From 0c417aaa02c5cc8bb6a9629ac2502e0c4d200071 Mon Sep 17 00:00:00 2001
From: Determinant <tederminant@gmail.com>
Date: Thu, 20 Aug 2020 00:03:12 -0400
Subject: impl state transfer for C-to-X Tx

---
 plugin/evm/export_tx.go | 24 ++++++++++++++++++++++--
 plugin/evm/import_tx.go | 23 ++++++++++++++++-------
 plugin/evm/tx.go        |  2 +-
 plugin/evm/vm.go        |  9 +++++++++
 4 files changed, 48 insertions(+), 10 deletions(-)

diff --git a/plugin/evm/export_tx.go b/plugin/evm/export_tx.go
index 249b7cf..9af11e0 100644
--- a/plugin/evm/export_tx.go
+++ b/plugin/evm/export_tx.go
@@ -5,15 +5,17 @@ package evm
 
 import (
 	"fmt"
+	"math/big"
+
+	"github.com/ava-labs/coreth/core/state"
 
 	"github.com/ava-labs/gecko/database"
 	"github.com/ava-labs/gecko/ids"
 	"github.com/ava-labs/gecko/snow"
 	"github.com/ava-labs/gecko/utils/crypto"
+	safemath "github.com/ava-labs/gecko/utils/math"
 	"github.com/ava-labs/gecko/vms/components/avax"
 	"github.com/ava-labs/gecko/vms/secp256k1fx"
-
-	safemath "github.com/ava-labs/gecko/utils/math"
 )
 
 // UnsignedExportTx is an unsigned ExportTx
@@ -31,6 +33,8 @@ type UnsignedExportTx struct {
 	Ins []EVMInput `serialize:"true" json:"inputs"`
 	// Outputs that are exported to the chain
 	ExportedOutputs []*avax.TransferableOutput `serialize:"true" json:"exportedOutputs"`
+	// EVM nonce
+	nonce uint64
 }
 
 // InputUTXOs returns an empty set
@@ -144,3 +148,19 @@ func (vm *VM) newExportTx(
 	}
 	return tx, utx.Verify(vm.ctx.XChainID, vm.ctx, vm.txFee, vm.ctx.AVAXAssetID)
 }
+
+func (tx *UnsignedExportTx) EVMStateTransfer(state *state.StateDB) error {
+	for _, from := range tx.Ins {
+		amount := new(big.Int).Mul(
+			new(big.Int).SetUint64(from.Amount), x2cRate)
+		if state.GetBalance(from.Address).Cmp(amount) < 0 {
+			return errInsufficientFunds
+		}
+		state.SubBalance(from.Address, amount)
+		if state.GetNonce(from.Address) != tx.nonce {
+			return errInvalidNonce
+		}
+		state.SetNonce(from.Address, tx.nonce+1)
+	}
+	return nil
+}
diff --git a/plugin/evm/import_tx.go b/plugin/evm/import_tx.go
index 995e488..68e5fed 100644
--- a/plugin/evm/import_tx.go
+++ b/plugin/evm/import_tx.go
@@ -34,8 +34,8 @@ type UnsignedImportTx struct {
 	ImportedInputs []*avax.TransferableInput `serialize:"true" json:"importedInputs"`
 	// Outputs
 	Outs []EVMOutput `serialize:"true" json:"outputs"`
-	// Memo field contains arbitrary bytes, up to maxMemoSize
-	Memo []byte `serialize:"true" json:"memo"`
+	// EVM nonce
+	nonce uint64
 }
 
 // InputUTXOs returns the UTXOIDs of the imported funds
@@ -193,6 +193,10 @@ func (vm *VM) newImportTx(
 		})
 	}
 
+	nonce, err := vm.GetAcceptedNonce(to)
+	if err != nil {
+		return nil, err
+	}
 	// Create the transaction
 	utx := &UnsignedImportTx{
 		NetworkID:      vm.ctx.NetworkID,
@@ -200,6 +204,7 @@ func (vm *VM) newImportTx(
 		Outs:           outs,
 		ImportedInputs: importedInputs,
 		SourceChain:    chainID,
+		nonce:          nonce,
 	}
 	tx := &Tx{UnsignedTx: utx}
 	if err := tx.Sign(vm.codec, signers); err != nil {
@@ -208,11 +213,15 @@ func (vm *VM) newImportTx(
 	return tx, utx.Verify(vm.ctx.XChainID, vm.ctx, vm.txFee, vm.ctx.AVAXAssetID)
 }
 
-func (tx *UnsignedImportTx) EVMStateTransfer(state *state.StateDB) {
+func (tx *UnsignedImportTx) EVMStateTransfer(state *state.StateDB) error {
 	for _, to := range tx.Outs {
-		amount := new(big.Int).SetUint64(to.Amount)
-		state.AddBalance(to.Address, new(big.Int).Mul(amount, x2cRate))
-		nonce := state.GetNonce(to.Address)
-		state.SetNonce(to.Address, nonce+1)
+		state.AddBalance(to.Address,
+			new(big.Int).Mul(
+				new(big.Int).SetUint64(to.Amount), x2cRate))
+		if state.GetNonce(to.Address) != tx.nonce {
+			return errInvalidNonce
+		}
+		state.SetNonce(to.Address, tx.nonce+1)
 	}
+	return nil
 }
diff --git a/plugin/evm/tx.go b/plugin/evm/tx.go
index dfd49f0..7e60c79 100644
--- a/plugin/evm/tx.go
+++ b/plugin/evm/tx.go
@@ -65,7 +65,7 @@ type UnsignedAtomicTx interface {
 	// Accept this transaction with the additionally provided state transitions.
 	Accept(ctx *snow.Context, batch database.Batch) error
 
-	EVMStateTransfer(state *state.StateDB)
+	EVMStateTransfer(state *state.StateDB) error
 }
 
 // Tx is a signed transaction
diff --git a/plugin/evm/vm.go b/plugin/evm/vm.go
index 53810ee..6155728 100644
--- a/plugin/evm/vm.go
+++ b/plugin/evm/vm.go
@@ -95,6 +95,7 @@ var (
 	errNoExportOutputs            = errors.New("no export outputs")
 	errOutputsNotSorted           = errors.New("outputs not sorted")
 	errOverflowExport             = errors.New("overflow when computing export amount + txFee")
+	errInvalidNonce               = errors.New("invalid nonce")
 )
 
 func maxDuration(x, y time.Duration) time.Duration {
@@ -721,3 +722,11 @@ func (vm *VM) GetSpendableCanonical(keys []*crypto.PrivateKeySECP256K1R, amount
 	}
 	return inputs, signers, nil
 }
+
+func (vm *VM) GetAcceptedNonce(address common.Address) (uint64, error) {
+	state, err := vm.chain.BlockState(vm.lastAccepted.ethBlock)
+	if err != nil {
+		return 0, err
+	}
+	return state.GetNonce(address), nil
+}
-- 
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