h2/codec/
framed_write.rs

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1use crate::codec::UserError;
2use crate::codec::UserError::*;
3use crate::frame::{self, Frame, FrameSize};
4use crate::hpack;
5
6use bytes::{Buf, BufMut, BytesMut};
7use std::pin::Pin;
8use std::task::{Context, Poll};
9use tokio::io::{AsyncRead, AsyncWrite, ReadBuf};
10use tokio_util::io::poll_write_buf;
11
12use std::io::{self, Cursor};
13
14// A macro to get around a method needing to borrow &mut self
15macro_rules! limited_write_buf {
16    ($self:expr) => {{
17        let limit = $self.max_frame_size() + frame::HEADER_LEN;
18        $self.buf.get_mut().limit(limit)
19    }};
20}
21
22#[derive(Debug)]
23pub struct FramedWrite<T, B> {
24    /// Upstream `AsyncWrite`
25    inner: T,
26
27    encoder: Encoder<B>,
28}
29
30#[derive(Debug)]
31struct Encoder<B> {
32    /// HPACK encoder
33    hpack: hpack::Encoder,
34
35    /// Write buffer
36    ///
37    /// TODO: Should this be a ring buffer?
38    buf: Cursor<BytesMut>,
39
40    /// Next frame to encode
41    next: Option<Next<B>>,
42
43    /// Last data frame
44    last_data_frame: Option<frame::Data<B>>,
45
46    /// Max frame size, this is specified by the peer
47    max_frame_size: FrameSize,
48
49    /// Chain payloads bigger than this.
50    chain_threshold: usize,
51
52    /// Min buffer required to attempt to write a frame
53    min_buffer_capacity: usize,
54}
55
56#[derive(Debug)]
57enum Next<B> {
58    Data(frame::Data<B>),
59    Continuation(frame::Continuation),
60}
61
62/// Initialize the connection with this amount of write buffer.
63///
64/// The minimum MAX_FRAME_SIZE is 16kb, so always be able to send a HEADERS
65/// frame that big.
66const DEFAULT_BUFFER_CAPACITY: usize = 16 * 1_024;
67
68/// Chain payloads bigger than this when vectored I/O is enabled. The remote
69/// will never advertise a max frame size less than this (well, the spec says
70/// the max frame size can't be less than 16kb, so not even close).
71const CHAIN_THRESHOLD: usize = 256;
72
73/// Chain payloads bigger than this when vectored I/O is **not** enabled.
74/// A larger value in this scenario will reduce the number of small and
75/// fragmented data being sent, and hereby improve the throughput.
76const CHAIN_THRESHOLD_WITHOUT_VECTORED_IO: usize = 1024;
77
78// TODO: Make generic
79impl<T, B> FramedWrite<T, B>
80where
81    T: AsyncWrite + Unpin,
82    B: Buf,
83{
84    pub fn new(inner: T) -> FramedWrite<T, B> {
85        let chain_threshold = if inner.is_write_vectored() {
86            CHAIN_THRESHOLD
87        } else {
88            CHAIN_THRESHOLD_WITHOUT_VECTORED_IO
89        };
90        FramedWrite {
91            inner,
92            encoder: Encoder {
93                hpack: hpack::Encoder::default(),
94                buf: Cursor::new(BytesMut::with_capacity(DEFAULT_BUFFER_CAPACITY)),
95                next: None,
96                last_data_frame: None,
97                max_frame_size: frame::DEFAULT_MAX_FRAME_SIZE,
98                chain_threshold,
99                min_buffer_capacity: chain_threshold + frame::HEADER_LEN,
100            },
101        }
102    }
103
104    /// Returns `Ready` when `send` is able to accept a frame
105    ///
106    /// Calling this function may result in the current contents of the buffer
107    /// to be flushed to `T`.
108    pub fn poll_ready(&mut self, cx: &mut Context) -> Poll<io::Result<()>> {
109        if !self.encoder.has_capacity() {
110            // Try flushing
111            ready!(self.flush(cx))?;
112
113            if !self.encoder.has_capacity() {
114                return Poll::Pending;
115            }
116        }
117
118        Poll::Ready(Ok(()))
119    }
120
121    /// Buffer a frame.
