refactor(tvix/src/nar): drop NARCalculationService r/6270

There's only one way to calculate NAR files, by walking through them.

Things like caching such replies should be done closer to where we use
these, composing NARCalculationService doesn't actually give us much.

Instead, expose two functions, `nar::calculate_size_and_sha256` and
`nar::writer_nar`, the latter writing NAR to a writer, the former using
write_nar to only keeping the NAR size and digest.

Change-Id: Ie5d2cfea35470fdbb5cbf9da1136b0cdf0250266
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8723
Reviewed-by: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI
Autosubmit: flokli <flokli@flokli.de>

1 files changed, 113 insertions, 104 deletions

diff --git a/tvix/store/src/nar/renderer.rs b/tvix/store/src/nar/renderer.rs
index a9a6d989e1..6ea76e1429 100644
--- a/tvix/store/src/nar/renderer.rs
+++ b/tvix/store/src/nar/renderer.rs
@@ -5,131 +5,140 @@ use crate::{
     proto::{self, NamedNode},
     B3Digest,
 };
+use count_write::CountWrite;
 use nix_compat::nar;
+use sha2::{Digest, Sha256};
 use std::io::{self, BufReader};
 use tracing::warn;
 
-/// A NAR renderer, using a blob_service, chunk_service and directory_service
-/// to render a NAR to a writer.
-pub struct NARRenderer<DS: DirectoryService> {
-    blob_service: Box<dyn BlobService>,
+/// Invoke [render_nar], and return the size and sha256 digest of the produced
+/// NAR output.
+pub fn calculate_size_and_sha256<DS: DirectoryService + Clone>(
+    root_node: &proto::node::Node,
+    blob_service: &Box<dyn BlobService>,
     directory_service: DS,
+) -> Result<(u64, [u8; 32]), RenderError> {
+    let h = Sha256::new();
+    let mut cw = CountWrite::from(h);
+
+    writer_nar(&mut cw, root_node, blob_service, directory_service)?;
+
+    Ok((cw.count(), cw.into_inner().finalize().into()))
 }
 
-impl<DS: DirectoryService> NARRenderer<DS> {
-    pub fn new(blob_service: Box<dyn BlobService>, directory_service: DS) -> Self {
-        Self {
-            blob_service,
-            directory_service,
-        }
-    }
+/// Accepts a [proto::node::Node] pointing to the root of a (store) path,
+/// and uses the passed blob_service and directory_service to
+/// perform the necessary lookups as it traverses the structure.
+/// The contents in NAR serialization are writen to the passed [std::io::Write].
+pub fn writer_nar<W: std::io::Write, DS: DirectoryService + Clone>(
+    w: &mut W,
+    proto_root_node: &proto::node::Node,
+    blob_service: &Box<dyn BlobService>,
+    directory_service: DS,
+) -> Result<(), RenderError> {
+    // Initialize NAR writer
+    let nar_root_node = nar::writer::open(w).map_err(RenderError::NARWriterError)?;
 
-    /// Consumes a [proto::node::Node] pointing to the root of a (store) path,
-    /// and writes the contents in NAR serialization to the passed
-    /// [std::io::Write].
-    ///
-    /// It uses the different clients in the struct to perform the necessary
-    /// lookups as it traverses the structure.
-    pub fn write_nar<W: std::io::Write>(
-        &self,
-        w: &mut W,
-        proto_root_node: &proto::node::Node,
-    ) -> Result<(), RenderError> {
-        // Initialize NAR writer
-        let nar_root_node = nar::writer::open(w).map_err(RenderError::NARWriterError)?;
+    walk_node(
+        nar_root_node,
+        proto_root_node,
+        blob_service,
+        directory_service,
+    )
+}
 
-        self.walk_node(nar_root_node, proto_root_node)
-    }
+/// Process an intermediate node in the structure.
+/// This consumes the node.
+fn walk_node<DS: DirectoryService + Clone>(
+    nar_node: nar::writer::Node,
+    proto_node: &proto::node::Node,
+    blob_service: &Box<dyn BlobService>,
+    directory_service: DS,
+) -> Result<(), RenderError> {
+    match proto_node {
+        proto::node::Node::Symlink(proto_symlink_node) => {
+            nar_node
+                .symlink(&proto_symlink_node.target)
+                .map_err(RenderError::NARWriterError)?;
+        }
+        proto::node::Node::File(proto_file_node) => {
+            let digest = B3Digest::from_vec(proto_file_node.digest.clone()).map_err(|_e| {
+                warn!(
+                    file_node = ?proto_file_node,
+                    "invalid digest length in file node",
+                );
 
