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//! Utilities for encoding and decoding frames. //! //! Contains adapters to go from streams of bytes, [`AsyncRead`] and //! [`AsyncWrite`], to framed streams implementing [`Sink`] and [`Stream`]. //! Framed streams are also known as [transports]. //! //! [`AsyncRead`]: # //! [`AsyncWrite`]: # //! [`Sink`]: # //! [`Stream`]: # //! [transports]: # pub use codecs::{BytesCodec, LinesCodec}; pub use framed::{Framed, FramedParts}; pub use framed_read::{FramedRead, Decoder}; pub use framed_write::{FramedWrite, Encoder}; pub mod length_delimited { //! Frame a stream of bytes based on a length prefix //! //! Many protocols delimit their frames by prefacing frame data with a //! frame head that specifies the length of the frame. The //! `length_delimited` module provides utilities for handling the length //! based framing. This allows the consumer to work with entire frames //! without having to worry about buffering or other framing logic. //! //! # Getting started //! //! If implementing a protocol from scratch, using length delimited framing //! is an easy way to get started. [`Framed::new()`] will adapt a //! full-duplex byte stream with a length delimited framer using default //! configuration values. //! //! ``` //! use tokio_io::{AsyncRead, AsyncWrite}; //! use tokio_io::codec::length_delimited; //! //! fn bind_transport<T: AsyncRead + AsyncWrite>(io: T) //! -> length_delimited::Framed<T> //! { //! length_delimited::Framed::new(io) //! } //! ``` //! //! The returned transport implements `Sink + Stream` for `BytesMut`. It //! encodes the frame with a big-endian `u32` header denoting the frame //! payload length: //! //! ```text //! +----------+--------------------------------+ //! | len: u32 | frame payload | //! +----------+--------------------------------+ //! ``` //! //! Specifically, given the following: //! //! ``` //! # extern crate tokio_io; //! # extern crate bytes; //! # extern crate futures; //! # //! use tokio_io::{AsyncRead, AsyncWrite}; //! use tokio_io::codec::length_delimited; //! use bytes::BytesMut; //! use futures::{Sink, Future}; //! //! fn write_frame<T: AsyncRead + AsyncWrite>(io: T) { //! let mut transport = length_delimited::Framed::new(io); //! let frame = BytesMut::from("hello world"); //! //! transport.send(frame).wait().unwrap(); //! } //! # //! # pub fn main() {} //! ``` //! //! The encoded frame will look like this: //! //! ```text //! +---- len: u32 ----+---- data ----+ //! | \x00\x00\x00\x0b | hello world | //! +------------------+--------------+ //! ``` //! //! # Decoding //! //! [`FramedRead`] adapts an [`AsyncRead`] into a `Stream` of [`BytesMut`], //! such that each yielded [`BytesMut`] value contains the contents of an //! entire frame. There are many configuration parameters enabling //! [`FrameRead`] to handle a wide range of protocols. Here are some //! examples that will cover the various options at a high level. //! //! ## Example 1 //! //! The following will parse a `u16` length field at offset 0, including the //! frame head in the yielded `BytesMut`. //! //! ``` //! # use tokio_io::AsyncRead; //! # use tokio_io::codec::length_delimited; //! # fn bind_read<T: AsyncRead>(io: T) { //! length_delimited::Builder::new() //! .length_field_offset(0) // default value //! .length_field_length(2) //! .length_adjustment(0) // default value //! .num_skip(0) // Do not strip frame header //! .new_read(io); //! # } //! ``` //! //! The following frame will be decoded as such: //! //! ```text //! INPUT DECODED //! +-- len ---+--- Payload ---+ +-- len ---+--- Payload ---+ //! | \x00\x0B | Hello world | --> | \x00\x0B | Hello world | //! +----------+---------------+ +----------+---------------+ //! ``` //! //! The value of the length field is 11 (`\x0B`) which represents the length //! of the payload, `hello world`. By default, [`FramedRead`] assumes that //! the length field represents the number of bytes