core/vm: Refactor tracing to make Tracer the main interface

This CL makes several refactors:
 - Define a Tracer interface, implementing the `CaptureState` method
 - Add the VM environment as the first argument of
   `Tracer.CaptureState`
 - Rename existing functionality `StructLogger` an make it an
   implementation of `Tracer`
 - Delete `StructLogCollector` and make `StructLogger` collect the logs
   directly
 - Change all callers to use the new `StructLogger` where necessary and
   extract logs from that.
 - Deletes the apparently obsolete and likely nonfunctional 'TraceCall'
   from the eth API.

Callers that only wish accumulated logs can use the `StructLogger`
implementation straightforwardly. Callers that wish to efficiently
capture VM traces and operate on them without excessive copying can now
implement the `Tracer` interface to receive VM state at each step and
do with it as they wish.

This CL also removes the accumulation of logs from the vm.Environment;
this was necessary as part of the refactor, but also simplifies it by
removing a responsibility that doesn't directly belong to the
Environment.

11 files changed, 136 insertions, 162 deletions

diff --git a/core/vm/environment.go b/core/vm/environment.go
index 664887454..747627565 100644
--- a/core/vm/environment.go
+++ b/core/vm/environment.go
@@ -73,8 +73,6 @@ type Environment interface {
 	DelegateCall(me ContractRef, addr common.Address, data []byte, gas, price *big.Int) ([]byte, error)
 	// Create a new contract
 	Create(me ContractRef, data []byte, gas, price, value *big.Int) ([]byte, common.Address, error)
-
-	StructLogs() []StructLog
 }
 
 // Vm is the basic interface for an implementation of the EVM.
diff --git a/core/vm/gas.go b/core/vm/gas.go
index 09feddd7d..eb2c16346 100644
--- a/core/vm/gas.go
+++ b/core/vm/gas.go
@@ -38,7 +38,7 @@ var (
 )
 
 // baseCheck checks for any stack error underflows
-func baseCheck(op OpCode, stack *stack, gas *big.Int) error {
+func baseCheck(op OpCode, stack *Stack, gas *big.Int) error {
 	// PUSH and DUP are a bit special. They all cost the same but we do want to have checking on stack push limit
 	// PUSH is also allowed to calculate the same price for all PUSHes
 	// DUP requirements are handled elsewhere (except for the stack limit check)
diff --git a/core/vm/instructions.go b/core/vm/instructions.go
index e2fc5ee0f..a95ba26c5 100644
--- a/core/vm/instructions.go
+++ b/core/vm/instructions.go
@@ -27,14 +27,14 @@ import (
 
 type programInstruction interface {
 	// executes the program instruction and allows the instruction to modify the state of the program
-	do(program *Program, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) ([]byte, error)
+	do(program *Program, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) ([]byte, error)
 	// returns whether the program instruction halts the execution of the JIT
 	halts() bool
 	// Returns the current op code (debugging purposes)
 	Op() OpCode
 }
 
-type instrFn func(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack)
+type instrFn func(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack)
 
 type instruction struct {
 	op   OpCode
@@ -58,7 +58,7 @@ func jump(mapping map[uint64]uint64, destinations map[uint64]struct{}, contract
 	return mapping[to.Uint64()], nil
 }
 
-func (instr instruction) do(program *Program, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) ([]byte, error) {
+func (instr instruction) do(program *Program, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) ([]byte, error) {
 	// calculate the new memory size and gas price for the current executing opcode
 	newMemSize, cost, err := jitCalculateGasAndSize(env, contract, instr, env.Db(), memory, stack)
 	if err != nil {
@@ -114,26 +114,26 @@ func (instr instruction) Op() OpCode {
 	return instr.op
 }
 
-func opStaticJump(instr instruction, pc *uint64, ret *big.Int, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opStaticJump(instr instruction, pc *uint64, ret *big.Int, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	ret.Set(instr.data)
 }
 
-func opAdd(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opAdd(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	x, y := stack.pop(), stack.pop()
 	stack.push(U256(x.Add(x, y)))
 }
 
-func opSub(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opSub(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	x, y := stack.pop(), stack.pop()
 	stack.push(U256(x.Sub(x, y)))
 }
 
-func opMul(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opMul(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	x, y := stack.pop(), stack.pop()
 	stack.push(U256(x.Mul(x, y)))
 }
 
-func opDiv(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opDiv(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	x, y := stack.pop(), stack.pop()
 	if y.Cmp(common.Big0) != 0 {
 		stack.push(U256(x.Div(x, y)))
@@ -142,7 +142,7 @@ func opDiv(instr instruction, pc *uint64, env Environment, contract *Contract, m
 	}
 }
 
