distkit 0.2.2

A toolkit of distributed systems primitives for Rust, backed by Redis
Documentation 
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//! Instance-aware counters that track each running instance's contribution separately.
//!
//! This module provides [`StrictInstanceAwareCounter`] (immediate consistency) and
//! [`LaxInstanceAwareCounter`] (eventual consistency with in-memory buffering). Both
//! implement [`InstanceAwareCounterTrait`].

#[cfg(test)]
mod tests;

mod strict_instance_aware_counter;
pub use strict_instance_aware_counter::*;

mod lax_instance_aware_counter;
pub use lax_instance_aware_counter::*;
use uuid::Uuid;

use crate::{DistkitError, RedisKey};

// ---------------------------------------------------------------------------
// Trait
// ---------------------------------------------------------------------------

/// Async interface for instance-aware distributed counter operations.
///
/// [`StrictInstanceAwareCounter`] implements this trait, allowing generic
/// code to work with any instance-aware counter implementation.
#[async_trait::async_trait]
pub trait InstanceAwareCounterTrait {
    /// Returns this instance's unique identifier.
    ///
    /// Each counter instance is assigned a UUID on construction. The ID is
    /// used to namespace per-instance contributions in Redis and to distinguish
    /// live instances from dead ones during cleanup.
    ///
    /// # Examples
    ///
    /// ```rust
    /// # use distkit::{RedisKey, icounter::InstanceAwareCounterTrait};
    /// # #[tokio::main]
    /// # async fn main() -> Result<(), Box<dyn std::error::Error>> {
    /// # let counter = distkit::__doctest_helpers::strict_icounter().await?;
    /// let id = counter.instance_id();
    /// assert!(!id.is_empty());
    /// # Ok(())
    /// # }
    /// ```
    fn instance_id(&self) -> &str;

    /// Increments the counter for `key` by `count` (stale-aware).
    ///
    /// Returns `(cumulative, instance_count)` where `cumulative` is the sum
    /// across all live instances and `instance_count` is this instance's slice.
    ///
    /// # Examples
    ///
    /// ```rust
    /// # use distkit::{RedisKey, icounter::InstanceAwareCounterTrait};
    /// # #[tokio::main]
    /// # async fn main() -> Result<(), Box<dyn std::error::Error>> {
    /// # let (server_a, server_b) = distkit::__doctest_helpers::two_strict_icounters().await?;
    /// let key = RedisKey::try_from("connections".to_string())?;
    /// let (cumulative_a, slice_a) = server_a.inc(&key, 3).await?;
    /// assert_eq!(cumulative_a, 3);
    /// assert_eq!(slice_a, 3);
    /// let (cumulative_b, slice_b) = server_b.inc(&key, 5).await?;
    /// assert_eq!(cumulative_b, 8); // both contributions
    /// assert_eq!(slice_b, 5);      // only server_b's slice
    /// # Ok(())
    /// # }
    /// ```
    async fn inc(&self, key: &RedisKey, count: i64) -> Result<(i64, i64), DistkitError>;

    /// Decrements the counter for `key` by `count` (stale-aware).
    ///
    /// Equivalent to `inc(key, -count)`. Returns `(cumulative, instance_count)`.
    ///
    /// # Examples
    ///
    /// ```rust
    /// # use distkit::{RedisKey, icounter::InstanceAwareCounterTrait};
    /// # #[tokio::main]
    /// # async fn main() -> Result<(), Box<dyn std::error::Error>> {
    /// # let counter = distkit::__doctest_helpers::strict_icounter().await?;
    /// let key = RedisKey::try_from("connections".to_string())?;
    /// counter.inc(&key, 10).await?;
    /// let (cumulative, slice) = counter.dec(&key, 4).await?;
    /// assert_eq!(cumulative, 6);
    /// assert_eq!(slice, 6);
    /// # Ok(())
    /// # }
    /// ```
    async fn dec(&self, key: &RedisKey, count: i64) -> Result<(i64, i64), DistkitError>;

