package yggdrasil // A chord-like Distributed Hash Table (DHT). // Used to look up coords given a NodeID and bitmask (taken from an IPv6 address). // Keeps track of immediate successor, predecessor, and all peers. // Also keeps track of other nodes if they're closer in tree space than all other known nodes encountered when heading in either direction to that point, under the hypothesis that, for the kinds of networks we care about, this should probabilistically include the node needed to keep lookups to near O(logn) steps. import ( "sort" "time" ) const dht_lookup_size = 16 // dhtInfo represents everything we know about a node in the DHT. // This includes its key, a cache of it's NodeID, coords, and timing/ping related info for deciding who/when to ping nodes for maintenance. type dhtInfo struct { nodeID_hidden *NodeID key boxPubKey coords []byte recv time.Time // When we last received a message pings int // Time out if at least 3 consecutive maintenance pings drop throttle time.Duration } // Returns the *NodeID associated with dhtInfo.key, calculating it on the fly the first time or from a cache all subsequent times. func (info *dhtInfo) getNodeID() *NodeID { if info.nodeID_hidden == nil { info.nodeID_hidden = getNodeID(&info.key) } return info.nodeID_hidden } // Request for a node to do a lookup. // Includes our key and coords so they can send a response back, and the destination NodeID we want to ask about. type dhtReq struct { Key boxPubKey // Key of whoever asked Coords []byte // Coords of whoever asked Dest NodeID // NodeID they're asking about } // Response to a DHT lookup. // Includes the key and coords of the node that's responding, and the destination they were asked about. // The main part is Infos []*dhtInfo, the lookup response. type dhtRes struct { Key boxPubKey // key of the sender Coords []byte // coords of the sender Dest NodeID Infos []*dhtInfo // response } // The main DHT struct. type dht struct { core *Core nodeID NodeID peers chan *dhtInfo // other goroutines put incoming dht updates here reqs map[boxPubKey]map[NodeID]time.Time // These next two could be replaced by a single linked list or similar... table map[NodeID]*dhtInfo imp []*dhtInfo } // Initializes the DHT. func (t *dht) init(c *Core) { t.core = c t.nodeID = *t.core.GetNodeID() t.peers = make(chan *dhtInfo, 1024) t.reset() } // Resets the DHT in response to coord changes. // This empties all info from the DHT and drops outstanding requests. func (t *dht) reset() { t.reqs = make(map[boxPubKey]map[NodeID]time.Time) t.table = make(map[NodeID]*dhtInfo) t.imp = nil } // Does a DHT lookup and returns up to dht_lookup_size results. func (t *dht) lookup(nodeID *NodeID, everything bool) []*dhtInfo { results := make([]*dhtInfo, 0, len(t.table)) for _, info := range t.table { results = append(results, info) } if len(results) > dht_lookup_size { // Drop the middle part, so we keep some nodes before and after. // This should help to bootstrap / recover more quickly. sort.SliceStable(results, func(i, j int) bool { return dht_ordered(nodeID, results[i].getNodeID(), results[j].getNodeID()) }) newRes := make([]*dhtInfo, 0, len(results)) newRes = append(newRes, results[len(results)-dht_lookup_size/2:]...) newRes = append(newRes, results[:len(results)-dht_lookup_size/2]...) results = newRes results = results[:dht_lookup_size] } return results } // Insert into table, preserving the time we last sent a packet if the node was already in the table, otherwise setting that time to now. func (t *dht) insert(info *dhtInfo) { if *info.getNodeID() == t.nodeID { // This shouldn't happen, but don't add it if it does return } info.recv = time.Now() if oldInfo, isIn := t.table[*info.getNodeID()]; isIn { sameCoords := true if len(info.coords) != len(oldInfo.coords) { sameCoords = false } else { for idx := 0; idx < len(info.coords); idx++ { if info.coords[idx] != oldInfo.coords[idx] { sameCoords = false break } } } if sameCoords { info.throttle = oldInfo.throttle } } t.imp = nil // It needs to update to get a pointer to the new info t.table[*info.getNodeID()] = info } // Return true if first/second/third are (partially) ordered correctly. func dht_ordered(first, second, third *NodeID) bool { lessOrEqual := func(first, second *NodeID) bool { for idx := 0; idx < NodeIDLen; idx++ { if first[idx] > second[idx] { return false } if first[idx] < second[idx] { return true } } return true } firstLessThanSecond := lessOrEqual(first, second) secondLessThanThird := lessOrEqual(second, third) thirdLessThanFirst := lessOrEqual(third, first) switch { case firstLessThanSecond && secondLessThanThird: // Nothing wrapped around 0, the easy case return true case thirdLessThanFirst && firstLessThanSecond: // Third wrapped around 0 return true case secondLessThanThird && thirdLessThanFirst: // Second (and third) wrapped around 0 return true } return false } // Reads a request, performs a lookup, and responds. // Update info about the node that sent the request. func (t *dht) handleReq(req *dhtReq) { // Send them what they asked for loc := t.core.switchTable.getLocator() coords := loc.getCoords() res := dhtRes{ Key: t.core.boxPub, Coords: coords, Dest: req.Dest, Infos: t.lookup(&req.Dest, false), } t.sendRes(&res, req) // Also