Read Reader r until EOF (null) and resolve to the content as Uint8Array`.

import { Buffer } from "https://deno.land/std@0.199.0/io/buffer.ts";
import { readAll } from "https://deno.land/std@0.199.0/streams/read_all.ts";

// Example from stdin
const stdinContent = await readAll(Deno.stdin);

// Example from file
const file = await Deno.open("my_file.txt", {read: true});
const myFileContent = await readAll(file);
file.close();

// Example from buffer
const myData = new Uint8Array(100);
// ... fill myData array with data
const reader = new Buffer(myData.buffer);
const bufferContent = await readAll(reader);