Implement Packed encoding (#154)

* Fix typo in TypeEncoder test

* Implement packed encoding

Closes #139

Author: alisinabh

lib/abi.ex

@@ -58,7 +58,33 @@ defmodule ABI do
   end
 
   def encode(%FunctionSelector{} = function_selector, data, data_type) do
-    TypeEncoder.encode(data, function_selector, data_type)
+    TypeEncoder.encode(data, function_selector, data_type, :standard)
+  end
+
+  @doc """
+  Encodes the given data into the given types in packed encoding mode.
+
+  Note that packed encoding mode is ambiguous and cannot be decoded (there are no decode_packed functions).
+  Also, tuples (structs) and nester arrays are not supported.
+
+  More info https://docs.soliditylang.org/en/latest/abi-spec.html#non-standard-packed-mode
+
+  ## Examples
+
+      iex> ABI.encode_packed([{:uint, 16}], [0x12])
+      ...> |> Base.encode16(case: :lower)
+      "0012"
+
+      iex> ABI.encode_packed([:string, {:uint, 16}], ["Elixir ABI", 0x12])
+      ...> |> Base.encode16(case: :lower)
+      "456c69786972204142490012"
+
+      iex> ABI.encode_packed([{:int, 16}, {:bytes, 1}, {:uint, 16}, :string], [-1, <<0x42>>, 0x03, "Hello, world!"])
+      ...> |> Base.encode16(case: :lower)
+      "ffff42000348656c6c6f2c20776f726c6421"
+  """
+  def encode_packed(types, data) when is_list(types) do
+    TypeEncoder.encode(data, types, :input, :packed)
   end
 
   @doc """

lib/abi/type_encoder.ex

@@ -9,33 +9,39 @@ defmodule ABI.TypeEncoder do
 
   @doc """
   Encodes the given data based on the function selector.
+
+  ## Parameters
+  - data: The data to encode
+  - selector_or_types: Either a FunctionSelector struct or a list of types to encode the data with
+  - data_type: Determines which types to use from a FunctionSelector struct. Can be `:input` or `:output`.
+  - mode: Encoding mode. Can be `:standard` or `:packed`.
   """
 
-  def encode(data, selector_or_types, data_type \\ :input)
+  def encode(data, selector_or_types, data_type \\ :input, mode \\ :standard)
 
-  def encode(data, %FunctionSelector{function: nil, types: types}, :input) do
-    do_encode(data, types)
+  def encode(data, %FunctionSelector{function: nil, types: types}, :input, mode) do
+    do_encode(data, types, mode)
   end
 
-  def encode(data, %FunctionSelector{types: types} = function_selector, :input) do
-    encode_method_id(function_selector) <> do_encode(data, types)
+  def encode(data, %FunctionSelector{types: types} = function_selector, :input, mode) do
+    encode_method_id(function_selector) <> do_encode(data, types, mode)
   end
 
-  def encode(data, %FunctionSelector{returns: types}, :output) do
-    do_encode(data, types)
+  def encode(data, %FunctionSelector{returns: types}, :output, mode) do
+    do_encode(data, types, mode)
   end
 
-  def encode(data, types, _) when is_list(types) do
-    do_encode(data, types)
+  def encode(data, types, _, mode) when is_list(types) do
+    do_encode(data, types, mode)
   end
 
-  def encode_raw(data, types) when is_list(types) do
-    do_encode(data, types)
+  def encode_raw(data, types, mode) when is_list(types) do
+    do_encode(data, types, mode)
   end
 
-  defp do_encode(params, types, static_acc \\ [], dynamic_acc \\ [])
+  defp do_encode(params, types, static_acc \\ [], dynamic_acc \\ [], mode)
 
-  defp do_encode([], [], reversed_static_acc, reversed_dynamic_acc) do
+  defp do_encode([], [], reversed_static_acc, reversed_dynamic_acc, :standard) do
     static_acc = Enum.reverse(reversed_static_acc)
     dynamic_acc = Enum.reverse(reversed_dynamic_acc)
 
