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

use std::cell::RefCell;
use std::fmt::{self, Write};
use std::str;
use std::time::{Duration, SystemTime};

#[cfg(feature = "http2")]
use http::header::HeaderValue;
use httpdate::HttpDate;

// "Sun, 06 Nov 1994 08:49:37 GMT".len()
pub(crate) const DATE_VALUE_LENGTH: usize = 29;

#[cfg(feature = "http1")]
pub(crate) fn extend(dst: &mut Vec<u8>) {
    CACHED.with(|cache| {
        dst.extend_from_slice(cache.borrow().buffer());
    })
}

#[cfg(feature = "http1")]
pub(crate) fn update() {
    CACHED.with(|cache| {
        cache.borrow_mut().check();
    })
}

#[cfg(feature = "http2")]
pub(crate) fn update_and_header_value() -> HeaderValue {
    CACHED.with(|cache| {
        let mut cache = cache.borrow_mut();
        cache.check();
        cache.header_value.clone()
    })
}

struct CachedDate {
    bytes: [u8; DATE_VALUE_LENGTH],
    pos: usize,
    #[cfg(feature = "http2")]
    header_value: HeaderValue,
    next_update: SystemTime,
}

thread_local!(static CACHED: RefCell<CachedDate> = RefCell::new(CachedDate::new()));

impl CachedDate {
    fn new() -> Self {
        let mut cache = CachedDate {
            bytes: [0; DATE_VALUE_LENGTH],
            pos: 0,
            #[cfg(feature = "http2")]
            header_value: HeaderValue::from_static(""),
            next_update: SystemTime::now(),
        };
        cache.update(cache.next_update);
        cache
    }

    fn buffer(&self) -> &[u8] {
        &self.bytes[..]
    }

    fn check(&mut self) {
        let now = SystemTime::now();
        if now > self.next_update {
            self.update(now);
        }
    }

    fn update(&mut self, now: SystemTime) {
        self.render(now);
        self.next_update = now + Duration::new(1, 0);
    }

    fn render(&mut self, now: SystemTime) {
        self.pos = 0;
        let _ = write!(self, "{}", HttpDate::from(now));
        debug_assert!(self.pos == DATE_VALUE_LENGTH);
        self.render_http2();
    }

    #[cfg(feature = "http2")]
    fn render_http2(&mut self) {
        self.header_value = HeaderValue::from_bytes(self.buffer())
            .expect("Date format should be valid HeaderValue");
    }

    #[cfg(not(feature = "http2"))]
    fn render_http2(&mut self) {}
}

impl fmt::Write for CachedDate {
    fn write_str(&mut self, s: &str) -> fmt::Result {
        let len = s.len();
        self.bytes[self.pos..self.pos + len].copy_from_slice(s.as_bytes());
        self.pos += len;
        Ok(())
    }
}

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

    #[cfg(feature = "nightly")]
    use test::Bencher;

    #[test]
    fn test_date_len() {
        assert_eq!(DATE_VALUE_LENGTH, "Sun, 06 Nov 1994 08:49:37 GMT".len());
    }

    #[cfg(feature = "nightly")]
    #[bench]
    fn bench_date_check(b: &mut Bencher) {
        let mut date = CachedDate::new();
        // cache the first update
        date.check();

        b.iter(|| {
            date.check();
        });
    }

    #[cfg(feature = "nightly")]
    #[bench]
    fn bench_date_render(b: &mut Bencher) {
        let mut date = CachedDate::new();
        let now = SystemTime::now();
        date.render(now);
        b.bytes = date.buffer().len() as u64;

        b.iter(|| {
            date.render(now);
            test::black_box(&date);
        });
    }
}