historical slashing w ocw w adhoc tree creation (paritytech#6220)

* draft

* steps

* chore: fmt

* step by step

* more details

* make test public

* refactor: split into on and offchain

* test stab

* tabs my friend

* offchain overlay: split key into prefix and true key

Simplifies inspection and makes key actually unique.

* test: share state

* fix & test

* docs improv

* address review comments

* cleanup test chore

* refactor, abbrev link text

* chore: linewidth

* fix prefix key split fallout

* minor fallout

* minor changes

* addresses review comments

* rename historical.rs -> historical/mod.rs

* avoid shared::* wildcard import

* fix: add missing call to store_session_validator_set_to_offchain

* fix/compile: missing shared:: prefix

* fix/test: flow

* fix/review: Apply suggestions from code review

Co-authored-by: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

* fix/review: more review comment fixes

* fix/review: make ValidatorSet private

* fix/include: core -> sp_core

* fix/review: fallout

* fix/visbility: make them public API

Ref paritytech#6358

* fix/review: review changes fallout - again

Co-authored-by: Bernhard Schuster <bernhard@parity.io>
Co-authored-by: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

client/db/src/lib.rs

@@ -544,7 +544,12 @@ pub struct BlockImportOperation<Block: BlockT> {
 
 impl<Block: BlockT> BlockImportOperation<Block> {
 	fn apply_offchain(&mut self, transaction: &mut Transaction<DbHash>) {
-		for (key, value_operation) in self.offchain_storage_updates.drain() {
+		for ((prefix, key), value_operation) in self.offchain_storage_updates.drain() {
+			let key: Vec<u8> = prefix
+				.into_iter()
+				.chain(sp_core::sp_std::iter::once(b'/'))
+				.chain(key.into_iter())
+				.collect();
 			match value_operation {
 				OffchainOverlayedChange::SetValue(val) => transaction.set_from_vec(columns::OFFCHAIN, &key, val),
 				OffchainOverlayedChange::Remove => transaction.remove(columns::OFFCHAIN, &key),

frame/session/Cargo.toml

@@ -14,7 +14,9 @@ targets = ["x86_64-unknown-linux-gnu"]
 [dependencies]
 serde = { version = "1.0.101", optional = true }
 codec = { package = "parity-scale-codec", version = "1.3.0", default-features = false, features = ["derive"] }
+sp-core = { version = "2.0.0-rc3", default-features = false, path = "../../primitives/core" }
 sp-std = { version = "2.0.0-rc3", default-features = false, path = "../../primitives/std" }
+sp-io = { version = "2.0.0-rc3", default-features = false, path = "../../primitives/io" }
 sp-runtime = { version = "2.0.0-rc3", default-features = false, path = "../../primitives/runtime" }
 sp-session = { version = "2.0.0-rc3", default-features = false, path = "../../primitives/session" }
 sp-staking = { version = "2.0.0-rc3", default-features = false, path = "../../primitives/staking" }
@@ -25,8 +27,6 @@ sp-trie = { version = "2.0.0-rc3", optional = true, default-features = false, pa
 impl-trait-for-tuples = "0.1.3"
 
 [dev-dependencies]
-sp-core = { version = "2.0.0-rc3", path = "../../primitives/core" }
-sp-io ={ version = "2.0.0-rc3", path = "../../primitives/io" }
 sp-application-crypto = { version = "2.0.0-rc3", path = "../../primitives/application-crypto" }
 lazy_static = "1.4.0"
 
@@ -37,7 +37,9 @@ std = [
 	"serde",
 	"codec/std",
 	"sp-std/std",
+	"sp-io/std",
 	"frame-support/std",
+	"sp-core/std",
 	"sp-runtime/std",
 	"sp-session/std",
 	"sp-staking/std",

frame/session/src/historical.rs → frame/session/src/historical/mod.rs

@@ -37,6 +37,10 @@ use sp_trie::{MemoryDB, Trie, TrieMut, Recorder, EMPTY_PREFIX};
 use sp_trie::trie_types::{TrieDBMut, TrieDB};
 use super::{SessionIndex, Module as SessionModule};
 
