smoltcp/src/socket/udp.rs

use core::cmp::min;
#[cfg(feature = "async")]
use core::task::Waker;

use crate::{Error, Result};
use crate::socket::{Socket, SocketMeta, SocketHandle, PollAt};
use crate::storage::{PacketBuffer, PacketMetadata};
use crate::wire::{IpProtocol, IpRepr, IpEndpoint, UdpRepr};
#[cfg(feature = "async")]
use crate::socket::WakerRegistration;

/// A UDP packet metadata.
pub type UdpPacketMetadata = PacketMetadata<IpEndpoint>;

/// A UDP packet ring buffer.
pub type UdpSocketBuffer<'a> = PacketBuffer<'a, IpEndpoint>;

/// A User Datagram Protocol socket.
///
/// A UDP socket is bound to a specific endpoint, and owns transmit and receive
/// packet buffers.
#[derive(Debug)]
pub struct UdpSocket<'a> {
    pub(crate) meta: SocketMeta,
    endpoint:  IpEndpoint,
    rx_buffer: UdpSocketBuffer<'a>,
    tx_buffer: UdpSocketBuffer<'a>,
    /// The time-to-live (IPv4) or hop limit (IPv6) value used in outgoing packets.
    hop_limit: Option<u8>,
    #[cfg(feature = "async")]
    rx_waker: WakerRegistration,
    #[cfg(feature = "async")]
    tx_waker: WakerRegistration,
}

impl<'a> UdpSocket<'a> {
    /// Create an UDP socket with the given buffers.
    pub fn new(rx_buffer: UdpSocketBuffer<'a>,
               tx_buffer: UdpSocketBuffer<'a>) -> UdpSocket<'a> {
        UdpSocket {
            meta:      SocketMeta::default(),
            endpoint:  IpEndpoint::default(),
            rx_buffer: rx_buffer,
            tx_buffer: tx_buffer,
            hop_limit: None,
            #[cfg(feature = "async")]
            rx_waker: WakerRegistration::new(),
            #[cfg(feature = "async")]
            tx_waker: WakerRegistration::new(),
        }
    }

    /// Register a waker for receive operations.
    ///
    /// The waker is woken on state changes that might affect the return value
    /// of `recv` method calls, such as receiving data, or the socket closing.
    ///
    /// Notes:
    ///
    /// - Only one waker can be registered at a time. If another waker was previously registered,
    ///   it is overwritten and will no longer be woken.
    /// - The Waker is woken only once. Once woken, you must register it again to receive more wakes.
    /// - "Spurious wakes" are allowed: a wake doesn't guarantee the result of `recv` has
    ///   necessarily changed.
    #[cfg(feature = "async")]
    pub fn register_recv_waker(&mut self, waker: &Waker) {
        self.rx_waker.register(waker)
    }

    /// Register a waker for send operations.
    ///
    /// The waker is woken on state changes that might affect the return value
    /// of `send` method calls, such as space becoming available in the transmit
    /// buffer, or the socket closing.
    ///
    /// Notes:
    ///
    /// - Only one waker can be registered at a time. If another waker was previously registered,
    ///   it is overwritten and will no longer be woken.
    /// - The Waker is woken only once. Once woken, you must register it again to receive more wakes.
    /// - "Spurious wakes" are allowed: a wake doesn't guarantee the result of `send` has
    ///   necessarily changed.
    #[cfg(feature = "async")]
    pub fn register_send_waker(&mut self, waker: &Waker) {
        self.tx_waker.register(waker)
    }

    /// Return the socket handle.
    #[inline]
    pub fn handle(&self) -> SocketHandle {
        self.meta.handle
    }

    /// Return the bound endpoint.
    #[inline]
    pub fn endpoint(&self) -> IpEndpoint {
        self.endpoint
    }

    /// Return the time-to-live (IPv4) or hop limit (IPv6) value used in outgoing packets.
    ///
    /// See also the [set_hop_limit](#method.set_hop_limit) method
    pub fn hop_limit(&self) -> Option<u8> {
        self.hop_limit
    }

