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    use std::any::Any;
    use std::error::Error as StdError;
    use std::fmt;
    use std::io::Error as IoError;
    use std::sync::mpsc::{RecvError, SendError};

    pub type Result<T> = ::std::result::Result<T, Error>;

    /// An enumeration over JPEG features (currently) unsupported by this library.
    ///
    /// Support for features listed here may be included in future versions of this library.
    #[derive(Debug)]
    pub enum UnsupportedFeature {
        /// Hierarchical JPEG.
        Hierarchical,
        /// Lossless JPEG.
        Lossless,
        /// JPEG using arithmetic entropy coding instead of Huffman coding.
        ArithmeticEntropyCoding,
        /// Sample precision in bits. 8 bit sample precision is what is currently supported.
        SamplePrecision(u8),
        /// Number of components in an image. 1, 3 and 4 components are currently supported.
        ComponentCount(u8),
        /// An image can specify a zero height in the frame header and use the DNL (Define Number of
        /// Lines) marker at the end of the first scan to define the number of lines in the frame.
        DNL,
        /// Subsampling ratio.
        SubsamplingRatio,
        /// A subsampling ratio not representable as an integer.
        NonIntegerSubsamplingRatio,
    }

    /// Errors that can occur while decoding a JPEG image.
    #[derive(Debug)]
    pub enum Error {
        /// The image is not formatted properly. The string contains detailed information about the
        /// error.
        Format(String),
        /// The image makes use of a JPEG feature not (currently) supported by this library.
        Unsupported(UnsupportedFeature),
        /// An I/O error occurred while decoding the image.
        Io(IoError),
        /// An internal error occurred while decoding the image.
        Internal(Box<StdError>),
    }

    impl fmt::Display for Error {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            match *self {
                Error::Format(ref desc)      => write!(f, "invalid JPEG format: {}", desc),
                Error::Unsupported(ref feat) => write!(f, "unsupported JPEG feature: {:?}", feat),
                Error::Io(ref err)           => err.fmt(f),
                Error::Internal(ref err)     => err.fmt(f),
            }
        }
    }

    impl StdError for Error {
        fn description(&self) -> &str {
            match *self {
                Error::Format(_)         => "invalid JPEG format",
                Error::Unsupported(_)    => "unsupported JPEG feature",
                Error::Io(ref err)       => err.description(),
                Error::Internal(ref err) => err.description(),
            }
        }

        fn cause(&self) -> Option<&StdError> {
            match *self {
                Error::Io(ref err) => Some(err),
                Error::Internal(ref err) => Some(&**err),
                _ => None,
            }
        }
    }

    impl From<IoError> for Error {
        fn from(err: IoError) -> Error {
            Error::Io(err)
        }
    }

    impl From<RecvError> for Error {
        fn from(err: RecvError) -> Error {
            Error::Internal(Box::new(err))
        }
    }

    impl<T: Any + Send> From<SendError<T>> for Error {
        fn from(err: SendError<T>) -> Error {
            Error::Internal(Box::new(err))
        }
    }

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