1 files changed, 261 insertions, 0 deletions
diff --git a/tvix/castore/src/directoryservice/object_store.rs b/tvix/castore/src/directoryservice/object_store.rs
new file mode 100644
index 000000000000..64ce335edb86
--- /dev/null
+++ b/tvix/castore/src/directoryservice/object_store.rs
@@ -0,0 +1,261 @@
+use std::collections::HashSet;
+use std::sync::Arc;
+
+use data_encoding::HEXLOWER;
+use futures::future::Either;
+use futures::stream::BoxStream;
+use futures::SinkExt;
+use futures::StreamExt;
+use futures::TryFutureExt;
+use futures::TryStreamExt;
+use object_store::{path::Path, ObjectStore};
+use prost::Message;
+use tokio::io::AsyncWriteExt;
+use tokio_util::codec::LengthDelimitedCodec;
+use tonic::async_trait;
+use tracing::{instrument, trace, warn, Level};
+use url::Url;
+
+use super::{ClosureValidator, DirectoryPutter, DirectoryService};
+use crate::{proto, B3Digest, Error};
+
+/// Stores directory closures in an object store.
+/// Notably, this makes use of the option to disallow accessing child directories except when
+/// fetching them recursively via the top-level directory, since all batched writes
+/// (using `put_multiple_start`) are stored in a single object.
+/// Directories are stored in a length-delimited format with a 1MiB limit. The length field is a
+/// u32 and the directories are stored in root-to-leaves topological order, the same way they will
+/// be returned to the client in get_recursive.
+#[derive(Clone)]
+pub struct ObjectStoreDirectoryService {
+    object_store: Arc<dyn ObjectStore>,
+    base_path: Path,
+}
+
+#[instrument(level=Level::TRACE, skip_all,fields(base_path=%base_path,blob.digest=%digest),ret(Display))]
+fn derive_dirs_path(base_path: &Path, digest: &B3Digest) -> Path {
+    base_path
+        .child("dirs")
+        .child("b3")
+        .child(HEXLOWER.encode(&digest.as_slice()[..2]))
+        .child(HEXLOWER.encode(digest.as_slice()))
+}
+
+#[allow(clippy::identity_op)]
+const MAX_FRAME_LENGTH: usize = 1 * 1024 * 1024 * 1000; // 1 MiB
+                                                        //
+impl ObjectStoreDirectoryService {
+    /// Constructs a new [ObjectStoreBlobService] from a [Url] supported by
+    /// [object_store].
+    /// Any path suffix becomes the base path of the object store.
+    /// additional options, the same as in [object_store::parse_url_opts] can
+    /// be passed.
+    pub fn parse_url_opts<I, K, V>(url: &Url, options: I) -> Result<Self, object_store::Error>
+    where
+        I: IntoIterator<Item = (K, V)>,
+        K: AsRef<str>,
+        V: Into<String>,
+    {
+        let (object_store, path) = object_store::parse_url_opts(url, options)?;
+
+        Ok(Self {
+            object_store: Arc::new(object_store),
+            base_path: path,
+        })
+    }
+
+    /// Like [Self::parse_url_opts], except without the options.
+    pub fn parse_url(url: &Url) -> Result<Self, object_store::Error> {
+        Self::parse_url_opts(url, Vec::<(String, String)>::new())
+    }
+}
+
+#[async_trait]
+impl DirectoryService for ObjectStoreDirectoryService {
+    /// This is the same steps as for get_recursive anyways, so we just call get_recursive and
+    /// return the first element of the stream and drop the request.
+    #[instrument(skip(self, digest), fields(directory.digest = %digest))]
+    async fn get(&self, digest: &B3Digest) -> Result<Option<proto::Directory>, Error> {
+        self.get_recursive(digest).take(1).next().await.transpose()
+    }
+
+    #[instrument(skip(self, directory), fields(directory.digest = %directory.digest()))]
+    async fn put(&self, directory: proto::Directory) -> Result<B3Digest, Error> {
+        if !directory.directories.is_empty() {
+            return Err(Error::InvalidRequest(
+                    "only put_multiple_start is supported by the ObjectStoreDirectoryService for directories with children".into(),
+            ));
+        }
+
+        let mut handle = self.put_multiple_start();
+        handle.put(directory).await?;
+        handle.close().await
+    }
+
+    #[instrument(skip_all, fields(directory.digest = %root_directory_digest))]
+    fn get_recursive(
+        &self,
+        root_directory_digest: &B3Digest,
+    ) -> BoxStream<'static, Result<proto::Directory, Error>> {
+        // The Directory digests we're expecting to receive.
+        let mut expected_directory_digests: HashSet<B3Digest> =
+            HashSet::from([root_directory_digest.clone()]);
+
+        let dir_path = derive_dirs_path(&self.base_path, root_directory_digest);
+        let object_store = self.object_store.clone();
+
+        Box::pin(
+            (async move {
+                let stream = match object_store.get(&dir_path).await {
+                    Ok(v) => v.into_stream(),
+                    Err(object_store::Error::NotFound { .. }) => {
+                        return Ok(Either::Left(futures::stream::empty()))
+                    }
+                    Err(e) => return Err(std::io::Error::from(e).into()),
+                };
+
+                // get a reader of the response body.
