accounts, consensus, core, eth: make chain maker consensus agnostic (#15497)

* accounts, consensus, core, eth: make chain maker consensus agnostic

* consensus, core: move CalcDifficulty to Engine interface

* consensus: add docs for calcDifficulty function

* consensus, core: minor comment fixups

4 files changed, 41 insertions, 12 deletions

diff --git a/consensus/clique/clique.go b/consensus/clique/clique.go
index a98058141..2bdad9092 100644
--- a/consensus/clique/clique.go
+++ b/consensus/clique/clique.go
@@ -510,7 +510,6 @@ func (c *Clique) Prepare(chain consensus.ChainReader, header *types.Header) erro
 	header.Nonce = types.BlockNonce{}
 
 	number := header.Number.Uint64()
-
 	// Assemble the voting snapshot to check which votes make sense
 	snap, err := c.snapshot(chain, number-1, header.ParentHash, nil)
 	if err != nil {
@@ -538,10 +537,8 @@ func (c *Clique) Prepare(chain consensus.ChainReader, header *types.Header) erro
 		c.lock.RUnlock()
 	}
 	// Set the correct difficulty
-	header.Difficulty = diffNoTurn
-	if snap.inturn(header.Number.Uint64(), c.signer) {
-		header.Difficulty = diffInTurn
-	}
+	header.Difficulty = CalcDifficulty(snap, c.signer)
+
 	// Ensure the extra data has all it's components
 	if len(header.Extra) < extraVanity {
 		header.Extra = append(header.Extra, bytes.Repeat([]byte{0x00}, extraVanity-len(header.Extra))...)
@@ -655,6 +652,27 @@ func (c *Clique) Seal(chain consensus.ChainReader, block *types.Block, stop <-ch
 	return block.WithSeal(header), nil
 }
 
+// CalcDifficulty is the difficulty adjustment algorithm. It returns the difficulty
+// that a new block should have based on the previous blocks in the chain and the
+// current signer.
+func (c *Clique) CalcDifficulty(chain consensus.ChainReader, time uint64, parent *types.Header) *big.Int {
+	snap, err := c.snapshot(chain, parent.Number.Uint64(), parent.Hash(), nil)
+	if err != nil {
+		return nil
+	}
+	return CalcDifficulty(snap, c.signer)
+}
+
+// CalcDifficulty is the difficulty adjustment algorithm. It returns the difficulty
+// that a new block should have based on the previous blocks in the chain and the
+// current signer.
+func CalcDifficulty(snap *Snapshot, signer common.Address) *big.Int {
+	if snap.inturn(snap.Number+1, signer) {
+		return new(big.Int).Set(diffInTurn)
+	}
+	return new(big.Int).Set(diffNoTurn)
+}
+
 // APIs implements consensus.Engine, returning the user facing RPC API to allow
 // controlling the signer voting.
 func (c *Clique) APIs(chain consensus.ChainReader) []rpc.API {
diff --git a/consensus/consensus.go b/consensus/consensus.go
index 865238cee..be5e661c1 100644
--- a/consensus/consensus.go
+++ b/consensus/consensus.go
@@ -23,6 +23,7 @@ import (
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/params"
 	"github.com/ethereum/go-ethereum/rpc"
+	"math/big"
 )
 
 // ChainReader defines a small collection of methods needed to access the local
@@ -88,6 +89,10 @@ type Engine interface {
 	// seal place on top.
 	Seal(chain ChainReader, block *types.Block, stop <-chan struct{}) (*types.Block, error)
 
