Add Runtime API to execute runtime calls (#777)

* rpc: Add RuntimeAPI call via `state_call` method

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

* subxt: Add runtime API

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

* Expose the RuntimeAPI client

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

* tests: Test the runtime API call against the metadata

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

* client: Fetch the metadata from runtime API

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

* blocks: Fix doc typo

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

* blocks: Use &str instead of String to identify fn names

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

* Update subxt/src/runtime_api/runtime_client.rs

Co-authored-by: Niklas Adolfsson <niklasadolfsson1@gmail.com>

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>
Co-authored-by: Niklas Adolfsson <niklasadolfsson1@gmail.com>

subxt/src/client/offline_client.rs

@@ -7,6 +7,7 @@ use crate::{
     constants::ConstantsClient,
     events::EventsClient,
     rpc::types::RuntimeVersion,
+    runtime_api::RuntimeApiClient,
     storage::StorageClient,
     tx::TxClient,
     Config,
@@ -49,6 +50,11 @@ pub trait OfflineClientT<T: Config>: Clone + Send + Sync + 'static {
     fn blocks(&self) -> BlocksClient<T, Self> {
         BlocksClient::new(self.clone())
     }
+
+    /// Work with runtime API.
+    fn runtime_api(&self) -> RuntimeApiClient<T, Self> {
+        RuntimeApiClient::new(self.clone())
+    }
 }
 
 /// A client that is capable of performing offline-only operations.

subxt/src/client/online_client.rs

@@ -19,12 +19,18 @@ use crate::{
         Rpc,
         RpcClientT,
     },
+    runtime_api::RuntimeApiClient,
     storage::StorageClient,
     tx::TxClient,
     Config,
     Metadata,
 };
+use codec::{
+    Compact,
+    Decode,
+};
 use derivative::Derivative;
+use frame_metadata::RuntimeMetadataPrefixed;
 use futures::future;
 use parking_lot::RwLock;
 use std::sync::Arc;
@@ -95,7 +101,7 @@ impl<T: Config> OnlineClient<T> {
         let (genesis_hash, runtime_version, metadata) = future::join3(
             rpc.genesis_hash(),
             rpc.runtime_version(None),
-            rpc.metadata(None),
+            OnlineClient::fetch_metadata(&rpc),
         )
         .await;
 
@@ -109,6 +115,15 @@ impl<T: Config> OnlineClient<T> {
         })
     }
 
+    /// Fetch the metadata from substrate using the runtime API.
+    async fn fetch_metadata(rpc: &Rpc<T>) -> Result<Metadata, Error> {
+        let bytes = rpc.state_call("Metadata_metadata", None, None).await?;
+        let cursor = &mut &*bytes;
+        let _ = <Compact<u32>>::decode(cursor)?;
+        let meta: RuntimeMetadataPrefixed = Decode::decode(cursor)?;
+        Ok(meta.try_into()?)
+    }
+
     /// Create an object which can be used to keep the runtime up to date
     /// in a separate thread.
     ///
@@ -214,6 +229,11 @@ impl<T: Config> OnlineClient<T> {
     pub fn blocks(&self) -> BlocksClient<T, Self> {
         <Self as OfflineClientT<T>>::blocks(self)
     }
+
+    /// Work with runtime API.
+    pub fn runtime_api(&self) -> RuntimeApiClient<T, Self> {
+        <Self as OfflineClientT<T>>::runtime_api(self)
+    }
 }
 
 impl<T: Config> OfflineClientT<T> for OnlineClient<T> {