Refactor triedb constructors to error on invalid state root (#1230)

* add TrieError, refactor Trie DB creation

* remove Result type alias due to glob import conflicts

* fix fallout in state.rs

* add debug, display impl for TrieError

* fix fallout in account.rs

* ethcore::Error::TrieError variant

* fix remaining fallout in ethcore crate

* added From<TrieError> impl for Error, removed map_err calls

* fix test breakages

* fix doc tests

* update docs

[ci skip]

ethcore/src/account.rs

@@ -116,7 +116,12 @@ impl Account {
 	/// Get (and cache) the contents of the trie's storage at `key`.
 	pub fn storage_at(&self, db: &AccountDB, key: &H256) -> H256 {
 		self.storage_overlay.borrow_mut().entry(key.clone()).or_insert_with(||{
-			(Filth::Clean, H256::from(SecTrieDB::new(db, &self.storage_root).get(key.bytes()).map_or(U256::zero(), |v| -> U256 {decode(v)})))
+			let db = SecTrieDB::new(db, &self.storage_root)
+				.expect("Account storage_root initially set to zero (valid) and only altered by SecTrieDBMut. \
+				SecTrieDBMut would not set it to an invalid state root. Therefore the root is valid and DB creation \
+				using it will not fail.");
+
+			(Filth::Clean, H256::from(db.get(key.bytes()).map_or(U256::zero(), |v| -> U256 {decode(v)})))
 		}).1.clone()
 	}
 
@@ -204,7 +209,10 @@ impl Account {
 
 	/// Commit the `storage_overlay` to the backing DB and update `storage_root`.
 	pub fn commit_storage(&mut self, db: &mut AccountDBMut) {
-		let mut t = SecTrieDBMut::from_existing(db, &mut self.storage_root);
+		let mut t = SecTrieDBMut::from_existing(db, &mut self.storage_root)
+			.expect("Account storage_root initially set to zero (valid) and only altered by SecTrieDBMut. \
+				SecTrieDBMut would not set it to an invalid state root. Therefore the root is valid and DB creation \
+				using it will not fail.");
 		for (k, &mut (ref mut f, ref mut v)) in self.storage_overlay.borrow_mut().iter_mut() {
 			if f == &Filth::Dirty {
 				// cast key and value to trait type,

ethcore/src/basic_authority.rs

@@ -278,7 +278,7 @@ mod tests {
 		spec.ensure_db_good(db.as_hashdb_mut());
 		let last_hashes = vec![genesis_header.hash()];
 		let vm_factory = Default::default();
-		let b = OpenBlock::new(engine.deref(), &vm_factory, false, db, &genesis_header, last_hashes, addr.clone(), 3141562.into(), vec![]);
+		let b = OpenBlock::new(engine.deref(), &vm_factory, false, db, &genesis_header, last_hashes, addr.clone(), 3141562.into(), vec![]).unwrap();
 		let b = b.close_and_lock();
 		let seal = engine.generate_seal(b.block(), Some(&tap)).unwrap();
 

ethcore/src/block.rs

@@ -228,9 +228,20 @@ pub struct SealedBlock {
 impl<'x> OpenBlock<'x> {
 	#[cfg_attr(feature="dev", allow(too_many_arguments))]
 	/// Create a new `OpenBlock` ready for transaction pushing.
-	pub fn new(engine: &'x Engine, vm_factory: &'x EvmFactory, tracing: bool, db: Box<JournalDB>, parent: &Header, last_hashes: LastHashes, author: Address, gas_floor_target: U256, extra_data: Bytes) -> Self {
+	pub fn new(
+		engine: &'x Engine,
+		vm_factory: &'x EvmFactory,
+		tracing: bool,
+		db: Box<JournalDB>,
+		parent: &Header,
+		last_hashes: LastHashes,
+		author: Address,
+		gas_floor_target: U256,
+		extra_data: Bytes
+	) -> Result<Self, Error> {
+		let state = try!(State::from_existing(db, parent.state_root().clone(), engine.account_start_nonce()));
 		let mut r = OpenBlock {
-			block: ExecutedBlock::new(State::from_existing(db, parent.state_root().clone(), engine.account_start_nonce()), tracing),
+			block: ExecutedBlock::new(state, tracing),
 			engine: engine,
 			vm_factory: vm_factory,
 			last_hashes: last_hashes,
@@ -245,7 +256,7 @@ impl<'x> OpenBlock<'x> {
 
 		engine.populate_from_parent(&mut r.block.base.header, parent, gas_floor_target);
 		engine.on_new_block(&mut r.block);
-		r
+		Ok(r)
 	}
 
