1 files changed, 105 insertions, 0 deletions
diff --git a/tvix/castore/src/blobservice/mod.rs b/tvix/castore/src/blobservice/mod.rs
new file mode 100644
index 0000000000..4ba56a4af7
--- /dev/null
+++ b/tvix/castore/src/blobservice/mod.rs
@@ -0,0 +1,105 @@
+use std::io;
+use tonic::async_trait;
+
+use crate::proto::stat_blob_response::ChunkMeta;
+use crate::B3Digest;
+
+mod chunked_reader;
+mod combinator;
+mod from_addr;
+mod grpc;
+mod memory;
+mod naive_seeker;
+mod object_store;
+mod sled;
+
+#[cfg(test)]
+pub mod tests;
+
+pub use self::chunked_reader::ChunkedReader;
+pub use self::combinator::CombinedBlobService;
+pub use self::from_addr::from_addr;
+pub use self::grpc::GRPCBlobService;
+pub use self::memory::MemoryBlobService;
+pub use self::object_store::ObjectStoreBlobService;
+pub use self::sled::SledBlobService;
+
+/// The base trait all BlobService services need to implement.
+/// It provides functions to check whether a given blob exists,
+/// a way to read (and seek) a blob, and a method to create a blobwriter handle,
+/// which will implement a writer interface, and also provides a close funtion,
+/// to finalize a blob and get its digest.
+#[async_trait]
+pub trait BlobService: Send + Sync {
+    /// Check if the service has the blob, by its content hash.
+    /// On implementations returning chunks, this must also work for chunks.
+    async fn has(&self, digest: &B3Digest) -> io::Result<bool>;
+
+    /// Request a blob from the store, by its content hash.
+    /// On implementations returning chunks, this must also work for chunks.
+    async fn open_read(&self, digest: &B3Digest) -> io::Result<Option<Box<dyn BlobReader>>>;
+
+    /// Insert a new blob into the store. Returns a [BlobWriter], which
+    /// implements [tokio::io::AsyncWrite] and a [BlobWriter::close] to finalize
+    /// the blob and get its digest.
+    async fn open_write(&self) -> Box<dyn BlobWriter>;
+
+    /// Return a list of chunks for a given blob.
+    /// There's a distinction between returning Ok(None) and Ok(Some(vec![])).
+    /// The former return value is sent in case the blob is not present at all,
+    /// while the second one is sent in case there's no more granular chunks (or
+    /// the backend does not support chunking).
+    /// A default implementation checking for existence and then returning it
+    /// does not have more granular chunks available is provided.
+    async fn chunks(&self, digest: &B3Digest) -> io::Result<Option<Vec<ChunkMeta>>> {
+        if !self.has(digest).await? {
+            return Ok(None);
+        }
+        // default implementation, signalling the backend does not have more
+        // granular chunks available.
+        Ok(Some(vec![]))
+    }
+}
+
+#[async_trait]
+impl<A> BlobService for A
+where
+    A: AsRef<dyn BlobService> + Send + Sync,
+{
+    async fn has(&self, digest: &B3Digest) -> io::Result<bool> {
+        self.as_ref().has(digest).await
+    }
+
+    async fn open_read(&self, digest: &B3Digest) -> io::Result<Option<Box<dyn BlobReader>>> {
+        self.as_ref().open_read(digest).await
+    }
+
+    async fn open_write(&self) -> Box<dyn BlobWriter> {
+        self.as_ref().open_write().await
+    }
+
+    async fn chunks(&self, digest: &B3Digest) -> io::Result<Option<Vec<ChunkMeta>>> {
+        self.as_ref().chunks(digest).await
+    }
+}
+
+/// A [tokio::io::AsyncWrite] that the user needs to close() afterwards for persist.
+/// On success, it returns the digest of the written blob.
+#[async_trait]
+pub trait BlobWriter: tokio::io::AsyncWrite + Send + Unpin {
+    /// Signal there's no more data to be written, and return the digest of the
+    /// contents written.
+    ///
+    /// Closing a already-closed BlobWriter is a no-op.
+    async fn close(&mut self) -> io::Result<B3Digest>;
+}
+
+/// BlobReader is a [tokio::io::AsyncRead] that also allows seeking.
+pub trait BlobReader: tokio::io::AsyncRead + tokio::io::AsyncSeek + Send + Unpin + 'static {}
+
+/// A [`io::Cursor<Vec<u8>>`] can be used as a BlobReader.
+impl BlobReader for io::Cursor<&'static [u8]> {}
+impl BlobReader for io::Cursor<&'static [u8; 0]> {}
+impl BlobReader for io::Cursor<Vec<u8>> {}
+impl BlobReader for io::Cursor<bytes::Bytes> {}
+impl BlobReader for tokio::fs::File {}