[Question] Does CalculateNetworkFee(DataCache snapshot, Transaction tx) needs to be inside Wallet? Make network fee calculation more generic.

[vncoelho]

The call

neo/src/neo/Wallets/Wallet.cs

Lines 356 to 421 in d73d190

	public long CalculateNetworkFee(DataCache snapshot, Transaction tx)
	{
	UInt160[] hashes = tx.GetScriptHashesForVerifying(snapshot);
	// base size for transaction: includes const_header + signers + attributes + script + hashes
	int size = Transaction.HeaderSize + tx.Signers.GetVarSize() + tx.Attributes.GetVarSize() + tx.Script.GetVarSize() + IO.Helper.GetVarSize(hashes.Length);
	uint exec_fee_factor = NativeContract.Policy.GetExecFeeFactor(snapshot);
	long networkFee = 0;
	foreach (UInt160 hash in hashes)
	{
	byte[] witness_script = GetAccount(hash)?.Contract?.Script;
	if (witness_script is null && tx.Witnesses != null)
	{
	// Try to find the script in the witnesses
	foreach (var witness in tx.Witnesses)
	{
	if (witness.ScriptHash == hash)
	{
	witness_script = witness.VerificationScript;
	break;
	}
	}
	}
	if (witness_script is null)
	{
	var contract = NativeContract.ContractManagement.GetContract(snapshot, hash);
	if (contract is null) continue;
	var md = contract.Manifest.Abi.GetMethod("verify", 0);
	if (md is null)
	throw new ArgumentException($"The smart contract {contract.Hash} haven't got verify method without arguments");
	if (md.ReturnType != ContractParameterType.Boolean)
	throw new ArgumentException("The verify method doesn't return boolean value.");
	// Empty invocation and verification scripts
	size += Array.Empty<byte>().GetVarSize() * 2;
	// Check verify cost
	using ApplicationEngine engine = ApplicationEngine.Create(TriggerType.Verification, tx, snapshot.CreateSnapshot(), settings: ProtocolSettings);
	engine.LoadContract(contract, md, CallFlags.None);
	if (engine.Execute() == VMState.FAULT) throw new ArgumentException($"Smart contract {contract.Hash} verification fault.");
	if (!engine.ResultStack.Pop().GetBoolean()) throw new ArgumentException($"Smart contract {contract.Hash} returns false.");
	networkFee += engine.GasConsumed;
	}
	else if (witness_script.IsSignatureContract())
	{
	size += 67 + witness_script.GetVarSize();
	networkFee += exec_fee_factor * SignatureContractCost();
	}
	else if (witness_script.IsMultiSigContract(out int m, out int n))
	{
	int size_inv = 66 * m;
	size += IO.Helper.GetVarSize(size_inv) + size_inv + witness_script.GetVarSize();
	networkFee += exec_fee_factor * MultiSignatureContractCost(m, n);
	}
	else
	{
	//We can support more contract types in the future.
	}
	}
	networkFee += size * NativeContract.Policy.GetFeePerByte(snapshot);
	return networkFee;
	}

is currently inside Wallet and this makes it requires a Dummy Wallet on neo-modules RpcServer https://github.com/neo-project/neo-modules/blob/ccc2ff93599c8127ad2d5a2a21f99360d84c79b3/src/RpcServer/RpcServer.Wallet.cs#L124.

What necessarily makes it need an open wallet to make this calculation?

On NEO 2 perhaps yes, due to UTXO calculations regarding size.
However, now, we mostly just use UInt160[] hashes = tx.GetScriptHashesForVerifying(snapshot); which are already created and then we get the VerificationScript using GetAccount(hash)?.Contract?.Script;

I suggested to restructure these functions to a different place on the neo-core and even move them from the Rpc-Wallet, making them more user friendly in a way that VerificationScripts can be passed as parameters for a generic calculation.

[Qiao-Jin]

I think we still need some features in Wallet such as func GetAccount for this calculation

[erikzhang]

I think we still need some features in Wallet such as func GetAccount for this calculation

Agree.