-    /// Process an intermediate node in the structure.
-    /// This consumes the node.
-    fn walk_node(
-        &self,
-        nar_node: nar::writer::Node,
-        proto_node: &proto::node::Node,
-    ) -> Result<(), RenderError> {
-        match proto_node {
-            proto::node::Node::Symlink(proto_symlink_node) => {
-                nar_node
-                    .symlink(&proto_symlink_node.target)
-                    .map_err(RenderError::NARWriterError)?;
-            }
-            proto::node::Node::File(proto_file_node) => {
-                let digest = B3Digest::from_vec(proto_file_node.digest.clone()).map_err(|_e| {
-                    warn!(
-                        file_node = ?proto_file_node,
-                        "invalid digest length in file node",
-                    );
+                RenderError::StoreError(crate::Error::StorageError(
+                    "invalid digest len in file node".to_string(),
+                ))
+            })?;
 
+            let mut blob_reader = match blob_service
+                .open_read(&digest)
+                .map_err(RenderError::StoreError)?
+            {
+                Some(blob_reader) => Ok(BufReader::new(blob_reader)),
+                None => Err(RenderError::NARWriterError(io::Error::new(
+                    io::ErrorKind::NotFound,
+                    format!("blob with digest {} not found", &digest),
+                ))),
+            }?;
+
+            nar_node
+                .file(
+                    proto_file_node.executable,
+                    proto_file_node.size.into(),
+                    &mut blob_reader,
+                )
+                .map_err(RenderError::NARWriterError)?;
+        }
+        proto::node::Node::Directory(proto_directory_node) => {
+            let digest =
+                B3Digest::from_vec(proto_directory_node.digest.to_vec()).map_err(|_e| {
                     RenderError::StoreError(crate::Error::StorageError(
-                        "invalid digest len in file node".to_string(),
+                        "invalid digest len in directory node".to_string(),
                     ))
                 })?;
 
-                let mut blob_reader = match self
-                    .blob_service
-                    .open_read(&digest)
-                    .map_err(RenderError::StoreError)?
-                {
-                    Some(blob_reader) => Ok(BufReader::new(blob_reader)),
-                    None => Err(RenderError::NARWriterError(io::Error::new(
-                        io::ErrorKind::NotFound,
-                        format!("blob with digest {} not found", &digest),
-                    ))),
-                }?;
-
-                nar_node
-                    .file(
-                        proto_file_node.executable,
-                        proto_file_node.size.into(),
-                        &mut blob_reader,
-                    )
-                    .map_err(RenderError::NARWriterError)?;
-            }
-            proto::node::Node::Directory(proto_directory_node) => {
-                let digest =
-                    B3Digest::from_vec(proto_directory_node.digest.to_vec()).map_err(|_e| {
-                        RenderError::StoreError(crate::Error::StorageError(
-                            "invalid digest len in directory node".to_string(),
-                        ))
-                    })?;
-
-                // look it up with the directory service
-                let resp = self
-                    .directory_service
-                    .get(&digest)
-                    .map_err(RenderError::StoreError)?;
+            // look it up with the directory service
+            let resp = directory_service
+                .get(&digest)
+                .map_err(RenderError::StoreError)?;
 
-                match resp {
-                    // if it's None, that's an error!
-                    None => {
-                        return Err(RenderError::DirectoryNotFound(
-                            digest,
-                            proto_directory_node.name.to_owned(),
-                        ))
-                    }
-                    Some(proto_directory) => {
-                        // start a directory node
-                        let mut nar_node_directory =
-                            nar_node.directory().map_err(RenderError::NARWriterError)?;
-
-                        // for each node in the directory, create a new entry with its name,
-                        // and then invoke walk_node on that entry.
-                        for proto_node in proto_directory.nodes() {
-                            let child_node = nar_node_directory
-                                .entry(proto_node.get_name())
-                                .map_err(RenderError::NARWriterError)?;
-                            self.walk_node(child_node, &proto_node)?;
-                        }
+            match resp {
+                // if it's None, that's an error!
+                None => {
+                    return Err(RenderError::DirectoryNotFound(
+                        digest,
+                        proto_directory_node.name.to_owned(),
+                    ))
+                }
+                Some(proto_directory) => {
+                    // start a directory node
+                    let mut nar_node_directory =
+                        nar_node.directory().map_err(RenderError::NARWriterError)?;
 
-                        // close the directory
-                        nar_node_directory
-                            .close()
+                    // for each node in the directory, create a new entry with its name,
+                    // and then invoke walk_node on that entry.
+                    for proto_node in proto_directory.nodes() {
+                        let child_node = nar_node_directory
+                            .entry(proto_node.get_name())
                             .map_err(RenderError::NARWriterError)?;
+                        walk_node(
+                            child_node,
+                            &proto_node,
+                            blob_service,
+                            directory_service.clone(),
+                        )?;
                     }
+
+                    // close the directory
+                    nar_node_directory
+                        .close()
+                        .map_err(RenderError::NARWriterError)?;
                 }
             }
         }
-        Ok(())
     }
+    Ok(())
 }