The connection permutation in get_addrs uses a weak and inefficient shuffle
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Key: ZOOKEEPER-1018
URL: https://issues.apache.org/jira/browse/ZOOKEEPER-1018
Project: ZooKeeper
Issue Type: Improvement
Components: c client
Affects Versions: 3.3.2
Reporter: Stephen Tyree
Priority: Minor
After determining all of the addresses in the get_addrs function in the C
client, the connection is permuted using the following code:
setup_random();
/* Permute */
for(i = 0; i < zh->addrs_count; i++) {
struct sockaddr_storage *s1 = zh->addrs + random()%zh->addrs_count;
struct sockaddr_storage *s2 = zh->addrs + random()%zh->addrs_count;
if (s1 != s2) {
struct sockaddr_storage t = *s1;
*s1 = *s2;
*s2 = t;
}
}
Not only does this shuffle produce an uneven permutation, but it is half as
efficient as the Fisher-Yates shuffle which produces an unbiased one. It seems
like it would be a simple fix to increase the randomness and efficiency of the
shuffle by switching over to using Fisher-Yates.
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