feat: ssz support nested containers (#509)

lib/ssz_ex.ex

@@ -380,8 +380,22 @@ defmodule LambdaEthereumConsensus.SszEx do
   defp get_fixed_size({:int, size}), do: div(size, @bits_per_byte)
   defp get_fixed_size({:bytes, size}), do: size
 
+  defp get_fixed_size(module) when is_atom(module) do
+    schemas = module.schema()
+
+    schemas
+    |> Enum.map(fn {_, schema} -> get_fixed_size(schema) end)
+    |> Enum.sum()
+  end
+
   defp variable_size?({:list, _, _}), do: true
   defp variable_size?(:bool), do: false
   defp variable_size?({:int, _}), do: false
   defp variable_size?({:bytes, _}), do: false
+
+  defp variable_size?(module) when is_atom(module) do
+    module.schema()
+    |> Enum.map(fn {_, schema} -> variable_size?(schema) end)
+    |> Enum.any?()
+  end
 end

lib/ssz_types/beacon_chain/attestation_data.ex

@@ -4,6 +4,8 @@ defmodule SszTypes.AttestationData do
   Related definitions in `native/ssz_nif/src/types/`.
   """
 
+  @behaviour LambdaEthereumConsensus.Container
+
   fields = [
     :slot,
     :index,
@@ -22,4 +24,15 @@ defmodule SszTypes.AttestationData do
           source: SszTypes.Checkpoint.t(),
           target: SszTypes.Checkpoint.t()
         }
+
+  @impl LambdaEthereumConsensus.Container
+  def schema do
+    [
+      {:slot, {:int, 64}},
+      {:index, {:int, 64}},
+      {:beacon_block_root, {:bytes, 32}},
+      {:source, SszTypes.Checkpoint},
+      {:target, SszTypes.Checkpoint}
+    ]
+  end
 end

lib/ssz_types/beacon_chain/checkpoint.ex

@@ -4,6 +4,7 @@ defmodule SszTypes.Checkpoint do
   Related definitions in `native/ssz_nif/src/types/`.
   """
 
+  @behaviour LambdaEthereumConsensus.Container
   fields = [
     :root,
     :epoch
@@ -16,4 +17,11 @@ defmodule SszTypes.Checkpoint do
           epoch: SszTypes.epoch(),
           root: SszTypes.root()
         }
+
+  def schema do
+    [
+      {:epoch, {:int, 64}},
+      {:root, {:bytes, 32}}
+    ]
+  end
 end

lib/ssz_types/beacon_chain/indexed_attestation.ex

@@ -3,6 +3,7 @@ defmodule SszTypes.IndexedAttestation do
   Struct definition for `IndexedAttestation`.
   Related definitions in `native/ssz_nif/src/types/`.
   """
+  @behaviour LambdaEthereumConsensus.Container
 
   fields = [
     :attesting_indices,
@@ -19,4 +20,13 @@ defmodule SszTypes.IndexedAttestation do
           data: SszTypes.AttestationData.t(),
           signature: SszTypes.bls_signature()
         }
+
+  @impl LambdaEthereumConsensus.Container
+  def schema do
+    [
+      {:attesting_indices, {:list, {:int, 64}, 2048}},
+      {:data, SszTypes.AttestationData},
+      {:signature, {:bytes, 96}}
+    ]
+  end
 end

test/unit/ssz_ex_test.exs

@@ -28,6 +28,60 @@ defmodule Unit.SSZExTest do
     assert_roundtrip(<<0>>, false, :bool)
   end
 
