Myujth

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:

View in the playground

// 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>> DownloadFileError::CreateFile(err));

 Box::new(
 response_future
 .join(create_file_future)
 .and_then(move 

However, I get the following error:

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

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.

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.

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()
.map(drop)

See also:

• How do I write a futures::Stream to disk without storing it entirely in memory first?


• How to save a file downloaded from S3 with Rusoto to my hard drive?