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
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
// Copyright (C) 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/>.

//! Helper for handling (i.e. answering) state requests from a remote peer via the
//! `crate::request_responses::RequestResponsesBehaviour`.

use crate::{
	schema::v1::{KeyValueStateEntry, StateEntry, StateRequest, StateResponse},
	LOG_TARGET,
};

use codec::{Decode, Encode};
use futures::{channel::oneshot, stream::StreamExt};
use log::{debug, trace};
use prost::Message;
use sc_network_types::PeerId;
use schnellru::{ByLength, LruMap};

use sc_client_api::{BlockBackend, ProofProvider};
use sc_network::{
	config::ProtocolId,
	request_responses::{IncomingRequest, OutgoingResponse},
	NetworkBackend, MAX_RESPONSE_SIZE,
};
use sp_runtime::traits::Block as BlockT;

use std::{
	hash::{Hash, Hasher},
	sync::Arc,
	time::Duration,
};

const MAX_RESPONSE_BYTES: usize = 2 * 1024 * 1024; // Actual reponse may be bigger.
const MAX_NUMBER_OF_SAME_REQUESTS_PER_PEER: usize = 2;

mod rep {
	use sc_network::ReputationChange as Rep;

	/// Reputation change when a peer sent us the same request multiple times.
	pub const SAME_REQUEST: Rep = Rep::new(i32::MIN, "Same state request multiple times");
}

/// Generates a `RequestResponseProtocolConfig` for the state request protocol, refusing incoming
/// requests.
pub fn generate_protocol_config<
	Hash: AsRef<[u8]>,
	B: BlockT,
	N: NetworkBackend<B, <B as BlockT>::Hash>,
>(
	protocol_id: &ProtocolId,
	genesis_hash: Hash,
	fork_id: Option<&str>,
	inbound_queue: async_channel::Sender<IncomingRequest>,
) -> N::RequestResponseProtocolConfig {
	N::request_response_config(
		generate_protocol_name(genesis_hash, fork_id).into(),
		std::iter::once(generate_legacy_protocol_name(protocol_id).into()).collect(),
		1024 * 1024,
		MAX_RESPONSE_SIZE,
		Duration::from_secs(40),
		Some(inbound_queue),
	)
}

/// Generate the state protocol name from the genesis hash and fork id.
fn generate_protocol_name<Hash: AsRef<[u8]>>(genesis_hash: Hash, fork_id: Option<&str>) -> String {
	let genesis_hash = genesis_hash.as_ref();
	if let Some(fork_id) = fork_id {
		format!("/{}/{}/state/2", array_bytes::bytes2hex("", genesis_hash), fork_id)
	} else {
		format!("/{}/state/2", array_bytes::bytes2hex("", genesis_hash))
	}
}

/// Generate the legacy state protocol name from chain specific protocol identifier.
fn generate_legacy_protocol_name(protocol_id: &ProtocolId) -> String {
	format!("/{}/state/2", protocol_id.as_ref())
}

/// The key of [`BlockRequestHandler::seen_requests`].
#[derive(Eq, PartialEq, Clone)]
struct SeenRequestsKey<B: BlockT> {
	peer: PeerId,
	block: B::Hash,
	start: Vec<Vec<u8>>,
}

#[allow(clippy::derived_hash_with_manual_eq)]
impl<B: BlockT> Hash for SeenRequestsKey<B> {
	fn hash<H: Hasher>(&self, state: &mut H) {
		self.peer.hash(state);
		self.block.hash(state);
		self.start.hash(state);
	}
}

/// The value of [`StateRequestHandler::seen_requests`].
enum SeenRequestsValue {
	/// First time we have seen the request.
	First,
	/// We have fulfilled the request `n` times.
	Fulfilled(usize),
}

/// Handler for incoming block requests from a remote peer.
pub struct StateRequestHandler<B: BlockT, Client> {
	client: Arc<Client>,
	request_receiver: async_channel::Receiver<IncomingRequest>,
	/// Maps from request to number of times we have seen this request.
	///
	/// This is used to check if a peer is spamming us with the same request.
	seen_requests: LruMap<SeenRequestsKey<B>, SeenRequestsValue>,
}

impl<B, Client> StateRequestHandler<B, Client>
where
	B: BlockT,
	Client: BlockBackend<B> + ProofProvider<B> + Send + Sync + 'static,
{
	/// Create a new [`StateRequestHandler`].
	pub fn new<N: NetworkBackend<B, <B as BlockT>::Hash>>(
		protocol_id: &ProtocolId,
		fork_id: Option<&str>,
		client: Arc<Client>,
		num_peer_hint: usize,
	) -> (Self, N::RequestResponseProtocolConfig) {
		// Reserve enough request slots for one request per peer when we are at the maximum
		// number of peers.
		let capacity = std::cmp::max(num_peer_hint, 1);
		let (tx, request_receiver) = async_channel::bounded(capacity);

		let protocol_config = generate_protocol_config::<_, B, N>(
			protocol_id,
			client
				.block_hash(0u32.into())
				.ok()
				.flatten()
				.expect("Genesis block exists; qed"),
			fork_id,
			tx,
		);

		let capacity = ByLength::new(num_peer_hint.max(1) as u32 * 2);
		let seen_requests = LruMap::new(capacity);

