# nim-eth - Node Discovery Protocol v5 # Copyright (c) 2020-2021 Status Research & Development GmbH # Licensed and distributed under either of # * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT). # * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0). # at your option. This file may not be copied, modified, or distributed except according to those terms. {.push raises: [Defect].} import std/[algorithm, times, sequtils, bitops, sets, options], bearssl/rand, stint, chronicles, metrics, chronos, stew/shims/net as stewNet, ../../net/utils, "."/[node, random2, enr] export options declarePublicGauge routing_table_nodes, "Discovery routing table nodes", labels = ["state"] type DistanceProc* = proc(a, b: NodeId): NodeId {.raises: [Defect], gcsafe, noSideEffect.} LogDistanceProc* = proc(a, b: NodeId): uint16 {.raises: [Defect], gcsafe, noSideEffect.} IdAtDistanceProc* = proc (id: NodeId, dist: uint16): NodeId {.raises: [Defect], gcsafe, noSideEffect.} DistanceCalculator* = object calculateDistance*: DistanceProc calculateLogDistance*: LogDistanceProc calculateIdAtDistance*: IdAtDistanceProc RoutingTable* = object localNode*: Node buckets*: seq[KBucket] bitsPerHop: int ## This value indicates how many bits (at minimum) you get ## closer to finding your target per query. Practically, it tells you also ## how often your "not in range" branch will split off. Setting this to 1 ## is the basic, non accelerated version, which will never split off the ## not in range branch and which will result in log base2 n hops per lookup. ## Setting it higher will increase the amount of splitting on a not in range ## branch (thus holding more nodes with a better keyspace coverage) and this ## will result in an improvement of log base(2^b) n hops per lookup. ipLimits: IpLimits ## IP limits for total routing table: all buckets and ## replacement caches. distanceCalculator: DistanceCalculator rng: ref HmacDrbgContext KBucket = ref object istart, iend: NodeId ## Range of NodeIds this KBucket covers. This is not a ## simple logarithmic distance as buckets can be split over a prefix that ## does not cover the `localNode` id. nodes*: seq[Node] ## Node entries of the KBucket. Sorted according to last ## time seen. First entry (head) is considered the most recently seen node ## and the last entry (tail) is considered the least recently seen node. ## Here "seen" means a successful request-response. This can also not have ## occurred yet. replacementCache: seq[Node] ## Nodes that could not be added to the `nodes` ## seq as it is full and without stale nodes. This is practically a small ## LRU cache. ipLimits: IpLimits ## IP limits for bucket: node entries and replacement ## cache entries combined. ## The routing table IP limits are applied on both the total table, and on the ## individual buckets. In each case, the active node entries, but also the ## entries waiting in the replacement cache are accounted for. This way, the ## replacement cache can't get filled with nodes that then can't be added due ## to the limits that apply. ## ## As entries are not verified (=contacted) immediately before or on entry, it ## is possible that a malicious node could fill (poison) the routing table or ## a specific bucket with ENRs with IPs it does not control. The effect of ## this would be that a node that actually owns the IP could have a difficult ## time getting its ENR distributed in the DHT and as a consequence would ## not be reached from the outside as much (or at all). However, that node can ## still search and find nodes to connect to. So it would practically be a ## similar situation as a node that is not reachable behind the NAT because ## port mapping is not set up properly. ## There is the possibility to set the IP limit on verified (=contacted) nodes ## only, but that would allow for lookups to be done on a higher set of nodes ## owned by the same identity. This is a worse alternative. ## Next, doing lookups only on verified nodes would slow down discovery start ## up. TableIpLimits* = object tableIpLimit*: uint bucketIpLimit*: uint NodeStatus* = enum Added LocalNode Existing IpLimitReached ReplacementAdded ReplacementExisting NoAddress # xor distance functions