Merge pull request lightningnetwork#5207 from carlaKC/4727-singleinvoice

invoicesrpc: terminate SubscribeSingleInvoice once invoice reaches a final state

channeldb/invoices.go

@@ -362,6 +362,11 @@ func (c ContractState) String() string {
 	return "Unknown"
 }
 
+// IsFinal returns a boolean indicating whether an invoice state is final
+func (c ContractState) IsFinal() bool {
+	return c == ContractSettled || c == ContractCanceled
+}
+
 // ContractTerm is a companion struct to the Invoice struct. This struct houses
 // the necessary conditions required before the invoice can be considered fully
 // settled by the payee.

lnrpc/invoicesrpc/invoices_server.go

@@ -247,6 +247,12 @@ func (s *Server) SubscribeSingleInvoice(req *SubscribeSingleInvoiceRequest,
 				return err
 			}
 
+			// If we have reached a terminal state, close the
+			// stream with no error.
+			if newInvoice.State.IsFinal() {
+				return nil
+			}
+
 		case <-s.quit:
 			return nil
 		}