Remove MAX_SAFE_INTEGER limitation

[roman-khimov]

Summary or problem description
Following https://github.com/neo-project/proposals/pull/126/files#r522304412 discussion and nspcc-dev/neofs-node#122 (comment) problem. We use 256-bit integers in VM, but they don't always convert to/from JSON nicely because of MAX_SAFE_INTEGER limitation and this limit is too low, even 100M with 8 decimals can't fit there.

Do you have any solution you want to propose?
I see two options:

• dropping MAX_SAFE_INTEGER limitation, staying with decimal representation and leaving this as a client problem (RFC 7159 recommends to stay within [-(2⁵³)+1, (2⁵³)-1], but JSON technically doesn't impose any hard limit)
• using hex encoding (either always or when the number doesn't fit), but that may be not very convenient

Neo Version

• Neo 3

Where in the software does this update applies to?

• RPC (HTTP)

[shargon]

If we remove the limit, it's very possible that we will need a custom json implementation in all languages (like go), isn't it?

[roman-khimov]

It's very easy to fix for me while still staying decimal, but I'm not so sure about other client/server implementations. We need to solve this one way or another though.

[ixje]

If we remove the limit, it's very possible that we will need a custom json implementation in all languages (like go), isn't it?

Pretty much everything needs a custom implementation if you want to be strict compliant with how C# works, so that's nothing new for me.

[roman-khimov]

This still is a problem, create some NEP-17 token with 16 decimals and try to work with it via RPC, there will be problems doing so.

[erikzhang]

This still is a problem, create some NEP-17 token with 16 decimals and try to work with it via RPC, there will be problems doing so.

The best way is to use string.

[csmuller]

The best way is to use string.

If we use strings for large integers in JSON, I think there will be a problem with StdLib.JsonDeserialize(...) in smart contracts because it will deserialize the former integers to strings instead.