feat(async): add async_compatible methods to identify backend compa…

…tibility (#355)

Add `getters` to warn about `async_incompatible` backends.

Using the type system or fixing all async compatibility issue is big and
structural work.
To avoid runtime crash for our users I suggest using this getter as a
temporary fix.

tracking issue: rustic-rs/rustic#1181 (see for more details)

---------

Co-authored-by: simonsan <[email protected]>

crates/backend/src/local.rs

@@ -417,6 +417,13 @@ impl ReadBackend for LocalBackend {
 
         Ok(vec.into())
     }
+
+    /// [`LocalBackend`] doesn't use `async`, even under the hood.
+    ///
+    /// So it can be called from `async` features.
+    fn is_async_compatible(&self) -> bool {
+        true
+    }
 }
 
 impl WriteBackend for LocalBackend {

crates/backend/src/opendal.rs

@@ -386,6 +386,15 @@ impl ReadBackend for OpenDALBackend {
             )?
             .to_bytes())
     }
+
+    /// [`OpenDALBackend`] is `sync` and uses `block_on(async Fn)` under the hood.
+    ///
+    /// When implementing `rustic_core` using this backend in some `async` features will not work.
+    ///
+    /// see <https://github.com/rustic-rs/rustic/issues/1181>
+    fn is_async_compatible(&self) -> bool {
+        false
+    }
 }
 
 impl WriteBackend for OpenDALBackend {

crates/backend/src/rclone.rs

@@ -353,6 +353,11 @@ impl ReadBackend for RcloneBackend {
     ) -> RusticResult<Bytes> {
         self.rest.read_partial(tpe, id, cacheable, offset, length)
     }
+
+    /// [`RcloneBackend`] uses [`RestBackend`].
+    fn is_async_compatible(&self) -> bool {
+        self.rest.is_async_compatible()
+    }
 }
 
 impl WriteBackend for RcloneBackend {

crates/backend/src/rest.rs

@@ -350,6 +350,16 @@ impl ReadBackend for RestBackend {
         })
         .map_err(construct_backoff_error)
     }
+
+    /// [`RestBackend`] uses `reqwest` which blocking implementation
+    /// uses an `async` runtime under the hood.
+    ///
+    /// When implementing `rustic_core` using this backend in some `async` features will not work.
+    ///
+    /// see <https://github.com/rustic-rs/rustic/issues/1181>
+    fn is_async_compatible(&self) -> bool {
+        false
+    }
 }
 
 fn construct_join_url_error(

crates/core/src/backend.rs

@@ -174,6 +174,21 @@ pub trait ReadBackend: Send + Sync + 'static {
     fn warm_up(&self, _tpe: FileType, _id: &Id) -> RusticResult<()> {
         Ok(())
     }
+
+    /// Getter to determine if some backend is compatible
+    /// with async features in `rustic_core` implementations.
+    ///
+    /// ## Default impl
+    ///
+    /// A default impl allow these change to be non-breaking.
+    /// By default it is `false`, async compatibility is opt-in.
+    ///
+    /// ## Temporary
+    ///
+    /// see <https://github.com/rustic-rs/rustic/issues/1181>
+    fn is_async_compatible(&self) -> bool {
+        false
+    }
 }
 
 /// Trait for Searching in a backend.
@@ -343,7 +358,7 @@ pub trait WriteBackend: ReadBackend {
 mock! {
     Backend {}
 
-    impl ReadBackend for Backend{
+    impl ReadBackend for Backend {
         fn location(&self) -> String;
         fn list_with_size(&self, tpe: FileType) -> RusticResult<Vec<(Id, u32)>>;
         fn read_full(&self, tpe: FileType, id: &Id) -> RusticResult<Bytes>;
@@ -355,6 +370,7 @@ mock! {
             offset: u32,
             length: u32,
         ) -> RusticResult<Bytes>;
+        fn is_async_compatible(&self) -> bool;
     }
 
     impl WriteBackend for Backend {
@@ -400,6 +416,9 @@ impl ReadBackend for Arc<dyn WriteBackend> {
         self.deref()
             .read_partial(tpe, id, cacheable, offset, length)
     }
+    fn is_async_compatible(&self) -> bool {
+        self.deref().is_async_compatible()
+    }
 }
 
 impl std::fmt::Debug for dyn WriteBackend {

crates/core/src/backend/cache.rs

@@ -177,6 +177,10 @@ impl ReadBackend for CachedBackend {
     fn warm_up(&self, tpe: FileType, id: &Id) -> RusticResult<()> {
         self.be.warm_up(tpe, id)
     }
+
+    fn is_async_compatible(&self) -> bool {
+        self.be.is_async_compatible()
+    }
 }
 
 impl WriteBackend for CachedBackend {

crates/core/src/backend/decrypt.rs

@@ -216,7 +216,7 @@ pub trait DecryptWriteBackend: WriteBackend + Clone + 'static {
     ///
     /// # Returns
     ///
-    /// The processed data, the original data length and when compression is used, the uncomressed length
+    /// The processed data, the original data length and when compression is used, the uncompressed length
     fn process_data(&self, data: &[u8]) -> RusticResult<(Vec<u8>, u32, Option<NonZeroU32>)>;
 
