feat: add bitlist and bitvector ssz support #494
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f3r10
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f3r10
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lib/ssz_ex.ex
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| num_bytes = byte_size(bit_list) | ||
| num_bits = num_bytes * @bits_per_byte | ||
| padding = num_bits - bit_size(bit_list) | ||
| formatted_bit_list = <<0::size(padding), bit_list::bitstring>> | ||
| len = length_of_bitlist(formatted_bit_list) | ||
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| cond do | ||
| len < 0 -> | ||
| {:error, "missing length information"} | ||
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| div(len, @bits_per_byte) + 1 != num_bytes -> | ||
| {:error, "invalid byte count"} | ||
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| len > max_size -> | ||
| {:error, "out of bounds"} | ||
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| true -> | ||
| pre_trailing_bits_size = (num_bytes - 1) * @bits_per_byte | ||
| <<pre::size(pre_trailing_bits_size), last_byte::binary>> = formatted_bit_list | ||
| <<_trailing::1, last::size(7)>> = last_byte | ||
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| cond do | ||
| last == 0 -> | ||
| {:ok, pre} | ||
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| pre == 0 -> | ||
| {:ok, <<last::size(len)>>} | ||
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| true -> | ||
| {:ok, <<pre::size(pre_trailing_bits_size), last::size(len - pre_trailing_bits_size)>>} |
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This is still overly complicated and doesn't address the padding problem. We can simplify this to something shorter:
Again, let's address this. It can be done in a simpler way:
<<pre::size(byte_size(bitlist)-1), last_byte::1>> = bitlist
decoded = <<pre, remove_trailing_bit(last_byte)>>
cond do
decoded == <<>> -> {:error, "missing length information"}
# Other edge cases
true -> decoded
endAnd that's it. The only missing thing is to code the removal of the trailing bit. Instead of using the length_of_bitlist you can just code a new function that's similar to leading_zeros (matching each possible byte) that ignores the first 1 bit and returns the rest. In the case of a <<0>> byte you can just return <<>> and the rest of the functionality will stil work.
lib/ssz_ex.ex
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| end | ||
| end | ||
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| defp encode_bitvector(bit_vector, size) when bit_size(bit_vector) == size, do: {:ok, bit_vector} |
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Instead of {:ok, bit_vector} here let's return {:ok, BitVector.to_bytes(bit_vector)}, which is a fix that has been added a couple of weeks ago (BitVector.new() was modified too).
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there is a warning about the opaque type:
Call does not have expected opaque term of type LambdaEthereumConsensus.Utils.BitVector.t() in the 1st position 🤔
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Can we add a BitVector.bit_size guard in the BitVector and use it here to see if the issue gets fixed? On guards: https://hexdocs.pm/elixir/main/Kernel.html#defguard/1
Motivation
Closes #479 and #480 only encoding/decoding support