90 lines
2.8 KiB
Python
90 lines
2.8 KiB
Python
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# Implementation of 99% fault tolerant consensus as decribed by Leslie Lamport
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# on page 391 of https://people.eecs.berkeley.edu/~luca/cs174/byzantine.pdf
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import random
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TIMEOUT = 10
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LATENCY = 5
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# Network simulator
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class Network():
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def __init__(self):
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self.queue = {}
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self.time = 0
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def add_node(self, node):
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self.queue[node.id] = {-1: node}
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def broadcast(self, msg, at=0):
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for q in self.queue.keys():
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self.send_to(msg, q, at)
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def send_to(self, msg, id, at):
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q = self.queue[id]
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newtime = max(self.time, at) + random.randrange(LATENCY * 2 - 1) + 1
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if newtime not in q:
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q[newtime] = []
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q[newtime].append(msg)
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def tick(self):
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self.time += 1
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for q in self.queue.values():
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if self.time in q:
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for msg in q[self.time]:
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q[-1].on_receive(msg)
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# A node in the network (not including the "commander")
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class Node():
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def __init__(self, network, id, honest=True):
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self.seen = {}
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self.id = id
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self.network = network
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self.network.add_node(self)
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self.honest = honest
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# Upon receiving a message...
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def on_receive(self, msg):
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if self.id == 0 and len(msg) == 1:
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print('Seen', msg[0], self.network.time, 'already seen', sorted(self.seen.keys()))
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# Only proceed if v not in V_i...
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# Byzantine nodes ignore this rule 5% of the time
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if (msg[0] in self.seen) and (self.honest or random.random() < 0.95):
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return
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# Timeout logic (see page 399)
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# Byzantine nodes ignore this rule
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if (len(msg) * TIMEOUT < self.network.time) and self.honest:
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return
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self.seen[msg[0]] = True
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new_msg = msg + [self.id]
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# Broadcast v:0:j1...jk:i
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# Byzantine nodes delay broadcast to split honest receiving nodes by timeout
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self.network.broadcast(new_msg, at=self.network.time if self.honest else self.network.time + int(TIMEOUT / 1.5))
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def choice(self):
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return max(self.seen.keys())
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def test():
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n = Network()
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nodes = [Node(n, i, i%4==0) for i in range(20)]
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for i in range(30):
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for _ in range(2):
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z = random.randrange(20)
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n.send_to([1000 + i], z, at=5+i*2)
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for i in range(21 * LATENCY):
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n.tick()
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if i % 10 == 0:
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print("Value sets", [sorted(node.seen.keys()) for node in nodes])
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countz = {}
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maxval = ""
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for node in nodes:
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if node.honest:
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k = str(sorted(node.seen.keys()))
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countz[k] = countz.get(k, 0) + 1
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if countz[k] > countz.get(maxval, 0):
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maxval = k
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print("Most popular: %s" % maxval, "with %d agreeing" % countz[maxval])
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if __name__ == '__main__':
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test()
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