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p2p/discover: force refresh if the table is empty

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This commit is contained in:
Péter Szilágyi 2015-05-25 15:57:44 +03:00 committed by Felix Lange
parent 5076170f34
commit f539ed1e66
1 changed files with 41 additions and 13 deletions
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54
p2p/discover/table.go
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@ -191,6 +191,12 @@ func (tab *Table) Lookup(targetID NodeID) []*Node {
result := tab.closest(target, bucketSize)
tab.mutex.Unlock()
// If the result set is empty, all nodes were dropped, refresh
if len(result.entries) == 0 {
tab.refresh()
return nil
}
for {
// ask the alpha closest nodes that we haven't asked yet
for i := 0; i < len(result.entries) && pendingQueries < alpha; i++ {
@ -207,7 +213,7 @@ func (tab *Table) Lookup(targetID NodeID) []*Node {
tab.db.updateFindFails(n.ID, fails)
glog.V(logger.Detail).Infof("Bumping failures for %x: %d", n.ID[:8], fails)
if fails > maxFindnodeFailures {
if fails >= maxFindnodeFailures {
glog.V(logger.Detail).Infof("Evacuating node %x: %d findnode failures", n.ID[:8], fails)
tab.del(n)
}
@ -232,19 +238,41 @@ func (tab *Table) Lookup(targetID NodeID) []*Node {
return result.entries
}
// refresh performs a lookup for a random target to keep buckets full.
// refresh performs a lookup for a random target to keep buckets full, or seeds
// the table if it is empty (initial bootstrap or discarded faulty peers).
func (tab *Table) refresh() {
// The Kademlia paper specifies that the bucket refresh should
// perform a refresh in the least recently used bucket. We cannot
// adhere to this because the findnode target is a 512bit value
// (not hash-sized) and it is not easily possible to generate a
// sha3 preimage that falls into a chosen bucket.
//
// We perform a lookup with a random target instead.
var target NodeID
rand.Read(target[:])
result := tab.Lookup(target)
if len(result) == 0 {
seed := true
// If the discovery table is empty, seed with previously known nodes
tab.mutex.Lock()
for _, bucket := range tab.buckets {
if len(bucket.entries) > 0 {
seed = false
break
}
}
tab.mutex.Unlock()
// If the table is not empty, try to refresh using the live entries
if !seed {
// The Kademlia paper specifies that the bucket refresh should
// perform a refresh in the least recently used bucket. We cannot
// adhere to this because the findnode target is a 512bit value
// (not hash-sized) and it is not easily possible to generate a
// sha3 preimage that falls into a chosen bucket.
//
// We perform a lookup with a random target instead.
var target NodeID
rand.Read(target[:])
result := tab.Lookup(target)
if len(result) == 0 {
// Lookup failed, seed after all
seed = true
}
}
if seed {
// Pick a batch of previously know seeds to lookup with
seeds := tab.db.querySeeds(10)
for _, seed := range seeds {