more useful Engine::verify_seal

ethcore/src/block.rs

@@ -26,7 +26,7 @@ use util::error::{Mismatch, OutOfBounds};
 
 use basic_types::{LogBloom, Seal};
 use env_info::{EnvInfo, LastHashes};
-use engines::Engine;
+use engines::{Engine, ValidationProof};
 use error::{Error, BlockError, TransactionError};
 use factory::Factories;
 use header::Header;
@@ -484,10 +484,15 @@ impl LockedBlock {
 	/// Provide a valid seal in order to turn this into a `SealedBlock`.
 	/// This does check the validity of `seal` with the engine.
 	/// Returns the `ClosedBlock` back again if the seal is no good.
-	pub fn try_seal(self, engine: &Engine, seal: Vec<Bytes>) -> Result<SealedBlock, (Error, LockedBlock)> {
+	pub fn try_seal(
+		self,
+		engine: &Engine,
+		seal: Vec<Bytes>,
+		proof: Option<ValidationProof>,
+	) -> Result<SealedBlock, (Error, LockedBlock)> {
 		let mut s = self;
 		s.block.header.set_seal(seal);
-		match engine.verify_block_seal(&s.block.header) {
+		match engine.verify_block_seal(&s.block.header, proof) {
 			Err(e) => Err((e, s)),
 			_ => Ok(SealedBlock { block: s.block, uncle_bytes: s.uncle_bytes }),
 		}

ethcore/src/engines/authority_round.rs

@@ -464,14 +464,14 @@ mod tests {
 
 		engine.set_signer(tap.clone(), addr1, "1".into());
 		if let Seal::Regular(seal) = engine.generate_seal(b1.block()) {
-			assert!(b1.clone().try_seal(engine, seal).is_ok());
+			assert!(b1.clone().try_seal(engine, seal, None).is_ok());
 			// Second proposal is forbidden.
 			assert!(engine.generate_seal(b1.block()) == Seal::None);
 		}
 
 		engine.set_signer(tap, addr2, "2".into());
 		if let Seal::Regular(seal) = engine.generate_seal(b2.block()) {
-			assert!(b2.clone().try_seal(engine, seal).is_ok());
+			assert!(b2.clone().try_seal(engine, seal, None).is_ok());
 			// Second proposal is forbidden.
 			assert!(engine.generate_seal(b2.block()) == Seal::None);
 		}

ethcore/src/engines/basic_authority.rs

@@ -258,7 +258,7 @@ mod tests {
 		let b = OpenBlock::new(engine, Default::default(), false, db, &genesis_header, last_hashes, addr, (3141562.into(), 31415620.into()), vec![]).unwrap();
 		let b = b.close_and_lock();
 		if let Seal::Regular(seal) = engine.generate_seal(b.block()) {
-			assert!(b.try_seal(engine, seal).is_ok());
+			assert!(b.try_seal(engine, seal, None).is_ok());
 		}
 	}
 

ethcore/src/engines/instant_seal.rs

@@ -89,7 +89,7 @@ mod tests {
 		let b = OpenBlock::new(engine, Default::default(), false, db, &genesis_header, last_hashes, Address::default(), (3141562.into(), 31415620.into()), vec![]).unwrap();
 		let b = b.close_and_lock();
 		if let Seal::Regular(seal) = engine.generate_seal(b.block()) {
-			assert!(b.try_seal(engine, seal).is_ok());
+			assert!(b.try_seal(engine, seal, None).is_ok());
 		}
 	}
 

ethcore/src/engines/mod.rs

@@ -33,18 +33,20 @@ pub use self::authority_round::AuthorityRound;
 pub use self::tendermint::Tendermint;
 
 use std::sync::Weak;
-use util::*;
-use ethkey::Signature;
+
 use account_provider::AccountProvider;
 use block::ExecutedBlock;
 use builtin::Builtin;
+use client::Client;
 use env_info::EnvInfo;
 use error::{Error, TransactionError};
-use spec::CommonParams;
 use evm::Schedule;
 use header::Header;
+use spec::CommonParams;
 use transaction::{UnverifiedTransaction, SignedTransaction};
-use client::Client;
+
+use ethkey::Signature;
+use util::*;
 
