Merge pull request #665 from Arceliar/search

More reliable search

src/yggdrasil/dht.go

@@ -260,9 +260,7 @@ func (t *dht) handleRes(res *dhtRes) {
 		key:    res.Key,
 		coords: res.Coords,
 	}
-	if t.isImportant(&rinfo) {
-		t.insert(&rinfo)
-	}
+	t.insert(&rinfo)
 	for _, info := range res.Infos {
 		if *info.getNodeID() == t.nodeID {
 			continue

src/yggdrasil/search.go

@@ -4,15 +4,13 @@ package yggdrasil
 
 // The basic idea is as follows:
 //  We may know a NodeID (with a mask) and want to connect
-//  We begin a search by initializing a list of all nodes in our DHT, sorted by closest to the destination
-//  We then iteratively ping nodes from the search, marking each pinged node as visited
-//  We add any unvisited nodes from ping responses to the search, truncating to some maximum search size
-//  This stops when we either run out of nodes to ping (we hit a dead end where we can't make progress without going back), or we reach the destination
-//  A new search packet is sent immediately after receiving a response
-//  A new search packet is sent periodically, once per second, in case a packet was dropped (this slowly causes the search to become parallel if the search doesn't timeout but also doesn't finish within 1 second for whatever reason)
-
-// TODO?
-//  Some kind of max search steps, in case the node is offline, so we don't crawl through too much of the network looking for a destination that isn't there?
+//  We begin a search by sending a dht lookup to ourself
+//  Each time a node responds, we sort the results and filter to only include useful nodes
+//  We then periodically send a packet to the first node from the list (after re-filtering)
+//  This happens in parallel for each node that replies
+//  Meanwhile, we keep a list of the (up to) 16 closest nodes to the destination that we've visited
+//  We only consider an unvisited node useful if either the list isn't full or the unvisited node is closer to the destination than the furthest node on the list
+//  That gives the search some chance to recover if it hits a dead end where a node doesn't know everyone it should
 
 import (
 	"errors"
@@ -24,7 +22,8 @@ import (
 
 // This defines the time after which we time out a search (so it can restart).
 const search_RETRY_TIME = 3 * time.Second
-const search_STEP_TIME = 100 * time.Millisecond
+const search_STEP_TIME = time.Second
+const search_MAX_RESULTS = dht_lookup_size
 
