Add a LightSyncState field to the chain spec (#6894)

* Reset code, almost ready for PR

* Improved build_hardcoded_spec

* Fix line widths

* Fix tests

* Fix sc-service-test

* Suggestions from code review

* Rename to LightSyncState

* It's not syncing :^(

* It syncs!

* Remove rpc call

* Convert spaces to tabs

* Moved sc-service things to export_sync_state.rs

* Fix tests

* Wait for syncing with network_status_sinks

* Remove sc-network from node-template

* Apply suggestions from code review

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* Various changes, split the flag up into 2 pieces to make testing easier.

* Update client/cli/src/commands/build_spec_cmd.rs

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* Revert a lot of changes

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

substrate/client/service/src/chain_ops/build_spec.rs

@@ -0,0 +1,82 @@
+// Copyright 2020 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Substrate is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+use sp_runtime::traits::{Block as BlockT, NumberFor, Saturating, One};
+use sp_blockchain::HeaderBackend;
+use crate::{TFullBackend, TLightBackend};
+use std::sync::Arc;
+use sp_runtime::generic::BlockId;
+
+/// An error for if this function is being called on a full node.
+pub const CHT_ROOT_ERROR: &str =
+	"Backend doesn't store CHT roots. Make sure you're calling this on a light client.";
+
+/// Something that might allow access to a `ChtRootStorage`.
+pub trait MaybeChtRootStorageProvider<Block> {
+	/// Potentially get a reference to a `ChtRootStorage`.
+	fn cht_root_storage(&self) -> Option<&dyn sc_client_api::light::ChtRootStorage<Block>>;
+}
+
+impl<Block: BlockT> MaybeChtRootStorageProvider<Block> for TFullBackend<Block> {
+	fn cht_root_storage(&self) -> Option<&dyn sc_client_api::light::ChtRootStorage<Block>> {
+		None
+	}
+}
+
+impl<Block: BlockT> MaybeChtRootStorageProvider<Block> for TLightBackend<Block> {
+	fn cht_root_storage(&self) -> Option<&dyn sc_client_api::light::ChtRootStorage<Block>> {
+		Some(self.blockchain().storage())
+	}
+}
+
+/// Build a `LightSyncState` from the CHT roots stored in a backend.
+pub fn build_light_sync_state<TBl, TCl, TBackend>(
+	client: Arc<TCl>,
+	backend: Arc<TBackend>,
+) -> Result<sc_chain_spec::LightSyncState<TBl>, sp_blockchain::Error>
+	where
+		TBl: BlockT,
+		TCl: HeaderBackend<TBl>,
+		TBackend: MaybeChtRootStorageProvider<TBl>,
+{
+	let storage = backend.cht_root_storage().ok_or(CHT_ROOT_ERROR)?;
+
+	let finalized_hash = client.info().finalized_hash;
+	let finalized_number = client.info().finalized_number;
+
+	use sc_client_api::cht;
+
+	let mut chts = Vec::new();
+
+	// We can't fetch a CHT root later than `finalized_number - 2 * cht_size`.
+	let cht_size_x_2 = cht::size::<NumberFor::<TBl>>() * NumberFor::<TBl>::from(2);
+
+	let mut number = NumberFor::<TBl>::one();
+
+	while number <= finalized_number.saturating_sub(cht_size_x_2) {
+		match storage.header_cht_root(cht::size(), number)? {
+			Some(cht_root) => chts.push(cht_root),
+			None => log::error!("No CHT found for block {}", number),
+		}
+
+		number += cht::size();
+	}
+
+	Ok(sc_chain_spec::LightSyncState {
+		header: client.header(BlockId::Hash(finalized_hash))?.unwrap(),
+		chts,
+	})
+}

substrate/client/service/src/chain_ops/mod.rs

@@ -21,9 +21,11 @@ mod export_blocks;
 mod export_raw_state;
 mod import_blocks;
 mod revert_chain;
+mod build_spec;
 
 pub use check_block::*;
 pub use export_blocks::*;
 pub use export_raw_state::*;
 pub use import_blocks::*;
 pub use revert_chain::*;
+pub use build_spec::*;