 	/// Alter the author for the block.
@@ -464,12 +475,12 @@ impl IsBlock for SealedBlock {
 pub fn enact(header: &Header, transactions: &[SignedTransaction], uncles: &[Header], engine: &Engine, tracing: bool, db: Box<JournalDB>, parent: &Header, last_hashes: LastHashes, vm_factory: &EvmFactory) -> Result<LockedBlock, Error> {
 	{
 		if ::log::max_log_level() >= ::log::LogLevel::Trace {
-			let s = State::from_existing(db.boxed_clone(), parent.state_root().clone(), engine.account_start_nonce());
+			let s = try!(State::from_existing(db.boxed_clone(), parent.state_root().clone(), engine.account_start_nonce()));
 			trace!("enact(): root={}, author={}, author_balance={}\n", s.root(), header.author(), s.balance(&header.author()));
 		}
 	}
 
-	let mut b = OpenBlock::new(engine, vm_factory, tracing, db, parent, last_hashes, header.author().clone(), 3141562.into(), header.extra_data().clone());
+	let mut b = try!(OpenBlock::new(engine, vm_factory, tracing, db, parent, last_hashes, header.author().clone(), 3141562.into(), header.extra_data().clone()));
 	b.set_difficulty(*header.difficulty());
 	b.set_gas_limit(*header.gas_limit());
 	b.set_timestamp(header.timestamp());
@@ -514,7 +525,7 @@ mod tests {
 		spec.ensure_db_good(db.as_hashdb_mut());
 		let last_hashes = vec![genesis_header.hash()];
 		let vm_factory = Default::default();
-		let b = OpenBlock::new(engine.deref(), &vm_factory, false, db, &genesis_header, last_hashes, Address::zero(), 3141562.into(), vec![]);
+		let b = OpenBlock::new(engine.deref(), &vm_factory, false, db, &genesis_header, last_hashes, Address::zero(), 3141562.into(), vec![]).unwrap();
 		let b = b.close_and_lock();
 		let _ = b.seal(engine.deref(), vec![]);
 	}
@@ -530,7 +541,8 @@ mod tests {
 		let mut db = db_result.take();
 		spec.ensure_db_good(db.as_hashdb_mut());
 		let vm_factory = Default::default();
-		let b = OpenBlock::new(engine.deref(), &vm_factory, false, db, &genesis_header, vec![genesis_header.hash()], Address::zero(), 3141562.into(), vec![]).close_and_lock().seal(engine.deref(), vec![]).unwrap();
+		let b = OpenBlock::new(engine.deref(), &vm_factory, false, db, &genesis_header, vec![genesis_header.hash()], Address::zero(), 3141562.into(), vec![]).unwrap()
+			.close_and_lock().seal(engine.deref(), vec![]).unwrap();
 		let orig_bytes = b.rlp_bytes();
 		let orig_db = b.drain();
 
@@ -557,7 +569,7 @@ mod tests {
 		let mut db = db_result.take();
 		spec.ensure_db_good(db.as_hashdb_mut());
 		let vm_factory = Default::default();
-		let mut open_block = OpenBlock::new(engine.deref(), &vm_factory, false, db, &genesis_header, vec![genesis_header.hash()], Address::zero(), 3141562.into(), vec![]);
+		let mut open_block = OpenBlock::new(engine.deref(), &vm_factory, false, db, &genesis_header, vec![genesis_header.hash()], Address::zero(), 3141562.into(), vec![]).unwrap();
 		let mut uncle1_header = Header::new();
 		uncle1_header.extra_data = b"uncle1".to_vec();
 		let mut uncle2_header = Header::new();

ethcore/src/client/client.rs

@@ -386,18 +386,14 @@ impl<V> Client<V> where V: Verifier {
 
 			let root = HeaderView::new(&header).state_root();
 
