Don't include :code by default in storage proofs (#5060)

* Adds test to verify that the runtime currently is always contained in
the proof

* Start passing the runtime wasm code from the outside

* Fix compilation

* More build fixes

* Make the test work as expected now :)

* Last fixes

* Fixes benchmarks

* Review feedback

* Apply suggestions from code review

Co-Authored-By: Sergei Pepyakin <sergei@parity.io>

* Review feedback

* Fix compilation

Co-authored-by: Sergei Pepyakin <s.pepyakin@gmail.com>

substrate/primitives/api/test/Cargo.toml

@@ -24,6 +24,7 @@ rustversion = "1.0.0"
 [dev-dependencies]
 criterion = "0.3.0"
 substrate-test-runtime-client = { version = "2.0.0-dev", path = "../../../test-utils/runtime/client" }
+sp-core = { version = "2.0.0-alpha.1", path = "../../core" }
 
 [[bench]]
 name = "bench"

substrate/primitives/api/test/tests/runtime_calls.rs

@@ -164,6 +164,12 @@ fn record_proof_works() {
 	let block_id = BlockId::Number(client.chain_info().best_number);
 	let storage_root = longest_chain.best_chain().unwrap().state_root().clone();
 
+	let runtime_code = sp_core::traits::RuntimeCode {
+		code: client.code_at(&block_id).unwrap(),
+		hash: vec![1],
+		heap_pages: None,
+	};
+
 	let transaction = Transfer {
 		amount: 1000,
 		nonce: 0,
@@ -192,5 +198,6 @@ fn record_proof_works() {
 		&executor,
 		"Core_execute_block",
 		&block.encode(),
+		&runtime_code,
 	).expect("Executes block while using the proof backend");
 }

substrate/primitives/core/src/traits.rs

@@ -98,6 +98,7 @@ pub trait CodeExecutor: Sized + Send + Sync + CallInWasm + Clone + 'static {
 	>(
 		&self,
 		ext: &mut E,
+		runtime_code: &RuntimeCode,
 		method: &str,
 		data: &[u8],
 		use_native: bool,
@@ -105,6 +106,70 @@ pub trait CodeExecutor: Sized + Send + Sync + CallInWasm + Clone + 'static {
 	) -> (Result<crate::NativeOrEncoded<R>, Self::Error>, bool);
 }
 
+
+/// The Wasm code of a Substrate runtime.
+#[derive(Debug, Clone, codec::Encode, codec::Decode)]
+pub struct RuntimeCode {
+	/// The actual Wasm code as binary blob.
+	pub code: Vec<u8>,
+	/// The optional heap pages this `code` should be executed with.
+	///
+	/// If `None` are given, the default value of the executor will be used.
+	pub heap_pages: Option<u64>,
+	/// The SCALE encoded hash of `code`.
+	///
+	/// The hashing algorithm isn't that important, as long as all runtime
+	/// code instances use the same.
+	pub hash: Vec<u8>,
+}
+
+impl PartialEq for RuntimeCode {
+	fn eq(&self, other: &Self) -> bool {
+		self.hash == other.hash
+	}
+}
+
+impl RuntimeCode {
+	/// Create an `RuntimeCode` instance from the given `Externalities`.
+	///
+	/// Extracts the code and the heap pages using the well known keys.
+	///
+	/// Returns an error if the code could not be found.
+	pub fn from_externalities(ext: &dyn Externalities) -> Result<Self, CodeNotFound> {
+		let code = ext.storage(sp_storage::well_known_keys::CODE).ok_or(CodeNotFound)?;
+		let hash = ext.storage_hash(sp_storage::well_known_keys::CODE).ok_or(CodeNotFound)?;
+		let heap_pages = ext.storage(sp_storage::well_known_keys::HEAP_PAGES)
+			.and_then(|hp| codec::Decode::decode(&mut &hp[..]).ok());
+
+		Ok(Self {
+			code,
+			hash,
+			heap_pages,
+		})
+	}
+
+	/// Create an empty instance.
+	///
+	/// This is only useful for tests that don't want to execute any code.
+	pub fn empty() -> Self {
+		Self {
+			code: Vec::new(),
+			hash: Vec::new(),
+			heap_pages: None,
+		}
+	}
+}
+
+/// Could not find the `:code` in the externalities while initializing the [`RuntimeCode`].
+#[derive(Debug)]
+pub struct CodeNotFound;
+
+impl std::fmt::Display for CodeNotFound {
+	fn fmt(&self, f: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> {
+		write!(f, "the storage entry `:code` doesn't have any code")
+	}
+}
+
 /// Something that can call a method in a WASM blob.
 pub trait CallInWasm: Send + Sync {
 	/// Call the given `method` in the given `wasm_blob` using `call_data` (SCALE encoded arguments)

