1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
//! Adaptors from `AsyncRead`/`AsyncWrite` to Stream/Sink
//!
//! Raw I/O objects work with byte sequences, but higher-level code usually
//! wants to batch these into meaningful chunks, called "frames".
//!
//! This module 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.
//!
//! # Example encoding using `LinesCodec`
//!
//! The following example demonstrates how to use a codec such as [`LinesCodec`] to
//! write framed data. [`FramedWrite`] can be used to achieve this. Data sent to
//! [`FramedWrite`] are first framed according to a specific codec, and then sent to
//! an implementor of [`AsyncWrite`].
//!
//! ```
//! use futures::sink::SinkExt;
//! use tokio_util::codec::LinesCodec;
//! use tokio_util::codec::FramedWrite;
//!
//! #[tokio::main]
//! async fn main() {
//!     let buffer = Vec::new();
//!     let messages = vec!["Hello", "World"];
//!     let encoder = LinesCodec::new();
//!
//!     // FramedWrite is a sink which means you can send values into it
//!     // asynchronously.
//!     let mut writer = FramedWrite::new(buffer, encoder);
//!
//!     // To be able to send values into a FramedWrite, you need to bring the
//!     // `SinkExt` trait into scope.
//!     writer.send(messages[0]).await.unwrap();
//!     writer.send(messages[1]).await.unwrap();
//!
//!     let buffer = writer.get_ref();
//!
//!     assert_eq!(buffer.as_slice(), "Hello\nWorld\n".as_bytes());
//! }
//!```
//!
//! # Example decoding using `LinesCodec`
//! The following example demonstrates how to use a codec such as [`LinesCodec`] to
//! read a stream of framed data. [`FramedRead`] can be used to achieve this. [`FramedRead`]
//! will keep reading from an [`AsyncRead`] implementor until a whole frame, according to a codec,
//! can be parsed.
//!
//!```
//! use tokio_stream::StreamExt;
//! use tokio_util::codec::LinesCodec;
//! use tokio_util::codec::FramedRead;
//!
//! #[tokio::main]
//! async fn main() {
//!     let message = "Hello\nWorld".as_bytes();
//!     let decoder = LinesCodec::new();
//!
//!     // FramedRead can be used to read a stream of values that are framed according to
//!     // a codec. FramedRead will read from its input (here `buffer`) until a whole frame
//!     // can be parsed.
//!     let mut reader = FramedRead::new(message, decoder);
//!
//!     // To read values from a FramedRead, you need to bring the
//!     // `StreamExt` trait into scope.
//!     let frame1 = reader.next().await.unwrap().unwrap();
//!     let frame2 = reader.next().await.unwrap().unwrap();
//!
//!     assert!(reader.next().await.is_none());
//!     assert_eq!(frame1, "Hello");
//!     assert_eq!(frame2, "World");
//! }
//! ```
//!
//! # The Decoder trait
//!
//! A [`Decoder`] is used together with [`FramedRead`] or [`Framed`] to turn an
//! [`AsyncRead`] into a [`Stream`]. The job of the decoder trait is to specify
//! how sequences of bytes are turned into a sequence of frames, and to
//! determine where the boundaries between frames are.  The job of the
//! `FramedRead` is to repeatedly switch between reading more data from the IO
//! resource, and asking the decoder whether we have received enough data to
//! decode another frame of data.
//!
//! The main method on the `Decoder` trait is the [`decode`] method. This method
//! takes as argument the data that has been read so far, and when it is called,
//! it will be in one of the following situations:
//!
//!  1. The buffer contains less than a full frame.
//!  2. The buffer contains exactly a full frame.
//!  3. The buffer contains more than a full frame.
//!
//! In the first situation, the decoder should return `Ok(None)`.
//!
//! In the second situation, the decoder should clear the provided buffer and
//! return `Ok(Some(the_decoded_frame))`.
//!
//! In the third situation, the decoder should use a method such as [`split_to`]
//! or [`advance`] to modify the buffer such that the frame is removed from the
//! buffer, but any data in the buffer after that frame should still remain in
//! the buffer. The decoder should also return `Ok(Some(the_decoded_frame))` in
//! this case.
//!
//! Finally the decoder may return an error if the data is invalid in some way.
//! The decoder should _not_ return an error just because it has yet to receive
//! a full frame.
//!
//! It is guaranteed that, from one call to `decode` to another, the provided
