openethereum/ethcore/sync/src/chain/supplier.rs

// Copyright 2015-2020 Parity Technologies (UK) Ltd.
// This file is part of Open Ethereum.

// Open Ethereum 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.

// Open Ethereum 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 Open Ethereum.  If not, see <http://www.gnu.org/licenses/>.

use std::cmp;
use std::time::{Duration, Instant};

use crate::sync_io::SyncIo;

use bytes::Bytes;
use enum_primitive::FromPrimitive;
use ethereum_types::H256;
use log::{debug, trace, warn};
use network::{self, PeerId};
use parking_lot::RwLock;
use rlp::{Rlp, RlpStream};
use common_types::{ids::BlockId, BlockNumber};

use super::sync_packet::{PacketInfo, SyncPacket};
use super::sync_packet::SyncPacket::{
	StatusPacket,
	TransactionsPacket,
	GetBlockHeadersPacket,
	BlockHeadersPacket,
	GetBlockBodiesPacket,
	BlockBodiesPacket,
	GetNodeDataPacket,
	NodeDataPacket,
	GetReceiptsPacket,
	ReceiptsPacket,
	GetSnapshotManifestPacket,
	SnapshotManifestPacket,
	GetSnapshotDataPacket,
	SnapshotDataPacket,
	ConsensusDataPacket,
	GetPrivateStatePacket,
	PrivateStatePacket,
};

use super::{
	ChainSync,
	SyncHandler,
	RlpResponseResult,
	PacketDecodeError,
	MAX_BODIES_TO_SEND,
	MAX_HEADERS_TO_SEND,
	MAX_NODE_DATA_TO_SEND,
	MAX_NODE_DATA_TOTAL_DURATION,
	MAX_NODE_DATA_SINGLE_DURATION,
	MAX_RECEIPTS_HEADERS_TO_SEND,
};

/// The Chain Sync Supplier: answers requests from peers with available data
pub struct SyncSupplier;

impl SyncSupplier {
	/// Dispatch incoming requests and responses
	// Take a u8 and not a SyncPacketId because this is the entry point
	// to chain sync from the outside world.
	pub fn dispatch_packet(sync: &RwLock<ChainSync>, io: &mut dyn SyncIo, peer: PeerId, packet_id: u8, data: &[u8]) {
		let rlp = Rlp::new(data);

		if let Some(id) = SyncPacket::from_u8(packet_id) {
			let result = match id {
				GetBlockBodiesPacket => SyncSupplier::return_rlp(
					io, &rlp, peer,
					SyncSupplier::return_block_bodies,
					|e| format!("Error sending block bodies: {:?}", e)),

				GetBlockHeadersPacket => SyncSupplier::return_rlp(
					io, &rlp, peer,
					SyncSupplier::return_block_headers,
					|e| format!("Error sending block headers: {:?}", e)),

				GetReceiptsPacket => SyncSupplier::return_rlp(
					io, &rlp, peer,
					SyncSupplier::return_receipts,
					|e| format!("Error sending receipts: {:?}", e)),

				GetNodeDataPacket => SyncSupplier::return_rlp(
					io, &rlp, peer,
					SyncSupplier::return_node_data,
					|e| format!("Error sending nodes: {:?}", e)),

				GetSnapshotManifestPacket => SyncSupplier::return_rlp(
					io, &rlp, peer,
					SyncSupplier::return_snapshot_manifest,
					|e| format!("Error sending snapshot manifest: {:?}", e)),

				GetSnapshotDataPacket => SyncSupplier::return_rlp(
					io, &rlp, peer,
					SyncSupplier::return_snapshot_data,
					|e| format!("Error sending snapshot data: {:?}", e)),

				GetPrivateStatePacket => SyncSupplier::return_rlp(
					io, &rlp, peer,
					SyncSupplier::return_private_state,
					|e| format!("Error sending private state data: {:?}", e)),

