1 files changed, 136 insertions, 0 deletions
diff --git a/tvix/store/src/nar/renderer.rs b/tvix/store/src/nar/renderer.rs
new file mode 100644
index 000000000000..c10f2ddf52fa
--- /dev/null
+++ b/tvix/store/src/nar/renderer.rs
@@ -0,0 +1,136 @@
+use super::RenderError;
+use crate::{
+    blobservice::BlobService,
+    directoryservice::DirectoryService,
+    proto::{self, NamedNode},
+    B3Digest,
+};
+use nix_compat::nar;
+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.
+#[derive(Clone)]
+pub struct NARRenderer<BS: BlobService, DS: DirectoryService> {
+    blob_service: BS,
+    directory_service: DS,
+}
+
+impl<BS: BlobService, DS: DirectoryService> NARRenderer<BS, DS> {
+    pub fn new(blob_service: BS, directory_service: DS) -> Self {
+        Self {
+            blob_service,
+            directory_service,
+        }
+    }
+
+    /// 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)?;
+
+        self.walk_node(nar_root_node, proto_root_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 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)?;
+
+                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)?;
+                        }
+
+                        // close the directory
+                        nar_node_directory
+                            .close()
+                            .map_err(RenderError::NARWriterError)?;
+                    }
+                }
+            }
+        }
+        Ok(())
+    }
+}