开发基于Tower的TCP回声服务器时，Tokio TcpListener无incoming方法报错

你遇到的“未找到结构体tokio::net::TcpListener的incoming方法”报错，可通过以下两种方式解决：

方案一：修复incoming流的调用问题 #

TcpListener::incoming()返回的是异步流（Stream类型），要调用next().await迭代流，必须导入futures::StreamExt trait。同时确认你的依赖配置中Tokio的full特性已启用（你当前的配置没问题）。

修改后的完整代码：

/*
[dependencies]
futures = "0.3"
tokio = { version = "1", features = ["full"] }
tower = { version = "0.4", features = ["full"] }
*/

use tokio::net::TcpListener;
use tower::Service;

// 导入StreamExt以支持异步流的next()方法
use futures::{future, StreamExt};
use std::task::{Context, Poll};

struct Echo;

impl Service<Vec<u8>> for Echo {
    type Response = Vec<u8>;
    type Error = std::io::Error;
    type Future = future::Ready<Result<Self::Response, Self::Error>>;

    fn poll_ready(&mut self, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
        Poll::Ready(Ok(()))
    }

    fn call(&mut self, req: Vec<u8>) -> Self::Future {
        future::ok(req)
    }
}

#[tokio::main]
async fn main() {
    let addr = "127.0.0.1:8080".parse().unwrap();
    let listener = TcpListener::bind(&addr).await.unwrap();

    let mut incoming = listener.incoming();
    while let Some(socket) = incoming.next().await {
        let socket = socket.unwrap();
        tokio::spawn(async move {
            let (reader, writer) = socket.split();
            let echo = Echo;
            tower::service_fn(move |req| echo.call(req)).serve(reader, writer).await
        });
    }
}

方案二：使用Tower原生服务编排（更推荐） #

Tower提供了tower::serve函数，可直接将服务绑定到TcpListener上，自动处理连接监听、流迭代和服务分发，无需手动调用incoming()，代码更简洁且符合Tower的设计理念：

/*
[dependencies]
futures = "0.3"
tokio = { version = "1", features = ["full"] }
tower = { version = "0.4", features = ["full"] }
*/

use tokio::net::TcpListener;
use tower::{Service, service_fn};

use futures::future;
use std::task::{Context, Poll};

struct Echo;

impl Service<Vec<u8>> for Echo {
    type Response = Vec<u8>;
    type Error = std::io::Error;
    type Future = future::Ready<Result<Self::Response, Self::Error>>;

    fn poll_ready(&mut self, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
        Poll::Ready(Ok(()))
    }

    fn call(&mut self, req: Vec<u8>) -> Self::Future {
        future::ok(req)
    }
}

#[tokio::main]
async fn main() {
    let addr = "127.0.0.1:8080".parse().unwrap();
    let listener = TcpListener::bind(&addr).await.unwrap();

    // Tower自动处理连接生命周期和服务调用
    tower::serve(listener, service_fn(|req: Vec<u8>| {
        let echo = Echo;
        echo.call(req)
    })).await.unwrap();
}

内容的提问来源于stack exchange，提问作者Blank