midir 0.11.0

A cross-platform, realtime MIDI processing library, inspired by RtMidi.
Documentation 
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use std::error::Error;
use std::io::{stdin, stdout, Write};

use midir::{Ignore, MidiIO, MidiInput, MidiOutput};

fn main() {
    env_logger::init();
    match run() {
        Ok(_) => (),
        Err(err) => println!("Error: {}", err),
    }
}

#[cfg(not(target_arch = "wasm32"))] // conn_out is not `Send` in Web MIDI, which means it cannot be passed to connect
fn run() -> Result<(), Box<dyn Error>> {
    let mut midi_in = MidiInput::new("midir forwarding input")?;
    midi_in.ignore(Ignore::None);
    let midi_out = MidiOutput::new("midir forwarding output")?;

    let in_port = select_port(&midi_in, "input")?;
    println!();
    let out_port = select_port(&midi_out, "output")?;

    println!("\nOpening connections");
    let in_port_name = midi_in.port_name(&in_port)?;
    let out_port_name = midi_out.port_name(&out_port)?;

    let mut conn_out = midi_out.connect(&out_port, "midir-forward")?;

    // _conn_in needs to be a named parameter, because it needs to be kept alive until the end of the scope
    let _conn_in = midi_in.connect(
        &in_port,
        "midir-forward",
        move |stamp, message, _| {
            conn_out
                .send(message)
                .unwrap_or_else(|_| println!("Error when forwarding message ..."));
            println!("{}: {:?} (len = {})", stamp, message, message.len());
        },
        (),
    )?;

    println!(
        "Connections open, forwarding from '{}' to '{}' (press enter to exit) ...",
        in_port_name, out_port_name
    );

    let mut input = String::new();
    stdin().read_line(&mut input)?; // wait for next enter key press

    println!("Closing connections");
    Ok(())
}

fn select_port<T: MidiIO>(midi_io: &T, descr: &str) -> Result<T::Port, Box<dyn Error>> {
    println!("Available {} ports:", descr);
    let midi_ports = midi_io.ports();
    for (i, p) in midi_ports.iter().enumerate() {
        println!("{}: {}", i, midi_io.port_name(p)?);
    }
    print!("Please select {} port: ", descr);
    stdout().flush()?;
    let mut input = String::new();
    stdin().read_line(&mut input)?;
    let port = midi_ports
        .get(input.trim().parse::<usize>()?)
        .ok_or("Invalid port number")?;
    Ok(port.clone())
}

#[cfg(target_arch = "wasm32")]
fn run() -> Result<(), Box<dyn Error>> {
    println!("test_forward cannot run on Web MIDI");
    Ok(())
}