How to specify lifetime of return type equal to lifetime of an argument for async function

I am trying to extract common code from my API handlers, which look like the following:

async fn api_handler(_req: HttpRequest, mut body: web::Payload) -> Result<HttpResponse, Error> {
    let mut bytes = web::BytesMut::new();
    while let Some(item) = {
        let item: web::Bytes = item?;
    let body = std::str::from_utf8(&bytes)?;


The only way to move this block to a common function is to require one more String construction, like the following:

pub async fn receive_body_as_string(mut body: actix_web::web::Payload) -> Result<String, actix_web::Error> {
    let mut bytes = actix_web::web::BytesMut::new();
    while let Some(item) = {
        let item: actix_web::web::Bytes = item?;
        if bytes.len() > MAX_MESSAGE_SIZE {
    let body = std::str::from_utf8(&bytes)
        .map_err(|_| Error::InvalidBodyUtf8)?;

    let body = String::from(body);

Is there any way to return body = std::str::from_utf8(&bytes) directly out of the function without wrapping it in a string?

To return the reference, you must take some reference and then make the output reference a view into data referenced by the input reference. So, you could try to replace mut body: actix_web::web::Paypoad with body: &mut actix_web::web::Payload, but I'm not sure if this will help: your return value references bytes, which looks like not referencing the body, but rather building locally based on it.

Yes, I tried this. But then the compiler complains that body does not live long enough after next().await

Well, that's exactly what I was afraid of. You can't return the body as reference, since there's nothing in the function arguments to borrow it from.

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