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
use std::io;
use std::net::{SocketAddr, Ipv4Addr, SocketAddrV4};

use futures::{Async, Poll, Stream, Sink, StartSend, AsyncSink};

use net::UdpSocket;

/// Encoding of frames via buffers.
///
/// This trait is used when constructing an instance of `UdpFramed` and provides
/// the `In` and `Out` types which are decoded and encoded from the socket,
/// respectively.
///
/// Because UDP is a connectionless protocol, the `decode` method receives the
/// address where data came from and the `encode` method is also responsible for
/// determining the remote host to which the datagram should be sent
///
/// The trait itself is implemented on a type that can track state for decoding
/// or encoding, which is particularly useful for streaming parsers. In many
/// cases, though, this type will simply be a unit struct (e.g. `struct
/// HttpCodec`).
pub trait UdpCodec {
    /// The type of decoded frames.
    type In;

    /// The type of frames to be encoded.
    type Out;

    /// Attempts to decode a frame from the provided buffer of bytes.
    ///
    /// This method is called by `UdpFramed` on a single datagram which has been
    /// read from a socket. The `buf` argument contains the data that was
    /// received from the remote address, and `src` is the address the data came
    /// from. Note that typically this method should require the entire contents
    /// of `buf` to be valid or otherwise return an error with trailing data.
    ///
    /// 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.
    fn decode(&mut self, src: &SocketAddr, buf: &[u8]) -> io::Result<Self::In>;

    /// Encodes a frame into the buffer provided.
    ///
    /// This method will encode `msg` into the byte buffer provided by `buf`.
    /// The `buf` provided is an internal buffer of the `Framed` instance and
    /// will be written out when possible.
    ///
    /// The encode method also determines the destination to which the buffer
    /// should be directed, which will be returned as a `SocketAddr`.
    fn encode(&mut self, msg: Self::Out, buf: &mut Vec<u8>) -> SocketAddr;
}

/// A unified `Stream` and `Sink` interface to an underlying `UdpSocket`, using
/// the `UdpCodec` trait to encode and decode frames.
///
/// You can acquire a `UdpFramed` instance by using the `UdpSocket::framed`
/// adapter.
#[must_use = "sinks do nothing unless polled"]
pub struct UdpFramed<C> {
    socket: UdpSocket,
    codec: C,
    rd: Vec<u8>,
    wr: Vec<u8>,
    out_addr: SocketAddr,
    flushed: bool,
}

impl<C: UdpCodec> Stream for UdpFramed<C> {
    type Item = C::In;
    type Error = io::Error;

    fn poll(&mut self) -> Poll<Option<C::In>, io::Error> {
        let (n, addr) = try_nb!(self.socket.recv_from(&mut self.rd));
        trace!("received {} bytes, decoding", n);
        let frame = try!(self.codec.decode(&addr, &self.rd[..n]));
        trace!("frame decoded from buffer");
        Ok(Async::Ready(Some(frame)))
    }
}

impl<C: UdpCodec> Sink for UdpFramed<C> {
    type SinkItem = C::Out;
    type SinkError = io::Error;

    fn start_send(&mut self, item: C::Out) -> StartSend<C::Out, io::Error> {
        trace!("sending frame");

        if !self.flushed {
            match try!(self.poll_complete()) {
                Async::Ready(()) => {},
                Async::NotReady => return Ok(AsyncSink::NotReady(item)),
            }
        }

        self.out_addr = self.codec.encode(item, &mut self.wr);
        self.flushed = false;
        trace!("frame encoded; length={}", self.wr.len());

        Ok(AsyncSink::Ready)
    }

    fn poll_complete(&mut self) -> Poll<(), io::Error> {
        if self.flushed {
            return Ok(Async::Ready(()))
        }

        trace!("flushing frame; length={}", self.wr.len());
        let n = try_nb!(self.socket.send_to(&self.wr, &self.out_addr));
        trace!("written {}", n);

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

        if wrote_all {
            Ok(Async::Ready(()))
        } else {
            Err(io::Error::new(io::ErrorKind::Other,
                               "failed to write entire datagram to socket"))
        }
    }

    fn close(&mut self) -> Poll<(), io::Error> {
        try_ready!(self.poll_complete());
        Ok(().into())
    }
}

pub fn new<C: UdpCodec>(socket: UdpSocket, codec: C) -> UdpFramed<C> {
    UdpFramed {
        socket: socket,
        codec: codec,
        out_addr: SocketAddr::V4(SocketAddrV4::new(Ipv4Addr::new(0, 0, 0, 0), 0)),
        rd: vec![0; 64 * 1024],
        wr: Vec::with_capacity(8 * 1024),
        flushed: true,
    }
}

impl<C> UdpFramed<C> {
    /// Returns a reference to the underlying I/O stream wrapped by `Framed`.
    ///
    /// Note that 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) -> &UdpSocket {
        &self.socket
    }

    /// Returns a mutable reference to the underlying I/O stream wrapped by
    /// `Framed`.
    ///
    /// Note that 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 UdpSocket {
        &mut self.socket
    }

    /// Consumes the `Framed`, returning its underlying I/O stream.
    ///
    /// Note that 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 into_inner(self) -> UdpSocket {
        self.socket
    }
}