     /// Writes the given data to the backend without compression and returns the id of the data.
@@ -559,7 +559,7 @@ impl<C: CryptoKey> DecryptWriteBackend for DecryptBackend<C> {
     ///
     /// # Arguments
     ///
-    /// * `extra_echeck` - The compression level to use for zstd.
+    /// * `extra_verify` - The compression level to use for zstd.
     fn set_extra_verify(&mut self, extra_verify: bool) {
         self.extra_verify = extra_verify;
     }
@@ -622,6 +622,10 @@ impl<C: CryptoKey> ReadBackend for DecryptBackend<C> {
     ) -> RusticResult<Bytes> {
         self.be.read_partial(tpe, id, cacheable, offset, length)
     }
+
+    fn is_async_compatible(&self) -> bool {
+        self.be.is_async_compatible()
+    }
 }
 
 impl<C: CryptoKey> WriteBackend for DecryptBackend<C> {

crates/core/src/backend/dry_run.rs

@@ -103,6 +103,10 @@ impl<BE: DecryptFullBackend> ReadBackend for DryRunBackend<BE> {
     ) -> RusticResult<Bytes> {
         self.be.read_partial(tpe, id, cacheable, offset, length)
     }
+
+    fn is_async_compatible(&self) -> bool {
+        self.be.is_async_compatible()
+    }
 }
 
 impl<BE: DecryptFullBackend> DecryptWriteBackend for DryRunBackend<BE> {

crates/core/src/backend/hotcold.rs

@@ -75,6 +75,10 @@ impl ReadBackend for HotColdBackend {
     fn warm_up(&self, tpe: FileType, id: &Id) -> RusticResult<()> {
         self.be.warm_up(tpe, id)
     }
+
+    fn is_async_compatible(&self) -> bool {
+        self.be.is_async_compatible()
+    }
 }
 
 impl WriteBackend for HotColdBackend {

crates/core/src/backend/warm_up.rs

@@ -59,6 +59,10 @@ impl ReadBackend for WarmUpAccessBackend {
         _ = self.be.read_partial(tpe, id, false, 0, 1);
         Ok(())
     }
+
+    fn is_async_compatible(&self) -> bool {
+        self.be.is_async_compatible()
+    }
 }
 
 impl WriteBackend for WarmUpAccessBackend {

crates/core/src/repository.rs

@@ -708,6 +708,19 @@ impl<P, S> Repository<P, S> {
     pub fn list<T: RepoId>(&self) -> RusticResult<impl Iterator<Item = T>> {
         Ok(self.be.list(T::TYPE)?.into_iter().map(Into::into))
     }
+
+    /// Check if one of this repository backend is incompatible
+    /// with async features in `rustic_core` implementations.
+    ///
+    /// see <https://github.com/rustic-rs/rustic/issues/1181>
+    pub fn is_async_compatible(&self) -> bool {
+        // check if be or be_hot is incompatible with async
+        self.be.is_async_compatible()
+            && self
+                .be_hot
+                .as_ref()
+                .map_or(true, ReadBackend::is_async_compatible)
+    }
 }
 
 impl<P: ProgressBars, S> Repository<P, S> {
@@ -1896,7 +1909,7 @@ impl<P: ProgressBars, S: IndexedTree> Repository<P, S> {
 impl<P: ProgressBars, S: IndexedIds> Repository<P, S> {
     /// Run a backup of `source` using the given options.
     ///
-    /// You have to give a preflled [`SnapshotFile`] which is modified and saved.
+    /// You have to give a prefilled [`SnapshotFile`] which is modified and saved.
     ///
     /// # Arguments
     ///

crates/testing/src/backend.rs

@@ -58,6 +58,11 @@ pub mod in_memory_backend {
         ) -> RusticResult<Bytes> {
             Ok(self.0.read().unwrap()[tpe][id].slice(offset as usize..(offset + length) as usize))
         }
+
+        /// [`InMemoryBackend`] doesn't use `async`, even under the hood.
+        fn is_async_compatible(&self) -> bool {
+            true
+        }
     }
 
     impl WriteBackend for InMemoryBackend {