Streaming client body into a file

[poelzi]

I spent the whole day trying to stream the body of a client into a file in a async context, but there seems no example of this. Nothing I found works with current tokio/hyper. I couldn't imagine that it this must be hard, but apperently, it is not obvious how to do this.

use warp::hyper::http::Request;
use warp::hyper::{Body, Client, Uri};
use hyper_tls::HttpsConnector;
use tokio::fs::File;
use tokio::io;
use tokio_util::compat::{FuturesAsyncWriteCompatExt, FuturesAsyncReadCompatExt};
use crate::error::{EResult};

use std::error::Error;

pub const VERSION: Option<&str> = option_env!("CARGO_PKG_VERSION");

pub async fn download_file(url: String, output: String) -> EResult<()> {
    let https = HttpsConnector::new();
    let client = Client::builder().build::<_, Body>(https);

    let request = Request::get(url).body(Body::empty())?;
    let response = client.request(request).await?;

    let mut stream = response
        .body()
        .map(|result| result.map_err(|error| std::io::Error::new(std::io::ErrorKind::Other, "Error!")))
        .into_async_read();
    
    let mut file = File::create(output).await?;
    tokio::io::copy(&mut stream, &mut file).await?;
    Ok(())
}

But I get this error:

error[E0277]: the trait bound `IntoAsyncRead<futures::stream::Map<Body, [closure@src/utils.rs:24:14: 24:103]>>: tokio::io::AsyncRead` is not satisfied
   --> src/utils.rs:28:21
    |
28  |     tokio::io::copy(&mut stream, &mut file).await?;
    |     --------------- ^^^^^^^^^^^ the trait `tokio::io::AsyncRead` is not implemented for `IntoAsyncRead<futures::stream::Map<Body, [closure@src/utils.rs:24:14: 24:103]>>`
    |     |
    |     required by a bound introduced by this call
    |
note: required by a bound in `tokio::io::copy`
   --> /home/poelzi/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.20.1/src/io/util/copy.rs:151:12
    |
151 |         R: AsyncRead + Unpin + ?Sized,
    |            ^^^^^^^^^ required by this bound in `tokio::io::copy`

For more information about this error, try `rustc --explain E0277`.
error: could not compile `erratad` due to previous error

I think it would make sense to have a example for something like this.

[seanmonstar]

Instead of .into_async_read(), what if you used https://docs.rs/tokio-util/latest/tokio_util/io/struct.StreamReader.html