如何在 Rust 中声明 `Cow<'_, str>`.borrow() 类型？

Question

代码如下：

use std::io::{Read, Write};
use std::net::{TcpListener, TcpStream};

use std::fs::read;

use std::thread;

use std::borrow::Borrow;


fn handle_client(stream: TcpStream) -> () {
   let mut buffer = [0; 4096];

   stream.read(&mut buffer).expect("read fail");

   let path_request = String::from_utf8_lossy(&buffer[..]);
   println!("request \"{}\" received", path_request);

   let content_response = read(path_request.borrow()).unwrap();
   stream.write(&content_response).expect("response fail");
}

编译时出现下一个错误：

error[E0283]: type annotations needed
  --> src/main.rs:20:27
   |
20 |    let content_response = read(path_request.borrow()).unwrap();
   |                           ^^^^              ------ type must be known at this point
   |                           |
   |                           cannot infer type of the type parameter `P` declared on the function `read`

问题是如何声明借用的返回类型

Cow<'_, str>

？

Answer 1

在当前情况下是<&str>

String::from_utf8_lossy() 返回类型为

Cow<'_, str>

且

Cow<'_, str>.borrow()

返回类型为 <&str>

因此，没有编译错误的工作代码是：

use std::io::{Read, Write};
use std::net::{TcpListener, TcpStream};

use std::fs::read;

use std::thread;

use std::borrow::Borrow;


fn handle_client(stream: TcpStream) -> () {
   let mut buffer = [0; 4096];

   stream.read(&mut buffer).expect("read fail");

   let path_request = String::from_utf8_lossy(&buffer[..]);
   println!("request \"{}\" received", path_request);

   let content_response = read::<&str>(path_request.borrow()).unwrap();
   stream.write(&content_response).expect("response fail");
}