310 lines
8.9 KiB
Rust
310 lines
8.9 KiB
Rust
use anyhow::{bail, Result};
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use serde::{Deserialize, Deserializer, Serialize, Serializer};
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use im::{OrdMap, OrdSet, ordset};
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use aero_bayou::*;
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use crate::unique_ident::{gen_ident, UniqueIdent};
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/// Parents are only persisted in the event log,
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/// not in the checkpoints.
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pub type Token = UniqueIdent;
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pub type Parents = Vec<Token>;
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pub type SyncDesc = (Parents, Token);
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pub type BlobId = UniqueIdent;
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pub type Etag = String;
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pub type FileName = String;
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pub type IndexEntry = (BlobId, FileName, Etag);
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#[derive(Clone, Default)]
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pub struct DavDag {
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/// Source of trust
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pub table: OrdMap<UniqueIdent, IndexEntry>,
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/// Indexes optimized for queries
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pub idx_by_filename: OrdMap<FileName, UniqueIdent>,
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/// Partial synchronization graph
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pub ancestors: OrdMap<UniqueIdent, OrdSet<UniqueIdent>>,
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/// All nodes
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pub all_nodes: OrdSet<UniqueIdent>,
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/// Head nodes
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pub heads: OrdSet<UniqueIdent>,
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/// Origin nodes
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pub origins: OrdSet<UniqueIdent>,
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}
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#[derive(Clone, Serialize, Deserialize, Debug)]
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pub enum DavDagOp {
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/// Merge is a virtual operation run when multiple heads are discovered
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Merge(SyncDesc),
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/// Add an item to the collection
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Put(SyncDesc, IndexEntry),
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/// Delete an item from the collection
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Delete(SyncDesc, BlobId),
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}
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impl DavDagOp {
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pub fn token(&self) -> Token {
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match self {
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Self::Merge((_, t)) => *t,
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Self::Put((_, t), _) => *t,
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Self::Delete((_, t), _) => *t,
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}
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}
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}
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impl DavDag {
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pub fn op_merge(&self) -> DavDagOp {
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DavDagOp::Merge(self.sync_desc())
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}
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pub fn op_put(&self, entry: IndexEntry) -> DavDagOp {
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DavDagOp::Put(self.sync_desc(), entry)
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}
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pub fn op_delete(&self, ident: BlobId) -> DavDagOp {
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DavDagOp::Delete(self.sync_desc(), ident)
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}
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// HELPER functions
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pub fn heads_vec(&self) -> Vec<Token> {
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self.heads.clone().into_iter().collect()
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}
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/// A sync descriptor
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pub fn sync_desc(&self) -> SyncDesc {
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(self.heads_vec(), gen_ident())
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}
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/// Resolve a sync token
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pub fn resolve(&self, known: UniqueIdent) -> Result<OrdSet<UniqueIdent>> {
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let already_known = self.all_ancestors(known);
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// We can't capture all missing events if we are not connected
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// to all sinks of the graph,
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// ie. if we don't already know all the sinks,
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// ie. if we are missing so much history that
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// the event log has been transformed into a checkpoint
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if !self.origins.is_subset(already_known.clone()) {
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bail!("Not enough history to produce a correct diff, a full resync is needed");
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}
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// Missing items are *all existing graph items* from which
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// we removed *all items known by the given node*.
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// In other words, all values in `all_nodes` that are not in `already_known`.