substrate/primitives/runtime/src/generic/block.rs

@@ -25,7 +25,10 @@ use serde::{Deserialize, Serialize};
 use sp_std::prelude::*;
 use sp_core::RuntimeDebug;
 use crate::codec::{Codec, Encode, Decode};
-use crate::traits::{self, Member, Block as BlockT, Header as HeaderT, MaybeSerialize, MaybeMallocSizeOf};
+use crate::traits::{
+	self, Member, Block as BlockT, Header as HeaderT, MaybeSerialize, MaybeMallocSizeOf,
+	NumberFor,
+};
 use crate::Justification;
 
 /// Something to identify a block.
@@ -35,9 +38,9 @@ use crate::Justification;
 #[cfg_attr(feature = "std", serde(deny_unknown_fields))]
 pub enum BlockId<Block: BlockT> {
 	/// Identify by block header hash.
-	Hash(<<Block as BlockT>::Header as HeaderT>::Hash),
+	Hash(Block::Hash),
 	/// Identify by block number.
-	Number(<<Block as BlockT>::Header as HeaderT>::Number),
+	Number(NumberFor<Block>),
 }
 
 impl<Block: BlockT> BlockId<Block> {
@@ -47,7 +50,7 @@ impl<Block: BlockT> BlockId<Block> {
 	}
 
 	/// Create a block ID from a number.
-	pub fn number(number: <Block::Header as HeaderT>::Number) -> Self {
+	pub fn number(number: NumberFor<Block>) -> Self {
 		BlockId::Number(number)
 	}
 }

substrate/primitives/state-machine/src/backend.rs

@@ -18,9 +18,9 @@
 
 use log::warn;
 use hash_db::Hasher;
-use codec::Encode;
+use codec::{Decode, Encode};
 
-use sp_core::storage::{ChildInfo, OwnedChildInfo};
+use sp_core::{traits::RuntimeCode, storage::{ChildInfo, OwnedChildInfo, well_known_keys}};
 use sp_trie::{TrieMut, MemoryDB, trie_types::TrieDBMut};
 
 use crate::{
@@ -359,3 +359,22 @@ pub(crate) fn insert_into_memory_db<H, I>(mdb: &mut MemoryDB<H>, input: I) -> Op
 
 	Some(root)
 }
+
+/// Get the runtime code from the given `backend`.
+///
+/// Returns an error if the `:code` could not be found.
+pub fn get_runtime_code<H: Hasher, B: Backend<H>>(backend: &B) -> Result<RuntimeCode, &'static str>
+	where H::Out: Encode,
+{
+	let code = backend.storage(well_known_keys::CODE)
+		.ok()
+		.flatten()
+		.ok_or("`:code` not found")?;
+	let hash = H::hash(&code).encode();
+	let heap_pages = backend.storage(well_known_keys::HEAP_PAGES)
+		.ok()
+		.flatten()
+		.and_then(|d| Decode::decode(&mut &d[..]).ok());
+
+	Ok(RuntimeCode { code, hash, heap_pages })
+}

