Fix purging of cancelled invoices (#37)

Fix a bug in purging of settled invoices on the LND REST API backend.
This caused future pending invoice queries to fail because the internal
administration no longer aligned with the LND pending invoices and
caused the invoice watch to fail.

src/backends/lnd-rest/i-invoice.ts

@@ -1,4 +1,4 @@
-export interface ILndInvoice {
+export interface ILndInvoice extends ILndResponse {
   memo: string
   r_preimage: string
   r_hash: string
@@ -26,6 +26,12 @@ export interface ILndInvoice {
   payment_addr: string
 }
 
+interface ILndResponse {
+  code: number
+  message: string
+  details: any[]
+}
+
 interface IFeature {
   name: string
   is_required: boolean

src/backends/lnd-rest/lnd-rest.ts

@@ -38,6 +38,10 @@ export default class LndRest extends Backend {
     const options = this.getRequestOptions(EHttpVerb.GET, '/v1/invoice/' + hash)
     const response = await this.request(options) as ILndInvoice
 
+    // With certain LND configurations, invoices are purged immediately on expiry
+    // https://github.com/lightningnetwork/lnd/issues/6299
+    if (response.code) return Promise.reject(new Error(response.message)) 
+
     return this.toInvoice(response)
   }
 

src/backends/tools.ts

@@ -24,11 +24,19 @@ export const watchInvoices = (backend: IBackend, intervalMs: number | null = nul
           if (invoice.status !== invoiceToWatch.status) {
             backend.invoiceEmitter.emit('invoice-updated', invoice)
             if (invoice.status !== EInvoiceStatus.Pending) {
-              const indexToRemove = backend.invoicesToWatch.findIndex(i => i.paymentHash !== invoiceToWatch.paymentHash)
+              const indexToRemove = backend.invoicesToWatch.findIndex(i => i.paymentHash === invoiceToWatch.paymentHash)
               backend.invoicesToWatch.splice(indexToRemove)
             }
           }
-        }).catch(err => console.error('Unable to fetch invoice', err))
+        }).catch(err => {
+          const indexToRemove = backend.invoicesToWatch.findIndex((i) => i.paymentHash === invoiceToWatch.paymentHash);
+          const cancelledInvoice = backend.invoicesToWatch[indexToRemove]
+          if (cancelledInvoice) {
+            cancelledInvoice.status = EInvoiceStatus.Cancelled
+            backend.invoiceEmitter.emit("invoice-updated", cancelledInvoice);
+            backend.invoicesToWatch.splice(indexToRemove);
+          }
+        })
       }
     }).catch(err => console.error('Unable to fetch pending invoices', err))
   }, intervalMs ?? 5000)