    /// Set the time-to-live (IPv4) or hop limit (IPv6) value used in outgoing packets.
    ///
    /// A socket without an explicitly set hop limit value uses the default [IANA recommended]
    /// value (64).
    ///
    /// # Panics
    ///
    /// This function panics if a hop limit value of 0 is given. See [RFC 1122 § 3.2.1.7].
    ///
    /// [IANA recommended]: https://www.iana.org/assignments/ip-parameters/ip-parameters.xhtml
    /// [RFC 1122 § 3.2.1.7]: https://tools.ietf.org/html/rfc1122#section-3.2.1.7
    pub fn set_hop_limit(&mut self, hop_limit: Option<u8>) {
        // A host MUST NOT send a datagram with a hop limit value of 0
        if let Some(0) = hop_limit {
            panic!("the time-to-live value of a packet must not be zero")
        }

        self.hop_limit = hop_limit
    }

    /// Bind the socket to the given endpoint.
    ///
    /// This function returns `Err(Error::Illegal)` if the socket was open
    /// (see [is_open](#method.is_open)), and `Err(Error::Unaddressable)`
    /// if the port in the given endpoint is zero.
    pub fn bind<T: Into<IpEndpoint>>(&mut self, endpoint: T) -> Result<()> {
        let endpoint = endpoint.into();
        if endpoint.port == 0 { return Err(Error::Unaddressable) }

        if self.is_open() { return Err(Error::Illegal) }

        self.endpoint = endpoint;

        #[cfg(feature = "async")]
        {
            self.rx_waker.wake();
            self.tx_waker.wake();
        }

        Ok(())
    }

    /// Check whether the socket is open.
    #[inline]
    pub fn is_open(&self) -> bool {
        self.endpoint.port != 0
    }

    /// Check whether the transmit buffer is full.
    #[inline]
    pub fn can_send(&self) -> bool {
        !self.tx_buffer.is_full()
    }

    /// Check whether the receive buffer is not empty.
    #[inline]
    pub fn can_recv(&self) -> bool {
        !self.rx_buffer.is_empty()
    }

    /// Return the maximum number packets the socket can receive.
    #[inline]
    pub fn packet_recv_capacity(&self) -> usize {
        self.rx_buffer.packet_capacity()
    }

    /// Return the maximum number packets the socket can transmit.
    #[inline]
    pub fn packet_send_capacity(&self) -> usize {
        self.tx_buffer.packet_capacity()
    }

    /// Return the maximum number of bytes inside the recv buffer.
    #[inline]
    pub fn payload_recv_capacity(&self) -> usize {
        self.rx_buffer.payload_capacity()
    }

    /// Return the maximum number of bytes inside the transmit buffer.
    #[inline]
    pub fn payload_send_capacity(&self) -> usize {
        self.tx_buffer.payload_capacity()
    }

    /// Enqueue a packet to be sent to a given remote endpoint, and return a pointer
    /// to its payload.
    ///
    /// This function returns `Err(Error::Exhausted)` if the transmit buffer is full,
    /// `Err(Error::Unaddressable)` if local or remote port, or remote address are unspecified,
    /// and `Err(Error::Truncated)` if there is not enough transmit buffer capacity
    /// to ever send this packet.
    pub fn send(&mut self, size: usize, endpoint: IpEndpoint) -> Result<&mut [u8]> {
        if self.endpoint.port == 0 { return Err(Error::Unaddressable) }
        if !endpoint.is_specified() { return Err(Error::Unaddressable) }

        let payload_buf = self.tx_buffer.enqueue(size, endpoint)?;

        net_trace!("{}:{}:{}: buffer to send {} octets",
                   self.meta.handle, self.endpoint, endpoint, size);
        Ok(payload_buf)
    }

    /// Enqueue a packet to be sent to a given remote endpoint, and fill it from a slice.
    ///
    /// See also [send](#method.send).
    pub fn send_slice(&mut self, data: &[u8], endpoint: IpEndpoint) -> Result<()> {
        self.send(data.len(), endpoint)?.copy_from_slice(data);
        Ok(())
    }

    /// Dequeue a packet received from a remote endpoint, and return the endpoint as well
    /// as a pointer to the payload.
    ///
    /// This function returns `Err(Error::Exhausted)` if the receive buffer is empty.
    pub fn recv(&mut self) -> Result<(&[u8], IpEndpoint)> {
        let (endpoint, payload_buf) = self.rx_buffer.dequeue()?;

        net_trace!("{}:{}:{}: receive {} buffered octets",
                   self.meta.handle, self.endpoint,
                   endpoint, payload_buf.len());
        Ok((payload_buf, endpoint))
    }

