1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
// This file is part of Substrate.

// Copyright (C) Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0

// This program 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.

// This program 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 this program. If not, see <https://www.gnu.org/licenses/>.

//! A RPC handler to create sync states for light clients.
//!
//! Currently only usable with BABE + GRANDPA.
//!
//! # Usage
//!
//! To use the light sync state, it needs to be added as an extension to the chain spec:
//!
//! ```
//! use sc_sync_state_rpc::LightSyncStateExtension;
//!
//! #[derive(Default, Clone, serde::Serialize, serde::Deserialize, sc_chain_spec::ChainSpecExtension)]
//! #[serde(rename_all = "camelCase")]
//! pub struct Extensions {
//!    light_sync_state: LightSyncStateExtension,
//! }
//!
//! type ChainSpec = sc_chain_spec::GenericChainSpec<(), Extensions>;
//! ```
//!
//! If the [`LightSyncStateExtension`] is not added as an extension to the chain spec,
//! the [`SyncState`] will fail at instantiation.

#![deny(unused_crate_dependencies)]

use std::sync::Arc;

use jsonrpsee::{
	core::{async_trait, Error as JsonRpseeError, RpcResult},
	proc_macros::rpc,
	types::{error::CallError, ErrorObject},
};

use sc_client_api::StorageData;
use sc_consensus_babe::{BabeWorkerHandle, Error as BabeError};
use sp_blockchain::HeaderBackend;
use sp_runtime::traits::{Block as BlockT, NumberFor};

type SharedAuthoritySet<TBl> =
	sc_consensus_grandpa::SharedAuthoritySet<<TBl as BlockT>::Hash, NumberFor<TBl>>;

/// Error type used by this crate.
#[derive(Debug, thiserror::Error)]
#[allow(missing_docs)]
pub enum Error<Block: BlockT> {
	#[error(transparent)]
	Blockchain(#[from] sp_blockchain::Error),

	#[error("Failed to load the block weight for block {0:?}")]
	LoadingBlockWeightFailed(Block::Hash),

	#[error("Failed to load the BABE epoch data: {0}")]
	LoadingEpochDataFailed(BabeError<Block>),

	#[error("JsonRpc error: {0}")]
	JsonRpc(String),

	#[error(
		"The light sync state extension is not provided by the chain spec. \
		Read the `sc-sync-state-rpc` crate docs on how to do this!"
	)]
	LightSyncStateExtensionNotFound,
}

impl<Block: BlockT> From<Error<Block>> for JsonRpseeError {
	fn from(error: Error<Block>) -> Self {
		let message = match error {
			Error::JsonRpc(s) => s,
			_ => error.to_string(),
		};
		CallError::Custom(ErrorObject::owned(1, message, None::<()>)).into()
	}
}

/// Serialize the given `val` by encoding it with SCALE codec and serializing it as hex.
fn serialize_encoded<S: serde::Serializer, T: codec::Encode>(
	val: &T,
	s: S,
) -> Result<S::Ok, S::Error> {
	let encoded = StorageData(val.encode());
	serde::Serialize::serialize(&encoded, s)
}

/// The light sync state extension.
///
/// This represents a JSON serialized [`LightSyncState`]. It is required to be added to the
/// chain-spec as an extension.
pub type LightSyncStateExtension = Option<serde_json::Value>;

/// Hardcoded information that allows light clients to sync quickly.
#[derive(serde::Serialize, Clone)]
#[serde(rename_all = "camelCase")]
#[serde(deny_unknown_fields)]
pub struct LightSyncState<Block: BlockT> {
	/// The header of the best finalized block.
	#[serde(serialize_with = "serialize_encoded")]
	pub finalized_block_header: <Block as BlockT>::Header,
	/// The epoch changes tree for babe.
	#[serde(serialize_with = "serialize_encoded")]
	pub babe_epoch_changes: sc_consensus_epochs::EpochChangesFor<Block, sc_consensus_babe::Epoch>,
	/// The babe weight of the finalized block.
	pub babe_finalized_block_weight: sc_consensus_babe::BabeBlockWeight,
	/// The authority set for grandpa.
	#[serde(serialize_with = "serialize_encoded")]
	pub grandpa_authority_set:
		sc_consensus_grandpa::AuthoritySet<<Block as BlockT>::Hash, NumberFor<Block>>,
}

