我有一个客户端处理Future
,它会执行一些操作。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呢?
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
}
我无法在所有嵌套的闭包/未来中保留 io::Error
类型。编译器会抛出以下错误:
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`
我进行了链式 map/and_then 错误处理,但问题是我不知道如何在最终的 .then 闭包内获取 TcpStream。我发现唯一可以找到 TcpStream 的地方是 WriteAll 结构体内部,然而它是私有的。此外,write_all 会消耗流。
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);
}
map(... write_all)
,而不是使用and_then
呢?你不能随意更改调用的方法并期望它正常工作。使用and_then
时,未来的成功值是(TcpStream,Vec<u8>)
。 - Shepmasterserialize_addr(remote_addr).map_err(|_| io::Error::from(io::ErrorKind::AddrNotAvailable))
进行强制转换,我就无法使用.and_then
而不是.map
。 - abritov