voting module raises CriticalDuplicateVote if there's a duplicate vote

bigchaindb/exceptions.py

@@ -8,3 +8,7 @@ class CriticalDoubleSpend(BigchainDBError):
 
 class CriticalDoubleInclusion(BigchainDBError):
     """Data integrity error that requires attention"""
+
+
+class CriticalDuplicateVote(BigchainDBError):
+    """Data integrity error that requires attention"""

bigchaindb/voting.py

@@ -1,6 +1,7 @@
 import collections
 
 from bigchaindb.common.schema import SchemaValidationError, validate_vote_schema
+from bigchaindb.exceptions import CriticalDuplicateVote
 from bigchaindb.common.utils import serialize
 from bigchaindb.common.crypto import PublicKey
 
@@ -33,7 +34,8 @@ class Voting:
         n_voters = len(eligible_voters)
         eligible_votes, ineligible_votes = \
             cls.partition_eligible_votes(votes, eligible_voters)
-        results = cls.count_votes(eligible_votes)
+        by_voter = cls.dedupe_by_voter(eligible_votes)
+        results = cls.count_votes(by_voter)
         results['block_id'] = block['id']
         results['status'] = cls.decide_votes(n_voters, **results['counts'])
         results['ineligible'] = ineligible_votes
@@ -60,38 +62,29 @@ class Voting:
         return eligible, ineligible
 
     @classmethod
-    def count_votes(cls, eligible_votes):
+    def dedupe_by_voter(cls, eligible_votes):
+        """
+        Throw a critical error if there is a duplicate vote
+        """
+        by_voter = {}
+        for vote in eligible_votes:
+            pubkey = vote['node_pubkey']
+            if pubkey in by_voter:
+                raise CriticalDuplicateVote(pubkey)
+            by_voter[pubkey] = vote
+        return by_voter
+
+    @classmethod
+    def count_votes(cls, by_voter):
         """
         Given a list of eligible votes, (votes from known nodes that are listed
         as voters), produce the number that say valid and the number that say
-        invalid.
-
-        * Detect if there are multiple votes from a single node and return them
-          in a separate "cheat" dictionary.
-        * Votes must agree on previous block, otherwise they become invalid.
-
-        note:
-            The sum of votes returned by this function does not necessarily
-            equal the length of the list of votes fed in. It may differ for
-            example if there are found to be multiple votes submitted by a
-            single voter.
+        invalid. Votes must agree on previous block, otherwise they become invalid.
         """
         prev_blocks = collections.Counter()
-        cheat = []
         malformed = []
 
-        # Group by pubkey to detect duplicate voting
-        by_voter = collections.defaultdict(list)
-        for vote in eligible_votes:
-            by_voter[vote['node_pubkey']].append(vote)
-
-        for pubkey, votes in by_voter.items():
-            if len(votes) > 1:
-                cheat.append(votes)
-                continue
-
-            vote = votes[0]
-
+        for vote in by_voter.values():
             if not cls.verify_vote_schema(vote):
                 malformed.append(vote)
                 continue
@@ -111,7 +104,6 @@ class Voting:
                 'n_valid': n_valid,
                 'n_invalid': len(by_voter) - n_valid,
             },
-            'cheat': cheat,
             'malformed': malformed,
             'previous_block': prev_block,
             'other_previous_block': dict(prev_blocks),

tests/test_voting.py

@@ -2,6 +2,7 @@ import pytest
 from collections import Counter
 
 from bigchaindb.core import Bigchain
+from bigchaindb.exceptions import CriticalDuplicateVote
 from bigchaindb.voting import Voting, INVALID, VALID, UNDECIDED
 
 
@@ -37,24 +38,22 @@ def test_count_votes():
         def verify_vote_schema(cls, vote):
             return vote['node_pubkey'] != 'malformed'
 
-    voters = (['cheat', 'cheat', 'says invalid', 'malformed'] +
+    voters = (['says invalid', 'malformed'] +
               ['kosher' + str(i) for i in range(10)])
 
     votes = [Bigchain(v).vote('block', 'a', True) for v in voters]
-    votes[2]['vote']['is_block_valid'] = False
+    votes[0]['vote']['is_block_valid'] = False
     # Incorrect previous block subtracts from n_valid and adds to n_invalid
     votes[-1]['vote']['previous_block'] = 'z'
 
-    assert TestVoting.count_votes(votes) == {
+    by_voter = dict(enumerate(votes))
+
+    assert TestVoting.count_votes(by_voter) == {
         'counts': {
             'n_valid': 9,    # 9 kosher votes
-            'n_invalid': 4,  # 1 cheat, 1 invalid, 1 malformed, 1 rogue prev block
-            # One of the cheat votes counts towards n_invalid, the other is
-            # not counted here.
-            # len(cheat) + n_valid + n_invalid == len(votes)
+            'n_invalid': 3,  # 1 invalid, 1 malformed, 1 rogue prev block
         },
-        'cheat': [votes[:2]],
-        'malformed': [votes[3]],
+        'malformed': [votes[1]],
         'previous_block': 'a',
         'other_previous_block': {'z': 1},
     }
@@ -70,7 +69,8 @@ def test_must_agree_prev_block():
     votes = [Bigchain(v).vote('block', 'a', True) for v in voters]
     votes[0]['vote']['previous_block'] = 'b'
     votes[1]['vote']['previous_block'] = 'c'
-    assert TestVoting.count_votes(votes) == {
+    by_voter = dict(enumerate(votes))
+    assert TestVoting.count_votes(by_voter) == {
         'counts': {
             'n_valid': 2,
             'n_invalid': 2,
@@ -78,7 +78,6 @@ def test_must_agree_prev_block():
         'previous_block': 'a',
         'other_previous_block': {'b': 1, 'c': 1},
         'malformed': [],
-        'cheat': [],
     }
 
 
@@ -230,8 +229,22 @@ def test_block_election(b):
         'block_id': 'xyz',
         'counts': {'n_valid': 2, 'n_invalid': 0},
         'ineligible': [votes[-1]],
-        'cheat': [],
         'malformed': [],
         'previous_block': 'a',
         'other_previous_block': {},
     }
+
+
+def test_duplicate_vote_throws_critical_error(b):
+    class TestVoting(Voting):
+        @classmethod
+        def verify_vote_signature(cls, vote):
+            return True
+    keyring = 'abc'
+    block = {'id': 'xyz', 'block': {'voters': 'ab'}}
+    votes = [{
+        'node_pubkey': c,
+        'vote': {'is_block_valid': True, 'previous_block': 'a'}
+    } for c in 'aabc']
+    with pytest.raises(CriticalDuplicateVote):
+        TestVoting.block_election(block, votes, keyring)