-func opSdiv(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opSdiv(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	x, y := S256(stack.pop()), S256(stack.pop())
 	if y.Cmp(common.Big0) == 0 {
 		stack.push(new(big.Int))
@@ -162,7 +162,7 @@ func opSdiv(instr instruction, pc *uint64, env Environment, contract *Contract,
 	}
 }
 
-func opMod(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opMod(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	x, y := stack.pop(), stack.pop()
 	if y.Cmp(common.Big0) == 0 {
 		stack.push(new(big.Int))
@@ -171,7 +171,7 @@ func opMod(instr instruction, pc *uint64, env Environment, contract *Contract, m
 	}
 }
 
-func opSmod(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opSmod(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	x, y := S256(stack.pop()), S256(stack.pop())
 
 	if y.Cmp(common.Big0) == 0 {
@@ -191,12 +191,12 @@ func opSmod(instr instruction, pc *uint64, env Environment, contract *Contract,
 	}
 }
 
-func opExp(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opExp(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	x, y := stack.pop(), stack.pop()
 	stack.push(U256(x.Exp(x, y, Pow256)))
 }
 
-func opSignExtend(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opSignExtend(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	back := stack.pop()
 	if back.Cmp(big.NewInt(31)) < 0 {
 		bit := uint(back.Uint64()*8 + 7)
@@ -213,12 +213,12 @@ func opSignExtend(instr instruction, pc *uint64, env Environment, contract *Cont
 	}
 }
 
-func opNot(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opNot(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	x := stack.pop()
 	stack.push(U256(x.Not(x)))
 }
 
-func opLt(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opLt(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	x, y := stack.pop(), stack.pop()
 	if x.Cmp(y) < 0 {
 		stack.push(big.NewInt(1))
@@ -227,7 +227,7 @@ func opLt(instr instruction, pc *uint64, env Environment, contract *Contract, me
 	}
 }
 
-func opGt(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opGt(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	x, y := stack.pop(), stack.pop()
 	if x.Cmp(y) > 0 {
 		stack.push(big.NewInt(1))
@@ -236,7 +236,7 @@ func opGt(instr instruction, pc *uint64, env Environment, contract *Contract, me
 	}
 }
 
-func opSlt(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opSlt(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	x, y := S256(stack.pop()), S256(stack.pop())
 	if x.Cmp(S256(y)) < 0 {
 		stack.push(big.NewInt(1))
@@ -245,7 +245,7 @@ func opSlt(instr instruction, pc *uint64, env Environment, contract *Contract, m
 	}
 }
 
-func opSgt(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opSgt(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	x, y := S256(stack.pop()), S256(stack.pop())
 	if x.Cmp(y) > 0 {
 		stack.push(big.NewInt(1))
@@ -254,7 +254,7 @@ func opSgt(instr instruction, pc *uint64, env Environment, contract *Contract, m
 	}
 }
 
-func opEq(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opEq(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	x, y := stack.pop(), stack.pop()
 	if x.Cmp(y) == 0 {
 		stack.push(big.NewInt(1))
@@ -263,7 +263,7 @@ func opEq(instr instruction, pc *uint64, env Environment, contract *Contract, me
 	}
 }
 
-func opIszero(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opIszero(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	x := stack.pop()
 	if x.Cmp(common.Big0) > 0 {
 		stack.push(new(big.Int))
@@ -272,19 +272,19 @@ func opIszero(instr instruction, pc *uint64, env Environment, contract *Contract
 	}
 }
 
-func opAnd(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opAnd(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	x, y := stack.pop(), stack.pop()
 	stack.push(x.And(x, y))
 }
-func opOr(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opOr(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	x, y := stack.pop(), stack.pop()
 	stack.push(x.Or(x, y))
 }
-func opXor(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opXor(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	x, y := stack.pop(), stack.pop()
 	stack.push(x.Xor(x, y))
 }
-func opByte(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opByte(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	th, val := stack.pop(), stack.pop()
 	if th.Cmp(big.NewInt(32)) < 0 {
 		byte := big.NewInt(int64(common.LeftPadBytes(val.Bytes(), 32)[th.Int64()]))
@@ -293,7 +293,7 @@ func opByte(instr instruction, pc *uint64, env Environment, contract *Contract,
 		stack.push(new(big.Int))
 	}
 }
-func opAddmod(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opAddmod(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	x, y, z := stack.pop(), stack.pop(), stack.pop()
 	if z.Cmp(Zero) > 0 {
 		add := x.Add(x, y)
@@ -303,7 +303,7 @@ func opAddmod(instr instruction, pc *uint64, env Environment, contract *Contract
 		stack.push(new(big.Int))
 	}
 }
-func opMulmod(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opMulmod(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	x, y, z := stack.pop(), stack.pop(), stack.pop()
 	if z.Cmp(Zero) > 0 {
 		mul := x.Mul(x, y)
@@ -314,45 +314,45 @@ func opMulmod(instr instruction, pc *uint64, env Environment, contract *Contract
 	}
 }
 
