Print warnings when using dangerous settings for ValidatorSet (#10733)

* Stop breaking out of loop if a non-canonical hash is found

* include expected hash in log msg

* More logging

* Scope

* Syntax

* Log in blank RollingFinality
Escalate bad proposer to warning

* Check validator set size: warn if 1 or even number

* More readable code

* Use SimpleList::new

* Extensive logging on unexpected non-canonical hash

* Wording

* Update ethcore/blockchain/src/blockchain.rs

Co-Authored-By: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

* Improved logging, address grumbles

* Update ethcore/src/engines/validator_set/simple_list.rs

Co-Authored-By: Luke Schoen <ltfschoen@users.noreply.github.com>

ethcore/src/engines/authority_round/finality.rs

@@ -111,8 +111,6 @@ impl RollingFinality {
 	/// Returns a list of all newly finalized headers.
 	// TODO: optimize with smallvec.
 	pub fn push_hash(&mut self, head: H256, signers: Vec<Address>) -> Result<Vec<H256>, UnknownValidator> {
-		// TODO: seems bad to iterate over signers twice like this.
-		//       Can do the work in a single loop and call `clear()` if an unknown validator was found?
 		for their_signer in signers.iter() {
 			if !self.signers.contains(their_signer) {
 				warn!(target: "finality",  "Unknown validator: {}", their_signer);

ethcore/src/engines/validator_set/safe_contract.rs

@@ -208,11 +208,11 @@ impl ValidatorSafeContract {
 
 		match value {
 			Ok(new) => {
-				debug!(target: "engine", "Set of validators obtained: {:?}", new);
+				debug!(target: "engine", "Got validator set from contract: {:?}", new);
 				Some(SimpleList::new(new))
 			},
 			Err(s) => {
-				debug!(target: "engine", "Set of validators could not be updated: {}", s);
+				debug!(target: "engine", "Could not get validator set from contract: {}", s);
 				None
 			},
 		}
@@ -335,7 +335,7 @@ impl ValidatorSet for ValidatorSafeContract {
 			Some(receipts) => match self.extract_from_event(bloom, header, receipts) {
 				None => ::engines::EpochChange::No,
 				Some(list) => {
-					info!(target: "engine", "Signal for transition within contract. New list: {:?}",
+					info!(target: "engine", "Signal for transition within contract. New validator list: {:?}",
 						&*list);
 
 					let proof = encode_proof(&header, receipts);
@@ -359,7 +359,7 @@ impl ValidatorSet for ValidatorSafeContract {
 			let addresses = check_first_proof(machine, self.contract_address, old_header, &state_items)
 				.map_err(::engines::EngineError::InsufficientProof)?;
 
-			trace!(target: "engine", "extracted epoch set at #{}: {} addresses",
+			trace!(target: "engine", "Extracted epoch validator set at block #{}: {} addresses",
 				number, addresses.len());
 
 			Ok((SimpleList::new(addresses), Some(old_hash)))
@@ -380,7 +380,11 @@ impl ValidatorSet for ValidatorSafeContract {
 			let bloom = self.expected_bloom(&old_header);
 
 			match self.extract_from_event(bloom, &old_header, &receipts) {
-				Some(list) => Ok((list, Some(old_header.hash()))),
+				Some(list) => {
+					trace!(target: "engine", "Extracted epoch validator set at block #{}: {} addresses", old_header.number(), list.len());
+
+					Ok((list, Some(old_header.hash())))
+				},
 				None => Err(::engines::EngineError::InsufficientProof("No log event in proof.".into()).into()),
 			}
 		}

ethcore/src/engines/validator_set/simple_list.rs

@@ -33,9 +33,14 @@ pub struct SimpleList {
 impl SimpleList {
 	/// Create a new `SimpleList`.
 	pub fn new(validators: Vec<Address>) -> Self {
-		SimpleList {
-			validators: validators,
+		let validator_count = validators.len();
+		if validator_count == 1 {
+			warn!(target: "engine", "Running AuRa with a single validator implies instant finality. Use a database?");
 		}
+		if validator_count % 2 == 0 {
+			warn!(target: "engine", "Running AuRa with an even number of validators is not recommended (risk of network split).");
+		}
+		SimpleList { validators }
 	}
 
 	/// Convert into inner representation.
@@ -52,9 +57,7 @@ impl ::std::ops::Deref for SimpleList {
 
 impl From<Vec<Address>> for SimpleList {
 	fn from(validators: Vec<Address>) -> Self {
-		SimpleList {
-			validators: validators,
-		}
+		SimpleList::new(validators)
 	}
 }