How to stream a vector of bytes to BufWriter? - rust

Question

I'm trying to stream bytes to a tcp server by using io::copy(&mut reader, &mut writer), but it gives me this error: the trait "std::io::Read" is not implemented for "Vec<{integer}>". Here I have a vector of bytes which would be the same as me opening a file and converting it to bytes. I want to write the bytes to the BufWriter. What am I doing wrong?
use std::io;
use std::net::TcpStream;
use std::io::BufWriter;
pub fn connect() {
if let Ok(stream) = TcpStream::connect("localhost:8080") {
println!("Connection established!");
let mut reader = vec![
137, 80, 78, 71, 13, 10, 26, 10, 0, 0, 0, 13, 73, 72, 68, 82, 0, 0, 0, 70, 0, 0, 0, 70,
];
let mut writer = BufWriter::new(&stream);
io::copy(&mut reader, &mut writer).expect("Failed to write to stream");
} else {
println!("Couldn't connect to the server")
}
}
error[E0277]: the trait bound `Vec<{integer}>: std::io::Read` is not satisfied
--> src/lib.rs:12:31
|
12 | io::copy(&mut reader, &mut writer).expect("Failed to write to stream");
| -------- ^^^^^^^^^^^ the trait `std::io::Read` is not implemented for `Vec<{integer}>`
| |
| required by a bound introduced by this call
|
note: required by a bound in `std::io::copy`

Answer 1

the compiler have a little trouble here, Vec doesn't implement Read but &[u8] do, you just have a get a slice from the vec before create a mutable reference:
copy(&mut reader.as_slice(), &mut writer).expect("Failed to write to stream");
See also:
What is the difference between storing a Vec vs a Slice?
What are the differences between Rust's `String` and `str`?

Answer 2

Using .as_slice() like so works for me:
pub fn connect() {
if let Ok(stream) = TcpStream::connect("localhost:8080") {
println!("Connection established!");
let reader = vec![
137, 80, 78, 71, 13, 10, 26, 10, 0, 0, 0, 13, 73, 72, 68, 82, 0, 0, 0, 70, 0, 0, 0, 70,
];
let mut writer = BufWriter::new(&stream);
io::copy(&mut reader.as_slice(), &mut writer).expect("Failed to write to stream");
} else {
println!("Couldn't connect to the server")
}
}
That’s because std::io::Read supports slices.