Cairo 2.4.0 new types : bytes31 & ByteArray

[PhilippeR26]

Is your feature request related to a problem? Please describe.
I have analyzed the new Cairo v2.4.0 release, and searched what could be the impacts on Starknet.js.
I have found 2 new types that have been added in the abi :

• bytes31
• ByteArray

Describe the solution you'd like
Cairo team explained me how they are serialized :

bytes31

is just a Bigint limited to 31 bytes, representing a ShortString.

"type": "core::bytes_31::bytes31"

It will be straightforward to implement.

ByteArray

Here, it's more complicated. This type is an object representing a LongString.
In Cairo, it's used as a normal string ; nobody see the low level object.
But this complex object is used in the abi (similar to enums, but slightly more complicated).
I have coded/compiled a small cairo example. The result in the abi is :

{
      "type": "struct",
      "name": "core::byte_array::ByteArray",
      "members": [
        {
          "name": "data",
          "type": "core::array::Array::<core::bytes_31::bytes31>"
        },
        {
          "name": "pending_word",
          "type": "core::felt252"
        },
        {
          "name": "pending_word_len",
          "type": "core::integer::u32"
        }
      ]
    },

I think that on Starknet.js side, users want just to provide/receive a LongString in the calldata.
It means that we will not be in accordance with the abi for data input.
Will probably be interesting also for @haroune-mohammedi .
Cairo team has explained me how to read/write this struct ; I coded something that is conform.

One question is remaining : without Abi, what should be the behavior of CallData.compile in case of a string in the input data?
If it's a short string, deliver a Bigint, an array of Bigint, or a serialized ByteArray?
If it's a long string, deliver an array of Bigint, or a serialized ByteArray?

Describe alternatives you've considered
N/A

Additional context
As Cairo v2.4.0 is implemented for the first time in Starknet v0.13.0, it could be a good thing to implement these 2 new types in Starknet.js v6.0.

[PhilippeR26]

My code for CallData.compile() is working this way :

• If it's a short string, deliver a Bigint.
• If it's a long string, deliver a serialized ByteArray.
• If it's a short string, and if I want absolutely a ByteArray, deliver a serialized ByteArray with const myCalldata= CallData.compile({mess:byteArray.byteArrayFromString("Take care.")});
• If it's a long string, and if I want absolutely an array of shortString (for Cairo 0), deliver an array of felt with const myCalldata= CallData.compile({mess:shortString.splitLongString('Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore')})