BigInteger 0 isn't able to be convert to Byte[]{ 0 }

[superboyiii]

Due to #196, we've improved a lot on smart contract convertion method. However, I still find a little issue that BigInteger 0 isn't able to be convert to Byte[]{ 0 } by ToByteArray method. This will cause many issues such like balance exception when make transaction. I've made a little example to replay this situation. For example:

using Neo.SmartContract.Framework;
using Neo.SmartContract.Framework.Services.Neo;
using System;
using System.Numerics;

namespace TestConvert
{
    [Features(ContractFeatures.HasStorage | ContractFeatures.Payable)]
    public class Contract1 : SmartContract
    {
        public static object Main(string operation, object[] args)
        {
            BigInteger num = 0;
            byte[] byteNum = num.ToByteArray();
            Storage.Put(Storage.CurrentContext, "key", byteNum);
            return "TestConvertZero";
        }
    }
}

Then I could deploy it successfully, but I find the value is null in storage.

neo> deploy D:\Master-smoking\2020-03-13\neo-devpack-dotnet\TestConvert\bin\Debug\netstandard2.1\TestConvert.nef D:\Master-smoking\2020-03-13\neo-devpack-dotnet\TestConvert\bin\Debug\netstandard2.1\TestConvert.manifest.json
Script hash: 0x7b5ae605948a00b1beb37ffdb985fc385907d05b
Gas: 100000000

Signed and relayed transaction with hash=0x710cc5f6fb4b2b175ef90c6438112192f8d018539053d6de7f4bb1556d6325a7
neo> invoke 0x7b5ae605948a00b1beb37ffdb985fc385907d05b Main
Invoking script with: '10c00c044d61696e0c145bd0075938fc85b9fd7fb3beb1008a9405e65a7b41627d5b52'
VM State: HALT
Gas Consumed: 1389470
Evaluation Stack: [{"type":"ByteArray","value":"VGVzdENvbnZlcnRaZXJv"}]

relay tx(no|yes): y
Signed and relayed transaction with hash=0xde9bff4f091583f6dd681d1b3a007938d37a011c8bc0b2eb68435ec9d4aaf37c
neo>

Try GetStorage:

If I change this num to any num except 0, it works well.

using Neo.SmartContract.Framework;
using Neo.SmartContract.Framework.Services.Neo;
using System;
using System.Numerics;

namespace TestConvert
{
    [Features(ContractFeatures.HasStorage | ContractFeatures.Payable)]
    public class Contract1 : SmartContract
    {
        public static object Main(string operation, object[] args)
        {
            BigInteger num = 20;
            byte[] byteNum = num.ToByteArray();
            Storage.Put(Storage.CurrentContext, "key", byteNum);
            return "TestConvertZero";
        }
    }
}

neo> deploy D:\Master-smoking\2020-03-13\neo-devpack-dotnet\TestConvert\bin\Debug\netstandard2.1\TestConvert.nef D:\Master-smoking\2020-03-13\neo-devpack-dotnet\TestConvert\bin\Debug\netstandard2.1\TestConvert.manifest.json
Script hash: 0xa6fc45f3c8eeefcb2c7969bc0aab46a032ddd224
Gas: 100000000

Signed and relayed transaction with hash=0x784196a4a8a563c1559137e50550685fb87d2823fd1f884bca01140afcf3b2ed
neo> invoke 0xa6fc45f3c8eeefcb2c7969bc0aab46a032ddd224 Main
Invoking script with: '10c00c044d61696e0c1424d2dd32a046ab0abc69792ccbefeec8f345fca641627d5b52'
VM State: HALT
Gas Consumed: 1569620
Evaluation Stack: [{"type":"ByteArray","value":"VGVzdENvbnZlcnRaZXJv"}]

relay tx(no|yes): y
Signed and relayed transaction with hash=0x560797ed5900eb78aa9d6d3d667944861073b44f9b89e2395eb14116eca189e7
neo>

Try GetStorage:

@lightszero Sorry to bother you again.

[erikzhang]

Then I could deploy it successfully, but I find the value is null in storage.

I think it shouldn't be null. It should be an empty array of byte.

[lightszero]

In Neo Storage.Put a zero length bytearray means delete a Key @superboyiii

            private static bool PutExInternal(ApplicationEngine engine, StorageContext context, byte[] key, byte[] value, StorageFlags flags)
            {
                if (key.Length > MaxKeySize) return false;
                if (value.Length > MaxValueSize) return false;
                if (context.IsReadOnly) return false;

                StorageKey skey = new StorageKey
                {
                    Id = context.Id,
                    Key = key
                };

                if (engine.Snapshot.Storages.TryGet(skey)?.IsConstant == true) return false;

                if (value.Length == 0 && !flags.HasFlag(StorageFlags.Constant))
                {
                    // If put 'value' is empty (and non-const), we remove it (implicit `Storage.Delete`)
                    engine.Snapshot.Storages.Delete(skey);
                }

[superboyiii]

In Neo Storage.Put a zero length bytearray means delete a Key @superboyiii

            private static bool PutExInternal(ApplicationEngine engine, StorageContext context, byte[] key, byte[] value, StorageFlags flags)
            {
                if (key.Length > MaxKeySize) return false;
                if (value.Length > MaxValueSize) return false;
                if (context.IsReadOnly) return false;

                StorageKey skey = new StorageKey
                {
                    Id = context.Id,
                    Key = key
                };

                if (engine.Snapshot.Storages.TryGet(skey)?.IsConstant == true) return false;

                if (value.Length == 0 && !flags.HasFlag(StorageFlags.Constant))
                {
                    // If put 'value' is empty (and non-const), we remove it (implicit `Storage.Delete`)
                    engine.Snapshot.Storages.Delete(skey);
                }

I don't understand. This is correct. But what I expect is value.Length is 1 and value is { 0 }. I don't mean byte[0] but byte[1]{ 0 }. It shouldn't return null.

[lightszero]

Because BigInteger 0 convert to Bytes will got a Byte[0].
If you want get a Byte[1]{0},that 's a big change. many code about that in NEOVM.
@superboyiii
you can at guys to discuss if we should let BigInteger 0 Convert to byte[1]{0}.

[erikzhang]

In Neo Storage.Put a zero length bytearray means delete a Key

I remembered that in this case, it should really return null.

[superboyiii]

In Neo Storage.Put a zero length bytearray means delete a Key

I remembered that in this case, it should really return null.

If we don't change it to byte[1]{0}, we could meet issues in smart contract especially some cases of invoke balance. And we have to always notify developers we can't convert like this. This is a limit for sc. And for me, I think Byte[1]{0} is absolutely different from Byte[0], it should return Byte[1]{0}.

[Tommo-L]

I think we should convert 0 -> byte[1]{ 0 } for storage, which contains two meanings:

1. one is that the key value pair exists,
2. the other is that its value is 0.

If we convert 0 -> byte[0]{}, which means this is an nonexist key-pair. There is an example, it'll be difficult if we want to count how many registered users in a nep5.

If we convert 0 -> byte[1]{ 0 }, we should encourage/incentive users to release resources.

[erikzhang]

Perhaps putting 0 bytes of data should not be considered as deleting the record. Because the user can always call Delete to explicitly delete the record.

[Tommo-L]

Agree 100%

Therefore, we should incentive users to release resources.

[shargon]

Perhaps putting 0 bytes of data should not be considered as deleting the record. Because the user can always call Delete to explicitly delete the record.

Agree