Problem unpacking Result in main function

1

Executing the following code results in:
error[E0381]: borrow of possibly-uninitialized variable: nic

use std::io::Error;

fn main() {
    // let nic = get_network_interface_connection().unwrap(); //This works but I want explicit error handling

    let nic;

    match get_network_interface_connection() {
        Ok(new_nic) => nic = new_nic,  
        Err(e) => println!("{:?}", e),
    }

    let mut buf = [0u8; 1504];

    // PROBLEM HERE!! In next line... error[E0381]: borrow of possibly-uninitialized variable: `nic`
    let nbytes = nic.recv(&mut buf[..]); // PROBLEM HERE!! error[E0381]: borrow of possibly-uninitialized variable: `nic`
}

fn get_network_interface_connection() -> Result<tun_tap::Iface, Error> {
    let new_nic = tun_tap::Iface::new("tun0", tun_tap::Mode::Tun)?; //Network Interface Connection(nic)
    Ok(new_nic)
}

I understand if the match errors out then nic variable will never be initialized; so I tried to find a way to initialize the nic var in error clause, but couldn't.

I want to know how I can initialize nic if error happens to avoid error[E0381]........or if this is even the right concept to apply here.

The "let nbytes = ..." line will eventually be in a loop to receive packets via TCP.

2

Does this work? I've never used tun_tap, but I made your match statement return a value. And on error it just exits the program.

use std::io::Error;

fn main() {
    let nic = match get_network_interface_connection() {
        Ok(nic) => nic,  
        Err(e) => {
            println!("{:?}", e);
            return;
        } 
    }

    let mut buf = [0u8; 1504];

    // PROBLEM HERE!! In next line... error[E0381]: borrow of possibly-uninitialized variable: `nic`
    let nbytes = nic.recv(&mut buf[..]); // PROBLEM HERE!! error[E0381]: borrow of possibly-uninitialized variable: `nic`
}

fn get_network_interface_connection() -> Result<tun_tap::Iface, Error> {
    let new_nic = tun_tap::Iface::new("tun0", tun_tap::Mode::Tun)?; //Network Interface Connection(nic)
    Ok(new_nic)
}
3

@drewkett YES! This is the solution. Thank you so much for your speedy help.

4

Just to add a little bit to the answer. You rarely need to or want to declare a variable ahead of time like let nic; in rust. In a situation like yours, you'll typically either use a match statement as above or use the ? operator as you did you in your function which will early return any errors and extract a successful function call. In your case, since the variable was declared in main without a return type, the ? operator can't be used.

5

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