+	// CalcDifficulty is the difficulty adjustment algorithm. It returns the difficulty
+	// that a new block should have.
+	CalcDifficulty(chain ChainReader, time uint64, parent *types.Header) *big.Int
+
 	// APIs returns the RPC APIs this consensus engine provides.
 	APIs(chain ChainReader) []rpc.API
 }
diff --git a/consensus/ethash/consensus.go b/consensus/ethash/consensus.go
index 2bdb18677..5fe67c851 100644
--- a/consensus/ethash/consensus.go
+++ b/consensus/ethash/consensus.go
@@ -240,7 +240,8 @@ func (ethash *Ethash) verifyHeader(chain consensus.ChainReader, header, parent *
 		return errZeroBlockTime
 	}
 	// Verify the block's difficulty based in it's timestamp and parent's difficulty
-	expected := CalcDifficulty(chain.Config(), header.Time.Uint64(), parent)
+	expected := ethash.CalcDifficulty(chain, header.Time.Uint64(), parent)
+
 	if expected.Cmp(header.Difficulty) != 0 {
 		return fmt.Errorf("invalid difficulty: have %v, want %v", header.Difficulty, expected)
 	}
@@ -287,7 +288,13 @@ func (ethash *Ethash) verifyHeader(chain consensus.ChainReader, header, parent *
 // CalcDifficulty is the difficulty adjustment algorithm. It returns
 // the difficulty that a new block should have when created at time
 // given the parent block's time and difficulty.
-// TODO (karalabe): Move the chain maker into this package and make this private!
+func (ethash *Ethash) CalcDifficulty(chain consensus.ChainReader, time uint64, parent *types.Header) *big.Int {
+	return CalcDifficulty(chain.Config(), time, parent)
+}
+
+// CalcDifficulty is the difficulty adjustment algorithm. It returns
+// the difficulty that a new block should have when created at time
+// given the parent block's time and difficulty.
 func CalcDifficulty(config *params.ChainConfig, time uint64, parent *types.Header) *big.Int {
 	next := new(big.Int).Add(parent.Number, big1)
 	switch {
@@ -502,8 +509,7 @@ func (ethash *Ethash) Prepare(chain consensus.ChainReader, header *types.Header)
 	if parent == nil {
 		return consensus.ErrUnknownAncestor
 	}
-	header.Difficulty = CalcDifficulty(chain.Config(), header.Time.Uint64(), parent)
-
+	header.Difficulty = ethash.CalcDifficulty(chain, header.Time.Uint64(), parent)
 	return nil
 }
 
@@ -511,7 +517,7 @@ func (ethash *Ethash) Prepare(chain consensus.ChainReader, header *types.Header)
 // setting the final state and assembling the block.
 func (ethash *Ethash) Finalize(chain consensus.ChainReader, header *types.Header, state *state.StateDB, txs []*types.Transaction, uncles []*types.Header, receipts []*types.Receipt) (*types.Block, error) {
 	// Accumulate any block and uncle rewards and commit the final state root
-	AccumulateRewards(chain.Config(), state, header, uncles)
+	accumulateRewards(chain.Config(), state, header, uncles)
 	header.Root = state.IntermediateRoot(chain.Config().IsEIP158(header.Number))
 
 	// Header seems complete, assemble into a block and return
@@ -527,8 +533,7 @@ var (
 // AccumulateRewards credits the coinbase of the given block with the mining
 // reward. The total reward consists of the static block reward and rewards for
 // included uncles. The coinbase of each uncle block is also rewarded.
-// TODO (karalabe): Move the chain maker into this package and make this private!
-func AccumulateRewards(config *params.ChainConfig, state *state.StateDB, header *types.Header, uncles []*types.Header) {
+func accumulateRewards(config *params.ChainConfig, state *state.StateDB, header *types.Header, uncles []*types.Header) {
 	// Select the correct block reward based on chain progression
 	blockReward := FrontierBlockReward
 	if config.IsByzantium(header.Number) {
diff --git a/consensus/ethash/consensus_test.go b/consensus/ethash/consensus_test.go
index a58d220ef..438a99dd6 100644
--- a/consensus/ethash/consensus_test.go
+++ b/consensus/ethash/consensus_test.go
@@ -71,6 +71,7 @@ func TestCalcDifficulty(t *testing.T) {
 	}
 
 	config := &params.ChainConfig{HomesteadBlock: big.NewInt(1150000)}
+
 	for name, test := range tests {
 		number := new(big.Int).Sub(test.CurrentBlocknumber, big.NewInt(1))
 		diff := CalcDifficulty(config, test.CurrentTimestamp, &types.Header{