feat(tvix/castore): add composition module r/8365

Change-Id: I0868f3278db85ae5fe030089ee9033837bc08748
Signed-off-by: Yureka <tvl@yuka.dev>
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11853
Reviewed-by: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI

1 files changed, 29 insertions, 0 deletions

diff --git a/tvix/castore/src/directoryservice/combinators.rs b/tvix/castore/src/directoryservice/combinators.rs
index d3f351d6b689..2364a313d5f4 100644
--- a/tvix/castore/src/directoryservice/combinators.rs
+++ b/tvix/castore/src/directoryservice/combinators.rs
@@ -1,3 +1,5 @@
+use std::sync::Arc;
+
 use futures::stream::BoxStream;
 use futures::StreamExt;
 use futures::TryFutureExt;
@@ -6,6 +8,7 @@ use tonic::async_trait;
 use tracing::{instrument, trace};
 
 use super::{DirectoryGraph, DirectoryService, RootToLeavesValidator, SimplePutter};
+use crate::composition::{CompositionContext, ServiceBuilder};
 use crate::directoryservice::DirectoryPutter;
 use crate::proto;
 use crate::B3Digest;
@@ -140,3 +143,29 @@ where
         Box::new(SimplePutter::new((*self).clone()))
     }
 }
+
+#[derive(serde::Deserialize, Debug)]
+#[serde(deny_unknown_fields)]
+pub struct CacheConfig {
+    near: String,
+    far: String,
+}
+
+#[async_trait]
+impl ServiceBuilder for CacheConfig {
+    type Output = dyn DirectoryService;
+    async fn build<'a>(
+        &'a self,
+        _instance_name: &str,
+        context: &CompositionContext<dyn DirectoryService>,
+    ) -> Result<Arc<dyn DirectoryService>, Box<dyn std::error::Error + Send + Sync + 'static>> {
+        let (near, far) = futures::join!(
+            context.resolve(self.near.clone()),
+            context.resolve(self.far.clone())
+        );
+        Ok(Arc::new(Cache {
+            near: near?,
+            far: far?,
+        }))
+    }
+}