fix(snix/store): don't spawn tokio tasks in RedbPathInfoService.list

Fixes a panic in `list` impl of PathInfoService for fuse/virtiofs:
```
thread 'vring_worker' panicked at store/src/pathinfoservice/redb.rs:136:9:
there is no reactor running, must be called from the context of a Tokio 1.x runtime
```

Closes #147.

Change-Id: I2bed5157b30fa185276dcaefd35277159a01fe2d
Reviewed-on: https://cl.snix.dev/c/snix/+/30575
Reviewed-by: Florian Klink <flokli@flokli.de>
Tested-by: besadii

Author: rszyma

snix/store/src/pathinfoservice/redb.rs

@@ -1,15 +1,15 @@
 use super::{PathInfo, PathInfoService};
 use crate::proto;
+use async_stream::try_stream;
 use data_encoding::BASE64;
-use futures::{StreamExt, stream::BoxStream};
+use futures::stream::BoxStream;
 use prost::Message;
 use redb::{Database, ReadableTable, TableDefinition};
 use snix_castore::{
     Error,
     composition::{CompositionContext, ServiceBuilder},
 };
 use std::{path::PathBuf, sync::Arc};
-use tokio_stream::wrappers::ReceiverStream;
 use tonic::async_trait;
 use tracing::{instrument, warn};
 
@@ -130,37 +130,26 @@ impl PathInfoService for RedbPathInfoService {
 
     fn list(&self) -> BoxStream<'static, Result<PathInfo, Error>> {
         let db = self.db.clone();
-        let (tx, rx) = tokio::sync::mpsc::channel(50);
-
-        // Spawn a blocking task which writes all PathInfos to tx.
-        tokio::task::spawn_blocking({
-            move || -> Result<(), Error> {
-                let read_txn = db.begin_read()?;
-                let table = read_txn.open_table(PATHINFO_TABLE)?;
-
-                for elem in table.iter()? {
-                    let elem = elem?;
-                    tokio::runtime::Handle::current()
-                        .block_on(tx.send(Ok({
-                            let path_info_proto = proto::PathInfo::decode(
-                                elem.1.value().as_slice(),
-                            )
-                            .map_err(|e| {
-                                warn!(err=%e, "invalid PathInfo");
-                                Error::StorageError("invalid PathInfo".to_string())
-                            })?;
-                            PathInfo::try_from(path_info_proto).map_err(|e| {
-                                Error::StorageError(format!("Invalid path info: {e}"))
-                            })?
-                        })))
-                        .map_err(|e| Error::StorageError(e.to_string()))?;
+        Box::pin(try_stream! {
+            let read_txn = db.begin_read()?;
+            let table = read_txn.open_table(PATHINFO_TABLE)?;
+
+            for elem in table.iter()? {
+                let elem = elem?;
+                yield {
+                    let path_info_proto = proto::PathInfo::decode(
+                        elem.1.value().as_slice(),
+                    )
+                    .map_err(|e| {
+                        warn!(err=%e, "invalid PathInfo");
+                        Error::StorageError("invalid PathInfo".to_string())
+                    })?;
+                    PathInfo::try_from(path_info_proto).map_err(|e| {
+                        Error::StorageError(format!("Invalid path info: {e}"))
+                    })?
                 }
-
-                Ok(())
             }
-        });
-
-        ReceiverStream::from(rx).boxed()
+        })
     }
 }