chainHead based backend implementation (#1161)

* add follow_stream impl

* follow_stream_unpin first draft

* add tests for follow_stream_unpin

* more tests and fixes for follow_stream_unpin

* first pass follow_stream_driver

* follow_stream_driver: add tests, fix things, buffer events from last finalized

* First pass finishing Backend impl

* Fix test compile issues

* clippy fixes

* clippy fix and consistify light_client

* revert lightclient tweak

* revert other lightclient thing

* cargo fmt

* start testing unstable backend behind feature flag

* more test fixes and move test-runtime metadata path just incase

* fix compile error

* ensure transaction progress stream actually used and fix another test

* cargo fmt

* CI tweak

* improve some comments and address some feedback bits

* update CI to use our own nightly binary

* wait for finalized block perhaps

subxt/src/client/light_client/builder.rs

@@ -3,7 +3,7 @@
 // see LICENSE for license details.
 
 use super::{rpc::LightClientRpc, LightClient, LightClientError};
-use crate::backend::rpc::RpcClient;
+use crate::backend::{rpc::RpcClient, Backend};
 use crate::{config::Config, error::Error, OnlineClient};
 use std::num::NonZeroU32;
 use subxt_lightclient::{AddChainConfig, AddChainConfigJsonRpc, ChainId};

subxt/src/client/mod.rs

@@ -12,7 +12,7 @@ mod offline_client;
 mod online_client;
 
 #[cfg(feature = "unstable-light-client")]
-mod lightclient;
+mod light_client;
 
 pub use offline_client::{OfflineClient, OfflineClientT};
 pub use online_client::{
@@ -20,4 +20,4 @@ pub use online_client::{
 };
 
 #[cfg(feature = "unstable-light-client")]
-pub use lightclient::{LightClient, LightClientBuilder, LightClientError};
+pub use light_client::{LightClient, LightClientBuilder, LightClientError};

subxt/src/client/online_client.rs

@@ -106,7 +106,7 @@ impl<T: Config> OnlineClient<T> {
     /// Construct a new [`OnlineClient`] by providing an underlying [`Backend`]
     /// implementation to power it. Other details will be obtained from the chain.
     pub async fn from_backend<B: Backend<T>>(backend: Arc<B>) -> Result<OnlineClient<T>, Error> {
-        let latest_block = backend.latest_best_block_ref().await?;
+        let latest_block = backend.latest_finalized_block_ref().await?;
 
         let (genesis_hash, runtime_version, metadata) = future::join3(
             backend.genesis_hash(),
@@ -437,7 +437,7 @@ impl<T: Config> RuntimeUpdaterStream<T> {
             Err(err) => return Some(Err(err)),
         };
 
-        let latest_block_ref = match self.client.backend().latest_best_block_ref().await {
+        let latest_block_ref = match self.client.backend().latest_finalized_block_ref().await {
             Ok(block_ref) => block_ref,
             Err(e) => return Some(Err(e)),
         };