fix(snix/store/redb): no blocking IO in list() without spawn_blocking

All these functions do blocking IO, and don't yield back to the
executor, so we cannot invoke them directly, but have to use
spawn_blocking and a channel.

Instead of plainly reverting cl/30575, this keeps potential errors being
sent as the last element of the stream.

We need to make our error construction a bit more ergonomic, potentially
allow them to wrap other errors instead of the madness this currently
is, but this is something for a later CL.

Change-Id: Ifb05871741813a389ac00b4f2c468f984a689a18
Reviewed-on: https://cl.snix.dev/c/snix/+/30586
Reviewed-by: Vova Kryachko <v.kryachko@gmail.com>
Tested-by: besadii

snix/store/src/pathinfoservice/redb.rs

@@ -1,8 +1,7 @@
 use super::{PathInfo, PathInfoService};
 use crate::proto;
-use async_stream::try_stream;
 use data_encoding::BASE64;
-use futures::stream::BoxStream;
+use futures::{StreamExt, stream::BoxStream};
 use prost::Message;
 use redb::{Database, ReadableTable, TableDefinition};
 use snix_castore::{
@@ -10,6 +9,7 @@ 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};
 
@@ -130,26 +130,55 @@ impl PathInfoService for RedbPathInfoService {
 
     fn list(&self) -> BoxStream<'static, Result<PathInfo, Error>> {
         let db = self.db.clone();
-        Box::pin(try_stream! {
-            let read_txn = db.begin_read()?;
-            let table = read_txn.open_table(PATHINFO_TABLE)?;
+        let (tx, rx) = tokio::sync::mpsc::channel(64);
 
-            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())
+        tokio::task::spawn_blocking(move || {
+            // IIFE to be able to use ? for the error cases
+            let result = (|| -> Result<(), Error> {
+                let read_txn = db.begin_read().map_err(|err| {
+                    warn!(%err, "failed to open read transaction");
+                    Error::StorageError("failed to open read transaction".to_string())
+                })?;
+
+                let table = read_txn.open_table(PATHINFO_TABLE).map_err(|err| {
+                    warn!(%err, "failed to open table");
+                    Error::StorageError("failed to open table".to_string())
+                })?;
+
+                let table_iter = table.iter().map_err(|err| {
+                    warn!(%err, "failed to iterate over table items");
+                    Error::StorageError("failed to iterate over table items".into())
+                })?;
+
+                for elem in table_iter {
+                    let elem = elem.map_err(|err| {
+                        warn!(%err, "failed to retrieve item");
+                        Error::StorageError("failed to retrieve item".into())
                     })?;
-                    PathInfo::try_from(path_info_proto).map_err(|e| {
-                        Error::StorageError(format!("Invalid path info: {e}"))
-                    })?
+
+                    let path_info_proto = proto::PathInfo::decode(elem.1.value().as_slice())
+                        .map_err(|err| {
+                            warn!(%err, "invalid PathInfo");
+                            Error::StorageError("invalid PathInfo".into())
+                        })?;
+
+                    let path_info = PathInfo::try_from(path_info_proto)
+                        .map_err(|e| Error::StorageError(format!("Invalid path info: {e}")))?;
+
+                    if tx.blocking_send(Ok(path_info)).is_err() {
+                        break;
+                    }
                 }
+
+                Ok(())
+            })();
+
+            if let Err(err) = result {
+                let _ = tx.blocking_send(Err(err));
             }
-        })
+        });
+
+        ReceiverStream::new(rx).boxed()
     }
 }