-func opSha3(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opSha3(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	offset, size := stack.pop(), stack.pop()
 	hash := crypto.Keccak256(memory.Get(offset.Int64(), size.Int64()))
 
 	stack.push(common.BytesToBig(hash))
 }
 
-func opAddress(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opAddress(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	stack.push(common.Bytes2Big(contract.Address().Bytes()))
 }
 
-func opBalance(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opBalance(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	addr := common.BigToAddress(stack.pop())
 	balance := env.Db().GetBalance(addr)
 
 	stack.push(new(big.Int).Set(balance))
 }
 
-func opOrigin(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opOrigin(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	stack.push(env.Origin().Big())
 }
 
-func opCaller(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opCaller(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	stack.push(contract.Caller().Big())
 }
 
-func opCallValue(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opCallValue(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	stack.push(new(big.Int).Set(contract.value))
 }
 
-func opCalldataLoad(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opCalldataLoad(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	stack.push(common.Bytes2Big(getData(contract.Input, stack.pop(), common.Big32)))
 }
 
-func opCalldataSize(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opCalldataSize(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	stack.push(big.NewInt(int64(len(contract.Input))))
 }
 
-func opCalldataCopy(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opCalldataCopy(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	var (
 		mOff = stack.pop()
 		cOff = stack.pop()
@@ -361,18 +361,18 @@ func opCalldataCopy(instr instruction, pc *uint64, env Environment, contract *Co
 	memory.Set(mOff.Uint64(), l.Uint64(), getData(contract.Input, cOff, l))
 }
 
-func opExtCodeSize(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opExtCodeSize(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	addr := common.BigToAddress(stack.pop())
 	l := big.NewInt(int64(len(env.Db().GetCode(addr))))
 	stack.push(l)
 }
 
-func opCodeSize(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opCodeSize(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	l := big.NewInt(int64(len(contract.Code)))
 	stack.push(l)
 }
 
-func opCodeCopy(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opCodeCopy(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	var (
 		mOff = stack.pop()
 		cOff = stack.pop()
@@ -383,7 +383,7 @@ func opCodeCopy(instr instruction, pc *uint64, env Environment, contract *Contra
 	memory.Set(mOff.Uint64(), l.Uint64(), codeCopy)
 }
 
-func opExtCodeCopy(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opExtCodeCopy(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	var (
 		addr = common.BigToAddress(stack.pop())
 		mOff = stack.pop()
@@ -395,11 +395,11 @@ func opExtCodeCopy(instr instruction, pc *uint64, env Environment, contract *Con
 	memory.Set(mOff.Uint64(), l.Uint64(), codeCopy)
 }
 
-func opGasprice(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opGasprice(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	stack.push(new(big.Int).Set(contract.Price))
 }
 
-func opBlockhash(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opBlockhash(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	num := stack.pop()
 
 	n := new(big.Int).Sub(env.BlockNumber(), common.Big257)
@@ -410,43 +410,43 @@ func opBlockhash(instr instruction, pc *uint64, env Environment, contract *Contr
 	}
 }
 
-func opCoinbase(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opCoinbase(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	stack.push(env.Coinbase().Big())
 }
 
-func opTimestamp(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opTimestamp(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	stack.push(U256(new(big.Int).Set(env.Time())))
 }
 
-func opNumber(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opNumber(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	stack.push(U256(new(big.Int).Set(env.BlockNumber())))
 }
 
-func opDifficulty(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opDifficulty(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	stack.push(U256(new(big.Int).Set(env.Difficulty())))
 }
 
-func opGasLimit(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opGasLimit(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	stack.push(U256(new(big.Int).Set(env.GasLimit())))
 }
 
-func opPop(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opPop(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	stack.pop()
 }
 
-func opPush(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opPush(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	stack.push(new(big.Int).Set(instr.data))
 }
 
-func opDup(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opDup(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	stack.dup(int(instr.data.Int64()))
 }
 
-func opSwap(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opSwap(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	stack.swap(int(instr.data.Int64()))
 }
 
