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

use crate::socket::{
    error::SocketError,
    protocol::ProtocolParser,
};
use std::{
    collections::VecDeque,
    task::{Context, Poll},
    pin::Pin,
    marker::PhantomData
};
use serde::de::DeserializeOwned;
use futures::{Sink, Stream};
use pin_project::pin_project;

/// Contains `ProtocolParser` implementations for transforming communication protocol specific
/// messages into a generic output data structure.
pub mod protocol;

/// Custom `SocketError`s generated by an `ExchangeSocket`.
pub mod error;

/// `Transformer`s are capable of transforming any `Input` into an iterator of
/// `Result<Output, SocketError>`s.
pub trait Transformer<Output> {
    type Input;
    type OutputIter: IntoIterator<Item = Result<Output, SocketError>>;
    fn transform(&mut self, input: Self::Input) -> Self::OutputIter;
}

/// An `ExchangeSocket` is capable of acting as both a `Stream` and a `Sink` with any communication
/// protocol. It streams exchange messages from the inner socket and transform them into the
/// desired output data structure.
#[derive(Debug)]
#[pin_project]
pub struct ExchangeSocket<Protocol, Socket, ExchangeMessage, StreamTransformer, Output>
where
    Protocol: ProtocolParser,
    Socket: Sink<Protocol::ProtocolMessage> + Stream,
    ExchangeMessage: DeserializeOwned,
    StreamTransformer: Transformer<Output>,
{
    #[pin]
    pub socket: Socket,
    pub transformer: StreamTransformer,
    pub buffer: VecDeque<Result<Output, SocketError>>,
    pub protocol_marker: PhantomData<Protocol>,
    pub exchange_message_marker: PhantomData<ExchangeMessage>,
}

impl<Protocol, Socket, ExchangeMessage, StreamTransformer, Output> Stream
    for ExchangeSocket<Protocol, Socket, ExchangeMessage, StreamTransformer, Output>
where
    Protocol: ProtocolParser,
    Socket: Sink<Protocol::ProtocolMessage> + Stream<Item = Protocol::ProtocolMessage> + Unpin,
    ExchangeMessage: DeserializeOwned,
    StreamTransformer: Transformer<Output, Input = ExchangeMessage>,
{
    type Item = Result<Output, SocketError>;

    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
        loop {
            // Flush Self::Item buffer if it is not currently empty
            if let Some(output) = self.buffer.pop_front() {
                return Poll::Ready(Some(output))
            }

            // Poll underlying `Stream` for next `StreamItem` input
            let input = match self.as_mut().project().socket.poll_next(cx) {
                Poll::Ready(Some(input)) => input,
                Poll::Ready(None) => return Poll::Ready(None),
                Poll::Pending => return Poll::Pending,
            };

            // Parse input `StreamItem` into `ExchangeMessage`
            let exchange_message = match Protocol::parse::<ExchangeMessage>(input) {
                // `ProtocolParser` successfully deserialised `ExchangeMessage`
                Some(Ok(exchange_message)) => exchange_message,

                // If `ProtocolParser` returns an Err pass it downstream
                Some(Err(err)) => return Poll::Ready(Some(Err(err))),

                // If `ProtocolParser` returns None it's a safe-to-skip message
                None => return Poll::Pending,
            };

            // Transform `ExchangeMessage` into `Transformer::OutputIter`
            // ie/ IntoIterator<Item = Result<Output, SocketError>>
            self.transformer
                .transform(exchange_message)
                .into_iter()
                .for_each(|output| self.buffer.push_back(output));
        }
    }
}

impl<Protocol, Socket, ExchangeMessage, StreamTransformer, Output> Sink<Protocol::ProtocolMessage>
    for ExchangeSocket<Protocol, Socket, ExchangeMessage, StreamTransformer, Output>
where
    Protocol: ProtocolParser,
    Socket: Sink<Protocol::ProtocolMessage> + Stream,
    ExchangeMessage: DeserializeOwned,
    StreamTransformer: Transformer<Output>,
{
    type Error = SocketError;

    fn poll_ready(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
        self.project().socket.poll_ready(cx).map_err(|_| SocketError::Sink)
    }

    fn start_send(self: Pin<&mut Self>, item: Protocol::ProtocolMessage) -> Result<(), Self::Error> {
        self.project().socket.start_send(item).map_err(|_| SocketError::Sink)
    }

    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
        self.project().socket.poll_flush(cx).map_err(|_| SocketError::Sink)
    }

    fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
        self.project().socket.poll_close(cx).map_err(|_| SocketError::Sink)
    }
}

impl<Protocol, Socket, ExchangeMessage, StreamTransformer, Output>
    ExchangeSocket<Protocol, Socket, ExchangeMessage, StreamTransformer, Output>
where
    Protocol: ProtocolParser,
    Socket: Sink<Protocol::ProtocolMessage> + Stream,
    ExchangeMessage: DeserializeOwned,
    StreamTransformer: Transformer<Output>,
{
    pub fn new(socket: Socket, transformer: StreamTransformer) -> Self {
        Self {
            socket,
            transformer,
            buffer: VecDeque::with_capacity(6),
            protocol_marker: PhantomData::default(),
            exchange_message_marker: PhantomData::default(),
        }
    }
}