add them to our DHT info := dhtInfo{ key: req.Key, coords: req.Coords, } if _, isIn := t.table[*info.getNodeID()]; !isIn && t.isImportant(&info) { t.ping(&info, nil) } } // Sends a lookup response to the specified node. func (t *dht) sendRes(res *dhtRes, req *dhtReq) { // Send a reply for a dhtReq bs := res.encode() shared := t.core.sessions.getSharedKey(&t.core.boxPriv, &req.Key) payload, nonce := boxSeal(shared, bs, nil) p := wire_protoTrafficPacket{ Coords: req.Coords, ToKey: req.Key, FromKey: t.core.boxPub, Nonce: *nonce, Payload: payload, } packet := p.encode() t.core.router.out(packet) } // Reads a lookup response, checks that we had sent a matching request, and processes the response info. // This mainly consists of updating the node we asked in our DHT (they responded, so we know they're still alive), and deciding if we want to do anything with their responses func (t *dht) handleRes(res *dhtRes) { t.core.searches.handleDHTRes(res) reqs, isIn := t.reqs[res.Key] if !isIn { return } _, isIn = reqs[res.Dest] if !isIn { return } delete(reqs, res.Dest) rinfo := dhtInfo{ key: res.Key, coords: res.Coords, } if t.isImportant(&rinfo) { t.insert(&rinfo) } for _, info := range res.Infos { if *info.getNodeID() == t.nodeID { continue } // Skip self if _, isIn := t.table[*info.getNodeID()]; isIn { // TODO? don't skip if coords are different? continue } if t.isImportant(info) { t.ping(info, nil) } } } // Sends a lookup request to the specified node. func (t *dht) sendReq(req *dhtReq, dest *dhtInfo) { // Send a dhtReq to the node in dhtInfo bs := req.encode() shared := t.core.sessions.getSharedKey(&t.core.boxPriv, &dest.key) payload, nonce := boxSeal(shared, bs, nil) p := wire_protoTrafficPacket{ Coords: dest.coords, ToKey: dest.key, FromKey: t.core.boxPub, Nonce: *nonce, Payload: payload, } packet := p.encode() t.core.router.out(packet) reqsToDest, isIn := t.reqs[dest.key] if !isIn { t.reqs[dest.key] = make(map[NodeID]time.Time) reqsToDest, isIn = t.reqs[dest.key] if !isIn { panic("This should never happen") } } reqsToDest[req.Dest] = time.Now() } // Sends a lookup to this info, looking for the target. func (t *dht) ping(info *dhtInfo, target *NodeID) { // Creates a req for the node at dhtInfo, asking them about the target (if one is given) or themself (if no target is given) if target == nil { target = &t.nodeID } loc := t.core.switchTable.getLocator() coords := loc.getCoords() req := dhtReq{ Key: t.core.boxPub, Coords: coords, Dest: *target, } t.sendReq(&req, info) } // Periodic maintenance work to keep important DHT nodes alive. func (t *dht) doMaintenance() { now := time.Now() for infoID, info := range t.table { if now.Sub(info.recv) > time.Minute || info.pings > 3 { delete(t.table, infoID) t.imp = nil } } for _, info := range t.getImportant() { if now.Sub(info.recv) > info.throttle { t.ping(info, nil) info.pings++ info.throttle += time.Second if info.throttle > 30*time.Second { info.throttle = 30 * time.Second } } } } // Gets a list of important nodes, used by isImportant. func (t *dht) getImportant() []*dhtInfo { if t.imp == nil { // Get a list of all known nodes infos := make([]*dhtInfo, 0, len(t.table)) for _, info := range t.table { infos = append(infos, info) } // Sort them by increasing order in distance along the ring sort.SliceStable(infos, func(i, j int) bool { // Sort in order of predecessors (!), reverse from chord normal, because it plays nicer with zero bits for unknown parts of target addresses return dht_ordered(infos[j].getNodeID(), infos[i].getNodeID(), &t.nodeID) }) // Keep the ones that are no further than the closest seen so far minDist := ^uint64(0) loc := t.core.switchTable.getLocator() important := infos[:0] for _, info := range infos { dist := uint64(loc.dist(info.coords)) if dist < minDist { minDist = dist important = append(important, info) } } var temp []*dhtInfo minDist = ^uint64(0) for idx := len(infos) - 1; idx >= 0; idx-- { info := infos[idx] dist := uint64(loc.dist(info.coords)) if dist < minDist { minDist = dist temp = append(temp, info) } } for idx := len(temp) - 1; idx >= 0; idx-- { important = append(important, temp[idx]) } t.imp = important } return t.imp } // Returns true if this is a node we need to keep track of for the DHT to work. func (t *dht) isImportant(ninfo *dhtInfo) bool { important := t.getImportant() // Check if ninfo is of equal or greater importance to what we already know loc := t.core.switchTable.getLocator() ndist := uint64(loc.dist(ninfo.coords)) minDist := ^uint64(0) for _, info := range important { if (*info.getNodeID() == *ninfo.getNodeID()) || (ndist < minDist && dht_ordered(info.getNodeID(), ninfo.getNodeID(), &t.nodeID)) { // Either the same node, or a better one return true } dist := uint64(loc.dist(info.coords)) if dist < minDist { minDist = dist } } minDist = ^uint64(0) for idx := len(important) - 1; idx >= 0; idx-- { info := important[idx] if (*info.getNodeID() == *ninfo.getNodeID()) || (ndist < minDist && dht_ordered(&t.nodeID, ninfo.getNodeID(), info.getNodeID())) { // Either the same node, or a better one return true } dist := uint64(loc.dist(info.coords)) if dist < minDist { minDist = dist } } // We didn't find any important node that ninfo is better than return false }