Error when trying to create a vector to store message bytes

I am trying to stream a file through libflate gzip decoder. I get an error when trying to create a vector to store message bytes.

use std::io::Read;
use std::io::Cursor;
use libflate::gzip::Decoder;

fn main() {
    let mut f = std::fs::File::open("./20181002.bytes").unwrap();
    let mut decoder = Decoder::new(&f).unwrap();

    let mut dst = [0u8; 4];
    let msglen_bytes = decoder.read_exact(&mut dst).unwrap();
    println!("msglen_bytes: {}", msglen_bytes);

    let mut bytes = vec!(0u8, msglen_bytes, msglen_bytes);
    let msg_bytes = decoder.read_exact(&mut bytes).unwrap();

    let msg = root_as_flatbuffers_msg(&msg_bytes).expect("Bad Msg");

    println!("Msg: {:?}", msg);
}

error[E0308]: mismatched types
  --> src/main.rs:45:31
   |
45 |     let mut bytes = vec!(0u8, msglen_bytes, msglen_bytes);
   |                               ^^^^^^^^^^^^ expected `u8`, found `()`

error[E0308]: mismatched types
  --> src/main.rs:48:42
   |
48 |     let msg = root_as_flatbuffers_msg(&msg_bytes).expect("Bad Msg");
   |                                          ^^^^^^^^^^ expected slice `[u8]`, found `()`
   |
   = note: expected reference `&[u8]`
              found reference `&()`

>Solution :

read_exact() operates by side effect – it reads data into the provided slice, and its return value only exists to signal an error, if any. This is why you got () in msg_bytes (which turned into &() because you borrowed it).

To fix the issue, call read_exact() without capturing the return value and pass &bytes to root_as_flatbuffers_msg():

decoder.read_exact(&mut bytes).unwrap();
let msg = root_as_flatbuffers_msg(&bytes).expect("Bad Msg");