Evaluate blob transaction (Type 3) related fee in Neo X env

[txhsl]

Rationale

So far, we have modified the EIP-1559 dynamic fee calculation to a fixed MinGasTip and BaseFee. But if we are going to allow blob transactions, the EIP-4844 fee calculation should be evaluated as well.

This type of transaction is not activated yet, related to #189.

Implementation

Refer to.

https://github.com/bane-labs/go-ethereum/blob/v0.2.0/consensus/misc/eip4844/eip4844.go#L68-L81

[txhsl]

As it is mentioned in https://eips.ethereum.org/EIPS/eip-4844, the fee of a blob transaction consists of 3 parts, EVM base fee, EVM priority fee, and Blob base fee. The EVM base fee and EVM priority fee are described by EIP-1559, so only the Blob base fee is new.

The Blob base fee is independent of normal (EVM) gas and its price, although they have a similar name. So we only talk about the blob gas, which is all burned during mining.

1. The gas cost of every blob BlobTxBlobGasPerBlob is 2 ** 17 = 393216 blob gas;
2. The block gas limit MaxBlobGasPerBlock is 6 * BlobTxBlobGasPerBlob, so there are at most 6 blobs can be placed in 1 block;
3. The block gas target BlobTxTargetBlobGasPerBlock is 3 * BlobTxBlobGasPerBlob, which is a half of the limit;
4. The minimum blob gas price BlobTxMinBlobGasprice is 1 wei.

The blob fee calculation is similar to EVM fee, it is dynamic, so there can be a very low result with token GAS.

// CalcExcessBlobGas calculates the excess blob gas after applying the set of
// blobs on top of the excess blob gas.
func CalcExcessBlobGas(parentExcessBlobGas uint64, parentBlobGasUsed uint64) uint64 {
	excessBlobGas := parentExcessBlobGas + parentBlobGasUsed
	if excessBlobGas < params.BlobTxTargetBlobGasPerBlock {
		return 0
	}
	return excessBlobGas - params.BlobTxTargetBlobGasPerBlock
}

// CalcBlobFee calculates the blobfee from the header's excess blob gas field.
func CalcBlobFee(excessBlobGas uint64) *big.Int {
	return fakeExponential(minBlobGasPrice, new(big.Int).SetUint64(excessBlobGas), blobGaspriceUpdateFraction)
}

// fakeExponential approximates factor * e ** (numerator / denominator) using
// Taylor expansion.
func fakeExponential(factor, numerator, denominator *big.Int) *big.Int {
	var (
		output = new(big.Int)
		accum  = new(big.Int).Mul(factor, denominator)
	)
	for i := 1; accum.Sign() > 0; i++ {
		output.Add(output, accum)

		accum.Mul(accum, numerator)
		accum.Div(accum, denominator)
		accum.Div(accum, big.NewInt(int64(i)))
	}
	return output.Div(output, denominator)
}

There is no priority fee for blobs, which means the only profit of a blob transaction is the gas tip based on EVM gas.

So, I suggest increasing the BlobTxMinBlobGasprice to a reasonable value, or adding a changeable fixed value to Neo X Policy and dropping this dynamic computation like what we did to EIP-1559.

[txhsl]

Ethereum proposed https://eips.ethereum.org/EIPS/eip-7918 for Osaka, which may make things different.

[txhsl]

We keep the blob gas computation as it is in Ethereum. After some investigation, we know that this value is charged for the independent storage of blob data, not relevant to EVM.

1. In Geth, the EL, a blob transaction only carries an array of blob data hashes. So the main payload imported by EIP-4844 does not use any EVM resource or block storage resource;
2. The blob data, which is the main payload, is maintained by CL, and temporarily kept in its file system, so that we can regard it as an independent price system;
3. So there is no need to change the blob gas computation, at least I haven't seen the necessity.