keys: resolve subtle non-bug by exporting RaftLogKeyFromPrefix #82479
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This commit resolves a subtle interaction that came tantalizingly close to a bug in `StateLoader.LoadLastIndex`. The method uses the `StateLoader`'s underlying `keys.RangeIDPrefixBuf` to generate two keys (`RaftLogPrefix` and `RaftLogKey`) that are in use as the same time. `RangeIDPrefixBuf` avoids heap allocations by sharing a single byte slice across all keys that it generates. This is why the type has the comment: > The generated keys are only valid until the next call to one of the > key generation methods. As would be expected, given this comment, the second use of the `RangeIDPrefixBuf` overwrote the buffer and invalidated the first key. However, it happened to get lucky and generate a new key with the same prefix as the old key. As a result, the contents of the first key did not change. To make this aliasing more explicit and avoid this becoming a real bug in the future, we introduce a new `RaftLogKeyFromPrefix` function that callers can use to generate raft log entry keys from a raft log prefix.
…gKey This commit uses the new `RaftLogKeyFromPrefix` function to avoid some redundant encoding work elsewhere due to repeat calls to `RaftLogKey`. Instead of repeatedly encoding the Raft log prefix, we encoded it once and repeatedly rewrite the suffix.
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This did not belong in stateloader.go.
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tbg
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Jun 7, 2022
erikgrinaker
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Jun 7, 2022
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TFTRs! bors r=tbg,erikgrinaker |
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This commit resolves a subtle interaction that came tantalizingly close to a bug in
StateLoader.LoadLastIndex. The method uses theStateLoader's underlyingkeys.RangeIDPrefixBufto generate two keys (RaftLogPrefixandRaftLogKey) that are in use as the same time.RangeIDPrefixBufavoids heap allocations by sharing a single byte slice across all keys that it generates. This is why the type has the comment:As would be expected, given this comment, the second use of the
RangeIDPrefixBufoverwrote the buffer and invalidated the first key. However, it happened to get lucky and generate a new key with the same prefix as the old key. As a result, the contents of the first key did not change.To make this aliasing more explicit and avoid this becoming a real bug in the future, we introduce a new
RaftLogKeyFromPrefixfunction that callers can use to generate raft log entry keys from a raft log prefix.We then use this new function to avoid some redundant encoding work elsewhere due to repeated calls to
RaftLogKey.