38 lines
1.7 KiB
Markdown
38 lines
1.7 KiB
Markdown
# Bitfield Signing
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Validators vote on the availability of a backed candidate by issuing signed bitfields, where each bit corresponds to a
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single candidate. These bitfields can be used to compactly determine which backed candidates are available or not based
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on a 2/3+ quorum.
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## Protocol
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Input:
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There is no dedicated input mechanism for bitfield signing. Instead, Bitfield Signing produces a bitfield representing
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the current state of availability on `StartWork`.
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Output:
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- `BitfieldDistribution::DistributeBitfield`: distribute a locally signed bitfield
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- `AvailabilityStore::QueryChunk(CandidateHash, validator_index, response_channel)`
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## Functionality
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Upon receipt of an `ActiveLeavesUpdate`, launch bitfield signing job for each `activated` head referring to a fresh
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leaf. Stop the job for each `deactivated` head.
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## Bitfield Signing Job
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Localized to a specific relay-parent `r` If not running as a validator, do nothing.
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- For each fresh leaf, begin by waiting a fixed period of time so availability distribution has the chance to make
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candidates available.
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- Determine our validator index `i`, the set of backed candidates pending availability in `r`, and which bit of the
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bitfield each corresponds to.
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- Start with an empty bitfield. For each bit in the bitfield, if there is a candidate pending availability, query the
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[Availability Store](../utility/availability-store.md) for whether we have the availability chunk for our validator
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index. The `OccupiedCore` struct contains the candidate hash so the full candidate does not need to be fetched from
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runtime.
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- For all chunks we have, set the corresponding bit in the bitfield.
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- Sign the bitfield and dispatch a `BitfieldDistribution::DistributeBitfield` message.
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