non-contiguous round DRAND integration notes

drand-val.go

// Protocol Constants
// Time Drand network starts at
DRAND_START_ROUND 
// Time of one DRAND Round
DRAND_ROUND_TIME
// Number of epochs in the past that a filecoin block should sample DRAND entries from
DRANDLookback = 2 // might change to 5 for availability reasons


func ValidateBlock(b BlockHeader) {
  prevEntry := latestDrand(b)

  numEntries := len(b.DRANDEntries)  
  // Handle case where there is no drand in the header
  if numEntries == 0 {
    nextDRANDTime := DRAND_START_ROUND + DRAND_ROUND_TIME * ( prevEntry.Round + 1)
    assert(filecoinEpochFromTime(nextDRANDTime) > b.Height - DRANDLookback)
    validateElectionFromBeaconEntry(prevEntry, b)
  }
  
  // Handle case where there is a drand entry in header
  
  // Validate Drand entries link up
  validateDRANDParentChild(prevEntry, b.DRANDEntries[0])
  for i := 0; i < numEntries-1; i++ {
    validateDRANDIsParentChild(b.DRANDEntries[i], b.DRANDEntries[i+1])
  }
  
  // Validate that last Drand entry in block is last possible
  nextDRANDTime := DRAND_START_ROUND + DRAND_ROUND_TIME * (b.DRANDEntries[numEntries-1].Round + 1)
  assert(filecoinEpochFromTime(nextDRANDTime) > b.Height - DRANDLookback)
  validateElectionFromBeaconEntry(b.DRANDEntries[numEntries-1], b)
}

func latestDrand(b BlockHeader) drand.Entry {
  for {
    b := getParent(b)
    if len(b.DRANDEntries) > 0 {
      return b.DRANDEntries[len(b.DRANDEntries) -1]
    }
  }
}