pingora_cache/
variance.rs

1use std::{borrow::Cow, collections::BTreeMap};
2
3use blake2::Digest;
4
5use crate::key::{Blake2b128, HashBinary};
6
7/// A builder for variance keys, used for distinguishing multiple cached assets
8/// at the same URL. This is intended to be easily passed to helper functions,
9/// which can each populate a portion of the variance.
10pub struct VarianceBuilder<'a> {
11    values: BTreeMap<Cow<'a, str>, Cow<'a, [u8]>>,
12}
13
14impl<'a> VarianceBuilder<'a> {
15    /// Create an empty variance key. Has no variance by default - add some variance using
16    /// [`Self::add_value`].
17    pub fn new() -> Self {
18        VarianceBuilder {
19            values: BTreeMap::new(),
20        }
21    }
22
23    /// Add a byte string to the variance key. Not sensitive to insertion order.
24    /// `value` is intended to take either `&str` or `&[u8]`.
25    pub fn add_value(&mut self, name: &'a str, value: &'a (impl AsRef<[u8]> + ?Sized)) {
26        self.values
27            .insert(name.into(), Cow::Borrowed(value.as_ref()));
28    }
29
30    /// Move a byte string to the variance key. Not sensitive to insertion order. Useful when
31    /// writing helper functions which generate a value then add said value to the VarianceBuilder.
32    /// Without this, the helper function would have to move the value to the calling function
33    /// to extend its lifetime to at least match the VarianceBuilder.
34    pub fn add_owned_value(&mut self, name: &'a str, value: Vec<u8>) {
35        self.values.insert(name.into(), Cow::Owned(value));
36    }
37
38    /// Move String name and byte string value to the variance key. Not sensitive to insertion order.
39    /// Useful when both the name and value are generated at runtime.
40    pub fn add_owned_name_value(&mut self, name: String, value: Vec<u8>) {
41        self.values.insert(Cow::Owned(name), Cow::Owned(value));
42    }
43
44    /// Check whether this variance key actually has variance, or just refers to the root asset
45    pub fn has_variance(&self) -> bool {
46        !self.values.is_empty()
47    }
48
49    /// Hash this variance key. Returns [`None`] if [`Self::has_variance`] is false.
50    pub fn finalize(self) -> Option<HashBinary> {
51        const SALT: &[u8; 1] = &[0u8; 1];
52        if self.has_variance() {
53            let mut hash = Blake2b128::new();
54            for (name, value) in self.values.iter() {
55                hash.update(name.as_bytes());
56                hash.update(SALT);
57                hash.update(value);
58                hash.update(SALT);
59            }
60            Some(hash.finalize().into())
61        } else {
62            None
63        }
64    }
65}
66
67#[cfg(test)]
68mod test {
69    use super::*;
70
71    #[test]
72    fn test_basic() {
73        let key_empty = VarianceBuilder::new().finalize();
74        assert_eq!(None, key_empty);
75
76        let mut key_value = VarianceBuilder::new();
77        key_value.add_value("a", "a");
78        let key_value = key_value.finalize();
79
80        let mut key_owned_value = VarianceBuilder::new();
81        key_owned_value.add_owned_value("a", "a".as_bytes().to_vec());
82        let key_owned_value = key_owned_value.finalize();
83
84        assert_ne!(key_empty, key_value);
85        assert_ne!(key_empty, key_owned_value);
86        assert_eq!(key_value, key_owned_value);
87    }
88
89    #[test]
90    fn test_value_ordering() {
91        let mut key_abc = VarianceBuilder::new();
92        key_abc.add_value("a", "a");
93        key_abc.add_value("b", "b");
94        key_abc.add_value("c", "c");
95        let key_abc = key_abc.finalize().unwrap();
96
97        let mut key_bac = VarianceBuilder::new();
98        key_bac.add_value("b", "b");
99        key_bac.add_value("a", "a");
100        key_bac.add_value("c", "c");
101        let key_bac = key_bac.finalize().unwrap();
102
103        let mut key_cba = VarianceBuilder::new();
104        key_cba.add_value("c", "c");
105        key_cba.add_value("b", "b");
106        key_cba.add_value("a", "a");
107        let key_cba = key_cba.finalize().unwrap();
108
109        assert_eq!(key_abc, key_bac);
110        assert_eq!(key_abc, key_cba);
111    }
112
113    #[test]
114    fn test_value_overriding() {
115        let mut key_a = VarianceBuilder::new();
116        key_a.add_value("a", "a");
117        let key_a = key_a.finalize().unwrap();
118
119        let mut key_b = VarianceBuilder::new();
120        key_b.add_value("a", "b");
121        key_b.add_value("a", "a");
122        let key_b = key_b.finalize().unwrap();
123
124        assert_eq!(key_a, key_b);
125    }
126}
pingora_cache/variance.rs

pingora_cache/
variance.rs
