如何在Rust中将hyper::Body包装到BufReader中？

问题 #

我有一个hyper::Body，想把它包装进BufReader（比如tokio::io::BufReader或者futures_util::io::BufReader这类组件），直接编写代码时出现报错：

fn foo(body: hyper::Body) {
    let bufreader = tokio::io::BufReader::new(body);
}

报错信息：

error[E0277]: the trait bound `Body: AsyncRead` is not satisfied
  --> src/lib.rs:2:47
   |
2  |     let bufreader = tokio::io::BufReader::new(body);
   |                     ------------------------- ^^^^ the trait `AsyncRead` is not implemented for `Body`
   |                     |
   |                     required by a bound introduced by this call
   |
   = help: the following other types implement trait `AsyncRead`:
             &[u8]
             &mut T
             AddrStream
             Box<T>
             BufStream<RW>
             DuplexStream
             Pin<P>
             Upgraded
           and 20 others
note: required by a bound in `tokio::io::BufReader::<R>::new`
  --> /playground/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.23.0/src/io/util/buf_reader.rs:37:9
   |
37 | impl<R: AsyncRead> BufReader<R> {
   |         ^^^^^^^^^ required by this bound in `tokio::io::BufReader::<R>::new`

For more information about this error, try `rustc --explain E0277`.
error: could not compile `playground` due to previous error

我知道Rust中有多个AsyncRead实现，tokio_util::compat::*和futures_util::compat::*可用于转换，但hyper::Body似乎未实现任何一个。它实现了futures_core::stream::Stream，但我不知道如何将其传入BufReader。

解决方案 #

hyper::Body本质是Stream<Item = Result<Bytes, Error>>，要将它转换为AsyncRead类型后才能被BufReader包装，最直接的方式是使用tokio_util提供的StreamReader工具。

1. 添加依赖 #

确保Cargo.toml中包含所需依赖：

[dependencies]
hyper = { version = "1.0", features = ["full"] }
tokio = { version = "1.0", features = ["full"] }
tokio-util = { version = "0.7", features = ["io", "compat"] }
bytes = "1.0"

2. 转换并包装Body #

通过StreamReader把hyper::Body适配为AsyncRead，再传入BufReader：

use hyper::Body;
use tokio::io::BufReader;
use tokio_util::io::StreamReader;

fn foo(body: Body) {
    // 将Body转换为AsyncRead实现
    let stream_reader = StreamReader::new(body);
    // 包装进BufReader
    let buf_reader = BufReader::new(stream_reader);
    // 后续可直接使用buf_reader执行异步读取操作
}

补充说明 #

• StreamReader专门用于将输出Bytes的Stream转换成AsyncRead，完美匹配hyper::Body的类型定义。
• 若要使用futures_util::io::BufReader，只需替换tokio::io::BufReader即可——StreamReader同时实现了futures_core::io::AsyncRead，可直接兼容。
• 如果需要在tokio和futures的IO trait间切换，可借助tokio_util::compat模块的转换工具，但上述基础方案已能满足大部分场景需求。

内容的提问来源于stack exchange，提问作者kpcyrd