+mod shared;
+pub mod offchain;
+pub mod onchain;
+
 /// Trait necessary for the historical module.
 pub trait Trait: super::Trait {
 	/// Full identification of the validator.
@@ -116,6 +120,7 @@ impl<T: Trait, I> crate::SessionManager<T::ValidatorId> for NoteHistoricalRoot<T
 	where I: SessionManager<T::ValidatorId, T::FullIdentification>
 {
 	fn new_session(new_index: SessionIndex) -> Option<Vec<T::ValidatorId>> {
+
 		StoredRange::mutate(|range| {
 			range.get_or_insert_with(|| (new_index, new_index)).1 = new_index + 1;
 		});
@@ -143,18 +148,21 @@ impl<T: Trait, I> crate::SessionManager<T::ValidatorId> for NoteHistoricalRoot<T
 
 		new_validators
 	}
+
 	fn start_session(start_index: SessionIndex) {
 		<I as SessionManager<_, _>>::start_session(start_index)
 	}
+
 	fn end_session(end_index: SessionIndex) {
+		onchain::store_session_validator_set_to_offchain::<T>(end_index);
 		<I as SessionManager<_, _>>::end_session(end_index)
 	}
 }
 
 /// A tuple of the validator's ID and their full identification.
 pub type IdentificationTuple<T> = (<T as crate::Trait>::ValidatorId, <T as Trait>::FullIdentification);
 
-/// a trie instance for checking and generating proofs.
+/// A trie instance for checking and generating proofs.
 pub struct ProvingTrie<T: Trait> {
 	db: MemoryDB<T::Hashing>,
 	root: T::Hash,
@@ -250,7 +258,6 @@ impl<T: Trait> ProvingTrie<T> {
 			.ok()?
 			.and_then(|raw| <IdentificationTuple<T>>::decode(&mut &*raw).ok())
 	}
-
 }
 
 impl<T: Trait, D: AsRef<[u8]>> frame_support::traits::KeyOwnerProofSystem<(KeyTypeId, D)>
@@ -311,9 +318,9 @@ impl<T: Trait, D: AsRef<[u8]>> frame_support::traits::KeyOwnerProofSystem<(KeyTy
 }
 
 #[cfg(test)]
-mod tests {
+pub(crate) mod tests {
 	use super::*;
-	use sp_core::crypto::key_types::DUMMY;
+	use sp_runtime::key_types::DUMMY;
 	use sp_runtime::testing::UintAuthorityId;
 	use crate::mock::{
 		NEXT_VALIDATORS, force_new_session,
@@ -323,7 +330,7 @@ mod tests {
 
 	type Historical = Module<Test>;
 
-	fn new_test_ext() -> sp_io::TestExternalities {
+	pub(crate) fn new_test_ext() -> sp_io::TestExternalities {
 		let mut t = frame_system::GenesisConfig::default().build_storage::<Test>().unwrap();
 		crate::GenesisConfig::<Test> {
 			keys: NEXT_VALIDATORS.with(|l|

