tapchannel: add GetBuyQuoteFromRouteHints helper

Author: GeorgeTsagk

tapchannel/aux_invoice_manager.go

@@ -419,6 +419,38 @@ func IsAssetInvoice(invoice *lnrpc.Invoice, rfqLookup RfqLookup) bool {
 	return false
 }
 
+// GetBuyQuoteFromRouteHints is a helper method that extracts a buy quote from
+// the route hints of an invoice, given that the quote is accepted and has a
+// matching specifier. If no matching quote is found, it returns an error.
+func (s *AuxInvoiceManager) GetBuyQuoteFromRouteHints(invoice *lnrpc.Invoice,
+	specifier asset.Specifier) (*rfqmsg.BuyAccept, error) {
+
+	buyQuotes := s.cfg.RfqManager.PeerAcceptedBuyQuotes()
+	for _, hint := range invoice.RouteHints {
+		for _, h := range hint.HopHints {
+			scid := rfqmsg.SerialisedScid(h.ChanId)
+			buyQuote, ok := buyQuotes[scid]
+			if !ok {
+				continue
+			}
+
+			quoteSpecifier := buyQuote.Request.AssetSpecifier
+			areEqual, err := quoteSpecifier.Equal(&specifier, false)
+			if err != nil {
+				return nil, fmt.Errorf("error comparing "+
+					"specifiers: %w", err)
+			}
+
+			if areEqual {
+				return &buyQuote, nil
+			}
+		}
+	}
+
+	return nil, fmt.Errorf("no buy quote found for specifier %s",
+		specifier.String())
+}
+
 // validateAssetHTLC runs a couple of checks on the provided asset HTLC.
 func (s *AuxInvoiceManager) validateAssetHTLC(ctx context.Context,
 	htlc *rfqmsg.Htlc, circuitKey invoices.CircuitKey) error {