initial impl of fork choice rules. Main types sorted out

beacon_chain/datatypes.nim

@@ -61,7 +61,7 @@ type
     dynasty: int64                                # What dynasty the crosslink was submitted in
     hash: Blake2_256_Digest                       # The block hash
 
-  BLSPublicKey = object
+  BLSPublicKey* = object
     # Stub for BLS signature
     data: array[32, byte]
 
@@ -91,7 +91,7 @@ type
 
 const
   SHARD_COUNT*         = 1024 # a constant referring to the number of shards
-  DEPOSITE_SIZE*       = 32   # You need to deposit 32 ETH to be a validator in Casper
+  DEPOSIT_SIZE*        = 32   # You need to deposit 32 ETH to be a validator in Casper
   MAX_VALIDATOR_COUNT* = 2^22 # 4_194_304, this means that ~132M ETH can stake at the same time (= MaxValidator Count * DepositSize)
   SLOT_DURATION*       = 8    # seconds
   CYCLE_LENGTH*        = 64   # slots

beacon_chain/fork_choice_rule/fork_choice_rule.nim

@@ -0,0 +1,122 @@
+# beacon_chain
+# Copyright (c) 2018 Status Research & Development GmbH
+# Licensed and distributed under either of
+#   * MIT license (license terms in the root directory or at http://opensource.org/licenses/MIT).
+#   * Apache v2 license (license terms in the root directory or at http://www.apache.org/licenses/LICENSE-2.0).
+# at your option. This file may not be copied, modified, or distributed except according to those terms.
+
+# A port of https://github.com/ethereum/research/blob/master/clock_disparity/ghost_node.py
+# Specs: https://ethresear.ch/t/beacon-chain-casper-ffg-rpj-mini-spec/2760
+# Part of Casper+Sharding chain v2.1: https://notes.ethereum.org/SCIg8AH5SA-O4C1G1LYZHQ#
+
+import
+  tables, deques,   # Stdlib
+  nimcrypto,        # Nimble packages
+  # ../datatypes, # BeaconBlock is still different from the simulation blocks
+  ./networksim      # From repo
+
+import hashes
+func hash(x: MDigest): Hash =
+  # Allow usage of MDigest in hashtables
+  const bytes = x.type.bits div 8
+  result = x.unsafeAddr.hashData(bytes)
+
+const
+  NOTARIES = 100    # Committee size in Casper v2.1
+  SLOT_SIZE = 6     # Slot duration in Casper v2.1
+  EPOCH_LENGTH = 25 # Cycle length inCasper v2.
+
+    # TODO, clear up if reference semantics are needed
+    # for the tables, Block and Sig
+
+type
+  Block = ref object
+    contents: array[32, byte]
+    parent_hash: MDigest[256]
+    hash: MDigest[256]
+    height: int # slot in Casper v2.1 spec
+    proposer: int64
+    slot: int64
+
+func min_timestamp(self: Block): int64 =
+  SLOT_SIZE * self.slot
+
+let Genesis = Block()
+
+type
+  Sig = object
+    # TODO: unsure if this is still relevant in Casper v2.1
+    proposer: int64                 # the validator that creates a block
+    targets: seq[MDigest[256]]      # the hash of blocks proposed
+    slot: int64                     # slot number
+    timestamp: int64                # ts in the ref implementation
+    hash: MDigest[384]              # The signature (BLS12-384)
+
+type
+  Node = ref object
+
+    blocks: TableRef[MDigest[256], Block]
+    sigs: TableRef[MDigest[384], Sig]
+    main_chain: seq[MDigest[256]]
+    timequeue: seq[Block]
+    parentqueue: TableRef[MDigest[256], Node]
+    children: TableRef[MDigest[256], seq[MDigest[256]]]
+    scores: TableRef[MDigest[256], int]
+    scores_at_height: TableRef[MDigest[256], int] # Should be slot not height in v2.1
+    justified: TableRef[MDigest[256], bool]
+    finalized: TableRef[MDigest[256], bool]
+    timestamp: int64
+    id: int64
+    network: NetworkSimulator
+    used_parents: TableRef[MDigest[256], Node]
+    processed: TableRef[MDigest[256], Block]
+    sleepy: bool
+    careless: bool
+    first_round: bool
+    last_made_block: int64
+    last_made_sig: int64
+
+proc log(self: Node, words: string, lvl = 3, all = false) =
+  if (self.id == 0 or all) and lvl >= 2:
+    echo self.id, words
+
+func add_to_timequeue(self: Node, obj: Block) =
+  var i = 0
+  while i < self.timequeue.len and self.timequeue[i].min_timestamp < obj.min_timestamp:
+    inc i
+  self.timequeue.insert(obj, i)
+
+func add_to_multiset[K, V](self: Node, multiset: var TableRef[K, V], k: K, v: V) =
+  if k notin multiset:
+    multiset[k] = @[]
+  multiset[k].add v
+
+func change_head(self: Node, chain: var seq[MDigest[256]], new_head: Block) =
+  chain.add newSeq[MDigest[256]](new_head.height + 1 - chain.len)
+  var (i, c) = (new_head.height, new_head.hash)
+  while c != chain[i]:
+    chain[i] = c
+    c = self.blocks[c].parent_hash
+    dec i
+  for idx, val in chain:
+    doAssert self.blocks[val].height == idx
+
+func recalculate_head(self: Node) =
+  while true:
+    var
+      descendant_queue = initDeque[MDigest[256]]()
+      new_head: MDigest[256]
+      max_count = 0
+    descendant_queue.addFirst self.main_chain[^1]
+    while descendant_queue.len != 0:
+      let first = descendant_queue.popFirst()
+      if first in self.children:
+        for c in self.children[first]:
+          descendant_queue.addLast c
+      if self.scores.getOrDefault(first, 0) > max_count and first != self.main_chain[^1]:
+        new_head = first
+        max_count = self.scores.getOrDefault(first, 0)
+    if new_head != MDigest[256](): # != default init, a 32-byte array of 0
+      self.change_head(self.main_chain, self.blocks[new_head])
+    else:
+      return

beacon_chain/fork_choice_rule/networksim.nim

@@ -0,0 +1,21 @@
+# beacon_chain
+# Copyright (c) 2018 Status Research & Development GmbH
+# Licensed and distributed under either of
+#   * MIT license (license terms in the root directory or at http://opensource.org/licenses/MIT).
+#   * Apache v2 license (license terms in the root directory or at http://www.apache.org/licenses/LICENSE-2.0).
+# at your option. This file may not be copied, modified, or distributed except according to those terms.
+
+# A port of https://github.com/ethereum/research/blob/master/clock_disparity/ghost_node.py
+# Specs: https://ethresear.ch/t/beacon-chain-casper-ffg-rpj-mini-spec/2760
+# Part of Casper+Sharding chain v2.1: https://notes.ethereum.org/SCIg8AH5SA-O4C1G1LYZHQ#
+
+import tables
+
+type
+  NetworkSimulator* = ref object
+    agents*: seq[int]
+    latency_distribution_sample*: seq[int]
+    time*: int64
+    objqueue*: Table[int, int]
+    peers*: Table[int, int]
+    reliability*: float

nim.cfg

@@ -0,0 +1,5 @@
+# https://github.com/nim-lang/Nim/issues/8691#issuecomment-414662209
+# Doesn't work unfortunately
+@if nimHasForLoopMacros:
+--experimental:forLoopMacros
+@end