    /// Dequeue a packet received from a remote endpoint, copy the payload into the given slice,
    /// and return the amount of octets copied as well as the endpoint.
    ///
    /// See also [recv](#method.recv).
    pub fn recv_slice(&mut self, data: &mut [u8]) -> Result<(usize, IpEndpoint)> {
        let (buffer, endpoint) = self.recv()?;
        let length = min(data.len(), buffer.len());
        data[..length].copy_from_slice(&buffer[..length]);
        Ok((length, endpoint))
    }

    /// Peek at a packet received from a remote endpoint, and return the endpoint as well
    /// as a pointer to the payload without removing the packet from the receive buffer.
    /// This function otherwise behaves identically to [recv](#method.recv).
    ///
    /// It returns `Err(Error::Exhausted)` if the receive buffer is empty.
    pub fn peek(&mut self) -> Result<(&[u8], &IpEndpoint)> {
        let handle = self.meta.handle;
        let endpoint = self.endpoint;
        self.rx_buffer.peek().map(|(remote_endpoint, payload_buf)| {
            net_trace!("{}:{}:{}: peek {} buffered octets",
                       handle, endpoint,
                       remote_endpoint, payload_buf.len());
           (payload_buf, remote_endpoint)
        })
    }

    /// Peek at a packet received from a remote endpoint, copy the payload into the given slice,
    /// and return the amount of octets copied as well as the endpoint without removing the
    /// packet from the receive buffer.
    /// This function otherwise behaves identically to [recv_slice](#method.recv_slice).
    ///
    /// See also [peek](#method.peek).
    pub fn peek_slice(&mut self, data: &mut [u8]) -> Result<(usize, &IpEndpoint)> {
        let (buffer, endpoint) = self.peek()?;
        let length = min(data.len(), buffer.len());
        data[..length].copy_from_slice(&buffer[..length]);
        Ok((length, endpoint))
    }

    pub(crate) fn accepts(&self, ip_repr: &IpRepr, repr: &UdpRepr) -> bool {
        if self.endpoint.port != repr.dst_port { return false }
        if !self.endpoint.addr.is_unspecified() &&
            self.endpoint.addr != ip_repr.dst_addr() &&
            !ip_repr.dst_addr().is_broadcast() &&
            !ip_repr.dst_addr().is_multicast() { return false }

        true
    }

    pub(crate) fn process(&mut self, ip_repr: &IpRepr, repr: &UdpRepr, payload: &[u8]) -> Result<()> {
        debug_assert!(self.accepts(ip_repr, repr));

        let size = payload.len();

        let endpoint = IpEndpoint { addr: ip_repr.src_addr(), port: repr.src_port };
        self.rx_buffer.enqueue(size, endpoint)?.copy_from_slice(payload);

        net_trace!("{}:{}:{}: receiving {} octets",
                   self.meta.handle, self.endpoint,
                   endpoint, size);

        #[cfg(feature = "async")]
        self.rx_waker.wake();

        Ok(())
    }

    pub(crate) fn dispatch<F>(&mut self, emit: F) -> Result<()>
            where F: FnOnce((IpRepr, UdpRepr, &[u8])) -> Result<()> {
        let handle    = self.handle();
        let endpoint  = self.endpoint;
        let hop_limit = self.hop_limit.unwrap_or(64);

        self.tx_buffer.dequeue_with(|remote_endpoint, payload_buf| {
            net_trace!("{}:{}:{}: sending {} octets",
                        handle, endpoint,
                        endpoint, payload_buf.len());

            let repr = UdpRepr {
                src_port: endpoint.port,
                dst_port: remote_endpoint.port,
            };
            let ip_repr = IpRepr::Unspecified {
                src_addr:    endpoint.addr,
                dst_addr:    remote_endpoint.addr,
                protocol:    IpProtocol::Udp,
                payload_len: repr.header_len() + payload_buf.len(),
                hop_limit:   hop_limit,
            };
            emit((ip_repr, repr, payload_buf))
        })?;

        #[cfg(feature = "async")]
        self.tx_waker.wake();