-func opLog(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opLog(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	n := int(instr.data.Int64())
 	topics := make([]common.Hash, n)
 	mStart, mSize := stack.pop(), stack.pop()
@@ -459,55 +459,55 @@ func opLog(instr instruction, pc *uint64, env Environment, contract *Contract, m
 	env.AddLog(log)
 }
 
-func opMload(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opMload(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	offset := stack.pop()
 	val := common.BigD(memory.Get(offset.Int64(), 32))
 	stack.push(val)
 }
 
-func opMstore(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opMstore(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	// pop value of the stack
 	mStart, val := stack.pop(), stack.pop()
 	memory.Set(mStart.Uint64(), 32, common.BigToBytes(val, 256))
 }
 
-func opMstore8(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opMstore8(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	off, val := stack.pop().Int64(), stack.pop().Int64()
 	memory.store[off] = byte(val & 0xff)
 }
 
-func opSload(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opSload(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	loc := common.BigToHash(stack.pop())
 	val := env.Db().GetState(contract.Address(), loc).Big()
 	stack.push(val)
 }
 
-func opSstore(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opSstore(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	loc := common.BigToHash(stack.pop())
 	val := stack.pop()
 	env.Db().SetState(contract.Address(), loc, common.BigToHash(val))
 }
 
-func opJump(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opJump(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 }
-func opJumpi(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opJumpi(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 }
-func opJumpdest(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opJumpdest(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 }
 
-func opPc(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opPc(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	stack.push(new(big.Int).Set(instr.data))
 }
 
-func opMsize(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opMsize(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	stack.push(big.NewInt(int64(memory.Len())))
 }
 
-func opGas(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opGas(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	stack.push(new(big.Int).Set(contract.Gas))
 }
 
-func opCreate(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opCreate(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	var (
 		value        = stack.pop()
 		offset, size = stack.pop(), stack.pop()
@@ -529,7 +529,7 @@ func opCreate(instr instruction, pc *uint64, env Environment, contract *Contract
 	}
 }
 
-func opCall(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opCall(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	gas := stack.pop()
 	// pop gas and value of the stack.
 	addr, value := stack.pop(), stack.pop()
@@ -560,7 +560,7 @@ func opCall(instr instruction, pc *uint64, env Environment, contract *Contract,
 	}
 }
 
-func opCallCode(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opCallCode(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	gas := stack.pop()
 	// pop gas and value of the stack.
 	addr, value := stack.pop(), stack.pop()
@@ -591,7 +591,7 @@ func opCallCode(instr instruction, pc *uint64, env Environment, contract *Contra
 	}
 }
 
-func opDelegateCall(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opDelegateCall(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	gas, to, inOffset, inSize, outOffset, outSize := stack.pop(), stack.pop(), stack.pop(), stack.pop(), stack.pop(), stack.pop()
 
 	toAddr := common.BigToAddress(to)
@@ -605,12 +605,12 @@ func opDelegateCall(instr instruction, pc *uint64, env Environment, contract *Co
 	}
 }
 
-func opReturn(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opReturn(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 }
-func opStop(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opStop(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 }
 
-func opSuicide(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+func opSuicide(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 	balance := env.Db().GetBalance(contract.Address())
 	env.Db().AddBalance(common.BigToAddress(stack.pop()), balance)
 
@@ -621,7 +621,7 @@ func opSuicide(instr instruction, pc *uint64, env Environment, contract *Contrac
 
 // make log instruction function
 func makeLog(size int) instrFn {
-	return func(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+	return func(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 		topics := make([]common.Hash, size)
 		mStart, mSize := stack.pop(), stack.pop()
 		for i := 0; i < size; i++ {
@@ -636,7 +636,7 @@ func makeLog(size int) instrFn {
 
 // make push instruction function
 func makePush(size uint64, bsize *big.Int) instrFn {
-	return func(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+	return func(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 		byts := getData(contract.Code, new(big.Int).SetUint64(*pc+1), bsize)
 		stack.push(common.Bytes2Big(byts))
 		*pc += size
@@ -645,7 +645,7 @@ func makePush(size uint64, bsize *big.Int) instrFn {
 