-			// TODO [rob]: refactor State::from_existing so we avoid doing redundant lookups.
+			State::from_existing(db, root, self.engine.account_start_nonce()).ok()
-			if !db.contains(&root) {
-				return None;
-			}
-
-			Some(State::from_existing(db, root, self.engine.account_start_nonce()))
 		})
 	}
 
 	/// Get a copy of the best block's state.
 	pub fn state(&self) -> State {
 		State::from_existing(self.state_db.lock().unwrap().boxed_clone(), HeaderView::new(&self.best_block_header()).state_root(), self.engine.account_start_nonce())
+			.expect("State root of best block header always valid.")
 	}
 
 	/// Get info on the cache.
@@ -776,7 +772,8 @@ impl<V> MiningBlockChainClient for Client<V> where V: Verifier {
 			author,
 			gas_floor_target,
 			extra_data,
-		);
+		).expect("OpenBlock::new only fails if parent state root invalid. State root of best block's header is never invalid. \
+		         Therefore creating an OpenBlock with the best block's header will not fail.");
 
 		// Add uncles
 		self.chain

ethcore/src/error.rs

@@ -224,6 +224,8 @@ pub enum Error {
 	PowHashInvalid,
 	/// The value of the nonce or mishash is invalid.
 	PowInvalid,
+	/// Error concerning TrieDBs
+	TrieError(TrieError),
 }
 
 impl fmt::Display for Error {
@@ -239,6 +241,7 @@ impl fmt::Display for Error {
 				f.write_fmt(format_args!("Unknown engine name ({})", name)),
 			Error::PowHashInvalid => f.write_str("Invalid or out of date PoW hash."),
 			Error::PowInvalid => f.write_str("Invalid nonce or mishash"),
+			Error::TrieError(ref err) => f.write_fmt(format_args!("{}", err)),
 		}
 	}
 }
@@ -300,6 +303,12 @@ impl From<IoError> for Error {
 	}
 }
 
+impl From<TrieError> for Error {
+	fn from(err: TrieError) -> Error {
+		Error::TrieError(err)
+	}
+}
+
 // TODO: uncomment below once https://github.com/rust-lang/rust/issues/27336 sorted.
 /*#![feature(concat_idents)]
 macro_rules! assimilate {

ethcore/src/ethereum/ethash.rs

@@ -308,7 +308,7 @@ mod tests {
 		spec.ensure_db_good(db.as_hashdb_mut());
 		let last_hashes = vec![genesis_header.hash()];
 		let vm_factory = Default::default();
-		let b = OpenBlock::new(engine.deref(), &vm_factory, false, db, &genesis_header, last_hashes, Address::zero(), 3141562.into(), vec![]);
+		let b = OpenBlock::new(engine.deref(), &vm_factory, false, db, &genesis_header, last_hashes, Address::zero(), 3141562.into(), vec![]).unwrap();
 		let b = b.close();
 		assert_eq!(b.state().balance(&Address::zero()), U256::from_str("4563918244f40000").unwrap());
 	}
@@ -323,7 +323,7 @@ mod tests {
 		spec.ensure_db_good(db.as_hashdb_mut());
 		let last_hashes = vec![genesis_header.hash()];
 		let vm_factory = Default::default();
-		let mut b = OpenBlock::new(engine.deref(), &vm_factory, false, db, &genesis_header, last_hashes, Address::zero(), 3141562.into(), vec![]);
+		let mut b = OpenBlock::new(engine.deref(), &vm_factory, false, db, &genesis_header, last_hashes, Address::zero(), 3141562.into(), vec![]).unwrap();
 		let mut uncle = Header::new();
 		let uncle_author = address_from_hex("ef2d6d194084c2de36e0dabfce45d046b37d1106");
 		uncle.author = uncle_author.clone();

