nb-blocking-util

Procedural macro utility for removing async / await code from a function, assuming the interfaces have both an async and a blocking version of the functions called.

For example, reqwest's reqwest::Client and reqwest::blocking::Client expose a very similar interface, so often it is enough to just remove .awaits.

Example usage

Let's say you have a function that fetches https://rust-lang.org/, by using a reqwest client:

async fn fetch_rust_lang(client: &reqwest::Client) -> Result<String, reqwest::Error> {
    Ok(client.get("https://rust-lang.org/")
        .send()
        .await?
        .error_for_status()?
        .text()
        .await?)
}

And now you want to implement the same function if #[cfg(feature = "blocking")], but blocking, gating the previous behind #[cfg(not(feature = "blocking"))]

Of course you can do that, but this macro may help you get rid of duplicates like that:

// First expose a ReqwestClient to the function.
#[cfg(not(feature = "blocking"))]
type ReqwestClient = reqwest::Client;
#[cfg(feature = "blocking")]
type ReqwestClient = reqwest::blocking::Client;

// Then the function
async fn fetch_rust_lang(client: &ReqwestClient) -> Result<String, reqwest::Error> {
    Ok(client.get("https://rust-lang.org/")
        .send()
        .await?
        .error_for_status()?
        .text()
        .await?)
}

And now everything left is put it behind the #[blocking] attribute if #[cfg(feature = "blocking")]:

#[cfg_attr(feature = "blocking", nb_blocking_util::blocking)]
async fn fetch_rust_lang(client: &ReqwestClient) -> Result<String, reqwest::Error> {
    Ok(client.get("https://rust-lang.org/")
        .send()
        .await?
        .error_for_status()?
        .text()
        .await?)
}