 // make push instruction function
 func makeDup(size int64) instrFn {
-	return func(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+	return func(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 		stack.dup(int(size))
 	}
 }
@@ -654,7 +654,7 @@ func makeDup(size int64) instrFn {
 func makeSwap(size int64) instrFn {
 	// switch n + 1 otherwise n would be swapped with n
 	size += 1
-	return func(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) {
+	return func(instr instruction, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) {
 		stack.swap(int(size))
 	}
 }
diff --git a/core/vm/jit.go b/core/vm/jit.go
index e2374df42..460a68ddd 100644
--- a/core/vm/jit.go
+++ b/core/vm/jit.go
@@ -303,7 +303,7 @@ func RunProgram(program *Program, env Environment, contract *Contract, input []b
 	return runProgram(program, 0, NewMemory(), newstack(), env, contract, input)
 }
 
-func runProgram(program *Program, pcstart uint64, mem *Memory, stack *stack, env Environment, contract *Contract, input []byte) ([]byte, error) {
+func runProgram(program *Program, pcstart uint64, mem *Memory, stack *Stack, env Environment, contract *Contract, input []byte) ([]byte, error) {
 	contract.Input = input
 
 	var (
@@ -357,7 +357,7 @@ func validDest(dests map[uint64]struct{}, dest *big.Int) bool {
 
 // jitCalculateGasAndSize calculates the required given the opcode and stack items calculates the new memorysize for
 // the operation. This does not reduce gas or resizes the memory.
-func jitCalculateGasAndSize(env Environment, contract *Contract, instr instruction, statedb Database, mem *Memory, stack *stack) (*big.Int, *big.Int, error) {
+func jitCalculateGasAndSize(env Environment, contract *Contract, instr instruction, statedb Database, mem *Memory, stack *Stack) (*big.Int, *big.Int, error) {
 	var (
 		gas                 = new(big.Int)
 		newMemSize *big.Int = new(big.Int)
@@ -491,7 +491,7 @@ func jitCalculateGasAndSize(env Environment, contract *Contract, instr instructi
 
 // jitBaseCheck is the same as baseCheck except it doesn't do the look up in the
 // gas table. This is done during compilation instead.
-func jitBaseCheck(instr instruction, stack *stack, gas *big.Int) error {
+func jitBaseCheck(instr instruction, stack *Stack, gas *big.Int) error {
 	err := stack.require(instr.spop)
 	if err != nil {
 		return err
diff --git a/core/vm/jit_test.go b/core/vm/jit_test.go
index 403c15a8d..5e4bcfeef 100644
--- a/core/vm/jit_test.go
+++ b/core/vm/jit_test.go
@@ -179,11 +179,6 @@ func (self *Env) RuleSet() RuleSet       { return ruleSet{new(big.Int)} }
 func (self *Env) Vm() Vm                 { return self.evm }
 func (self *Env) Origin() common.Address { return common.Address{} }
 func (self *Env) BlockNumber() *big.Int  { return big.NewInt(0) }
-func (self *Env) AddStructLog(log StructLog) {
-}
-func (self *Env) StructLogs() []StructLog {
-	return nil
-}
 
 //func (self *Env) PrevHash() []byte      { return self.parent }
 func (self *Env) Coinbase() common.Address { return common.Address{} }
diff --git a/core/vm/logger.go b/core/vm/logger.go
index cbdc8a744..ae62b6b57 100644
--- a/core/vm/logger.go
+++ b/core/vm/logger.go
@@ -36,19 +36,12 @@ func (self Storage) Copy() Storage {
 	return cpy
 }
 
-// StructLogCollector is the basic interface to capture emited logs by the EVM logger.
-type StructLogCollector interface {
-	// Adds the structured log to the collector.
-	AddStructLog(StructLog)
-}
-
 // LogConfig are the configuration options for structured logger the EVM
 type LogConfig struct {
-	DisableMemory  bool               // disable memory capture
-	DisableStack   bool               // disable stack capture
-	DisableStorage bool               // disable storage capture
-	FullStorage    bool               // show full storage (slow)
-	Collector      StructLogCollector // the log collector
+	DisableMemory  bool // disable memory capture
+	DisableStack   bool // disable stack capture
+	DisableStorage bool // disable storage capture
+	FullStorage    bool // show full storage (slow)
 }
 
 // StructLog is emitted to the Environment each cycle and lists information about the current internal state
@@ -65,36 +58,42 @@ type StructLog struct {
 	Err     error
 }
 
-// Logger is an EVM state logger and implements VmLogger.
+// Tracer is used to collect execution traces from an EVM transaction
+// execution. CaptureState is called for each step of the VM with the
+// current VM state.
+// Note that reference types are actual VM data structures; make copies
+// if you need to retain them beyond the current call.
+type Tracer interface {
+	CaptureState(env Environment, pc uint64, op OpCode, gas, cost *big.Int, memory *Memory, stack *Stack, contract *Contract, depth int, err error)
+}
+
+// StructLogger is an EVM state logger and implements Tracer.
 //
-// Logger can capture state based on the given Log configuration and also keeps
+// StructLogger can capture state based on the given Log configuration and also keeps
 // a track record of modified storage which is used in reporting snapshots of the
 // contract their storage.
-type Logger struct {
+type StructLogger struct {
 	cfg LogConfig
 
