如何异步浏览目录及其子目录? [英] How to asynchronously explore a directory and its sub-directories?
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问题描述
我需要浏览目录及其所有子目录.我可以通过同步方式轻松地通过递归浏览目录:
I need to explore a directory and all its sub-directories. I can explore the directory easily with recursion in a synchronous way:
use failure::Error;
use std::fs;
use std::path::Path;
fn main() -> Result<(), Error> {
visit(Path::new("."))
}
fn visit(path: &Path) -> Result<(), Error> {
for e in fs::read_dir(path)? {
let e = e?;
let path = e.path();
if path.is_dir() {
visit(&path)?;
} else if path.is_file() {
println!("File: {:?}", path);
}
}
Ok(())
}
当我尝试使用tokio_fs以异步方式执行相同操作时:
When I try to do the same in an asynchronous manner using tokio_fs:
use failure::Error; // 0.1.6
use futures::Future; // 0.1.29
use std::path::PathBuf;
use tokio::{fs, prelude::*}; // 0.1.22
fn visit(path: PathBuf) -> impl Future<Item = (), Error = Error> {
let task = fs::read_dir(path)
.flatten_stream()
.for_each(|entry| {
println!("{:?}", entry.path());
let path = entry.path();
if path.is_dir() {
let task = visit(entry.path());
tokio::spawn(task.map_err(drop));
}
future::ok(())
})
.map_err(Error::from);
task
}
我收到以下错误:
error[E0391]: cycle detected when processing `visit::{{opaque}}#0`
--> src/lib.rs:6:28
|
6 | fn visit(path: PathBuf) -> impl Future<Item = (), Error = Error> {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
note: ...which requires processing `visit`...
--> src/lib.rs:6:1
|
6 | fn visit(path: PathBuf) -> impl Future<Item = (), Error = Error> {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
= note: ...which requires evaluating trait selection obligation `futures::future::map_err::MapErr<impl futures::future::Future, fn(failure::error::Error) {std::mem::drop::<failure::error::Error>}>: std::marker::Send`...
= note: ...which again requires processing `visit::{{opaque}}#0`, completing the cycle
note: cycle used when checking item types in top-level module
--> src/lib.rs:1:1
|
1 | / use failure::Error; // 0.1.6
2 | | use futures::Future; // 0.1.29
3 | | use std::path::PathBuf;
4 | | use tokio::{fs, prelude::*}; // 0.1.22
... |
20| | task
21| | }
| |_^
error[E0391]: cycle detected when processing `visit::{{opaque}}#0`
--> src/lib.rs:6:28
|
6 | fn visit(path: PathBuf) -> impl Future<Item = (), Error = Error> {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
note: ...which requires processing `visit`...
--> src/lib.rs:6:1
|
6 | fn visit(path: PathBuf) -> impl Future<Item = (), Error = Error> {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
= note: ...which again requires processing `visit::{{opaque}}#0`, completing the cycle
note: cycle used when checking item types in top-level module
--> src/lib.rs:1:1
|
1 | / use failure::Error; // 0.1.6
2 | | use futures::Future; // 0.1.29
3 | | use std::path::PathBuf;
4 | | use tokio::{fs, prelude::*}; // 0.1.22
... |
20| | task
21| | }
| |_^
在传播所有错误的同时异步浏览目录及其子目录的正确方法是什么?
What is the correct way of exploring a directory and its sub-directories asynchronously while propagating all the errors?
推荐答案
我将对 rodrigo的现有答案进行几处修改:
- 从函数中返回
Stream，允许调用者通过给定的文件条目执行所需的操作. - 返回
impl Stream而不是Box<dyn Stream>.这为实现中的更大灵活性留出了空间.例如，可以创建一个使用内部堆栈而不是效率较低的递归类型的自定义类型. - 从函数中返回
io::Error以允许用户处理任何错误. - 接受
impl Into<PathBuf>允许使用更好的API. - 创建一个内部隐藏的实现函数，该函数在其API中使用具体类型.
- Return a
Streamfrom the function, allowing the caller to do what they need with a given file entry. - Return an
impl Streaminstead of aBox<dyn Stream>. This leaves room for more flexibility in implementation. For example, a custom type could be created that uses an internal stack instead of the less-efficient recursive types. - Return
io::Errorfrom the function to allow the user to deal with any errors. - Accept a
impl Into<PathBuf>to allow a nicer API. - Create an inner hidden implementation function that uses concrete types in its API.
未来0.3/东京0.2
在此版本中，我避免了深度递归调用，而是将访问的路径保留在本地堆栈(to_visit).
use futures::{stream, Stream, StreamExt}; // 0.3.1
use std::{io, path::PathBuf};
use tokio::fs::{self, DirEntry}; // 0.2.4
fn visit(path: impl Into<PathBuf>) -> impl Stream<Item = io::Result<DirEntry>> + Send + 'static {
async fn one_level(path: PathBuf, to_visit: &mut Vec<PathBuf>) -> io::Result<Vec<DirEntry>> {
let mut dir = fs::read_dir(path).await?;
let mut files = Vec::new();
while let Some(child) = dir.next_entry().await? {
if child.metadata().await?.is_dir() {
to_visit.push(child.path());
} else {
files.push(child)
}
}
Ok(files)
}
stream::unfold(vec![path.into()], |mut to_visit| {
async {
let path = to_visit.pop()?;
let file_stream = match one_level(path, &mut to_visit).await {
Ok(files) => stream::iter(files).map(Ok).left_stream(),
Err(e) => stream::once(async { Err(e) }).right_stream(),
};
Some((file_stream, to_visit))
}
})
.flatten()
}
#[tokio::main]
async fn main() {
let root_path = std::env::args().nth(1).expect("One argument required");
let paths = visit(root_path);
paths
.for_each(|entry| {
async {
match entry {
Ok(entry) => println!("visiting {:?}", entry),
Err(e) => eprintln!("encountered an error: {}", e),
}
}
})
.await;
}
期货0.1/东京0.1
use std::path::PathBuf;
use tokio::{fs, prelude::*}; // 0.1.22
use tokio_fs::DirEntry; // 1.0.6
fn visit(
path: impl Into<PathBuf>,
) -> impl Stream<Item = DirEntry, Error = std::io::Error> + Send + 'static {
fn visit_inner(
path: PathBuf,
) -> Box<dyn Stream<Item = DirEntry, Error = std::io::Error> + Send + 'static> {
Box::new({
fs::read_dir(path)
.flatten_stream()
.map(|entry| {
let path = entry.path();
if path.is_dir() {
// Optionally include `entry` if you want to
// include directories in the resulting
// stream.
visit_inner(path)
} else {
Box::new(stream::once(Ok(entry)))
}
})
.flatten()
})
}
visit_inner(path.into())
}
fn main() {
tokio::run({
let root_path = std::env::args().nth(1).expect("One argument required");
let paths = visit(root_path);
paths
.then(|entry| {
match entry {
Ok(entry) => println!("visiting {:?}", entry),
Err(e) => eprintln!("encountered an error: {}", e),
};
Ok(())
})
.for_each(|_| Ok(()))
});
}
另请参阅:
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