1 files changed, 96 insertions, 0 deletions
diff --git a/src/model/k2v/causality.rs b/src/model/k2v/causality.rs
new file mode 100644
index 00000000..8c76a32b
--- /dev/null
+++ b/src/model/k2v/causality.rs
@@ -0,0 +1,96 @@
+use std::collections::BTreeMap;
+use std::convert::TryInto;
+
+use serde::{Deserialize, Serialize};
+
+use garage_util::data::*;
+
+/// Node IDs used in K2V are u64 integers that are the abbreviation
+/// of full Garage node IDs which are 256-bit UUIDs.
+pub type K2VNodeId = u64;
+
+pub fn make_node_id(node_id: Uuid) -> K2VNodeId {
+	let mut tmp = [0u8; 8];
+	tmp.copy_from_slice(&node_id.as_slice()[..8]);
+	u64::from_be_bytes(tmp)
+}
+
+#[derive(PartialEq, Debug, Serialize, Deserialize)]
+pub struct CausalContext {
+	pub vector_clock: BTreeMap<K2VNodeId, u64>,
+}
+
+impl CausalContext {
+	/// Empty causality context
+	pub fn new_empty() -> Self {
+		Self {
+			vector_clock: BTreeMap::new(),
+		}
+	}
+	/// Make binary representation and encode in base64
+	pub fn serialize(&self) -> String {
+		let mut ints = Vec::with_capacity(2 * self.vector_clock.len());
+		for (node, time) in self.vector_clock.iter() {
+			ints.push(*node);
+			ints.push(*time);
+		}
+		let checksum = ints.iter().fold(0, |acc, v| acc ^ *v);
+
+		let mut bytes = u64::to_be_bytes(checksum).to_vec();
+		for i in ints {
+			bytes.extend(u64::to_be_bytes(i));
+		}
+
+		base64::encode_config(bytes, base64::URL_SAFE_NO_PAD)
+	}
+	/// Parse from base64-encoded binary representation
+	pub fn parse(s: &str) -> Result<Self, String> {
+		let bytes = base64::decode_config(s, base64::URL_SAFE_NO_PAD)
+			.map_err(|e| format!("bad causality token base64: {}", e))?;
+		if bytes.len() % 16 != 8 || bytes.len() < 8 {
+			return Err("bad causality token length".into());
+		}
+
+		let checksum = u64::from_be_bytes(bytes[..8].try_into().unwrap());
+		let mut ret = CausalContext {
+			vector_clock: BTreeMap::new(),
+		};
+
+		for i in 0..(bytes.len() / 16) {
+			let node_id = u64::from_be_bytes(bytes[8 + i * 16..16 + i * 16].try_into().unwrap());
+			let time = u64::from_be_bytes(bytes[16 + i * 16..24 + i * 16].try_into().unwrap());
+			ret.vector_clock.insert(node_id, time);
+		}
+
+		let check = ret.vector_clock.iter().fold(0, |acc, (n, t)| acc ^ *n ^ *t);
+
+		if check != checksum {
+			return Err("bad causality token checksum".into());
+		}
+
+		Ok(ret)
+	}
+	/// Check if this causal context contains newer items than another one
+	pub fn is_newer_than(&self, other: &Self) -> bool {
+		self.vector_clock
+			.iter()
+			.any(|(k, v)| v > other.vector_clock.get(k).unwrap_or(&0))
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+
+	#[test]
+	fn test_causality_token_serialization() {
+		let ct = CausalContext {
+			vector_clock: [(4, 42), (1928131023, 76), (0xefc0c1c47f9de433, 2)]
+				.iter()
+				.cloned()
+				.collect(),
+		};
+
+		assert_eq!(CausalContext::parse(&ct.serialize()).unwrap(), ct);
+	}
+}