substrate/primitives/state-machine/src/lib.rs

@@ -23,8 +23,8 @@ use log::{warn, trace};
 use hash_db::Hasher;
 use codec::{Decode, Encode, Codec};
 use sp_core::{
-	storage::ChildInfo, NativeOrEncoded, NeverNativeValue,
-	traits::{CodeExecutor, CallInWasmExt}, hexdisplay::HexDisplay,
+	storage::ChildInfo, NativeOrEncoded, NeverNativeValue, hexdisplay::HexDisplay,
+	traits::{CodeExecutor, CallInWasmExt, RuntimeCode},
 };
 use overlayed_changes::OverlayedChangeSet;
 use sp_externalities::Extensions;
@@ -42,7 +42,7 @@ mod trie_backend;
 mod trie_backend_essence;
 mod stats;
 
-pub use sp_trie::{trie_types::{Layout, TrieDBMut}, TrieMut, DBValue, MemoryDB};
+pub use sp_trie::{trie_types::{Layout, TrieDBMut}, StorageProof, TrieMut, DBValue, MemoryDB};
 pub use testing::TestExternalities;
 pub use basic::BasicExternalities;
 pub use ext::Ext;
@@ -67,8 +67,7 @@ pub use overlayed_changes::{
 	StorageCollection, ChildStorageCollection,
 };
 pub use proving_backend::{
-	create_proof_check_backend, create_proof_check_backend_storage, merge_storage_proofs,
-	ProofRecorder, ProvingBackend, ProvingBackendRecorder, StorageProof,
+	create_proof_check_backend, ProofRecorder, ProvingBackend, ProvingBackendRecorder,
 };
 pub use trie_backend_essence::{TrieBackendStorage, Storage};
 pub use trie_backend::TrieBackend;
@@ -191,6 +190,7 @@ pub struct StateMachine<'a, B, H, N, Exec>
 	changes_trie_state: Option<ChangesTrieState<'a, H, N>>,
 	_marker: PhantomData<(H, N)>,
 	storage_transaction_cache: Option<&'a mut StorageTransactionCache<B::Transaction, H, N>>,
+	runtime_code: &'a RuntimeCode,
 }
 
 impl<'a, B, H, N, Exec> StateMachine<'a, B, H, N, Exec> where
@@ -209,6 +209,7 @@ impl<'a, B, H, N, Exec> StateMachine<'a, B, H, N, Exec> where
 		method: &'a str,
 		call_data: &'a [u8],
 		mut extensions: Extensions,
+		runtime_code: &'a RuntimeCode,
 	) -> Self {
 		extensions.register(CallInWasmExt::new(exec.clone()));
 
@@ -222,6 +223,7 @@ impl<'a, B, H, N, Exec> StateMachine<'a, B, H, N, Exec> where
 			changes_trie_state,
 			_marker: PhantomData,
 			storage_transaction_cache: None,
+			runtime_code,
 		}
 	}
 
@@ -292,6 +294,7 @@ impl<'a, B, H, N, Exec> StateMachine<'a, B, H, N, Exec> where
 
 		let (result, was_native) = self.exec.call(
 			&mut ext,
+			self.runtime_code,
 			self.method,
 			self.call_data,
 			use_native,
@@ -436,6 +439,7 @@ pub fn prove_execution<B, H, N, Exec>(
 	exec: &Exec,
 	method: &str,
 	call_data: &[u8],
+	runtime_code: &RuntimeCode,
 ) -> Result<(Vec<u8>, StorageProof), Box<dyn Error>>
 where
 	B: Backend<H>,
@@ -446,7 +450,14 @@ where
 {
 	let trie_backend = backend.as_trie_backend()
 		.ok_or_else(|| Box::new(ExecutionError::UnableToGenerateProof) as Box<dyn Error>)?;
-	prove_execution_on_trie_backend::<_, _, N, _>(trie_backend, overlay, exec, method, call_data)
+	prove_execution_on_trie_backend::<_, _, N, _>(
+		trie_backend,
+		overlay,
+		exec,
+		method,
+		call_data,
+		runtime_code,
+	)
 }
 
