无法读取通过 hyper：：client：：客户端发出 HTTP 请求的简单有效负载：不满足绑定的"body：未来"特征

Question

我正在尝试将Result转换为 Buffer：

let ufc_root: String =
    String::from("https://www.ufc.com/athletes/all?filters%5B0%5D=status%3A23");
// let ufc_root: String = String::from("https://www.google.com");
let https = HttpsConnector::new(4).unwrap();
let client = Client::builder().build::<_, hyper::Body>(https);
client
    .get(ufc_root.parse::<hyper::Uri>().unwrap())
    .and_then(|res| {
        println!("http status code: {}", res.status());
        println!("http response headers:n{:?}: ", res.headers());
        res.into_body()
    })
    .from_err::<WebScrapeError>()
    .and_then(|body| {
        body.for_each(|chunk| {
            println!("{}", chunk.into_bytes());
        });
        let jon_jones = Subject {
            name: "Jon Jones".to_string(),
            link: "http://www.jonjones.com".to_string(),
        };
        let subjects = vec![jon_jones];
        Ok(subjects)
    })
    .from_err()

error[E0277]: the trait bound `hyper::Body: hyper::rt::Future` is not satisfied
  --> src/scrapper.rs:24:14
   |
24 |             .and_then(|res| {
   |              ^^^^^^^^ the trait `hyper::rt::Future` is not implemented for `hyper::Body`
   |
   = note: required because of the requirements on the impl of `futures::future::IntoFuture` for `hyper::Body`
error[E0599]: no method named `from_err` found for type `futures::future::and_then::AndThen<hyper::client::ResponseFuture, hyper::Body, [closure@src/scrapper.rs:24:23: 28:14]>` in the current scope
  --> src/scrapper.rs:29:14
   |
29 |             .from_err::<WebScrapeError>()
   |              ^^^^^^^^
   |
   = note: the method `from_err` exists but the following trait bounds were not satisfied:
           `&mut futures::future::and_then::AndThen<hyper::client::ResponseFuture, hyper::Body, [closure@src/scrapper.rs:24:23: 28:14]> : hyper::rt::Future`
           `&mut futures::future::and_then::AndThen<hyper::client::ResponseFuture, hyper::Body, [closure@src/scrapper.rs:24:23: 28:14]> : hyper::rt::Stream`
           `futures::future::and_then::AndThen<hyper::client::ResponseFuture, hyper::Body, [closure@src/scrapper.rs:24:23: 28:14]> : hyper::rt::Future`

为什么不编译？

Answer 1

and_then必须返回未来，或者可以通过IntoFuture特征转换为未来的东西。您正在返回res.into_body()，这不是未来 - 它实际上是流。

要使此功能正常，您需要将该流转换为代表已经完全阅读的身体的未来。这里有几种可用的选项：

• res.into_body().concat2()，将所有读字节连接到单个缓冲区
• res.into_body().collect()，将所有字节的所有块收集到 Vec
• res.into_body().into_future()，它将解析为包含流中的第一项的元组以及流本身的其余部分（即 (T, Stream<Item = T>)）

有多种不同（同样有效的）将Stream表示为Future的事实可能是为什么前者没有IntoFuture的毯子实现。

使用concat2的一个示例在Hyper Docs中显示。