				StatusPacket => {
					sync.write().on_packet(io, peer, packet_id, data);
					Ok(())
				},
				// Packets that require the peer to be confirmed
				_ => {
					if !sync.read().peers.contains_key(&peer) {
						debug!(target:"sync", "Unexpected packet {} from unregistered peer: {}:{}", packet_id, peer, io.peer_version(peer));
						return;
					}
					trace!(target: "sync", "{} -> Dispatching packet: {}", peer, packet_id);

					match id {
						ConsensusDataPacket => {
							SyncHandler::on_consensus_packet(io, peer, &rlp)
						},
						TransactionsPacket => {
							let res = {
								let sync_ro = sync.read();
								SyncHandler::on_peer_transactions(&*sync_ro, io, peer, rlp)
							};
							if res.is_err() {
								// peer sent invalid data, disconnect.
								io.disable_peer(peer);
								sync.write().deactivate_peer(io, peer);
							}
						},
						_ => {
							sync.write().on_packet(io, peer, packet_id, data);
						}
					}

					Ok(())
				}
			};

			result.unwrap_or_else(|e| {
				debug!(target:"sync", "{} -> Malformed packet {} : {}", peer, packet_id, e);
			})
		}
	}

	/// Respond to GetBlockHeaders request
	fn return_block_headers(io: &dyn SyncIo, r: &Rlp, peer_id: PeerId) -> RlpResponseResult {
		let payload_soft_limit = io.payload_soft_limit();
		// Packet layout:
		// [ block: { P , B_32 }, maxHeaders: P, skip: P, reverse: P in { 0 , 1 } ]
		let max_headers: usize = r.val_at(1)?;
		let skip: usize = r.val_at(2)?;
		let reverse: bool = r.val_at(3)?;
		let last = io.chain().chain_info().best_block_number;
		let number = if r.at(0)?.size() == 32 {
			// id is a hash
			let hash: H256 = r.val_at(0)?;
			trace!(target: "sync", "{} -> GetBlockHeaders (hash: {}, max: {}, skip: {}, reverse:{})", peer_id, hash, max_headers, skip, reverse);
			match io.chain().block_header(BlockId::Hash(hash)) {
				Some(hdr) => {
					let number = hdr.number().into();
					debug_assert_eq!(hdr.hash(), hash);

					if max_headers == 1 || io.chain().block_hash(BlockId::Number(number)) != Some(hash) {
						// Non canonical header or single header requested
						// TODO: handle single-step reverse hashchains of non-canon hashes
						trace!(target:"sync", "Returning single header: {:?}", hash);
						let mut rlp = RlpStream::new_list(1);
						rlp.append_raw(&hdr.into_inner(), 1);
						return Ok(Some((BlockHeadersPacket.id(), rlp)));
					}
					number
				}
				None => return Ok(Some((BlockHeadersPacket.id(), RlpStream::new_list(0)))) //no such header, return nothing
			}
		} else {
			let number = r.val_at::<BlockNumber>(0)?;
			trace!(target: "sync", "{} -> GetBlockHeaders (number: {}, max: {}, skip: {}, reverse:{})", peer_id, number, max_headers, skip, reverse);
			number
		};

		let mut number = if reverse {
			cmp::min(last, number)
		} else {
			cmp::max(0, number)
		};
		let max_count = cmp::min(MAX_HEADERS_TO_SEND, max_headers);
		let mut count = 0;
		let mut data = Bytes::new();
		let inc = skip.saturating_add(1) as BlockNumber;
		let overlay = io.chain_overlay().read();

		// We are checking the `overlay` as well since it's where the ForkBlock
		// header is cached : so peers can confirm we are on the right fork,
		// even if we are not synced until the fork block
		while (number <= last || overlay.contains_key(&number)) && count < max_count {
			if let Some(hdr) = overlay.get(&number) {
				trace!(target: "sync", "{}: Returning cached fork header", peer_id);
				data.extend_from_slice(hdr);
				count += 1;
			} else if let Some(hdr) = io.chain().block_header(BlockId::Number(number)) {
				data.append(&mut hdr.into_inner());
				count += 1;
				// Check that the packet won't be oversized
				if data.len() > payload_soft_limit {
					break;
				}
			} else {
				// No required block.
				break;
			}
			if reverse {
				if number <= inc || number == 0 {
					break;
				}
				number = number.saturating_sub(inc);
			} else {
				number = number.saturating_add(inc);
			}
		}
		let mut rlp = RlpStream::new_list(count as usize);
		rlp.append_raw(&data, count as usize);
		trace!(target: "sync", "{} -> GetBlockHeaders: returned {} entries", peer_id, count);
		Ok(Some((BlockHeadersPacket.id(), rlp)))
	}

