import { readVarbig } from "https://deno.land/x/denjucks@1.1.1/src/deps/path/std/encoding/binary.ts";
Reads an integer from r, comsuming sizeof(o.dataType) bytes. Data-type defaults to int64.
Returns it as bigint, or throws Deno.errors.UnexpectedEof if not enough bytes can be read.
Parameters
r: Deno.Reader
optional
o: VarbigOptions = [UNSUPPORTED]