Logic for checking Substrate proofs from within runtime module. (#3783)

srml/bridge/Cargo.toml

@@ -8,15 +8,18 @@ edition = "2018"
 
 [dependencies]
 codec = { package = "parity-scale-codec", version = "1.0.0", default-features = false }
+hash-db = { version = "0.15.2", default-features = false }
 session = { package = "srml-session", path = "../session", default-features = false, features = ["historical"] }
 serde = { version = "1.0", optional = true }
 sr-primitives = { path = "../../core/sr-primitives", default-features = false }
 support = { package = "srml-support", path = "../support", default-features = false }
 system = { package = "srml-system", path = "../system", default-features = false }
+trie = { package = "substrate-trie", path = "../../core/trie", default-features = false }
 
 [dev-dependencies]
 primitives = { package = "substrate-primitives",  path = "../../core/primitives" }
 runtime-io = { package = "sr-io", path = "../../core/sr-io", default-features = false }
+state-machine = { package = "substrate-state-machine",  path = "../../core/state-machine" }
 
 [features]
 default = ["std"]
@@ -27,5 +30,6 @@ std = [
 	"sr-primitives/std",
 	"support/std",
 	"system/std",
+	"trie/std",
 	"runtime-io/std",
 ]

srml/bridge/src/error.rs

@@ -0,0 +1,25 @@
+// Copyright 2017-2019 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/>.
+
+//! Common error types for the srml-bridge crate.
+
+#[derive(PartialEq)]
+#[cfg_attr(feature = "std", derive(Debug))]
+pub enum Error {
+	StorageRootMismatch,
+	StorageValueUnavailable,
+}
+

srml/bridge/src/lib.rs

@@ -32,6 +32,9 @@
 // Ensure we're `no_std` when compiling for Wasm.
 #![cfg_attr(not(feature = "std"), no_std)]
 
+mod error;
+mod storage_proof;
+
 use codec::{Encode, Decode};
 use sr_primitives::traits::{Header, Member};
 use support::{
@@ -148,7 +151,7 @@ mod tests {
 
 	use primitives::{H256, Blake2Hasher};
 	use sr_primitives::{
-		Perbill, traits::IdentityLookup, testing::Header, generic::Digest
+		Perbill, traits::{Header as HeaderT, IdentityLookup}, testing::Header, generic::Digest,
 	};
 	use support::{assert_ok, impl_outer_origin, parameter_types};
 	use runtime_io::with_externalities;
@@ -223,6 +226,7 @@ mod tests {
 			extrinsics_root: H256::default(),
 			digest: Digest::default(),
 		};
+		let test_hash = test_header.hash();
 
 		with_externalities(&mut new_test_ext(), || {
 			assert_eq!(MockBridge::num_bridges(), 0);
@@ -242,7 +246,7 @@ mod tests {
 				MockBridge::tracked_bridges(1),
 				Some(BridgeInfo {
 					last_finalized_block_number: 42,
-					last_finalized_block_hash: test_header.hash(), // FIXME: This is broken
+					last_finalized_block_hash: test_hash,
 					last_finalized_state_root: dummy_state_root,
 					current_validator_set: vec![1, 2, 3],
 				}));

srml/bridge/src/storage_proof.rs

@@ -0,0 +1,103 @@
+// Copyright 2017-2019 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/>.
+
+//! Logic for checking Substrate storage proofs.
+
+use hash_db::{Hasher, HashDB, EMPTY_PREFIX};
+use trie::{MemoryDB, Trie, trie_types::TrieDB};
+
+use crate::error::Error;
+
+/// This struct is used to read storage values from a subset of a Merklized database. The "proof"
+/// is a subset of the nodes in the Merkle structure of the database, so that it provides
+/// authentication against a known Merkle root as well as the values in the database themselves.
+pub struct StorageProofChecker<H>
+	where H: Hasher
+{
+	root: H::Out,
+	db: MemoryDB<H>,
+}
+
+impl<H> StorageProofChecker<H>
+	where H: Hasher
+{
+	/// Constructs a new storage proof checker.
+	///
+	/// This returns an error if the given proof is invalid with respect to the given root.
+	pub fn new(root: H::Out, proof: Vec<Vec<u8>>) -> Result<Self, Error> {
+		let mut db = MemoryDB::default();
+		for item in proof {
+			db.insert(EMPTY_PREFIX, &item);
+		}
+		let checker = StorageProofChecker {
+			root,
+			db,
+		};
+		// Return error if trie would be invalid.
+		let _ = checker.trie()?;
+		Ok(checker)
+	}
+
+	/// Reads a value from the available subset of storage. If the value cannot be read due to an
+	/// incomplete or otherwise invalid proof, this returns an error.
+	pub fn read_value(&self, key: &[u8]) -> Result<Option<Vec<u8>>, Error> {
+		self.trie()?
+			.get(key)
+			.map(|value| value.map(|value| value.into_vec()))
+			.map_err(|_| Error::StorageValueUnavailable)
+	}
+
+	fn trie(&self) -> Result<TrieDB<H>, Error> {
+		TrieDB::new(&self.db, &self.root)
+			.map_err(|_| Error::StorageRootMismatch)
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+
+	use primitives::{Blake2Hasher, H256};
+	use state_machine::{prove_read, backend::{Backend, InMemory}};
+	// use trie::{PrefixedMemoryDB, TrieDBMut};
+
+	#[test]
+	fn storage_proof_check() {
+		// construct storage proof
+		let backend = <InMemory<Blake2Hasher>>::from(vec![
+			(None, b"key1".to_vec(), Some(b"value1".to_vec())),
+			(None, b"key2".to_vec(), Some(b"value2".to_vec())),
+			(None, b"key3".to_vec(), Some(b"value3".to_vec())),
+			// Value is too big to fit in a branch node
+			(None, b"key11".to_vec(), Some(vec![0u8; 32])),
+		]);
+		let root = backend.storage_root(std::iter::empty()).0;
+		let proof = prove_read(backend, &[&b"key1"[..], &b"key2"[..], &b"key22"[..]]).unwrap();
+
+		// check proof in runtime
+		let checker = <StorageProofChecker<Blake2Hasher>>::new(root, proof.clone()).unwrap();
+		assert_eq!(checker.read_value(b"key1"), Ok(Some(b"value1".to_vec())));
+		assert_eq!(checker.read_value(b"key2"), Ok(Some(b"value2".to_vec())));
+		assert_eq!(checker.read_value(b"key11111"), Err(Error::StorageValueUnavailable));
+		assert_eq!(checker.read_value(b"key22"), Ok(None));
+
+		// checking proof against invalid commitment fails
+		assert_eq!(
+			<StorageProofChecker<Blake2Hasher>>::new(H256::random(), proof).err(),
+			Some(Error::StorageRootMismatch)
+		);
+	}
+}