	/// Respond to GetBlockBodies request
	fn return_block_bodies(io: &dyn SyncIo, r: &Rlp, peer_id: PeerId) -> RlpResponseResult {
		let payload_soft_limit = io.payload_soft_limit();
		let mut count = r.item_count().unwrap_or(0);
		if count == 0 {
			debug!(target: "sync", "Empty GetBlockBodies request, ignoring.");
			return Ok(None);
		}
		count = cmp::min(count, MAX_BODIES_TO_SEND);
		let mut added = 0usize;
		let mut data = Bytes::new();
		for i in 0..count {
			if let Some(body) = io.chain().block_body(BlockId::Hash(r.val_at::<H256>(i)?)) {
				data.append(&mut body.into_inner());
				added += 1;
				// Check that the packet won't be oversized
				if data.len() > payload_soft_limit {
					break;
				}
			}
		}
		let mut rlp = RlpStream::new_list(added);
		rlp.append_raw(&data, added);
		trace!(target: "sync", "{} -> GetBlockBodies: returned {} entries", peer_id, added);
		Ok(Some((BlockBodiesPacket.id(), rlp)))
	}

	/// Respond to GetNodeData request
	fn return_node_data(io: &dyn SyncIo, r: &Rlp, peer_id: PeerId) -> RlpResponseResult {
		let payload_soft_limit = io.payload_soft_limit(); // 4Mb
		let mut count = r.item_count().unwrap_or(0);
		trace!(target: "sync", "{} -> GetNodeData: {} entries requested", peer_id, count);
		if count == 0 {
			debug!(target: "sync", "Empty GetNodeData request, ignoring.");
			return Ok(None);
		}
		count = cmp::min(count, MAX_NODE_DATA_TO_SEND);
		let mut added = 0usize;
		let mut data = Vec::new();
		let mut total_bytes = 0;
		let mut total_elapsed = Duration::from_secs(0);
		for i in 0..count {
			let hash = &r.val_at(i)?;
			let now = Instant::now();
			let state = io.chain().state_data(hash);

			let elapsed = now.elapsed();
			total_elapsed += elapsed;
			if elapsed > MAX_NODE_DATA_SINGLE_DURATION || total_elapsed > MAX_NODE_DATA_TOTAL_DURATION {
				warn!(
					target: "sync", "{} -> GetNodeData:   item {}/{} – slow state fetch for hash {:?}; took {:?}, total {:?}",
					peer_id, i, count, hash, elapsed, total_elapsed,
				);
				break;
			}
			if let Some(node) = state {
				total_bytes += node.len();
				if total_bytes > payload_soft_limit {
					break;
				}
				data.push(node);
				added += 1;
			}
		}
		trace!(target: "sync", "{} -> GetNodeData: returning {}/{} entries ({} bytes total in {:?})",
			peer_id, added, count, total_bytes, total_elapsed);
		let mut rlp = RlpStream::new_list(added);
		for d in data {
			rlp.append(&d);
		}
		Ok(Some((NodeDataPacket.id(), rlp)))
	}

	fn return_receipts(io: &dyn SyncIo, rlp: &Rlp, peer_id: PeerId) -> RlpResponseResult {
		let payload_soft_limit = io.payload_soft_limit();
		let mut count = rlp.item_count().unwrap_or(0);
		trace!(target: "sync", "{} -> GetReceipts: {} entries", peer_id, count);
		if count == 0 {
			debug!(target: "sync", "Empty GetReceipts request, ignoring.");
			return Ok(None);
		}
		count = cmp::min(count, MAX_RECEIPTS_HEADERS_TO_SEND);
		let mut added_headers = 0usize;
		let mut data = Bytes::new();
		let mut total_bytes = 0;
		for i in 0..count {
			if let Some(receipts) = io.chain().block_receipts(&rlp.val_at::<H256>(i)?) {
				let mut receipts_bytes = ::rlp::encode(&receipts);
				total_bytes += receipts_bytes.len();
				if total_bytes > payload_soft_limit { break; }
				data.append(&mut receipts_bytes);
				added_headers += 1;
			}
		}
		let mut rlp_result = RlpStream::new_list(added_headers);
		rlp_result.append_raw(&data, added_headers);
		Ok(Some((ReceiptsPacket.id(), rlp_result)))
	}