 /// Voting errors.
 #[derive(Debug)]
@@ -59,6 +61,8 @@ pub enum EngineError {
 	UnexpectedMessage,
 	/// Seal field has an unexpected size.
 	BadSealFieldSize(OutOfBounds<usize>),
+	/// Needs a validation proof for the given block hash before verification can continue.
+	NeedsValidationProof(H256),
 }
 
 impl fmt::Display for EngineError {
@@ -70,6 +74,7 @@ impl fmt::Display for EngineError {
 			NotAuthorized(ref address) => format!("Signer {} is not authorized.", address),
 			UnexpectedMessage => "This Engine should not be fed messages.".into(),
 			BadSealFieldSize(ref oob) => format!("Seal field has an unexpected length: {}", oob),
+			NeedsValidationProof(ref hash) => format!("Needs validation proof of block {} to verify seal.", hash),
 		};
 
 		f.write_fmt(format_args!("Engine error ({})", msg))
@@ -87,6 +92,12 @@ pub enum Seal {
 	None,
 }
 
+/// A validation proof, required for validation of a block header.
+pub type ValidationProof = Vec<DBValue>;
+
+/// Type alias for a function we can make calls through synchronously.
+pub type Call = Fn(Address, Bytes) -> Result<Bytes, String>;
+
 /// A consensus mechanism for the chain. Generally either proof-of-work or proof-of-stake-based.
 /// Provides hooks into each of the major parts of block import.
 pub trait Engine : Sync + Send {
@@ -180,10 +191,25 @@ pub trait Engine : Sync + Send {
 	/// Verify the seal of a block. This is an auxilliary method that actually just calls other `verify_` methods
 	/// to get the job done. By default it must pass `verify_basic` and `verify_block_unordered`. If more or fewer
 	/// methods are needed for an Engine, this may be overridden.
-	fn verify_block_seal(&self, header: &Header) -> Result<(), Error> {
+	fn verify_block_seal(&self, header: &Header, _proof: Option<ValidationProof>) -> Result<(), Error> {
 		self.verify_block_basic(header, None).and_then(|_| self.verify_block_unordered(header, None))
 	}
 
+	/// Generate a validation proof for the given block header.
+	///
+	/// All values queried during execution of given  will go into the proof.
+	/// This may only be called for blocks indicated in "needs validation proof"
+	/// errors.
+	///
+	/// Engines which don't draw consensus information from the state (e.g. PoW)
+	/// don't need to change anything here.
+	///
+	/// Engines which do draw consensus information from the state may only do so
+	/// here.
+	fn generate_validation_proof(&self, _call: &Call) -> ValidationProof {
+		ValidationProof::default()
+	}
+
 	/// Populate a header's fields based on its parent's header.
 	/// Usually implements the chain scoring rule based on weight.
 	/// The gas floor target must not be lower than the engine's minimum gas limit.

ethcore/src/engines/tendermint/mod.rs

@@ -864,7 +864,7 @@ mod tests {
 		let proposer = insert_and_register(&tap, spec.engine.as_ref(), "1");
 
 		let (b, seal) = propose_default(&spec, proposer);
-		assert!(b.lock().try_seal(spec.engine.as_ref(), seal).is_ok());
+		assert!(b.lock().try_seal(spec.engine.as_ref(), seal, None).is_ok());
 	}
 
 	#[test]

ethcore/src/miner/miner.rs

@@ -1133,7 +1133,7 @@ impl MinerService for Miner {
 				|b| &b.hash() == &block_hash
 			) {
 				trace!(target: "miner", "Submitted block {}={}={} with seal {:?}", block_hash, b.hash(), b.header().bare_hash(), seal);
-				b.lock().try_seal(&*self.engine, seal).or_else(|(e, _)| {
+				b.lock().try_seal(&*self.engine, seal, None).or_else(|(e, _)| {
 					warn!(target: "miner", "Mined solution rejected: {}", e);
 					Err(Error::PowInvalid)
 				})

ethcore/src/snapshot/mod.rs

@@ -567,7 +567,7 @@ pub fn verify_old_block(rng: &mut OsRng, header: &Header, engine: &Engine, chain
 	if always || rng.gen::<f32>() <= POW_VERIFY_RATE {
 		match chain.block_header(header.parent_hash()) {
 			Some(parent) => engine.verify_block_family(header, &parent, body),
-			None => engine.verify_block_seal(header),
+			None => engine.verify_block_seal(header, None), // TODO: fetch validation proof as necessary.
 		}
 	} else {
 		engine.verify_block_basic(header, body)