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finished initial networking impl

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Signed-off-by: Sienna Meridian Satterwhite <sienna@r3t.io>
This commit is contained in:
Sienna Meridian Satterwhite
2025-11-16 16:34:55 +00:00
parent 0f65b1baa2
commit 7acbadbc4a
28 changed files with 7117 additions and 13 deletions
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crates/lib/src/networking/rga.rs Normal file
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//! RGA (Replicated Growable Array) CRDT implementation
//!
//! This module provides a conflict-free replicated sequence that maintains
//! consistent ordering across concurrent insert and delete operations.
//!
//! ## RGA Semantics
//!
//! - **Causal ordering**: Elements inserted after position P stay after P
//! - **Concurrent inserts**: Resolved by timestamp + node ID tiebreaker
//! - **Tombstones**: Deleted elements remain in structure to preserve positions
//! - **Unique operation IDs**: Each insert gets a UUID for referencing
//!
//! ## Example
//!
//! ```
//! use lib::networking::Rga;
//! use uuid::Uuid;
//!
//! let node1 = Uuid::new_v4();
//! let node2 = Uuid::new_v4();
//!
//! // Node 1 creates sequence: [A, B]
//! let mut seq1: Rga<char> = Rga::new();
//! let (id_a, _) = seq1.insert_at_beginning('A', node1);
//! let (id_b, _) = seq1.insert_after(Some(id_a), 'B', node1);
//!
//! // Node 2 concurrently inserts C after A
//! let mut seq2 = seq1.clone();
//! seq2.insert_after(Some(id_a), 'C', node2);
//!
//! // Node 1 inserts D after A
//! seq1.insert_after(Some(id_a), 'D', node1);
//!
//! // Merge - concurrent inserts after A are ordered by timestamp + node ID
//! seq1.merge(&seq2);
//!
//! let values: Vec<char> = seq1.values().copied().collect();
//! assert_eq!(values.len(), 4); // A, (C or D), (D or C), B
//! ```
use std::collections::HashMap;
use bevy::prelude::*;
use serde::{
Deserialize,
Serialize,
};
use crate::networking::vector_clock::{
NodeId,
VectorClock,
};
/// An element in an RGA sequence
///
/// Each element has a unique ID and tracks its logical position in the sequence
/// via the "after" pointer.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct RgaElement<T> {
/// Unique ID for this element
pub id: uuid::Uuid,
/// The actual value
pub value: T,
/// ID of the element this was inserted after (None = beginning)
pub after_id: Option<uuid::Uuid>,
/// Node that performed the insert
pub inserting_node: NodeId,
/// Vector clock when inserted (for ordering concurrent inserts)
pub vector_clock: VectorClock,
/// Whether this element has been deleted (tombstone)
pub is_deleted: bool,
}
/// RGA (Replicated Growable Array) CRDT
///
/// A replicated sequence supporting concurrent insert/delete with consistent
/// ordering based on causal relationships.
///
/// # Type Parameters
///
/// - `T`: The element type (must be Clone, Serialize, Deserialize)
///
/// # Internal Structure
///
/// Elements are stored in a HashMap by ID. Each element tracks which element
/// it was inserted after, forming a linked list structure. Deleted elements
/// remain as tombstones to preserve positions for concurrent operations.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Rga<T> {
/// Map from element ID to element
elements: HashMap<uuid::Uuid, RgaElement<T>>,
}
impl<T> Rga<T>
where
T: Clone + Serialize + for<'de> Deserialize<'de>,
{
/// Create a new empty RGA sequence
pub fn new() -> Self {
Self {
elements: HashMap::new(),
}
}
/// Insert an element at the beginning of the sequence
///
/// Returns (element_id, position) where position is the index in the
/// visible sequence.
///
/// # Example
///
/// ```
/// use lib::networking::Rga;
/// use uuid::Uuid;
///
/// let node = Uuid::new_v4();
/// let mut seq: Rga<char> = Rga::new();
///
/// let (id, pos) = seq.insert_at_beginning('A', node);
/// assert_eq!(pos, 0);
/// ```
pub fn insert_at_beginning(&mut self, value: T, node_id: NodeId) -> (uuid::Uuid, usize) {
let id = uuid::Uuid::new_v4();
let mut clock = VectorClock::new();
clock.increment(node_id);
let element = RgaElement {
id,
value,
after_id: None,
inserting_node: node_id,
vector_clock: clock,
is_deleted: false,
};
self.elements.insert(id, element);
(id, 0)
}
/// Insert an element after a specific element ID
///
/// If after_id is None, inserts at the beginning.