        Ok(())
    }

    pub(crate) fn poll_at(&self) -> PollAt {
        if self.tx_buffer.is_empty() {
            PollAt::Ingress
        } else {
            PollAt::Now
        }
    }
}

impl<'a> Into<Socket<'a>> for UdpSocket<'a> {
    fn into(self) -> Socket<'a> {
        Socket::Udp(self)
    }
}

#[cfg(test)]
mod test {
    use crate::wire::{IpAddress, IpRepr, UdpRepr};
    #[cfg(feature = "proto-ipv4")]
    use crate::wire::Ipv4Repr;
    #[cfg(feature = "proto-ipv6")]
    use crate::wire::Ipv6Repr;
    use crate::wire::ip::test::{MOCK_IP_ADDR_1, MOCK_IP_ADDR_2, MOCK_IP_ADDR_3};
    use super::*;

    fn buffer(packets: usize) -> UdpSocketBuffer<'static> {
        UdpSocketBuffer::new(vec![UdpPacketMetadata::EMPTY; packets], vec![0; 16 * packets])
    }

    fn socket(rx_buffer: UdpSocketBuffer<'static>,
              tx_buffer: UdpSocketBuffer<'static>)
            -> UdpSocket<'static> {
        UdpSocket::new(rx_buffer, tx_buffer)
    }

    const LOCAL_PORT:  u16        = 53;
    const REMOTE_PORT: u16        = 49500;

    pub const LOCAL_END:   IpEndpoint = IpEndpoint { addr: MOCK_IP_ADDR_1, port: LOCAL_PORT  };
    pub const REMOTE_END:  IpEndpoint = IpEndpoint { addr: MOCK_IP_ADDR_2, port: REMOTE_PORT };

    pub const LOCAL_IP_REPR: IpRepr = IpRepr::Unspecified {
        src_addr: MOCK_IP_ADDR_1,
        dst_addr: MOCK_IP_ADDR_2,
        protocol: IpProtocol::Udp,
        payload_len: 8 + 6,
        hop_limit: 64,
    };

    const LOCAL_UDP_REPR: UdpRepr = UdpRepr {
        src_port: LOCAL_PORT,
        dst_port: REMOTE_PORT,
    };

    const REMOTE_UDP_REPR: UdpRepr = UdpRepr {
        src_port: REMOTE_PORT,
        dst_port: LOCAL_PORT,
    };

    const PAYLOAD: &[u8] = b"abcdef";

    fn remote_ip_repr() -> IpRepr {
        match (MOCK_IP_ADDR_2, MOCK_IP_ADDR_1) {
            #[cfg(feature = "proto-ipv4")]
            (IpAddress::Ipv4(src), IpAddress::Ipv4(dst)) => IpRepr::Ipv4(Ipv4Repr {
                src_addr: src,
                dst_addr: dst,
                protocol: IpProtocol::Udp,
                payload_len: 8 + 6,
                hop_limit: 64
            }),
            #[cfg(feature = "proto-ipv6")]
            (IpAddress::Ipv6(src), IpAddress::Ipv6(dst)) => IpRepr::Ipv6(Ipv6Repr {
                src_addr: src,
                dst_addr: dst,
                next_header: IpProtocol::Udp,
                payload_len: 8 + 6,
                hop_limit: 64
            }),
            _ => unreachable!()
        }
    }

    #[test]
    fn test_bind_unaddressable() {
        let mut socket = socket(buffer(0), buffer(0));
        assert_eq!(socket.bind(0), Err(Error::Unaddressable));
    }

    #[test]
    fn test_bind_twice() {
        let mut socket = socket(buffer(0), buffer(0));
        assert_eq!(socket.bind(1), Ok(()));
        assert_eq!(socket.bind(2), Err(Error::Illegal));
    }

    #[test]
    #[should_panic(expected = "the time-to-live value of a packet must not be zero")]
    fn test_set_hop_limit_zero() {
        let mut s = socket(buffer(0), buffer(1));
        s.set_hop_limit(Some(0));
    }

    #[test]
    fn test_send_unaddressable() {
        let mut socket = socket(buffer(0), buffer(1));
        assert_eq!(socket.send_slice(b"abcdef", REMOTE_END), Err(Error::Unaddressable));
        assert_eq!(socket.bind(LOCAL_PORT), Ok(()));
        assert_eq!(socket.send_slice(b"abcdef",
                                     IpEndpoint { addr: IpAddress::Unspecified, ..REMOTE_END }),
                   Err(Error::Unaddressable));
        assert_eq!(socket.send_slice(b"abcdef",
                                     IpEndpoint { port: 0, ..REMOTE_END }),
                   Err(Error::Unaddressable));
        assert_eq!(socket.send_slice(b"abcdef", REMOTE_END), Ok(()));
    }

