refactor(tvix/store/blobsvc): make BlobStore async r/6606

We previously kept the trait of a BlobService sync.

This however had some annoying consequences:

 - It became more and more complicated to track when we're in a context
   with an async runtime in the context or not, producing bugs like
   https://b.tvl.fyi/issues/304
 - The sync trait shielded away async clients from async worloads,
   requiring manual block_on code inside the gRPC client code, and
   spawn_blocking calls in consumers of the trait, even if they were
   async (like the gRPC server)
 - We had to write our own custom glue code (SyncReadIntoAsyncRead)
   to convert a sync io::Read into a tokio::io::AsyncRead, which already
   existed in tokio internally, but upstream ia hesitant to expose.

This now makes the BlobService trait async (via the async_trait macro,
like we already do in various gRPC parts), and replaces the sync readers
and writers with their async counterparts.

Tests interacting with a BlobService now need to have an async runtime
available, the easiest way for this is to mark the test functions
with the tokio::test macro, allowing us to directly .await in the test
function.

In places where we don't have an async runtime available from context
(like tvix-cli), we can pass one down explicitly.

Now that we don't provide a sync interface anymore, the (sync) FUSE
library now holds a pointer to a tokio runtime handle, and needs to at
least have 2 threads available when talking to a blob service (which is
why some of the tests now use the multi_thread flavor).

The FUSE tests got a bit more verbose, as we couldn't use the
setup_and_mount function accepting a callback anymore. We can hopefully
move some of the test fixture setup to rstest in the future to make this
less repetitive.

Co-Authored-By: Connor Brewster <cbrewster@hey.com>
Change-Id: Ia0501b606e32c852d0108de9c9016b21c94a3c05
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9329
Reviewed-by: Connor Brewster <cbrewster@hey.com>
Tested-by: BuildkiteCI
Reviewed-by: raitobezarius <tvl@lahfa.xyz>

1 files changed, 17 insertions, 10 deletions

diff --git a/tvix/store/src/blobservice/mod.rs b/tvix/store/src/blobservice/mod.rs
index 33cfb113edd3..5ecf25ac1337 100644
--- a/tvix/store/src/blobservice/mod.rs
+++ b/tvix/store/src/blobservice/mod.rs
@@ -1,11 +1,12 @@
 use std::io;
+use tonic::async_trait;
 
 use crate::{B3Digest, Error};
 
-mod dumb_seeker;
 mod from_addr;
 mod grpc;
 mod memory;
+mod naive_seeker;
 mod sled;
 
 #[cfg(test)]
@@ -21,35 +22,41 @@ pub use self::sled::SledBlobService;
 /// a way to get a [io::Read] to a blob, and a method to initiate writing a new
 /// Blob, which will return something implmenting io::Write, and providing a
 /// close funtion, to finalize a blob and get its digest.
+#[async_trait]
 pub trait BlobService: Send + Sync {
     /// Create a new instance by passing in a connection URL.
+    /// TODO: check if we want to make this async, instead of lazily connecting
     fn from_url(url: &url::Url) -> Result<Self, Error>
     where
         Self: Sized;
 
     /// Check if the service has the blob, by its content hash.
-    fn has(&self, digest: &B3Digest) -> Result<bool, Error>;
+    async fn has(&self, digest: &B3Digest) -> Result<bool, Error>;
 
     /// Request a blob from the store, by its content hash.
-    fn open_read(&self, digest: &B3Digest) -> Result<Option<Box<dyn BlobReader>>, Error>;
+    async fn open_read(&self, digest: &B3Digest) -> Result<Option<Box<dyn BlobReader>>, Error>;
 
     /// Insert a new blob into the store. Returns a [BlobWriter], which
     /// implements [io::Write] and a [BlobWriter::close].
-    fn open_write(&self) -> Box<dyn BlobWriter>;
+    async fn open_write(&self) -> Box<dyn BlobWriter>;
 }
 
-/// A [io::Write] that you need to close() afterwards, and get back the digest
-/// of the written blob.
-pub trait BlobWriter: io::Write + Send + Sync + 'static {
+/// A [tokio::io::AsyncWrite] that you need to close() afterwards, and get back
+/// the digest of the written blob.
+#[async_trait]
+pub trait BlobWriter: tokio::io::AsyncWrite + Send + Sync + Unpin + 'static {
     /// 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.
-    fn close(&mut self) -> Result<B3Digest, Error>;
+    async fn close(&mut self) -> Result<B3Digest, Error>;
 }
 
-/// A [io::Read] that also allows seeking.
-pub trait BlobReader: io::Read + io::Seek + Send + 'static {}
+/// A [tokio::io::AsyncRead] that also allows seeking.
+pub trait BlobReader:
+    tokio::io::AsyncRead + tokio::io::AsyncSeek + tokio::io::AsyncBufRead + Send + Unpin + 'static
+{
+}
 
 /// A [`io::Cursor<Vec<u8>>`] can be used as a BlobReader.
 impl BlobReader for io::Cursor<Vec<u8>> {}