rfq: add EstimateAssetUnits helper

Author: GeorgeTsagk

rfq/manager.go

@@ -15,6 +15,7 @@ import (
 	"github.com/lightninglabs/taproot-assets/address"
 	"github.com/lightninglabs/taproot-assets/asset"
 	"github.com/lightninglabs/taproot-assets/fn"
+	"github.com/lightninglabs/taproot-assets/rfqmath"
 	"github.com/lightninglabs/taproot-assets/rfqmsg"
 	lfn "github.com/lightningnetwork/lnd/fn/v2"
 	"github.com/lightningnetwork/lnd/lnutils"
@@ -1062,6 +1063,33 @@ func (m *Manager) publishSubscriberEvent(event fn.Event) {
 	)
 }
 
+// EstimateAssetUnits is a helper function that queries our price oracle to find
+// out how many units of an asset are needed to evaluate to the provided amount
+// in msats.
+func EstimateAssetUnits(ctx context.Context, oracle PriceOracle,
+	specifier asset.Specifier,
+	amtMsat lnwire.MilliSatoshi) (uint64, error) {
+
+	oracleRes, err := oracle.QueryBidPrice(
+		ctx, specifier, fn.None[uint64](), fn.Some(amtMsat),
+		fn.None[rfqmsg.AssetRate](),
+	)
+	if err != nil {
+		return 0, err
+	}
+
+	if oracleRes.Err != nil {
+		return 0, fmt.Errorf("cannot query oracle: %v",
+			oracleRes.Err.Error())
+	}
+
+	assetUnits := rfqmath.MilliSatoshiToUnits(
+		amtMsat, oracleRes.AssetRate.Rate,
+	)
+
+	return assetUnits.ScaleTo(0).ToUint64(), nil
+}
+
 // PeerAcceptedBuyQuoteEvent is an event that is broadcast when the RFQ manager
 // receives an accept quote message from a peer. This is a quote which was
 // requested by our node and has been accepted by a peer.

rpcserver.go

@@ -7938,25 +7938,13 @@ func calculateAssetMaxAmount(ctx context.Context, priceOracle rfq.PriceOracle,
 	// query our oracle first to get an estimation on the asset rate. This
 	// will help us establish a quote with the correct amount of asset
 	// units.
-	oracleRes, err := priceOracle.QueryBidPrice(
-		ctx, specifier, fn.None[uint64](), fn.Some(amtMsat),
-		fn.None[rfqmsg.AssetRate](),
+	maxUnits, err := rfq.EstimateAssetUnits(
+		ctx, priceOracle, specifier, amtMsat,
 	)
 	if err != nil {
 		return 0, err
 	}
 
-	if oracleRes.Err != nil {
-		return 0, fmt.Errorf("cannot query oracle: %v",
-			oracleRes.Err.Error())
-	}
-
-	assetUnits := rfqmath.MilliSatoshiToUnits(
-		amtMsat, oracleRes.AssetRate.Rate,
-	)
-
-	maxUnits := assetUnits.ToUint64()
-
 	maxMathUnits := rfqmath.NewBigIntFromUint64(maxUnits)
 
 	// Since we used a different oracle price query above calculate the max