AsByteArray() isn't able to convert BigInteger to ByteArray

[superboyiii]

When I test nep5 sc, I'd like to put 0 into account storage when balanceOf return null, so I write as below:

        [DisplayName("BalanceOf")]
        public static BigInteger BalanceOf(byte[] account)
        {
            if (account.Length != 20)
                throw new InvalidOperationException("The parameter account SHOULD be 20-byte addresses");
            var balance = Storage.Get(Storage.CurrentContext, account);
            BigInteger zero = 0;
            byte[] byteZero = zero.AsByteArray();
            if (balance is null)
            {
                Storage.Put(Storage.CurrentContext, account, byteZero);
            }
            return Storage.Get(Storage.CurrentContext, account).AsBigInteger();
        }

Then I found this byteZero is not a byteArray but still return BigInteger 0 which cause RPC getBalance return 0 if one of addresses in a wallet doesn't have balance.
Then I tried another style, it works well. This means AsByteArray() here isn't work normally.

Then I found AsByteArray() isn't able to conver BigInteger to ByteArray but just transfer it to VM. This makes me a little confused. Since native C# conversion method ToByteArray() isn't able to be used in sc.framework, we don't have a method support BigInteger to ByteArray on sc framework.
@erikzhang @lightszero @shargon

[Tommo-L]

Currently, the AsByteArray is an empty script.

neo-devpack-dotnet/src/Neo.SmartContract.Framework/Helper.cs

Lines 50 to 55 in adf9425

	/// <summary>
	/// Converts BigInteger to byte[]. No guarantees are assumed regarding BigInteger working range.
	/// Examples: 10 -> [0x0a]; 10 -> [0x0a00]; -128 -> [0x80]; -128 -> [0x80ff]; 0 -> []; 0 -> [0x00]; 255 -> [0xff00]
	/// </summary>
	[Script]
	public extern static byte[] AsByteArray(this BigInteger source);

I think there are two options:
option1: Add a new opcode Cast for converting.
option2: Add a new method AsByteArray in StackItem.

[shargon]

we have the CONVERT opcode, we can use it

[lightszero]

'CONVERT', that's new for me.sounds it fit this issue. I will working on it.

[lightszero]

I had create a unittest, it worked.

    class Contract_TypeConvert : SmartContract.Framework.SmartContract
    {
        //Integer = 0x21,
        //ByteArray = 0x28,
        [OpCode(SmartContract.Framework.OpCode.CONVERT, "0x28")]
        public extern static byte[] ConvertToByteArray(object from);


        [OpCode(SmartContract.Framework.OpCode.CONVERT, "0x21")]
        public extern static BigInteger ConvertToInteger(byte[] from);




        public static object testType()
        {
            BigInteger int0 = 0;
            var bts0 = ConvertToByteArray(int0);
            BigInteger int1 = 2;
            var bts1 = ConvertToByteArray(int1);

            var bts2=new byte[1] { 3 };
            var int2 = ConvertToInteger(bts2);

            var bts3 = ConvertToByteArray(new byte[0]) ;
            var int3 = ConvertToInteger(bts3);

            var arrobj = new object[8];
            arrobj[0] = int0;
            arrobj[1] = bts0;
            arrobj[2] = int1;
            arrobj[3] = bts1;
            arrobj[4] = bts2;
            arrobj[5] = int2;
            arrobj[6] = bts3;
            arrobj[7] = int3;
            return arrobj;
        }


    }