Solve the compatibility problem between EIP-1559 and Policies

[txhsl]

Rationale

Briefly speaking, we are not fully compatible with EIP-1559 after #6 and #166. The compatibility problem between EIP-1559 and Policies are caused by a different economic model.

• As I've mentioned in Implement minGasTipCap as minimum effective gas tip #186, EIP-1559 proposed a dynamic fee market scheme with baseFee and gasTip. Generally, when there is a network traffic, the gas price increases. But if there is no transaction in the network, baseFee and gasTip may drop to nearly 0;
• But in N3, we don't have a dynamic price model. Instead, we maintain some price factors in the Neo Policy. As a result, the system fee remains the same regardless of traffic, and the only difference is the network fee.

There are also several facts I've noticed on testnet:

1. It is frequent that CNs create empty blocks, so the gasPrice/baseFee is pretty low;
2. To achieve a cost about 0.01 GAS per native transfer transaction (costs 21000 gas in EVM), we need a gasPrice about 0.01 * 10 ^ 18 / 21000 ≈ 500 Gwei, which is incredibly higher than other EVM chains, e.g. 7 Gwei on Ethereum, 1 Gwei on BNB Smart Chain, 100 Gwei on Polygon and 0.1 Gwei on Optimistic/Arbitrum;

Empty blocks and high gas price may cause problems in EIP-1559 compatible tools, e.g. MetaMask.

We've already modified some RPC APIs to suite Neo X Policies, like changing eth_gasPrice and eth_maxPriorityFeePerGas to provide a minimum acceptable value so that a transaction will not be rejected by txpool. But eth_feeHistory is somehow conflict with our Policy idea, it returns a fee list of recently accepted transactions. It would be confusing when the list is empty, for EIP-1559 compatible tools, this case equals to a zero eth_maxPriorityFeePerGas. Their logics don't consider a minimum value, so when I increase the minGasTipCap limit, MetaMask hits RPC errors.

Implementation

For the MetaMask problem, I found it can be solved by disabling eth_feeHistory RPC API. But this compatibility issue may happen on other tools or custom codes. Maybe they use 0.8*eth_maxPriorityFeePerGas and hit an error.

So we may need a discussion, are we good to continue with this EIP-1559 incompatible? Or we have other ideas about the price thing?

[txhsl]

@gsmachado @chenquanyu @AnnaShaleva @roman-khimov @steven1227

[gsmachado]

This is concerning, in my opinion.

We'll certainly have cases where tools would get confused on gas estimation -- and devs would dislike it, saying "you guys promised an EVM-compatible chain, but it's not".

We need to brainstorm about how to progress on this. Maybe we should collect concrete use cases of dApps or other tools that would get lost by not sticking to EIP-1559? Then we'd be able to come up with strategies on how to overcome it.

I don't know... just brainstorming out loud.

[roman-khimov]

Glancing over https://eips.ethereum.org/EIPS/eip-1559 I'm not sure how many tools do validate_block(). Nodes obviously do that, but node can be fixed, otherwise base_fee_per_gas can be set to whatever value we need and dynamic calculation just be disabled.

The next option of course is to drop ErrUnderpriced and follow the EIP-1559 economics completely. But no one knows how many transactions we are going to have on mainnet. If it's around the same as for N3 then prices are gonna be close to zero and validators would get nothing. At the same time, close to zero prices may be incentivizing at least some activity. Nothing is certain here.

Then gas_limit (and/or ELASTICITY_MULTIPLIER/BASE_FEE_MAX_CHANGE_DENOMINATOR). These can be played to affect EIP-1559 calculations, maybe some combination can be good enough for Bane economics.

[steven1227]

I suggest change feeHistory rpc makes more compatible with Eip1559 and Bane economics.

[txhsl]

Considering the above comments, @chenquanyu, @steven1227 and I had a discussion.

We decided to keep going with this N3-like pricing method, by maintaining baseFee and minGasTip in Policy contract, so that the price won't go to 0.

To avoid potential problems due to empty blocks, we decided to modify eth_gasPrice, eth_maxPriorityFeePerGas and eth_feeHistory RPCs to provide a default-and-suggested "price space" which should be compatible for most of the tools.

[txhsl]

The annoying MetaMask fee history fallback was removed 2 days ago in MetaMask/core#4210.

[txhsl]

This compatibility problem is solved since MetaMask extension v11.15.2.