Add legacy RPC usage example (#1279)

* Add example using legacy rpc * Illustrate how account_nonce and system_acc_next eventaully cathces up * Adapt and add rpc_legacy example to book. Add missing light_client example too * cargo fmt --------- Co-authored-by: Fredrik Simonsson <fredrik@nodle.com>
2026-06-18 07:11:03 +00:00 · 2023-11-23 17:14:17 +00:00
parent 2fe7b5c14c
commit 5764c8e68e
8 changed files with 100 additions and 7 deletions
@@ -0,0 +1,101 @@
+use futures::StreamExt;
+use std::{iter, num::NonZeroU32};
+use subxt::{
+    client::{LightClient, RawLightClient},
+    PolkadotConfig,
+};
+
+// Generate an interface that we can use from the node's metadata.
+#[subxt::subxt(runtime_metadata_path = "../artifacts/polkadot_metadata_small.scale")]
+pub mod polkadot {}
+
+const POLKADOT_SPEC: &str = include_str!("../../artifacts/demo_chain_specs/polkadot.json");
+const ASSET_HUB_SPEC: &str =
+    include_str!("../../artifacts/demo_chain_specs/polkadot_asset_hub.json");
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    // The smoldot logs are informative:
+    tracing_subscriber::fmt::init();
+
+    // Connecting to a parachain is a multi step process.
+
+    // Step 1. Construct a new smoldot client.
+    let mut client =
+        subxt_lightclient::smoldot::Client::new(subxt_lightclient::smoldot::DefaultPlatform::new(
+            "subxt-example-light-client".into(),
+            "version-0".into(),
+        ));
+
+    // Step 2. Connect to the relay chain of the parachain. For this example, the Polkadot relay chain.
+    let polkadot_connection = client
+        .add_chain(subxt_lightclient::smoldot::AddChainConfig {
+            specification: POLKADOT_SPEC,
+            json_rpc: subxt_lightclient::smoldot::AddChainConfigJsonRpc::Enabled {
+                max_pending_requests: NonZeroU32::new(128).unwrap(),
+                max_subscriptions: 1024,
+            },
+            potential_relay_chains: iter::empty(),
+            database_content: "",
+            user_data: (),
+        })
+        .expect("Light client chain added with valid spec; qed");
+    let polkadot_json_rpc_responses = polkadot_connection
+        .json_rpc_responses
+        .expect("Light client configured with json rpc enabled; qed");
+    let polkadot_chain_id = polkadot_connection.chain_id;
+
+    // Step 3. Connect to the parachain. For this example, the Asset hub parachain.
+    let assethub_connection = client
+        .add_chain(subxt_lightclient::smoldot::AddChainConfig {
+            specification: ASSET_HUB_SPEC,
+            json_rpc: subxt_lightclient::smoldot::AddChainConfigJsonRpc::Enabled {
+                max_pending_requests: NonZeroU32::new(128).unwrap(),
+                max_subscriptions: 1024,
+            },
+            // The chain specification of the asset hub parachain mentions that the identifier
+            // of its relay chain is `polkadot`.
+            potential_relay_chains: [polkadot_chain_id].into_iter(),
+            database_content: "",
+            user_data: (),
+        })
+        .expect("Light client chain added with valid spec; qed");
+    let parachain_json_rpc_responses = assethub_connection
+        .json_rpc_responses
+        .expect("Light client configured with json rpc enabled; qed");
+    let parachain_chain_id = assethub_connection.chain_id;
+
+    // Step 4. Turn the smoldot client into a raw client.
+    let raw_light_client = RawLightClient::builder()
+        .add_chain(polkadot_chain_id, polkadot_json_rpc_responses)
+        .add_chain(parachain_chain_id, parachain_json_rpc_responses)
+        .build(client)
+        .await?;
+
+    // Step 5. Obtain a client to target the relay chain and the parachain.
+    let polkadot_api: LightClient<PolkadotConfig> =
+        raw_light_client.for_chain(polkadot_chain_id).await?;
+    let parachain_api: LightClient<PolkadotConfig> =
+        raw_light_client.for_chain(parachain_chain_id).await?;
+
+    // Step 6. Subscribe to the finalized blocks of the chains.
+    let polkadot_sub = polkadot_api
+        .blocks()
+        .subscribe_finalized()
+        .await?
+        .map(|block| ("Polkadot", block));
+    let parachain_sub = parachain_api
+        .blocks()
+        .subscribe_finalized()
+        .await?
+        .map(|block| ("AssetHub", block));
+    let mut stream_combinator = futures::stream::select(polkadot_sub, parachain_sub);
+
+    while let Some((chain, block)) = stream_combinator.next().await {
+        let block = block?;
+
+        println!("     Chain {:?} hash={:?}", chain, block.hash());
+    }
+
+    Ok(())
+}