implementation.rs

// Copyright 2019-2021 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 Cumulus. If not, see <http://www.gnu.org/licenses/>.

//! The actual implementation of the validate block functionality.

use super::MemoryOptimizedValidationParams;
use cumulus_primitives_core::{
	relay_chain::Hash as RHash, ParachainBlockData, PersistedValidationData,
};
use cumulus_primitives_parachain_inherent::ParachainInherentData;

use polkadot_parachain::primitives::{
	HeadData, RelayChainBlockNumber, ValidationParams, ValidationResult,
};

use codec::{Decode, Encode};

use frame_support::traits::{ExecuteBlock, ExtrinsicCall, Get, IsSubType};
use sp_core::storage::{ChildInfo, StateVersion};
use sp_externalities::{set_and_run_with_externalities, Externalities};
use sp_io::KillStorageResult;
use sp_runtime::traits::{Block as BlockT, Extrinsic, HashFor, Header as HeaderT};
use sp_std::{mem, prelude::*};
use sp_trie::MemoryDB;

type TrieBackend<B> = sp_state_machine::TrieBackend<MemoryDB<HashFor<B>>, HashFor<B>>;

type Ext<'a, B> = sp_state_machine::Ext<'a, HashFor<B>, TrieBackend<B>>;

fn with_externalities<F: FnOnce(&mut dyn Externalities) -> R, R>(f: F) -> R {
	sp_externalities::with_externalities(f).expect("Environmental externalities not set.")
}

/// Validate the given parachain block.
///
/// This function is doing roughly the following:
///
/// 1. We decode the [`ParachainBlockData`] from the `block_data` in `params`.
///
/// 2. We are doing some security checks like checking that the `parent_head` in `params`
/// is the parent of the block we are going to check. We also ensure that the `set_validation_data`
/// inherent is present in the block and that the validation data matches the values in `params`.
///
/// 3. We construct the sparse in-memory database from the storage proof inside the block data and
/// then ensure that the storage root matches the storage root in the `parent_head`.
///
/// 4. We replace all the storage related host functions with functions inside the wasm blob.
/// This means instead of calling into the host, we will stay inside the wasm execution. This is
/// very important as the relay chain validator hasn't the state required to verify the block. But
/// we have the in-memory database that contains all the values from the state of the parachain
/// that we require to verify the block.
///
/// 5. We are going to run `check_inherents`. This is important to check stuff like the timestamp
/// matching the real world time.
///
/// 6. The last step is to execute the entire block in the machinery we just have setup. Executing
/// the blocks include running all transactions in the block against our in-memory database and
/// ensuring that the final storage root matches the storage root in the header of the block. In the
/// end we return back the [`ValidationResult`] with all the required information for the validator.
#[doc(hidden)]
pub fn validate_block<
	B: BlockT,
	E: ExecuteBlock<B>,
	PSC: crate::Config,
	CI: crate::CheckInherents<B>,
>(
	MemoryOptimizedValidationParams {
		block_data,
		parent_head,
		relay_parent_number,
		relay_parent_storage_root,
	}: MemoryOptimizedValidationParams,
) -> ValidationResult
where
	B::Extrinsic: ExtrinsicCall,
	<B::Extrinsic as Extrinsic>::Call: IsSubType<crate::Call<PSC>>,
{
	let block_data = codec::decode_from_bytes::<ParachainBlockData<B>>(block_data)
		.expect("Invalid parachain block data");

	let parent_header =
		codec::decode_from_bytes::<B::Header>(parent_head.clone()).expect("Invalid parent head");

	let (header, extrinsics, storage_proof) = block_data.deconstruct();

	let block = B::new(header, extrinsics);
	assert!(parent_header.hash() == *block.header().parent_hash(), "Invalid parent hash");

	let inherent_data = extract_parachain_inherent_data(&block);

	validate_validation_data(
		&inherent_data.validation_data,
		relay_parent_number,
		relay_parent_storage_root,
		parent_head,
	);

	// Create the db
	let db = match storage_proof.to_memory_db(Some(parent_header.state_root())) {
		Ok((db, _)) => db,
		Err(_) => panic!("Compact proof decoding failure."),
	};

	sp_std::mem::drop(storage_proof);

	// We use the storage root of the `parent_head` to ensure that it is the correct root.
	// This is already being done above while creating the in-memory db, but let's be paranoid!!
	let backend =
		sp_state_machine::TrieBackendBuilder::new(db, *parent_header.state_root()).build();

