我正在使用 reqwest,并尝试每 97 毫秒发送一个请求。但是,我不想等待最后一个请求发生或读取它。
我只想每 97 毫秒发送一次请求,并始终将输出发送到 stdout。
我的(当前)代码是这样的:(keys
是一个带有 api 键的数组)
loop {
for i in keys.iter() {
let url = format!("https://api.[insertsite].com/blahblah&apiKey={}", i);
let res = client
.get(url)
.send()
.await?
.text()
.await?;
sleep(Duration::from_millis(97)).await;
println!("{:?}", res);
}
}
如果我删除等待,编译器会告诉我错误[E0599]:在当前范围内没有为不透明类型“impl std::future::Future”找到名为“text”的方法
。
TL;DR:我想每 97 毫秒发送一次 get 请求,无论有任何响应。如果/当有一个响应管道响应标准输出。
编辑:
我尝试使用线程,但我真的不知道如何使用。这是我想到的:
#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
let keys = ["key", "key", "key"];
let client = reqwest::Client::builder()
.build()?;
for i in keys.iter() {
tokio::spawn(async move {
let url = format!("https://api[insertsite].com/blahblah&apiKey={}", i);
let res = client
.get(url)
.send()
.await
.text()
.await;
println!("{:?}", res);
});
sleep(Duration::from_millis(97)).await;
}
}
尝试运行时出现此错误:
error[E0599]: no method named `text` found for enum `std::result::Result<reqwest::Response, reqwest::Error>` in the current scope
--> src/main.rs:22:18
|
22 | .text()
| ^^^^ method not found in `std::result::Result<reqwest::Response, reqwest::Error>`
最佳答案
您已经发现 tokio::spawn
是完成此任务的正确工具,因为您本质上希望以“即发即忘”的方式使用一些异步代码,而不是在主程序流中等待它。您只需要对代码进行一些调整。
首先,对于您引用的错误 - 这是由于您必须以某种方式处理请求期间可能出现的错误。您只需在每个 await
之后添加问号即可返回Result
,但随后您会遇到以下情况:
error[E0277]: the `?` operator can only be used in an async block that returns `Result` or `Option` (or another type that implements `Try`)
--> src/main.rs:11:23
|
9 | tokio::spawn(async move {
| _________________________________-
10 | | let url = format!("https://api[insertsite].com/blahblah&apiKey={}", i);
11 | | let res = client.get(url).send().await?.text().await?;
| | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot use the `?` operator in an async block that returns `()`
12 | | println!("{:?}", res);
13 | | });
| |_________- this function should return `Result` or `Option` to accept `?`
|
= help: the trait `Try` is not implemented for `()`
= note: required by `from_error`
“这个函数”位可能有点误导,因为错误的其余部分正在谈论“异步 block ”,但要点很简单:如果您使用问号将错误从某个地方冒出来,那么幸福的路径必须返回Result
, 也。好吧,我们简单地添加 Ok(())
到异步 block 的末尾,这是下一个错误:
error[E0282]: type annotations needed
--> src/main.rs:11:51
|
11 | let res = client.get(url).send().await?.text().await?;
| ^ cannot infer type of error for `?` operator
|
= note: `?` implicitly converts the error value into a type implementing `From<reqwest::Error>`
这也是预期的 - 在普通函数中返回类型将由其签名提供,但在异步 block 中这不是一个选项。但是,我们可以使用涡轮鱼:
tokio::spawn(async move {
// snip
Ok::<_, Box<dyn std::error::Error + Send + Sync>>(())
});
请注意,我们需要 Send
和Sync
:前者对于生成的错误能够跨越异步 block 边界是必要的,后者是因为 Box<dyn Error + Send>
can't be created with From/Into
conversion from other errors .
现在,我们还剩下两个编译错误,与之前的错误无关:
error[E0597]: `keys` does not live long enough
--> src/main.rs:8:14
|
8 | for i in keys.iter() {
| ^^^^
| |
| borrowed value does not live long enough
| cast requires that `keys` is borrowed for `'static`
...
18 | }
| - `keys` dropped here while still borrowed
error[E0382]: use of moved value: `client`
--> src/main.rs:9:33
|
7 | let client = reqwest::Client::builder().build()?;
| ------ move occurs because `client` has type `reqwest::Client`, which does not implement the `Copy` trait
8 | for i in keys.iter() {
9 | tokio::spawn(async move {
| _________________________________^
10 | | let url = format!("https://api[insertsite].com/blahblah&apiKey={}", i);
11 | | let res = client.get(url).send().await?.text().await?;
| | ------ use occurs due to use in generator
12 | | println!("{:?}", res);
13 | | Ok::<_, Box<dyn std::error::Error + Send + Sync>>(())
14 | | });
| |_________^ value moved here, in previous iteration of loop
第一个问题可以通过三种可能的方式修复:
- 使用
Vec
安装数组并删除.iter()
, - 使用
std::array::IntoIter
, - 使用
.iter().copied()
。 在每种情况下,我们都会得到&'static str
,可以传递到异步 block 中。
第二个更简单:我们可以简单地执行let client = client.clone();
在每次迭代开始时,tokio::spawn
之前。这很便宜,因为 Client
uses Arc
internally .
这是playground ,进行上述所有更改。
最后,这是我个人建议您的代码所基于的版本,因为它不仅可以编译,而且不会消除根据请求可能出现的错误:
use core::time::Duration;
use tokio::time::sleep;
#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
let keys = ["key", "key", "key"];
let client = reqwest::Client::builder().build()?;
for i in std::array::IntoIter::new(keys) {
let client = client.clone();
tokio::spawn(async move {
let url = format!("https://api[insertsite].com/blahblah&apiKey={}", i);
// moved actual request into inner block...
match async move {
let res = client.get(url).send().await?.text().await?;
// ...returning Result with explicit error type,
// so that the wholeinner async block is treated as "try"-block...
Ok::<_, Box<dyn std::error::Error + Send + Sync>>(res)
}
.await
{
// ...and matching on the result, to have either text or error
// (here it'll always be error, due to invalid URL)
Ok(res) => println!("{:?}", res),
Err(er) => println!("{}", er),
}
});
sleep(Duration::from_millis(97)).await;
}
// just to wait for responses
sleep(Duration::from_millis(1000)).await;
Ok(())
}
关于http - 如何在不等待的情况下发送请求?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/67944699/