-	env           Environment
+	logs          []StructLog
 	changedValues map[common.Address]Storage
 }
 
-// newLogger returns a new logger
-func newLogger(cfg LogConfig, env Environment) *Logger {
-	return &Logger{
-		cfg:           cfg,
-		env:           env,
+// NewLogger returns a new logger
+func NewStructLogger(cfg *LogConfig) *StructLogger {
+	logger := &StructLogger{
 		changedValues: make(map[common.Address]Storage),
 	}
+	if cfg != nil {
+		logger.cfg = *cfg
+	}
+	return logger
 }
 
 // captureState logs a new structured log message and pushes it out to the environment
 //
 // captureState also tracks SSTORE ops to track dirty values.
-func (l *Logger) captureState(pc uint64, op OpCode, gas, cost *big.Int, memory *Memory, stack *stack, contract *Contract, depth int, err error) {
-	// short circuit if no log collector is present
-	if l.cfg.Collector == nil {
-		return
-	}
-
+func (l *StructLogger) CaptureState(env Environment, pc uint64, op OpCode, gas, cost *big.Int, memory *Memory, stack *Stack, contract *Contract, depth int, err error) {
 	// initialise new changed values storage container for this contract
 	// if not present.
 	if l.changedValues[contract.Address()] == nil {
@@ -139,7 +138,7 @@ func (l *Logger) captureState(pc uint64, op OpCode, gas, cost *big.Int, memory *
 			storage = make(Storage)
 			// Get the contract account and loop over each storage entry. This may involve looping over
 			// the trie and is a very expensive process.
-			l.env.Db().GetAccount(contract.Address()).ForEachStorage(func(key, value common.Hash) bool {
+			env.Db().GetAccount(contract.Address()).ForEachStorage(func(key, value common.Hash) bool {
 				storage[key] = value
 				// Return true, indicating we'd like to continue.
 				return true
@@ -150,9 +149,14 @@ func (l *Logger) captureState(pc uint64, op OpCode, gas, cost *big.Int, memory *
 		}
 	}
 	// create a new snaptshot of the EVM.
-	log := StructLog{pc, op, new(big.Int).Set(gas), cost, mem, stck, storage, l.env.Depth(), err}
-	// Add the log to the collector
-	l.cfg.Collector.AddStructLog(log)
+	log := StructLog{pc, op, new(big.Int).Set(gas), cost, mem, stck, storage, env.Depth(), err}
+
+	l.logs = append(l.logs, log)
+}
+
+// StructLogs returns a list of captured log entries
+func (l *StructLogger) StructLogs() []StructLog {
+	return l.logs
 }
 
 // StdErrFormat formats a slice of StructLogs to human readable format
diff --git a/core/vm/logger_test.go b/core/vm/logger_test.go
index 144569865..a8c4cbc0b 100644
--- a/core/vm/logger_test.go
+++ b/core/vm/logger_test.go
@@ -54,12 +54,11 @@ func newDummyEnv(ref *dummyContractRef) *dummyEnv {
 func (d dummyEnv) GetAccount(common.Address) Account {
 	return d.ref
 }
-func (d dummyEnv) AddStructLog(StructLog) {}
 
 func TestStoreCapture(t *testing.T) {
 	var (
 		env      = NewEnv(true, false)
-		logger   = newLogger(LogConfig{Collector: env}, env)
+		logger   = NewStructLogger(nil)
 		mem      = NewMemory()
 		stack    = newstack()
 		contract = NewContract(&dummyContractRef{}, &dummyContractRef{}, new(big.Int), new(big.Int), new(big.Int))
@@ -69,7 +68,7 @@ func TestStoreCapture(t *testing.T) {
 
 	var index common.Hash
 
-	logger.captureState(0, SSTORE, new(big.Int), new(big.Int), mem, stack, contract, 0, nil)
+	logger.CaptureState(env, 0, SSTORE, new(big.Int), new(big.Int), mem, stack, contract, 0, nil)
 	if len(logger.changedValues[contract.Address()]) == 0 {
 		t.Fatalf("expected exactly 1 changed value on address %x, got %d", contract.Address(), len(logger.changedValues[contract.Address()]))
 	}
@@ -86,18 +85,18 @@ func TestStorageCapture(t *testing.T) {
 		ref      = &dummyContractRef{}
 		contract = NewContract(ref, ref, new(big.Int), new(big.Int), new(big.Int))
 		env      = newDummyEnv(ref)
-		logger   = newLogger(LogConfig{Collector: env}, env)
+		logger   = NewStructLogger(nil)
 		mem      = NewMemory()
 		stack    = newstack()
 	)
 