	/// Respond to GetSnapshotManifest request
	fn return_snapshot_manifest(io: &dyn SyncIo, r: &Rlp, peer_id: PeerId) -> RlpResponseResult {
		let count = r.item_count().unwrap_or(0);
		trace!(target: "warp", "{} -> GetSnapshotManifest", peer_id);
		if count != 0 {
			debug!(target: "warp", "Invalid GetSnapshotManifest request, ignoring.");
			return Ok(None);
		}
		let rlp = match io.snapshot_service().manifest() {
			Some(manifest) => {
				trace!(target: "warp", "{} <- SnapshotManifest", peer_id);
				let mut rlp = RlpStream::new_list(1);
				rlp.append_raw(&manifest.into_rlp(), 1);
				rlp
			},
			None => {
				trace!(target: "warp", "{}: No snapshot manifest to return", peer_id);
				RlpStream::new_list(0)
			}
		};
		Ok(Some((SnapshotManifestPacket.id(), rlp)))
	}

	/// Respond to GetSnapshotData request
	fn return_snapshot_data(io: &dyn SyncIo, r: &Rlp, peer_id: PeerId) -> RlpResponseResult {
		let hash: H256 = r.val_at(0)?;
		trace!(target: "warp", "{} -> GetSnapshotData {:?}", peer_id, hash);
		let rlp = match io.snapshot_service().chunk(hash) {
			Some(data) => {
				let mut rlp = RlpStream::new_list(1);
				trace!(target: "warp", "{} <- SnapshotData", peer_id);
				rlp.append(&data);
				rlp
			},
			None => {
				trace!(target: "warp", "{}: No snapshot data to return", peer_id);
				RlpStream::new_list(0)
			}
		};
		Ok(Some((SnapshotDataPacket.id(), rlp)))
	}

	/// Respond to GetPrivateStatePacket
	fn return_private_state(io: &dyn SyncIo, r: &Rlp, peer_id: PeerId) -> RlpResponseResult {
		let hash: H256 = r.val_at(0)?;
		trace!(target: "privatetx", "{} -> GetPrivateStatePacket {:?}", peer_id, hash);
		io.private_state().map_or(Ok(None), |db| {
			let state = db.state(&hash);
			match state {
				Err(err) => {
					trace!(target: "privatetx", "Cannot retrieve state from db {:?}", err);
					Ok(None)
				}
				Ok(bytes) => {
					let mut rlp = RlpStream::new_list(1);
					rlp.append(&bytes);
					Ok(Some((PrivateStatePacket.id(), rlp)))
				}
			}
		})
	}

	fn return_rlp<FRlp, FError>(io: &mut dyn SyncIo, rlp: &Rlp, peer: PeerId, rlp_func: FRlp, error_func: FError) -> Result<(), PacketDecodeError>
		where FRlp : Fn(&dyn SyncIo, &Rlp, PeerId) -> RlpResponseResult,
			FError : FnOnce(network::Error) -> String
	{
		let response = rlp_func(io, rlp, peer);
		match response {
			Err(e) => Err(e),
			Ok(Some((packet_id, rlp_stream))) => {
				io.respond(packet_id, rlp_stream.out()).unwrap_or_else(
					|e| debug!(target: "sync", "{:?}", error_func(e)));
				Ok(())
			}
			_ => Ok(())
		}
	}
}

#[cfg(test)]
mod test {
	use std::{collections::VecDeque, str::FromStr};

	use crate::{
		blocks::SyncHeader,
		chain::RlpResponseResult,
		tests::{helpers::TestIo, snapshot::TestSnapshotService}
	};

	use super::{
		SyncPacket::{GetReceiptsPacket, GetNodeDataPacket},
		BlockNumber, BlockId, SyncSupplier, PacketInfo
	};

	use super::super::tests::dummy_sync_with_peer;

	use bytes::Bytes;
	use client_traits::BlockChainClient;
	use ethcore::test_helpers::{EachBlockWith, TestBlockChainClient};
	use ethereum_types::H256;
	use parking_lot::RwLock;
	use rlp::{Rlp, RlpStream};

