runtime: add cache backend factory seam

crates/crank-runtime/src/cache_factory.rs

@@ -0,0 +1,47 @@
+use std::sync::Arc;
+
+use async_trait::async_trait;
+
+use crate::{
+    RuntimeCacheConfig, RuntimeCacheStoreInitError, RuntimeCacheStores,
+};
+
+#[async_trait]
+pub trait CacheBackendFactory: Send + Sync {
+    async fn build(
+        &self,
+        config: &RuntimeCacheConfig,
+    ) -> Result<RuntimeCacheStores, RuntimeCacheStoreInitError>;
+}
+
+pub type SharedCacheBackendFactory = Arc<dyn CacheBackendFactory>;
+
+#[derive(Clone, Copy, Debug, Default)]
+pub struct BuiltinCacheBackendFactory;
+
+#[async_trait]
+impl CacheBackendFactory for BuiltinCacheBackendFactory {
+    async fn build(
+        &self,
+        config: &RuntimeCacheConfig,
+    ) -> Result<RuntimeCacheStores, RuntimeCacheStoreInitError> {
+        RuntimeCacheStores::from_config(config).await
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{CacheBackendFactory, RuntimeCacheConfig};
+
+    use super::BuiltinCacheBackendFactory;
+
+    #[tokio::test]
+    async fn builtin_factory_builds_default_memory_stores() {
+        let stores = BuiltinCacheBackendFactory
+            .build(&RuntimeCacheConfig::default())
+            .await
+            .unwrap();
+
+        assert_eq!(stores.backend, crank_core::CacheBackend::Memory);
+    }
+}

crates/crank-runtime/src/lib.rs

@@ -1,6 +1,7 @@
 mod aggregation;
 mod auth;
 mod cache;
+mod cache_factory;
 mod error;
 mod executor;
 mod executor_builder;
@@ -18,6 +19,9 @@ pub use cache::{
     InMemoryResponseCacheStore, RedisCacheStore, RuntimeCacheConfig, RuntimeCacheConfigError,
     RuntimeCacheStoreInitError, RuntimeCacheStores,
 };
+pub use cache_factory::{
+    BuiltinCacheBackendFactory, CacheBackendFactory, SharedCacheBackendFactory,
+};
 pub use error::RuntimeError;
 pub use executor::RuntimeExecutor;
 pub use executor_builder::{RuntimeExecutorBuilder, community_default};