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

snix/store/src/pathinfoservice/redb.rs

@@ -1,7 +1,8 @@
 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::{
@@ -9,7 +10,6 @@ use snix_castore::{
     composition::{CompositionContext, ServiceBuilder},
 };
 use std::{path::PathBuf, sync::Arc};
-use tokio_stream::wrappers::ReceiverStream;
 use tonic::async_trait;
 use tracing::{instrument, warn};
 
@@ -130,18 +130,13 @@ 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> {
+        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?;
-                    tokio::runtime::Handle::current()
-                        .block_on(tx.send(Ok({
+                yield {
                     let path_info_proto = proto::PathInfo::decode(
                         elem.1.value().as_slice(),
                     )
@@ -152,15 +147,9 @@ impl PathInfoService for RedbPathInfoService {
                     PathInfo::try_from(path_info_proto).map_err(|e| {
                         Error::StorageError(format!("Invalid path info: {e}"))
                     })?
-                        })))
-                        .map_err(|e| Error::StorageError(e.to_string()))?;
                 }
-
-                Ok(())
             }
-        });
-
-        ReceiverStream::from(rx).boxed()
+        })
     }
 }