	let _guard = (
		// Replace storage calls with our own implementations
		sp_io::storage::host_read.replace_implementation(host_storage_read),
		sp_io::storage::host_set.replace_implementation(host_storage_set),
		sp_io::storage::host_get.replace_implementation(host_storage_get),
		sp_io::storage::host_exists.replace_implementation(host_storage_exists),
		sp_io::storage::host_clear.replace_implementation(host_storage_clear),
		sp_io::storage::host_root.replace_implementation(host_storage_root),
		sp_io::storage::host_clear_prefix.replace_implementation(host_storage_clear_prefix),
		sp_io::storage::host_append.replace_implementation(host_storage_append),
		sp_io::storage::host_next_key.replace_implementation(host_storage_next_key),
		sp_io::storage::host_start_transaction
			.replace_implementation(host_storage_start_transaction),
		sp_io::storage::host_rollback_transaction
			.replace_implementation(host_storage_rollback_transaction),
		sp_io::storage::host_commit_transaction
			.replace_implementation(host_storage_commit_transaction),
		sp_io::default_child_storage::host_get
			.replace_implementation(host_default_child_storage_get),
		sp_io::default_child_storage::host_read
			.replace_implementation(host_default_child_storage_read),
		sp_io::default_child_storage::host_set
			.replace_implementation(host_default_child_storage_set),
		sp_io::default_child_storage::host_clear
			.replace_implementation(host_default_child_storage_clear),
		sp_io::default_child_storage::host_storage_kill
			.replace_implementation(host_default_child_storage_storage_kill),
		sp_io::default_child_storage::host_exists
			.replace_implementation(host_default_child_storage_exists),
		sp_io::default_child_storage::host_clear_prefix
			.replace_implementation(host_default_child_storage_clear_prefix),
		sp_io::default_child_storage::host_root
			.replace_implementation(host_default_child_storage_root),
		sp_io::default_child_storage::host_next_key
			.replace_implementation(host_default_child_storage_next_key),
		sp_io::offchain_index::host_set.replace_implementation(host_offchain_index_set),
		sp_io::offchain_index::host_clear.replace_implementation(host_offchain_index_clear),
	);

	run_with_externalities::<B, _, _>(&backend, || {
		let relay_chain_proof = crate::RelayChainStateProof::new(
			PSC::SelfParaId::get(),
			inherent_data.validation_data.relay_parent_storage_root,
			inherent_data.relay_chain_state.clone(),
		)
		.expect("Invalid relay chain state proof");

		let res = CI::check_inherents(&block, &relay_chain_proof);

		if !res.ok() {
			if log::log_enabled!(log::Level::Error) {
				res.into_errors().for_each(|e| {
					log::error!("Checking inherent with identifier `{:?}` failed", e.0)
				});
			}

			panic!("Checking inherents failed");
		}
	});

	run_with_externalities::<B, _, _>(&backend, || {
		let head_data = HeadData(block.header().encode());

		E::execute_block(block);

		let new_validation_code = crate::NewValidationCode::<PSC>::get();
		let upward_messages = crate::UpwardMessages::<PSC>::get();
		let processed_downward_messages = crate::ProcessedDownwardMessages::<PSC>::get();
		let horizontal_messages = crate::HrmpOutboundMessages::<PSC>::get();
		let hrmp_watermark = crate::HrmpWatermark::<PSC>::get();

		let head_data =
			if let Some(custom_head_data) = crate::CustomValidationHeadData::<PSC>::get() {
				HeadData(custom_head_data)
			} else {
				head_data
			};

		ValidationResult {
			head_data,
			new_validation_code: new_validation_code.map(Into::into),
			upward_messages,
			processed_downward_messages,
			horizontal_messages,
			hrmp_watermark,
		}
	})
}

/// Extract the [`ParachainInherentData`].
fn extract_parachain_inherent_data<B: BlockT, PSC: crate::Config>(
	block: &B,
) -> &ParachainInherentData
where
	B::Extrinsic: ExtrinsicCall,
	<B::Extrinsic as Extrinsic>::Call: IsSubType<crate::Call<PSC>>,
{
	block
		.extrinsics()
		.iter()
		// Inherents are at the front of the block and are unsigned.
		//
		// If `is_signed` is returning `None`, we keep it safe and assume that it is "signed".
		// We are searching for unsigned transactions anyway.
		.take_while(|e| !e.is_signed().unwrap_or(true))
		.filter_map(|e| e.call().is_sub_type())
		.find_map(|c| match c {
			crate::Call::set_validation_data { data: validation_data } => Some(validation_data),
			_ => None,
		})
		.expect("Could not find `set_validation_data` inherent")
}

/// Validate the given [`PersistedValidationData`] against the [`ValidationParams`].
fn validate_validation_data(
	validation_data: &PersistedValidationData,
	relay_parent_number: RelayChainBlockNumber,
	relay_parent_storage_root: RHash,
	parent_head: bytes::Bytes,
) {
	assert_eq!(parent_head, validation_data.parent_head.0, "Parent head doesn't match");
	assert_eq!(
		relay_parent_number, validation_data.relay_parent_number,
		"Relay parent number doesn't match",
	);
	assert_eq!(
		relay_parent_storage_root, validation_data.relay_parent_storage_root,
		"Relay parent storage root doesn't match",
	);
}

