subxt: Use unstable backend for light client

Signed-off-by: Alexandru Vasile <[email protected]>

subxt/Cargo.toml

@@ -61,7 +61,7 @@ unstable-metadata = []
 
 # Activate this to expose the Light Client functionality.
 # Note that this feature is experimental and things may break or not work as expected.
-unstable-light-client = ["subxt-lightclient", "tokio-stream"]
+unstable-light-client = ["subxt-lightclient", "tokio-stream", "tokio"]
 
 [dependencies]
 async-trait = { workspace = true }
@@ -117,6 +117,7 @@ getrandom = { workspace = true, optional = true }
 
 # Included if "native" feature is enabled
 tokio-util = { workspace = true, features = ["compat"], optional = true }
+tokio = { workspace = true, features = ["macros", "time", "rt-multi-thread"], optional = true }
 
 [dev-dependencies]
 bitvec = { workspace = true }

subxt/src/client/light_client/mod.rs

@@ -93,7 +93,29 @@ impl RawLightClient {
     ) -> Result<LightClient<TChainConfig>, crate::Error> {
         let raw_rpc = self.raw_rpc.for_chain(chain_id);
         let rpc_client = RpcClient::new(raw_rpc.clone());
-        let client = OnlineClient::<TChainConfig>::from_rpc_client(rpc_client).await?;
+
+        use crate::backend::unstable::UnstableBackend;
+        use std::sync::Arc;
+        let (backend, mut driver) = UnstableBackend::builder().build(rpc_client);
+        let future = async move {
+            use futures::StreamExt;
+            while let Some(val) = driver.next().await {
+                if let Err(e) = val {
+                    // This is a test; bail if something does wrong and try to
+                    // ensure that the message makes it to some logs.
+                    eprintln!("Error driving unstable backend in tests (will panic): {e}");
+                    panic!("Error driving unstable backend in tests: {e}");
+                }
+            }
+        };
+        // The unstable backend needs driving:
+        #[cfg(feature = "native")]
+        tokio::spawn(future);
+        #[cfg(feature = "web")]
+        wasm_bindgen_futures::spawn_local(future);
+        let client = OnlineClient::from_backend(Arc::new(backend))
+            .await
+            .map_err(|e| format!("Cannot construct OnlineClient from backend: {e}"))?;
 
         Ok(LightClient { client, chain_id })
     }