@@ -61,104 +67,131 @@ defmodule ABI.TypeEncoder do
     {complete_static_part, _} =
       Enum.reduce(dynamic_indexes, {static_acc, static_part_size}, fn {index, byte_size},
                                                                       {acc, size_acc} ->
-        new_static_acc = List.replace_at(acc, index, encode_uint(size_acc, 256))
-        new_prefix_size = byte_size + size_acc
+        new_static_acc = List.replace_at(acc, index, encode_uint(size_acc, 256, :standard))
 
-        {new_static_acc, new_prefix_size}
+        {new_static_acc, byte_size + size_acc}
       end)
 
     Enum.join(complete_static_part ++ dynamic_acc)
   end
 
+  defp do_encode([], [], static_acc, dynamic_acc, :packed) do
+    {values_acc, []} =
+      Enum.reduce(static_acc, {[], dynamic_acc}, fn
+        {:dynamic, _}, {values_acc, [value | dynamic_acc]} ->
+          {[value | values_acc], dynamic_acc}
+
+        value, {values_acc, dynamic_acc} ->
+          {[value | values_acc], dynamic_acc}
+      end)
+
+    Enum.join(values_acc)
+  end
+
   defp do_encode(
          [current_parameter | remaining_parameters],
          [current_type | remaining_types],
          static_acc,
-         dynamic_acc
+         dynamic_acc,
+         mode
        ) do
     {new_static_acc, new_dynamic_acc} =
-      do_encode_type(current_type, current_parameter, static_acc, dynamic_acc)
+      do_encode_type(current_type, current_parameter, static_acc, dynamic_acc, mode)
 
-    do_encode(remaining_parameters, remaining_types, new_static_acc, new_dynamic_acc)
+    do_encode(remaining_parameters, remaining_types, new_static_acc, new_dynamic_acc, mode)
   end
 
-  defp do_encode_type(:bool, parameter, static_part, dynamic_part) do
+  defp do_encode_type(:bool, parameter, static_part, dynamic_part, mode) do
     value =
       case parameter do
-        true -> encode_uint(1, 8)
-        false -> encode_uint(0, 8)
+        true -> encode_uint(1, 8, mode)
+        false -> encode_uint(0, 8, mode)
         _ -> raise "Invalid data for bool: #{inspect(parameter)}"
       end
 
     {[value | static_part], dynamic_part}
   end
 
-  defp do_encode_type({:uint, size}, parameter, static_part, dynamic_part) do
-    value = encode_uint(parameter, size)
+  defp do_encode_type({:uint, size}, parameter, static_part, dynamic_part, mode) do
+    value = encode_uint(parameter, size, mode)
 
     {[value | static_part], dynamic_part}
   end
 
-  defp do_encode_type({:int, size}, parameter, static_part, dynamic_part) do
-    value = encode_int(parameter, size)
+  defp do_encode_type({:int, size}, parameter, static_part, dynamic_part, mode) do
+    value = encode_int(parameter, size, mode)
 
     {[value | static_part], dynamic_part}
   end
 
-  defp do_encode_type(:string, parameter, static_part, dynamic_part) do
-    do_encode_type(:bytes, parameter, static_part, dynamic_part)
+  defp do_encode_type(:string, parameter, static_part, dynamic_part, mode) do
+    do_encode_type(:bytes, parameter, static_part, dynamic_part, mode)
   end
 
-  defp do_encode_type(:bytes, parameter, static_part, dynamic_part) do
+  defp do_encode_type(:bytes, parameter, static_part, dynamic_part, mode) do
     binary_param = maybe_encode_unsigned(parameter)
-    value = encode_uint(byte_size(binary_param), 256) <> encode_bytes(binary_param)
+
+    value =
+      case mode do
+        :standard ->
+          encode_uint(byte_size(binary_param), 256, mode) <> encode_bytes(binary_param, mode)
+
+        :packed ->
+          encode_bytes(binary_param, mode)
+      end
 
     dynamic_part_byte_size = byte_size(value)
 
