expected struct `Vec`, found enum `Result` in tokio, cacache and match-CodePudding

I find it difficult to understand what's wrong with the below code. I'm getting expected struct Vec, found enum Result error at Ok(from_cache), but I have adopted the code from https://github.com/platy/update-tracker/blob/843092708906063704442f352231bfbac5b06196/server/src/web/mod.rs#L216-L226

During web scraping, I'm trying to cache the content of the URL in the cache and trying to reuse it.

use std::error::Error;

#[tokio::main]
async fn main() ->  Result<(), Box<dyn Error>> {
    let url: &str = "https://example.com/";
    let html = match cacache::read("./cache", url).await? {
        Ok(from_cache) => String::from_utf8(from_cache),
        Err(_) => {
            let t_html = reqwest::get(url).await?.text().await?;
            cacache::write("./cache", url, &t_html).await?;
            t_html
        },
    };
    println!("html = {:?}", html);

    Ok(())
}

Here's the playground (but, it shows other errors due to missing dependencies). Can anyone please explain this or share any relevant guide to gather more information about this topic?

CodePudding user response：

Recall that the ? operator unwraps a Result (or Option) by propagating the Err (or None) case out of the current function. Therefore, this expression:

cacache::read("./cache", url).await?

Has type Vec<u8> as the ? operator has unwrapped the Result. If you want to handle errors yourself, then omit the ? operator:

cacache::read("./cache", url).await