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use std::io; use bytes::BytesMut; use {AsyncWrite, AsyncRead}; use super::encoder::Encoder; use ::_tokio_codec::Framed; /// Decoding of frames via buffers. /// /// This trait is used when constructing an instance of `Framed` or /// `FramedRead`. An implementation of `Decoder` takes a byte stream that has /// already been buffered in `src` and decodes the data into a stream of /// `Self::Item` frames. /// /// Implementations are able to track state on `self`, which enables /// implementing stateful streaming parsers. In many cases, though, this type /// will simply be a unit struct (e.g. `struct HttpDecoder`). // Note: We can't deprecate this trait, because the deprecation carries through to tokio-codec, and // there doesn't seem to be a way to un-deprecate the re-export. pub trait Decoder { /// The type of decoded frames. type Item; /// The type of unrecoverable frame decoding errors. /// /// If an individual message is ill-formed but can be ignored without /// interfering with the processing of future messages, it may be more /// useful to report the failure as an `Item`. /// /// `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 `FramedRead` whenever bytes are ready to be /// parsed. The provided buffer of bytes is what's been read so far, and /// this instance of `Decode` can determine whether an entire frame is in /// the buffer and is ready to be returned. /// /// If an entire frame is available, then this instance will remove those /// bytes from the buffer provided and return them as a decoded /// frame. Note that removing bytes from the provided buffer doesn't always /// necessarily copy the bytes, so this should be an efficient operation in /// most circumstances. /// /// If the bytes look valid, but a frame isn't fully available yet, then /// `Ok(None)` is returned. This indicates to the `Framed` instance that /// it needs to read some more bytes before calling this method again. /// /// Note that the bytes provided may be empty. If a previous call to /// `decode` consumed all the bytes in the buffer then `decode` will be /// called again until it returns `None`, indicating that more bytes need to /// be read. /// /// 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: &mut BytesMut) -> Result<Option<Self::Item>, Self::Error>; /// A default method available to be called when there are no more bytes /// available to be read from the underlying I/O. /// /// This method defaults to calling `decode` and returns an error if /// `Ok(None)` is returned while there is unconsumed data in `buf`. /// Typically this doesn't need to be implemented unless the framing /// protocol differs near the end of the stream. /// /// Note that the `buf` argument may be empty. If a previous call to /// `decode_eof` consumed all the bytes in the buffer, `decode_eof` will be /// called again until it returns `None`, indicating that there are no more /// frames to yield. This behavior enables returning finalization frames /// that may not be based on inbound data. fn decode_eof(&mut self, buf: &mut BytesMut) -> Result<Option<Self::Item>, Self::Error> { match try!(self.decode(buf)) { Some(frame) => Ok(Some(frame)), None => { if buf.is_empty() { Ok(None) } else { Err(io::Error::new(io::ErrorKind::Other, "bytes remaining on stream").into()) } } } } /// Provides a `Stream` and `Sink` interface for reading and writing to this /// `Io` object, using `Decode` and `Encode` to read and write the raw data. /// /// Raw I/O objects work with byte sequences, but higher-level code usually /// wants to batch these into meaningful chunks, called "frames". This /// method layers framing on top of an I/O object, by using the `Codec` /// traits to handle encoding and decoding of messages frames. Note that /// the incoming and outgoing frame types may be distinct. /// /// This function returns a *single* object that is both `Stream` and /// `Sink`; grouping this into a single object is often useful for layering /// things like gzip or TLS, which require both read and write access to the /// underlying object. /// /// If you want to work more directly with the streams and sink, consider /// calling `split` on the `Framed` returned by this method, which will /// break them into separate objects, allowing them to interact more easily. fn framed<T: AsyncRead + AsyncWrite + Sized>(self, io: T) -> Framed<T, Self> where Self: Encoder + Sized, { Framed::new(io, self) } }