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    use std::prelude::v1::*;
    use std::any::Any;
    use std::panic::{catch_unwind, UnwindSafe, AssertUnwindSafe};
    use std::mem;

    use super::super::{Poll, Async};
    use super::Stream;

    /// Stream for the `catch_unwind` combinator.
    ///
    /// This is created by the `Stream::catch_unwind` method.
    #[derive(Debug)]
    #[must_use = "streams do nothing unless polled"]
    pub struct CatchUnwind<S> where S: Stream {
        state: CatchUnwindState<S>,
    }

    pub fn new<S>(stream: S) -> CatchUnwind<S>
        where S: Stream + UnwindSafe,
    {
        CatchUnwind {
            state: CatchUnwindState::Stream(stream),
        }
    }

    #[derive(Debug)]
    enum CatchUnwindState<S> {
        Stream(S),
        Eof,
        Done,
    }

    impl<S> Stream for CatchUnwind<S>
        where S: Stream + UnwindSafe,
    {
        type Item = Result<S::Item, S::Error>;
        type Error = Box<Any + Send>;

        fn poll(&mut self) -> Poll<Option<Self::Item>, Self::Error> {
            let mut stream = match mem::replace(&mut self.state, CatchUnwindState::Eof) {
                CatchUnwindState::Done => panic!("cannot poll after eof"),
                CatchUnwindState::Eof => {
                    self.state = CatchUnwindState::Done;
                    return Ok(Async::Ready(None));
                }
                CatchUnwindState::Stream(stream) => stream,
            };
            let res = catch_unwind(|| (stream.poll(), stream));
            match res {
                Err(e) => Err(e), // and state is already Eof
                Ok((poll, stream)) => {
                    self.state = CatchUnwindState::Stream(stream);
                    match poll {
                        Err(e) => Ok(Async::Ready(Some(Err(e)))),
                        Ok(Async::NotReady) => Ok(Async::NotReady),
                        Ok(Async::Ready(Some(r))) => Ok(Async::Ready(Some(Ok(r)))),
                        Ok(Async::Ready(None)) => Ok(Async::Ready(None)),
                    }
                }
            }
        }
    }

    impl<S: Stream> Stream for AssertUnwindSafe<S> {
        type Item = S::Item;
        type Error = S::Error;

        fn poll(&mut self) -> Poll<Option<S::Item>, S::Error> {
            self.0.poll()
        }
    }

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