 /// Prove execution using the given trie backend, overlayed changes, and call executor.
@@ -464,6 +475,7 @@ pub fn prove_execution_on_trie_backend<S, H, N, Exec>(
 	exec: &Exec,
 	method: &str,
 	call_data: &[u8],
+	runtime_code: &RuntimeCode,
 ) -> Result<(Vec<u8>, StorageProof), Box<dyn Error>>
 where
 	S: trie_backend_essence::TrieBackendStorage<H>,
@@ -474,7 +486,14 @@ where
 {
 	let proving_backend = proving_backend::ProvingBackend::new(trie_backend);
 	let mut sm = StateMachine::<_, H, N, Exec>::new(
-		&proving_backend, None, overlay, exec, method, call_data, Extensions::default(),
+		&proving_backend,
+		None,
+		overlay,
+		exec,
+		method,
+		call_data,
+		Extensions::default(),
+		runtime_code,
 	);
 
 	let result = sm.execute_using_consensus_failure_handler::<_, NeverNativeValue, fn() -> _>(
@@ -493,6 +512,7 @@ pub fn execution_proof_check<H, N, Exec>(
 	exec: &Exec,
 	method: &str,
 	call_data: &[u8],
+	runtime_code: &RuntimeCode,
 ) -> Result<Vec<u8>, Box<dyn Error>>
 where
 	H: Hasher,
@@ -501,7 +521,14 @@ where
 	N: crate::changes_trie::BlockNumber,
 {
 	let trie_backend = create_proof_check_backend::<H>(root.into(), proof)?;
-	execution_proof_check_on_trie_backend::<_, N, _>(&trie_backend, overlay, exec, method, call_data)
+	execution_proof_check_on_trie_backend::<_, N, _>(
+		&trie_backend,
+		overlay,
+		exec,
+		method,
+		call_data,
+		runtime_code,
+	)
 }
 
 /// Check execution proof on proving backend, generated by `prove_execution` call.
@@ -511,6 +538,7 @@ pub fn execution_proof_check_on_trie_backend<H, N, Exec>(
 	exec: &Exec,
 	method: &str,
 	call_data: &[u8],
+	runtime_code: &RuntimeCode,
 ) -> Result<Vec<u8>, Box<dyn Error>>
 where
 	H: Hasher,
@@ -519,7 +547,14 @@ where
 	N: crate::changes_trie::BlockNumber,
 {
 	let mut sm = StateMachine::<_, H, N, Exec>::new(
-		trie_backend, None, overlay, exec, method, call_data, Extensions::default(),
+		trie_backend,
+		None,
+		overlay,
+		exec,
+		method,
+		call_data,
+		Extensions::default(),
+		runtime_code,
 	);
 
 	sm.execute_using_consensus_failure_handler::<_, NeverNativeValue, fn() -> _>(
@@ -692,7 +727,9 @@ mod tests {
 	use super::*;
 	use super::ext::Ext;
 	use super::changes_trie::Configuration as ChangesTrieConfig;
-	use sp_core::{Blake2Hasher, map, traits::Externalities, storage::ChildStorageKey};
+	use sp_core::{
+		Blake2Hasher, map, traits::{Externalities, RuntimeCode}, storage::ChildStorageKey,
+	};
 
