feat: add default methods for all schemas/ssz types (#947)

Author: Arkenan

lib/lambda_ethereum_consensus/validator/validator.ex

@@ -344,7 +344,7 @@ defmodule LambdaEthereumConsensus.Validator do
       }
     }
 
-    bits = BitList.default(committee_length) |> BitList.set(index_in_committee)
+    bits = BitList.zero(committee_length) |> BitList.set(index_in_committee)
 
     signature = Utils.get_attestation_signature(head_state, attestation_data, privkey)
 

lib/ssz_ex.ex

@@ -428,6 +428,25 @@ defmodule LambdaEthereumConsensus.SszEx do
     (size + @bits_per_chunk - 1) |> div(@bits_per_chunk)
   end
 
+  @doc """
+  Returns the default value for a schema, which can be a basic or composite type.
+  """
+  def default({:int, _}), do: 0
+  def default(:bool), do: false
+  def default({:bytes, size}), do: <<0::size(size * 8)>>
+  def default({:list, :bytes, _size}), do: <<>>
+  def default({:list, _, _}), do: []
+  def default({:vector, :bytes, size}), do: <<0::size(size * 8)>>
+  def default({:vector, inner_type, size}), do: default(inner_type) |> List.duplicate(size)
+  def default({:bitlist, _}), do: BitList.default()
+  def default({:bitvector, size}), do: BitVector.new(size)
+
+  def default(module) when is_atom(module) do
+    module.schema()
+    |> Enum.map(fn {attr, schema} -> {attr, default(schema)} end)
+    |> then(&struct!(module, &1))
+  end
+
   #################
   ### Private functions
   #################

lib/utils/bit_list.ex

@@ -9,10 +9,16 @@ defmodule LambdaEthereumConsensus.Utils.BitList do
   @bits_in_sentinel_bit 1
 
   @doc """
-  Creates a new bit_list with the given size.
+  Creates a bit_list full of zeroes, with the given size.
   """
-  @spec default(non_neg_integer) :: t
-  def default(size), do: <<0::size(size)>>
+  @spec zero(non_neg_integer) :: t
+  def zero(size), do: <<0::size(size)>>
+
+  @doc """
+  Creates a default (empty/size 0) bit list.
+  """
+  @spec default :: t
+  def default, do: <<>>
 
   @doc """
   Creates a new bit_list from bitstring.

test/unit/ssz_ex_test.exs

@@ -1,6 +1,16 @@
 defmodule Unit.SSZExTest do
+  alias LambdaEthereumConsensus.Utils.Diff
+
+  alias Types.{
+    BeaconBlock,
+    BeaconBlockBody,
+    Checkpoint,
+    Eth1Data,
+    ExecutionPayload,
+    SyncAggregate
+  }
+
   alias LambdaEthereumConsensus.SszEx
-  alias Types.Checkpoint
   use ExUnit.Case
 
   def assert_roundtrip(serialized, deserialized, schema) do
@@ -463,6 +473,64 @@ defmodule Unit.SSZExTest do
     assert_roundtrip(serialized, validator, Types.Validator)
   end
 
+  @root_size 32
+  @signature_size 96
+  @default_signature <<0::size(@signature_size * 8)>>
+  @default_root <<0::size(@root_size * 8)>>
+  @default_hash @default_root
+
+  test "default block" do
+    default = SszEx.default(BeaconBlock)
+
+    expected = %BeaconBlock{
+      slot: 0,
+      proposer_index: 0,
+      parent_root: @default_root,
+      state_root: @default_root,
+      body: %BeaconBlockBody{
+        randao_reveal: @default_signature,
+        eth1_data: %Eth1Data{
+          deposit_root: @default_root,
+          deposit_count: 0,
+          block_hash: @default_hash
+        },
+        graffiti: <<0::size(32 * 8)>>,
+        proposer_slashings: [],
+        attester_slashings: [],
+        attestations: [],
+        deposits: [],
+        voluntary_exits: [],
+        sync_aggregate: %SyncAggregate{
+          sync_committee_bits: <<0::size(ChainSpec.get("SYNC_COMMITTEE_SIZE"))>>,
+          sync_committee_signature: @default_signature
+        },
+        execution_payload: %ExecutionPayload{
+          parent_hash: @default_hash,
+          fee_recipient: <<0::size(20 * 8)>>,
+          state_root: @default_root,
+          receipts_root: @default_root,
+          logs_bloom: <<0::size(ChainSpec.get("BYTES_PER_LOGS_BLOOM") * 8)>>,
+          prev_randao: <<0::size(32 * 8)>>,
+          block_number: 0,
+          gas_limit: 0,
+          gas_used: 0,
+          timestamp: 0,
+          extra_data: <<>>,
+          base_fee_per_gas: 0,
+          block_hash: @default_hash,
+          transactions: [],
+          withdrawals: [],
+          blob_gas_used: 0,
+          excess_blob_gas: 0
+        },
+        bls_to_execution_changes: [],
+        blob_kzg_commitments: []
+      }
+    }
+
+    assert Diff.diff(default, expected) == :unchanged
+  end
+
   test "serialize and deserialize bitlist" do
     encoded_bytes = <<160, 92, 1>>
     assert {:ok, decoded_bytes} = SszEx.decode(encoded_bytes, {:bitlist, 16})