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, 6 insertions, 4 deletions

diff --git a/tvix/store/src/proto/grpc_pathinfoservice_wrapper.rs b/tvix/store/src/proto/grpc_pathinfoservice_wrapper.rs
index 16a2fd51d0df..33861d9ffa4e 100644
--- a/tvix/store/src/proto/grpc_pathinfoservice_wrapper.rs
+++ b/tvix/store/src/proto/grpc_pathinfoservice_wrapper.rs
@@ -71,10 +71,12 @@ impl proto::path_info_service_server::PathInfoService for GRPCPathInfoServiceWra
         match request.into_inner().node {
             None => Err(Status::invalid_argument("no root node sent")),
             Some(root_node) => {
-                let (nar_size, nar_sha256) = self
-                    .path_info_service
-                    .calculate_nar(&root_node)
-                    .expect("error during nar calculation"); // TODO: handle error
+                let path_info_service = self.path_info_service.clone();
+                let (nar_size, nar_sha256) =
+                    task::spawn_blocking(move || path_info_service.calculate_nar(&root_node))
+                        .await
+                        .unwrap()
+                        .expect("error during nar calculation"); // TODO: handle error
 
                 Ok(Response::new(proto::CalculateNarResponse {
                     nar_size,