Idiomatic way to use unwrap_or/unwrap_or_else with functional casting

Question

I have a situation where I want to read some headers via reqwest::header::HeaderValue

I am doing so using

#[tokio::main]
async fn main() -> Result<(), reqwest::Error> {
    let url = "https://httpbin.org/get";
    let resp = reqwest::Client::new().get(url).send().await?;

    // read response headers
    // default if the header does not exist
    let resp_headers: &str = resp
        .headers()
        .get("content-length")
        .unwrap_or(&reqwest::header::HeaderValue::from_str("100").unwrap())
        .to_str()
        .unwrap_or("100");
    println!("{}", resp_headers);

    Ok(())
}

This doesn't seem idiomatic and won't compile. Looking for how to approach a scenario like this where there are several necessary unwraps to process and cast a type into desired end result.

Answer 1

You could use a named block and let-else statements.

let resp_headers: &str = 'block: {
    let Some(content_length) = resp.headers().get(reqwest::header::CONTENT_LENGTH) else {
        break 'block "100";
    };
    let Ok(content_length) = content_length.to_str() else {
        break 'block "100";
    };
    content_length
};

Or if you intend to keep the two unwrap values the same, you could use Option::and_then.

let resp_headers: &str = resp
    .headers()
    .get(reqwest::header::CONTENT_LENGTH)
    .and_then(|content_length| content_length.to_str().ok())
    .unwrap_or("100");

Or you can put this in a function and use ?.

fn read_content_length(resp: &reqwest::Response) -> Option<&str> {
    resp.headers()
        .get(reqwest::header::CONTENT_LENGTH)?
        .to_str()
        .ok()
}

let resp_headers: &str = read_content_length(&resp).unwrap_or("100");

But specifically for the content-length header, there is Response::content_length.

let resp_headers: u64 = resp.content_length().unwrap_or(100);