     {[{:dynamic, dynamic_part_byte_size} | static_part], [value | dynamic_part]}
   end
 
-  defp do_encode_type({:bytes, size}, parameter, static_part, dynamic_part)
+  defp do_encode_type({:bytes, size}, parameter, static_part, dynamic_part, mode)
        when is_binary(parameter) and byte_size(parameter) <= size do
-    value = encode_bytes(parameter)
+    value = encode_bytes(parameter, mode)
 
     {[value | static_part], dynamic_part}
   end
 
-  defp do_encode_type({:bytes, size}, data, _, _) when is_binary(data) do
+  defp do_encode_type({:bytes, size}, data, _, _, _) when is_binary(data) do
     raise "size mismatch for bytes#{size}: #{inspect(data)}"
   end
 
-  defp do_encode_type({:bytes, size}, data, static_part, dynamic_part) when is_integer(data) do
+  defp do_encode_type({:bytes, size}, data, static_part, dynamic_part, mode)
+       when is_integer(data) do
     binary_param = maybe_encode_unsigned(data)
 
-    do_encode_type({:bytes, size}, binary_param, static_part, dynamic_part)
+    do_encode_type({:bytes, size}, binary_param, static_part, dynamic_part, mode)
   end
 
-  defp do_encode_type({:bytes, size}, data, _, _) do
+  defp do_encode_type({:bytes, size}, data, _, _, _) do
     raise "wrong datatype for bytes#{size}: #{inspect(data)}"
   end
 
-  defp do_encode_type({:array, type}, data, static_acc, dynamic_acc) do
+  defp do_encode_type({:array, type}, data, static_acc, dynamic_acc, mode) do
     param_count = Enum.count(data)
 
-    encoded_size = encode_uint(param_count, 256)
-
     types = List.duplicate(type, param_count)
 
-    result = do_encode(data, types)
+    result = do_encode(data, types, mode)
 
-    dynamic_acc_with_size = [encoded_size | dynamic_acc]
+    {dynamic_acc_with_size, data_bytes_size} =
+      case mode do
+        :standard ->
+          encoded_size = encode_uint(param_count, 256, mode)
+          # length is included and also length size is added
+          {[encoded_size | dynamic_acc], byte_size(result) + 32}
 
-    # number of elements count + data size
-    data_bytes_size = byte_size(result) + 32
+        :packed ->
+          # ignoring length of array
+          {dynamic_acc, byte_size(result)}
+      end
 
     {[{:dynamic, data_bytes_size} | static_acc], [result | dynamic_acc_with_size]}
   end
 
-  defp do_encode_type({:array, type, size}, data, static_acc, dynamic_acc) do
+  defp do_encode_type({:array, type, size}, data, static_acc, dynamic_acc, mode) do
     types = List.duplicate(type, size)
-    result = do_encode(data, types)
+    result = do_encode(data, types, mode)
 
     if FunctionSelector.is_dynamic?(type) do
       data_bytes_size = byte_size(result)
@@ -169,20 +202,30 @@ defmodule ABI.TypeEncoder do
     end
   end
 
-  defp do_encode_type(:address, data, static_acc, dynamic_acc) do
-    do_encode_type({:uint, 160}, data, static_acc, dynamic_acc)
+  defp do_encode_type(:address, data, static_acc, dynamic_acc, mode) do
+    do_encode_type({:uint, 160}, data, static_acc, dynamic_acc, mode)
+  end
+
+  defp do_encode_type({:tuple, _types}, _, _, _, :packed) do
+    raise RuntimeError, "Structs (tuples) are not supported in packed mode encoding"
   end
 
-  defp do_encode_type(type = {:tuple, _types}, tuple_parameters, static_acc, dynamic_acc)
+  defp do_encode_type(
+         type = {:tuple, _types},
+         tuple_parameters,
+         static_acc,
+         dynamic_acc,
+         :standard
+       )
        when is_tuple(tuple_parameters) do
     list_parameters = Tuple.to_list(tuple_parameters)
 
