refactor(tvix/store): drop calculate_nar from PathInfoService

This shouldn't be part of the PathInfoService trait.

Pretty much none of the PathInfoServices do implement it, and requiring
them to implement it means they also cannot make use of this calculation
already being done by other PathInfoServices.

Move it out into its own NarCalculationService trait, defined somewhere
at tvix_store::nar, and have everyone who wants to trigger nar
calculation use nar_calculation_service directly, which now is an
additional field in TvixStoreIO for example.

It being moved outside the PathInfoService trait doesn't prohibit
specific implementations to implement it (like the GRPC client for the
`PathInfoService` does.

This is currently wired together in a bit of a hacky fashion - as of
now, everything uses the naive implementation that traverses blob and
directoryservice, rather than composing it properly. I want to leave
that up to a later CL, dealing with other parts of store composition
too.

Change-Id: I18d07ea4301d4a07651b8218bc5fe95e4e307208
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11619
Reviewed-by: Connor Brewster <cbrewster@hey.com>
Autosubmit: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI

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)]

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>(