Deserialize serialized default bls values (#388)

Ugly workaround to quick-fix broken network/interop sim

beacon_chain/spec/crypto.nim

@@ -212,10 +212,18 @@ else:
     ValidatorSig(kind: Real, blsValue: key.sign(domain, msg))
 
 proc fromBytes*[T](R: type BlsValue[T], bytes: openarray[byte]): R =
-  when defined(ssz_testing):
-    result = R(kind: OpaqueBlob, blob: toArray(result.blob.len, bytes))
+  # This is a workaround, so that we can deserialize the serialization of a
+  # default-initialized BlsValue without raising an exception
+  # TODO don't use exceptions for parsing, ever. Handle deserialization issues
+  #      sanely, always.
+  const allZeroes = T()
+  if bytes == allZeroes.getBytes():
+    R(kind: Real)
   else:
-    result = R(kind: Real, blsValue: init(T, bytes))
+    when defined(ssz_testing):
+      R(kind: OpaqueBlob, blob: toArray(result.blob.len, bytes))
+    else:
+      R(kind: Real, blsValue: init(T, bytes))
 
 proc initFromBytes*[T](val: var BlsValue[T], bytes: openarray[byte]) =
   val = fromBytes(BlsValue[T], bytes)

tests/test_beacon_chain_db.nim

@@ -6,8 +6,8 @@
 # at your option. This file may not be copied, modified, or distributed except according to those terms.
 
 import  options, unittest, sequtils, strutils, eth/trie/[db],
-  ../beacon_chain/[beacon_chain_db, ssz],
-  ../beacon_chain/spec/[datatypes, digest, crypto],
+  ../beacon_chain/[beacon_chain_db, extras, interop, ssz],
+  ../beacon_chain/spec/[beaconstate, datatypes, digest, crypto],
   # test utilies
   ./testutil
 
@@ -87,3 +87,22 @@ suite "Beacon chain DB" & preset():
 
     doAssert toSeq(db.getAncestors(a0r)) == [(a0r, a0)]
     doAssert toSeq(db.getAncestors(a2r)) == [(a2r, a2), (a1r, a1), (a0r, a0)]
+
+  test "sanity check genesis roundtrip" & preset():
+    # This is a really dumb way of checking that we can roundtrip a genesis
+    # state. We've been bit by this because we've had a bug in the BLS
+    # serialization where an all-zero default-initialized bls signature could
+    # not be deserialized because the deserialization was too strict.
+    var
+      db = init(BeaconChainDB, newMemoryDB())
+
+    let
+      state = initialize_beacon_state_from_eth1(
+        eth1BlockHash, 0, makeInitialDeposits(SLOTS_PER_EPOCH), {skipValidation})
+      root = hash_tree_root(state)
+
+    db.putState(state)
+
+    check:
+      db.containsState(root)
+      db.getState(root).get() == state