//! buffer will contain the exact same data as before, except that if more data
//! has arrived through the IO resource, that data will have been appended to
//! the buffer.  This means that reading frames from a `FramedRead` is
//! essentially equivalent to the following loop:
//!
//! ```no_run
//! use tokio::io::AsyncReadExt;
//! # // This uses async_stream to create an example that compiles.
//! # fn foo() -> impl futures_core::Stream<Item = std::io::Result<bytes::BytesMut>> { async_stream::try_stream! {
//! # use tokio_util::codec::Decoder;
//! # let mut decoder = tokio_util::codec::BytesCodec::new();
//! # let io_resource = &mut &[0u8, 1, 2, 3][..];
//!
//! let mut buf = bytes::BytesMut::new();
//! loop {
//!     // The read_buf call will append to buf rather than overwrite existing data.
//!     let len = io_resource.read_buf(&mut buf).await?;
//!
//!     if len == 0 {
//!         while let Some(frame) = decoder.decode_eof(&mut buf)? {
//!             yield frame;
//!         }
//!         break;
//!     }
//!
//!     while let Some(frame) = decoder.decode(&mut buf)? {
//!         yield frame;
//!     }
//! }
//! # }}
//! ```
//! The example above uses `yield` whenever the `Stream` produces an item.
//!
//! ## Example decoder
//!
//! As an example, consider a protocol that can be used to send strings where
//! each frame is a four byte integer that contains the length of the frame,
//! followed by that many bytes of string data. The decoder fails with an error
//! if the string data is not valid utf-8 or too long.
//!
//! Such a decoder can be written like this:
//! ```
//! use tokio_util::codec::Decoder;
//! use bytes::{BytesMut, Buf};
//!
//! struct MyStringDecoder {}
//!
//! const MAX: usize = 8 * 1024 * 1024;
//!
//! impl Decoder for MyStringDecoder {
//!     type Item = String;
//!     type Error = std::io::Error;
//!
//!     fn decode(
//!         &mut self,
//!         src: &mut BytesMut
//!     ) -> Result<Option<Self::Item>, Self::Error> {
//!         if src.len() < 4 {
//!             // Not enough data to read length marker.
//!             return Ok(None);
//!         }
//!
//!         // Read length marker.
//!         let mut length_bytes = [0u8; 4];
//!         length_bytes.copy_from_slice(&src[..4]);
//!         let length = u32::from_le_bytes(length_bytes) as usize;
//!
//!         // Check that the length is not too large to avoid a denial of
//!         // service attack where the server runs out of memory.
//!         if length > MAX {
//!             return Err(std::io::Error::new(
//!                 std::io::ErrorKind::InvalidData,
//!                 format!("Frame of length {} is too large.", length)
//!             ));
//!         }
//!
//!         if src.len() < 4 + length {
//!             // The full string has not yet arrived.
//!             //
//!             // We reserve more space in the buffer. This is not strictly
//!             // necessary, but is a good idea performance-wise.
//!             src.reserve(4 + length - src.len());
//!
//!             // We inform the Framed that we need more bytes to form the next
//!             // frame.
//!             return Ok(None);
//!         }
//!
//!         // Use advance to modify src such that it no longer contains
//!         // this frame.
//!         let data = src[4..4 + length].to_vec();
//!         src.advance(4 + length);
//!
//!         // Convert the data to a string, or fail if it is not valid utf-8.
//!         match String::from_utf8(data) {
//!             Ok(string) => Ok(Some(string)),
//!             Err(utf8_error) => {
//!                 Err(std::io::Error::new(
//!                     std::io::ErrorKind::InvalidData,
//!                     utf8_error.utf8_error(),
//!                 ))
//!             },
//!         }
//!     }
//! }
//! ```
//!
//! # The Encoder trait
//!
//! An [`Encoder`] is used together with [`FramedWrite`] or [`Framed`] to turn
//! an [`AsyncWrite`] into a [`Sink`]. The job of the encoder trait is to
//! specify how frames are turned into a sequences of bytes.  The job of the
//! `FramedWrite` is to take the resulting sequence of bytes and write it to the
//! IO resource.
//!
//! The main method on the `Encoder` trait is the [`encode`] method. This method
//! takes an item that is being written, and a buffer to write the item to. The
//! buffer may already contain data, and in this case, the encoder should append
