tapchannel: add assetIDFromQuote helper

We add a simple assetIDFromQuote function that fetches the asset ID
associated with a certain accepted quote identified by its rfq ID. We
will later use this in the handleInvoice function to compare the asset
ID of the quote with that of the HTLCs.

tapchannel/aux_invoice_manager.go

@@ -7,6 +7,7 @@ import (
 
 	"github.com/lightninglabs/lndclient"
 	"github.com/lightninglabs/taproot-assets/address"
+	"github.com/lightninglabs/taproot-assets/asset"
 	"github.com/lightninglabs/taproot-assets/fn"
 	"github.com/lightninglabs/taproot-assets/rfq"
 	"github.com/lightninglabs/taproot-assets/rfqmath"
@@ -247,6 +248,34 @@ func (s *AuxInvoiceManager) handleInvoiceAccept(_ context.Context,
 	return resp, nil
 }
 
+// assetIDFromQuote retrieves the quote by looking up the rfq manager's maps of
+// accepted quotes based on the passed rfq ID. If there's a match, the asset
+// ID is returned.
+func (s *AuxInvoiceManager) assetIDFromQuote(
+	rfqID rfqmsg.ID) (*asset.ID, error) {
+
+	acceptedBuyQuotes := s.cfg.RfqManager.PeerAcceptedBuyQuotes()
+	acceptedSellQuotes := s.cfg.RfqManager.LocalAcceptedSellQuotes()
+
+	buyQuote, isBuy := acceptedBuyQuotes[rfqID.Scid()]
+	sellQuote, isSell := acceptedSellQuotes[rfqID.Scid()]
+
+	switch {
+	case isBuy:
+		if buyQuote.Request.AssetSpecifier.HasId() {
+			return buyQuote.Request.AssetSpecifier.UnwrapIdToPtr(), nil
+		}
+
+	case isSell:
+		if sellQuote.Request.AssetSpecifier.HasId() {
+			return sellQuote.Request.AssetSpecifier.UnwrapIdToPtr(), nil
+		}
+	}
+
+	return nil, fmt.Errorf("rfqID does not match any accepted buy or " +
+		"sell quote")
+}
+
 // priceFromQuote retrieves the price from the accepted quote for the given RFQ
 // ID. We allow the quote to either be a buy or a sell quote, since we don't
 // know if this is a direct peer payment or a payment that is routed through the