import { io } from "https://deno.land/x/s3si@gui-v0.4.16/deps.ts";
const { Buffer } = io;
Reads data from r until EOF (null) and appends it to the buffer,
growing the buffer as needed. It resolves to the number of bytes read.
If the buffer becomes too large, .readFrom() will reject with an error.
Based on Go Lang's Buffer.ReadFrom.