der/asn1/
utc_time.rs

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
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
//! ASN.1 `UTCTime` support.

use crate::{
    datetime::{self, DateTime},
    ord::OrdIsValueOrd,
    DecodeValue, EncodeValue, Error, ErrorKind, FixedTag, Header, Length, Reader, Result, Tag,
    Writer,
};
use core::time::Duration;

#[cfg(feature = "std")]
use std::time::SystemTime;

/// ASN.1 `UTCTime` type.
///
/// This type implements the validity requirements specified in
/// [RFC 5280 Section 4.1.2.5.1][1], namely:
///
/// > For the purposes of this profile, UTCTime values MUST be expressed in
/// > Greenwich Mean Time (Zulu) and MUST include seconds (i.e., times are
/// > `YYMMDDHHMMSSZ`), even where the number of seconds is zero.  Conforming
/// > systems MUST interpret the year field (`YY`) as follows:
/// >
/// > - Where `YY` is greater than or equal to 50, the year SHALL be
/// >   interpreted as `19YY`; and
/// > - Where `YY` is less than 50, the year SHALL be interpreted as `20YY`.
///
/// Note: Due to common operations working on `UNIX_EPOCH` [`UtcTime`]s are
/// only supported for the years 1970-2049.
///
/// [1]: https://tools.ietf.org/html/rfc5280#section-4.1.2.5.1
#[derive(Copy, Clone, Debug, Eq, PartialEq, PartialOrd, Ord)]
pub struct UtcTime(DateTime);

impl UtcTime {
    /// Length of an RFC 5280-flavored ASN.1 DER-encoded [`UtcTime`].
    pub const LENGTH: usize = 13;

    /// Maximum year that can be represented as a `UTCTime`.
    pub const MAX_YEAR: u16 = 2049;

    /// Create a [`UtcTime`] from a [`DateTime`].
    pub fn from_date_time(datetime: DateTime) -> Result<Self> {
        if datetime.year() <= UtcTime::MAX_YEAR {
            Ok(Self(datetime))
        } else {
            Err(Self::TAG.value_error())
        }
    }

    /// Convert this [`UtcTime`] into a [`DateTime`].
    pub fn to_date_time(&self) -> DateTime {
        self.0
    }

    /// Create a new [`UtcTime`] given a [`Duration`] since `UNIX_EPOCH`
    /// (a.k.a. "Unix time")
    pub fn from_unix_duration(unix_duration: Duration) -> Result<Self> {
        DateTime::from_unix_duration(unix_duration)?.try_into()
    }

    /// Get the duration of this timestamp since `UNIX_EPOCH`.
    pub fn to_unix_duration(&self) -> Duration {
        self.0.unix_duration()
    }

    /// Instantiate from [`SystemTime`].
    #[cfg(feature = "std")]
    pub fn from_system_time(time: SystemTime) -> Result<Self> {
        DateTime::try_from(time)
            .map_err(|_| Self::TAG.value_error())?
            .try_into()
    }

    /// Convert to [`SystemTime`].
    #[cfg(feature = "std")]
    pub fn to_system_time(&self) -> SystemTime {
        self.0.to_system_time()
    }
}

impl_any_conversions!(UtcTime);

impl<'a> DecodeValue<'a> for UtcTime {
    fn decode_value<R: Reader<'a>>(reader: &mut R, header: Header) -> Result<Self> {
        if Self::LENGTH != usize::try_from(header.length)? {
            return Err(Self::TAG.value_error());
        }

        let mut bytes = [0u8; Self::LENGTH];
        reader.read_into(&mut bytes)?;

        match bytes {
            // RFC 5280 requires mandatory seconds and Z-normalized time zone
            [year1, year2, mon1, mon2, day1, day2, hour1, hour2, min1, min2, sec1, sec2, b'Z'] => {
                let year = u16::from(datetime::decode_decimal(Self::TAG, year1, year2)?);
                let month = datetime::decode_decimal(Self::TAG, mon1, mon2)?;
                let day = datetime::decode_decimal(Self::TAG, day1, day2)?;
                let hour = datetime::decode_decimal(Self::TAG, hour1, hour2)?;
                let minute = datetime::decode_decimal(Self::TAG, min1, min2)?;
                let second = datetime::decode_decimal(Self::TAG, sec1, sec2)?;

                // RFC 5280 rules for interpreting the year
                let year = if year >= 50 {
                    year.checked_add(1900)
                } else {
                    year.checked_add(2000)
                }
                .ok_or(ErrorKind::DateTime)?;

