feat(tvix/store/pathinfosvc): provide listing

This provides an additional method in the PathInfoService trait, as
well as an RPC method on the gRPC layer to list all PathInfo objects in
a PathInfoService.

Change-Id: I7378f6bbd334bd6ac4e9be92505bd099a1c2b19a
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9216
Reviewed-by: tazjin <tazjin@tvl.su>
Autosubmit: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI

tvix/store/src/pathinfoservice/memory.rs

@@ -85,6 +85,18 @@ impl PathInfoService for MemoryPathInfoService {
         )
         .map_err(|e| Error::StorageError(e.to_string()))
     }
+
+    fn list(&self) -> Box<dyn Iterator<Item = Result<proto::PathInfo, Error>> + Send + '_> {
+        let db = self.db.read().unwrap();
+
+        // Copy all elements into a list.
+        // This is a bit ugly, because we can't have db escape the lifetime
+        // of this function, but elements need to be returned owned anyways, and this in-
+        // memory impl is only for testing purposes anyways.
+        let items: Vec<_> = db.iter().map(|(_k, v)| Ok(v.clone())).collect();
+
+        Box::new(items.into_iter())
+    }
 }
 
 #[cfg(test)]