that **follows** the //! length field. Thus, the entire frame has a length of 13: 2 bytes for the //! frame head + 11 bytes for the payload. //! //! ## Example 2 //! //! The following will parse a `u16` length field at offset 0, omitting the //! frame head in the yielded `BytesMut`. //! //! ``` //! # use tokio_io::AsyncRead; //! # use tokio_io::codec::length_delimited; //! # fn bind_read<T: AsyncRead>(io: T) { //! length_delimited::Builder::new() //! .length_field_offset(0) // default value //! .length_field_length(2) //! .length_adjustment(0) // default value //! // `num_skip` is not needed, the default is to skip //! .new_read(io); //! # } //! ``` //! //! The following frame will be decoded as such: //! //! ```text //! INPUT DECODED //! +-- len ---+--- Payload ---+ +--- Payload ---+ //! | \x00\x0B | Hello world | --> | Hello world | //! +----------+---------------+ +---------------+ //! ``` //! //! This is similar to the first example, the only difference is that the //! frame head is **not** included in the yielded `BytesMut` value. //! //! ## Example 3 //! //! The following will parse a `u16` length field at offset 0, including the //! frame head in the yielded `BytesMut`. In this case, the length field //! **includes** the frame head length. //! //! ``` //! # use tokio_io::AsyncRead; //! # use tokio_io::codec::length_delimited; //! # fn bind_read<T: AsyncRead>(io: T) { //! length_delimited::Builder::new() //! .length_field_offset(0) // default value //! .length_field_length(2) //! .length_adjustment(-2) // size of head //! .num_skip(0) //! .new_read(io); //! # } //! ``` //! //! The following frame will be decoded as such: //! //! ```text //! INPUT DECODED //! +-- len ---+--- Payload ---+ +-- len ---+--- Payload ---+ //! | \x00\x0D | Hello world | --> | \x00\x0D | Hello world | //! +----------+---------------+ +----------+---------------+ //! ``` //! //! In most cases, the length field represents the length of the payload //! only, as shown in the previous examples. However, in some protocols the //! length field represents the length of the whole frame, including the //! head. In such cases, we specify a negative `length_adjustment` to adjust //! the value provided in the frame head to represent the payload length. //! //! ## Example 4 //! //! The following will parse a 3 byte length field at offset 0 in a 5 byte //! frame head, including the frame head in the yielded `BytesMut`. //! //! ``` //! # use tokio_io::AsyncRead; //! # use tokio_io::codec::length_delimited; //! # fn bind_read<T: AsyncRead>(io: T) { //! length_delimited::Builder::new() //! .length_field_offset(0) // default value //! .length_field_length(3) //! .length_adjustment(2) // remaining head //! .num_skip(0) //! .new_read(io); //! # } //! ``` //! //! The following frame will be decoded as such: //! //! ```text //! INPUT //! +---- len -----+- head -+--- Payload ---+ //! | \x00\x00\x0B | \xCAFE | Hello world | //! +--------------+--------+---------------+ //! //! DECODED //! +---- len -----+- head -+--- Payload ---+ //! | \x00\x00\x0B | \xCAFE | Hello world | //! +--------------+--------+---------------+ //! ``` //! //! A more advanced example that shows a case where there is extra frame //! head data between the length field and the payload. In such cases, it is //! usually desirable to include the frame head as part of the yielded //! `BytesMut`. This lets consumers of the length delimited framer to //! process the frame head as needed. //! //! The positive `length_adjustment` value lets `FramedRead` factor in the //! additional head into the frame length calculation. //! //! ## Example 5 //! //! The following will parse a `u16` length field at offset 1 of a 4 byte //! frame head. The first byte and the length field will be omitted from the //! yielded `BytesMut`, but the trailing 2 bytes of the frame head will be //! included. //! //! ``` //! # use tokio_io::AsyncRead; //! # use tokio_io::codec::length_delimited; //! # fn