Async example doesn't work at all

[autarchprinceps]

I tried to apply the async backoff example to my code, but kept running into errors, so I just tried to compile the raw example, but it fails with exactly the same errors.
This code:

use backoff::{future::FutureOperation as _, ExponentialBackoff};

async fn fetch_url(url: &str) -> Result<String, reqwest::Error> {
  (|| async {
    println!("Fetching {}", url);
    Ok(reqwest::get(url).await?.text().await?)
  })
    .retry(ExponentialBackoff::default())
    .await
}

#[tokio::main]
async fn main() {
  match fetch_url("https://www.rust-lang.org").await {
    Ok(_) => println!("Successfully fetched"),
    Err(err) => panic!("Failed to fetch: {}", err),
  }
}

causes these errors:

error[E0432]: unresolved import `backoff::future`
 --> src/main.rs:1:15
  |
1 | use backoff::{future::FutureOperation as _, ExponentialBackoff};
  |               ^^^^^^ could not find `future` in `backoff`

error[E0599]: no method named `retry` found for closure `[closure@src/main.rs:4:3: 7:5 url:_]` in the current scope
 --> src/main.rs:8:6
  |
8 |     .retry(ExponentialBackoff::default())
  |      ^^^^^ method not found in `[closure@src/main.rs:4:3: 7:5 url:_]`
  |
  = note: `(|| async {
              println!("Fetching {}", url);
              Ok(reqwest::get(url).await?.text().await?)
            })` is a function, perhaps you wish to call it

with a cargo toml dependency including backoff = ">=0.2.1"

[tobymurray]

Did you try adding the async-std feature? e.g. backoff = { version = "0.2.1", features = ["async-std"] }? Related to #14 I think.

I'm not sure how a user is supposed to discover the async-std feature even exists, or that it's needed - perhaps missing documentation? I found it by looking at the source after running into the same issue as you.

[autarchprinceps]

The feature sync-std does fix the default sample. This should definitively be documented.
As for my real code, it still fails. From what this tells me, I assume this means it doesn't like the error type, but I'm not sure. The actual call I'm making, is to rusoto, which has it's own error types, that do work with Result and match, but apparently not with backoff.

299 |   match (|| async {
    |         ---------
    |         |
    |         doesn't satisfy `<_ as std::ops::FnOnce<()>>::Output = std::result::Result<_, backoff::error::Error<_>>`
    |         doesn't satisfy `_: backoff::retry::Operation<_, _>`
300 |     client.list_stacks(list_stacks_input.clone()).await
301 |   }).retry(ExponentialBackoff::default()).await {
    |      ^^^^^ method not found in `[closure@src/main.rs:299:9: 301:5 client:_, list_stacks_input:_]`

[sander2]

299 |   match (|| async {
    |         ---------
    |         |
    |         doesn't satisfy `<_ as std::ops::FnOnce<()>>::Output = std::result::Result<_, backoff::error::Error<_>>`
    |         doesn't satisfy `_: backoff::retry::Operation<_, _>`
300 |     client.list_stacks(list_stacks_input.clone()).await
301 |   }).retry(ExponentialBackoff::default()).await {
    |      ^^^^^ method not found in `[closure@src/main.rs:299:9: 301:5 client:_, list_stacks_input:_]`

I think you need to convert the Error type. Try Ok(client.list_stacks(list_stacks_input.clone()).await?), or use map_err(|e| e.into())

[ihrwein]

@autarchprinceps I'm sorry for taking so long to reply to this issue. Did you manage to solve it eventually?

I agree with @sander2's suggestion above, .map_err(backoff::Error::Transient) might solve your issue.

You can find an example here which uses the latest master, reqwest anyhow: https://github.com/ihrwein/backoff-issue-22/blob/main/src/lib.rs

[ihrwein]

Closing due to inactivity.