///
/// Returns (element_id, position) where position is the index in the
/// visible sequence.
///
/// # Example
///
/// ```
/// use lib::networking::Rga;
/// use uuid::Uuid;
///
/// let node = Uuid::new_v4();
/// let mut seq: Rga<char> = Rga::new();
///
/// let (id_a, _) = seq.insert_at_beginning('A', node);
/// let (id_b, pos) = seq.insert_after(Some(id_a), 'B', node);
/// assert_eq!(pos, 1);
///
/// let values: Vec<char> = seq.values().copied().collect();
/// assert_eq!(values, vec!['A', 'B']);
/// ```
pub fn insert_after(
&mut self,
after_id: Option<uuid::Uuid>,
value: T,
node_id: NodeId,
) -> (uuid::Uuid, usize) {
let id = uuid::Uuid::new_v4();
let mut clock = VectorClock::new();
clock.increment(node_id);
let element = RgaElement {
id,
value,
after_id,
inserting_node: node_id,
vector_clock: clock,
is_deleted: false,
};
self.elements.insert(id, element);
// Calculate position
let position = self.calculate_position(id);
(id, position)
}
/// Insert an element with explicit vector clock
///
/// This is used when applying remote operations that already have
/// a vector clock.
pub fn insert_with_clock(
&mut self,
id: uuid::Uuid,
after_id: Option<uuid::Uuid>,
value: T,
node_id: NodeId,
vector_clock: VectorClock,
) -> usize {
let element = RgaElement {
id,
value,
after_id,
inserting_node: node_id,
vector_clock,
is_deleted: false,
};
self.elements.insert(id, element);
self.calculate_position(id)
}
/// Delete an element by ID
///
/// The element becomes a tombstone - it remains in the structure but
/// is hidden from the visible sequence.
///
/// # Example
///
/// ```
/// use lib::networking::Rga;
/// use uuid::Uuid;
///
/// let node = Uuid::new_v4();
/// let mut seq: Rga<char> = Rga::new();
///
/// let (id, _) = seq.insert_at_beginning('A', node);
/// assert_eq!(seq.len(), 1);
///
/// seq.delete(id);
/// assert_eq!(seq.len(), 0);
/// assert!(seq.is_deleted(id));
/// ```
pub fn delete(&mut self, element_id: uuid::Uuid) {
if let Some(element) = self.elements.get_mut(&element_id) {
element.is_deleted = true;
}
}
/// Check if an element is deleted
pub fn is_deleted(&self, element_id: uuid::Uuid) -> bool {
self.elements
.get(&element_id)
.map(|e| e.is_deleted)
.unwrap_or(false)
}
/// Get the visible length of the sequence (excluding tombstones)
pub fn len(&self) -> usize {
self.elements.values().filter(|e| !e.is_deleted).count()
}
/// Check if the sequence is empty (no visible elements)
pub fn is_empty(&self) -> bool {
self.len() == 0
}
/// Get all visible values in order
///
/// Returns an iterator over the values in their proper sequence order.
pub fn values(&self) -> impl Iterator<Item = &T> {
let ordered = self.get_ordered_elements();
ordered.into_iter().filter_map(move |id| {
self.elements.get(&id).and_then(|e| {
if !e.is_deleted {
Some(&e.value)
} else {
None
}
})
})
}
/// Get all visible elements with their IDs in order
pub fn elements_with_ids(&self) -> Vec<(uuid::Uuid, &T)> {
let ordered = self.get_ordered_elements();
ordered
.into_iter()
.filter_map(|id| {
self.elements.get(&id).and_then(|e| {
if !e.is_deleted {
Some((id, &e.value))
} else {
None
}
})
})
.collect()
}
/// Merge another RGA into this one
///
/// Implements CRDT merge by combining all elements from both sequences
/// and resolving positions based on causal ordering.
///
/// # Example
///
/// ```
/// use lib::networking::Rga;
/// use uuid::Uuid;
///
/// let node1 = Uuid::new_v4();
/// let node2 = Uuid::new_v4();
///
/// let mut seq1: Rga<char> = Rga::new();
/// seq1.insert_at_beginning('A', node1);
///
/// let mut seq2: Rga<char> = Rga::new();
/// seq2.insert_at_beginning('B', node2);
///
/// seq1.merge(&seq2);
/// assert_eq!(seq1.len(), 2);
/// ```
pub fn merge(&mut self, other: &Rga<T>) {
for (id, element) in &other.elements {
// Insert or update element
self.elements
.entry(*id)
.and_modify(|existing| {
// If other's element is deleted, mark ours as deleted too
if element.is_deleted {
existing.is_deleted = true;
}
})
.or_insert_with(|| element.clone());
}
}
/// Clear the sequence
///
/// Removes all elements and tombstones.
pub fn clear(&mut self) {
self.elements.clear();
}
/// Garbage collect tombstones
///
/// Removes deleted elements that have no children (nothing inserted after them).