func distance*(a, b: NodeId): UInt256 = ## Calculate the distance to a NodeId. a xor b func logDistance*(a, b: NodeId): uint16 = ## Calculate the logarithmic distance between two `NodeId`s. ## ## According the specification, this is the log base 2 of the distance. But it ## is rather the log base 2 of the distance + 1, as else the 0 value can not ## be used (e.g. by FindNode call to return peer its own ENR) ## For NodeId of 256 bits, range is 0-256. let a = a.toBytesBE let b = b.toBytesBE var lz = 0 for i in 0.. int: cmp(a.iend, b) # Prevent cases where `lowerBound` returns an out of range index e.g. at empty # openArray, or when the id is out range for all buckets in the openArray. if bucketPos < buckets.len: let bucket = buckets[bucketPos] if bucket.istart <= id and id <= bucket.iend: result = bucket proc computeSharedPrefixBits(nodes: openArray[NodeId]): int = ## Count the number of prefix bits shared by all nodes. if nodes.len < 2: return ID_SIZE var mask = zero(UInt256) let one = one(UInt256) for i in 1 .. ID_SIZE: mask = mask or (one shl (ID_SIZE - i)) let reference = nodes[0] and mask for j in 1 .. nodes.high: if (nodes[j] and mask) != reference: return i - 1 for n in nodes: echo n.toHex() # Reaching this would mean that all node ids are equal. doAssert(false, "Unable to calculate number of shared prefix bits") proc init*(T: type RoutingTable, localNode: Node, bitsPerHop = DefaultBitsPerHop, ipLimits = DefaultTableIpLimits, rng: ref HmacDrbgContext, distanceCalculator = XorDistanceCalculator): T = ## Initialize the routing table for provided `Node` and bitsPerHop value. ## `bitsPerHop` is default set to 5 as recommended by original Kademlia paper. RoutingTable( localNode: localNode, buckets: @[KBucket.new(0.u256, high(UInt256), ipLimits.bucketIpLimit)], bitsPerHop: bitsPerHop, ipLimits: IpLimits(limit: ipLimits.tableIpLimit), distanceCalculator: distanceCalculator, rng: rng) proc splitBucket(r: var RoutingTable, index: int) = let bucket = r.buckets[index] let (a, b) = bucket.split() r.buckets[index] = a r.buckets.insert(b, index + 1) proc bucketForNode(r: RoutingTable, id: NodeId): KBucket = result = binaryGetBucketForNode(r.buckets, id) doAssert(not result.isNil(), "Routing table should always cover the full id space") proc addReplacement(r: var RoutingTable, k: KBucket, n: Node): NodeStatus = ## Add the node to the tail of the replacement cache of the KBucket. ## ## If the replacement cache is full, the oldest (first entry) node will be ## removed. If the node is already in the replacement cache, it will be moved ## to the tail. ## When the IP of the node has reached the IP limits for the bucket or the ## total routing table, the node will not be added to the replacement cache. let nodeIdx = k.replacementCache.find(n) if nodeIdx != -1: if k.replacementCache[nodeIdx].record.seqNum <= n.record.seqNum: # In case the record sequence number is higher or the same, the new node # gets moved to the tail. if k.replacementCache[nodeIdx].address.get().ip != n.address.get().ip: if not ipLimitInc(r, k, n): return IpLimitReached ipLimitDec(r, k, k.replacementCache[nodeIdx]) k.replacementCache.delete(nodeIdx) k.replacementCache.add(n) return ReplacementExisting elif not ipLimitInc(r, k, n): return IpLimitReached else: doAssert(k.replacementCache.len <= REPLACEMENT_CACHE_SIZE) if k.replacementCache.len == REPLACEMENT_CACHE_SIZE: # Remove ip from limits for the to be deleted node. ipLimitDec(r, k, k.replacementCache[0]) k.replacementCache.delete(0) k.replacementCache.add(n) return ReplacementAdded proc addNode*(r: var RoutingTable, n: Node): NodeStatus = ## Try to add the node to the routing table. ## ## First, an attempt will be done to add the node to the bucket in its range. ## If this fails, the bucket will be split if it is eligible for splitting. ## If so, a new attempt will be done to add the node. If not, the node will be ## added to the replacement cache. ## ## In case the node was already in the table, it will be updated if it has a ## newer record. ## When the IP of the node has reached the IP limits for the bucket or the ## total routing table, the node will not be added to the bucket, nor its ## replacement cache. # Don't allow