//! the new frame the to buffer rather than overwrite the existing data.
//!
//! It is guaranteed that, from one call to `encode` to another, the provided
//! buffer will contain the exact same data as before, except that some of the
//! data may have been removed from the front of the buffer. Writing to a
//! `FramedWrite` is essentially equivalent to the following loop:
//!
//! ```no_run
//! use tokio::io::AsyncWriteExt;
//! use bytes::Buf; // for advance
//! # use tokio_util::codec::Encoder;
//! # async fn next_frame() -> bytes::Bytes { bytes::Bytes::new() }
//! # async fn no_more_frames() { }
//! # #[tokio::main] async fn main() -> std::io::Result<()> {
//! # let mut io_resource = tokio::io::sink();
//! # let mut encoder = tokio_util::codec::BytesCodec::new();
//!
//! const MAX: usize = 8192;
//!
//! let mut buf = bytes::BytesMut::new();
//! loop {
//!     tokio::select! {
//!         num_written = io_resource.write(&buf), if !buf.is_empty() => {
//!             buf.advance(num_written?);
//!         },
//!         frame = next_frame(), if buf.len() < MAX => {
//!             encoder.encode(frame, &mut buf)?;
//!         },
//!         _ = no_more_frames() => {
//!             io_resource.write_all(&buf).await?;
//!             io_resource.shutdown().await?;
//!             return Ok(());
//!         },
//!     }
//! }
//! # }
//! ```
//! Here the `next_frame` method corresponds to any frames you write to the
//! `FramedWrite`. The `no_more_frames` method corresponds to closing the
//! `FramedWrite` with [`SinkExt::close`].
//!
//! ## Example encoder
//!
//! As an example, consider a protocol that can be used to send strings where
//! each frame is a four byte integer that contains the length of the frame,
//! followed by that many bytes of string data. The encoder will fail if the
//! string is too long.
//!
//! Such an encoder can be written like this:
//! ```
//! use tokio_util::codec::Encoder;
//! use bytes::BytesMut;
//!
//! struct MyStringEncoder {}
//!
//! const MAX: usize = 8 * 1024 * 1024;
//!
//! impl Encoder<String> for MyStringEncoder {
//!     type Error = std::io::Error;
//!
//!     fn encode(&mut self, item: String, dst: &mut BytesMut) -> Result<(), Self::Error> {
//!         // Don't send a string if it is longer than the other end will
//!         // accept.
//!         if item.len() > MAX {
//!             return Err(std::io::Error::new(
//!                 std::io::ErrorKind::InvalidData,
//!                 format!("Frame of length {} is too large.", item.len())
//!             ));
//!         }
//!
//!         // Convert the length into a byte array.
//!         // The cast to u32 cannot overflow due to the length check above.
//!         let len_slice = u32::to_le_bytes(item.len() as u32);
//!
//!         // Reserve space in the buffer.
//!         dst.reserve(4 + item.len());
//!
//!         // Write the length and string to the buffer.
//!         dst.extend_from_slice(&len_slice);
//!         dst.extend_from_slice(item.as_bytes());
//!         Ok(())
//!     }
//! }
//! ```
//!
//! [`AsyncRead`]: tokio::io::AsyncRead
//! [`AsyncWrite`]: tokio::io::AsyncWrite
//! [`Stream`]: futures_core::Stream
//! [`Sink`]: futures_sink::Sink
//! [`SinkExt`]: futures::sink::SinkExt
//! [`SinkExt::close`]: https://docs.rs/futures/0.3/futures/sink/trait.SinkExt.html#method.close
//! [`FramedRead`]: struct@crate::codec::FramedRead
//! [`FramedWrite`]: struct@crate::codec::FramedWrite
//! [`Framed`]: struct@crate::codec::Framed
//! [`Decoder`]: trait@crate::codec::Decoder
//! [`decode`]: fn@crate::codec::Decoder::decode
//! [`encode`]: fn@crate::codec::Encoder::encode
//! [`split_to`]: fn@bytes::BytesMut::split_to
//! [`advance`]: fn@bytes::Buf::advance

mod bytes_codec;
pub use self::bytes_codec::BytesCodec;

mod decoder;
pub use self::decoder::Decoder;

mod encoder;
pub use self::encoder::Encoder;

mod framed_impl;
#[allow(unused_imports)]
pub(crate) use self::framed_impl::{FramedImpl, RWFrames, ReadFrame, WriteFrame};

mod framed;
pub use self::framed::{Framed, FramedParts};

mod framed_read;
pub use self::framed_read::FramedRead;

mod framed_write;
pub use self::framed_write::FramedWrite;

pub mod length_delimited;
pub use self::length_delimited::{LengthDelimitedCodec, LengthDelimitedCodecError};

mod lines_codec;
pub use self::lines_codec::{LinesCodec, LinesCodecError};

mod any_delimiter_codec;
pub use self::any_delimiter_codec::{AnyDelimiterCodec, AnyDelimiterCodecError};