actordb 0.4.0

// Copyright (c) Sean Lawlor
//
// This source code is licensed under both the MIT license found in the
// LICENSE-MIT file in the root directory of this source tree.

//! Pluggable durable storage for a node's local copy.
//!
//! A [`KvStore`](crate::store::KvStore) persists the batches the [`KvActor`](crate::actor::KvActor)
//! flushes and reloads them on boot. Persistence itself is optional:
//! `NodeConfig.store` is `None` by default (a pure in-memory node).
//! The default crate includes no bundled storage backend. Enable the `rocksdb`
//! cargo feature for `RocksDbStore`, the preferred durable implementation, or
//! bring your own. The independent `memory` feature enables `MemoryStore`, a
//! no-op test double for exercising the persistence plumbing without a database.
//! Neither feature enables the other; the Node's volatile actor cache does not
//! depend on either backend.
//!
//! Shared contracts, identities, capability types, and backend options live in
//! this parent module. Each implementation has its own child module:
//! the `memory` feature enables the test double in `store::memory`,
//! [`prefixed`](crate::store::prefixed) contains the fragment namespace adapter,
//! and the `rocksdb` feature enables the offered RocksDB
//! backend in `store::rocksdb`. Existing `store::*` type imports remain available
//! through reexports when the corresponding feature is enabled. `KvStore` and
//! the `PrefixedStore` namespace wrapper remain available without a backend.
//!
//! A caller-supplied store works with the backend-free default crate:
//!
//! ```
//! use actordb::{actor::VersionedValue, shard::FragmentId};
//! use actordb::store::{KvStore, PrefixedStore, StoreError};
//! use std::sync::Arc;
//!
//! struct CallerStore;
//! impl KvStore for CallerStore {
//!     fn load(&self) -> Result<Vec<(Vec<u8>, VersionedValue)>, StoreError> {
//!         Ok(Vec::new())
//!     }
//!     fn write_batch(&self, _: &[(Vec<u8>, VersionedValue)]) -> Result<(), StoreError> {
//!         Ok(())
//!     }
//! }
//! let root: Arc<dyn KvStore> = Arc::new(CallerStore);
//! let fragment = PrefixedStore::new(root, FragmentId(0));
//! assert!(fragment.load().unwrap().is_empty());
//! ```

#![cfg_attr(
    not(feature = "memory"),
    doc = r#"
Without `memory`, neither the root reexport nor the backend module is public:

```compile_fail
use actordb::store::MemoryStore;
```

```compile_fail
use actordb::store::memory::MemoryStore;
```
"#
)]
#![cfg_attr(
    not(feature = "rocksdb"),
    doc = r#"
Without `rocksdb`, neither the root reexport nor the backend module is public:

```compile_fail
use actordb::store::RocksDbStore;
```

```compile_fail
use actordb::store::rocksdb::RocksDbStore;
```

RocksDB open options and Node's convenience constructor are also opt-in:

```compile_fail
use actordb::store::RocksDbOptions;
```

```compile_fail
let config = actordb::node::NodeConfig::with_rocksdb("./data/node-a");
```
"#
)]

use std::fmt;

use crate::actor::VersionedValue;

#[cfg(feature = "memory")]
pub mod memory;
pub mod prefixed;
#[cfg(feature = "rocksdb")]
pub mod rocksdb;

#[cfg(feature = "memory")]
pub use memory::MemoryStore;
pub use prefixed::PrefixedStore;
#[cfg(feature = "rocksdb")]
pub use rocksdb::RocksDbStore;

/// Error from a [`KvStore`] operation.
#[derive(Debug)]
pub struct StoreError(pub String);

impl fmt::Display for StoreError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "store error: {}", self.0)
    }
}

impl std::error::Error for StoreError {}

/// Immutable identity of one node's durable keyspace.
///
/// A backend may persist this identity and reject a later attachment under a
/// different node id or fragment count. The offered RocksDB backend does so:
/// changing either value without an explicit migration can otherwise hide
/// prefixed records or mount one node's local copy as another node.
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct StoreIdentity {
    node_id: String,
    fragment_count: u32,
}

impl StoreIdentity {
    /// Describe the node and fragment layout which will use a store.
    pub fn new(node_id: String, fragment_count: u32) -> Self {
        Self {
            node_id,
            fragment_count,
        }
    }

    /// Node id permanently associated with the store.
    pub fn node_id(&self) -> &str {
        &self.node_id
    }

    /// Fragment count permanently associated with the store.
    pub fn fragment_count(&self) -> u32 {
        self.fragment_count
    }
}

/// RAII ownership returned when a node attaches to a store.
///
/// Custom stores receive an unmanaged binding from the default
/// [`KvStore::bind`] implementation. RocksDB uses a managed binding to reject
/// two live nodes sharing one `RocksDbStore` instance; dropping the binding
/// releases that in-process attachment.
pub struct StoreBinding {
    release: Option<Box<dyn FnOnce() + Send + Sync>>,
}

impl StoreBinding {
    /// Construct a binding with no release action.
    ///
    /// This is useful to custom stores which validate [`StoreIdentity`] but do
    /// not need to own an exclusive backend lease.
    pub fn unmanaged() -> Self {
        Self { release: None }
    }