frame/session/src/historical/offchain.rs

@@ -0,0 +1,263 @@
+// This file is part of Substrate.
+
+// Copyright (C) 2019-2020 Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! Off-chain logic for creating a proof based data provided by on-chain logic.
+//!
+//! Validator-set extracting an iterator from an off-chain worker stored list containing
+//! historical validator-sets.
+//! Based on the logic of historical slashing, but the validation is done off-chain.
+//! Use [`fn store_current_session_validator_set_to_offchain()`](super::onchain) to store the
+//! required data to the offchain validator set.
+//! This is used in conjunction with [`ProvingTrie`](super::ProvingTrie) and
+//! the off-chain indexing API.
+
+use sp_runtime::{offchain::storage::StorageValueRef, KeyTypeId};
+use sp_session::MembershipProof;
+
+use super::super::{Module as SessionModule, SessionIndex};
+use super::{IdentificationTuple, ProvingTrie, Trait};
+
+use super::shared;
+use sp_std::prelude::*;
+
+
+/// A set of validators, which was used for a fixed session index.
+struct ValidatorSet<T: Trait> {
+	validator_set: Vec<IdentificationTuple<T>>,
+}
+
+impl<T: Trait> ValidatorSet<T> {
+	/// Load the set of validators for a particular session index from the off-chain storage.
+	///
+	/// If none is found or decodable given `prefix` and `session`, it will return `None`.
+	/// Empty validator sets should only ever exist for genesis blocks.
+	pub fn load_from_offchain_db(session_index: SessionIndex) -> Option<Self> {
+		let derived_key = shared::derive_key(shared::PREFIX, session_index);
+		StorageValueRef::persistent(derived_key.as_ref())
+			.get::<Vec<(T::ValidatorId, T::FullIdentification)>>()
+			.flatten()
+			.map(|validator_set| Self { validator_set })
+	}
+
+	#[inline]
+	fn len(&self) -> usize {
+		self.validator_set.len()
+	}
+}
+
+/// Implement conversion into iterator for usage
+/// with [ProvingTrie](super::ProvingTrie::generate_for).
+impl<T: Trait> sp_std::iter::IntoIterator for ValidatorSet<T> {
+	type Item = (T::ValidatorId, T::FullIdentification);
+	type IntoIter = sp_std::vec::IntoIter<Self::Item>;
+	fn into_iter(self) -> Self::IntoIter {
+		self.validator_set.into_iter()
+	}
+}
+
+/// Create a proof based on the data available in the off-chain database.
+///
+/// Based on the yielded `MembershipProof` the implementer may decide what
+/// to do, i.e. in case of a failed proof, enqueue a transaction back on
+/// chain reflecting that, with all its consequences such as i.e. slashing.
+pub fn prove_session_membership<T: Trait, D: AsRef<[u8]>>(
+	session_index: SessionIndex,
+	session_key: (KeyTypeId, D),
+) -> Option<MembershipProof> {
+	let validators = ValidatorSet::<T>::load_from_offchain_db(session_index)?;
+	let count = validators.len() as u32;
+	let trie = ProvingTrie::<T>::generate_for(validators.into_iter()).ok()?;
+
+	let (id, data) = session_key;
+	trie.prove(id, data.as_ref())
+		.map(|trie_nodes| MembershipProof {
+			session: session_index,
+			trie_nodes,
+			validator_count: count,
+		})
+}
+
+
+/// Attempt to prune anything that is older than `first_to_keep` session index.
+///
+/// Due to re-organisation it could be that the `first_to_keep` might be less
+/// than the stored one, in which case the conservative choice is made to keep records
+/// up to the one that is the lesser.
+pub fn prune_older_than<T: Trait>(first_to_keep: SessionIndex) {
+	let derived_key = shared::LAST_PRUNE.to_vec();
+	let entry = StorageValueRef::persistent(derived_key.as_ref());
+	match entry.mutate(|current: Option<Option<SessionIndex>>| -> Result<_, ()> {
+		match current {
+			Some(Some(current)) if current < first_to_keep => Ok(first_to_keep),
+			// do not move the cursor, if the new one would be behind ours
+			Some(Some(current)) => Ok(current),
+			None => Ok(first_to_keep),
+			// if the storage contains undecodable data, overwrite with current anyways
+			// which might leak some entries being never purged, but that is acceptable
+			// in this context
+			Some(None) => Ok(first_to_keep),
+		}
+	}) {
+		Ok(Ok(new_value)) => {