nodes without an address field in the ENR to be added. # This could also be reworked by having another Node type that always has an # address. if n.address.isNone(): return NoAddress if n == r.localNode: return LocalNode let bucket = r.bucketForNode(n.id) ## Check if the node is already present. If so, check if the record requires ## updating. let nodeIdx = bucket.nodes.find(n) if nodeIdx != -1: if bucket.nodes[nodeIdx].record.seqNum < n.record.seqNum: # In case of a newer record, it gets replaced. if bucket.nodes[nodeIdx].address.get().ip != n.address.get().ip: if not ipLimitInc(r, bucket, n): return IpLimitReached ipLimitDec(r, bucket, bucket.nodes[nodeIdx]) # Copy over the seen status, we trust here that after the ENR update the # node will still be reachable, but it might not be the case. n.seen = bucket.nodes[nodeIdx].seen bucket.nodes[nodeIdx] = n return Existing # If the bucket has fewer than `BUCKET_SIZE` entries, it is inserted as the # last entry of the bucket (least recently seen node). If the bucket is # full, it might get split and adding is retried, else it is added as a # replacement. # Reasoning here is that adding nodes will happen for a big part from # lookups, which do not necessarily return nodes that are (still) reachable. # So, more trust is put in the own ordering by actually contacting peers and # newly additions are added as least recently seen (in fact they have not been # seen yet from our node its perspective). # However, in discovery v5 a node can also be added after a incoming request # if a handshake is done and an ENR is provided, and considering that this # handshake needs to be done, it is more likely that this node is reachable. # However, it is not certain and depending on different NAT mechanisms and # timers it might still fail. For this reason we currently do not add a way to # immediately add nodes to the most recently seen spot. if bucket.len < BUCKET_SIZE: if not ipLimitInc(r, bucket, n): return IpLimitReached bucket.add(n) else: # Bucket must be full, but lets see if it should be split the bucket. # Calculate the prefix shared by all nodes in the bucket's range, not the # ones actually in the bucket. let depth = computeSharedPrefixBits(@[bucket.istart, bucket.iend]) # Split if the bucket has the local node in its range or if the depth is not # congruent to 0 mod `bitsPerHop` if bucket.inRange(r.localNode) or (depth mod r.bitsPerHop != 0 and depth != ID_SIZE): r.splitBucket(r.buckets.find(bucket)) return r.addNode(n) # retry adding else: # When bucket doesn't get split the node is added to the replacement cache return r.addReplacement(bucket, n) proc removeNode*(r: var RoutingTable, n: Node) = ## Remove the node `n` from the routing table. let b = r.bucketForNode(n.id) if b.remove(n): ipLimitDec(r, b, n) proc replaceNode*(r: var RoutingTable, n: Node) = ## Replace node `n` with last entry in the replacement cache. If there are ## no entries in the replacement cache, node `n` will simply be removed. # TODO: Kademlia paper recommends here to not remove nodes if there are no # replacements. However, that would require a bit more complexity in the # revalidation as you don't want to try pinging that node all the time. let b = r.bucketForNode(n.id) if b.remove(n): ipLimitDec(r, b, n) if b.replacementCache.len > 0: # Nodes in the replacement cache are already included in the ip limits. b.add(b.replacementCache[high(b.replacementCache)]) b.replacementCache.delete(high(b.replacementCache)) proc getNode*(r: RoutingTable, id: NodeId): Option[Node] = ## Get the `Node` with `id` as `NodeId` from the routing table. ## If no node with provided node id can be found,`none` is returned . let b = r.bucketForNode(id) for n in b.nodes: if n.id == id: return some(n) proc contains*(r: RoutingTable, n: Node): bool = n in r.bucketForNode(n.id) # Check if the routing table contains node `n`. proc bucketsByDistanceTo(r: RoutingTable, id: NodeId): seq[KBucket] = sortedByIt(r.buckets, r.distance(it.midpoint, id)) proc nodesByDistanceTo(r: RoutingTable, k: KBucket, id: NodeId): seq[Node] = sortedByIt(k.nodes, r.distance(it.id, id)) proc neighbours*(r: RoutingTable, id: NodeId, k: int = BUCKET_SIZE, seenOnly = false): seq[Node] = ## Return up to k neighbours of the given node id. ## When seenOnly is set to true, only nodes that have been contacted ## previously successfully will be selected. result = newSeqOfCap[Node](k * 2) block addNodes: for bucket in r.bucketsByDistanceTo(id): for n in r.nodesByDistanceTo(bucket, id): # Only provide actively seen nodes when `seenOnly` set. if not seenOnly or n.seen: result.add(n) if result.len == k * 2: break addNodes # TODO: is this sort still needed? Can we get nodes closer from the "next" # bucket? result = sortedByIt(result, r.distance(it.id, id)) if result.len > k: result.setLen(k) proc neighboursAtDistance*(r: RoutingTable, distance: uint16, k: int = BUCKET_SIZE, seenOnly = false): seq[Node] = ## Return up to k neighbours at given logarithmic distance. result = r.neighbours(r.idAtDistance(r.localNode.id, distance), k, seenOnly) # This is a bit silly, first getting closest nodes then to only keep the ones # that are exactly the requested distance. keepIf(result, proc(n: Node): bool = r.logDistance(n.id, r.localNode.id) == distance) proc neighboursAtDistances*(r: RoutingTable, distances: seq[uint16], k: int = BUCKET_SIZE, seenOnly = false): seq[Node] = ## Return up to k neighbours at given logarithmic distances. # TODO: This will currently return nodes with neighbouring distances on the # first one prioritize. It might end up not including all the node distances # requested. Need to rework the logic here and not use the neighbours call. if distances.len > 0: result = r.neighbours(r.idAtDistance(r.localNode.id, distances[0]), k, seenOnly) # This is a bit silly, first getting closest nodes then to only keep the ones # that are exactly the requested distances. keepIf(result, proc(n: Node): bool = distances.contains(r.logDistance(n.id, r.localNode.id))) proc len*(r: RoutingTable): int = for b in r.buckets: result += b.len proc moveRight[T](arr: var openArray[T], a, b: int) = ## In `arr` move elements in range [a, b] right by 1. var t: T shallowCopy(t, arr[b + 1]) for i in countdown(b, a): shallowCopy(arr[i + 1], arr[i]) shallowCopy(arr[a], t) proc setJustSeen*(r: RoutingTable, n: Node) = ## Move `n` to the head (most recently seen) of its bucket. ## If `n` is not in the routing table, do nothing. let b = r.bucketForNode(n.id) let idx = b.nodes.find(n) if idx >= 0: if idx != 0: b.nodes.moveRight(0, idx - 1) if not n.seen: b.nodes[0].seen = true routing_table_nodes.inc(labelValues = ["seen"]) proc nodeToRevalidate*(r: RoutingTable): Node = ## Return a node to revalidate. The least recently seen node from a random ## bucket is selected. var buckets = r.buckets r.rng[].shuffle(buckets) # TODO: Should we prioritize less-recently-updated buckets instead? Could # store a `now` Moment at setJustSeen or at revalidate per bucket. for b in buckets: if b.len > 0: return b.nodes[^1] proc randomNodes*(r: RoutingTable, maxAmount: int, pred: proc(x: Node): bool {.gcsafe, noSideEffect.} = nil): seq[Node] = ## Get a `maxAmount` of random nodes from the routing table with the `pred` ## predicate function applied as filter on the nodes selected. var maxAmount = maxAmount let sz = r.len if maxAmount > sz: debug "Less peers in routing table than maximum requested", requested = maxAmount, present = sz maxAmount = sz result = newSeqOfCap[Node](maxAmount) var seen = initHashSet[Node]() # This is a rather inefficient way of randomizing nodes from all buckets, but even if we # iterate over all nodes in the routing table, the time it takes would still be # insignificant compared to the time it takes for the network roundtrips when connecting # to nodes. # However, "time it takes" might not be relevant, as there might be no point # in providing more `randomNodes` as the routing table might not have anything # new to provide. And there is no way for the calling code to know this. So # while it will take less total time compared to e.g. an (async) # randomLookup, the time might be wasted as all nodes are possibly seen # already. while len(seen) < maxAmount: let bucket = r.rng[].sample(r.buckets) if bucket.nodes.len != 0: let node = r.rng[].sample(bucket.nodes) if node notin seen: seen.incl(node) if pred.isNil() or node.pred: result.add(node)