	#[test]
	fn return_block_headers() {
		fn make_hash_req(h: &H256, count: usize, skip: usize, reverse: bool) -> Bytes {
			let mut rlp = RlpStream::new_list(4);
			rlp.append(h);
			rlp.append(&count);
			rlp.append(&skip);
			rlp.append(&if reverse {1u32} else {0u32});
			rlp.out()
		}

		fn make_num_req(n: usize, count: usize, skip: usize, reverse: bool) -> Bytes {
			let mut rlp = RlpStream::new_list(4);
			rlp.append(&n);
			rlp.append(&count);
			rlp.append(&skip);
			rlp.append(&if reverse {1u32} else {0u32});
			rlp.out()
		}

		fn to_header_vec(rlp: RlpResponseResult) -> Vec<SyncHeader> {
			Rlp::new(&rlp.unwrap().unwrap().1.out()).iter().map(|r| SyncHeader::from_rlp(r.as_raw().to_vec()).unwrap()).collect()
		}

		let mut client = TestBlockChainClient::new();
		client.add_blocks(100, EachBlockWith::Nothing);
		let blocks: Vec<_> = (0 .. 100)
			.map(|i| (&client as &dyn BlockChainClient).block(BlockId::Number(i as BlockNumber)).map(|b| b.into_inner()).unwrap()).collect();
		let headers: Vec<_> = blocks.iter().map(|b| SyncHeader::from_rlp(Rlp::new(b).at(0).unwrap().as_raw().to_vec()).unwrap()).collect();
		let hashes: Vec<_> = headers.iter().map(|h| h.header.hash()).collect();

		let queue = RwLock::new(VecDeque::new());
		let ss = TestSnapshotService::new();
		let io = TestIo::new(&mut client, &ss, &queue, None, None);

		let unknown: H256 = H256::zero();
		let result = SyncSupplier::return_block_headers(&io, &Rlp::new(&make_hash_req(&unknown, 1, 0, false)), 0);
		assert!(to_header_vec(result).is_empty());
		let result = SyncSupplier::return_block_headers(&io, &Rlp::new(&make_hash_req(&unknown, 1, 0, true)), 0);
		assert!(to_header_vec(result).is_empty());

		let result = SyncSupplier::return_block_headers(&io, &Rlp::new(&make_hash_req(&hashes[2], 1, 0, true)), 0);
		assert_eq!(to_header_vec(result), vec![headers[2].clone()]);

		let result = SyncSupplier::return_block_headers(&io, &Rlp::new(&make_hash_req(&hashes[2], 1, 0, false)), 0);
		assert_eq!(to_header_vec(result), vec![headers[2].clone()]);

		let result = SyncSupplier::return_block_headers(&io, &Rlp::new(&make_hash_req(&hashes[50], 3, 5, false)), 0);
		assert_eq!(to_header_vec(result), vec![headers[50].clone(), headers[56].clone(), headers[62].clone()]);

		let result = SyncSupplier::return_block_headers(&io, &Rlp::new(&make_hash_req(&hashes[50], 3, 5, true)), 0);
		assert_eq!(to_header_vec(result), vec![headers[50].clone(), headers[44].clone(), headers[38].clone()]);

		let result = SyncSupplier::return_block_headers(&io, &Rlp::new(&make_num_req(2, 1, 0, true)), 0);
		assert_eq!(to_header_vec(result), vec![headers[2].clone()]);

		let result = SyncSupplier::return_block_headers(&io, &Rlp::new(&make_num_req(2, 1, 0, false)), 0);
		assert_eq!(to_header_vec(result), vec![headers[2].clone()]);

		let result = SyncSupplier::return_block_headers(&io, &Rlp::new(&make_num_req(50, 3, 5, false)), 0);
		assert_eq!(to_header_vec(result), vec![headers[50].clone(), headers[56].clone(), headers[62].clone()]);

		let result = SyncSupplier::return_block_headers(&io, &Rlp::new(&make_num_req(50, 3, 5, true)), 0);
		assert_eq!(to_header_vec(result), vec![headers[50].clone(), headers[44].clone(), headers[38].clone()]);
	}

	#[test]
	fn respect_packet_limit() {
		let small_num_blocks = 10;
		let large_num_blocks = 50;
		let tx_per_block = 100;

		let mut client = TestBlockChainClient::new();
		client.add_blocks(large_num_blocks, EachBlockWith::Transactions(tx_per_block));

		let mut small_rlp_request = RlpStream::new_list(small_num_blocks);
		let mut large_rlp_request = RlpStream::new_list(large_num_blocks);

		for i in 0..small_num_blocks {
			let hash: H256 = client.block_hash(BlockId::Number(i as u64)).unwrap();
			small_rlp_request.append(&hash);
			large_rlp_request.append(&hash);
		}