/// This is safe because if no element references a tombstone as its parent,
/// it can be removed without affecting the sequence.
pub fn garbage_collect(&mut self) {
// Find all IDs that are referenced as after_id
let mut referenced_ids = std::collections::HashSet::new();
for element in self.elements.values() {
if let Some(after_id) = element.after_id {
referenced_ids.insert(after_id);
}
}
// Remove deleted elements that aren't referenced
self.elements.retain(|id, element| {
!element.is_deleted || referenced_ids.contains(id)
});
}
/// Get ordered list of element IDs
///
/// This builds the proper sequence order by following the after_id pointers
/// and resolving concurrent inserts using vector clocks + node IDs.
fn get_ordered_elements(&self) -> Vec<uuid::Uuid> {
// Build a map of after_id -> list of elements inserted after it
let mut children: HashMap<Option<uuid::Uuid>, Vec<uuid::Uuid>> = HashMap::new();
for (id, element) in &self.elements {
children
.entry(element.after_id)
.or_insert_with(Vec::new)
.push(*id);
}
// Sort children by vector clock, then node ID (for deterministic ordering)
for child_list in children.values_mut() {
child_list.sort_by(|a, b| {
let elem_a = &self.elements[a];
let elem_b = &self.elements[b];
// Compare vector clocks
match elem_a.vector_clock.compare(&elem_b.vector_clock) {
Ok(std::cmp::Ordering::Less) => std::cmp::Ordering::Less,
Ok(std::cmp::Ordering::Greater) => std::cmp::Ordering::Greater,
Ok(std::cmp::Ordering::Equal) | Err(_) => {
// If clocks are equal or concurrent, use node ID as tiebreaker
elem_a.inserting_node.cmp(&elem_b.inserting_node)
}
}
});
}
// Build ordered list by traversing from None (beginning)
let mut result = Vec::new();
let mut to_visit = vec![None];
while let Some(current_id) = to_visit.pop() {
if let Some(child_ids) = children.get(&current_id) {
// Visit children in reverse order (since we're using a stack)
for child_id in child_ids.iter().rev() {
result.push(*child_id);
to_visit.push(Some(*child_id));
}
}
}
result
}
/// Calculate the visible position of an element
fn calculate_position(&self, element_id: uuid::Uuid) -> usize {
let ordered = self.get_ordered_elements();
ordered
.iter()
.position(|id| id == &element_id)
.unwrap_or(0)
}
}
impl<T> Default for Rga<T>
where
T: Clone + Serialize + for<'de> Deserialize<'de>,
{
fn default() -> Self {
Self::new()
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_rga_new() {
let seq: Rga<char> = Rga::new();
assert!(seq.is_empty());
assert_eq!(seq.len(), 0);
}
#[test]
fn test_rga_insert_at_beginning() {
let node = uuid::Uuid::new_v4();
let mut seq: Rga<char> = Rga::new();
let (_, pos) = seq.insert_at_beginning('A', node);
assert_eq!(pos, 0);
assert_eq!(seq.len(), 1);
let values: Vec<char> = seq.values().copied().collect();
assert_eq!(values, vec!['A']);
}
#[test]
fn test_rga_insert_after() {
let node = uuid::Uuid::new_v4();
let mut seq: Rga<char> = Rga::new();
let (id_a, _) = seq.insert_at_beginning('A', node);
let (_, pos_b) = seq.insert_after(Some(id_a), 'B', node);
assert_eq!(pos_b, 1);
let values: Vec<char> = seq.values().copied().collect();
assert_eq!(values, vec!['A', 'B']);
}
#[test]
fn test_rga_delete() {
let node = uuid::Uuid::new_v4();
let mut seq: Rga<char> = Rga::new();
let (id_a, _) = seq.insert_at_beginning('A', node);
let (id_b, _) = seq.insert_after(Some(id_a), 'B', node);
assert_eq!(seq.len(), 2);
seq.delete(id_a);
assert_eq!(seq.len(), 1);
assert!(seq.is_deleted(id_a));
let values: Vec<char> = seq.values().copied().collect();
assert_eq!(values, vec!['B']);
}