		(Self { client, request_receiver, seen_requests }, protocol_config)
	}

	/// Run [`StateRequestHandler`].
	pub async fn run(mut self) {
		while let Some(request) = self.request_receiver.next().await {
			let IncomingRequest { peer, payload, pending_response } = request;

			match self.handle_request(payload, pending_response, &peer) {
				Ok(()) => debug!(target: LOG_TARGET, "Handled block request from {}.", peer),
				Err(e) => debug!(
					target: LOG_TARGET,
					"Failed to handle state request from {}: {}", peer, e,
				),
			}
		}
	}

	fn handle_request(
		&mut self,
		payload: Vec<u8>,
		pending_response: oneshot::Sender<OutgoingResponse>,
		peer: &PeerId,
	) -> Result<(), HandleRequestError> {
		let request = StateRequest::decode(&payload[..])?;
		let block: B::Hash = Decode::decode(&mut request.block.as_ref())?;

		let key = SeenRequestsKey { peer: *peer, block, start: request.start.clone() };

		let mut reputation_changes = Vec::new();

		match self.seen_requests.get(&key) {
			Some(SeenRequestsValue::First) => {},
			Some(SeenRequestsValue::Fulfilled(ref mut requests)) => {
				*requests = requests.saturating_add(1);

				if *requests > MAX_NUMBER_OF_SAME_REQUESTS_PER_PEER {
					reputation_changes.push(rep::SAME_REQUEST);
				}
			},
			None => {
				self.seen_requests.insert(key.clone(), SeenRequestsValue::First);
			},
		}

		trace!(
			target: LOG_TARGET,
			"Handling state request from {}: Block {:?}, Starting at {:x?}, no_proof={}",
			peer,
			request.block,
			&request.start,
			request.no_proof,
		);

		let result = if reputation_changes.is_empty() {
			let mut response = StateResponse::default();

			if !request.no_proof {
				let (proof, _count) = self.client.read_proof_collection(
					block,
					request.start.as_slice(),
					MAX_RESPONSE_BYTES,
				)?;
				response.proof = proof.encode();
			} else {
				let entries = self.client.storage_collection(
					block,
					request.start.as_slice(),
					MAX_RESPONSE_BYTES,
				)?;
				response.entries = entries
					.into_iter()
					.map(|(state, complete)| KeyValueStateEntry {
						state_root: state.state_root,
						entries: state
							.key_values
							.into_iter()
							.map(|(key, value)| StateEntry { key, value })
							.collect(),
						complete,
					})
					.collect();
			}

			trace!(
				target: LOG_TARGET,
				"StateResponse contains {} keys, {}, proof nodes, from {:?} to {:?}",
				response.entries.len(),
				response.proof.len(),
				response.entries.get(0).and_then(|top| top
					.entries
					.first()
					.map(|e| sp_core::hexdisplay::HexDisplay::from(&e.key))),
				response.entries.get(0).and_then(|top| top
					.entries
					.last()
					.map(|e| sp_core::hexdisplay::HexDisplay::from(&e.key))),
			);
			if let Some(value) = self.seen_requests.get(&key) {
				// If this is the first time we have processed this request, we need to change
				// it to `Fulfilled`.
				if let SeenRequestsValue::First = value {
					*value = SeenRequestsValue::Fulfilled(1);
				}
			}

			let mut data = Vec::with_capacity(response.encoded_len());
			response.encode(&mut data)?;
			Ok(data)
		} else {
			Err(())
		};

		pending_response
			.send(OutgoingResponse { result, reputation_changes, sent_feedback: None })
			.map_err(|_| HandleRequestError::SendResponse)
	}
}

#[derive(Debug, thiserror::Error)]
enum HandleRequestError {
	#[error("Failed to decode request: {0}.")]
	DecodeProto(#[from] prost::DecodeError),

	#[error("Failed to encode response: {0}.")]
	EncodeProto(#[from] prost::EncodeError),

	#[error("Failed to decode block hash: {0}.")]
	InvalidHash(#[from] codec::Error),

	#[error(transparent)]
	Client(#[from] sp_blockchain::Error),

	#[error("Failed to send response.")]
	SendResponse,
}