hitbox-fn

Function memoization for the Hitbox caching framework.

This crate provides tools for caching async function results using the hitbox FSM. It wraps function arguments and return types into the hitbox pipeline, handling cache key generation, serialization, and upstream execution.

Overview

• [Cache] - Pre-configured cache with backend, policy, and concurrency settings
• [#[cached]] - Attribute macro that transforms async functions into cacheable functions
• [KeyExtract] - Trait for types to describe their cache key contribution
• [Arg] / [Skipped] - Wrappers to include or exclude function parameters from cache keys
• [FnExtractor] - Bridges KeyExtract to hitbox's Extractor trait
• [FnUpstream] - Adapts async functions to hitbox's Upstream trait

Quick Start

use hitbox_fn::prelude::*;
use hitbox_moka::MokaBackend;
use std::time::Duration;

#[derive(KeyExtract)]
struct UserId(u64);

#[cached]
async fn fetch_user(id: UserId) -> Result<User, Error> {
    // expensive operation
}

// Build a reusable cache
let cache = Cache::builder()
    .backend(MokaBackend::builder().max_entries(1000).build())
    .policy(PolicyConfig::builder().ttl(Duration::from_secs(60)).build())
    .build();

// Call through cache
let user = fetch_user(UserId(42))
    .cache(&cache)
    .await?;

// With cache context (hit/miss/stale info)
let (user, ctx) = fetch_user(UserId(42))
    .cache(&cache)
    .with_context()
    .await;

// Or call directly without caching (passthrough)
let user = fetch_user(UserId(42)).await?;

Feature Flags

• derive - Enable derive macros (#[cached], #[derive(KeyExtract)], etc.) via hitbox-derive
• rkyv_format - Enable rkyv zero-copy serialization support