如何在哈希映射字段中保存对处理程序的引用

Question

我正在学习 Rust 并尝试编写一个 websocket 服务器。逻辑如下：WSConnectionFactory 创建 WSHandler，它处理传入的消息并根据任意规则将它们发送到其他客户端。问题是我不知道如何实现这种行为。

限制：我无法更改工厂和处理程序特征的签名，因为它们是由 ws-rs 库提供的。

问：如何使用RefCell/Cell实现这一点？

extern crate rand;
extern crate rustc_serialize;
extern crate ws;
#[macro_use]
extern crate log;
#[macro_use]
extern crate env_logger;
use std::cell::RefCell;
use std::collections::HashMap;
use rand::random;
use ws::{Factory, Sender, Handler, Handshake, Message, CloseCode, WebSocket};
use ws::Result as WSResult;
use ws::util::Token;
struct WSConnectionFactory<'p> {
    handlers: HashMap<&'p u32, RefCell<&'p WSHandler<'p>>>,
}
#[derive(Debug)]
struct WSHandler<'h> {
    uid: &'h u32,
    ws: RefCell<&'h Sender>,
}
impl<'p> Factory for WSConnectionFactory<'p> {
    type Handler = WSHandler<'p>;
    fn connection_made(&mut self, ws: Sender) -> Self::Handler {
        println!("factory.connection_made token={:?}", &ws.token());
        let uid = &random::<u32>();
        let handler = WSHandler {
            uid: uid,
            ws: RefCell::new(&ws),
        };
        self.handlers.insert(uid, RefCell::new(&handler));
        handler
    }
}
impl<'h> Handler for WSHandler<'h> {
    fn on_open(&mut self, _handshake: Handshake) -> WSResult<()> {
        println!("handler.on_open");
        Ok(())
    }
    fn on_message(&mut self, msg: Message) -> WSResult<()> {
        println!("handler.on_message {:?}", msg);
        Ok(())
    }
    fn on_timeout(&mut self, _token: Token) -> WSResult<()> {
        println!("handler.on_timeout {:?}", _token);
        Ok(())
    }
    fn on_close(&mut self, code: CloseCode, reason: &str) {
        println!("handler.on_close code={:?}, reason={:?}", code, reason);
    }
}
fn main() {
    let factory = WSConnectionFactory { handlers: HashMap::new() };
    let ws_socket = WebSocket::new(factory).expect("Can't create WebSocket");
    ws_socket.listen("127.0.0.1:8080").expect("Can't bind to socket");
}

Answer 1

您正在尝试从connection_made返回WSHandler，同时还在WSConnectionFactory结构中存储对WSHandler的引用。这是不可能的（使用借用的指针），因为通过返回WSHandler，您无法控制它将会发生什么（它可能会被移动或删除，这将使您的指针无效）。当您应该直接存储值时，您也在存储借用的指针。

WSConnectionFactory创建处理传入消息并根据任意规则将它们发送到其他客户端的WSHandler。

如果要向其他客户端发送消息，实际上需要一个Sender，而不是WSHandler。值得庆幸的是，Sender实现了Clone，并且通过快速查看代码，克隆Sender应该为您提供到同一端点的第二个"句柄"。因此，你应该在你的HashMap放一个Sender，而不是一个WSHandler。

extern crate rand;
extern crate rustc_serialize;
extern crate ws;
#[macro_use]
extern crate log;
#[macro_use]
extern crate env_logger;
use std::collections::HashMap;
use rand::random;
use ws::{Factory, Sender, Handler, Handshake, Message, CloseCode, WebSocket};
use ws::Result as WSResult;
use ws::util::Token;
struct WSConnectionFactory {
    handlers: HashMap<u32, Sender>,
}
#[derive(Debug)]
struct WSHandler {
    uid: u32,
    ws: Sender,
}
impl Factory for WSConnectionFactory {
    type Handler = WSHandler;
    fn connection_made(&mut self, ws: Sender) -> Self::Handler {
        println!("factory.connection_made token={:?}", &ws.token());
        let uid = random::<u32>();
        let handler = WSHandler {
            uid: uid,
            ws: ws.clone(),
        };
        self.handlers.insert(uid, ws);
        handler
    }
}
impl Handler for WSHandler {
    fn on_open(&mut self, _handshake: Handshake) -> WSResult<()> {
        println!("handler.on_open");
        Ok(())
    }
    fn on_message(&mut self, msg: Message) -> WSResult<()> {
        println!("handler.on_message {:?}", msg);
        Ok(())
    }
    fn on_timeout(&mut self, _token: Token) -> WSResult<()> {
        println!("handler.on_timeout {:?}", _token);
        Ok(())
    }
    fn on_close(&mut self, code: CloseCode, reason: &str) {
        println!("handler.on_close code={:?}, reason={:?}", code, reason);
    }
}
fn main() {
    let factory = WSConnectionFactory { handlers: HashMap::new() };
    let ws_socket = WebSocket::new(factory).expect("Can't create WebSocket");
    ws_socket.listen("127.0.0.1:8080").expect("Can't bind to socket");
}