/// An api for sync state RPC calls.
#[rpc(client, server)]
pub trait SyncStateApi {
	/// Returns the JSON serialized chainspec running the node, with a sync state.
	#[method(name = "sync_state_genSyncSpec")]
	async fn system_gen_sync_spec(&self, raw: bool) -> RpcResult<serde_json::Value>;
}

/// An api for sync state RPC calls.
pub struct SyncState<Block: BlockT, Client> {
	chain_spec: Box<dyn sc_chain_spec::ChainSpec>,
	client: Arc<Client>,
	shared_authority_set: SharedAuthoritySet<Block>,
	babe_worker_handle: BabeWorkerHandle<Block>,
}

impl<Block, Client> SyncState<Block, Client>
where
	Block: BlockT,
	Client: HeaderBackend<Block> + sc_client_api::AuxStore + 'static,
{
	/// Create a new sync state RPC helper.
	pub fn new(
		chain_spec: Box<dyn sc_chain_spec::ChainSpec>,
		client: Arc<Client>,
		shared_authority_set: SharedAuthoritySet<Block>,
		babe_worker_handle: BabeWorkerHandle<Block>,
	) -> Result<Self, Error<Block>> {
		if sc_chain_spec::get_extension::<LightSyncStateExtension>(chain_spec.extensions())
			.is_some()
		{
			Ok(Self { chain_spec, client, shared_authority_set, babe_worker_handle })
		} else {
			Err(Error::<Block>::LightSyncStateExtensionNotFound)
		}
	}

	async fn build_sync_state(&self) -> Result<LightSyncState<Block>, Error<Block>> {
		let epoch_changes = self
			.babe_worker_handle
			.epoch_data()
			.await
			.map_err(Error::LoadingEpochDataFailed)?;

		let finalized_hash = self.client.info().finalized_hash;
		let finalized_header = self
			.client
			.header(finalized_hash)?
			.ok_or_else(|| sp_blockchain::Error::MissingHeader(finalized_hash.to_string()))?;

		let finalized_block_weight =
			sc_consensus_babe::aux_schema::load_block_weight(&*self.client, finalized_hash)?
				.ok_or(Error::LoadingBlockWeightFailed(finalized_hash))?;

		Ok(LightSyncState {
			finalized_block_header: finalized_header,
			babe_epoch_changes: epoch_changes,
			babe_finalized_block_weight: finalized_block_weight,
			grandpa_authority_set: self.shared_authority_set.clone_inner(),
		})
	}
}

#[async_trait]
impl<Block, Backend> SyncStateApiServer for SyncState<Block, Backend>
where
	Block: BlockT,
	Backend: HeaderBackend<Block> + sc_client_api::AuxStore + 'static,
{
	async fn system_gen_sync_spec(&self, raw: bool) -> RpcResult<serde_json::Value> {
		let current_sync_state = self.build_sync_state().await?;
		let mut chain_spec = self.chain_spec.cloned_box();

		let extension = sc_chain_spec::get_extension_mut::<LightSyncStateExtension>(
			chain_spec.extensions_mut(),
		)
		.ok_or(Error::<Block>::LightSyncStateExtensionNotFound)?;

		let val = serde_json::to_value(&current_sync_state)?;
		*extension = Some(val);

		let json_str = chain_spec.as_json(raw).map_err(|e| Error::<Block>::JsonRpc(e))?;
		serde_json::from_str(&json_str).map_err(Into::into)
	}
}