-	logger.captureState(0, STOP, new(big.Int), new(big.Int), mem, stack, contract, 0, nil)
+	logger.CaptureState(env, 0, STOP, new(big.Int), new(big.Int), mem, stack, contract, 0, nil)
 	if ref.calledForEach {
 		t.Error("didn't expect for each to be called")
 	}
 
-	logger = newLogger(LogConfig{Collector: env, FullStorage: true}, env)
-	logger.captureState(0, STOP, new(big.Int), new(big.Int), mem, stack, contract, 0, nil)
+	logger = NewStructLogger(&LogConfig{FullStorage: true})
+	logger.CaptureState(env, 0, STOP, new(big.Int), new(big.Int), mem, stack, contract, 0, nil)
 	if !ref.calledForEach {
 		t.Error("expected for each to be called")
 	}
diff --git a/core/vm/runtime/env.go b/core/vm/runtime/env.go
index d8c98e545..a4793c98f 100644
--- a/core/vm/runtime/env.go
+++ b/core/vm/runtime/env.go
@@ -39,8 +39,6 @@ type Env struct {
 	difficulty *big.Int
 	gasLimit   *big.Int
 
-	logs []vm.StructLog
-
 	getHashFn func(uint64) common.Hash
 
 	evm *vm.EVM
@@ -62,23 +60,11 @@ func NewEnv(cfg *Config, state *state.StateDB) vm.Environment {
 		Debug:     cfg.Debug,
 		EnableJit: !cfg.DisableJit,
 		ForceJit:  !cfg.DisableJit,
-
-		Logger: vm.LogConfig{
-			Collector: env,
-		},
 	})
 
 	return env
 }
 
-func (self *Env) StructLogs() []vm.StructLog {
-	return self.logs
-}
-
-func (self *Env) AddStructLog(log vm.StructLog) {
-	self.logs = append(self.logs, log)
-}
-
 func (self *Env) RuleSet() vm.RuleSet      { return self.ruleSet }
 func (self *Env) Vm() vm.Vm                { return self.evm }
 func (self *Env) Origin() common.Address   { return self.origin }
diff --git a/core/vm/segments.go b/core/vm/segments.go
index c69ceddf4..648d8a04a 100644
--- a/core/vm/segments.go
+++ b/core/vm/segments.go
@@ -24,7 +24,7 @@ type jumpSeg struct {
 	gas *big.Int
 }
 
-func (j jumpSeg) do(program *Program, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) ([]byte, error) {
+func (j jumpSeg) do(program *Program, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) ([]byte, error) {
 	if !contract.UseGas(j.gas) {
 		return nil, OutOfGasError
 	}
@@ -42,7 +42,7 @@ type pushSeg struct {
 	gas  *big.Int
 }
 
-func (s pushSeg) do(program *Program, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *stack) ([]byte, error) {
+func (s pushSeg) do(program *Program, pc *uint64, env Environment, contract *Contract, memory *Memory, stack *Stack) ([]byte, error) {
 	// Use the calculated gas. When insufficient gas is present, use all gas and return an
 	// Out Of Gas error
 	if !contract.UseGas(s.gas) {
diff --git a/core/vm/stack.go b/core/vm/stack.go
index 0046edec2..f6c1f76e4 100644
--- a/core/vm/stack.go
+++ b/core/vm/stack.go
@@ -24,58 +24,58 @@ import (
 // stack is an object for basic stack operations. Items popped to the stack are
 // expected to be changed and modified. stack does not take care of adding newly
 // initialised objects.
-type stack struct {
+type Stack struct {
 	data []*big.Int
 }
 
-func newstack() *stack {
-	return &stack{}
+func newstack() *Stack {
+	return &Stack{}
 }
 
-func (st *stack) Data() []*big.Int {
+func (st *Stack) Data() []*big.Int {
 	return st.data
 }
 
-func (st *stack) push(d *big.Int) {
+func (st *Stack) push(d *big.Int) {
 	// NOTE push limit (1024) is checked in baseCheck
 	//stackItem := new(big.Int).Set(d)
 	//st.data = append(st.data, stackItem)
 	st.data = append(st.data, d)
 }
-func (st *stack) pushN(ds ...*big.Int) {
+func (st *Stack) pushN(ds ...*big.Int) {
 	st.data = append(st.data, ds...)
 }
 