 	#[derive(Clone)]
 	struct DummyCodeExecutor {
@@ -714,6 +751,7 @@ mod tests {
 		>(
 			&self,
 			ext: &mut E,
+			_: &RuntimeCode,
 			_method: &str,
 			_data: &[u8],
 			use_native: bool,
@@ -767,6 +805,7 @@ mod tests {
 	fn execute_works() {
 		let backend = trie_backend::tests::test_trie();
 		let mut overlayed_changes = Default::default();
+		let wasm_code = RuntimeCode::empty();
 
 		let mut state_machine = StateMachine::new(
 			&backend,
@@ -781,6 +820,7 @@ mod tests {
 			"test",
 			&[],
 			Default::default(),
+			&wasm_code,
 		);
 
 		assert_eq!(
@@ -794,6 +834,7 @@ mod tests {
 	fn execute_works_with_native_else_wasm() {
 		let backend = trie_backend::tests::test_trie();
 		let mut overlayed_changes = Default::default();
+		let wasm_code = RuntimeCode::empty();
 
 		let mut state_machine = StateMachine::new(
 			&backend,
@@ -808,6 +849,7 @@ mod tests {
 			"test",
 			&[],
 			Default::default(),
+			&wasm_code,
 		);
 
 		assert_eq!(state_machine.execute(ExecutionStrategy::NativeElseWasm).unwrap(), vec![66]);
@@ -818,6 +860,7 @@ mod tests {
 		let mut consensus_failed = false;
 		let backend = trie_backend::tests::test_trie();
 		let mut overlayed_changes = Default::default();
+		let wasm_code = RuntimeCode::empty();
 
 		let mut state_machine = StateMachine::new(
 			&backend,
@@ -832,6 +875,7 @@ mod tests {
 			"test",
 			&[],
 			Default::default(),
+			&wasm_code,
 		);
 
 		assert!(
@@ -864,6 +908,7 @@ mod tests {
 			&executor,
 			"test",
 			&[],
+			&RuntimeCode::empty(),
 		).unwrap();
 
 		// check proof locally
@@ -874,6 +919,7 @@ mod tests {
 			&executor,
 			"test",
 			&[],
+			&RuntimeCode::empty(),
 		).unwrap();
 
 		// check that both results are correct

substrate/primitives/state-machine/src/proving_backend.rs

@@ -18,19 +18,19 @@
 
 use std::sync::Arc;
 use parking_lot::RwLock;
-use codec::{Decode, Encode, Codec};
+use codec::{Decode, Codec};
 use log::debug;
 use hash_db::{Hasher, HashDB, EMPTY_PREFIX, Prefix};
 use sp_trie::{
 	MemoryDB, default_child_trie_root, read_trie_value_with, read_child_trie_value_with,
-	record_all_keys
+	record_all_keys, StorageProof,
 };
 pub use sp_trie::Recorder;
 pub use sp_trie::trie_types::{Layout, TrieError};
 use crate::trie_backend::TrieBackend;
 use crate::trie_backend_essence::{Ephemeral, TrieBackendEssence, TrieBackendStorage};
 use crate::{Error, ExecutionError, Backend};
-use std::collections::{HashMap, HashSet};
+use std::collections::HashMap;
 use crate::DBValue;
 use sp_core::storage::ChildInfo;
 
@@ -40,82 +40,6 @@ pub struct ProvingBackendRecorder<'a, S: 'a + TrieBackendStorage<H>, H: 'a + Has
 	pub(crate) proof_recorder: &'a mut Recorder<H::Out>,
 }
 