+                let r = tokio_util::io::StreamReader::new(stream);
+                let decompressed_stream = async_compression::tokio::bufread::ZstdDecoder::new(r);
+
+                // the subdirectories are stored in a length delimited format
+                let delimited_stream = LengthDelimitedCodec::builder()
+                    .max_frame_length(MAX_FRAME_LENGTH)
+                    .length_field_type::<u32>()
+                    .new_read(decompressed_stream);
+
+                let dirs_stream = delimited_stream.map_err(Error::from).and_then(move |buf| {
+                    futures::future::ready((|| {
+                        let mut hasher = blake3::Hasher::new();
+                        let digest: B3Digest = hasher.update(&buf).finalize().as_bytes().into();
+
+                        // Ensure to only decode the directory objects whose digests we trust
+                        let was_expected = expected_directory_digests.remove(&digest);
+                        if !was_expected {
+                            return Err(crate::Error::StorageError(format!(
+                                "received unexpected directory {}",
+                                digest
+                            )));
+                        }
+
+                        let directory = proto::Directory::decode(&*buf).map_err(|e| {
+                            warn!("unable to parse directory {}: {}", digest, e);
+                            Error::StorageError(e.to_string())
+                        })?;
+
+                        for directory in &directory.directories {
+                            // Allow the children to appear next
+                            expected_directory_digests.insert(
+                                B3Digest::try_from(directory.digest.clone())
+                                    .map_err(|e| Error::StorageError(e.to_string()))?,
+                            );
+                        }
+
+                        Ok(directory)
+                    })())
+                });
+
+                Ok(Either::Right(dirs_stream))
+            })
+            .try_flatten_stream(),
+        )
+    }
+
+    #[instrument(skip_all)]
+    fn put_multiple_start(&self) -> Box<(dyn DirectoryPutter + 'static)>
+    where
+        Self: Clone,
+    {
+        Box::new(ObjectStoreDirectoryPutter::new(
+            self.object_store.clone(),
+            self.base_path.clone(),
+        ))
+    }
+}
+
+struct ObjectStoreDirectoryPutter {
+    object_store: Arc<dyn ObjectStore>,
+    base_path: Path,
+
+    directory_validator: Option<ClosureValidator>,
+}
+
+impl ObjectStoreDirectoryPutter {
+    fn new(object_store: Arc<dyn ObjectStore>, base_path: Path) -> Self {
+        Self {
+            object_store,
+            base_path,
+            directory_validator: Some(Default::default()),
+        }
+    }
+}
+
+#[async_trait]
+impl DirectoryPutter for ObjectStoreDirectoryPutter {
+    #[instrument(level = "trace", skip_all, fields(directory.digest=%directory.digest()), err)]
+    async fn put(&mut self, directory: proto::Directory) -> Result<(), Error> {
+        match self.directory_validator {
+            None => return Err(Error::StorageError("already closed".to_string())),
+            Some(ref mut validator) => {
+                validator.add(directory)?;
+            }
+        }
+
+        Ok(())
+    }
+
+    #[instrument(level = "trace", skip_all, ret, err)]
+    async fn close(&mut self) -> Result<B3Digest, Error> {
+        let validator = match self.directory_validator.take() {
+            None => return Err(Error::InvalidRequest("already closed".to_string())),
+            Some(validator) => validator,
+        };
+
+        // retrieve the validated directories.
+        // It is important that they are in topological order (root first),
+        // since that's how we want to retrieve them from the object store in the end.
+        let directories = validator.finalize_root_to_leaves()?;
+
+        // Get the root digest
+        let root_digest = directories
+            .first()
+            .ok_or_else(|| Error::InvalidRequest("got no directories".to_string()))?
+            .digest();
+
+        let dir_path = derive_dirs_path(&self.base_path, &root_digest);
+
+        match self.object_store.head(&dir_path).await {
+            // directory tree already exists, nothing to do
+            Ok(_) => {
+                trace!("directory tree already exists");
+            }
+
+            // directory tree does not yet exist, compress and upload.
+            Err(object_store::Error::NotFound { .. }) => {
+                trace!("uploading directory tree");
+
+                let object_store_writer =
+                    object_store::buffered::BufWriter::new(self.object_store.clone(), dir_path);
+                let compressed_writer =
+                    async_compression::tokio::write::ZstdEncoder::new(object_store_writer);
+                let mut directories_sink = LengthDelimitedCodec::builder()
+                    .max_frame_length(MAX_FRAME_LENGTH)
+                    .length_field_type::<u32>()
+                    .new_write(compressed_writer);
+
+                for directory in directories {
+                    directories_sink
+                        .send(directory.encode_to_vec().into())
+                        .await?;
+                }
+
+                let mut compressed_writer = directories_sink.into_inner();
+                compressed_writer.shutdown().await?;
+            }
+            // other error
+            Err(err) => Err(std::io::Error::from(err))?,
+        }
+
+        Ok(root_digest)
+    }
+}