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| </pre><pre class="rust"><code><span class="kw">use </span><span class="kw">crate</span>::codec::Framed; |
| |
| <span class="kw">use </span>tokio::io::{AsyncRead, AsyncWrite}; |
| |
| <span class="kw">use </span>bytes::BytesMut; |
| <span class="kw">use </span>std::io; |
| |
| <span class="doccomment">/// 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`). |
| /// |
| /// For some underlying data-sources, namely files and FIFOs, |
| /// it's possible to temporarily read 0 bytes by reaching EOF. |
| /// |
| /// In these cases `decode_eof` will be called until it signals |
| /// fulfillment of all closing frames by returning `Ok(None)`. |
| /// After that, repeated attempts to read from the [`Framed`] or [`FramedRead`] |
| /// will not invoke `decode` or `decode_eof` again, until data can be read |
| /// during a retry. |
| /// |
| /// It is up to the Decoder to keep track of a restart after an EOF, |
| /// and to decide how to handle such an event by, for example, |
| /// allowing frames to cross EOF boundaries, re-emitting opening frames, or |
| /// resetting the entire internal state. |
| /// |
| /// [`Framed`]: crate::codec::Framed |
| /// [`FramedRead`]: crate::codec::FramedRead |
| </span><span class="kw">pub trait </span>Decoder { |
| <span class="doccomment">/// The type of decoded frames. |
| </span><span class="kw">type </span>Item; |
| |
| <span class="doccomment">/// 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. |
| /// |
| /// [`FramedRead`]: crate::codec::FramedRead |
| </span><span class="kw">type </span>Error: From<io::Error>; |
| |
| <span class="doccomment">/// 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 `Ok(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. |
| /// |
| /// [`Framed`]: crate::codec::Framed |
| /// [`FramedRead`]: crate::codec::FramedRead |
| /// |
| /// # Buffer management |
| /// |
| /// Before returning from the function, implementations should ensure that |
| /// the buffer has appropriate capacity in anticipation of future calls to |
| /// `decode`. Failing to do so leads to inefficiency. |
| /// |
| /// For example, if frames have a fixed length, or if the length of the |
| /// current frame is known from a header, a possible buffer management |
| /// strategy is: |
| /// |
| /// ```no_run |
| /// # use std::io; |
| /// # |
| /// # use bytes::BytesMut; |
| /// # use tokio_util::codec::Decoder; |
| /// # |
| /// # struct MyCodec; |
| /// # |
| /// impl Decoder for MyCodec { |
| /// // ... |
| /// # type Item = BytesMut; |
| /// # type Error = io::Error; |
| /// |
| /// fn decode(&mut self, src: &mut BytesMut) -> Result<Option<Self::Item>, Self::Error> { |
| /// // ... |
| /// |
| /// // Reserve enough to complete decoding of the current frame. |
| /// let current_frame_len: usize = 1000; // Example. |
| /// // And to start decoding the next frame. |
| /// let next_frame_header_len: usize = 10; // Example. |
| /// src.reserve(current_frame_len + next_frame_header_len); |
| /// |
| /// return Ok(None); |
| /// } |
| /// } |
| /// ``` |
| /// |
| /// An optimal buffer management strategy minimizes reallocations and |
| /// over-allocations. |
| </span><span class="kw">fn </span>decode(<span class="kw-2">&mut </span><span class="self">self</span>, src: <span class="kw-2">&mut </span>BytesMut) -> <span class="prelude-ty">Result</span><<span class="prelude-ty">Option</span><<span class="self">Self</span>::Item>, <span class="self">Self</span>::Error>; |
| |
| <span class="doccomment">/// 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, or if you need to construct |
| /// frames _across_ eof boundaries on sources that can be resumed. |
| /// |
| /// 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. |
| /// |
| /// Once `None` has been returned, `decode_eof` won't be called again until |
| /// an attempt to resume the stream has been made, where the underlying stream |
| /// actually returned more data. |
| </span><span class="kw">fn </span>decode_eof(<span class="kw-2">&mut </span><span class="self">self</span>, buf: <span class="kw-2">&mut </span>BytesMut) -> <span class="prelude-ty">Result</span><<span class="prelude-ty">Option</span><<span class="self">Self</span>::Item>, <span class="self">Self</span>::Error> { |
| <span class="kw">match </span><span class="self">self</span>.decode(buf)<span class="question-mark">? </span>{ |
| <span class="prelude-val">Some</span>(frame) => <span class="prelude-val">Ok</span>(<span class="prelude-val">Some</span>(frame)), |
| <span class="prelude-val">None </span>=> { |
| <span class="kw">if </span>buf.is_empty() { |
| <span class="prelude-val">Ok</span>(<span class="prelude-val">None</span>) |
| } <span class="kw">else </span>{ |
| <span class="prelude-val">Err</span>(io::Error::new(io::ErrorKind::Other, <span class="string">"bytes remaining on stream"</span>).into()) |
| } |
| } |
| } |
| } |
| |
| <span class="doccomment">/// 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. |
| /// |
| /// [`Stream`]: futures_core::Stream |
| /// [`Sink`]: futures_sink::Sink |
| /// [`Framed`]: crate::codec::Framed |
| </span><span class="kw">fn </span>framed<T: AsyncRead + AsyncWrite + Sized>(<span class="self">self</span>, io: T) -> Framed<T, <span class="self">Self</span>> |
| <span class="kw">where |
| </span><span class="self">Self</span>: Sized, |
| { |
| Framed::new(io, <span class="self">self</span>) |
| } |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../../" data-current-crate="tokio_util" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
