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

use std::prelude::v1::*;

use std::fmt;
use std::mem;

use {Async, IntoFuture, Poll, Future};
use stream::{Stream, Fuse};

/// An adaptor for a stream of futures to execute the futures concurrently, if
/// possible.
///
/// This adaptor will buffer up a list of pending futures, and then return their
/// results in the order that they were pulled out of the original stream. This
/// is created by the `Stream::buffered` method.
#[must_use = "streams do nothing unless polled"]
pub struct Buffered<S>
    where S: Stream,
          S::Item: IntoFuture,
{
    stream: Fuse<S>,
    futures: Vec<State<<S::Item as IntoFuture>::Future>>,
    cur: usize,
}

impl<S> fmt::Debug for Buffered<S>
    where S: Stream + fmt::Debug,
          S::Item: IntoFuture,
          <<S as Stream>::Item as IntoFuture>::Future: fmt::Debug,
          <<S as Stream>::Item as IntoFuture>::Item: fmt::Debug,
          <<S as Stream>::Item as IntoFuture>::Error: fmt::Debug,
{
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        fmt.debug_struct("Stream")
            .field("stream", &self.stream)
            .field("futures", &self.futures)
            .field("cur", &self.cur)
            .finish()
    }
}

#[derive(Debug)]
enum State<S: Future> {
    Empty,
    Running(S),
    Finished(Result<S::Item, S::Error>),
}

pub fn new<S>(s: S, amt: usize) -> Buffered<S>
    where S: Stream,
          S::Item: IntoFuture<Error=<S as Stream>::Error>,
{
    Buffered {
        stream: super::fuse::new(s),
        futures: (0..amt).map(|_| State::Empty).collect(),
        cur: 0,
    }
}

// Forwarding impl of Sink from the underlying stream
impl<S> ::sink::Sink for Buffered<S>
    where S: ::sink::Sink + Stream,
          S::Item: IntoFuture,
{
    type SinkItem = S::SinkItem;
    type SinkError = S::SinkError;

    fn start_send(&mut self, item: S::SinkItem) -> ::StartSend<S::SinkItem, S::SinkError> {
        self.stream.start_send(item)
    }

    fn poll_complete(&mut self) -> Poll<(), S::SinkError> {
        self.stream.poll_complete()
    }

    fn close(&mut self) -> Poll<(), S::SinkError> {
        self.stream.close()
    }
}

impl<S> Stream for Buffered<S>
    where S: Stream,
          S::Item: IntoFuture<Error=<S as Stream>::Error>,
{
    type Item = <S::Item as IntoFuture>::Item;
    type Error = <S as Stream>::Error;

    fn poll(&mut self) -> Poll<Option<Self::Item>, Self::Error> {
        // First, try to fill in all the futures
        for i in 0..self.futures.len() {
            let mut idx = self.cur + i;
            if idx >= self.futures.len() {
                idx -= self.futures.len();
            }

            if let State::Empty = self.futures[idx] {
                match try!(self.stream.poll()) {
                    Async::Ready(Some(future)) => {
                        let future = future.into_future();
                        self.futures[idx] = State::Running(future);
                    }
                    Async::Ready(None) => break,
                    Async::NotReady => break,
                }
            }
        }

        // Next, try and step all the futures forward
        for future in self.futures.iter_mut() {
            let result = match *future {
                State::Running(ref mut s) => {
                    match s.poll() {
                        Ok(Async::NotReady) => continue,
                        Ok(Async::Ready(e)) => Ok(e),
                        Err(e) => Err(e),
                    }
                }
                _ => continue,
            };
            *future = State::Finished(result);
        }

        // Check to see if our current future is done.
        if let State::Finished(_) = self.futures[self.cur] {
            let r = match mem::replace(&mut self.futures[self.cur], State::Empty) {
                State::Finished(r) => r,
                _ => panic!(),
            };
            self.cur += 1;
            if self.cur >= self.futures.len() {
                self.cur = 0;
            }
            return Ok(Async::Ready(Some(try!(r))))
        }

        if self.stream.is_done() {
            if let State::Empty = self.futures[self.cur] {
                return Ok(Async::Ready(None))
            }
        }
        Ok(Async::NotReady)
    }
}