Improvements and optimisations to estimate_gas (#4142)

* Return 0 instead of error with out of gas on estimate_gas

* Fix stuff up.

* Another estimate gas fix.

* Alter balance to maximum possible rather than GP=0.

* Only increase to amount strictly necessary.

* Improvements and optimisations to estimate_gas.

- Introduce proper error type
- Avoid building costly traces

* Fix tests.

* Actually fix testsActually fix tests

ethcore/src/client/client.rs

@@ -908,7 +908,7 @@ impl BlockChainClient for Client {
 
 			Executive::new(&mut state, &env_info, &*self.engine, &self.factories.vm)
 				.transact(&tx, options.clone())
-				.map(|r| r.trace[0].result.succeeded())
+				.map(|r| r.exception.is_some())
 				.unwrap_or(false)
 		};
 

ethcore/src/evm/evm.rs

@@ -22,7 +22,7 @@ use action_params::ActionParams;
 use evm::Ext;
 
 /// Evm errors.
-#[derive(Debug, Clone, Copy)]
+#[derive(Debug, Clone, Copy, PartialEq)]
 pub enum Error {
 	/// `OutOfGas` is returned when transaction execution runs out of gas.
 	/// The state should be reverted to the state from before the

ethcore/src/executive.rs

@@ -463,8 +463,9 @@ impl<'a> Executive<'a> {
 
 		match result {
 			Err(evm::Error::Internal) => Err(ExecutionError::Internal),
-			Err(_) => {
+			Err(exception) => {
 				Ok(Executed {
+					exception: Some(exception),
 					gas: t.gas,
 					gas_used: t.gas,
 					refunded: U256::zero(),
@@ -479,6 +480,7 @@ impl<'a> Executive<'a> {
 			},
 			_ => {
 				Ok(Executed {
+					exception: None,
 					gas: t.gas,
 					gas_used: gas_used,
 					refunded: refunded,

ethcore/src/types/executed.rs

@@ -18,6 +18,7 @@
 
 use util::{Bytes, U256, Address, U512};
 use rlp::*;
+use evm;
 use trace::{VMTrace, FlatTrace};
 use types::log_entry::LogEntry;
 use types::state_diff::StateDiff;
@@ -65,6 +66,9 @@ impl Decodable for CallType {
 #[derive(Debug, PartialEq, Clone)]
 #[cfg_attr(feature = "ipc", binary)]
 pub struct Executed {
+	/// True if the outer call/create resulted in an exceptional exit.
+	pub exception: Option<evm::Error>,
+
 	/// Gas paid up front for execution of transaction.
 	pub gas: U256,
 
@@ -178,6 +182,8 @@ pub enum CallError {
 	TransactionNotFound,
 	/// Couldn't find requested block's state in the chain.
 	StatePruned,
+	/// Couldn't find an amount of gas that didn't result in an exception.
+	Exceptional,
 	/// Error executing.
 	Execution(ExecutionError),
 }
@@ -195,6 +201,7 @@ impl fmt::Display for CallError {
 		let msg = match *self {
 			TransactionNotFound => "Transaction couldn't be found in the chain".into(),
 			StatePruned => "Couldn't find the transaction block's state in the chain".into(),
+			Exceptional => "An exception happened in the execution".into(),
 			Execution(ref e) => format!("{}", e),
 		};