Add background polling for unpaid LN invoices to prevent stuck checkouts

Co-authored-by: danieldaquino <24692108+danieldaquino@users.noreply.github.com>

Author: Copilot

src/invoicing.js

@@ -3,6 +3,7 @@ const { add_successful_transactions_to_account } = require('./user_management')
 const { nip19 } = require('nostr-tools')
 const { v4: uuidv4 } = require('uuid')
 const { current_time } = require('./utils')
+const error = require("debug")("api:error")
 
 const PURPLE_ONE_MONTH = "purple_one_month"
 const PURPLE_ONE_YEAR = "purple_one_year"
@@ -68,6 +69,9 @@ class PurpleInvoiceManager {
     if (PURGE_OLD_INVOICES) {
       this.purging_interval_timer = setInterval(() => this.purge_old_invoices(), 10 * 60 * 1000)
     }
+    // Poll for unpaid invoices periodically to handle cases where the client failed to complete the checkout flow
+    const polling_interval_ms = parseInt(process.env.LN_INVOICE_POLLING_INTERVAL_MS) || 60 * 1000
+    this.polling_interval_timer = setInterval(() => this.poll_unpaid_invoices(), polling_interval_ms)
   }
 
   // Purge old invoices from the database
@@ -139,17 +143,40 @@ class PurpleInvoiceManager {
   // Checks the status of the invoice associated with the given checkout object directly with the LN node, and handles successful payments.
   async check_checkout_object_invoice(checkout_id) {
     const checkout_object = await this.get_checkout_object(checkout_id)
+    if (!checkout_object) {
+      return null
+    }
+    if (checkout_object.completed) {
+      return checkout_object  // Already completed, nothing to do
+    }
     if (checkout_object?.invoice) {
       checkout_object.invoice.paid = await this.check_invoice_is_paid(checkout_object.invoice.label)
       if (checkout_object.invoice.paid) {
-        this.handle_successful_payment(checkout_object)
+        await this.handle_successful_payment(checkout_object)
         checkout_object.completed = true
         await this.checkout_sessions_db.put(checkout_id, checkout_object)  // Update the checkout object since the state has changed
       }
     }
     return checkout_object
   }
 
+  // Polls all incomplete checkout sessions to check for successful payments.
+  // Returns a promise that resolves when all checks are done.
+  async poll_unpaid_invoices() {
+    const checks = []
+    for (const checkout_id of this.checkout_sessions_db.getKeys()) {
+      const checkout_object = this.checkout_sessions_db.get(checkout_id)
+      if (!checkout_object.completed && checkout_object.invoice) {
+        checks.push(
+          this.check_checkout_object_invoice(checkout_id).catch(e => {
+            error("Error polling invoice for checkout %s: %s", checkout_id, e.toString())
+          })
+        )
+      }
+    }
+    return Promise.all(checks)
+  }
+
   // Call this when the user wants to checkout a purple subscription and needs an invoice to pay
   async request_invoice(npub, template_name) {
     if (!this.invoice_templates[template_name]) {
@@ -240,6 +267,9 @@ class PurpleInvoiceManager {
     if (this.purging_interval_timer) {
       clearInterval(this.purging_interval_timer)
     }
+    if (this.polling_interval_timer) {
+      clearInterval(this.polling_interval_timer)
+    }
   }
 }
 

test/controllers/purple_test_controller.js

@@ -105,6 +105,9 @@ class PurpleTestController {
 
   async connect_and_init() {
     this.test_request = await supertest_client(this.purple_api.router, this.t);
+    this.t.teardown(async () => {
+      await this.purple_api.invoice_manager.disconnect()
+    })
   }
 
   static async new(t) {

test/ln_flow.test.js

@@ -204,3 +204,39 @@ test('LN Flow — Renewals, expiration and expiry bumping', async (t) => {
 
   t.end();
 });
+
+test('LN Flow — Background polling processes paid invoices without client check', async (t) => {
+  // Initialize the PurpleTestController
+  const purple_api_controller = await PurpleTestController.new(t);
+
+  // Instantiate a new client
+  const user_pubkey_1 = purple_api_controller.new_client();
+
+  // Get the account info (should not exist yet)
+  const response = await purple_api_controller.clients[user_pubkey_1].get_account();
+  t.same(response.statusCode, 404);
+
+  // Start a new checkout
+  const new_checkout_response = await purple_api_controller.clients[user_pubkey_1].new_checkout(PURPLE_ONE_MONTH);
+  t.same(new_checkout_response.statusCode, 200);
+
+  // Verify the checkout (generates invoice)
+  const verify_checkout_response = await purple_api_controller.clients[user_pubkey_1].verify_checkout(new_checkout_response.body.id);
+  t.same(verify_checkout_response.statusCode, 200);
+  t.ok(verify_checkout_response.body.invoice?.bolt11);
+
+  // Pay the invoice without notifying the server (simulates client failure to call check-invoice)
+  purple_api_controller.mock_ln_node_controller.simulate_pay_for_invoice(verify_checkout_response.body.invoice?.bolt11);
+
+  // Trigger background polling directly (simulates the server's periodic poll)
+  await purple_api_controller.purple_api.invoice_manager.poll_unpaid_invoices();
+
+  // The account should now be active — processed by the background poll
+  const account_info_response = await purple_api_controller.clients[user_pubkey_1].get_account();
+  t.same(account_info_response.statusCode, 200);
+  t.same(account_info_response.body.pubkey, user_pubkey_1);
+  t.same(account_info_response.body.active, true);
+  t.same(account_info_response.body.expiry, purple_api_controller.current_time() + 30 * 24 * 60 * 60);
+
+  t.end();
+});