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fix voting bug with prev_block

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This commit is contained in:
Scott Sadler 2017-02-25 10:21:40 +01:00
parent f860753192
commit f858fc8f8d
2 changed files with 127 additions and 93 deletions
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49
bigchaindb/voting.py
View File

@ -1,5 +1,5 @@
import collections
from bigchaindb.backend.exceptions import BigchainDBCritical
from bigchaindb.common.schema import SchemaValidationError, validate_vote_schema
from bigchaindb.common.utils import serialize
from bigchaindb.common.crypto import PublicKey
@ -56,31 +56,30 @@ class Voting:
except ValueError:
pass
ineligible.append(vote)
return eligible, ineligible
@classmethod
def count_votes(cls, eligible_votes):
"""
Given a list of eligible votes, (votes from known nodes that are listed
as voters), count the votes to produce three quantities:
as voters), produce the number that say valid and the number that say
invalid.
Number of votes that say valid
Number of votes that say invalid
Highest agreement on previous block ID
Also, detect if there are multiple votes from a single node and return them
* 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.
"""
by_voter = collections.defaultdict(list)
for vote in eligible_votes:
by_voter[vote['node_pubkey']].append(vote)
n_valid = 0
n_invalid = 0
prev_blocks = collections.Counter()
cheat = []
malformed = []
prev_block = None
# 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:
@ -101,20 +100,28 @@ class Voting:
else:
n_invalid += 1
n_prev = prev_blocks.most_common()[0][1] if prev_blocks else 0
# Neutralise difference between valid block and previous block,
# so that nodes must agree on previous block
if n_valid:
prev_block, n_prev = prev_blocks.most_common()[0]
del prev_blocks[prev_block]
diff = n_valid - n_prev
n_valid -= diff
n_invalid += diff
return {
'counts': {
'n_valid': n_valid,
'n_invalid': n_invalid,
'n_agree_prev_block': n_prev,
},
'cheat': cheat,
'malformed': malformed,
'previous_block': prev_block,
'other_previous_block': dict(prev_blocks),
}
@classmethod
def decide_votes(cls, n_voters, n_valid, n_invalid, n_agree_prev_block):
def decide_votes(cls, n_voters, n_valid, n_invalid):
"""
Decide on votes.
@ -124,22 +131,10 @@ class Voting:
A tie on an even number of votes counts as INVALID so the >= operator is
used.
"""
# Check insane cases. This is basic, not exhaustive.
if n_valid + n_invalid > n_voters or n_agree_prev_block > n_voters:
raise BigchainDBCritical('Arguments not sane: %s' % {
'n_voters': n_voters,
'n_valid': n_valid,
'n_invalid': n_invalid,
'n_agree_prev_block': n_agree_prev_block,
})
if n_invalid * 2 >= n_voters:
return INVALID
if n_valid * 2 > n_voters:
if n_agree_prev_block * 2 > n_voters:
return VALID
return INVALID
return UNDECIDED
@classmethod

