Error when decoding array

[saneery]

When I try to decode an array of addresses, I get an error

iex(1)> data = Base.decode16!("000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000000000030000000000000000000000000b2f5e2f3cbd864eaa2c642e3769c1582361caf6000000000000000000000000aa94b687d3f9552a453b81b2834ca53778980dc0000000000000000000000000312c230e7d6db05224f60208a656e3541c5c42ba", case: :lower)
<<0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  0, 0, 0, 0, 0, 32, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, ...>>
iex(2)> selector = %ABI.FunctionSelector{function: nil, types: [array: :address]}                                
%ABI.FunctionSelector{
  function: nil,
  input_names: [],
  inputs_indexed: nil,
  method_id: nil,
  returns: [],
  type: nil,
  types: [array: :address]
}
iex(3)> ABI.TypeDecoder.decode(data, selector)
** (MatchError) no match of right hand side value: ""
    (ex_abi) lib/abi/type_decoder.ex:195: ABI.TypeDecoder.decode_bytes/3
    (ex_abi) lib/abi/type_decoder.ex:233: anonymous fn/2 in ABI.TypeDecoder.decode_type/2
    (elixir) lib/enum.ex:1940: Enum."-reduce/3-lists^foldl/2-0-"/3
    (ex_abi) lib/abi/type_decoder.ex:228: ABI.TypeDecoder.decode_type/2
    (ex_abi) lib/abi/type_decoder.ex:222: ABI.TypeDecoder.decode_type/2
    (ex_abi) lib/abi/type_decoder.ex:173: anonymous fn/2 in ABI.TypeDecoder.do_decode_raw/2
    (elixir) lib/enum.ex:1940: Enum."-reduce/3-lists^foldl/2-0-"/3
    (ex_abi) lib/abi/type_decoder.ex:172: ABI.TypeDecoder.do_decode_raw/2

On the 0.1.18 version all right:

...
iex(3)> ABI.TypeDecoder.decode(data, selector)
[
  [
    <<11, 47, 94, 47, 60, 189, 134, 78, 170, 44, 100, 46, 55, 105, 193, 88, 35,
      97, 202, 246>>,
    <<170, 148, 182, 135, 211, 249, 85, 42, 69, 59, 129, 178, 131, 76, 165, 55,
      120, 152, 13, 192>>,
    <<49, 44, 35, 14, 125, 109, 176, 82, 36, 246, 2, 8, 166, 86, 227, 84, 28,
      92, 66, 186>>
  ]
]

[saneery]

I think, there is a bug in TypeDecoder.decode_uint/2

ex_abi/lib/abi/type_decoder.ex

Lines 215 to 218 in 1feae1b

	defp decode_type({:array, type}, data) do
	{count, bytes} = decode_uint(data, 256)
	decode_type({:array, type, count}, bytes)
	end

when I set IO.inspect(count), it returns 32

[volnyvolnyvolny]

@saneery, it seems that you trying to decode value that is wrapped in a tuple:

iex(1)> addresses = [
...(1)>     <<11, 47, 94, 47, 60, 189, 134, 78, 170, 44, 100, 46, 55, 105, 193, 88, 35,
...(1)>       97, 202, 246>>, r
...(1)>     <<170, 148, 182, 135, 211, 249, 85, 42, 69, 59, 129, 178, 131, 76, 165, 55,
...(1)>       120, 152, 13, 192>>,
...(1)>     <<49, 44, 35, 14, 125, 109, 176, 82, 36, 246, 2, 8, 166, 86, 227, 84, 28,
...(1)>       92, 66, 186>>
...(1)>   ]
iex(2)> value = "000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000000000030000000000000000000000000b2f5e2f3cbd864eaa2c642e3769c1582361caf6000000000000000000000000aa94b687d3f9552a453b81b2834ca53778980dc0000000000000000000000000312c230e7d6db05224f60208a656e3541c5c42ba"
iex(3)> value == ABI.TypeEncoder.encode_raw([{addresses}], [{:tuple, [array: :address]}]) |> Base.encode16(case: :lower)
true

If you look at the:

iex(4)> for <<b::binary-64 <- value>>, do: b 
["0000000000000000000000000000000000000000000000000000000000000020",
 "0000000000000000000000000000000000000000000000000000000000000003",
 "0000000000000000000000000b2f5e2f3cbd864eaa2c642e3769c1582361caf6",
 "000000000000000000000000aa94b687d3f9552a453b81b2834ca53778980dc0",
 "000000000000000000000000312c230e7d6db05224f60208a656e3541c5c42ba"]

you'll notice that the first 32 bytes represent the array offset:

 "0000000000000000000000000000000000000000000000000000000000000020"

The correct representation is:

iex(5)> enc = ABI.TypeEncoder.encode_raw([addresses], [array: :address]) |> Base.encode16(case: :lower)
iex(6)> for <<b::binary-64 <- enc>>, do: b
["0000000000000000000000000000000000000000000000000000000000000003",
 "0000000000000000000000000b2f5e2f3cbd864eaa2c642e3769c1582361caf6",
 "000000000000000000000000aa94b687d3f9552a453b81b2834ca53778980dc0",
 "000000000000000000000000312c230e7d6db05224f60208a656e3541c5c42ba"]

You can test it with:

iex(7)> selector = %ABI.FunctionSelector{types: [array: :address]}
iex(8)> data = Base.decode16!(String.slice(value, 64..-1), case: :lower)
iex(9)> ABI.TypeDecoder.decode(data, selector)
[
  [
    <<11, 47, 94, 47, 60, 189, 134, 78, 170, 44, 100, 46, 55, 105, 193, 88, 35,
      97, 202, 246>>,
    <<170, 148, 182, 135, 211, 249, 85, 42, 69, 59, 129, 178, 131, 76, 165, 55,
      120, 152, 13, 192>>,
    <<49, 44, 35, 14, 125, 109, 176, 82, 36, 246, 2, 8, 166, 86, 227, 84, 28,
      92, 66, 186>>
  ]
]

[vbaranov]

@zergera Thanks for the thorough explanation of dynamic size array ABI decoding. Nevertheless, ABI.TypeDecoder.decode(data, selector) should decode to an array without additional step which makes an offset

data = Base.decode16!(String.slice(value, 64..-1), case: :lower)

It should be made inside the decoding method. And this is done in the recently issued 0.3.0 version of the library. I am closing this issue.