122    ///
123    /// `poll_ready` must be called first to ensure that a frame may be
124    /// accepted.
125    pub fn buffer(&mut self, item: Frame<B>) -> Result<(), UserError> {
126        self.encoder.buffer(item)
127    }
128
129    /// Flush buffered data to the wire
130    pub fn flush(&mut self, cx: &mut Context) -> Poll<io::Result<()>> {
131        let span = tracing::trace_span!("FramedWrite::flush");
132        let _e = span.enter();
133
134        loop {
135            while !self.encoder.is_empty() {
136                match self.encoder.next {
137                    Some(Next::Data(ref mut frame)) => {
138                        tracing::trace!(queued_data_frame = true);
139                        let mut buf = (&mut self.encoder.buf).chain(frame.payload_mut());
140                        ready!(poll_write_buf(Pin::new(&mut self.inner), cx, &mut buf))?
141                    }
142                    _ => {
143                        tracing::trace!(queued_data_frame = false);
144                        ready!(poll_write_buf(
145                            Pin::new(&mut self.inner),
146                            cx,
147                            &mut self.encoder.buf
148                        ))?
149                    }
150                };
151            }
152
153            match self.encoder.unset_frame() {
154                ControlFlow::Continue => (),
155                ControlFlow::Break => break,
156            }
157        }
158
159        tracing::trace!("flushing buffer");
160        // Flush the upstream
161        ready!(Pin::new(&mut self.inner).poll_flush(cx))?;
162
163        Poll::Ready(Ok(()))
164    }
165
166    /// Close the codec
167    pub fn shutdown(&mut self, cx: &mut Context) -> Poll<io::Result<()>> {
168        ready!(self.flush(cx))?;
169        Pin::new(&mut self.inner).poll_shutdown(cx)
170    }
171}
172
173#[must_use]
174enum ControlFlow {
175    Continue,
176    Break,
177}
178
179impl<B> Encoder<B>
180where
181    B: Buf,
182{
183    fn unset_frame(&mut self) -> ControlFlow {
184        // Clear internal buffer
185        self.buf.set_position(0);
186        self.buf.get_mut().clear();
187
188        // The data frame has been written, so unset it
189        match self.next.take() {
190            Some(Next::Data(frame)) => {
191                self.last_data_frame = Some(frame);
192                debug_assert!(self.is_empty());
193                ControlFlow::Break
194            }
195            Some(Next::Continuation(frame)) => {
196                // Buffer the continuation frame, then try to write again
197                let mut buf = limited_write_buf!(self);
198                if let Some(continuation) = frame.encode(&mut buf) {
199                    self.next = Some(Next::Continuation(continuation));
200                }
201                ControlFlow::Continue
202            }
203            None => ControlFlow::Break,
204        }
205    }
206
207    fn buffer(&mut self, item: Frame<B>) -> Result<(), UserError> {
208        // Ensure that we have enough capacity to accept the write.
209        assert!(self.has_capacity());
210        let span = tracing::trace_span!("FramedWrite::buffer", frame = ?item);
211        let _e = span.enter();
212
213        tracing::debug!(frame = ?item, "send");
214
215        match item {
216            Frame::Data(mut v) => {
217                // Ensure that the payload is not greater than the max frame.
218                let len = v.payload().remaining();
219
220                if len > self.max_frame_size() {
221                    return Err(PayloadTooBig);
222                }
223
224                if len >= self.chain_threshold {
225                    let head = v.head();
226
227                    // Encode the frame head to the buffer
228                    head.encode(len, self.buf.get_mut());
229
230                    if self.buf.get_ref().remaining() < self.chain_threshold {
231                        let extra_bytes = self.chain_threshold - self.buf.remaining();
232                        self.buf.get_mut().put(v.payload_mut().take(extra_bytes));
233                    }
234
235                    // Save the data frame
236                    self.next = Some(Next::Data(v));
237                } else {
238                    v.encode_chunk(self.buf.get_mut());
239
240                    // The chunk has been fully encoded, so there is no need to
241                    // keep it around
242                    assert_eq!(v.payload().remaining(), 0, "chunk not fully encoded");
243
244                    // Save off the last frame...