#[test]
fn test_rga_insert_delete_insert() {
let node = uuid::Uuid::new_v4();
let mut seq: Rga<char> = Rga::new();
let (id_a, _) = seq.insert_at_beginning('A', node);
seq.delete(id_a);
assert_eq!(seq.len(), 0);
seq.insert_at_beginning('B', node);
assert_eq!(seq.len(), 1);
let values: Vec<char> = seq.values().copied().collect();
assert_eq!(values, vec!['B']);
}
#[test]
fn test_rga_merge_simple() {
let node1 = uuid::Uuid::new_v4();
let node2 = uuid::Uuid::new_v4();
let mut seq1: Rga<char> = Rga::new();
seq1.insert_at_beginning('A', node1);
let mut seq2: Rga<char> = Rga::new();
seq2.insert_at_beginning('B', node2);
seq1.merge(&seq2);
assert_eq!(seq1.len(), 2);
}
#[test]
fn test_rga_merge_preserves_order() {
let node = uuid::Uuid::new_v4();
let mut seq1: Rga<char> = Rga::new();
let (id_a, _) = seq1.insert_at_beginning('A', node);
let (id_b, _) = seq1.insert_after(Some(id_a), 'B', node);
seq1.insert_after(Some(id_b), 'C', node);
let seq2 = seq1.clone();
seq1.merge(&seq2);
let values: Vec<char> = seq1.values().copied().collect();
assert_eq!(values, vec!['A', 'B', 'C']);
}
#[test]
fn test_rga_merge_deletion() {
let node = uuid::Uuid::new_v4();
let mut seq1: Rga<char> = Rga::new();
let (id_a, _) = seq1.insert_at_beginning('A', node);
seq1.insert_after(Some(id_a), 'B', node);
let mut seq2 = seq1.clone();
seq2.delete(id_a);
seq1.merge(&seq2);
let values: Vec<char> = seq1.values().copied().collect();
assert_eq!(values, vec!['B']);
}
#[test]
fn test_rga_concurrent_inserts() {
let node1 = uuid::Uuid::new_v4();
let node2 = uuid::Uuid::new_v4();
// Both start with [A]
let mut seq1: Rga<char> = Rga::new();
let (id_a, _) = seq1.insert_at_beginning('A', node1);
let mut seq2 = seq1.clone();
// seq1 inserts B after A
seq1.insert_after(Some(id_a), 'B', node1);
// seq2 inserts C after A (concurrent)
seq2.insert_after(Some(id_a), 'C', node2);
// Merge
seq1.merge(&seq2);
// Should have A followed by B and C in some deterministic order
assert_eq!(seq1.len(), 3);
let values: Vec<char> = seq1.values().copied().collect();
assert_eq!(values[0], 'A');
assert!(values.contains(&'B'));
assert!(values.contains(&'C'));
}
#[test]
fn test_rga_clear() {
let node = uuid::Uuid::new_v4();
let mut seq: Rga<char> = Rga::new();
seq.insert_at_beginning('A', node);
seq.insert_at_beginning('B', node);
assert_eq!(seq.len(), 2);
seq.clear();
assert!(seq.is_empty());
}
#[test]
fn test_rga_garbage_collect() {
let node = uuid::Uuid::new_v4();
let mut seq: Rga<char> = Rga::new();
let (id_a, _) = seq.insert_at_beginning('A', node);
let (id_b, _) = seq.insert_after(Some(id_a), 'B', node);
let (_, _) = seq.insert_after(Some(id_b), 'C', node);
// Delete A (has child B, so should be kept)
seq.delete(id_a);
// Delete B (has child C, so should be kept)
seq.delete(id_b);
assert_eq!(seq.elements.len(), 3);
seq.garbage_collect();
// A and B should still be there (referenced by children)
// Only C is visible
assert_eq!(seq.len(), 1);
assert!(seq.elements.contains_key(&id_a));
assert!(seq.elements.contains_key(&id_b));
}
#[test]
fn test_rga_serialization() -> bincode::Result<()> {
let node = uuid::Uuid::new_v4();
let mut seq: Rga<String> = Rga::new();
let (id_a, _) = seq.insert_at_beginning("foo".to_string(), node);
seq.insert_after(Some(id_a), "bar".to_string(), node);
let bytes = bincode::serialize(&seq)?;
let deserialized: Rga<String> = bincode::deserialize(&bytes)?;
assert_eq!(deserialized.len(), 2);
let values: Vec<String> = deserialized.values().cloned().collect();
assert_eq!(values, vec!["foo".to_string(), "bar".to_string()]);
Ok(())
}
}