jsonrpc: Create a struct for notifications that we send

Signed-off-by: Christian Decker <decker.christian@gmail.com>

lightningd/jsonrpc.c

@@ -1004,6 +1004,26 @@ static struct command_result *param_command(struct command *cmd,
 			    tok->end - tok->start, buffer + tok->start);
 }
 
+struct jsonrpc_notification *jsonrpc_notification_start(const tal_t *ctx, const char *method)
+{
+	struct jsonrpc_notification *n = tal(ctx, struct jsonrpc_notification);
+	n->method = tal_strdup(n, method);
+	n->stream = new_json_stream(n, NULL);
+	json_object_start(n->stream, NULL);
+	json_add_string(n->stream, "jsonrpc", "2.0");
+	json_add_string(n->stream, "method", method);
+	json_object_start(n->stream, "params");
+
+	return n;
+}
+
+void jsonrpc_notification_end(struct jsonrpc_notification *n)
+{
+	json_object_end(n->stream); /* closes '.params' */
+	json_object_end(n->stream); /* closes '.' */
+	json_stream_append(n->stream, "\n\n");
+}
+
 /* We add this destructor as a canary to detect cmd failing. */
 static void destroy_command_canary(struct command *cmd, bool *failed)
 {

lightningd/jsonrpc.h

@@ -58,6 +58,14 @@ struct json_command {
 	const char *verbose;
 };
 
+struct jsonrpc_notification {
+	/* The topic that this notification is for. Internally this
+	 * will be serialized as "method", hence the different name
+	 * here */
+	const char *method;
+	struct json_stream *stream;
+};
+
 /**
  * json_stream_success - start streaming a successful json result.
  * @cmd: the command we're running.
@@ -162,5 +170,18 @@ bool jsonrpc_command_add(struct jsonrpc *rpc, struct json_command *command);
  */
 void jsonrpc_command_remove(struct jsonrpc *rpc, const char *method);
 
+/**
+ * Begin a JSON-RPC notification with the specified topic.
+ *
+ * Automatically starts the `params` object, hence only key-value
+ * based params are supported at the moment.
+ */
+struct jsonrpc_notification *jsonrpc_notification_start(const tal_t *ctx, const char *topic);
+
+/**
+ * Counterpart to jsonrpc_notification_start.
+ */
+void jsonrpc_notification_end(struct jsonrpc_notification *n);
+
 AUTODATA_TYPE(json_command, struct json_command);
 #endif /* LIGHTNING_LIGHTNINGD_JSONRPC_H */