    /// Sets the cumulative total for `key` to `count`, bumping the epoch.
    ///
    /// All other instances see their stored count as stale on their next
    /// operation. The calling instance becomes sole owner of the entire count.
    /// Returns `(cumulative, instance_count)`.
    ///
    /// # Examples
    ///
    /// ```rust
    /// # use distkit::{RedisKey, icounter::InstanceAwareCounterTrait};
    /// # #[tokio::main]
    /// # async fn main() -> Result<(), Box<dyn std::error::Error>> {
    /// # let (server_a, server_b) = distkit::__doctest_helpers::two_strict_icounters().await?;
    /// let key = RedisKey::try_from("connections".to_string())?;
    /// server_a.inc(&key, 10).await?;
    /// server_b.inc(&key, 5).await?;
    /// // Epoch bumps; all previous per-instance contributions are cleared.
    /// let (cumulative, slice) = server_a.set(&key, 100).await?;
    /// assert_eq!(cumulative, 100);
    /// assert_eq!(slice, 100); // server_a now owns the entire count
    /// # Ok(())
    /// # }
    /// ```
    async fn set(&self, key: &RedisKey, count: i64) -> Result<(i64, i64), DistkitError>;

    /// Sets only this instance's contribution for `key` to `count`, without
    /// bumping the epoch.
    ///
    /// Other instances' slices are preserved. Returns `(new_cumulative, instance_count)`.
    ///
    /// # Examples
    ///
    /// ```rust
    /// # use distkit::{RedisKey, icounter::InstanceAwareCounterTrait};
    /// # #[tokio::main]
    /// # async fn main() -> Result<(), Box<dyn std::error::Error>> {
    /// # let (server_a, server_b) = distkit::__doctest_helpers::two_strict_icounters().await?;
    /// let key = RedisKey::try_from("connections".to_string())?;
    /// server_a.inc(&key, 10).await?;
    /// server_b.inc(&key, 5).await?;
    /// // No epoch bump: server_b's slice is not evicted.
    /// let (cumulative, slice) = server_a.set_on_instance(&key, 7).await?;
    /// assert_eq!(slice, 7);
    /// assert_eq!(cumulative, 12); // server_a: 7 + server_b: 5
    /// # Ok(())
    /// # }
    /// ```
    async fn set_on_instance(
        &self,
        key: &RedisKey,
        count: i64,
    ) -> Result<(i64, i64), DistkitError>;

    /// Returns `(cumulative, instance_count)` for `key`.
    ///
    /// A missing key returns `(0, 0)`. Dead-instance cleanup runs as a side
    /// effect.
    ///
    /// # Examples
    ///
    /// ```rust
    /// # use distkit::{RedisKey, icounter::InstanceAwareCounterTrait};
    /// # #[tokio::main]
    /// # async fn main() -> Result<(), Box<dyn std::error::Error>> {
    /// # let counter = distkit::__doctest_helpers::strict_icounter().await?;
    /// let key = RedisKey::try_from("connections".to_string())?;
    /// // A missing key returns (0, 0).
    /// assert_eq!(counter.get(&key).await?, (0, 0));
    /// counter.inc(&key, 5).await?;
    /// assert_eq!(counter.get(&key).await?, (5, 5));
    /// # Ok(())
    /// # }
    /// ```
    async fn get(&self, key: &RedisKey) -> Result<(i64, i64), DistkitError>;