-/// A proof that some set of key-value pairs are included in the storage trie. The proof contains
-/// the storage values so that the partial storage backend can be reconstructed by a verifier that
-/// does not already have access to the key-value pairs.
-///
-/// The proof consists of the set of serialized nodes in the storage trie accessed when looking up
-/// the keys covered by the proof. Verifying the proof requires constructing the partial trie from
-/// the serialized nodes and performing the key lookups.
-#[derive(Debug, PartialEq, Eq, Clone, Encode, Decode)]
-pub struct StorageProof {
-	trie_nodes: Vec<Vec<u8>>,
-}
-
-impl StorageProof {
-	/// Constructs a storage proof from a subset of encoded trie nodes in a storage backend.
-	pub fn new(trie_nodes: Vec<Vec<u8>>) -> Self {
-		StorageProof { trie_nodes }
-	}
-
-	/// Returns a new empty proof.
-	///
-	/// An empty proof is capable of only proving trivial statements (ie. that an empty set of
-	/// key-value pairs exist in storage).
-	pub fn empty() -> Self {
-		StorageProof {
-			trie_nodes: Vec::new(),
-		}
-	}
-
-	/// Returns whether this is an empty proof.
-	pub fn is_empty(&self) -> bool {
-		self.trie_nodes.is_empty()
-	}
-
-	/// Create an iterator over trie nodes constructed from the proof. The nodes are not guaranteed
-	/// to be traversed in any particular order.
-	pub fn iter_nodes(self) -> StorageProofNodeIterator {
-		StorageProofNodeIterator::new(self)
-	}
-}
-
-/// An iterator over trie nodes constructed from a storage proof. The nodes are not guaranteed to
-/// be traversed in any particular order.
-pub struct StorageProofNodeIterator {
-	inner: <Vec<Vec<u8>> as IntoIterator>::IntoIter,
-}
-
-impl StorageProofNodeIterator {
-	fn new(proof: StorageProof) -> Self {
-		StorageProofNodeIterator {
-			inner: proof.trie_nodes.into_iter(),
-		}
-	}
-}
-
-impl Iterator for StorageProofNodeIterator {
-	type Item = Vec<u8>;
-
-	fn next(&mut self) -> Option<Self::Item> {
-		self.inner.next()
-	}
-}
-
-/// Merges multiple storage proofs covering potentially different sets of keys into one proof
-/// covering all keys. The merged proof output may be smaller than the aggregate size of the input
-/// proofs due to deduplication of trie nodes.
-pub fn merge_storage_proofs<I>(proofs: I) -> StorageProof
-	where I: IntoIterator<Item=StorageProof>
-{
-	let trie_nodes = proofs.into_iter()
-		.flat_map(|proof| proof.iter_nodes())
-		.collect::<HashSet<_>>()
-		.into_iter()
-		.collect();
-	StorageProof { trie_nodes }
-}
-
 impl<'a, S, H> ProvingBackendRecorder<'a, S, H>
 	where
 		S: TrieBackendStorage<H>,
@@ -222,7 +146,7 @@ impl<'a, S: 'a + TrieBackendStorage<H>, H: 'a + Hasher> ProvingBackend<'a, S, H>
 		let root = essence.root().clone();
 		let recorder = ProofRecorderBackend {
 			backend: essence.backend_storage(),
-			proof_recorder: proof_recorder,
+			proof_recorder,
 		};
 		ProvingBackend(TrieBackend::new(recorder, root))
 	}
@@ -370,7 +294,7 @@ where
 	H: Hasher,
 	H::Out: Codec,
 {
-	let db = create_proof_check_backend_storage(proof);
+	let db = proof.into_memory_db();
 
 	if db.contains(&root, EMPTY_PREFIX) {
 		Ok(TrieBackend::new(db, root))
@@ -379,20 +303,6 @@ where
 	}
 }
 
-/// Create in-memory storage of proof check backend.
-pub fn create_proof_check_backend_storage<H>(
-	proof: StorageProof,
-) -> MemoryDB<H>
-where
-	H: Hasher,
-{
-	let mut db = MemoryDB::default();
-	for item in proof.iter_nodes() {
-		db.insert(EMPTY_PREFIX, &item);
-	}
-	db
-}
-
 #[cfg(test)]
 mod tests {
 	use crate::InMemoryBackend;

substrate/primitives/trie/src/lib.rs

@@ -21,6 +21,7 @@
 mod error;
 mod node_header;
 mod node_codec;
+mod storage_proof;
 mod trie_stream;
 
 use sp_std::boxed::Box;
@@ -35,6 +36,7 @@ pub use error::Error;
 pub use trie_stream::TrieStream;
 /// The Substrate format implementation of `NodeCodec`.
 pub use node_codec::NodeCodec;
+pub use storage_proof::StorageProof;
 /// Various re-exports from the `trie-db` crate.
 pub use trie_db::{
 	Trie, TrieMut, DBValue, Recorder, CError, Query, TrieLayout, TrieConfiguration, nibble_ops, TrieDBIterator,

