTF_8), Value.decoder());
+
+    public static Decoder<Entry> decoder() {
+      return DECODER;
+    }
+  }
+
+  private static final Decoder<Summary> DECODER =
+      Decoder.ofStructure(Summary.class, Decoder.ofArray(Entry.decoder()), Metadata.decoder());
+
+  public static Decoder<Summary> decoder() {
+    return DECODER;
+  }
+}
diff --git a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/SummarySignature.java b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/SummarySignature.java
new file mode 100644
index 0000000..a05b96d
--- /dev/null
+++ b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/SummarySignature.java
@@ -0,0 +1,35 @@
+package eu.mulk.jgvariant.ostree;
+
+import eu.mulk.jgvariant.core.Decoder;
+import eu.mulk.jgvariant.core.Variant;
+import java.nio.charset.StandardCharsets;
+import java.util.List;
+
+/**
+ * A collection of cryptographic signatures for a {@link Summary}.
+ *
+ * <p>Stored as a file named {@code summary.sig} in the OSTree repository root.
+ *
+ * <p>Reference: {@code ostree-repo-static-delta-private.h#OSTREE_SUMMARY_SIG_GVARIANT_STRING}
+ */
+public record SummarySignature(List<Signature> signatures) {
+
+  /** A cryptographic signature. */
+  public record Signature(String key, Variant data) {
+
+    private static final Decoder<Signature> DECODER =
+        Decoder.ofStructure(
+            Signature.class, Decoder.ofString(StandardCharsets.UTF_8), Decoder.ofVariant());
+
+    public static Decoder<Signature> decoder() {
+      return DECODER;
+    }
+  }
+
+  private static final Decoder<SummarySignature> DECODER =
+      Decoder.ofArray(Signature.decoder()).map(SummarySignature::new);
+
+  public static Decoder<SummarySignature> decoder() {
+    return DECODER;
+  }
+}
diff --git a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Xattr.java b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Xattr.java
new file mode 100644
index 0000000..68628c4
--- /dev/null
+++ b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/Xattr.java
@@ -0,0 +1,18 @@
+package eu.mulk.jgvariant.ostree;
+
+import eu.mulk.jgvariant.core.Decoder;
+
+/**
+ * Reference: (embedded in other data types, e.g. {@code
+ * ostree-core.h#OSTREE_DIRMETA_GVARIANT_STRING}, {@code
+ * ostree-core.h#OSTREE_FILEMETA_GVARIANT_STRING})
+ */
+public record Xattr(ByteString name, ByteString value) {
+
+  private static final Decoder<Xattr> DECODER =
+      Decoder.ofStructure(Xattr.class, ByteString.decoder(), ByteString.decoder());
+
+  public static Decoder<Xattr> decoder() {
+    return DECODER;
+  }
+}
diff --git a/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/package-info.java b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/package-info.java
new file mode 100644
index 0000000..c6a61f1
--- /dev/null
+++ b/jgvariant-ostree/src/main/java/eu/mulk/jgvariant/ostree/package-info.java
@@ -0,0 +1,10 @@
+/**
+ * Provides record classes describing the elements of <a
+ * href="https://ostreedev.github.io/ostree/">OSTree</a> repositories and factory methods to create
+ * {@link eu.mulk.jgvariant.core.Decoder} instances for them.
+ */
+@API(status = Status.EXPERIMENTAL)
+package eu.mulk.jgvariant.ostree;
+
+import org.apiguardian.api.API;
+import org.apiguardian.api.API.Status;
diff --git a/jgvariant-ostree/src/main/java/module-info.java b/jgvariant-ostree/src/main/java/module-info.java
new file mode 100644
index 0000000..e51c586
--- /dev/null
+++ b/jgvariant-ostree/src/main/java/module-info.java
@@ -0,0 +1,85 @@
+/**
+ * Provides a parser for the <a href="https://docs.gtk.org/glib/struct.Variant.html">GVariant</a>
+ * serialization format.
+ *
+ * <ul>
+ *   <li><a href="#sect-overview">Overview</a>
+ *   <li><a href="#sect-installation">Installation</a>
+ * </ul>
+ *
+ * <h2 id="sect-overview">Overview</h2>
+ *
+ * <p>The {@link eu.mulk.jgvariant.ostree} package contains record classes describing the elements
+ * of <a href="https://ostreedev.github.io/ostree/">OSTree</a> repositories and factory methods to
+ * create {@link eu.mulk.jgvariant.core.Decoder} instances for them.
+ *
+ * <h2 id="sect-installation">Installation</h2>
+ *
+ * <ul>
+ *   <li><a href="#sect-installation-maven">Usage with Maven</a>
+ *   <li><a href="#sect-installation-gradle">Usage with Gradle</a>
+ * </ul>
+ *
+ * <h3 id="sect-installation-maven">Usage with Maven</h3>
+ *
+ * <pre>{@code
+ * <project>
+ *   ...
+ *
+ *   <dependencyManagement>
+ *     ...
+ *
+ *     <dependencies>
+ *       <dependency>
+ *         <groupId>eu.mulk.jgvariant</groupId>
+ *         <artifactId>jgvariant-bom</artifactId>
+ *         <version>0.1.4</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>
+ * }</pre>
+ *
+ * <h3 id="sect-installation-gradle">Usage with Gradle</h3>
+ *
+ * <pre>{@code
+ * dependencies {
+ *   ...
+ *
+ *   implementation(platform("eu.mulk.jgvariant:jgvariant-bom:0.1.4")
+ *   implementation("eu.mulk.jgvariant:jgvariant-core")
+ *   implementation("eu.mulk.jgvariant:jgvariant-ostree")
+ *
+ *   ...
+ * }
+ * }</pre>
+ */
+module eu.mulk.jgvariant.gvariant {
+  requires transitive eu.mulk.jgvariant.core;
+  requires com.google.errorprone.annotations;
+  requires org.jetbrains.annotations;
+  requires org.apiguardian.api;
+
+  exports eu.mulk.jgvariant.ostree;
+}