167
tests/test_voting.py
View File

@ -1,6 +1,6 @@
import pytest
from collections import Counter
from bigchaindb.backend.exceptions import BigchainDBCritical
from bigchaindb.core import Bigchain
from bigchaindb.voting import Voting, INVALID, VALID, UNDECIDED
@ -37,21 +37,45 @@ def test_count_votes():
def verify_vote_schema(cls, vote):
return vote['node_pubkey'] != 'malformed'
voters = ['cheat', 'cheat', 'says invalid', 'malformed']
voters += ['kosher' + str(i) for i in range(10)]
voters = (['cheat', 'cheat', '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
# Incorrect previous block subtracts from n_valid and adds to n_invalid
votes[-1]['vote']['previous_block'] = 'z'
assert TestVoting.count_votes(votes) == {
'counts': {
'n_valid': 10,
'n_invalid': 3,
'n_agree_prev_block': 9
'n_valid': 9, # 9 kosher votes
'n_invalid': 4, # 1 cheat, 1 invalid, 1 malformed, 1 rogue prev block
},
'cheat': [votes[:2]],
'malformed': [votes[3]],
'previous_block': 'a',
'other_previous_block': {'z': 1},
}
def test_must_agree_prev_block():
class TestVoting(Voting):
@classmethod
def verify_vote_schema(cls, vote):
return True
voters = 'abcd'
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) == {
'counts': {
'n_valid': 2,
'n_invalid': 2,
},
'previous_block': 'a',
'other_previous_block': {'b': 1, 'c': 1},
'malformed': [],
'cheat': [],
}
@ -60,16 +84,16 @@ def test_count_votes():
DECISION_TESTS = [dict(
zip(['n_voters', 'n_valid', 'n_invalid', 'n_agree_prev_block'], t))
zip(['n_voters', 'n_valid', 'n_invalid'], t))
for t in [
(1, 1, 1, 1),
(2, 2, 1, 2),
(3, 2, 2, 2),
(4, 3, 2, 3),
(5, 3, 3, 3),
(6, 4, 3, 4),
(7, 4, 4, 4),
(8, 5, 4, 5),
(1, 1, 1),
(2, 2, 1),
(3, 2, 2),
(4, 3, 2),
(5, 3, 3),
(6, 4, 3),
(7, 4, 4),
(8, 5, 4),
]
]
@ -79,8 +103,6 @@ def test_decide_votes_valid(kwargs):
kwargs = kwargs.copy()
kwargs['n_invalid'] = 0
assert Voting.decide_votes(**kwargs) == VALID
kwargs['n_agree_prev_block'] -= 1
assert Voting.decide_votes(**kwargs) == INVALID
kwargs['n_valid'] -= 1
assert Voting.decide_votes(**kwargs) == UNDECIDED
@ -94,16 +116,67 @@ def test_decide_votes_invalid(kwargs):
assert Voting.decide_votes(**kwargs) == UNDECIDED
def test_decide_votes_checks_arguments():
with pytest.raises(BigchainDBCritical):
Voting.decide_votes(n_voters=1, n_valid=2, n_invalid=0,
n_agree_prev_block=0)
with pytest.raises(BigchainDBCritical):
Voting.decide_votes(n_voters=1, n_valid=0, n_invalid=2,
n_agree_prev_block=0)
with pytest.raises(BigchainDBCritical):
Voting.decide_votes(n_voters=1, n_valid=0, n_invalid=0,
n_agree_prev_block=2)
################################################################################
# Actions - test state transitions
@pytest.mark.parametrize('n_voters', range(8))
def test_vote_actions(n_voters):
"""
* Legal transitions are UNDECIDED -> [VALID|INVALID] only
* Block is never left UNDECIDED after voting
* Accomodates rogues on previous block / invalid schema
"""
class TestVoting(Voting):
@classmethod
def verify_vote_schema(cls, vote):
return type(vote['vote']['is_block_valid']) == bool
@classmethod
def verify_vote_signature(cls, vote):
return True
keyring = 'abcdefghijklmnopqrstuvwxyz'[:n_voters]
block = {'id': 'block', 'block': {'voters': keyring}}
state = UNDECIDED
todo = [(state, [], [])]
def branch(p, r):
todo.append((state, votes, votes + [{
'node_pubkey': keyring[len(votes)],
'vote': {'previous_block': p, 'is_block_valid': r}
}]))
while todo:
prev_state, prev_votes, votes = todo.pop(0)
results = Counter(v['vote']['is_block_valid'] for v in votes)
prev_blocks = Counter(v['vote']['previous_block'] for v in votes)
majority = n_voters // 2 + 1
honest = (len(votes) == majority and len(prev_blocks) == 1 and
not results['lol'] and len(results) == 1)
closed = len(votes) == n_voters
# Test legal transition
if votes:
state = TestVoting.block_election(block, votes, keyring)['status']
assert prev_state in [state, UNDECIDED]
# Test that decision has been reached
if honest or closed:
assert state != UNDECIDED or n_voters == 0
if closed:
continue
# Can accomodate more votes, add them to the todo list.
# This vote is the good case
branch('A', True)
# This vote disagrees on previous block
branch('B', True)
# This vote says the block is invalid
branch('A', False)
# This vote is invalid
branch('A', 'lol')
################################################################################
@ -113,10 +186,6 @@ def test_decide_votes_checks_arguments():
def test_verify_vote_signature_passes(b):
vote = b.vote('block', 'a', True)
assert Voting.verify_vote_signature(vote)
def test_verify_vote_signature_fails(b):
vote = b.vote('block', 'a', True)
vote['signature'] = ''
assert not Voting.verify_vote_signature(vote)
@ -128,37 +197,7 @@ def test_verify_vote_signature_fails(b):
def test_verify_vote_schema(b):
vote = b.vote('b' * 64, 'a' * 64, True)
assert Voting.verify_vote_schema(vote)
vote = b.vote('b', 'a', True)
vote = b.vote('b' * 64, 'a', True)
assert not Voting.verify_vote_schema(vote)
vote = b.vote('b', 'a' * 64, True)
assert not Voting.verify_vote_schema(vote)
################################################################################
# block_election tests
# A more thorough test will follow as part of #1217
def test_block_election(b):
class TestVoting(Voting):
@classmethod
def verify_vote_signature(cls, vote):
return True
@classmethod
def verify_vote_schema(cls, vote):
return True
keyring = 'abc'
block = {'block': {'voters': 'ab'}}
votes = [{
'node_pubkey': c,
'vote': {'is_block_valid': True, 'previous_block': 'a'}
} for c in 'abc']
assert TestVoting.block_election(block, votes, keyring) == {
'status': VALID,
'counts': {'n_agree_prev_block': 2, 'n_valid': 2, 'n_invalid': 0},
'ineligible': [votes[-1]],
'cheat': [],
'malformed': [],
}