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|
//! Implements a CausalContext, which is a set of timestamps for each
//! node -- a vector clock --, indicating that the versions with
//! timestamps <= these numbers have been seen and can be
//! overwritten by a subsequent write.
//!
//! The textual representation of a CausalContext, which we call a
//! "causality token", is used in the API and must be sent along with
//! each write or delete operation to indicate the previously seen
//! versions that we want to overwrite or delete.
use base64::prelude::*;
use std::collections::BTreeMap;
use std::convert::TryInto;
use serde::{Deserialize, Serialize};
use garage_util::data::*;
use crate::helper::error::{Error as HelperError, OkOrBadRequest};
/// 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 type VectorClock = BTreeMap<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)
}
pub fn vclock_gt(a: &VectorClock, b: &VectorClock) -> bool {
a.iter().any(|(n, ts)| ts > b.get(n).unwrap_or(&0))
}
pub fn vclock_max(a: &VectorClock, b: &VectorClock) -> VectorClock {
let mut ret = a.clone();
for (n, ts) in b.iter() {
let ent = ret.entry(*n).or_insert(0);
*ent = std::cmp::max(*ts, *ent);
}
ret
}
#[derive(PartialEq, Eq, Debug, Serialize, Deserialize, Default)]
pub struct CausalContext {
pub vector_clock: VectorClock,
}
impl CausalContext {
/// Empty causality context
pub fn new() -> Self {
Self::default()
}
/// 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_URL_SAFE_NO_PAD.encode(bytes)
}
/// Parse from base64-encoded binary representation.
/// Returns None on error.
pub fn parse(s: &str) -> Option<Self> {
let bytes = BASE64_URL_SAFE_NO_PAD.decode(s).ok()?;
if bytes.len() % 16 != 8 || bytes.len() < 8 {
return None;
}
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 None;
}
Some(ret)
}
pub fn parse_helper(s: &str) -> Result<Self, HelperError> {
Self::parse(s).ok_or_bad_request("Invalid causality token")
}
/// Check if this causal context contains newer items than another one
pub fn is_newer_than(&self, other: &Self) -> bool {
vclock_gt(&self.vector_clock, &other.vector_clock)
}
}
#[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);
}
}
|