+			// on a re-org this is not necessarily true, with the above they might be equal
+			if new_value < first_to_keep {
+				for session_index in new_value..first_to_keep {
+					let derived_key = shared::derive_key(shared::PREFIX, session_index);
+					let _ = StorageValueRef::persistent(derived_key.as_ref()).clear();
+				}
+			}
+		}
+		Ok(Err(_)) => {} // failed to store the value calculated with the given closure
+		Err(_) => {}     // failed to calculate the value to store with the given closure
+	}
+}
+
+/// Keep the newest `n` items, and prune all items older than that.
+pub fn keep_newest<T: Trait>(n_to_keep: usize) {
+	let session_index = <SessionModule<T>>::current_index();
+	let n_to_keep = n_to_keep as SessionIndex;
+	if n_to_keep < session_index {
+		prune_older_than::<T>(session_index - n_to_keep)
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::super::{onchain, Module};
+	use super::*;
+	use crate::mock::{
+		force_new_session, set_next_validators, Session, System, Test, NEXT_VALIDATORS,
+	};
+	use codec::Encode;
+	use frame_support::traits::{KeyOwnerProofSystem, OnInitialize};
+	use sp_core::crypto::key_types::DUMMY;
+	use sp_core::offchain::{
+		testing::TestOffchainExt,
+		OffchainExt,
+		StorageKind,
+	};
+
+	use sp_runtime::testing::UintAuthorityId;
+
+	type Historical = Module<Test>;
+
+	pub fn new_test_ext() -> sp_io::TestExternalities {
+		let mut ext = frame_system::GenesisConfig::default()
+			.build_storage::<Test>()
+			.expect("Failed to create test externalities.");
+
+		crate::GenesisConfig::<Test> {
+			keys: NEXT_VALIDATORS.with(|l| {
+				l.borrow()
+					.iter()
+					.cloned()
+					.map(|i| (i, i, UintAuthorityId(i).into()))
+					.collect()
+			}),
+		}
+		.assimilate_storage(&mut ext)
+		.unwrap();
+
+
+		let mut ext = sp_io::TestExternalities::new(ext);
+
+		let (offchain, offchain_state) = TestOffchainExt::with_offchain_db(ext.offchain_db());
+
+		const ITERATIONS: u32 = 5u32;
+		let mut seed = [0u8; 32];
+		seed[0..4].copy_from_slice(&ITERATIONS.to_le_bytes());
+		offchain_state.write().seed = seed;
+
+		ext.register_extension(OffchainExt::new(offchain));
+		ext
+	}
+
+	#[test]
+	fn encode_decode_roundtrip() {
+		use codec::{Decode, Encode};
+		use super::super::super::Trait as SessionTrait;
+		use super::super::Trait as HistoricalTrait;
+
+		let sample = (
+				22u32 as <Test as SessionTrait>::ValidatorId,
+				7_777_777 as <Test as HistoricalTrait>::FullIdentification);
+
+		let encoded = sample.encode();
+		let decoded = Decode::decode(&mut encoded.as_slice()).expect("Must decode");
+		assert_eq!(sample, decoded);
+	}
+
+	#[test]
+	fn onchain_to_offchain() {
+		let mut ext = new_test_ext();
+
+		const DATA: &[u8] = &[7,8,9,10,11];
+		ext.execute_with(|| {
+			b"alphaomega"[..].using_encoded(|key| sp_io::offchain_index::set(key, DATA));
+		});
+
+		ext.persist_offchain_overlay();
+
+		ext.execute_with(|| {
+			let data =
+			b"alphaomega"[..].using_encoded(|key| {
+				sp_io::offchain::local_storage_get(StorageKind::PERSISTENT, key)
+			});
+			assert_eq!(data, Some(DATA.to_vec()));
+		});
+	}
+
+
+	#[test]
+	fn historical_proof_offchain() {
+		let mut ext = new_test_ext();
+		let encoded_key_1 = UintAuthorityId(1).encode();
+
+		ext.execute_with(|| {
+			set_next_validators(vec![1, 2]);
+			force_new_session();
+
+			System::set_block_number(1);
+			Session::on_initialize(1);
+
+			// "on-chain"
+			onchain::store_current_session_validator_set_to_offchain::<Test>();
+			assert_eq!(<SessionModule<Test>>::current_index(), 1);
+
+			set_next_validators(vec![7, 8]);
+
+			force_new_session();
+		});
+
+		ext.persist_offchain_overlay();
+
+		ext.execute_with(|| {
+
+
+			System::set_block_number(2);
+			Session::on_initialize(2);
+			assert_eq!(<SessionModule<Test>>::current_index(), 2);
+
+			// "off-chain"
+			let proof = prove_session_membership::<Test, _>(1, (DUMMY, &encoded_key_1));
+			assert!(proof.is_some());
+			let proof = proof.expect("Must be Some(Proof)");
+
+			assert!(Historical::check_proof((DUMMY, &encoded_key_1[..]), proof.clone()).is_some());
+		});
+	}
+}