    /// Deletes `key` globally, bumping the epoch to invalidate all instances.
    ///
    /// Returns `(old_cumulative, old_instance_count)`. After deletion, a
    /// subsequent `inc` starts fresh from `0`.
    ///
    /// # Examples
    ///
    /// ```rust
    /// # use distkit::{RedisKey, icounter::InstanceAwareCounterTrait};
    /// # #[tokio::main]
    /// # async fn main() -> Result<(), Box<dyn std::error::Error>> {
    /// # let (server_a, server_b) = distkit::__doctest_helpers::two_strict_icounters().await?;
    /// let key = RedisKey::try_from("connections".to_string())?;
    /// server_a.inc(&key, 3).await?;
    /// server_b.inc(&key, 7).await?;
    /// let (old_cumulative, _) = server_a.del(&key).await?;
    /// assert_eq!(old_cumulative, 10);
    /// // After deletion both instances start fresh from 0.
    /// assert_eq!(server_b.inc(&key, 1).await?, (1, 1));
    /// # Ok(())
    /// # }
    /// ```
    async fn del(&self, key: &RedisKey) -> Result<(i64, i64), DistkitError>;

    /// Removes only this instance's contribution for `key`, without bumping
    /// the epoch.
    ///
    /// Returns `(new_cumulative, removed_count)`. Other instances are not
    /// affected.
    ///
    /// # Examples
    ///
    /// ```rust
    /// # use distkit::{RedisKey, icounter::InstanceAwareCounterTrait};
    /// # #[tokio::main]
    /// # async fn main() -> Result<(), Box<dyn std::error::Error>> {
    /// # let (server_a, server_b) = distkit::__doctest_helpers::two_strict_icounters().await?;
    /// let key = RedisKey::try_from("connections".to_string())?;
    /// server_a.inc(&key, 3).await?;
    /// server_b.inc(&key, 7).await?;
    /// // Only server_a's slice is removed; server_b is unaffected.
    /// let (new_cumulative, removed) = server_a.del_on_instance(&key).await?;
    /// assert_eq!(removed, 3);
    /// assert_eq!(new_cumulative, 7); // server_b's slice remains
    /// # Ok(())
    /// # }
    /// ```
    async fn del_on_instance(&self, key: &RedisKey) -> Result<(i64, i64), DistkitError>;

    /// Clears all keys and all instance state from Redis.
    ///
    /// # Examples
    ///
    /// ```rust
    /// # use distkit::{RedisKey, icounter::InstanceAwareCounterTrait};
    /// # #[tokio::main]
    /// # async fn main() -> Result<(), Box<dyn std::error::Error>> {
    /// # let counter = distkit::__doctest_helpers::strict_icounter().await?;
    /// let k1 = RedisKey::try_from("a".to_string())?;
    /// let k2 = RedisKey::try_from("b".to_string())?;
    /// counter.inc(&k1, 10).await?;
    /// counter.inc(&k2, 20).await?;
    /// counter.clear().await?;
    /// assert_eq!(counter.get(&k1).await?, (0, 0));
    /// assert_eq!(counter.get(&k2).await?, (0, 0));
    /// # Ok(())
    /// # }
    /// ```
    async fn clear(&self) -> Result<(), DistkitError>;

    /// Removes only this instance's contributions for all keys, without
    /// affecting other instances.
    ///
    /// # Examples
    ///
    /// ```rust
    /// # use distkit::{RedisKey, icounter::InstanceAwareCounterTrait};
    /// # #[tokio::main]
    /// # async fn main() -> Result<(), Box<dyn std::error::Error>> {
    /// # let (server_a, server_b) = distkit::__doctest_helpers::two_strict_icounters().await?;
    /// let key = RedisKey::try_from("connections".to_string())?;
    /// server_a.inc(&key, 3).await?;
    /// server_b.inc(&key, 7).await?;
    /// // Only server_a's contributions are removed; server_b's slice survives.
    /// server_a.clear_on_instance().await?;
    /// assert_eq!(server_b.get(&key).await?, (7, 7));
    /// # Ok(())
    /// # }
    /// ```
    async fn clear_on_instance(&self) -> Result<(), DistkitError>;
}

// ---------------------------------------------------------------------------
// Helpers
// ---------------------------------------------------------------------------

fn generate_instance_id() -> String {
    Uuid::new_v4().to_string()
}