    #[test]
    fn test_send_dispatch() {
        let mut socket = socket(buffer(0), buffer(1));
        assert_eq!(socket.bind(LOCAL_END), Ok(()));

        assert!(socket.can_send());
        assert_eq!(socket.dispatch(|_| unreachable!()),
                   Err(Error::Exhausted));

        assert_eq!(socket.send_slice(b"abcdef", REMOTE_END), Ok(()));
        assert_eq!(socket.send_slice(b"123456", REMOTE_END), Err(Error::Exhausted));
        assert!(!socket.can_send());

        assert_eq!(socket.dispatch(|(ip_repr, udp_repr, payload)| {
            assert_eq!(ip_repr, LOCAL_IP_REPR);
            assert_eq!(udp_repr, LOCAL_UDP_REPR);
            assert_eq!(payload, PAYLOAD);
            Err(Error::Unaddressable)
        }), Err(Error::Unaddressable));
        assert!(!socket.can_send());

        assert_eq!(socket.dispatch(|(ip_repr, udp_repr, payload)| {
            assert_eq!(ip_repr, LOCAL_IP_REPR);
            assert_eq!(udp_repr, LOCAL_UDP_REPR);
            assert_eq!(payload, PAYLOAD);
            Ok(())
        }), Ok(()));
        assert!(socket.can_send());
    }

    #[test]
    fn test_recv_process() {
        let mut socket = socket(buffer(1), buffer(0));
        assert_eq!(socket.bind(LOCAL_PORT), Ok(()));

        assert!(!socket.can_recv());
        assert_eq!(socket.recv(), Err(Error::Exhausted));

        assert!(socket.accepts(&remote_ip_repr(), &REMOTE_UDP_REPR));
        assert_eq!(socket.process(&remote_ip_repr(), &REMOTE_UDP_REPR, PAYLOAD),
                   Ok(()));
        assert!(socket.can_recv());

        assert!(socket.accepts(&remote_ip_repr(), &REMOTE_UDP_REPR));
        assert_eq!(socket.process(&remote_ip_repr(), &REMOTE_UDP_REPR, PAYLOAD),
                   Err(Error::Exhausted));
        assert_eq!(socket.recv(), Ok((&b"abcdef"[..], REMOTE_END)));
        assert!(!socket.can_recv());
    }

    #[test]
    fn test_peek_process() {
        let mut socket = socket(buffer(1), buffer(0));
        assert_eq!(socket.bind(LOCAL_PORT), Ok(()));

        assert_eq!(socket.peek(), Err(Error::Exhausted));

        assert_eq!(socket.process(&remote_ip_repr(), &REMOTE_UDP_REPR, PAYLOAD),
                   Ok(()));
        assert_eq!(socket.peek(), Ok((&b"abcdef"[..], &REMOTE_END)));
        assert_eq!(socket.recv(), Ok((&b"abcdef"[..], REMOTE_END)));
        assert_eq!(socket.peek(), Err(Error::Exhausted));
    }

    #[test]
    fn test_recv_truncated_slice() {
        let mut socket = socket(buffer(1), buffer(0));
        assert_eq!(socket.bind(LOCAL_PORT), Ok(()));

        assert!(socket.accepts(&remote_ip_repr(), &REMOTE_UDP_REPR));
        assert_eq!(socket.process(&remote_ip_repr(), &REMOTE_UDP_REPR, PAYLOAD),
                   Ok(()));

        let mut slice = [0; 4];
        assert_eq!(socket.recv_slice(&mut slice[..]), Ok((4, REMOTE_END)));
        assert_eq!(&slice, b"abcd");
    }

