No easy way to report errors that occur in UdpCodec::encode about tokio

[kpp]

@uberblah is it enough for you? I may do some more fixes.

pub trait UdpCodec {
    /// The type of decoded frames.
    type In;

    /// The type of frames to be encoded.
    type Out;

    /// The type of unrecoverable frame encoding/decoding errors.
    ///
    /// `From<io::Error>` is required in the interest of making `Error` suitable
    /// for returning directly from a `FramedRead`, and to enable the default
    /// implementation of `decode_eof` to yield an `io::Error` when the decoder
    /// fails to consume all available data.
    ///
    /// Note that implementors of this trait can simply indicate `type Error =
    /// io::Error` to use I/O errors as this type.
    type Error: From<io::Error>;

    /// Attempts to decode a frame from the provided buffer of bytes.
    ///
    /// This method is called by `UdpFramed` on a single datagram which has been
    /// read from a socket. The `buf` argument contains the data that was
    /// received from the remote address, and `src` is the address the data came
    /// from. Note that typically this method should require the entire contents
    /// of `buf` to be valid or otherwise return an error with trailing data.
    ///
    /// Finally, if the bytes in the buffer are malformed then an error is
    /// returned indicating why. This informs `Framed` that the stream is now
    /// corrupt and should be terminated.
    fn decode(&mut self, src: &SocketAddr, buf: &[u8]) -> Result<Self::In, Self::Error>;

    /// Encodes a frame into the buffer provided.
    ///
    /// This method will encode `msg` into the byte buffer provided by `buf`.
    /// The `buf` provided is an internal buffer of the `Framed` instance and
    /// will be written out when possible.
    ///
    /// The encode method also determines the destination to which the buffer
    /// should be directed, which will be returned as a `SocketAddr`.
    fn encode(&mut self, msg: Self::Out, buf: &mut Vec<u8>) -> Result<SocketAddr, Self::Error>;
}

[uberblah]

That would be excellent! Thank you!