Introduce CommitSig alias for Vote in Commit (#3245)

* types: memoize height/round in commit instead of first vote

* types: commit.ValidateBasic in VerifyCommit

* types: new CommitSig alias for Vote

In preparation for reducing the redundancy in Commits, we introduce the
CommitSig as an alias for Vote. This is non-breaking on the protocol,
and minor breaking on the Go API, as Commit now contains a list of
CommitSig instead of Vote.

* remove dependence on ToVote

* update some comments

* fix tests

* fix tests

* fixes from review

types/block.go

@@ -477,39 +477,77 @@ func (h *Header) StringIndented(indent string) string {
 
 //-------------------------------------
 
+// CommitSig is a vote included in a Commit.
+// For now, it is identical to a vote,
+// but in the future it will contain fewer fields
+// to eliminate the redundancy in commits.
+// See https://github.com/tendermint/tendermint/issues/1648.
+type CommitSig Vote
+
+// String returns the underlying Vote.String()
+func (cs *CommitSig) String() string {
+	return cs.toVote().String()
+}
+
+// toVote converts the CommitSig to a vote.
+// Once CommitSig has fewer fields than vote,
+// converting to a Vote will require more information.
+func (cs *CommitSig) toVote() *Vote {
+	if cs == nil {
+		return nil
+	}
+	v := Vote(*cs)
+	return &v
+}
+
 // Commit contains the evidence that a block was committed by a set of validators.
 // NOTE: Commit is empty for height 1, but never nil.
 type Commit struct {
 	// NOTE: The Precommits are in order of address to preserve the bonded ValidatorSet order.
 	// Any peer with a block can gossip precommits by index with a peer without recalculating the
 	// active ValidatorSet.
-	BlockID    BlockID `json:"block_id"`
-	Precommits []*Vote `json:"precommits"`
+	BlockID    BlockID      `json:"block_id"`
+	Precommits []*CommitSig `json:"precommits"`
 
 	// Volatile
-	firstPrecommit *Vote
-	hash           cmn.HexBytes
-	bitArray       *cmn.BitArray
+	height   int64
+	round    int
+	hash     cmn.HexBytes
+	bitArray *cmn.BitArray
 }
 
-// FirstPrecommit returns the first non-nil precommit in the commit.
-// If all precommits are nil, it returns an empty precommit with height 0.
-func (commit *Commit) FirstPrecommit() *Vote {
+// VoteSignBytes constructs the SignBytes for the given CommitSig.
+// The only unique part of the SignBytes is the Timestamp - all other fields
+// signed over are otherwise the same for all validators.
+func (commit *Commit) VoteSignBytes(chainID string, cs *CommitSig) []byte {
+	return cs.toVote().SignBytes(chainID)
+}
+
+// memoizeHeightRound memoizes the height and round of the commit using
+// the first non-nil vote.
+func (commit *Commit) memoizeHeightRound() {
 	if len(commit.Precommits) == 0 {
-		return nil
+		return
 	}
-	if commit.firstPrecommit != nil {
-		return commit.firstPrecommit
+	if commit.height > 0 {
+		return
 	}
 	for _, precommit := range commit.Precommits {
 		if precommit != nil {
-			commit.firstPrecommit = precommit
-			return precommit
+			commit.height = precommit.Height
+			commit.round = precommit.Round
+			return
 		}
 	}
-	return &Vote{
-		Type: PrecommitType,
-	}
+}
+
+// ToVote converts a CommitSig to a Vote.
+// If the CommitSig is nil, the Vote will be nil.
+// When CommitSig is reduced to contain fewer fields,
+// this will need access to the ValidatorSet to properly
+// reconstruct the vote.
+func (commit *Commit) ToVote(cs *CommitSig) *Vote {
+	return cs.toVote()
 }
 
 // Height returns the height of the commit
@@ -517,7 +555,8 @@ func (commit *Commit) Height() int64 {
 	if len(commit.Precommits) == 0 {
 		return 0
 	}
-	return commit.FirstPrecommit().Height
+	commit.memoizeHeightRound()
+	return commit.height
 }
 
 // Round returns the round of the commit
@@ -525,7 +564,8 @@ func (commit *Commit) Round() int {
 	if len(commit.Precommits) == 0 {
 		return 0
 	}
-	return commit.FirstPrecommit().Round
+	commit.memoizeHeightRound()
+	return commit.round
 }
 
 // Type returns the vote type of the commit, which is always VoteTypePrecommit
@@ -554,12 +594,13 @@ func (commit *Commit) BitArray() *cmn.BitArray {
 	return commit.bitArray
 }
 
-// GetByIndex returns the vote corresponding to a given validator index
+// GetByIndex returns the vote corresponding to a given validator index.
+// Implements VoteSetReader.
 func (commit *Commit) GetByIndex(index int) *Vote {
-	return commit.Precommits[index]
+	return commit.Precommits[index].toVote()
 }
 
-// IsCommit returns true if there is at least one vote
+// IsCommit returns true if there is at least one vote.
 func (commit *Commit) IsCommit() bool {
 	return len(commit.Precommits) != 0
 }

types/block_test.go

@@ -198,7 +198,6 @@ func TestCommit(t *testing.T) {
 	commit, err := MakeCommit(lastID, h-1, 1, voteSet, vals)
 	require.NoError(t, err)
 
-	assert.NotNil(t, commit.FirstPrecommit())
 	assert.Equal(t, h-1, commit.Height())
 	assert.Equal(t, 1, commit.Round())
 	assert.Equal(t, PrecommitType, SignedMsgType(commit.Type()))

types/validator_set.go

@@ -368,6 +368,10 @@ func (vals *ValidatorSet) Iterate(fn func(index int, val *Validator) bool) {
 
