Add version table fuzz

fuzz/Cargo.toml

@@ -18,3 +18,9 @@ path = "../src/table"
 path = "../src/model"
 features = ["arbitrary"]
 
+[[bin]]
+name = "version_crdt"
+path = "fuzz_targets/version_crdt.rs"
+test = false
+doc = false
+bench = false

fuzz/fuzz_targets/version_crdt.rs

@@ -0,0 +1,94 @@
+#![no_main]
+
+use garage_model::s3::version_table::{Version, VersionBacklink, VersionBlock, VersionBlockKey};
+use garage_table::crdt::Crdt;
+use libfuzzer_sys::fuzz_target;
+
+/// Build a Version from an arbitrary deleted flag and block list, using a fixed uuid/backlink
+/// so that CRDT state can be compared across merge results.
+/// Duplicate block keys are dropped before construction.
+/// If deleted, blocks are cleared to ensure a valid initial CRDT state.
+fn make_version(deleted: bool, mut blocks: Vec<(VersionBlockKey, VersionBlock)>) -> Version {
+	blocks.sort_by_key(|(k, _)| *k);
+	blocks.dedup_by_key(|(k, _)| *k);
+	let mut v = Version::new(
+		[0u8; 32].into(),
+		VersionBacklink::Object {
+			bucket_id: [0u8; 32].into(),
+			key: String::new(),
+		},
+		deleted,
+	);
+	for (key, block) in blocks {
+		v.blocks.put(key, block);
+	}
+	if v.deleted.get() {
+		v.blocks.clear();
+	}
+	v
+}
+
+fn crdt_state(v: &Version) -> (bool, &[(VersionBlockKey, VersionBlock)]) {
+	(v.deleted.get(), v.blocks.items())
+}
+
+fuzz_target!(|inputs: (
+	(bool, Vec<(VersionBlockKey, VersionBlock)>),
+	(bool, Vec<(VersionBlockKey, VersionBlock)>),
+	(bool, Vec<(VersionBlockKey, VersionBlock)>)
+)| {
+	let ((d1, b1), (d2, b2), (d3, b3)) = inputs;
+	let a = make_version(d1, b1);
+	let b = make_version(d2, b2);
+	let c = make_version(d3, b3);
+
+	// Idempotency: merge(a, a) == a
+	{
+		let mut a2 = a.clone();
+		a2.merge(&a.clone());
+		assert_eq!(
+			crdt_state(&a2),
+			crdt_state(&a),
+			"merge is not idempotent: {a2:#?} != {a:#?}"
+		);
+	}
+
+	// Commutativity: crdt_state(merge(a, b)) == crdt_state(merge(b, a))
+	let ab = {
+		let mut t = a.clone();
+		t.merge(&b);
+		t
+	};
+	let ba = {
+		let mut t = b.clone();
+		t.merge(&a);
+		t
+	};
+	assert_eq!(
+		crdt_state(&ab),
+		crdt_state(&ba),
+		"merge is not commutative: {ab:#?} != {ba:#?}"
+	);
+
+	// Associativity: crdt_state(merge(merge(a, b), c)) == crdt_state(merge(a, merge(b, c)))
+	let ab_c = {
+		let mut t = ab.clone();
+		t.merge(&c);
+		t
+	};
+	let bc = {
+		let mut t = b.clone();
+		t.merge(&c);
+		t
+	};
+	let a_bc = {
+		let mut t = a.clone();
+		t.merge(&bc);
+		t
+	};
+	assert_eq!(
+		crdt_state(&ab_c),
+		crdt_state(&a_bc),
+		"merge is not associative: {ab_c:#?} != {a_bc:#?}"
+	);
+});

src/model/s3/version_table.rs

@@ -41,6 +41,7 @@ mod v08 {
 	}
 
 	#[derive(PartialEq, Eq, Clone, Copy, Debug, Serialize, Deserialize)]
+	#[cfg_attr(feature = "arbitrary", derive(arbitrary::Arbitrary))]
 	pub struct VersionBlockKey {
 		/// Number of the part
 		pub part_number: u64,
@@ -51,6 +52,7 @@ mod v08 {
 
 	/// Information about a single block
 	#[derive(PartialEq, Eq, Ord, PartialOrd, Clone, Copy, Debug, Serialize, Deserialize)]
+	#[cfg_attr(feature = "arbitrary", derive(arbitrary::Arbitrary))]
 	pub struct VersionBlock {
 		/// Blake2 sum of the block
 		pub hash: Hash,
@@ -91,6 +93,7 @@ pub(crate) mod v09 {
 	}
 
 	#[derive(PartialEq, Eq, Clone, Debug, Serialize, Deserialize)]
+	#[cfg_attr(feature = "arbitrary", derive(arbitrary::Arbitrary))]
 	pub enum VersionBacklink {
 		Object {
 			/// Bucket in which the related object is stored