    #[test]
    fn test_peek_truncated_slice() {
        let mut socket = socket(buffer(1), buffer(0));
        assert_eq!(socket.bind(LOCAL_PORT), Ok(()));

        assert_eq!(socket.process(&remote_ip_repr(), &REMOTE_UDP_REPR, PAYLOAD),
                   Ok(()));

        let mut slice = [0; 4];
        assert_eq!(socket.peek_slice(&mut slice[..]), Ok((4, &REMOTE_END)));
        assert_eq!(&slice, b"abcd");
        assert_eq!(socket.recv_slice(&mut slice[..]), Ok((4, REMOTE_END)));
        assert_eq!(&slice, b"abcd");
        assert_eq!(socket.peek_slice(&mut slice[..]), Err(Error::Exhausted));
    }

    #[test]
    fn test_set_hop_limit() {
        let mut s = socket(buffer(0), buffer(1));
        assert_eq!(s.bind(LOCAL_END), Ok(()));

        s.set_hop_limit(Some(0x2a));
        assert_eq!(s.send_slice(b"abcdef", REMOTE_END), Ok(()));
        assert_eq!(s.dispatch(|(ip_repr, _, _)| {
            assert_eq!(ip_repr, IpRepr::Unspecified{
                src_addr: MOCK_IP_ADDR_1,
                dst_addr: MOCK_IP_ADDR_2,
                protocol: IpProtocol::Udp,
                payload_len: 8 + 6,
                hop_limit: 0x2a,
            });
            Ok(())
        }), Ok(()));
    }

    #[test]
    fn test_doesnt_accept_wrong_port() {
        let mut socket = socket(buffer(1), buffer(0));
        assert_eq!(socket.bind(LOCAL_PORT), Ok(()));

        let mut udp_repr = REMOTE_UDP_REPR;
        assert!(socket.accepts(&remote_ip_repr(), &udp_repr));
        udp_repr.dst_port += 1;
        assert!(!socket.accepts(&remote_ip_repr(), &udp_repr));
    }

    #[test]
    fn test_doesnt_accept_wrong_ip() {
        fn generate_bad_repr() -> IpRepr {
            match (MOCK_IP_ADDR_2, MOCK_IP_ADDR_3) {
                #[cfg(feature = "proto-ipv4")]
                (IpAddress::Ipv4(src), IpAddress::Ipv4(dst)) => IpRepr::Ipv4(Ipv4Repr {
                    src_addr: src,
                    dst_addr: dst,
                    protocol: IpProtocol::Udp,
                    payload_len: 8 + 6,
                    hop_limit: 64
                }),
                #[cfg(feature = "proto-ipv6")]
                (IpAddress::Ipv6(src), IpAddress::Ipv6(dst)) => IpRepr::Ipv6(Ipv6Repr {
                    src_addr: src,
                    dst_addr: dst,
                    next_header: IpProtocol::Udp,
                    payload_len: 8 + 6,
                    hop_limit: 64
                }),
                _ => unreachable!()
            }
        }

        let mut port_bound_socket = socket(buffer(1), buffer(0));
        assert_eq!(port_bound_socket.bind(LOCAL_PORT), Ok(()));
        assert!(port_bound_socket.accepts(&generate_bad_repr(), &REMOTE_UDP_REPR));

        let mut ip_bound_socket = socket(buffer(1), buffer(0));
        assert_eq!(ip_bound_socket.bind(LOCAL_END), Ok(()));
        assert!(!ip_bound_socket.accepts(&generate_bad_repr(), &REMOTE_UDP_REPR));
    }

    #[test]
    fn test_send_large_packet() {
        // buffer(4) creates a payload buffer of size 16*4
        let mut socket = socket(buffer(0), buffer(4));
        assert_eq!(socket.bind(LOCAL_END), Ok(()));

        let too_large = b"0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdefx";
        assert_eq!(socket.send_slice(too_large, REMOTE_END), Err(Error::Truncated));
        assert_eq!(socket.send_slice(&too_large[..16*4], REMOTE_END), Ok(()));
    }

    #[test]
    fn test_process_empty_payload() {
        let recv_buffer = UdpSocketBuffer::new(vec![UdpPacketMetadata::EMPTY; 1], vec![]);
        let mut socket = socket(recv_buffer, buffer(0));
        assert_eq!(socket.bind(LOCAL_PORT), Ok(()));

        let repr = UdpRepr {
            src_port: REMOTE_PORT,
            dst_port: LOCAL_PORT,
        };
        assert_eq!(socket.process(&remote_ip_repr(), &repr, &[]), Ok(()));
        assert_eq!(socket.recv(), Ok((&[][..], REMOTE_END)));
    }
}