2 files changed, 62 insertions, 1 deletions
diff --git a/tvix/store/src/nar/mod.rs b/tvix/store/src/nar/mod.rs
index 4d5101f9d558..164748a655e8 100644
--- a/tvix/store/src/nar/mod.rs
+++ b/tvix/store/src/nar/mod.rs
@@ -1,3 +1,4 @@
+use tonic::async_trait;
 use tvix_castore::B3Digest;
 
 mod import;
@@ -5,6 +6,31 @@ mod renderer;
 pub use import::ingest_nar;
 pub use renderer::calculate_size_and_sha256;
 pub use renderer::write_nar;
+pub use renderer::SimpleRenderer;
+use tvix_castore::proto as castorepb;
+
+#[async_trait]
+pub trait NarCalculationService: Send + Sync {
+    /// Return the nar size and nar sha256 digest for a given root node.
+    /// This can be used to calculate NAR-based output paths.
+    async fn calculate_nar(
+        &self,
+        root_node: &castorepb::node::Node,
+    ) -> Result<(u64, [u8; 32]), tvix_castore::Error>;
+}
+
+#[async_trait]
+impl<A> NarCalculationService for A
+where
+    A: AsRef<dyn NarCalculationService> + Send + Sync,
+{
+    async fn calculate_nar(
+        &self,
+        root_node: &castorepb::node::Node,
+    ) -> Result<(u64, [u8; 32]), tvix_castore::Error> {
+        self.as_ref().calculate_nar(root_node).await
+    }
+}
 
 /// Errors that can encounter while rendering NARs.
 #[derive(Debug, thiserror::Error)]
diff --git a/tvix/store/src/nar/renderer.rs b/tvix/store/src/nar/renderer.rs
index 3b39f700bd38..efd67671db70 100644
--- a/tvix/store/src/nar/renderer.rs
+++ b/tvix/store/src/nar/renderer.rs
@@ -1,16 +1,51 @@
 use crate::utils::AsyncIoBridge;
 
-use super::RenderError;
+use super::{NarCalculationService, RenderError};
 use count_write::CountWrite;
 use nix_compat::nar::writer::r#async as nar_writer;
 use sha2::{Digest, Sha256};
 use tokio::io::{self, AsyncWrite, BufReader};
+use tonic::async_trait;
 use tvix_castore::{
     blobservice::BlobService,
     directoryservice::DirectoryService,
     proto::{self as castorepb, NamedNode},
 };
 
+pub struct SimpleRenderer<BS, DS> {
+    blob_service: BS,
+    directory_service: DS,
+}
+
+impl<BS, DS> SimpleRenderer<BS, DS> {
+    pub fn new(blob_service: BS, directory_service: DS) -> Self {
+        Self {
+            blob_service,
+            directory_service,
+        }
+    }
+}
+
+#[async_trait]
+impl<BS, DS> NarCalculationService for SimpleRenderer<BS, DS>
+where
+    BS: BlobService + Clone,
+    DS: DirectoryService + Clone,
+{
+    async fn calculate_nar(
+        &self,
+        root_node: &castorepb::node::Node,
+    ) -> Result<(u64, [u8; 32]), tvix_castore::Error> {
+        calculate_size_and_sha256(
+            root_node,
+            self.blob_service.clone(),
+            self.directory_service.clone(),
+        )
+        .await
+        .map_err(|e| tvix_castore::Error::StorageError(format!("failed rendering nar: {}", e)))
+    }
+}
+
 /// Invoke [write_nar], and return the size and sha256 digest of the produced
 /// NAR output.
 pub async fn calculate_size_and_sha256<BS, DS>(