substrate/primitives/trie/src/storage_proof.rs

@@ -0,0 +1,109 @@
+// Copyright 2020 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Parity 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.
+
+// Parity 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 Parity.  If not, see <http://www.gnu.org/licenses/>.
+
+use sp_std::vec::Vec;
+use codec::{Encode, Decode};
+use hash_db::{Hasher, HashDB};
+
+/// A proof that some set of key-value pairs are included in the storage trie. The proof contains
+/// the storage values so that the partial storage backend can be reconstructed by a verifier that
+/// does not already have access to the key-value pairs.
+///
+/// The proof consists of the set of serialized nodes in the storage trie accessed when looking up
+/// the keys covered by the proof. Verifying the proof requires constructing the partial trie from
+/// the serialized nodes and performing the key lookups.
+#[derive(Debug, PartialEq, Eq, Clone, Encode, Decode)]
+pub struct StorageProof {
+	trie_nodes: Vec<Vec<u8>>,
+}
+
+impl StorageProof {
+	/// Constructs a storage proof from a subset of encoded trie nodes in a storage backend.
+	pub fn new(trie_nodes: Vec<Vec<u8>>) -> Self {
+		StorageProof { trie_nodes }
+	}
+
+	/// Returns a new empty proof.
+	///
+	/// An empty proof is capable of only proving trivial statements (ie. that an empty set of
+	/// key-value pairs exist in storage).
+	pub fn empty() -> Self {
+		StorageProof {
+			trie_nodes: Vec::new(),
+		}
+	}
+
+	/// Returns whether this is an empty proof.
+	pub fn is_empty(&self) -> bool {
+		self.trie_nodes.is_empty()
+	}
+
+	/// Create an iterator over trie nodes constructed from the proof. The nodes are not guaranteed
+	/// to be traversed in any particular order.
+	pub fn iter_nodes(self) -> StorageProofNodeIterator {
+		StorageProofNodeIterator::new(self)
+	}
+
+	/// Creates a `MemoryDB` from `Self`.
+	pub fn into_memory_db<H: Hasher>(self) -> crate::MemoryDB<H> {
+		self.into()
+	}
+
+	/// Merges multiple storage proofs covering potentially different sets of keys into one proof
+	/// covering all keys. The merged proof output may be smaller than the aggregate size of the input
+	/// proofs due to deduplication of trie nodes.
+	pub fn merge<I>(proofs: I) -> Self where I: IntoIterator<Item=Self> {
+		let trie_nodes = proofs.into_iter()
+			.flat_map(|proof| proof.iter_nodes())
+			.collect::<sp_std::collections::btree_set::BTreeSet<_>>()
+			.into_iter()
+			.collect();
+
+		Self { trie_nodes }
+	}
+}
+
+/// An iterator over trie nodes constructed from a storage proof. The nodes are not guaranteed to
+/// be traversed in any particular order.
+pub struct StorageProofNodeIterator {
+	inner: <Vec<Vec<u8>> as IntoIterator>::IntoIter,
+}
+
+impl StorageProofNodeIterator {
+	fn new(proof: StorageProof) -> Self {
+		StorageProofNodeIterator {
+			inner: proof.trie_nodes.into_iter(),
+		}
+	}
+}
+
+impl Iterator for StorageProofNodeIterator {
+	type Item = Vec<u8>;
+
+	fn next(&mut self) -> Option<Self::Item> {
+		self.inner.next()
+	}
+}
+
+impl<H: Hasher> From<StorageProof> for crate::MemoryDB<H> {
+	fn from(proof: StorageProof) -> Self {
+		let mut db = crate::MemoryDB::default();
+		for item in proof.iter_nodes() {
+			db.insert(crate::EMPTY_PREFIX, &item);
+		}
+		db
+	}
+}