fix: preserve lnurl msat precision

Made-with: Cursor

Author: piotr-iohk

CHANGELOG.md

@@ -11,6 +11,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Show ready-to-copy settle and cancel commands in `holdinvoice` output
 - Simplify LND funding step in README to a single command instead of clipboard-based two-step flow
 
+### Fixed
+- Validate LNURL-withdraw callback invoices by millisatoshis (`num_msat`) to preserve msat precision for min/max range checks
+- Preserve LNURL-pay invoice millisatoshi precision by creating invoices with LND `value_msat` instead of truncating callback amounts to sats
+
 ### Added
 - `bolt11` command in `bitcoin-cli` for creating regular Lightning invoices (supports `--msat` and `-m` memo)
 - LND hold invoice commands in `bitcoin-cli`: `holdinvoice`, `settleinvoice`, `cancelinvoice`

lnurl-server/routes/pay.js

@@ -47,12 +47,12 @@ router.get('/:paymentId/callback', asyncHandler(async (req, res) => {
         throw new ValidationError(validationErrors.join(', '));
     }
 
-    const amountMsat = parseInt(amount);
+    const amountMsat = parseInt(amount, 10);
     const amountSats = Math.floor(amountMsat / 1000);
 
     // Create invoice
-    const invoice = await lndService.createInvoice(
-        amountSats,
+    const invoice = await lndService.createInvoiceMsat(
+        amountMsat,
         comment ? `LNURL Payment ${paymentId} - ${comment}` : `LNURL Payment ${paymentId}`,
         3600
     );

lnurl-server/routes/withdraw.js

@@ -59,20 +59,19 @@ router.get('/callback', asyncHandler(async (req, res) => {
     const minValue = minWithdrawable ? parseInt(minWithdrawable, 10) : config.limits.minWithdrawable;
     const maxValue = maxWithdrawable ? parseInt(maxWithdrawable, 10) : config.limits.maxWithdrawable;
 
-    // Convert msats to sats for validation
-    const minSats = Math.ceil(minValue / 1000);
-    const maxSats = Math.floor(maxValue / 1000);
-
     try {
         // Decode the invoice to get the amount
         const decodedInvoice = await lndService.decodePayReq(pr);
-        const invoiceAmountSats = decodedInvoice.num_satoshis;
+        const invoiceAmountSats = parseInt(decodedInvoice.num_satoshis, 10);
+        const invoiceAmountMsat = decodedInvoice.num_msat
+            ? parseInt(decodedInvoice.num_msat, 10)
+            : invoiceAmountSats * 1000;
 
-        Logger.withdrawal('processing', { k1, amount: invoiceAmountSats, minSats, maxSats });
+        Logger.withdrawal('processing', { k1, amountSats: invoiceAmountSats, amountMsat: invoiceAmountMsat, minWithdrawable: minValue, maxWithdrawable: maxValue });
 
-        // Validate amount is within limits
-        if (!Validation.isAmountInRange(invoiceAmountSats, minSats, maxSats)) {
-            throw new ValidationError(`Amount out of range (${minSats} - ${maxSats} sats)`);
+        // Validate msat amount is within limits
+        if (!Validation.isAmountInRange(invoiceAmountMsat, minValue, maxValue)) {
+            throw new ValidationError(`Amount out of range (${minValue} - ${maxValue} msat)`);
         }
 
         // Pay the invoice

lnurl-server/services/lnd.js

@@ -111,6 +111,14 @@ class LNDService {
         });
     }
 
+    async createInvoiceMsat(valueMsat, memo, expiry = 3600) {
+        return this.call('invoices', {
+            value_msat: valueMsat.toString(),
+            memo: memo,
+            expiry: expiry
+        });
+    }
+
     async getInvoice(paymentHash) {
         return this.rest(`/v1/invoice/${paymentHash}`, 'GET');
     }