database: downcast methods for NostrDatabase trait

Cargo.toml

@@ -33,6 +33,7 @@ nostr-relay-builder = { version = "0.42", path = "./crates/nostr-relay-builder",
 nostr-relay-pool = { version = "0.42", path = "./crates/nostr-relay-pool", default-features = false }
 nostr-sdk = { version = "0.42", path = "./crates/nostr-sdk", default-features = false }
 reqwest = { version = "0.12", default-features = false }
+rustversion = "1.0"
 serde = { version = "1.0", default-features = false }
 serde_json = { version = "1.0", default-features = false }
 tempfile = "3.19"

crates/nostr-database/Cargo.toml

@@ -19,6 +19,7 @@ flatbuf = ["dep:flatbuffers"]
 flatbuffers = { version = "23.5", optional = true }
 lru.workspace = true
 nostr = { workspace = true, features = ["std"] }
+rustversion.workspace = true
 tokio = { workspace = true, features = ["sync"] }
 
 [dev-dependencies]

crates/nostr-database/src/lib.rs

@@ -193,6 +193,43 @@ pub trait NostrDatabase: Any + Debug + Send + Sync {
     fn wipe(&self) -> BoxedFuture<Result<(), DatabaseError>>;
 }
 
+#[rustversion::since(1.86)]
+impl dyn NostrDatabase {
+    /// Upcast to [`Any`].
+    #[inline]
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+
+    /// Upcast to [`Any`].
+    #[inline]
+    fn as_any_arc(self: Arc<Self>) -> Arc<dyn Any + Send + Sync> {
+        self
+    }
+
+    /// Downcast [`NostrDatabase`] to a concrete type reference.
+    ///
+    /// **Requires rustc >= 1.86!**
+    #[inline]
+    pub fn downcast_ref<T>(&self) -> Option<&T>
+    where
+        T: NostrDatabase,
+    {
+        self.as_any().downcast_ref()
+    }
+
+    /// Downcast [`NostrDatabase`] to a concrete type.
+    ///
+    /// **Requires rustc >= 1.86!**
+    #[inline]
+    pub fn downcast<T>(self: Arc<Self>) -> Option<Arc<T>>
+    where
+        T: NostrDatabase,
+    {
+        self.as_any_arc().downcast().ok()
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

crates/nostr-sdk/examples/lmdb.rs

@@ -58,5 +58,10 @@ async fn main() -> Result<()> {
     let events = client.database().query(filter).await?;
     println!("Events: {events:?}");
 
+    // Database downcasting to access to specific APIs
+    if let Some(_lmdb) = client.database().downcast_ref::<NostrLMDB>() {
+        // Access specific APIs here
+    }
+
     Ok(())
 }

crates/nostr-sdk/examples/nostrdb.rs

@@ -35,5 +35,10 @@ async fn main() -> Result<()> {
     let events = client.database().query(filter).await?;
     println!("Events: {events:?}");
 
+    // Database downcasting to access to specific APIs
+    if let Some(ndb) = client.database().downcast_ref::<NdbDatabase>() {
+        println!("Subscription counts: {}", ndb.subscription_count());
+    }
+
     Ok(())
 }