/// Run the given closure with the externalities set.
fn run_with_externalities<B: BlockT, R, F: FnOnce() -> R>(
	backend: &TrieBackend<B>,
	execute: F,
) -> R {
	let mut overlay = sp_state_machine::OverlayedChanges::default();
	let mut cache = Default::default();
	let mut ext = Ext::<B>::new(&mut overlay, &mut cache, backend);

	set_and_run_with_externalities(&mut ext, || execute())
}

fn host_storage_read(key: &[u8], value_out: &mut [u8], value_offset: u32) -> Option<u32> {
	match with_externalities(|ext| ext.storage(key)) {
		Some(value) => {
			let value_offset = value_offset as usize;
			let data = &value[value_offset.min(value.len())..];
			let written = sp_std::cmp::min(data.len(), value_out.len());
			value_out[..written].copy_from_slice(&data[..written]);
			Some(value.len() as u32)
		},
		None => None,
	}
}

fn host_storage_set(key: &[u8], value: &[u8]) {
	with_externalities(|ext| ext.place_storage(key.to_vec(), Some(value.to_vec())))
}

fn host_storage_get(key: &[u8]) -> Option<bytes::Bytes> {
	with_externalities(|ext| ext.storage(key).map(|value| value.into()))
}

fn host_storage_exists(key: &[u8]) -> bool {
	with_externalities(|ext| ext.exists_storage(key))
}

fn host_storage_clear(key: &[u8]) {
	with_externalities(|ext| ext.place_storage(key.to_vec(), None))
}

fn host_storage_root(version: StateVersion) -> Vec<u8> {
	with_externalities(|ext| ext.storage_root(version))
}

fn host_storage_clear_prefix(prefix: &[u8], limit: Option<u32>) -> KillStorageResult {
	with_externalities(|ext| ext.clear_prefix(prefix, limit, None).into())
}

fn host_storage_append(key: &[u8], value: Vec<u8>) {
	with_externalities(|ext| ext.storage_append(key.to_vec(), value))
}

fn host_storage_next_key(key: &[u8]) -> Option<Vec<u8>> {
	with_externalities(|ext| ext.next_storage_key(key))
}

fn host_storage_start_transaction() {
	with_externalities(|ext| ext.storage_start_transaction())
}

fn host_storage_rollback_transaction() {
	with_externalities(|ext| ext.storage_rollback_transaction().ok())
		.expect("No open transaction that can be rolled back.");
}

fn host_storage_commit_transaction() {
	with_externalities(|ext| ext.storage_commit_transaction().ok())
		.expect("No open transaction that can be committed.");
}

fn host_default_child_storage_get(storage_key: &[u8], key: &[u8]) -> Option<Vec<u8>> {
	let child_info = ChildInfo::new_default(storage_key);
	with_externalities(|ext| ext.child_storage(&child_info, key))
}

fn host_default_child_storage_read(
	storage_key: &[u8],
	key: &[u8],
	value_out: &mut [u8],
	value_offset: u32,
) -> Option<u32> {
	let child_info = ChildInfo::new_default(storage_key);
	match with_externalities(|ext| ext.child_storage(&child_info, key)) {
		Some(value) => {
			let value_offset = value_offset as usize;
			let data = &value[value_offset.min(value.len())..];
			let written = sp_std::cmp::min(data.len(), value_out.len());
			value_out[..written].copy_from_slice(&data[..written]);
			Some(value.len() as u32)
		},
		None => None,
	}
}

fn host_default_child_storage_set(storage_key: &[u8], key: &[u8], value: &[u8]) {
	let child_info = ChildInfo::new_default(storage_key);
	with_externalities(|ext| {
		ext.place_child_storage(&child_info, key.to_vec(), Some(value.to_vec()))
	})
}

fn host_default_child_storage_clear(storage_key: &[u8], key: &[u8]) {
	let child_info = ChildInfo::new_default(storage_key);
	with_externalities(|ext| ext.place_child_storage(&child_info, key.to_vec(), None))
}

fn host_default_child_storage_storage_kill(
	storage_key: &[u8],
	limit: Option<u32>,
) -> KillStorageResult {
	let child_info = ChildInfo::new_default(storage_key);
	with_externalities(|ext| ext.kill_child_storage(&child_info, limit, None).into())
}

fn host_default_child_storage_exists(storage_key: &[u8], key: &[u8]) -> bool {
	let child_info = ChildInfo::new_default(storage_key);
	with_externalities(|ext| ext.exists_child_storage(&child_info, key))
}

fn host_default_child_storage_clear_prefix(
	storage_key: &[u8],
	prefix: &[u8],
	limit: Option<u32>,
) -> KillStorageResult {
	let child_info = ChildInfo::new_default(storage_key);
	with_externalities(|ext| ext.clear_child_prefix(&child_info, prefix, limit, None).into())
}

fn host_default_child_storage_root(storage_key: &[u8], version: StateVersion) -> Vec<u8> {
	let child_info = ChildInfo::new_default(storage_key);
	with_externalities(|ext| ext.child_storage_root(&child_info, version))
}

fn host_default_child_storage_next_key(storage_key: &[u8], key: &[u8]) -> Option<Vec<u8>> {
	let child_info = ChildInfo::new_default(storage_key);
	with_externalities(|ext| ext.next_child_storage_key(&child_info, key))
}

fn host_offchain_index_set(_key: &[u8], _value: &[u8]) {}

fn host_offchain_index_clear(_key: &[u8]) {}