Move all chain parameters into `engine_params` and let Engine impl provide them.

src/engine.rs

@@ -1,5 +1,7 @@
 use std::collections::hash_map::*;
 use util::bytes::*;
+use util::uint::*;
+use util::rlp::*;
 use util::semantic_version::*;
 use util::error::*;
 use header::Header;
@@ -30,6 +32,16 @@ pub trait Engine {
 	/// Get the EVM schedule for 
 	fn evm_schedule(&self, env_info: &EnvInfo) -> EvmSchedule;
 
+	/// Some intrinsic operation parameters; by default they take their value from the `spec()`'s `engine_params`.
+	fn maximum_extra_data_size(&self, _env_info: &EnvInfo) -> usize { decode(&self.spec().engine_params.get("maximum_extra_data_size").unwrap()) }
+	fn account_start_nonce(&self, _env_info: &EnvInfo) -> U256 { decode(&self.spec().engine_params.get("account_start_nonce").unwrap()) }
+	// TODO: refactor in terms of `on_preseal_block`
+	fn block_reward(&self, _env_info: &EnvInfo) -> U256 { decode(&self.spec().engine_params.get("block_reward").unwrap()) }
+
+	/// Block transformation functions, before and after the transactions.
+//	fn on_new_block(&self, _env_info: &EnvInfo, _block: &mut Block) -> Result<(), EthcoreError> {}
+//	fn on_preseal_block(&self, _env_info: &EnvInfo, _block: &mut Block) -> Result<(), EthcoreError> {}
+
 	/// Verify that `header` is valid.
 	/// `parent` (the parent header) and `block` (the header's full block) may be provided for additional
 	/// checks. Returns either a null `Ok` or a general error detailing the problem with import.
@@ -42,8 +54,8 @@ pub trait Engine {
 	/// Don't forget to call Super::populateFromParent when subclassing & overriding.
 	fn populate_from_parent(&self, _header: &mut Header, _parent: &Header) -> Result<(), EthcoreError> { Ok(()) }
 
-	// TODO: buildin contract routing - this will require removing the built-in configuration reading logic from Spec
-	// into here and removing the Spec::builtins field. It's a big job.
+	// TODO: buildin contract routing - to do this properly, it will require removing the built-in configuration-reading logic
+	// from Spec into here and removing the Spec::builtins field.
 /*	fn is_builtin(&self, a: Address) -> bool;
 	fn cost_of_builtin(&self, a: Address, in: &[u8]) -> bignum;
 	fn execute_builtin(&self, a: Address, in: &[u8], out: &mut [u8]);

src/spec.rs

@@ -19,11 +19,9 @@ pub struct Spec {
 	// What engine are we using for this?
 	pub engine_name: String,
 
-	// Various parameters for the chain operation.
-	pub block_reward: U256,
-	pub maximum_extra_data_size: U256,
-	pub account_start_nonce: U256,
-	pub misc: HashMap<String, Bytes>,
+	// Parameters concerning operation of the specific engine we're using.
+	// Name -> RLP-encoded value
+	pub engine_params: HashMap<String, Bytes>,
 
 	// Builtin-contracts are here for now but would like to abstract into Engine API eventually.
 	pub builtins: HashMap<Address, Builtin>,
@@ -62,10 +60,6 @@ impl Spec {
 		Ref::map(self.state_root_memo.borrow(), |x|x.as_ref().unwrap())
 	}
 
-	pub fn block_reward(&self) -> U256 { self.block_reward }
-	pub fn maximum_extra_data_size(&self) -> U256 { self.maximum_extra_data_size }
-	pub fn account_start_nonce(&self) -> U256 { self.account_start_nonce }
-
 	/// Compose the genesis block for this chain.
 	pub fn genesis_block(&self) -> Bytes {
 		// TODO
@@ -78,10 +72,10 @@ impl Spec {
 	pub fn olympic() -> Spec {
 		Spec {
 			engine_name: "Ethash".to_string(),
-			block_reward: finney() * U256::from(1500u64),
-			maximum_extra_data_size: U256::from(1024u64),
-			account_start_nonce: U256::from(0u64),
-			misc: vec![
+			engine_params: vec![
+				("block_reward", encode(&(finney() * U256::from(1500u64)))),
+				("maximum_extra_data_size", encode(&U256::from(1024u64))),
+				("account_start_nonce", encode(&U256::from(0u64))),
 				("gas_limit_bounds_divisor", encode(&1024u64)), 
 				("minimum_difficulty", encode(&131_072u64)), 
 				("difficulty_bound_divisor", encode(&2048u64)), 
@@ -115,10 +109,10 @@ impl Spec {
 	pub fn frontier() -> Spec {
 		Spec {
 			engine_name: "Ethash".to_string(),
-			block_reward: ether() * U256::from(5u64),
-			maximum_extra_data_size: U256::from(32u64),
-			account_start_nonce: U256::from(0u64),
-			misc: vec![
+			engine_params: vec![
+				("block_reward", encode(&(ether() * U256::from(5u64)))),
+				("maximum_extra_data_size", encode(&U256::from(32u64))),
+				("account_start_nonce", encode(&U256::from(0u64))),
 				("gas_limit_bounds_divisor", encode(&1024u64)), 
 				("minimum_difficulty", encode(&131_072u64)), 
 				("difficulty_bound_divisor", encode(&2048u64)), 
@@ -152,10 +146,10 @@ impl Spec {
 	pub fn morden() -> Spec {
 		Spec {
 			engine_name: "Ethash".to_string(),
-			block_reward: ether() * U256::from(5u64),
-			maximum_extra_data_size: U256::from(32u64),
-			account_start_nonce: U256::from(1u64) << 20,
-			misc: vec![
+			engine_params: vec![
+				("block_reward", encode(&(ether() * U256::from(5u64)))),
+				("maximum_extra_data_size", encode(&U256::from(32u64))),
+				("account_start_nonce", encode(&(U256::from(1u64) << 20))),
 				("gas_limit_bounds_divisor", encode(&1024u64)), 
 				("minimum_difficulty", encode(&131_072u64)), 
 				("difficulty_bound_divisor", encode(&2048u64)),