-func (st *stack) pop() (ret *big.Int) {
+func (st *Stack) pop() (ret *big.Int) {
 	ret = st.data[len(st.data)-1]
 	st.data = st.data[:len(st.data)-1]
 	return
 }
 
-func (st *stack) len() int {
+func (st *Stack) len() int {
 	return len(st.data)
 }
 
-func (st *stack) swap(n int) {
+func (st *Stack) swap(n int) {
 	st.data[st.len()-n], st.data[st.len()-1] = st.data[st.len()-1], st.data[st.len()-n]
 }
 
-func (st *stack) dup(n int) {
+func (st *Stack) dup(n int) {
 	st.push(new(big.Int).Set(st.data[st.len()-n]))
 }
 
-func (st *stack) peek() *big.Int {
+func (st *Stack) peek() *big.Int {
 	return st.data[st.len()-1]
 }
 
-func (st *stack) require(n int) error {
+func (st *Stack) require(n int) error {
 	if st.len() < n {
 		return fmt.Errorf("stack underflow (%d <=> %d)", len(st.data), n)
 	}
 	return nil
 }
 
-func (st *stack) Print() {
+func (st *Stack) Print() {
 	fmt.Println("### stack ###")
 	if len(st.data) > 0 {
 		for i, val := range st.data {
diff --git a/core/vm/vm.go b/core/vm/vm.go
index 52e782b23..9d7b55058 100644
--- a/core/vm/vm.go
+++ b/core/vm/vm.go
@@ -33,7 +33,7 @@ type Config struct {
 	Debug     bool
 	EnableJit bool
 	ForceJit  bool
-	Logger    LogConfig
+	Tracer    Tracer
 }
 
 // EVM is used to run Ethereum based contracts and will utilise the
@@ -44,22 +44,14 @@ type EVM struct {
 	env       Environment
 	jumpTable vmJumpTable
 	cfg       Config
-
-	logger *Logger
 }
 
 // New returns a new instance of the EVM.
 func New(env Environment, cfg Config) *EVM {
-	var logger *Logger
-	if cfg.Debug {
-		logger = newLogger(cfg.Logger, env)
-	}
-
 	return &EVM{
 		env:       env,
 		jumpTable: newJumpTable(env.RuleSet(), env.BlockNumber()),
 		cfg:       cfg,
-		logger:    logger,
 	}
 }
 
@@ -149,7 +141,7 @@ func (evm *EVM) Run(contract *Contract, input []byte) (ret []byte, err error) {
 	// User defer pattern to check for an error and, based on the error being nil or not, use all gas and return.
 	defer func() {
 		if err != nil && evm.cfg.Debug {
-			evm.logger.captureState(pc, op, contract.Gas, cost, mem, stack, contract, evm.env.Depth(), err)
+			evm.cfg.Tracer.CaptureState(evm.env, pc, op, contract.Gas, cost, mem, stack, contract, evm.env.Depth(), err)
 		}
 	}()
 
@@ -191,7 +183,7 @@ func (evm *EVM) Run(contract *Contract, input []byte) (ret []byte, err error) {
 		mem.Resize(newMemSize.Uint64())
 		// Add a log message
 		if evm.cfg.Debug {
-			evm.logger.captureState(pc, op, contract.Gas, cost, mem, stack, contract, evm.env.Depth(), nil)
+			evm.cfg.Tracer.CaptureState(evm.env, pc, op, contract.Gas, cost, mem, stack, contract, evm.env.Depth(), nil)
 		}
 
 		if opPtr := evm.jumpTable[op]; opPtr.valid {
@@ -241,7 +233,7 @@ func (evm *EVM) Run(contract *Contract, input []byte) (ret []byte, err error) {
 
 // calculateGasAndSize calculates the required given the opcode and stack items calculates the new memorysize for
 // the operation. This does not reduce gas or resizes the memory.
-func calculateGasAndSize(env Environment, contract *Contract, caller ContractRef, op OpCode, statedb Database, mem *Memory, stack *stack) (*big.Int, *big.Int, error) {
+func calculateGasAndSize(env Environment, contract *Contract, caller ContractRef, op OpCode, statedb Database, mem *Memory, stack *Stack) (*big.Int, *big.Int, error) {
 	var (
 		gas                 = new(big.Int)
 		newMemSize *big.Int = new(big.Int)