Attempt to bootstrap the db on connect (#2029)

Fixes #2024

Whenever `db.connect` is called, we will try to bootstrap the db if
required

Author: penberg

libsql/src/database.rs

@@ -682,6 +682,18 @@ impl Database {
                 };
                 use tokio::sync::Mutex;
 
+                let _ = tokio::task::block_in_place(move || {
+                    let rt = tokio::runtime::Builder::new_current_thread()
+                        .enable_all()
+                        .build()
+                        .unwrap();
+                    rt.block_on(async {
+                        // we will ignore if any errors occurred during the bootstrapping the db,
+                        // because the client could be offline when trying to connect.
+                        let _ = db.bootstrap_db().await;
+                    })
+                });
+
                 let local = db.connect()?;
 
                 if *remote_writes {

libsql/src/local/database.rs

@@ -465,11 +465,21 @@ impl Database {
     /// Sync WAL frames to remote.
     pub async fn sync_offline(&self) -> Result<crate::database::Replicated> {
         let mut sync_ctx = self.sync_ctx.as_ref().unwrap().lock().await;
+        // it is important we call `bootstrap` before we `sync`. Because sync uses a connection
+        // to the db and during bootstrap we replace the sqlite db file. This can lead to
+        // inconsistencies and data corruption.
         crate::sync::bootstrap_db(&mut sync_ctx).await?;
         let conn = self.connect()?;
         crate::sync::sync_offline(&mut sync_ctx, &conn).await
     }
 
+    #[cfg(feature = "sync")]
+    /// Brings the .db file from server, if required.
+    pub async fn bootstrap_db(&self) -> Result<()> {
+        let mut sync_ctx = self.sync_ctx.as_ref().unwrap().lock().await;
+        crate::sync::bootstrap_db(&mut sync_ctx).await
+    }
+
     pub(crate) fn path(&self) -> &str {
         &self.db_path
     }

libsql/src/sync.rs

@@ -686,6 +686,8 @@ async fn atomic_write<P: AsRef<Path>>(path: P, data: &[u8]) -> Result<()> {
 
 /// bootstrap_db brings the .db file from remote, if required. If the .db file already exists, then
 /// it does nothing. Calling this function multiple times is safe.
+/// However, make sure there are no existing active connections to the db file as this method can
+/// replace it
 pub async fn bootstrap_db(sync_ctx: &mut SyncContext) -> Result<()> {
     // todo: we are checking with the remote server only during initialisation. ideally,
     // we need to do this when we notice a large gap in generations, when bootstrapping is cheaper