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

use crate::codec::{Codec, StdError, WithOffset, WithSize};

#[derive(Clone, Copy, Debug, PartialEq)]
#[repr(u8)]
pub enum FlowType {
    U16 = 0,
    U32 = 1,
}

impl From<u8> for FlowType {
    fn from(n: u8) -> Self {
        match n {
            0 => FlowType::U16,
            1 => FlowType::U32,
            _ => unreachable!(),
        }
    }
}

#[derive(Clone, Copy, Debug, PartialEq)]
pub enum FlowSeqnum {
    U16(u16),
    U32(u32),
}

impl std::fmt::Display for FlowSeqnum {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        match self {
            Self::U16(v) => write!(f, "{}", v),
            Self::U32(v) => write!(f, "U32[{}]", v),
        }
    }
}

#[derive(Clone, Copy, Debug, PartialEq)]
pub struct Flow {
    pub flow: u8,
    pub seqnum: FlowSeqnum,
}

impl std::fmt::Display for Flow {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        write!(f, "Flow[{}]:{}", self.flow, self.seqnum)
    }
}

impl Codec for Flow {
    type Error = StdError;
    fn encoded_size(&self) -> usize {
        1 + 1
            + match self.seqnum {
                FlowSeqnum::U16(_) => 2,
                FlowSeqnum::U32(_) => 4,
            }
    }
    unsafe fn encode_in(&self, out: &mut [u8]) -> usize {
        out[0] |= (match self.seqnum {
            FlowSeqnum::U16(_) => FlowType::U16,
            FlowSeqnum::U32(_) => FlowType::U32,
        } as u8)
            << 7;
        out[1] = self.flow;

        let out = &mut out[2..];
        match self.seqnum {
            FlowSeqnum::U16(v) => {
                out[0..2].copy_from_slice(&v.to_be_bytes());
                2
            }
            FlowSeqnum::U32(v) => {
                out[0..4].copy_from_slice(&v.to_be_bytes());
                4
            }
        }
    }

    fn decode(out: &[u8]) -> Result<WithSize<Self>, WithOffset<Self::Error>> {
        if out.is_empty() {
            return Err(WithOffset::new_head(StdError::MissingBytes(1)));
        }
        let flow_type = FlowType::from(out[0] >> 7);
        let flow = out[1];
        let out = &out[2..];

        Ok(match flow_type {
            FlowType::U16 => {
                let mut bytes = [0; 2];
                bytes.copy_from_slice(&out[..2]);
                let value = u16::from_be_bytes(bytes);
                WithSize {
                    size: 4,
                    value: Flow {
                        flow,
                        seqnum: FlowSeqnum::U16(value),
                    },
                }
            }
            FlowType::U32 => {
                let mut bytes = [0; 4];
                bytes.copy_from_slice(&out[..4]);
                let value = u32::from_be_bytes(bytes);
                WithSize {
                    size: 6,
                    value: Flow {
                        flow,
                        seqnum: FlowSeqnum::U32(value),
                    },
                }
            }
        })
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn flow() {
        let flow = Flow {
            flow: 0x12,
            seqnum: FlowSeqnum::U16(0x1234),
        };
        let mut bytes = [0; 6];
        unsafe {
            flow.encode_in(&mut bytes);
        }
        let decoded = Flow::decode(&bytes).unwrap().value;
        assert_eq!(flow, decoded);

        let flow = Flow {
            flow: 0x34,
            seqnum: FlowSeqnum::U32(0x12345678),
        };
        let mut bytes = [0; 8];
        unsafe {
            flow.encode_in(&mut bytes);
        }
        let decoded = Flow::decode(&bytes).unwrap().value;
        assert_eq!(flow, decoded);

        let raw = "36 FD 0004";
        let raw = hex::decode(raw.replace(' ', "")).unwrap();
        let decoded = Flow::decode(&raw).unwrap().value;
        assert_eq!(
            decoded,
            Flow {
                flow: 0xFD,
                seqnum: FlowSeqnum::U16(0x0004)
            }
        );
    }
}