Replicate OfferCreate functionality in Payments to Self

[donovanhide]

Summary

I want to use Payments to condense multiple OfferCreates into a single Payment to self, i.e. a Payment where Account and Destination are the same. To do this I need to have a LimitAmount which exceeds the Amount of the Payment. If I were to consume the same chain of offers using OfferCreate no such LimitAmount would be required and in fact, no existing TrustLine/RippleState is required.

Motivation

To reduce transaction counts for arbitrage, by using fewer Payment transactions than OfferCreate transactions and to avoid unnecessary TrustSet transactions.

Solution

Remove the check for a LimitAmount exceeding Amount for Payments to self.

[donovanhide]

Relevant code is here:

rippled/src/xrpld/app/paths/detail/DirectStep.cpp

Lines 403 to 457 in e5aa605

	TER
	DirectIPaymentStep::check(
	StrandContext const& ctx,
	std::shared_ptr<const SLE> const& sleSrc) const
	{
	// Since this is a payment a trust line must be present. Perform all
	// trust line related checks.
	{
	auto const sleLine = ctx.view.read(keylet::line(src_, dst_, currency_));
	if (!sleLine)
	{
	JLOG(j_.trace()) << "DirectStepI: No credit line. " << *this;
	return terNO_LINE;
	}
	auto const authField = (src_ > dst_) ? lsfHighAuth : lsfLowAuth;
	if (((*sleSrc)[sfFlags] & lsfRequireAuth) &&
	!((*sleLine)[sfFlags] & authField) &&
	(*sleLine)[sfBalance] == beast::zero)
	{
	JLOG(j_.warn())
	<< "DirectStepI: can't receive IOUs from issuer without auth."
	<< " src: " << src_;
	return terNO_AUTH;
	}
	if (ctx.prevStep)
	{
	if (ctx.prevStep->bookStepBook())
	{
	auto const noRippleSrcToDst =
	((*sleLine)[sfFlags] &
	((src_ > dst_) ? lsfHighNoRipple : lsfLowNoRipple));
	if (noRippleSrcToDst)
	return terNO_RIPPLE;
	}
	}
	}
	{
	auto const owed = creditBalance(ctx.view, dst_, src_, currency_);
	if (owed <= beast::zero)
	{
	auto const limit = creditLimit(ctx.view, dst_, src_, currency_);
	if (-owed >= limit)
	{
	JLOG(j_.debug()) << "DirectStepI: dry: owed: " << owed
	<< " limit: " << limit;
	return tecPATH_DRY;
	}
	}
	}
	return tesSUCCESS;
	}

I'd argue, once the Auth and NoRipple checks are passed, if Payment's Account is equal to Destination, the line should be created, if it does not exist, and the LimitAmount ignored.

[tequdev]

I have previously written code that allows a Payment transaction (to self) to create a trustline automatically in the same way as OfferCreate.
If necessary, you can use this code.

https://github.com/tequdev/rippled/pull/3/files