一、使用async搭建简单的web服务

1、修改cargo.toml文件添加依赖

[dependencies]
futures = "0.3"
tokio = { version = "1", features = ["full"] }
[dependencies.async-std]
version = "1.6"
features = ["attributes"]

2、搭建web服务

（1）单线程并发处理请求

这里解释一下，单线程并发处理请求，其实每一个请求都是一个future，如果一个future卡了，会去处理别的future，async原理可以去看我关于async的博客

use async_std::net::TcpListener;
use async_std::net::TcpStream;
use futures::stream::StreamExt;

use std::fs;
use async_std::prelude::*;
use std::time::Duration;
use async_std::task;

#[async_std::main]
async fn main() {
    let listener = TcpListener::bind("127.0.0.1:7878").await.unwrap(); // 创建 TCP 监听器，绑定到本地 7878 端口
    listener
        .incoming() // 监听传入的连接
        .for_each_concurrent(/* limit */ None, |tcpstream| async move {//stream 流异步并发处理
            let tcpstream = tcpstream.unwrap(); // 获取传入连接
            handle_connection(tcpstream).await; // 处理连接的异步任务
        })
        .await; // 等待所有连接处理完毕
}

async fn handle_connection(mut stream: TcpStream) {
    let mut buffer = [0; 1024];
    stream.read(&mut buffer).await.unwrap(); // 读取 TCP 流数据到缓冲区

    let get = b"GET / HTTP/1.1\r\n";
    let sleep = b"GET /sleep HTTP/1.1\r\n";

    // 判断请求内容，确定响应状态行和文件名
    let (status_line, filename) = if buffer.starts_with(get) {
        ("HTTP/1.1 200 OK\r\n\r\n", "hello.html") // 如果请求是 GET /，返回 200 OK 状态和 hello.html 文件
    } else if buffer.starts_with(sleep) {
        task::sleep(Duration::from_secs(5)).await; // 如果请求是 GET /sleep，等待 5 秒钟
        ("HTTP/1.1 200 OK\r\n\r\n", "hello.html") // 然后返回 200 OK 状态和 hello.html 文件
    } else {
        ("HTTP/1.1 404 NOT FOUND\r\n\r\n", "404.html") // 其他情况返回 404 NOT FOUND 状态和 404.html 文件
    };
    
    // 读取文件内容到字符串
    let contents = fs::read_to_string(filename).unwrap();
    let response = format!("{status_line}{contents}"); // 构建响应字符串

    // 将响应字符串写入 TCP 流，并刷新
    stream.write(response.as_bytes()).await.unwrap();
    stream.flush().await.unwrap();
}

（2）多线程并发处理请求

lib.rs

// src/lib.rs
use std::{
  sync::{mpsc, Arc, Mutex},
  thread,
};

pub struct ThreadPool {
  workers: Vec<Worker>,
  sender: Option<mpsc::Sender<Job>>,
}

type Job = Box<dyn FnOnce() + Send + 'static>;

impl ThreadPool {
  /// Create a new ThreadPool.
  ///
  /// The size is the number of threads in the pool.
  ///
  /// # Panics
  ///
  /// The `new` function will panic if the size is zero.
  pub fn new(size: usize) -> ThreadPool {
      assert!(size > 0);

      let (sender, receiver) = mpsc::channel();

      let receiver = Arc::new(Mutex::new(receiver));

      let mut workers = Vec::with_capacity(size);

      for id in 0..size {
          workers.push(Worker::new(id, Arc::clone(&receiver)));
      }

      ThreadPool {
          workers,
          sender: Some(sender),
      }
  }

  pub fn execute<F>(&self, f: F)
  where
      F: FnOnce() + Send + 'static,
  {
      let job = Box::new(f);

      self.sender.as_ref().unwrap().send(job).unwrap();
  }
}

impl Drop for ThreadPool {
  fn drop(&mut self) {
      drop(self.sender.take());

      for worker in &mut self.workers {
          println!("Shutting down worker {}", worker.id);

          if let Some(thread) = worker.thread.take() {
              thread.join().unwrap();
          }
      }
  }
}

struct Worker {
  id: usize,
  thread: Option<thread::JoinHandle<()>>,
}

impl Worker {
  fn new(id: usize, receiver: Arc<Mutex<mpsc::Receiver<Job>>>) -> Worker {
      let thread = thread::spawn(move || loop {
          let message = receiver.lock().unwrap().recv();

          match message {
              Ok(job) => {
                  println!("Worker {id} got a job; executing.");

                  job();
              }
              Err(_) => {
                  println!("Worker {id} disconnected; shutting down.");
                  break;
              }
          }
      });

      Worker {
          id,
          thread: Some(thread),
      }
  }
}

main.rs

// src/main.rs
use hello_package::ThreadPool;
use std::fs;
use std::io::prelude::*;
use std::net::TcpListener;
use std::net::TcpStream;
use std::thread;
use std::time::Duration;

fn main() {
    let listener = TcpListener::bind("127.0.0.1:7878").unwrap();
    let pool = ThreadPool::new(4);

    for stream in listener.incoming().take(4) {//take限制请求次数
        let stream = stream.unwrap();

        pool.execute(|| {
            handle_connection(stream);
        });
    }

    println!("Shutting down.");
}

fn handle_connection(mut stream: TcpStream) {
    let mut buffer = [0; 1024];
    stream.read(&mut buffer).unwrap();

    let get = b"GET / HTTP/1.1\r\n";
    let sleep = b"GET /sleep HTTP/1.1\r\n";

    let (status_line, filename) = if buffer.starts_with(get) {
        ("HTTP/1.1 200 OK", "hello.html")
    } else if buffer.starts_with(sleep) {
        thread::sleep(Duration::from_secs(5));
        ("HTTP/1.1 200 OK", "hello.html")
    } else {
        ("HTTP/1.1 404 NOT FOUND", "404.html")
    };

    let contents = fs::read_to_string(filename).unwrap();

    let response = format!(
        "{}\r\nContent-Length: {}\r\n\r\n{}",
        status_line,
        contents.len(),
        contents
    );

    stream.write_all(response.as_bytes()).unwrap();
    stream.flush().unwrap();
}