245                    self.last_data_frame = Some(v);
246                }
247            }
248            Frame::Headers(v) => {
249                let mut buf = limited_write_buf!(self);
250                if let Some(continuation) = v.encode(&mut self.hpack, &mut buf) {
251                    self.next = Some(Next::Continuation(continuation));
252                }
253            }
254            Frame::PushPromise(v) => {
255                let mut buf = limited_write_buf!(self);
256                if let Some(continuation) = v.encode(&mut self.hpack, &mut buf) {
257                    self.next = Some(Next::Continuation(continuation));
258                }
259            }
260            Frame::Settings(v) => {
261                v.encode(self.buf.get_mut());
262                tracing::trace!(rem = self.buf.remaining(), "encoded settings");
263            }
264            Frame::GoAway(v) => {
265                v.encode(self.buf.get_mut());
266                tracing::trace!(rem = self.buf.remaining(), "encoded go_away");
267            }
268            Frame::Ping(v) => {
269                v.encode(self.buf.get_mut());
270                tracing::trace!(rem = self.buf.remaining(), "encoded ping");
271            }
272            Frame::WindowUpdate(v) => {
273                v.encode(self.buf.get_mut());
274                tracing::trace!(rem = self.buf.remaining(), "encoded window_update");
275            }
276
277            Frame::Priority(_) => {
278                /*
279                v.encode(self.buf.get_mut());
280                tracing::trace!("encoded priority; rem={:?}", self.buf.remaining());
281                */
282                unimplemented!();
283            }
284            Frame::Reset(v) => {
285                v.encode(self.buf.get_mut());
286                tracing::trace!(rem = self.buf.remaining(), "encoded reset");
287            }
288        }
289
290        Ok(())
291    }
292
293    fn has_capacity(&self) -> bool {
294        self.next.is_none()
295            && (self.buf.get_ref().capacity() - self.buf.get_ref().len()
296                >= self.min_buffer_capacity)
297    }
298
299    fn is_empty(&self) -> bool {
300        match self.next {
301            Some(Next::Data(ref frame)) => !frame.payload().has_remaining(),
302            _ => !self.buf.has_remaining(),
303        }
304    }
305}
306
307impl<B> Encoder<B> {
308    fn max_frame_size(&self) -> usize {
309        self.max_frame_size as usize
310    }
311}
312
313impl<T, B> FramedWrite<T, B> {
314    /// Returns the max frame size that can be sent
315    pub fn max_frame_size(&self) -> usize {
316        self.encoder.max_frame_size()
317    }
318
319    /// Set the peer's max frame size.
320    pub fn set_max_frame_size(&mut self, val: usize) {
321        assert!(val <= frame::MAX_MAX_FRAME_SIZE as usize);
322        self.encoder.max_frame_size = val as FrameSize;
323    }
324
325    /// Set the peer's header table size.
326    pub fn set_header_table_size(&mut self, val: usize) {
327        self.encoder.hpack.update_max_size(val);
328    }
329
330    /// Retrieve the last data frame that has been sent
331    pub fn take_last_data_frame(&mut self) -> Option<frame::Data<B>> {
332        self.encoder.last_data_frame.take()
333    }
334
335    pub fn get_mut(&mut self) -> &mut T {
336        &mut self.inner
337    }
338}
339
340impl<T: AsyncRead + Unpin, B> AsyncRead for FramedWrite<T, B> {
341    fn poll_read(
342        mut self: Pin<&mut Self>,
343        cx: &mut Context<'_>,
344        buf: &mut ReadBuf,
345    ) -> Poll<io::Result<()>> {
346        Pin::new(&mut self.inner).poll_read(cx, buf)
347    }
348}
349
350// We never project the Pin to `B`.
351impl<T: Unpin, B> Unpin for FramedWrite<T, B> {}
352
353#[cfg(feature = "unstable")]
354mod unstable {
355    use super::*;
356
357    impl<T, B> FramedWrite<T, B> {
358        pub fn get_ref(&self) -> &T {
359            &self.inner
360        }
361    }
362}
h2/codec/framed_write.rs

h2/codec/
framed_write.rs