-    do_encode_type(type, list_parameters, static_acc, dynamic_acc)
+    do_encode_type(type, list_parameters, static_acc, dynamic_acc, :standard)
   end
 
-  defp do_encode_type(type = {:tuple, types}, list_parameters, static_acc, dynamic_acc)
+  defp do_encode_type(type = {:tuple, types}, list_parameters, static_acc, dynamic_acc, :standard)
        when is_list(list_parameters) do
-    result = do_encode(list_parameters, types)
+    result = do_encode(list_parameters, types, :standard)
 
     if FunctionSelector.is_dynamic?(type) do
       data_bytes_size = byte_size(result)
@@ -193,8 +236,8 @@ defmodule ABI.TypeEncoder do
     end
   end
 
-  defp encode_bytes(bytes) do
-    pad(bytes, byte_size(bytes), :right)
+  defp encode_bytes(bytes, mode) do
+    pad(bytes, byte_size(bytes), :right, mode)
   end
 
   @spec encode_method_id(FunctionSelector.t()) :: binary()
@@ -216,7 +259,7 @@ defmodule ABI.TypeEncoder do
 
   # Note, we'll accept a binary or an integer here, so long as the
   # binary is not longer than our allowed data size
-  defp encode_uint(data, size_in_bits) when rem(size_in_bits, 8) == 0 do
+  defp encode_uint(data, size_in_bits, mode) when rem(size_in_bits, 8) == 0 do
     size_in_bytes = (size_in_bits / 8) |> round
     bin = maybe_encode_unsigned(data)
 
@@ -226,22 +269,22 @@ defmodule ABI.TypeEncoder do
           "Data overflow encoding uint, data `#{data}` cannot fit in #{size_in_bytes * 8} bits"
         )
 
-    bin |> pad(size_in_bytes, :left)
+    bin |> pad(size_in_bytes, :left, mode)
   end
 
-  defp encode_int(data, size_in_bits) when rem(size_in_bits, 8) == 0 do
+  defp encode_int(data, size_in_bits, mode) when rem(size_in_bits, 8) == 0 do
     if signed_overflow?(data, size_in_bits) do
       raise("Data overflow encoding int, data `#{data}` cannot fit in #{size_in_bits} bits")
     end
 
-    encode_int(data)
+    case mode do
+      :standard -> <<data::signed-256>>
+      :packed -> <<data::signed-size(size_in_bits)>>
+    end
   end
 
-  # encoding with integer-signed-256 we already get the right padding
-  defp encode_int(data), do: <<data::signed-256>>
-
   defp signed_overflow?(n, max_bits) do
-    n < :math.pow(2, max_bits - 1) * -1 + 1 || n > :math.pow(2, max_bits - 1) - 1
+    n < 2 ** (max_bits - 1) * -1 + 1 || n > 2 ** (max_bits - 1) - 1
   end
 
   def mod(x, n) do
@@ -252,7 +295,19 @@ defmodule ABI.TypeEncoder do
       else: remainder
   end
 
-  defp pad(bin, size_in_bytes, direction) do
+  defp pad(bin, size_in_bytes, _direction, :packed) when byte_size(bin) == size_in_bytes, do: bin
+
+  defp pad(bin, size_in_bytes, direction, :packed) when byte_size(bin) < size_in_bytes do
+    padding_size_bits = (size_in_bytes - byte_size(bin)) * 8
+    padding = <<0::size(padding_size_bits)>>
+
+    case direction do
+      :left -> padding <> bin
+      :right -> bin <> padding
+    end
+  end
+
+  defp pad(bin, size_in_bytes, direction, :standard) do
     total_size = size_in_bytes + mod(32 - size_in_bytes, 32)
     padding_size_bits = (total_size - byte_size(bin)) * 8
     padding = <<0::size(padding_size_bits)>>