 // Verify that +2/3 of the set had signed the given signBytes.
 func (vals *ValidatorSet) VerifyCommit(chainID string, blockID BlockID, height int64, commit *Commit) error {
+
+	if err := commit.ValidateBasic(); err != nil {
+		return err
+	}
 	if vals.Size() != len(commit.Precommits) {
 		return fmt.Errorf("Invalid commit -- wrong set size: %v vs %v", vals.Size(), len(commit.Precommits))
 	}
@@ -380,24 +384,14 @@ func (vals *ValidatorSet) VerifyCommit(chainID string, blockID BlockID, height i
 	}
 
 	talliedVotingPower := int64(0)
-	round := commit.Round()
 
 	for idx, precommit := range commit.Precommits {
 		if precommit == nil {
 			continue // OK, some precommits can be missing.
 		}
-		if precommit.Height != height {
-			return fmt.Errorf("Invalid commit -- wrong height: want %v got %v", height, precommit.Height)
-		}
-		if precommit.Round != round {
-			return fmt.Errorf("Invalid commit -- wrong round: want %v got %v", round, precommit.Round)
-		}
-		if precommit.Type != PrecommitType {
-			return fmt.Errorf("Invalid commit -- not precommit @ index %v", idx)
-		}
 		_, val := vals.GetByIndex(idx)
 		// Validate signature.
-		precommitSignBytes := precommit.SignBytes(chainID)
+		precommitSignBytes := commit.VoteSignBytes(chainID, precommit)
 		if !val.PubKey.VerifyBytes(precommitSignBytes, precommit.Signature) {
 			return fmt.Errorf("Invalid commit -- invalid signature: %v", precommit)
 		}
@@ -481,7 +475,7 @@ func (vals *ValidatorSet) VerifyFutureCommit(newSet *ValidatorSet, chainID strin
 		seen[idx] = true
 
 		// Validate signature.
-		precommitSignBytes := precommit.SignBytes(chainID)
+		precommitSignBytes := commit.VoteSignBytes(chainID, precommit)
 		if !val.PubKey.VerifyBytes(precommitSignBytes, precommit.Signature) {
 			return cmn.NewError("Invalid commit -- invalid signature: %v", precommit)
 		}

types/validator_set_test.go

@@ -565,7 +565,7 @@ func TestValidatorSetVerifyCommit(t *testing.T) {
 	vote.Signature = sig
 	commit := &Commit{
 		BlockID:    blockID,
-		Precommits: []*Vote{vote},
+		Precommits: []*CommitSig{vote.CommitSig()},
 	}
 
 	badChainID := "notmychainID"
@@ -573,7 +573,7 @@ func TestValidatorSetVerifyCommit(t *testing.T) {
 	badHeight := height + 1
 	badCommit := &Commit{
 		BlockID:    blockID,
-		Precommits: []*Vote{nil},
+		Precommits: []*CommitSig{nil},
 	}
 
 	// test some error cases

types/vote.go

@@ -59,6 +59,16 @@ type Vote struct {
 	Signature        []byte        `json:"signature"`
 }
 
+// CommitSig converts the Vote to a CommitSig.
+// If the Vote is nil, the CommitSig will be nil.
+func (vote *Vote) CommitSig() *CommitSig {
+	if vote == nil {
+		return nil
+	}
+	cs := CommitSig(*vote)
+	return &cs
+}
+
 func (vote *Vote) SignBytes(chainID string) []byte {
 	bz, err := cdc.MarshalBinaryLengthPrefixed(CanonicalizeVote(chainID, vote))
 	if err != nil {

types/vote_set.go

@@ -541,11 +541,13 @@ func (voteSet *VoteSet) MakeCommit() *Commit {
 	}
 
 	// For every validator, get the precommit
-	votesCopy := make([]*Vote, len(voteSet.votes))
-	copy(votesCopy, voteSet.votes)
+	commitSigs := make([]*CommitSig, len(voteSet.votes))
+	for i, v := range voteSet.votes {
+		commitSigs[i] = v.CommitSig()
+	}
 	return &Commit{
 		BlockID:    *voteSet.maj23,
-		Precommits: votesCopy,
+		Precommits: commitSigs,
 	}
 }
 

types/vote_test.go

@@ -7,6 +7,7 @@ import (
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+	amino "github.com/tendermint/go-amino"
 	"github.com/tendermint/tendermint/crypto"
 	"github.com/tendermint/tendermint/crypto/ed25519"
 	"github.com/tendermint/tendermint/crypto/tmhash"
@@ -43,6 +44,19 @@ func exampleVote(t byte) *Vote {
 	}
 }
 
+// Ensure that Vote and CommitSig have the same encoding.
+// This ensures using CommitSig isn't a breaking change.
+// This test will fail and can be removed once CommitSig contains only sigs and
+// timestamps.
+func TestVoteEncoding(t *testing.T) {
+	vote := examplePrecommit()
+	commitSig := vote.CommitSig()
+	cdc := amino.NewCodec()
+	bz1 := cdc.MustMarshalBinaryBare(vote)
+	bz2 := cdc.MustMarshalBinaryBare(commitSig)
+	assert.Equal(t, bz1, bz2)
+}
+
 func TestVoteSignable(t *testing.T) {
 	vote := examplePrecommit()
 	signBytes := vote.SignBytes("test_chain_id")