lnrpc/invoicesrpc: add is_key_send flag to rpc invoice

lnrpc/invoicesrpc/utils.go

@@ -146,6 +146,7 @@ func CreateRPCInvoice(invoice *channeldb.Invoice,
 		State:           state,
 		Htlcs:           rpcHtlcs,
 		Features:        CreateRPCFeatures(invoice.Terms.Features),
+		IsKeySend:       len(invoice.PaymentRequest) == 0,
 	}
 
 	if preimage != channeldb.UnknownPreimage {

lnrpc/rpc.proto

@@ -2545,6 +2545,12 @@ message Invoice {
 
     /// List of features advertised on the invoice.
     map<uint32, Feature> features = 24 [json_name = "features"];
+    
+    /**
+    Indicates if this invoice was a spontaneous payment that arrived via keysend
+    [EXPERIMENTAL].
+    */
+    bool is_key_send = 25 [json_name = "is_key_send"];
 }
 
 enum InvoiceHTLCState {

lnrpc/rpc.swagger.json

@@ -2896,6 +2896,11 @@
             "$ref": "#/definitions/lnrpcFeature"
           },
           "description": "/ List of features advertised on the invoice."
+        },
+        "is_key_send": {
+          "type": "boolean",
+          "format": "boolean",
+          "description": "*\nIndicates if this invoice was a spontaneous payment that arrived via keysend\n[EXPERIMENTAL]."
         }
       }
     },