import { io } from "https://deno.land/x/msgpack_rpc@v3.1.6/deps.ts";
const { Buffer } = io;
Reads data from r until EOF (null) and appends it to the buffer,
growing the buffer as needed. It returns the number of bytes read. If the
buffer becomes too large, .readFromSync() will throw an error.
Based on Go Lang's Buffer.ReadFrom.