calculateRequestSpan¶
| Source (upstream pre-purge) | Current | |
|---|---|---|
| File | eth/downloader/downloader.go |
downloader_pow.go |
| Symbol | calculateRequestSpan |
calculateRequestSpan |
| Ref | 45baf2111~1 |
etc/v1.17.3-full-node |
3-way merge — purge → getc ← upstream¶
pre-purge
↗// calculateRequestSpan calculates what headers to request from a peer when trying to determine the
// common ancestor.
// It returns parameters to be used for peer.RequestHeadersByNumber:
//
// from - starting block number
// count - number of headers to request
// skip - number of headers to skip
//
// and also returns 'max', the last block which is expected to be returned by the remote peers,
// given the (from,count,skip)
func calculateRequestSpan(remoteHeight, localHeight uint64) (int64, int, int, uint64) {
var (
from int
count int
MaxCount = MaxHeaderFetch / 16
)
// requestHead is the highest block that we will ask for. If requestHead is not offset,
// the highest block that we will get is 16 blocks back from head, which means we
// will fetch 14 or 15 blocks unnecessarily in the case the height difference
// between us and the peer is 1-2 blocks, which is most common
requestHead := int(remoteHeight) - 1
if requestHead < 0 {
requestHead = 0
}
// requestBottom is the lowest block we want included in the query
// Ideally, we want to include the one just below our own head
requestBottom := int(localHeight - 1)
if requestBottom < 0 {
requestBottom = 0
}
totalSpan := requestHead - requestBottom
span := 1 + totalSpan/MaxCount
if span < 2 {
span = 2
}
if span > 16 {
span = 16
}
↗ count = 1 + totalSpan/span
if count > MaxCount {
count = MaxCount
}
if count < 2 {
count = 2
}
from = requestHead - (count-1)*span
if from < 0 {
from = 0
}
max := from + (count-1)*span
return int64(from), count, span - 1, uint64(max)
}