    /// Construct a binding which runs `release` when it is cleanly dropped.
    ///
    /// Custom stores can use this to own an exclusive backend lease for the
    /// lifetime of a Node. actordb may deliberately abandon the callback when
    /// asynchronous Node startup or shutdown is cancelled and actor exit
    /// cannot be proven; in that case the callback and its captures are
    /// retained until process exit so an RAII capture cannot release the lease.
    pub fn managed(release: impl FnOnce() + Send + Sync + 'static) -> Self {
        Self {
            release: Some(Box::new(release)),
        }
    }

    /// Keep a managed backend fail-closed when its owner cannot prove that all
    /// users have stopped. Explicit Node shutdown releases normally; best-
    /// effort Drop abandons the release callback so the same live store object
    /// cannot be reattached while old actor tasks may still be exiting.
    pub(crate) fn abandon(&mut self) {
        if let Some(release) = self.release.take() {
            // Dropping a closure also drops its captures. A custom backend may
            // capture an RAII lease whose Drop releases exclusivity, so merely
            // discarding the callback would violate fail-closed cancellation.
            // There is no later join point which can safely release it; retain
            // the lease until process exit instead.
            std::mem::forget(release);
        }
    }
}

impl Drop for StoreBinding {
    fn drop(&mut self) {
        if let Some(release) = self.release.take() {
            release();
        }
    }
}

/// Whether a backend opts into lifecycle-driven prefix deletion.
///
/// The conservative default is [`PrefixDeleteSupport::Retained`], so adding
/// prefix retirement to actordb does not cause existing custom stores to begin
/// receiving destructive calls without an explicit implementation choice.
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
pub enum PrefixDeleteSupport {
    /// Keep retired namespaces. Callers must not invoke `delete_prefix` as an
    /// automatic lifecycle side effect.
    #[default]
    Retained,
    /// The backend supports quiesced, durable, idempotent prefix deletion.
    Supported,
}

/// Crash durability of an ordinary successful [`KvStore::write_batch`].
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
pub enum StoreCommitDurability {
    /// The backend accepted the write, but an operating-system crash or power
    /// loss may still discard it.
    #[default]
    Buffered,
    /// The backend reports that the write reached its stable crash-recovery
    /// boundary before returning.
    Stable,
}

/// Result of asking a store to remove a key prefix.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum PrefixDeleteOutcome {
    /// The prefix was durably made invisible before the call returned.
    Deleted,
    /// The backend retained the prefix. This is the source-compatible default
    /// for custom stores which have not implemented durable namespace cleanup.
    Retained,
}

/// Durable storage for a node's local copy.
///
/// Implementors must be thread-safe: different fragments can call the same
/// underlying store concurrently. `load` runs once at actor boot;
/// `write_batch` runs on every flush (see `NodeConfig` flush knobs). Writes
/// for one fragment are serialized, but a batch may be retried after a
/// failure or cancelled caller, so implementations must be idempotent for
/// the same key/value versions.
///
/// Keys are raw bytes. The actor works with `String` keys and converts
/// at the boundary (failing boot loudly on non-UTF-8 data); the store
/// itself never interprets key bytes.
///
/// Every persisted [`VersionedValue::node_id`] must contain 1 to 255 UTF-8
/// bytes. Node actors validate this before calling the store and again while
/// loading, but direct store users must preserve the same invariant.
pub trait KvStore: Send + Sync + 'static {
    /// Attach one live node and validate any backend identity metadata.
    ///
    /// The default is an unmanaged no-op so existing custom implementations
    /// remain source compatible. Backends which persist multiple fragment
    /// namespaces should bind at least the node id and fragment count. A
    /// wrapper around a backend which requires binding must delegate this call
    /// and retain the returned ownership rather than relying on the default.
    fn bind(&self, _identity: &StoreIdentity) -> Result<StoreBinding, StoreError> {
        Ok(StoreBinding::unmanaged())
    }
    /// Load the full backing dataset. The default [`KvStore::load_prefix`]
    /// implementation filters this result during fragment startup.
    fn load(&self) -> Result<Vec<(Vec<u8>, VersionedValue)>, StoreError>;
    /// Load only keys beginning with `prefix`. The default preserves source
    /// compatibility for custom stores; stores with ordered iteration should
    /// override it to avoid a full-dataset scan for every fragment.
    fn load_prefix(&self, prefix: &[u8]) -> Result<Vec<(Vec<u8>, VersionedValue)>, StoreError> {
        Ok(self
            .load()?
            .into_iter()
            .filter(|(key, _)| key.starts_with(prefix))
            .collect())
    }
    /// Crash durability provided by an ordinary successful `write_batch`.
    ///
    /// Existing custom stores default to [`StoreCommitDurability::Buffered`].
    /// A wrapper must delegate this method if the wrapped backend offers a
    /// stronger guarantee.
    fn commit_durability(&self) -> StoreCommitDurability {
        StoreCommitDurability::Buffered
    }
    /// Force writes completed before this call through the backend's strongest
    /// available crash-recovery fence.
    ///
    /// Callers flush actor-side buffers before invoking this method. The default
    /// performs no additional work and reports [`KvStore::commit_durability`],
    /// preserving compatibility for custom stores. Implementations may override
    /// it when an explicit fence can strengthen buffered ordinary writes.
    fn stable_fence(&self) -> Result<StoreCommitDurability, StoreError> {
        Ok(self.commit_durability())
    }
    /// Atomically persist a batch of winning writes. Each key occurs at most
    /// once in a batch.
    fn write_batch(&self, writes: &[(Vec<u8>, VersionedValue)]) -> Result<(), StoreError>;
    /// Declare whether lifecycle code may invoke [`KvStore::delete_prefix`].
    ///
    /// Existing custom stores retain namespaces by default. Opting in promises
    /// that `delete_prefix` obeys its quiescence, durability, and idempotency
    /// contract; the returned [`PrefixDeleteOutcome`] remains authoritative for
    /// each call.
    fn prefix_delete_support(&self) -> PrefixDeleteSupport {
        PrefixDeleteSupport::Retained
    }
    /// Durably remove keys beginning with `prefix` after their writers have
    /// been quiesced. The operation must be idempotent because lifecycle work
    /// can retry it after an ambiguous failure.
    ///
    /// Existing custom stores retain data by default. Returning
    /// [`PrefixDeleteOutcome::Deleted`] promises that a successful reopen will
    /// not expose any pre-call key in this prefix.
    fn delete_prefix(&self, _prefix: &[u8]) -> Result<PrefixDeleteOutcome, StoreError> {
        Ok(PrefixDeleteOutcome::Retained)
    }
}