ethcore/src/ethereum/mod.rs

@@ -62,7 +62,7 @@ mod tests {
 		let mut db_result = get_temp_journal_db();
 		let mut db = db_result.take();
 		spec.ensure_db_good(db.as_hashdb_mut());
-		let s = State::from_existing(db, genesis_header.state_root.clone(), engine.account_start_nonce());
+		let s = State::from_existing(db, genesis_header.state_root.clone(), engine.account_start_nonce()).unwrap();
 		assert_eq!(s.balance(&address_from_hex("0000000000000000000000000000000000000001")), U256::from(1u64));
 		assert_eq!(s.balance(&address_from_hex("0000000000000000000000000000000000000002")), U256::from(1u64));
 		assert_eq!(s.balance(&address_from_hex("0000000000000000000000000000000000000003")), U256::from(1u64));

ethcore/src/state.rs

@@ -44,6 +44,9 @@ pub struct State {
 	account_start_nonce: U256,
 }
 
+const SEC_TRIE_DB_UNWRAP_STR: &'static str = "A state can only be created with valid root. Creating a SecTrieDB with a valid root will not fail. \
+			 Therefore creating a SecTrieDB with this state's root will not fail.";
+
 impl State {
 	/// Creates new state with empty state root
 	#[cfg(test)]
@@ -64,18 +67,17 @@ impl State {
 	}
 
 	/// Creates new state with existing state root
-	pub fn from_existing(db: Box<JournalDB>, root: H256, account_start_nonce: U256) -> State {
+	pub fn from_existing(db: Box<JournalDB>, root: H256, account_start_nonce: U256) -> Result<State, TrieError> {
-		{
+		if !db.as_hashdb().contains(&root) {
-			// trie should panic! if root does not exist
+			Err(TrieError::InvalidStateRoot)
-			let _ = SecTrieDB::new(db.as_hashdb(), &root);
+		} else {
-		}
+			Ok(State {
-
-		State {
 				db: db,
 				root: root,
 				cache: RefCell::new(HashMap::new()),
 				snapshots: RefCell::new(Vec::new()),
 				account_start_nonce: account_start_nonce,
+			})
 		}
 	}
 
@@ -154,7 +156,8 @@ impl State {
 
 	/// Determine whether an account exists.
 	pub fn exists(&self, a: &Address) -> bool {
-		self.cache.borrow().get(&a).unwrap_or(&None).is_some() || SecTrieDB::new(self.db.as_hashdb(), &self.root).contains(&a)
+		let db = SecTrieDB::new(self.db.as_hashdb(), &self.root).expect(SEC_TRIE_DB_UNWRAP_STR);
+		self.cache.borrow().get(&a).unwrap_or(&None).is_some() || db.contains(&a)
 	}
 
 	/// Get the balance of account `a`.
@@ -245,7 +248,7 @@ impl State {
 		}
 
 		{
-			let mut trie = SecTrieDBMut::from_existing(db, root);
+			let mut trie = SecTrieDBMut::from_existing(db, root).unwrap();
 			for (address, ref a) in accounts.iter() {
 				match **a {
 					Some(ref account) => trie.insert(address, &account.rlp()),
@@ -308,7 +311,8 @@ impl State {
 	fn get<'a>(&'a self, a: &Address, require_code: bool) -> &'a Option<Account> {
 		let have_key = self.cache.borrow().contains_key(a);
 		if !have_key {
-			self.insert_cache(a, SecTrieDB::new(self.db.as_hashdb(), &self.root).get(&a).map(Account::from_rlp))
+			let db = SecTrieDB::new(self.db.as_hashdb(), &self.root).expect(SEC_TRIE_DB_UNWRAP_STR);
+			self.insert_cache(a, db.get(&a).map(Account::from_rlp))
 		}
 		if require_code {
 			if let Some(ref mut account) = self.cache.borrow_mut().get_mut(a).unwrap().as_mut() {
@@ -328,7 +332,8 @@ impl State {
 	fn require_or_from<'a, F: FnOnce() -> Account, G: FnOnce(&mut Account)>(&self, a: &Address, require_code: bool, default: F, not_default: G) -> &'a mut Account {
 		let have_key = self.cache.borrow().contains_key(a);
 		if !have_key {
-			self.insert_cache(a, SecTrieDB::new(self.db.as_hashdb(), &self.root).get(&a).map(Account::from_rlp))
+			let db = SecTrieDB::new(self.db.as_hashdb(), &self.root).expect(SEC_TRIE_DB_UNWRAP_STR);
+			self.insert_cache(a, db.get(&a).map(Account::from_rlp))
 		} else {
 			self.note_cache(a);
 		}
@@ -1145,7 +1150,7 @@ fn code_from_database() {
 		state.drop()
 	};
 