+  test "serialize and deserialize nested container" do
+    checkpoint_source = %SszTypes.Checkpoint{
+      epoch: 3_776_037_760_046_644_755,
+      root:
+        <<29, 22, 191, 147, 188, 238, 162, 89, 147, 162, 202, 111, 169, 162, 84, 95, 194, 85, 54,
+          172, 44, 74, 37, 128, 248, 21, 86, 246, 151, 54, 24, 54>>
+    }
+
+    checkpoint_target = %SszTypes.Checkpoint{
+      epoch: 2_840_053_453_521_072_037,
+      root:
+        <<15, 174, 23, 120, 4, 9, 2, 116, 67, 73, 254, 53, 197, 3, 191, 166, 104, 34, 121, 2, 57,
+          69, 75, 69, 254, 237, 132, 68, 254, 49, 127, 175>>
+    }
+
+    attestation_data = %SszTypes.AttestationData{
+      slot: 5_057_010_135_270_197_978,
+      index: 6_920_931_864_607_509_210,
+      beacon_block_root:
+        <<31, 38, 101, 174, 248, 168, 116, 226, 15, 39, 218, 148, 42, 8, 80, 80, 241, 149, 162,
+          32, 176, 208, 120, 120, 89, 123, 136, 115, 154, 28, 21, 174>>,
+      source: checkpoint_source,
+      target: checkpoint_target
+    }
+
+    indexed_attestation = %SszTypes.IndexedAttestation{
+      attesting_indices: [15_833_676_831_095_072_535, 7_978_643_446_947_046_229],
+      data: attestation_data,
+      signature:
+        <<46, 244, 83, 164, 182, 222, 218, 247, 8, 186, 138, 100, 5, 96, 34, 117, 134, 123, 219,
+          188, 181, 11, 209, 57, 207, 24, 249, 42, 74, 27, 228, 97, 73, 46, 219, 202, 122, 149,
+          135, 30, 91, 126, 180, 69, 129, 170, 147, 142, 242, 27, 233, 63, 242, 7, 144, 8, 192,
+          165, 194, 220, 77, 247, 128, 107, 41, 199, 166, 59, 34, 160, 222, 114, 250, 250, 3, 130,
+          145, 8, 45, 65, 13, 82, 44, 80, 30, 181, 239, 54, 152, 237, 244, 72, 231, 179, 239, 22>>
+    }
+
+    serialized =
+      <<228, 0, 0, 0, 218, 138, 84, 194, 236, 27, 46, 70, 218, 202, 156, 184, 220, 22, 12, 96, 31,
+        38, 101, 174, 248, 168, 116, 226, 15, 39, 218, 148, 42, 8, 80, 80, 241, 149, 162, 32, 176,
+        208, 120, 120, 89, 123, 136, 115, 154, 28, 21, 174, 19, 190, 10, 34, 86, 46, 103, 52, 29,
+        22, 191, 147, 188, 238, 162, 89, 147, 162, 202, 111, 169, 162, 84, 95, 194, 85, 54, 172,
+        44, 74, 37, 128, 248, 21, 86, 246, 151, 54, 24, 54, 165, 175, 62, 152, 145, 229, 105, 39,
+        15, 174, 23, 120, 4, 9, 2, 116, 67, 73, 254, 53, 197, 3, 191, 166, 104, 34, 121, 2, 57,
+        69, 75, 69, 254, 237, 132, 68, 254, 49, 127, 175, 46, 244, 83, 164, 182, 222, 218, 247, 8,
+        186, 138, 100, 5, 96, 34, 117, 134, 123, 219, 188, 181, 11, 209, 57, 207, 24, 249, 42, 74,
+        27, 228, 97, 73, 46, 219, 202, 122, 149, 135, 30, 91, 126, 180, 69, 129, 170, 147, 142,
+        242, 27, 233, 63, 242, 7, 144, 8, 192, 165, 194, 220, 77, 247, 128, 107, 41, 199, 166, 59,
+        34, 160, 222, 114, 250, 250, 3, 130, 145, 8, 45, 65, 13, 82, 44, 80, 30, 181, 239, 54,
+        152, 237, 244, 72, 231, 179, 239, 22, 23, 39, 193, 253, 47, 133, 188, 219, 85, 227, 198,
+        60, 241, 213, 185, 110>>
+
+    assert_roundtrip(serialized, indexed_attestation, SszTypes.IndexedAttestation)
+  end
+
   test "serialize and deserialize list" do
     # for test purposes only, do not use in practice
     assert_roundtrip(<<1, 1, 0>>, [true, true, false], {:list, :bool, 3})