core: set extended round block reward to zero (#298)

To discourage DKG set from prolonging the round indefinitely, we set the
block reward of the extended round to 0. The gas fee is send to the
DEXON governance owner for safe keeping and later used by the foundation.

2 files changed, 66 insertions, 1 deletions

diff --git a/core/chain_makers.go b/core/chain_makers.go
index 2566e382c..99f23c58d 100644
--- a/core/chain_makers.go
+++ b/core/chain_makers.go
@@ -86,6 +86,7 @@ func (b *BlockGen) SetNonce(nonce types.BlockNonce) {
 // added. Notably, contract code relying on the BLOCKHASH instruction
 // will panic during execution.
 func (b *BlockGen) AddTx(tx *types.Transaction) {
+	TestingMode = true
 	b.AddTxWithChain(nil, tx)
 }
 
diff --git a/core/state_transition.go b/core/state_transition.go
index 02d58575b..f5ac9bde6 100644
--- a/core/state_transition.go
+++ b/core/state_transition.go
@@ -21,7 +21,9 @@ import (
 	"flag"
 	"math"
 	"math/big"
+	"sync/atomic"
 
+	dexCore "github.com/dexon-foundation/dexon-consensus/core"
 	"github.com/dexon-foundation/dexon/common"
 	"github.com/dexon-foundation/dexon/core/vm"
 	"github.com/dexon-foundation/dexon/log"
@@ -29,11 +31,19 @@ import (
 )
 
 var legacyEvm = flag.Bool("legacy-evm", false, "make evm run origin logic")
+var TestingMode = false
 
 var (
 	errInsufficientBalanceForGas = errors.New("insufficient balance to pay for gas")
 )
 
+var lastInExtendedRoundResultCache atomic.Value
+
+type lastInExtendedRoundResultType struct {
+	Height uint64
+	Result bool
+}
+
 /*
 The State Transitioning Model
 
@@ -180,6 +190,53 @@ func (st *StateTransition) preCheck() error {
 	return st.buyGas()
 }
 
+func (st *StateTransition) inExtendedRound() bool {
+	// If we are running tests with chian_makers.go, there will be no valid
+	// blockchain instance for st.evm.StateAtNumber to work correctly. Simply
+	// return false in this case.
+	if TestingMode {
+		return false
+	}
+
+	if h := lastInExtendedRoundResultCache.Load(); h != nil {
+		res := h.(*lastInExtendedRoundResultType)
+		if res.Height == st.evm.BlockNumber.Uint64() {
+			return res.Result
+		}
+	}
+
+	gs := vm.GovernanceState{st.state}
+
+	round := st.evm.Round.Uint64()
+	if round < dexCore.ConfigRoundShift {
+		round = 0
+	} else {
+		round -= dexCore.ConfigRoundShift
+	}
+
+	configHeight := gs.RoundHeight(new(big.Int).SetUint64(round))
+	state, err := st.evm.StateAtNumber(configHeight.Uint64())
+	if err != nil {
+		panic(err)
+	}
+	rgs := vm.GovernanceState{state}
+
+	roundEnd := gs.RoundHeight(st.evm.Round).Uint64() + rgs.RoundLength().Uint64()
+
+	// Round 0 starts and height 0 instead of height 1.
+	if round == 0 {
+		roundEnd += 1
+	}
+
+	res := st.evm.BlockNumber.Uint64() >= roundEnd
+
+	lastInExtendedRoundResultCache.Store(&lastInExtendedRoundResultType{
+		Height: st.evm.BlockNumber.Uint64(),
+		Result: res,
+	})
+	return res
+}
+
 // TransitionDb will transition the state by applying the current message and
 // returning the result including the used gas. It returns an error if failed.
 // An error indicates a consensus issue.
@@ -230,7 +287,14 @@ func (st *StateTransition) TransitionDb() (ret []byte, usedGas uint64, failed bo
 	} else {
 		st.dexonRefundGas()
 	}
-	st.state.AddBalance(st.evm.Coinbase, new(big.Int).Mul(new(big.Int).SetUint64(st.gasUsed()), st.gasPrice))
+
+	receiver := st.evm.Coinbase
+	if !*legacyEvm && st.inExtendedRound() {
+		gs := vm.GovernanceState{st.state}
+		receiver = gs.Owner()
+	}
+
+	st.state.AddBalance(receiver, new(big.Int).Mul(new(big.Int).SetUint64(st.gasUsed()), st.gasPrice))
 
 	return ret, st.gasUsed(), vmerr != nil, err
 }