From 33f8943543b41ae6b0b798ffa85fdc165779fc21 Mon Sep 17 00:00:00 2001
From: Ethan Buchman <ethan@coinculture.info>
Date: Mon, 16 Mar 2015 17:28:53 -0700
Subject: [PATCH] consensus: broadcast evidence tx on
 ErrVoteConflictingSignature

---
 block/vote.go         | 18 +++++++++++++-----
 consensus/reactor.go  | 17 +++++++++++++++--
 consensus/vote_set.go |  5 ++++-
 state/state.go        |  2 +-
 4 files changed, 33 insertions(+), 9 deletions(-)

diff --git a/block/vote.go b/block/vote.go
index 079f8515d..b3425cf90 100644
--- a/block/vote.go
+++ b/block/vote.go
@@ -11,13 +11,21 @@ import (
 )
 
 var (
-	ErrVoteUnexpectedStep       = errors.New("Unexpected step")
-	ErrVoteInvalidAccount       = errors.New("Invalid round vote account")
-	ErrVoteInvalidSignature     = errors.New("Invalid round vote signature")
-	ErrVoteInvalidBlockHash     = errors.New("Invalid block hash")
-	ErrVoteConflictingSignature = errors.New("Conflicting round vote signature")
+	ErrVoteUnexpectedStep   = errors.New("Unexpected step")
+	ErrVoteInvalidAccount   = errors.New("Invalid round vote account")
+	ErrVoteInvalidSignature = errors.New("Invalid round vote signature")
+	ErrVoteInvalidBlockHash = errors.New("Invalid block hash")
 )
 
+type ErrVoteConflictingSignature struct {
+	VoteA *Vote
+	VoteB *Vote
+}
+
+func (err *ErrVoteConflictingSignature) Error() string {
+	return "Conflicting round vote signature"
+}
+
 // Represents a prevote, precommit, or commit vote from validators for consensus.
 // Commit votes get aggregated into the next block's Validaiton.
 // See the whitepaper for details.
diff --git a/consensus/reactor.go b/consensus/reactor.go
index a4381bf1a..7d1cd49d0 100644
--- a/consensus/reactor.go
+++ b/consensus/reactor.go
@@ -175,8 +175,21 @@ func (conR *ConsensusReactor) Receive(chId byte, peer *p2p.Peer, msgBytes []byte
 			address, _ := rs.Validators.GetByIndex(validatorIndex)
 			added, index, err := conR.conS.AddVote(address, vote)
 			if err != nil {
-				// Probably an invalid signature. Bad peer.
-				log.Warn("Error attempting to add vote", "error", err)
+				// If conflicting sig, broadcast evidence tx for slashing. Else punish peer.
+				if errDupe, ok := err.(*blk.ErrVoteConflictingSignature); ok {
+					log.Warn("Found conflicting vote. Publish evidence")
+					evidenceTx := &blk.DupeoutTx{
+						Address: address,
+						VoteA:   *errDupe.VoteA,
+						VoteB:   *errDupe.VoteB,
+					}
+					conR.conS.mempoolReactor.BroadcastTx(evidenceTx) // shouldn't need to check returned err
+				} else {
+					// Probably an invalid signature. Bad peer.
+					log.Warn("Error attempting to add vote", "error", err)
+
+					// TODO: punish peer
+				}
 			}
 			// Initialize Prevotes/Precommits/Commits if needed
 			ps.EnsureVoteBitArrays(rs.Height, rs.Validators.Size())
diff --git a/consensus/vote_set.go b/consensus/vote_set.go
index 9bf098cb6..627d0e2bb 100644
--- a/consensus/vote_set.go
+++ b/consensus/vote_set.go
@@ -106,7 +106,10 @@ func (voteSet *VoteSet) addVote(valIndex uint, vote *blk.Vote) (bool, uint, erro
 		if bytes.Equal(existingVote.BlockHash, vote.BlockHash) {
 			return false, 0, nil
 		} else {
-			return false, 0, blk.ErrVoteConflictingSignature
+			return false, 0, &blk.ErrVoteConflictingSignature{
+				VoteA: existingVote,
+				VoteB: vote,
+			}
 		}
 	}
 
diff --git a/state/state.go b/state/state.go
index 49881c548..ceca46323 100644
--- a/state/state.go
+++ b/state/state.go
@@ -388,7 +388,7 @@ func (s *State) ExecTx(tx_ blk.Tx) error {
 			return errors.New("DupeoutTx heights don't match")
 		}
 		if tx.VoteA.Type == blk.VoteTypeCommit && tx.VoteA.Round < tx.VoteB.Round {
-			// Check special case.
+			// Check special case (not an error, validator must be slashed!)
 			// Validators should not sign another vote after committing.
 		} else {
 			if tx.VoteA.Round != tx.VoteB.Round {