feat: support msat amounts in bolt11 generate endpoint

Add `amount_msat` query param to `/generate/bolt11` for sub-sat
precision invoices, complementing the existing `amount` (sats) param.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ovitrif

CHANGELOG.md

@@ -16,6 +16,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Preserve LNURL-pay invoice millisatoshi precision by creating invoices with LND `value_msat` instead of truncating callback amounts to sats
 
 ### Added
+- Support `amount_msat` query param in `/generate/bolt11` endpoint for sub-sat precision invoices
 - `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`
 - LND `getinfo` command in `bitcoin-cli` for connectivity debugging

README.md

@@ -63,6 +63,7 @@ A complete Docker-based development environment for Bitcoin and Lightning Networ
   - `/generate/pay` - Generate LNURL-pay
   - `/generate/channel` - Generate LNURL-channel
   - `/generate/auth` - Generate LNURL-auth
+  - `/generate/bolt11` - Generate Bolt11 invoice (`?amount=` sats, `?amount_msat=` msats)
   - `/.well-known/lnurlp/:username` - Lightning Address
 
 ### VSS Server

lnurl-server/routes/generate.js

@@ -185,17 +185,27 @@ const generateLnurlAuth = async (query) => {
 };
 
 const generateBolt11 = async (query) => {
-    const { amount } = query;
+    const { amount, amount_msat } = query;
 
-    // Default to 0 (zero-amount invoice) if not specified
-    const amountSats = amount ? parseInt(amount) : 0;
+    let invoice;
+    let amountDisplay;
 
-    if (isNaN(amountSats) || amountSats < 0) {
-        throw new ValidationError('Invalid amount. Must be zero or a positive integer.');
+    if (amount_msat) {
+        const msat = parseInt(amount_msat);
+        if (isNaN(msat) || msat < 0) {
+            throw new ValidationError('Invalid amount_msat. Must be zero or a positive integer.');
+        }
+        invoice = await lndService.createInvoiceMsat(msat, '', 3600);
+        amountDisplay = { msat };
+    } else {
+        const amountSats = amount ? parseInt(amount) : 0;
+        if (isNaN(amountSats) || amountSats < 0) {
+            throw new ValidationError('Invalid amount. Must be zero or a positive integer.');
+        }
+        invoice = await lndService.createInvoice(amountSats, '', 3600);
+        amountDisplay = { sats: amountSats };
     }
 
-    // Create invoice with LND
-    const invoice = await lndService.createInvoice(amountSats, '', 3600);
     const paymentRequest = invoice.payment_request;
 
     const qrCode = await QRCode.toDataURL(paymentRequest, {
@@ -207,13 +217,13 @@ const generateBolt11 = async (query) => {
         }
     });
 
-    Logger.info('Bolt11 invoice generated', { amount: amountSats, paymentHash: invoice.r_hash });
+    Logger.info('Bolt11 invoice generated', { amount: amountDisplay, paymentHash: invoice.r_hash });
 
     return {
         bolt11: paymentRequest,
         qrCode,
         type: 'bolt11',
-        amount: amountSats,
+        amount: amountDisplay,
         paymentHash: invoice.r_hash
     };
 };

lnurl-server/templates.js

@@ -681,7 +681,13 @@ const renderGeneratorPage = ({}) => {
                         {
                             method: 'GET',
                             path: '/generate/bolt11?amount=2000',
-                            description: 'Generate Bolt11 with custom amount',
+                            description: 'Generate Bolt11 with amount in sats',
+                            clickable: true
+                        },
+                        {
+                            method: 'GET',
+                            path: '/generate/bolt11?amount_msat=222222',
+                            description: 'Generate Bolt11 with amount in msats',
                             clickable: true
                         }
                     ]