Fields

• readCandidateChains :: STM m (Map peer (AnchoredFragment header))

  Read the K-suffixes of the candidate chains.

  Assumptions: * Their headers must be already validated. * They may contain fewer than K blocks. * Their anchor does not have to intersect with the current chain.

• readCurrentChain :: STM m (AnchoredFragment header)

  Read the K-suffix of the current chain.

  This must contain info on the last K blocks (unless we're near the chain genesis of course).

• readFetchMode :: STM m FetchMode

  Read the current fetch mode that the block fetch logic should use.

  The fetch mode is a dynamic part of the block fetch policy. In FetchModeBulkSync it follows a policy that optimises for expected bandwidth over latency to fetch any particular block, whereas in FetchModeDeadline it follows a policy optimises for the latency to fetch blocks, at the expense of wasting bandwidth.

  FetchModeGenesis should be used when the genesis node is syncing to ensure it isn't leashed.

  This mode should be set so that when the node's current chain is near to "now" it uses the deadline mode, and when it is far away it uses the bulk sync mode.

• readFetchedBlocks :: STM m (Point block -> Bool)

  Recent, only within last K

• mkAddFetchedBlock :: STM m (Point block -> block -> m ())

  This method allocates an addFetchedBlock function per client. That function and readFetchedBlocks are required to be linked. Upon successful completion of addFetchedBlock it must be the case that readFetchedBlocks reports the block.

• readFetchedMaxSlotNo :: STM m MaxSlotNo

  The highest stored/downloaded slot number.

  This is used to optimise the filtering of fragments in the block fetch logic: when removing already downloaded blocks from a fragment, the filtering (with a linear cost) is stopped as soon as a block has a slot number higher than this slot number, as it cannot have been downloaded anyway.

• readChainComparison :: STM m (WithFingerprint (ChainComparison header))

  Compare chain fragments. This might involve further state, such as Peras certificates (which give certain blocks additional weight).

• blockFetchSize :: header -> SizeInBytes

  Much of the logic for deciding which blocks to download from which peer depends on making estimates based on recent performance metrics. These estimates of course depend on the amount of data we will be downloading.

• blockMatchesHeader :: header -> block -> Bool

  Given a block header, validate the supposed corresponding block body.

• headerForgeUTCTime :: header -> UTCTime

  Calculate when a header's block was forged.

• readChainSelStarvation :: STM m ChainSelStarvation

  Information on the ChainSel starvation status; whether it is ongoing or has ended recently. Needed by the bulk sync decision logic.

• demoteChainSyncJumpingDynamo :: peer -> m ()

  Action to inform CSJ (ChainSync Jumping) that the given peer has not been performing adequately with respect to BlockFetch, and that it should be demoted from the dynamo role. Can be set to const (pure ()) in all other scenarios.

Fields

• plausibleCandidateChain :: HasCallStack => AnchoredFragment header -> AnchoredFragment header -> Bool

  Given the current chain, is the given chain plausible as a candidate chain. Classically for Ouroboros this would simply check if the candidate is strictly longer, but it can also involve further criteria:

  • Tiebreakers (e.g. based on the opcert numbers and VRFs) for chains of equal length.
  • Weight in the context of Ouroboros Peras, due to a boost from a Peras certificate.
• compareCandidateChains :: HasCallStack => AnchoredFragment header -> AnchoredFragment header -> Ordering

  Compare two candidate chains and return a preference ordering. This is used as part of selecting which chains to prioritise for downloading block bodies.

  PRECONDITION: The two fragments must intersect.

Fields

• forgetFingerprint :: !a
   
• getFingerprint :: !Fingerprint