Body of the request. The easiest way to consume the body is:

import { ServerRequest } from "https://deno.land/std@0.107.0/http/server_legacy.ts";
import { readAll } from "https://deno.land/std@0.107.0/io/util.ts";

const req = new ServerRequest();
const buf = await readAll(req.body);

Value of Content-Length header. If null, then content length is invalid or not given (e.g. chunked encoding).