+/*
+ * Sends on 'wsj1' a call to the method of 'api'/'verb' with arguments
+ * given by 'object'. If not NULL, 'object' should be a valid JSON string.
+ * On receiving the reply, the function 'on_reply' is called with 'closure'
+ * as its first argument and the message of the reply.
+ * Return 0 in case of success. Otherwise, returns -1 and set errno.
+ */