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, 8 insertions, 7 deletions

diff --git a/tvix/store/src/nar/renderer.rs b/tvix/store/src/nar/renderer.rs
index cc5af488abf8..4255148fc5e8 100644
--- a/tvix/store/src/nar/renderer.rs
+++ b/tvix/store/src/nar/renderer.rs
@@ -7,10 +7,8 @@ use crate::{
 use count_write::CountWrite;
 use nix_compat::nar;
 use sha2::{Digest, Sha256};
-use std::{
-    io::{self, BufReader},
-    sync::Arc,
-};
+use std::{io, sync::Arc};
+use tokio::io::BufReader;
 use tracing::warn;
 
 /// Invoke [write_nar], and return the size and sha256 digest of the produced
@@ -75,8 +73,11 @@ fn walk_node(
                 ))
             })?;
 
-            let mut blob_reader = match blob_service
-                .open_read(&digest)
+            // HACK: blob_service is async, but this function isn't async yet..
+            let tokio_handle = tokio::runtime::Handle::current();
+
+            let blob_reader = match tokio_handle
+                .block_on(async { blob_service.open_read(&digest).await })
                 .map_err(RenderError::StoreError)?
             {
                 Some(blob_reader) => Ok(BufReader::new(blob_reader)),
@@ -90,7 +91,7 @@ fn walk_node(
                 .file(
                     proto_file_node.executable,
                     proto_file_node.size.into(),
-                    &mut blob_reader,
+                    &mut tokio_util::io::SyncIoBridge::new(blob_reader),
                 )
                 .map_err(RenderError::NARWriterError)?;
         }