/// Crash policy for successful RocksDB write batches.
///
/// Both modes keep the write-ahead log enabled. The distinction is whether a
/// successful call forces that log through the operating-system buffer cache.
#[cfg(feature = "rocksdb")]
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
pub enum RocksDbDurability {
    /// Append to the WAL without synchronously flushing it to stable media.
    AsyncWal,
    /// Synchronously flush the WAL before reporting success.
    #[default]
    SyncWal,
}

/// Options used when opening the offered RocksDB backend.
#[cfg(feature = "rocksdb")]
#[derive(Clone, Copy, Debug, PartialEq, Eq, bon::Builder)]
pub struct RocksDbOptions {
    #[builder(default = RocksDbDurability::SyncWal)]
    durability: RocksDbDurability,
    #[builder(default = false, name = legacy_manifest_adoption)]
    adopt_legacy_manifest: bool,
}

#[cfg(feature = "rocksdb")]
impl Default for RocksDbOptions {
    fn default() -> Self {
        Self::builder().build()
    }
}

#[cfg(feature = "rocksdb")]
impl RocksDbOptions {
    /// Select the WAL completion policy for ordinary data batches.
    pub fn with_durability(mut self, durability: RocksDbDurability) -> Self {
        self.durability = durability;
        self
    }

    /// Explicitly allow a non-empty pre-manifest database to be adopted by the
    /// first [`StoreIdentity`] supplied to [`KvStore::bind`].
    ///
    /// This is a one-time migration escape hatch. A legacy database contains
    /// no trustworthy original node id, so callers must verify the path and
    /// take a backup before enabling it. Existing, corrupt, or mismatched
    /// manifests are never overwritten.
    pub fn with_legacy_manifest_adoption(mut self, allow: bool) -> Self {
        self.adopt_legacy_manifest = allow;
        self
    }

    /// Current ordinary-write durability policy.
    pub fn durability(&self) -> RocksDbDurability {
        self.durability
    }

    /// Whether this open may adopt a non-empty pre-manifest database.
    pub fn legacy_manifest_adoption(&self) -> bool {
        self.adopt_legacy_manifest
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn custom_store_capabilities_default_to_retention_and_buffering() {
        struct CustomStore;

        impl KvStore for CustomStore {
            fn load(&self) -> Result<Vec<(Vec<u8>, VersionedValue)>, StoreError> {
                Ok(Vec::new())
            }

            fn write_batch(&self, _writes: &[(Vec<u8>, VersionedValue)]) -> Result<(), StoreError> {
                Ok(())
            }
        }

        let store = CustomStore;
        assert_eq!(store.commit_durability(), StoreCommitDurability::Buffered);
        assert_eq!(
            store.stable_fence().unwrap(),
            StoreCommitDurability::Buffered
        );
        assert_eq!(store.prefix_delete_support(), PrefixDeleteSupport::Retained);
    }
}