 // Information about an ongoing search.
 // Includes the target NodeID, the bitmask to match it to an IP, and the list of nodes to visit / already visited.
@@ -33,7 +32,7 @@ type searchInfo struct {
 	dest     crypto.NodeID
 	mask     crypto.NodeID
 	time     time.Time
-	visited  crypto.NodeID // Closest address visited so far
+	visited  []*crypto.NodeID // Closest addresses visited so far
 	callback func(*sessionInfo, error)
 	// TODO context.Context for timeout and cancellation
 	send uint64 // log number of requests sent
@@ -75,6 +74,9 @@ func (s *searches) createSearch(dest *crypto.NodeID, mask *crypto.NodeID, callba
 // If there is, it adds the response info to the search and triggers a new search step.
 // If there's no ongoing search, or we if the dhtRes finished the search (it was from the target node), then don't do anything more.
 func (sinfo *searchInfo) handleDHTRes(res *dhtRes) {
+	if nfo := sinfo.searches.searches[sinfo.dest]; nfo != sinfo {
+		return // already done
+	}
 	if res != nil {
 		sinfo.recv++
 		if sinfo.checkDHTRes(res) {
@@ -105,16 +107,32 @@ func (sinfo *searchInfo) doSearchStep(infos []*dhtInfo) {
 // Get a list of search targets that are close enough to the destination to try
 // Requires an initial list as input
 func (sinfo *searchInfo) getAllowedInfos(infos []*dhtInfo) []*dhtInfo {
+	var temp []*dhtInfo
+	for _, info := range infos {
+		if false && len(sinfo.visited) < search_MAX_RESULTS {
+			// We're not full on results yet, so don't block anything yet
+		} else if !dht_ordered(&sinfo.dest, info.getNodeID(), sinfo.visited[len(sinfo.visited)-1]) {
+			// Too far away
+			continue
+		}
+		var known bool
+		for _, nfo := range sinfo.visited {
+			if *nfo == *info.getNodeID() {
+				known = true
+				break
+			}
+		}
+		if !known {
+			temp = append(temp, info)
+		}
+	}
+	infos = append(infos[:0], temp...) // restrict to only the allowed infos
 	sort.SliceStable(infos, func(i, j int) bool {
 		// Should return true if i is closer to the destination than j
 		return dht_ordered(&sinfo.dest, infos[i].getNodeID(), infos[j].getNodeID())
-	})
-	// Remove anything too far away to be useful
-	for idx, info := range infos {
-		if !dht_ordered(&sinfo.dest, info.getNodeID(), &sinfo.visited) {
-			infos = infos[:idx]
-			break
-		}
+	}) // Sort infos to start with the closest
+	if len(infos) > search_MAX_RESULTS {
+		infos = infos[:search_MAX_RESULTS] // Limit max number of infos
 	}
 	return infos
 }
@@ -164,6 +182,7 @@ func (sinfo *searchInfo) startSearch() {
 			if elapsed > search_RETRY_TIME {
 				// cleanup
 				delete(sinfo.searches.searches, sinfo.dest)
+				sinfo.searches.router.core.log.Debugln("search timeout:", &sinfo.dest, sinfo.send, sinfo.recv)
 				sinfo.callback(nil, errors.New("search reached dead end"))
 				return
 			}
@@ -176,7 +195,7 @@ func (sinfo *searchInfo) startSearch() {
 // Calls create search, and initializes the iterative search parts of the struct before returning it.
 func (s *searches) newIterSearch(dest *crypto.NodeID, mask *crypto.NodeID, callback func(*sessionInfo, error)) *searchInfo {
 	sinfo := s.createSearch(dest, mask, callback)
-	sinfo.visited = s.router.dht.nodeID
+	sinfo.visited = append(sinfo.visited, &s.router.dht.nodeID)
 	return sinfo
 }
 
@@ -185,13 +204,29 @@ func (s *searches) newIterSearch(dest *crypto.NodeID, mask *crypto.NodeID, callb
 // Otherwise return false.
 func (sinfo *searchInfo) checkDHTRes(res *dhtRes) bool {
 	from := dhtInfo{key: res.Key, coords: res.Coords}
-	if *from.getNodeID() != sinfo.visited && dht_ordered(&sinfo.dest, from.getNodeID(), &sinfo.visited) {
-		// Closer to the destination, so update visited
-		sinfo.searches.router.core.log.Debugln("Updating search:", &sinfo.dest, from.getNodeID(), sinfo.send, sinfo.recv)
-		sinfo.visited = *from.getNodeID()
-		sinfo.time = time.Now()
-	}
 	them := from.getNodeID()
+	var known bool
+	for _, v := range sinfo.visited {
+		if *v == *them {
+			known = true
+			break
+		}
+	}
+	if !known {
+		if len(sinfo.visited) < search_MAX_RESULTS || dht_ordered(&sinfo.dest, them, sinfo.visited[len(sinfo.visited)-1]) {
+			// Closer to the destination than the threshold, so update visited
+			sinfo.searches.router.core.log.Debugln("Updating search:", &sinfo.dest, them, sinfo.send, sinfo.recv)
+			sinfo.visited = append(sinfo.visited, them)
+			sort.SliceStable(sinfo.visited, func(i, j int) bool {
+				// Should return true if i is closer to the destination than j
+				return dht_ordered(&sinfo.dest, sinfo.visited[i], sinfo.visited[j])
+			}) // Sort infos to start with the closest
+			if len(sinfo.visited) > search_MAX_RESULTS {
+				sinfo.visited = sinfo.visited[:search_MAX_RESULTS]
+			}
+			sinfo.time = time.Now()
+		}
+	}
 	var destMasked crypto.NodeID
 	var themMasked crypto.NodeID
 	for idx := 0; idx < crypto.NodeIDLen; idx++ {