我是用actix_web 2.0。 根据官方教程，我使用 serde 解 json。于是有了如下代码：

async fn deserialize_json<'a, T>(mut payload: web::Payload) -> Result<T, Error>
where
    T: 'a + serde::Deserialize<'a>,
{
    const MAX_SIZE: usize = 262_144; // max payload size is 256k

    // payload is a stream of Bytes objects
    let mut body:BytesMut= BytesMut::new();
    while let Some(chunk) = payload.next().await {
        let chunk = chunk?;
        // limit max size of in-memory payload
        if (body.len() + chunk.len()) > MAX_SIZE {
            return Err(error::ErrorBadRequest("overflow"));
        }
        body.extend_from_slice(&chunk);
    }

    // body is loaded, now we can deserialize serde-json
    let obj = serde_json::from_slice::<T>(&body)?;
    Ok(obj)
}

然后编译器报错：body does not live long enough 具体如下

   |
45 | async fn deserialize_json<'a, T>(mut payload: web::Payload) -> Result<T, Error>
   |                           -- lifetime `'a` defined here
...
63 |     let obj:T = serde_json::from_slice::<T>(&body)?;
   |                 ----------------------------^^^^^-
   |                 |                           |
   |                 |                           borrowed value does not live long enough
   |                 argument requires that `body` is borrowed for `'a`
64 |     Ok(obj)
65 | }
   | - `body` dropped here while still borrowed

然后，我分析了一波。我把T换成一个确定的结构体，然后编译通过了，并且跑的结果也正确。具体结构体如下：

#[derive(Serialize, Deserialize, Debug)]
pub struct LoginStruct {
    username: String,
    password: String,
}

然后我就没有思路了，搜了半天生命周期和泛型，毫无头绪。

最后我加了一个参数，从外部传入一个 BytesMut 来做 body 的owner，然而编译器的报错一个字都没变。改后具体代码如下：

async fn deserialize_json<'a, T>(mut payload: web::Payload,  buffer: &'a mut BytesMut) -> Result<T, Error>
where
    T: serde::Deserialize<'a>,
{
    const MAX_SIZE: usize = 262_144; // max payload size is 256k

    // payload is a stream of Bytes objects
    let mut body = buffer;
    while let Some(chunk) = payload.next().await {
        let chunk = chunk?;
        // limit max size of in-memory payload
        if (body.len() + chunk.len()) > MAX_SIZE {
            return Err(error::ErrorBadRequest("overflow"));
        }
        body.extend_from_slice(&chunk);
    }

    // body is loaded, now we can deserialize serde-json
    let obj = serde_json::from_slice::<T>(&body)?;
    Ok(obj)
}

请教各位大神，如何才能延长body的生命周期，使函数编译通过？

刚刚开始学rust,谢谢大家