diff --git a/src/backend/backend_file.rs b/src/backend/backend_file.rs
index 593252c..8af5bb2 100644
--- a/src/backend/backend_file.rs
+++ b/src/backend/backend_file.rs
@@ -1 +1,100 @@
-//todo
+use std::future::Future;
+
+use log::{error, info};
+
+use crate::backend::FindError;
+
+use crate::device::{DeviceAndSub, DeviceUpdate};
+use crate::episode::{Episode, EpisodeRaw};
+use crate::podsync::{QueryEpisodes, Url};
+use crate::subscription::SubscriptionChangesFromClient;
+use crate::user::User;
+use crate::Timestamp;
+
+type Result<T> = std::result::Result<T, ()>;
+
+pub struct Backend;
+
+pub async fn init() {
+}
+
+impl Backend {
+    pub async fn new() -> Self {
+        Self
+    }
+}
+
+impl Backend {
+    pub async fn find_user(&self, username: &str) -> std::result::Result<User, FindError> {
+        todo!()
+    }
+
+    /// session_id: set to None to logout / make NULL
+    pub async fn update_user(&self, username: &str, session_id: Option<&str>) -> bool {
+        todo!()
+    }
+
+    pub async fn users_with_session(&self, session_id: &str) -> Result<Vec<User>> {
+        todo!()
+    }
+}
+
+impl Backend {
+    pub async fn devices_for_user(&self, username: &str) -> Result<Vec<DeviceAndSub>> {
+        todo!()
+    }
+
+    pub async fn update_device(
+        &self,
+        username: &str,
+        device_id: &str,
+        update: DeviceUpdate,
+    ) -> Result<()> {
+        todo!()
+    }
+}
+
+impl Backend {
+    pub async fn subscriptions(
+        &self,
+        username: &str,
+        device_id: &str,
+        since: Timestamp,
+    ) -> Result<Vec<Url>> {
+        todo!()
+    }
+
+    pub async fn update_subscriptions(
+        &self,
+        username: &str,
+        device_id: &str,
+        changes: &SubscriptionChangesFromClient,
+        now: Timestamp,
+    ) -> Result<()> {
+        todo!()
+    }
+}
+
+impl Backend {
+    pub async fn episodes(&self, username: &str, query: &QueryEpisodes) -> Result<Vec<EpisodeRaw>> {
+        todo!()
+    }
+
+    pub async fn update_episodes(
+        &self,
+        username: &str,
+        now: Timestamp,
+        changes: Vec<Episode>,
+    ) -> Result<()> {
+        todo!()
+    }
+}
+
+#[cfg(test)]
+pub mod test {
+    use sqlx::{migrate::MigrateDatabase, Pool, Sqlite, SqlitePool};
+
+    pub async fn create_db() -> Pool<Sqlite> {
+        todo!()
+    }
+}