我有一个客户端处理Future
做一些事情。是否可以使用impl Future<Item = (), Error = io::Error>
作为返回类型并进行更好的错误处理?
pub fn handle_client(client: Client) -> impl Future<Item = (), Error = io::Error> {
let magic = client.header.magic;
let stream_client = TcpStream::connect(&client.addr).and_then(|stream| {
let addr: Vec<u8> = serialize_addr(stream.local_addr()?, magic)?;
write_all(stream, addr).then(|result| {
// some code
Ok(())
})
});
stream_client
}
我无法通过所有嵌套闭包/期货保持io::Error
类型。编译器抛出错误
error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `std::ops::Try`)
--> src/client.rs:134:29
|
134 | let addr: Vec<u8> = serialize_addr(stream.local_addr()?, magic)?;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot use the `?` operator in a function that returns `futures::future::then::Then<tokio_io::io::write_all::WriteAll<tokio_tcp::stream::TcpStream, std::vec::Vec<u8>>, std::result::Result<(), std::io::Error>, [closure@src/client.rs:135:38: 138:10]>`
|
= help: the trait `std::ops::Try` is not implemented for `futures::future::then::Then<tokio_io::io::write_all::WriteAll<tokio_tcp::stream::TcpStream, std::vec::Vec<u8>>, std::result::Result<(), std::io::Error>, [closure@src/client.rs:135:38: 138:10]>`
= note: required by `std::ops::Try::from_error`
我做了链接地图/并且然后错误处理,但问题是我不知道如何在最终的TcpStream
关闭内获得.then
。我发现TcpStream
唯一的地方是WriteAll结构,但它是私有的。此外,write_all消耗流
use futures::Future;
use std::{io, net::SocketAddr};
use tokio::{
io::{write_all, AsyncRead, AsyncWrite},
net::TcpStream,
};
type Error = Box<dyn std::error::Error>;
fn serialize_addr(addr: SocketAddr) -> Result<Vec<u8>, Error> {
Ok(vec![])
}
fn handle_client(addr: &SocketAddr) -> impl Future<Item = (), Error = Error> {
TcpStream::connect(addr)
.map_err(Into::into)
.and_then(|stream| stream.local_addr().map(|stream_addr| (stream, stream_addr)))
.map_err(Into::into)
.and_then(|(stream, stream_addr)| serialize_addr(stream_addr).map(|info| (stream, info)))
.map(|(stream, info)| write_all(stream, info))
.then(|result| {
let result = result.unwrap();
let stream = match result.state {
Writing { a } => a,
_ => panic!("cannot get stream"),
};
// some code
Ok(())
})
}
fn main() {
let addr = "127.0.0.1:8900".parse().unwrap();
handle_client(&addr);
}
TL; DR:你不使用?
算子。
由于你没有提供一个,这里是你问题的MCVE。请注意,我们不知道你的serialize_addr
函数的错误类型是什么,所以我不得不选择一些东西:
use futures::Future;
use std::{io, net::SocketAddr};
use tokio::{io::write_all, net::TcpStream};
fn serialize_addr() -> Result<Vec<u8>, Box<dyn std::error::Error>> {
Ok(vec![])
}
pub fn handle_client(addr: &SocketAddr) -> impl Future<Item = (), Error = io::Error> {
TcpStream::connect(addr).and_then(|stream| {
let addr = serialize_addr()?;
write_all(stream, addr).then(|_result| Ok(()))
})
}
error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `std::ops::Try`)
--> src/lib.rs:11:20
|
11 | let addr = serialize_addr()?;
| ^^^^^^^^^^^^^^^^^ cannot use the `?` operator in a function that returns `futures::future::then::Then<tokio_io::io::write_all::WriteAll<tokio_tcp::stream::TcpStream, std::vec::Vec<u8>>, std::result::Result<(), std::io::Error>, [closure@src/lib.rs:12:38: 14:10]>`
|
= help: the trait `std::ops::Try` is not implemented for `futures::future::then::Then<tokio_io::io::write_all::WriteAll<tokio_tcp::stream::TcpStream, std::vec::Vec<u8>>, std::result::Result<(), std::io::Error>, [closure@src/lib.rs:12:38: 14:10]>`
= note: required by `std::ops::Try::from_error`
如错误消息所示:
?
运算符只能在返回Result
或Option
(或其他实现std::ops::Try
的类型)的函数中使用
和
不能在返回
?
的函数中使用Then<WriteAll<TcpStream, Vec<u8>>, Result<(), io::Error>, [closure]>
运算符
相反,利用Result
可以被视为未来并让它参与功能链的事实。
此外,就像Rust中的其他地方一样,您需要具有统一的错误类型。为简单起见,我选择了Box<dyn Error>
。这可以使用map_err
和Into::into
来实现
use futures::Future;
use std::net::SocketAddr;
use tokio::{io::write_all, net::TcpStream};
type Error = Box<dyn std::error::Error>;
fn serialize_addr() -> Result<Vec<u8>, Error> {
Ok(vec![])
}
pub fn handle_client(addr: &SocketAddr) -> impl Future<Item = (), Error = Error> {
TcpStream::connect(addr)
.map_err(Into::into)
.and_then(|stream| serialize_addr().map(|addr| (stream, addr)))
.and_then(|(stream, addr)| write_all(stream, addr).map_err(Into::into))
.then(|_result| Ok(()))
}
在未来,async
/ await
语法将使这更容易遵循。
两个流的解决方案:
fn handle_client(addr: &SocketAddr) -> impl Future<Item = (), Error = Error> {
TcpStream::connect(addr)
.map_err(Into::into)
.and_then(|remote_stream| {
remote_stream
.local_addr()
.map(|remote_addr| (remote_stream, remote_addr))
})
.map_err(Into::into)
.and_then(|(remote_stream, remote_addr)| {
TcpStream::connect(&"".parse().unwrap())
.map(move |proxy_stream| (remote_stream, proxy_stream, remote_addr))
})
.and_then(|(remote_stream, proxy_stream, remote_addr)| {
serialize_addr(remote_addr)
.map(|info| (remote_stream, proxy_stream, info))
.map_err(|_| io::Error::from(io::ErrorKind::AddrNotAvailable))
})
.and_then(|(remote_stream, proxy_stream, info)| {
write_all(proxy_stream, info).map(|proxy_stream| (remote_stream, proxy_stream.0))
})
.and_then(|(remote_stream, proxy_stream)| {
// working with streams
})
.then(|_result| Ok(()))
}