		for i in small_num_blocks..large_num_blocks {
			let hash: H256 = client.block_hash(BlockId::Number(i as u64)).unwrap();
			large_rlp_request.append(&hash);
		}

		let queue = RwLock::new(VecDeque::new());
		let ss = TestSnapshotService::new();
		let io = TestIo::new(&mut client, &ss, &queue, None, None);

		let small_result = SyncSupplier::return_block_bodies(&io, &Rlp::new(&small_rlp_request.out()), 0);
		let small_result = small_result.unwrap().unwrap().1;
		assert_eq!(Rlp::new(&small_result.out()).item_count().unwrap(), small_num_blocks);

		let large_result = SyncSupplier::return_block_bodies(&io, &Rlp::new(&large_rlp_request.out()), 0);
		let large_result = large_result.unwrap().unwrap().1;
		assert!(Rlp::new(&large_result.out()).item_count().unwrap() < large_num_blocks);
	}

	#[test]
	fn return_nodes() {
		let mut client = TestBlockChainClient::new();
		let queue = RwLock::new(VecDeque::new());
		let sync = dummy_sync_with_peer(H256::zero(), &client);
		let ss = TestSnapshotService::new();
		let mut io = TestIo::new(&mut client, &ss, &queue, None, None);

		let mut node_list = RlpStream::new_list(3);
		node_list.append(&H256::from_str("0000000000000000000000000000000000000000000000005555555555555555").unwrap());
		node_list.append(&H256::from_str("ffffffffffffffffffffffffffffffffffffffffffffaaaaaaaaaaaaaaaaaaaa").unwrap());
		node_list.append(&H256::from_str("aff0000000000000000000000000000000000000000000000000000000000000").unwrap());

		let node_request = node_list.out();
		// it returns rlp ONLY for hashes started with "f"
		let result = SyncSupplier::return_node_data(&io, &Rlp::new(&node_request.clone()), 0);

		assert!(result.is_ok());
		let rlp_result = result.unwrap();
		assert!(rlp_result.is_some());

		// the length of one rlp-encoded hash
		let rlp = rlp_result.unwrap().1.out();
		let rlp = Rlp::new(&rlp);
		assert_eq!(Ok(1), rlp.item_count());

		io.sender = Some(2usize);

		SyncSupplier::dispatch_packet(&RwLock::new(sync), &mut io, 0usize, GetNodeDataPacket.id(), &node_request);
		assert_eq!(1, io.packets.len());
	}

	#[test]
	fn return_receipts_empty() {
		let mut client = TestBlockChainClient::new();
		let queue = RwLock::new(VecDeque::new());
		let ss = TestSnapshotService::new();
		let io = TestIo::new(&mut client, &ss, &queue, None, None);

		let result = SyncSupplier::return_receipts(&io, &Rlp::new(&[0xc0]), 0);

		assert!(result.is_ok());
	}

	#[test]
	fn return_receipts() {
		let mut client = TestBlockChainClient::new();
		let queue = RwLock::new(VecDeque::new());
		let sync = dummy_sync_with_peer(H256::zero(), &client);
		let ss = TestSnapshotService::new();
		let mut io = TestIo::new(&mut client, &ss, &queue, None, None);

		let mut receipt_list = RlpStream::new_list(4);
		receipt_list.append(&H256::from_str("0000000000000000000000000000000000000000000000005555555555555555").unwrap());
		receipt_list.append(&H256::from_str("ff00000000000000000000000000000000000000000000000000000000000000").unwrap());
		receipt_list.append(&H256::from_str("fff0000000000000000000000000000000000000000000000000000000000000").unwrap());
		receipt_list.append(&H256::from_str("aff0000000000000000000000000000000000000000000000000000000000000").unwrap());

		let receipts_request = receipt_list.out();
		// it returns rlp ONLY for hashes started with "f"
		let result = SyncSupplier::return_receipts(&io, &Rlp::new(&receipts_request.clone()), 0);

		assert!(result.is_ok());
		let rlp_result = result.unwrap();
		assert!(rlp_result.is_some());

		// the length of two rlp-encoded receipts
		assert_eq!(603, rlp_result.unwrap().1.out().len());

		io.sender = Some(2usize);
		SyncSupplier::dispatch_packet(&RwLock::new(sync), &mut io, 0usize, GetReceiptsPacket.id(), &receipts_request);
		assert_eq!(1, io.packets.len());
	}
}