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Ok(self.all_nodes.clone().relative_complement(already_known))
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}
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/// Find all ancestors of a given node
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fn all_ancestors(&self, known: UniqueIdent) -> OrdSet<UniqueIdent> {
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let mut all_known: OrdSet<UniqueIdent> = OrdSet::new();
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let mut to_collect = vec![known];
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loop {
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let cursor = match to_collect.pop() {
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// Loop stops here
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None => break,
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Some(v) => v,
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};
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if all_known.insert(cursor).is_some() {
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// Item already processed
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continue
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}
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// Collect parents
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let parents = match self.ancestors.get(&cursor) {
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None => continue,
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Some(c) => c,
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};
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to_collect.extend(parents.iter());
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}
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all_known
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}
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// INTERNAL functions
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/// Register a WebDAV item (put, copy, move)
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fn register(&mut self, entry: IndexEntry) {
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let (blob_id, filename, _etag) = entry.clone();
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// Insert item in the source of trust
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self.table.insert(blob_id, entry);
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// Update the cache
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self.idx_by_filename.insert(filename, blob_id);
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}
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/// Unregister a WebDAV item (delete, move)
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fn unregister(&mut self, ident: &UniqueIdent) {
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// Query the source of truth to get the information we
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// need to clean the indexes
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let (_blob_id, filename, _etag) = match self.table.get(ident) {
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Some(v) => v,
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// Element does not exist, return early
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None => return,
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};
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self.idx_by_filename.remove(filename);
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// Finally clear item from the source of trust
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self.table.remove(ident);
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}
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/// When an event is processed, update the synchronization DAG
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fn sync_dag(&mut self, sync_desc: &SyncDesc) -> bool {
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let (parents, child) = sync_desc;
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// --- Update ANCESTORS
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// We register ancestors as it is required for the sync algorithm
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self.ancestors.insert(*child, parents.iter().fold(ordset![], |mut acc, p| {
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acc.insert(*p);
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acc
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}));
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// --- Update ORIGINS
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// If this event has no parents, it's an origin
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if parents.is_empty() {
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self.origins.insert(*child);
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}
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// --- Update HEADS
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// Remove from HEADS this event's parents
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parents.iter().for_each(|par| { self.heads.remove(par); });
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// This event becomes a new HEAD in turn
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self.heads.insert(*child);
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// --- Update ALL NODES
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self.all_nodes.insert(*child);
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true
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}
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}
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impl BayouState for DavDag {
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type Op = DavDagOp;
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fn apply(&self, op: &Self::Op) -> Self {
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let mut new = self.clone();
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match op {
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DavDagOp::Put(sync_desc, entry) => {
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if new.sync_dag(sync_desc) {
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new.register(entry.clone());
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}
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},
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DavDagOp::Delete(sync_desc, blob_id) => {
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if new.sync_dag(sync_desc) {
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new.unregister(blob_id);
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}
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},
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DavDagOp::Merge(sync_desc) => {
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new.sync_dag(sync_desc);
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}
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}
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new
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}
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}
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// CUSTOM SERIALIZATION & DESERIALIZATION
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#[derive(Serialize, Deserialize)]
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struct DavDagSerializedRepr {
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items: Vec<IndexEntry>,
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heads: Vec<UniqueIdent>,
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}
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impl<'de> Deserialize<'de> for DavDag {
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fn deserialize<D>(d: D) -> Result<Self, D::Error>
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where
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D: Deserializer<'de>,
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{
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let val: DavDagSerializedRepr = DavDagSerializedRepr::deserialize(d)?;
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let mut davdag = DavDag::default();
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// Build the table + index
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val.items.into_iter().for_each(|entry| davdag.register(entry));
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// Initialize the synchronization DAG with its roots
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val.heads.into_iter().for_each(|ident| {
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davdag.heads.insert(ident);
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davdag.origins.insert(ident);
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davdag.all_nodes.insert(ident);
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});
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Ok(davdag)
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}
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}
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impl Serialize for DavDag {
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fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
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where
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S: Serializer,
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{
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// Indexes are rebuilt on the fly, we serialize only the core database
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let items = self.table.iter().map(|(_, entry)| entry.clone()).collect();
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// We keep only the head entries from the sync graph,
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// these entries will be used to initialize it back when deserializing
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let heads = self.heads_vec();
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// Finale serialization object
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let val = DavDagSerializedRepr { items, heads };
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val.serialize(serializer)
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}
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}
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// ---- TESTS ----
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn base() {
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let mut state = DavDag::default();
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// Add item 1
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{
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let m = UniqueIdent([0x01; 24]);
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let ev = state.op_put((m, "cal.ics".into(), "321-321".into()));
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state = state.apply(&ev);
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assert_eq!(state.table.len(), 1);
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assert_eq!(state.resolve(ev.token()).unwrap().len(), 0);
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}
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// Add 2 concurrent items
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let (t1, t2) = {
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let blob1 = UniqueIdent([0x02; 24]);
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let ev1 = state.op_put((blob1, "cal2.ics".into(), "321-321".into()));
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let blob2 = UniqueIdent([0x01; 24]);
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let ev2 = state.op_delete(blob2);
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state = state.apply(&ev1);
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state = state.apply(&ev2);
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assert_eq!(state.table.len(), 1);
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assert_eq!(state.resolve(ev1.token()).unwrap(), ordset![ev2.token()]);
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(ev1.token(), ev2.token())
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};
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// Add later a new item
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{
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let blob3 = UniqueIdent([0x03; 24]);
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let ev = state.op_put((blob3, "cal3.ics".into(), "321-321".into()));
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state = state.apply(&ev);
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assert_eq!(state.table.len(), 2);
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assert_eq!(state.resolve(ev.token()).unwrap().len(), 0);
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assert_eq!(state.resolve(t1).unwrap(), ordset![t2, ev.token()]);
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}
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}
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}
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