How to stream a vector of bytes to BufWriter?

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`

Stargateur · Accepted Answer · 2021-12-17T22:01:15.377

2

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:

edited Dec 17 '21 at 22:01

answered Dec 17 '21 at 21:57

Stargateur

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Ok, what's a slice? – Nicke7117 Dec 17 '21 at 21:57
Now the server panics: `thread "main" panicked at "called "Result::unwrap()" on an "Err" value: Error { kind: InvalidData, message: "stream did not contain valid UTF-8" }"`. Isn't it possible to stream bytes to a tcp server? – Nicke7117 Dec 17 '21 at 22:03
@Nicke7117 that another problem with what you send I can't really help you there – Stargateur Dec 17 '21 at 22:09
@Nicke7117 It would be best to ask about your server panicking as a separate question. – effect Dec 18 '21 at 00:35
1

@Nicke7117 _"What's a slice?"_ → https://doc.rust-lang.org/reference/types/slice.html and https://doc.rust-lang.org/std/primitive.slice.html – Jmb Dec 18 '21 at 08:49

score 1 · Answer 2 · answered Dec 17 '21 at 21:56

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.

How to stream a vector of bytes to BufWriter?

2 Answers2