-	let state = State::from_existing(db, root, U256::from(0u8));
+	let state = State::from_existing(db, root, U256::from(0u8)).unwrap();
 	assert_eq!(state.code(&a), Some([1u8, 2, 3].to_vec()));
 }
 
@@ -1160,7 +1165,7 @@ fn storage_at_from_database() {
 		state.drop()
 	};
 
-	let s = State::from_existing(db, root, U256::from(0u8));
+	let s = State::from_existing(db, root, U256::from(0u8)).unwrap();
 	assert_eq!(s.storage_at(&a, &H256::from(&U256::from(01u64))), H256::from(&U256::from(69u64)));
 }
 
@@ -1177,7 +1182,7 @@ fn get_from_database() {
 		state.drop()
 	};
 
-	let state = State::from_existing(db, root, U256::from(0u8));
+	let state = State::from_existing(db, root, U256::from(0u8)).unwrap();
 	assert_eq!(state.balance(&a), U256::from(69u64));
 	assert_eq!(state.nonce(&a), U256::from(1u64));
 }
@@ -1210,7 +1215,7 @@ fn remove_from_database() {
 	};
 
 	let (root, db) = {
-		let mut state = State::from_existing(db, root, U256::from(0u8));
+		let mut state = State::from_existing(db, root, U256::from(0u8)).unwrap();
 		assert_eq!(state.exists(&a), true);
 		assert_eq!(state.nonce(&a), U256::from(1u64));
 		state.kill_account(&a);
@@ -1220,7 +1225,7 @@ fn remove_from_database() {
 		state.drop()
 	};
 
-	let state = State::from_existing(db, root, U256::from(0u8));
+	let state = State::from_existing(db, root, U256::from(0u8)).unwrap();
 	assert_eq!(state.exists(&a), false);
 	assert_eq!(state.nonce(&a), U256::from(0u64));
 }

util/src/trie/mod.rs

@@ -16,6 +16,8 @@
 
 //! Trie interface and implementation.
 
+use std::fmt;
+
 /// Export the trietraits module.
 pub mod trietraits;
 /// Export the standardmap module.
@@ -33,9 +35,22 @@ pub mod sectriedb;
 /// Export the sectriedbmut module.
 pub mod sectriedbmut;
 
-pub use self::trietraits::*;
+pub use self::trietraits::{Trie, TrieMut};
-pub use self::standardmap::*;
+pub use self::standardmap::{Alphabet, StandardMap, ValueMode};
-pub use self::triedbmut::*;
+pub use self::triedbmut::TrieDBMut;
-pub use self::triedb::*;
+pub use self::triedb::TrieDB;
-pub use self::sectriedbmut::*;
+pub use self::sectriedbmut::SecTrieDBMut;
-pub use self::sectriedb::*;
+pub use self::sectriedb::SecTrieDB;
+
+/// Trie Errors
+#[derive(Debug)]
+pub enum TrieError {
+	/// Attempted to create a trie with a state root not in the DB.
+	InvalidStateRoot,
+}
+
+impl fmt::Display for TrieError {
+	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+		write!(f, "Trie Error: Invalid state root.")
+	}
+}

util/src/trie/sectriedb.rs

@@ -16,9 +16,10 @@
 
 use hash::*;
 use sha3::*;
-use hashdb::*;
+use hashdb::HashDB;
-use super::triedb::*;
+use super::triedb::TrieDB;
-use super::trietraits::*;
+use super::trietraits::Trie;
+use super::TrieError;
 
