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

use core::{convert::TryInto, mem::size_of, ptr::slice_from_raw_parts, str::FromStr};

use scroll::{Pread, Pwrite};

// use alloc::borrow::ToOwned;

const GUID_STRING_LEN: usize = 36;
const GUID_SPLITTER: u8 = b'-';

// A GUID is a 128-bit integer (16 bytes) that can be
// used as a unique identifier.
#[repr(C)]
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, Pwrite, Pread)]
pub struct Guid {
    f0: u32,
    f1: u16,
    f2: u16,
    f3: [u8; 8],
}

#[derive(Debug)]
pub enum GuidParseError {
    InvalidInput,
}

impl Guid {
    // Create a GUID instance from several fields
    pub const fn from_fields(f0: u32, f1: u16, f2: u16, f3: [u8; 8]) -> Guid {
        Self { f0, f1, f2, f3 }
    }

    pub fn as_bytes(&self) -> &[u8; 16] {
        // Safe since the size of Guid is 16
        unsafe {
            (&*slice_from_raw_parts(self as *const Self as *const u8, size_of::<Self>()))
                .try_into()
                .unwrap()
        }
    }

    pub fn from_bytes(buffer: &[u8; 16]) -> Guid {
        let f0 = u32::from_le_bytes(buffer[0..4].try_into().unwrap());
        let f1 = u16::from_le_bytes(buffer[4..6].try_into().unwrap());
        let f2 = u16::from_le_bytes(buffer[6..8].try_into().unwrap());
        let mut f3: [u8; 8] = [0; 8];
        f3.copy_from_slice(&buffer[8..]);

        Self { f0, f1, f2, f3 }
    }
}

impl FromStr for Guid {
    type Err = GuidParseError;

    // Create a GUID instance from a string slice
    // Input should follow format strictly: "XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX"
    // For example: "F9168C5E-CEB2-4faa-B6BF-329BF39FA1E4"
    fn from_str(s: &str) -> Result<Self, Self::Err> {
        let b = s.as_bytes();
        if b.len() != GUID_STRING_LEN
            || b[8] != GUID_SPLITTER
            || b[13] != GUID_SPLITTER
            || b[18] != GUID_SPLITTER
            || b[23] != GUID_SPLITTER
        {
            return Err(GuidParseError::InvalidInput);
        }

        let parse_hex = |s: &str| -> Option<u64> {
            for c in s.as_bytes() {
                if !c.is_ascii_hexdigit() {
                    return None;
                }
            }
            u64::from_str_radix(s, 16).ok()
        };

        // Parse the string into fields
        let f0 = parse_hex(&s[0..8]).ok_or(GuidParseError::InvalidInput)? as u32;
        let f1 = parse_hex(&s[9..13]).ok_or(GuidParseError::InvalidInput)? as u16;
        let f2 = parse_hex(&s[14..18]).ok_or(GuidParseError::InvalidInput)? as u16;
        let mut f3 = parse_hex(&s[19..23]).ok_or(GuidParseError::InvalidInput)? << 48;
        f3 |= parse_hex(&s[24..36]).ok_or(GuidParseError::InvalidInput)?;

        // f3 is decoded from string so use big endian to encode into bytes
        Ok(Self {
            f0,
            f1,
            f2,
            f3: u64::to_be_bytes(f3),
        })
    }
}

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

    #[test]
    fn test_guid() {
        // F9168C5E-CEB2-4faa-B6BF-329BF39FA1E4
        let guid_bytes = [
            0x5E, 0x8C, 0x16, 0xF9, 0xB2, 0xCE, 0xaa, 0x4f, 0xB6, 0xBF, 0x32, 0x9B, 0xF3, 0x9F,
            0xA1, 0xE4,
        ];
        let guid_field = Guid::from_fields(
            0xF9168C5E,
            0xCEB2,
            0x4faa,
            [0xB6, 0xBF, 0x32, 0x9B, 0xF3, 0x9F, 0xA1, 0xE4],
        );

        assert_eq!(&guid_bytes, guid_field.as_bytes());

        let guid_str = Guid::from_str("F9168C5E-CEB2-4faa-B6BF-329BF39FA1E4").unwrap();
        assert_eq!(&guid_bytes, guid_str.as_bytes());

        let guid_str = Guid::from_str("F9168C5E");
        assert!(guid_str.is_err());

        let guid_str = Guid::from_str("F9168C5E-CEB2-4faa-B6BF-329");
        assert!(guid_str.is_err());

        let guid_str = Guid::from_str("F9168C5E-CEB2-4faaB6-BF-329BF39FA1E4");
        assert!(guid_str.is_err());

        let guid_str = Guid::from_str("+9168C5E-CEB2-4faa-B6BF-329BF39FA1E4");
        assert!(guid_str.is_err());

        let guid_str = Guid::from_str("F9168C5ECCEB2C4faaCB6BFC329BF39FA1E4");
        assert!(guid_str.is_err());
    }
}