使用hyper将块流异步写入文件 [英] Writing a chunk stream to a file asynchronously using hyper
问题描述
我正在尝试创建一个简单的函数，该函数使用hyper将远程文件下载到本地文件路径.我还需要文件写入也要异步(就我而言，我正在使用 tokio_fs ).这是代码:
I am trying to create a simple function that downloads a remote file to a local filepath using hyper. I need the file write to be asynchronous as well (in my case I am using tokio_fs for that). Here is the code:
// Parts of the code were omitted, see the playground for full source code
pub fn download_file(
uri: Uri,
file_location: &Path,
) -> Box<Future<Item = (), Error = DownloadFileError>> {
let temp_dir_path = tempfile::tempdir().unwrap().into_path();
let file_name = match file_location.file_name() {
Some(file_name) => file_name,
None => return Box::new(futures::failed(DownloadFileError::IncorrectFilePath)),
};
let temp_filepath = temp_dir_path.join(&file_name);
let connector = HttpsConnector::new(2).unwrap();
let client: Client<_, Body> = Client::builder().build(connector);
let response_future = client
.get(uri)
.map_err(|err| DownloadFileError::GetRequest(err));
let create_file_future =
File::create(temp_filepath).map_err(|err| DownloadFileError::CreateFile(err));
Box::new(
response_future
.join(create_file_future)
.and_then(move |(res, file)| {
res.into_body()
.map_err(|e| DownloadFileError::GetRequest(e))
.for_each(move |chunk| {
io::write_all(file, chunk)
.map(|_| ())
.map_err(|_| DownloadFileError::FileWrite)
})
}),
)
}
但是，出现以下错误:
error[E0507]: cannot move out of captured outer variable in an `FnMut` closure
--> src/lib.rs:79:39
|
75 | .and_then(move |(res, file)| {
| ---- captured outer variable
...
79 | io::write_all(file, chunk)
| ^^^^ cannot move out of captured outer variable in an `FnMut` closure
从概念上讲，我理解错误的含义:由于 FnMut 通过可变引用捕获变量，因此无法移动捕获的变量.但是，由于我需要将流写入 Join future返回的文件中，因此我在给定的示例中不了解如何解决此问题.
Conceptually, I understand what the error means: Since a FnMut captures variables by mutable reference, I cannot move a captured variable. However, I do not understand how can I work around this problem in the example given, since I need to write the stream to the file returned by the Join future.
Write 特性的 write_all 方法在这里可以使用，因为它将文件作为可变引用，但是问题在于它在同一线程上进行写操作
The write_all method from the Write trait would work here since it takes the file as a mutable reference, but the problem is that it does the writing on the same thread.
推荐答案
您不想使用 for_each . io :: write_all 消耗目标和缓冲区，以换取将来将在完成后返回目标和缓冲区的将来.您可以将其与 Stream结合使用::fold 重用文件:
You do not want to use for_each. io::write_all consumes the target and the buffer in exchange for a future that will return the target and the buffer when it is done. You can combine this with Stream::fold to reuse the file:
.fold(file, |file, chunk| {
io::write_all(file, chunk)
.map(|(f, _c)| f)
.map_err(|_| DownloadFileError::FileWrite)
})
.map(drop)
另请参阅:
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