rpc: Fetch chainHead genesis hash

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

examples/examples/chainhead_subscription.rs

@@ -28,6 +28,9 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
     // Create a client to use:
     let api = OnlineClient::<PolkadotConfig>::new().await?;
 
+    let genesis = api.rpc().get_chainhead_genesis_hash().await?;
+    println!("Genesis: {:?}", genesis);
+
     let mut follow_sub = api.blocks().subscribe_chainhead_finalized(true).await?;
     // Handle all subscriptions from the `chainHead_follow`.
     while let Some(block) = follow_sub.next().await {

subxt/src/blocks/block_types.rs

@@ -81,8 +81,6 @@ where
         if let Some(event) = sub.next().await {
             let event = event?;
 
-            println!("Got event: {:?}", event);
-
             return match event {
                 ChainHeadEvent::Done(ChainHeadResult { result }) => {
                     let bytes = hex::decode(result.trim_start_matches("0x"))
@@ -148,8 +146,6 @@ where
         if let Some(event) = sub.next().await {
             let event = event?;
 
-            println!("Got event: {:?}", event);
-
             return match event {
                 ChainHeadEvent::Done(ChainHeadResult { result }) => {
                     let result = match result {
@@ -195,8 +191,6 @@ where
         if let Some(event) = sub.next().await {
             let event = event?;
 
-            println!("Got event: {:?}", event);
-
             return match event {
                 ChainHeadEvent::Done(ChainHeadResult { result }) => {
                     let bytes = hex::decode(result.trim_start_matches("0x"))

subxt/src/rpc/rpc.rs

@@ -662,6 +662,21 @@ impl<T: Config> Rpc<T> {
         Ok(header)
     }
 
+    /// Get the chain head genesis hash.
+    pub async fn get_chainhead_genesis_hash(
+        &self,
+    ) -> Result<T::Hash, Error> {
+        let hash = self
+            .client
+            .request(
+                "chainHead_unstable_genesisHash",
+                rpc_params![],
+            )
+            .await?;
+
+        Ok(hash)
+    }
+
     /// Subscribe to the chain head storage.
     pub async fn subscribe_chainhead_storage(
         &self,