 /// A `Trie` implementation which hashes keys and uses a generic `HashDB` backing database.
 ///
@@ -29,10 +30,12 @@ pub struct SecTrieDB<'db> {
 
 impl<'db> SecTrieDB<'db> {
 	/// Create a new trie with the backing database `db` and empty `root`
+	///
 	/// Initialise to the state entailed by the genesis block.
 	/// This guarantees the trie is built correctly.
-	pub fn new(db: &'db HashDB, root: &'db H256) -> Self {
+	/// Returns an error if root does not exist.
-		SecTrieDB { raw: TrieDB::new(db, root) }
+	pub fn new(db: &'db HashDB, root: &'db H256) -> Result<Self, TrieError> {
+		Ok(SecTrieDB { raw: try!(TrieDB::new(db, root)) })
 	}
 
 	/// Get a reference to the underlying raw `TrieDB` struct.
@@ -60,8 +63,9 @@ impl<'db> Trie for SecTrieDB<'db> {
 
 #[test]
 fn trie_to_sectrie() {
-	use memorydb::*;
+	use memorydb::MemoryDB;
-	use super::triedbmut::*;
+	use super::triedbmut::TrieDBMut;
+	use super::trietraits::TrieMut;
 
 	let mut memdb = MemoryDB::new();
 	let mut root = H256::new();
@@ -69,6 +73,6 @@ fn trie_to_sectrie() {
 		let mut t = TrieDBMut::new(&mut memdb, &mut root);
 		t.insert(&(&[0x01u8, 0x23]).sha3(), &[0x01u8, 0x23]);
 	}
-	let t = SecTrieDB::new(&memdb, &root);
+	let t = SecTrieDB::new(&memdb, &root).unwrap();
 	assert_eq!(t.get(&[0x01u8, 0x23]).unwrap(), &[0x01u8, 0x23]);
 }

util/src/trie/sectriedbmut.rs

@@ -16,9 +16,10 @@
 
 use hash::*;
 use sha3::*;
-use hashdb::*;
+use hashdb::HashDB;
-use super::triedbmut::*;
+use super::triedbmut::TrieDBMut;
-use super::trietraits::*;
+use super::trietraits::{Trie, TrieMut};
+use super::TrieError;
 
 /// A mutable `Trie` implementation which hashes keys and uses a generic `HashDB` backing database.
 ///
@@ -35,10 +36,11 @@ impl<'db> SecTrieDBMut<'db> {
 		SecTrieDBMut { raw: TrieDBMut::new(db, root) }
 	}
 
-	/// Create a new trie with the backing database `db` and `root`
+	/// Create a new trie with the backing database `db` and `root`.
-	/// Panics, if `root` does not exist
+	///
-	pub fn from_existing(db: &'db mut HashDB, root: &'db mut H256) -> Self {
+	/// Returns an error if root does not exist.
-		SecTrieDBMut { raw: TrieDBMut::from_existing(db, root) }
+	pub fn from_existing(db: &'db mut HashDB, root: &'db mut H256) -> Result<Self, TrieError> {
+		Ok(SecTrieDBMut { raw: try!(TrieDBMut::from_existing(db, root)) })
 	}
 
 	/// Get the backing database.
@@ -81,6 +83,6 @@ fn sectrie_to_trie() {
 		let mut t = SecTrieDBMut::new(&mut memdb, &mut root);
 		t.insert(&[0x01u8, 0x23], &[0x01u8, 0x23]);
 	}
-	let t = TrieDB::new(&memdb, &root);
+	let t = TrieDB::new(&memdb, &root).unwrap();
 	assert_eq!(t.get(&(&[0x01u8, 0x23]).sha3()).unwrap(), &[0x01u8, 0x23]);
 }

util/src/trie/triedb.rs

@@ -18,8 +18,9 @@ use common::*;
 use hashdb::*;
 use nibbleslice::*;
 use rlp::*;
-use super::trietraits::*;
+use super::trietraits::Trie;
-use super::node::*;
+use super::node::Node;
+use super::TrieError;
 
