tokio_timer/
throttle.rs

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
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
//! Slow down a stream by enforcing a delay between items.

use {clock, Delay, Error};

use futures::future::Either;
use futures::{Async, Future, Poll, Stream};

use std::{
    error::Error as StdError,
    fmt::{Display, Formatter, Result as FmtResult},
    time::Duration,
};

/// Slow down a stream by enforcing a delay between items.
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct Throttle<T> {
    delay: Option<Delay>,
    duration: Duration,
    stream: T,
}

/// Either the error of the underlying stream, or an error within
/// tokio's timing machinery.
#[derive(Debug)]
pub struct ThrottleError<T>(Either<T, Error>);

impl<T> Throttle<T> {
    /// Slow down a stream by enforcing a delay between items.
    pub fn new(stream: T, duration: Duration) -> Self {
        Self {
            delay: None,
            duration: duration,
            stream: stream,
        }
    }

    /// Acquires a reference to the underlying stream that this combinator is
    /// pulling from.
    pub fn get_ref(&self) -> &T {
        &self.stream
    }

    /// Acquires a mutable reference to the underlying stream that this combinator
    /// is pulling from.
    ///
    /// Note that care must be taken to avoid tampering with the state of the stream
    /// which may otherwise confuse this combinator.
    pub fn get_mut(&mut self) -> &mut T {
        &mut self.stream
    }

    /// Consumes this combinator, returning the underlying stream.
    ///
    /// Note that this may discard intermediate state of this combinator, so care
    /// should be taken to avoid losing resources when this is called.
    pub fn into_inner(self) -> T {
        self.stream
    }
}

impl<T: Stream> Stream for Throttle<T> {
    type Item = T::Item;
    type Error = ThrottleError<T::Error>;

    fn poll(&mut self) -> Poll<Option<Self::Item>, Self::Error> {
        if let Some(ref mut delay) = self.delay {
            try_ready!({ delay.poll().map_err(ThrottleError::from_timer_err) });
        }

        self.delay = None;
        let value = try_ready!({ self.stream.poll().map_err(ThrottleError::from_stream_err) });

        if value.is_some() {
            self.delay = Some(Delay::new(clock::now() + self.duration));
        }

        Ok(Async::Ready(value))
    }
}

impl<T> ThrottleError<T> {
    /// Creates a new `ThrottleError` from the given stream error.
    pub fn from_stream_err(err: T) -> Self {
        ThrottleError(Either::A(err))
    }

    /// Creates a new `ThrottleError` from the given tokio timer error.
    pub fn from_timer_err(err: Error) -> Self {
        ThrottleError(Either::B(err))
    }

    /// Attempts to get the underlying stream error, if it is present.
    pub fn get_stream_error(&self) -> Option<&T> {
        match self.0 {
            Either::A(ref x) => Some(x),
            _ => None,
        }
    }

    /// Attempts to get the underlying timer error, if it is present.
    pub fn get_timer_error(&self) -> Option<&Error> {
        match self.0 {
            Either::B(ref x) => Some(x),
            _ => None,
        }
    }

    /// Attempts to extract the underlying stream error, if it is present.
    pub fn into_stream_error(self) -> Option<T> {
        match self.0 {
            Either::A(x) => Some(x),
            _ => None,
        }
    }

    /// Attempts to extract the underlying timer error, if it is present.
    pub fn into_timer_error(self) -> Option<Error> {
        match self.0 {
            Either::B(x) => Some(x),
            _ => None,
        }
    }

    /// Returns whether the throttle error has occured because of an error
    /// in the underlying stream.
    pub fn is_stream_error(&self) -> bool {
        !self.is_timer_error()
    }

    /// Returns whether the throttle error has occured because of an error
    /// in tokio's timer system.
    pub fn is_timer_error(&self) -> bool {
        match self.0 {
            Either::A(_) => false,
            Either::B(_) => true,
        }
    }
}

impl<T: StdError> Display for ThrottleError<T> {
    fn fmt(&self, f: &mut Formatter) -> FmtResult {
        match self.0 {
            Either::A(ref err) => write!(f, "stream error: {}", err),
            Either::B(ref err) => write!(f, "timer error: {}", err),
        }
    }
}

impl<T: StdError + 'static> StdError for ThrottleError<T> {
    fn description(&self) -> &str {
        match self.0 {
            Either::A(_) => "stream error",
            Either::B(_) => "timer error",
        }
    }

    // FIXME(taiki-e): When the minimum support version of tokio reaches Rust 1.30,
    // replace this with Error::source.
    #[allow(deprecated)]
    fn cause(&self) -> Option<&dyn StdError> {
        match self.0 {
            Either::A(ref err) => Some(err),
            Either::B(ref err) => Some(err),
        }
    }
}