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

//! Immutable storage of [`metric::Describable`].

use std::{collections::HashMap, sync::Arc};

use sealed::sealed;

use crate::{metric, Metric};

use super::KeyName;

/// Collection of [`Describable`] [`metric::Bundle`]s, stored in an immutable
/// [`Storage`].
///
/// [`Describable`]: metric::Describable
pub type Collection<M> = HashMap<KeyName, metric::Describable<M>>;

/// Snapshot of a [`mutable::Storage`], that is not capable of registering
/// metrics in a [`prometheus::Registry`] on the fly, but still allowing to
/// change their [`help` description] on the fly, once they were registered in
/// the [`mutable::Storage`] before snapshot.
///
/// In comparison with a [`metrics::Registry`], this immutable [`Storage`]
/// provides much less overhead of accessing an already registered metric (just
/// a simple [`HashMap`] lookup), however, is not capable of registering new
/// metrics on the fly.
///
/// [`metrics::Registry`]: metrics_util::registry::Registry
/// [`mutable::Storage`]: super::Mutable
/// [`help` description]: prometheus::proto::MetricFamily::get_help
#[derive(Debug)]
pub struct Storage {
    /// [`Collection`] of [`prometheus::IntCounter`] metrics registered in this
    /// immutable [`Storage`].
    counters: Collection<metric::PrometheusIntCounter>,

    /// [`Collection`] of [`prometheus::Gauge`] metrics registered in this
    /// immutable [`Storage`].
    gauges: Collection<metric::PrometheusGauge>,

    /// [`Collection`] of [`prometheus::Histogram`] metrics registered in this
    /// immutable [`Storage`].
    histograms: Collection<metric::PrometheusHistogram>,
}

#[sealed]
impl super::Get<Collection<metric::PrometheusIntCounter>> for Storage {
    fn collection(&self) -> &Collection<metric::PrometheusIntCounter> {
        &self.counters
    }
}

#[sealed]
impl super::Get<Collection<metric::PrometheusGauge>> for Storage {
    fn collection(&self) -> &Collection<metric::PrometheusGauge> {
        &self.gauges
    }
}

#[sealed]
impl super::Get<Collection<metric::PrometheusHistogram>> for Storage {
    fn collection(&self) -> &Collection<metric::PrometheusHistogram> {
        &self.histograms
    }
}

impl Storage {
    /// Changes the [`help` description] of the [`prometheus`] `M`etric
    /// identified by its `name`. No-op if this immutable [`Storage`] doesn't
    /// contain it.
    ///
    /// Accepts only the following [`prometheus`] `M`etrics:
    /// - [`prometheus::IntCounter`], [`prometheus::IntCounterVec`]
    /// - [`prometheus::Gauge`], [`prometheus::GaugeVec`]
    /// - [`prometheus::Histogram`], [`prometheus::HistogramVec`]
    ///
    /// Intended to be used in [`metrics::Recorder::describe_counter()`],
    /// [`metrics::Recorder::describe_gauge()`] and
    /// [`metrics::Recorder::describe_histogram()`] implementations.
    ///
    /// [`help` description]: prometheus::proto::MetricFamily::get_help
    pub fn describe<M>(&self, name: &str, description: String)
    where
        M: metric::Bundled,
        <M as metric::Bundled>::Bundle: metric::Bundle,
        Self: super::Get<Collection<<M as metric::Bundled>::Bundle>>,
    {
        use super::Get as _;

        if let Some(bundle) = self.collection().get(name) {
            bundle.description.store(Arc::new(description));
        };
    }

    /// Returns a [`prometheus`] `M`etric stored in this immutable [`Storage`]
    /// and identified by the provided [`metrics::Key`].
    ///
    /// Accepts only the following [`prometheus`] metrics:
    /// - [`prometheus::IntCounter`]
    /// - [`prometheus::Gauge`]
    /// - [`prometheus::Histogram`]
    ///
    /// Intended to be used in [`metrics::Recorder::register_counter()`],
    /// [`metrics::Recorder::register_gauge()`] and
    /// [`metrics::Recorder::register_histogram()`] implementations.
    ///
    /// # Errors
    ///
    /// If the identified [`prometheus`] `M`etric doesn't comply with the
    /// labeling of the provided [`metrics::Key`].
    pub fn get_metric<M>(
        &self,
        key: &metrics::Key,
    ) -> Option<Result<Metric<M>, prometheus::Error>>
    where
        M: metric::Bundled,
        <M as metric::Bundled>::Bundle: metric::Bundle<Single = M>,
        Self: super::Get<Collection<<M as metric::Bundled>::Bundle>>,
    {
        use super::Get as _;
        use metric::Bundle as _;

        self.collection().get(key.name()).map(|bundle| {
            bundle.metric.get_single_metric(key).map(Metric::wrap)
        })
    }
}

// PANIC: `RwLock` usage is fully panic-safe inside, so the `impl` is
//        infallible, in fact.
#[allow(clippy::fallible_impl_from)]
impl From<&super::mutable::Storage> for Storage {
    /// Creates a new immutable [`Storage`] by [draining] the referred
    /// [`mutable::Storage`] and leaving it empty.
    ///
    /// [`mutable::Storage`]: super::mutable::Storage
    /// [draining]: HashMap::drain
    fn from(mutable: &super::mutable::Storage) -> Self {
        // PANIC: `RwLock` usage is fully panic-safe here.
        #![allow(clippy::unwrap_used)]

        Self {
            counters: mutable
                .counters
                .write()
                .unwrap()
                .drain()
                .filter_map(|(name, bundle)| Some((name, bundle.transpose()?)))
                .collect(),
            gauges: mutable
                .gauges
                .write()
                .unwrap()
                .drain()
                .filter_map(|(name, bundle)| Some((name, bundle.transpose()?)))
                .collect(),
            histograms: mutable
                .histograms
                .write()
                .unwrap()
                .drain()
                .filter_map(|(name, bundle)| Some((name, bundle.transpose()?)))
                .collect(),
        }
    }
}