make instantSeal engine backwards compatible

ethcore/src/engines/instant_seal.rs

@@ -18,7 +18,7 @@ use engines::{Engine, Seal};
 use parity_machine::{Machine, Transactions, TotalScoredHeader};
 
 /// `InstantSeal` params.
-#[derive(Debug, PartialEq)]
+#[derive(Default, Debug, PartialEq)]
 pub struct InstantSealParams {
 	/// Whether to use millisecond timestamp
 	pub millisecond_timestamp: bool,

ethcore/src/engines/mod.rs

@@ -32,7 +32,7 @@ pub mod epoch;
 pub use self::authority_round::AuthorityRound;
 pub use self::basic_authority::BasicAuthority;
 pub use self::epoch::{EpochVerifier, Transition as EpochTransition};
-pub use self::instant_seal::InstantSeal;
+pub use self::instant_seal::{InstantSeal, InstantSealParams};
 pub use self::null_engine::NullEngine;
 pub use self::tendermint::Tendermint;
 

ethcore/src/spec/spec.rs

@@ -33,7 +33,10 @@ use vm::{EnvInfo, CallType, ActionValue, ActionParams, ParamsType};
 
 use builtin::Builtin;
 use encoded;
-use engines::{EthEngine, NullEngine, InstantSeal, BasicAuthority, AuthorityRound, Tendermint, DEFAULT_BLOCKHASH_CONTRACT};
+use engines::{
+	EthEngine, NullEngine, InstantSeal, InstantSealParams, BasicAuthority,
+	AuthorityRound, Tendermint, DEFAULT_BLOCKHASH_CONTRACT
+};
 use error::Error;
 use executive::Executive;
 use factory::Factories;
@@ -596,7 +599,8 @@ impl Spec {
 		match engine_spec {
 			ethjson::spec::Engine::Null(null) => Arc::new(NullEngine::new(null.params.into(), machine)),
 			ethjson::spec::Engine::Ethash(ethash) => Arc::new(::ethereum::Ethash::new(spec_params.cache_dir, ethash.params.into(), machine, spec_params.optimization_setting)),
-			ethjson::spec::Engine::InstantSeal(instant_seal) => Arc::new(InstantSeal::new(instant_seal.params.into(), machine)),
+			ethjson::spec::Engine::InstantSeal(Some(instant_seal)) => Arc::new(InstantSeal::new(instant_seal.params.into(), machine)),
+			ethjson::spec::Engine::InstantSeal(None) => Arc::new(InstantSeal::new(InstantSealParams::default(), machine)),
 			ethjson::spec::Engine::BasicAuthority(basic_authority) => Arc::new(BasicAuthority::new(basic_authority.params.into(), machine)),
 			ethjson::spec::Engine::AuthorityRound(authority_round) => AuthorityRound::new(authority_round.params.into(), machine)
 				.expect("Failed to start AuthorityRound consensus engine."),

json/src/spec/engine.rs

@@ -26,7 +26,7 @@ pub enum Engine {
 	Null(NullEngine),
 	/// Instantly sealing engine.
 	#[serde(rename="instantSeal")]
-	InstantSeal(InstantSeal),
+	InstantSeal(Option<InstantSeal>),
 	/// Ethash engine.
 	Ethash(Ethash),
 	/// BasicAuthority engine.
@@ -71,6 +71,17 @@ mod tests {
 			_ => panic!(),
 		};
 
+		let s = r#"{
+			"instantSeal": null
+		}"#;
+
+		let deserialized: Engine = serde_json::from_str(s).unwrap();
+		match deserialized {
+			Engine::InstantSeal(_) => {},	// instant seal is unit tested in its own file.
+			_ => panic!(),
+		};
+
+
 		let s = r#"{
 			"Ethash": {
 				"params": {