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downloader: extract findAncestor search functions #21744

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merged 3 commits into from
Jan 20, 2021
Merged

downloader: extract findAncestor search functions #21744

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bc4b7a1
downloader: extract findAncestor search functions
meowsbits Oct 22, 2020
85ac9b6
downloader: use errors chain to match target
meowsbits Nov 4, 2020
5f00c08
eth/downloader: lint
holiman Nov 24, 2020
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27 changes: 27 additions & 0 deletions eth/downloader/downloader.go
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Original file line number Diff line number Diff line change
Expand Up @@ -90,6 +90,7 @@ var (
errCanceled = errors.New("syncing canceled (requested)")
errNoSyncActive = errors.New("no sync active")
errTooOld = errors.New("peer's protocol version too old")
errNoAncestorFound = errors.New("no common ancestor found")
)

type Downloader struct {
Expand Down Expand Up @@ -814,6 +815,26 @@ func (d *Downloader) findAncestor(p *peerConnection, remoteHeader *types.Header)
}
}

ancestor, err := d.findAncestorSpanSearch(p, mode, remoteHeight, localHeight, floor)
if err == nil {
return ancestor, nil
}
// The returned error was not nil.
// If the error returned does not reflect that a common ancestor was not found, return it.
// If the error reflects that a common ancestor was not found, continue to binary search,
// where the error value will be reassigned.
if !errors.Is(err, errNoAncestorFound) {
return 0, err
}

ancestor, err = d.findAncestorBinarySearch(p, mode, remoteHeight, floor)
if err != nil {
return 0, err
}
return ancestor, nil
}

func (d *Downloader) findAncestorSpanSearch(p *peerConnection, mode SyncMode, remoteHeight, localHeight uint64, floor int64) (commonAncestor uint64, err error) {
from, count, skip, max := calculateRequestSpan(remoteHeight, localHeight)

p.log.Trace("Span searching for common ancestor", "count", count, "from", from, "skip", skip)
Expand Down Expand Up @@ -894,6 +915,12 @@ func (d *Downloader) findAncestor(p *peerConnection, remoteHeader *types.Header)
p.log.Debug("Found common ancestor", "number", number, "hash", hash)
return number, nil
}
return 0, errNoAncestorFound
}

func (d *Downloader) findAncestorBinarySearch(p *peerConnection, mode SyncMode, remoteHeight uint64, floor int64) (commonAncestor uint64, err error) {
hash := common.Hash{}

// Ancestor not found, we need to binary search over our chain
start, end := uint64(0), remoteHeight
if floor > 0 {
Expand Down