                DateTime::new(year, month, day, hour, minute, second)
                    .map_err(|_| Self::TAG.value_error())
                    .and_then(|dt| Self::from_unix_duration(dt.unix_duration()))
            }
            _ => Err(Self::TAG.value_error()),
        }
    }
}

impl EncodeValue for UtcTime {
    fn value_len(&self) -> Result<Length> {
        Self::LENGTH.try_into()
    }

    fn encode_value(&self, writer: &mut impl Writer) -> Result<()> {
        let year = match self.0.year() {
            y @ 1950..=1999 => y.checked_sub(1900),
            y @ 2000..=2049 => y.checked_sub(2000),
            _ => return Err(Self::TAG.value_error()),
        }
        .and_then(|y| u8::try_from(y).ok())
        .ok_or(ErrorKind::DateTime)?;

        datetime::encode_decimal(writer, Self::TAG, year)?;
        datetime::encode_decimal(writer, Self::TAG, self.0.month())?;
        datetime::encode_decimal(writer, Self::TAG, self.0.day())?;
        datetime::encode_decimal(writer, Self::TAG, self.0.hour())?;
        datetime::encode_decimal(writer, Self::TAG, self.0.minutes())?;
        datetime::encode_decimal(writer, Self::TAG, self.0.seconds())?;
        writer.write_byte(b'Z')
    }
}

impl FixedTag for UtcTime {
    const TAG: Tag = Tag::UtcTime;
}

impl OrdIsValueOrd for UtcTime {}

impl From<&UtcTime> for UtcTime {
    fn from(value: &UtcTime) -> UtcTime {
        *value
    }
}

impl From<UtcTime> for DateTime {
    fn from(utc_time: UtcTime) -> DateTime {
        utc_time.0
    }
}

impl From<&UtcTime> for DateTime {
    fn from(utc_time: &UtcTime) -> DateTime {
        utc_time.0
    }
}

impl TryFrom<DateTime> for UtcTime {
    type Error = Error;

    fn try_from(datetime: DateTime) -> Result<Self> {
        Self::from_date_time(datetime)
    }
}

impl TryFrom<&DateTime> for UtcTime {
    type Error = Error;

    fn try_from(datetime: &DateTime) -> Result<Self> {
        Self::from_date_time(*datetime)
    }
}

#[cfg(feature = "std")]
impl From<UtcTime> for SystemTime {
    fn from(utc_time: UtcTime) -> SystemTime {
        utc_time.to_system_time()
    }
}

// Implement by hand because the derive would create invalid values.
// Use the conversion from DateTime to create a valid value.
// The DateTime type has a way bigger range of valid years than UtcTime,
// so the DateTime year is mapped into a valid range to throw away less inputs.
#[cfg(feature = "arbitrary")]
impl<'a> arbitrary::Arbitrary<'a> for UtcTime {
    fn arbitrary(u: &mut arbitrary::Unstructured<'a>) -> arbitrary::Result<Self> {
        const MIN_YEAR: u16 = 1970;
        const VALID_YEAR_COUNT: u16 = UtcTime::MAX_YEAR - MIN_YEAR + 1;
        const AVERAGE_SECONDS_IN_YEAR: u64 = 31_556_952;

        let datetime = DateTime::arbitrary(u)?;
        let year = datetime.year();
        let duration = datetime.unix_duration();

        // Clamp the year into a valid range to not throw away too much input
        let valid_year = (year.saturating_sub(MIN_YEAR))
            .rem_euclid(VALID_YEAR_COUNT)
            .saturating_add(MIN_YEAR);
        let year_to_remove = year.saturating_sub(valid_year);
        let valid_duration = duration
            - Duration::from_secs(
                u64::from(year_to_remove).saturating_mul(AVERAGE_SECONDS_IN_YEAR),
            );

        Self::from_date_time(DateTime::from_unix_duration(valid_duration).expect("supported range"))
            .map_err(|_| arbitrary::Error::IncorrectFormat)
    }

    fn size_hint(depth: usize) -> (usize, Option<usize>) {
        DateTime::size_hint(depth)
    }
}

#[cfg(test)]
mod tests {
    use super::UtcTime;
    use crate::{Decode, Encode, SliceWriter};
    use hex_literal::hex;

    #[test]
    fn round_trip_vector() {
        let example_bytes = hex!("17 0d 39 31 30 35 30 36 32 33 34 35 34 30 5a");
        let utc_time = UtcTime::from_der(&example_bytes).unwrap();
        assert_eq!(utc_time.to_unix_duration().as_secs(), 673573540);

        let mut buf = [0u8; 128];
        let mut encoder = SliceWriter::new(&mut buf);
        utc_time.encode(&mut encoder).unwrap();
        assert_eq!(example_bytes, encoder.finish().unwrap());
    }
}