examples: Add light client example

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

Cargo.lock

@@ -4336,8 +4336,6 @@ dependencies = [
  "sp-keyring",
  "subxt",
  "tokio",
- "tracing",
- "tracing-subscriber 0.3.17",
 ]
 
 [[package]]

examples/Cargo.toml

@@ -13,7 +13,7 @@ homepage.workspace = true
 description = "Subxt example usage"
 
 [dev-dependencies]
-subxt = { workspace = true }
+subxt = { workspace = true, default-features = false, features = ["default", "experimental-light-client"]}
 tokio = { workspace = true }
 futures = { workspace = true }
 hex = { workspace = true }

examples/examples/tx_basic_light_client.rs

@@ -0,0 +1,38 @@
+use sp_keyring::AccountKeyring;
+use subxt::rpc::LightClient;
+use subxt::{tx::PairSigner, OnlineClient, PolkadotConfig};
+
+use std::sync::Arc;
+
+// 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 {}
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    // Create a light client from the provided chain spec.
+    let light_client = LightClient::new(include_str!("../../artifacts/dev_spec.json"))?;
+    let api = OnlineClient::<PolkadotConfig>::from_rpc_client(Arc::new(light_client)).await?;
+
+    // Build a balance transfer extrinsic.
+    let dest = AccountKeyring::Bob.to_account_id().into();
+    let balance_transfer_tx = polkadot::tx().balances().transfer(dest, 10_000);
+
+    // Submit the balance transfer extrinsic from Alice, and wait for it to be successful
+    // and in a finalized block. We get back the extrinsic events if all is well.
+    let from = PairSigner::new(AccountKeyring::Alice.pair());
+    let events = api
+        .tx()
+        .sign_and_submit_then_watch_default(&balance_transfer_tx, &from)
+        .await?
+        .wait_for_finalized_success()
+        .await?;
+
+    // Find a Transfer event and print it.
+    let transfer_event = events.find_first::<polkadot::balances::events::Transfer>()?;
+    if let Some(event) = transfer_event {
+        println!("Balance transfer success: {event:?}");
+    }
+
+    Ok(())
+}