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
use crate::codec::{Decoder, Encoder};

use futures_core::Stream;
use tokio::{io::ReadBuf, net::UdpSocket};

use bytes::{BufMut, BytesMut};
use futures_core::ready;
use futures_sink::Sink;
use std::pin::Pin;
use std::task::{Context, Poll};
use std::{
    borrow::Borrow,
    net::{Ipv4Addr, SocketAddr, SocketAddrV4},
};
use std::{io, mem::MaybeUninit};

/// A unified [`Stream`] and [`Sink`] interface to an underlying `UdpSocket`, using
/// the `Encoder` and `Decoder` traits to encode and decode frames.
///
/// Raw UDP sockets work with datagrams, but higher-level code usually wants to
/// batch these into meaningful chunks, called "frames". This method layers
/// framing on top of this socket by using the `Encoder` and `Decoder` 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 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 `UdpFramed` 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
/// [`split`]: https://docs.rs/futures/0.3/futures/stream/trait.StreamExt.html#method.split
#[must_use = "sinks do nothing unless polled"]
#[derive(Debug)]
pub struct UdpFramed<C, T = UdpSocket> {
    socket: T,
    codec: C,
    rd: BytesMut,
    wr: BytesMut,
    out_addr: SocketAddr,
    flushed: bool,
    is_readable: bool,
    current_addr: Option<SocketAddr>,
}

const INITIAL_RD_CAPACITY: usize = 64 * 1024;
const INITIAL_WR_CAPACITY: usize = 8 * 1024;

impl<C, T> Unpin for UdpFramed<C, T> {}

impl<C, T> Stream for UdpFramed<C, T>
where
    T: Borrow<UdpSocket>,
    C: Decoder,
{
    type Item = Result<(C::Item, SocketAddr), C::Error>;

    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
        let pin = self.get_mut();

        pin.rd.reserve(INITIAL_RD_CAPACITY);

        loop {
            // Are there still bytes left in the read buffer to decode?
            if pin.is_readable {
                if let Some(frame) = pin.codec.decode_eof(&mut pin.rd)? {
                    let current_addr = pin
                        .current_addr
                        .expect("will always be set before this line is called");

                    return Poll::Ready(Some(Ok((frame, current_addr))));
                }

                // if this line has been reached then decode has returned `None`.
                pin.is_readable = false;
                pin.rd.clear();
            }

            // We're out of data. Try and fetch more data to decode
            let addr = unsafe {
                // Convert `&mut [MaybeUnit<u8>]` to `&mut [u8]` because we will be
                // writing to it via `poll_recv_from` and therefore initializing the memory.
                let buf = &mut *(pin.rd.chunk_mut() as *mut _ as *mut [MaybeUninit<u8>]);
                let mut read = ReadBuf::uninit(buf);
                let ptr = read.filled().as_ptr();
                let res = ready!(pin.socket.borrow().poll_recv_from(cx, &mut read));

                assert_eq!(ptr, read.filled().as_ptr());
                let addr = res?;
                pin.rd.advance_mut(read.filled().len());
                addr
            };

            pin.current_addr = Some(addr);
            pin.is_readable = true;
        }
    }
}

impl<I, C, T> Sink<(I, SocketAddr)> for UdpFramed<C, T>
where
    T: Borrow<UdpSocket>,
    C: Encoder<I>,
{
    type Error = C::Error;

    fn poll_ready(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
        if !self.flushed {
            match self.poll_flush(cx)? {
                Poll::Ready(()) => {}
                Poll::Pending => return Poll::Pending,
            }
        }

        Poll::Ready(Ok(()))
    }

    fn start_send(self: Pin<&mut Self>, item: (I, SocketAddr)) -> Result<(), Self::Error> {
        let (frame, out_addr) = item;

        let pin = self.get_mut();

        pin.codec.encode(frame, &mut pin.wr)?;
        pin.out_addr = out_addr;
        pin.flushed = false;

        Ok(())
    }

    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
        if self.flushed {
            return Poll::Ready(Ok(()));
        }

        let Self {
            ref socket,
            ref mut out_addr,
            ref mut wr,
            ..
        } = *self;

        let n = ready!(socket.borrow().poll_send_to(cx, wr, *out_addr))?;

        let wrote_all = n == self.wr.len();
        self.wr.clear();
        self.flushed = true;

        let res = if wrote_all {
            Ok(())
        } else {
            Err(io::Error::new(
                io::ErrorKind::Other,
                "failed to write entire datagram to socket",
            )
            .into())
        };

        Poll::Ready(res)
    }

    fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
        ready!(self.poll_flush(cx))?;
        Poll::Ready(Ok(()))
    }
}

impl<C, T> UdpFramed<C, T>
where
    T: Borrow<UdpSocket>,
{
    /// Create a new `UdpFramed` backed by the given socket and codec.
    ///
    /// See struct level documentation for more details.
    pub fn new(socket: T, codec: C) -> UdpFramed<C, T> {
        Self {
            socket,
            codec,
            out_addr: SocketAddr::V4(SocketAddrV4::new(Ipv4Addr::new(0, 0, 0, 0), 0)),
            rd: BytesMut::with_capacity(INITIAL_RD_CAPACITY),
            wr: BytesMut::with_capacity(INITIAL_WR_CAPACITY),
            flushed: true,
            is_readable: false,
            current_addr: None,
        }
    }

    /// Returns a reference to the underlying I/O stream wrapped by `Framed`.
    ///
    /// # Note
    ///
    /// Care should be taken to not tamper with the underlying stream of data
    /// coming in as it may corrupt the stream of frames otherwise being worked
    /// with.
    pub fn get_ref(&self) -> &T {
        &self.socket
    }

    /// Returns a mutable reference to the underlying I/O stream wrapped by `Framed`.
    ///
    /// # Note
    ///
    /// Care should be taken to not tamper with the underlying stream of data
    /// coming in as it may corrupt the stream of frames otherwise being worked
    /// with.
    pub fn get_mut(&mut self) -> &mut T {
        &mut self.socket
    }

    /// Returns a reference to the underlying codec wrapped by
    /// `Framed`.
    ///
    /// Note that care should be taken to not tamper with the underlying codec
    /// as it may corrupt the stream of frames otherwise being worked with.
    pub fn codec(&self) -> &C {
        &self.codec
    }

    /// Returns a mutable reference to the underlying codec wrapped by
    /// `UdpFramed`.
    ///
    /// Note that care should be taken to not tamper with the underlying codec
    /// as it may corrupt the stream of frames otherwise being worked with.
    pub fn codec_mut(&mut self) -> &mut C {
        &mut self.codec
    }

    /// Returns a reference to the read buffer.
    pub fn read_buffer(&self) -> &BytesMut {
        &self.rd
    }

    /// Returns a mutable reference to the read buffer.
    pub fn read_buffer_mut(&mut self) -> &mut BytesMut {
        &mut self.rd
    }

    /// Consumes the `Framed`, returning its underlying I/O stream.
    pub fn into_inner(self) -> T {
        self.socket
    }
}