1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132

//! The main purpose of the crate is to retry `Futures` which may contain complex scenarios such as
//! not only handling errors but anything that should be retried. This may include
//! retrying 500's errors from http requests or retrying something like "pseudo" successes from
//! grpc requests.

pub mod error;
mod future;
mod retry_strategy;

pub use error::{Error, RetryError, TooManyAttempts};
pub use future::RetryFuture;
pub use retry_strategy::{
    ExponentialRetryStrategy, InfiniteRetryStrategy, LinearRetryStrategy, RetryStrategy,
};
use std::fmt::Debug;

/// Return type of [inner future](crate::future::FutureFactory::Future)
/// inside [RetryFuture](crate::future::RetryFuture)
///
/// `Fail` variant means unrecoverable error
///
/// If `future` propagates errors early by using `?` then
/// `Retry` will contain [error](error::Error) inside it.
///
/// If you want to provide some debug information about
/// why a `Future` failed, you can construct [error](error::Error) youself.
#[derive(Debug)]
pub enum RetryPolicy<E = String> {
    Retry(Option<Error>),
    /// Unrecoverable error which means that the [RetryFuture](crate::future::RetryFuture)
    /// `Future` will immediately return with an error
    Fail(E),
}

impl<E, T: Into<anyhow::Error>> From<T> for RetryPolicy<E> {
    fn from(t: T) -> Self {
        Self::Retry(Some(Error { error: t.into(), is_early_returned: true }))
    }
}

/// Return early with [RetryPolicy::Fail](crate::RetryPolicy::Fail)
#[macro_export]
macro_rules! fail {
    ($e:expr) => {
        return Err($crate::RetryPolicy::Fail($e))
    };
}

/// Return early with [RetryPolicy::Retry](crate::RetryPolicy::Retry)
#[macro_export]
macro_rules! retry {
    ($e:expr) => {
        return Err($crate::RetryPolicy::Retry(Some($crate::error::Error::msg($e))))
    };

    () => {
        return Err($crate::RetryPolicy::Retry(None))
    };
}

#[cfg(test)]
mod tests {
    pub use super::*;
    use futures::{
        future::{err, ok},
        TryFutureExt,
    };
    use std::time::Duration;

    struct MyRetryStrategy {
        max_attempts: usize,
        counter: Vec<u8>,
    }

    impl RetryStrategy for MyRetryStrategy {
        fn check_attempt(&mut self, attempts_before: usize) -> Result<Duration, TooManyAttempts> {
            if self.max_attempts == attempts_before {
                Err(TooManyAttempts)
            } else {
                self.counter.push(0);
                Ok(Duration::from_millis(1))
            }
        }

        fn retry_early_returned_errors(&self) -> bool {
            false
        }
    }

    #[tokio::test]
    async fn test_ok() {
        let f = RetryFuture::new(
            || ok::<_, u8>(255).map_err(|_| RetryPolicy::Fail("fail!")),
            MyRetryStrategy { max_attempts: 5, counter: vec![] },
        );
        assert_eq!(255, f.await.unwrap());
    }

    #[tokio::test]
    async fn test_fail() {
        let f = RetryFuture::new(
            || err::<u8, _>(RetryPolicy::Fail("fail")),
            MyRetryStrategy { max_attempts: 2, counter: vec![] },
        );
        let RetryPolicy::Fail(_) = f.await.unwrap_err().errors.last().unwrap() else {
            panic!("Fail error must be returned")
        };
    }

    #[tokio::test]
    async fn test_number_of_attempts() {
        let mut retry_strategy = MyRetryStrategy { max_attempts: 7, counter: vec![] };
        assert_eq!(0, retry_strategy.counter.len());
        let f = RetryFuture::new(
            || err::<u8, RetryPolicy>(RetryPolicy::Retry(None)),
            &mut retry_strategy,
        );
        f.await.unwrap_err();
        assert_eq!(7, retry_strategy.counter.len())
    }

    #[tokio::test]
    async fn test_return_early() {
        let mut retry_strategy = MyRetryStrategy { max_attempts: 7, counter: vec![] };
        let f = RetryFuture::new(
            || async { Ok::<_, RetryPolicy>("non-integer".parse::<u32>()?) },
            &mut retry_strategy,
        );
        f.await.unwrap_err();
        assert_eq!(0, retry_strategy.counter.len())
    }
}