 /// A `Trie` implementation using a generic `HashDB` backing database.
 ///
@@ -41,7 +42,7 @@ use super::node::*;
 ///   let mut memdb = MemoryDB::new();
 ///   let mut root = H256::new();
 ///   TrieDBMut::new(&mut memdb, &mut root).insert(b"foo", b"bar");
-///   let t = TrieDB::new(&memdb, &root);
+///   let t = TrieDB::new(&memdb, &root).unwrap();
 ///   assert!(t.contains(b"foo"));
 ///   assert_eq!(t.get(b"foo").unwrap(), b"bar");
 ///   assert!(t.db_items_remaining().is_empty());
@@ -57,16 +58,16 @@ pub struct TrieDB<'db> {
 #[cfg_attr(feature="dev", allow(wrong_self_convention))]
 impl<'db> TrieDB<'db> {
 	/// Create a new trie with the backing database `db` and `root`
-	/// Panics, if `root` does not exist
+	/// Returns an error if `root` does not exist
-	pub fn new(db: &'db HashDB, root: &'db H256) -> Self {
+	pub fn new(db: &'db HashDB, root: &'db H256) -> Result<Self, TrieError> {
 		if !db.contains(root) {
-			flushln!("TrieDB::new({}): Trie root not found!", root);
+			Err(TrieError::InvalidStateRoot)
-			panic!("Trie root not found!");
+		} else {
-		}
+			Ok(TrieDB {
-		TrieDB {
 				db: db,
 				root: root,
 				hash_count: 0
+			})
 		}
 	}
 
@@ -356,6 +357,7 @@ impl<'db> fmt::Debug for TrieDB<'db> {
 
 #[test]
 fn iterator() {
+	use super::trietraits::TrieMut;
 	use memorydb::*;
 	use super::triedbmut::*;
 
@@ -369,6 +371,6 @@ fn iterator() {
 			t.insert(&x, &x);
 		}
 	}
-	assert_eq!(d.iter().map(|i|i.to_vec()).collect::<Vec<_>>(), TrieDB::new(&memdb, &root).iter().map(|x|x.0).collect::<Vec<_>>());
+	assert_eq!(d.iter().map(|i|i.to_vec()).collect::<Vec<_>>(), TrieDB::new(&memdb, &root).unwrap().iter().map(|x|x.0).collect::<Vec<_>>());
-	assert_eq!(d, TrieDB::new(&memdb, &root).iter().map(|x|x.1).collect::<Vec<_>>());
+	assert_eq!(d, TrieDB::new(&memdb, &root).unwrap().iter().map(|x|x.1).collect::<Vec<_>>());
 }

util/src/trie/triedbmut.rs

@@ -18,9 +18,10 @@ use common::*;
 use hashdb::*;
 use nibbleslice::*;
 use rlp::*;
-use super::node::*;
+use super::node::Node;
-use super::journal::*;
+use super::journal::Journal;
-use super::trietraits::*;
+use super::trietraits::{Trie, TrieMut};
+use super::TrieError;
 
 /// A `Trie` implementation using a generic `HashDB` backing database.
 ///
@@ -84,17 +85,16 @@ impl<'db> TrieDBMut<'db> {
 	}
 
 	/// Create a new trie with the backing database `db` and `root`.
-	/// Panics, if `root` does not exist.
+	/// Returns an error if `root` does not exist.
-	// TODO: return Result<Self, TrieError>
+	pub fn from_existing(db: &'db mut HashDB, root: &'db mut H256) -> Result<Self, TrieError> {
-	pub fn from_existing(db: &'db mut HashDB, root: &'db mut H256) -> Self {
 		if !db.exists(root) {
-			flushln!("Trie root not found {}", root);
+			Err(TrieError::InvalidStateRoot)
-			panic!("Trie root not found!");
+		} else {
-		}
+			Ok(TrieDBMut {
-		TrieDBMut {
 				db: db,
 				root: root,
 				hash_count: 0
+			})
 		}
 	}