bind_read<T: AsyncRead>(io: T) { //! length_delimited::Builder::new() //! .length_field_offset(1) // length of hdr1 //! .length_field_length(2) //! .length_adjustment(1) // length of hdr2 //! .num_skip(3) // length of hdr1 + LEN //! .new_read(io); //! # } //! ``` //! //! The following frame will be decoded as such: //! //! ```text //! INPUT //! +- hdr1 -+-- len ---+- hdr2 -+--- Payload ---+ //! | \xCA | \x00\x0B | \xFE | Hello world | //! +--------+----------+--------+---------------+ //! //! DECODED //! +- hdr2 -+--- Payload ---+ //! | \xFE | Hello world | //! +--------+---------------+ //! ``` //! //! The length field is situated in the middle of the frame head. In this //! case, the first byte in the frame head could be a version or some other //! identifier that is not needed for processing. On the other hand, the //! second half of the head is needed. //! //! `length_field_offset` indicates how many bytes to skip before starting //! to read the length field. `length_adjustment` is the number of bytes to //! skip starting at the end of the length field. In this case, it is the //! second half of the head. //! //! ## Example 6 //! //! The following will parse a `u16` length field at offset 1 of a 4 byte //! frame head. The first byte and the length field will be omitted from the //! yielded `BytesMut`, but the trailing 2 bytes of the frame head will be //! included. In this case, the length field **includes** the frame head //! length. //! //! ``` //! # use tokio_io::AsyncRead; //! # use tokio_io::codec::length_delimited; //! # fn bind_read<T: AsyncRead>(io: T) { //! length_delimited::Builder::new() //! .length_field_offset(1) // length of hdr1 //! .length_field_length(2) //! .length_adjustment(-3) // length of hdr1 + LEN, negative //! .num_skip(3) //! .new_read(io); //! # } //! ``` //! //! The following frame will be decoded as such: //! //! ```text //! INPUT //! +- hdr1 -+-- len ---+- hdr2 -+--- Payload ---+ //! | \xCA | \x00\x0F | \xFE | Hello world | //! +--------+----------+--------+---------------+ //! //! DECODED //! +- hdr2 -+--- Payload ---+ //! | \xFE | Hello world | //! +--------+---------------+ //! ``` //! //! Similar to the example above, the difference is that the length field //! represents the length of the entire frame instead of just the payload. //! The length of `hdr1` and `len` must be counted in `length_adjustment`. //! Note that the length of `hdr2` does **not** need to be explicitly set //! anywhere because it already is factored into the total frame length that //! is read from the byte stream. //! //! # Encoding //! //! [`FramedWrite`] adapts an [`AsyncWrite`] into a `Sink` of [`BytesMut`], //! such that each submitted [`BytesMut`] is prefaced by a length field. //! There are fewer configuration options than [`FramedRead`]. Given //! protocols that have more complex frame heads, an encoder should probably //! be written by hand using [`Encoder`]. //! //! Here is a simple example, given a `FramedWrite` with the following //! configuration: //! //! ``` //! # extern crate tokio_io; //! # extern crate bytes; //! # use tokio_io::AsyncWrite; //! # use tokio_io::codec::length_delimited; //! # use bytes::BytesMut; //! # fn write_frame<T: AsyncWrite>(io: T) { //! # let _: length_delimited::FramedWrite<T, BytesMut> = //! length_delimited::Builder::new() //! .length_field_length(2) //! .new_write(io); //! # } //! # pub fn main() {} //! ``` //! //! A payload of `hello world` will be encoded as: //! //! ```text //! +- len: u16 -+---- data ----+ //! | \x00\x0b | hello world | //! +------------+--------------+ //! ``` //! //! [`FramedRead`]: struct.FramedRead.html //! [`FramedWrite`]: struct.FramedWrite.html //! [`AsyncRead`]: ../../trait.AsyncRead.html //! [`AsyncWrite`]: ../../trait.AsyncWrite.html //! [`Encoder`]: ../trait.Encoder.html //! [`BytesMut`]: https://docs.rs/bytes/~0.4/bytes/struct.BytesMut.html pub use ::length_delimited::*; }