docspec_http/metrics/
mod.rs

1//! Prometheus metrics for the `docspec-http` server.
2//!
3//! Each pod exposes its own `/metrics` endpoint. The Prometheus server
4//! scrapes each pod independently — no aggregation happens in-process.
5//!
6//! # Design
7//!
8//! This module owns all metric-name and label constants. Middleware (see
9//! [`middleware`]) records values; this module only declares and describes
10//! them. Call [`install_global`] once at startup before accepting requests,
11//! then mount the closure returned by [`metrics_handler`] at `/metrics`.
12
13pub mod middleware;
14
15use axum::http::header::CONTENT_TYPE;
16use metrics::{describe_counter, describe_histogram};
17use metrics_exporter_prometheus::{
18    BuildError, Matcher, PrometheusBuilder, PrometheusHandle, PrometheusRecorder,
19};
20
21// ─── Metric-name constants ─────────────────────────────────────────────────
22
23/// Counter: total number of HTTP requests received.
24pub const METRIC_HTTP_REQUESTS_TOTAL: &str = "docspec_http_requests_total";
25
26/// Histogram: HTTP request latency in seconds.
27pub const METRIC_HTTP_REQUEST_DURATION_SECONDS: &str = "docspec_http_request_duration_seconds";
28
29/// Histogram: HTTP request body size in bytes.
30pub const METRIC_HTTP_REQUEST_BODY_BYTES: &str = "docspec_http_request_body_bytes";
31
32/// Counter: total number of document conversions.
33pub const METRIC_CONVERSIONS_TOTAL: &str = "docspec_conversions_total";
34
35/// Histogram: document conversion duration in seconds.
36pub const METRIC_CONVERSION_DURATION_SECONDS: &str = "docspec_conversion_duration_seconds";
37
38/// Histogram: document conversion output size in bytes.
39pub const METRIC_CONVERSION_OUTPUT_BYTES: &str = "docspec_conversion_output_bytes";
40
41// ─── Label key constants ───────────────────────────────────────────────────
42
43/// Label key for the HTTP request method (GET, POST, …).
44pub const LABEL_METHOD: &str = "method";
45
46/// Label key for the matched route path pattern.
47pub const LABEL_PATH: &str = "path";
48
49/// Label key for the HTTP response status code.
50pub const LABEL_STATUS: &str = "status";
51
52/// Label key for the conversion outcome category.
53pub const LABEL_RESULT: &str = "result";
54
55/// Label key for the error class when a conversion fails.
56pub const LABEL_ERROR_CLASS: &str = "error_class";
57
58/// Label key for the input MIME type of the conversion request.
59pub const LABEL_INPUT_MIME_TYPE: &str = "input_mime_type";
60
61/// Label key for the output MIME type produced by the conversion.
62pub const LABEL_OUTPUT_MIME_TYPE: &str = "output_mime_type";
63
64// ─── Label value constants ─────────────────────────────────────────────────
65
66/// Value for [`LABEL_PATH`] when no route was matched by the router.
67pub const PATH_UNKNOWN: &str = "unknown";
68
69/// Value for [`LABEL_RESULT`] when a conversion succeeds.
70pub const RESULT_SUCCESS: &str = "success";
71
72/// Value for [`LABEL_RESULT`] when a conversion fails due to a client error.
73pub const RESULT_CLIENT_ERROR: &str = "client_error";
74
75/// Value for [`LABEL_RESULT`] when a conversion fails due to a server error.
76pub const RESULT_SERVER_ERROR: &str = "server_error";
77
78/// Value for [`LABEL_ERROR_CLASS`] when no error occurred.
79pub const ERROR_CLASS_NONE: &str = "none";
80
81/// Value for [`LABEL_INPUT_MIME_TYPE`] when the Content-Type header was absent.
82///
83/// This is a label sentinel, not a real MIME type. Real MIME types live in
84/// [`crate::mime`].
85pub const INPUT_MIME_NONE: &str = "none";
86
87/// Value for [`LABEL_INPUT_MIME_TYPE`] when the Content-Type header was present
88/// but not a supported reader format.
89///
90/// This is a label sentinel, not a real MIME type. Real MIME types live in
91/// [`crate::mime`].
92pub const INPUT_MIME_UNSUPPORTED: &str = "unsupported";
93
94/// Value for [`LABEL_OUTPUT_MIME_TYPE`] when no output was produced (any error path).
95///
96/// This is a label sentinel, not a real MIME type. Real MIME types live in
97/// [`crate::mime`].
98pub const OUTPUT_MIME_NONE: &str = "none";
99
100// ─── Histogram bucket arrays ───────────────────────────────────────────────
101
102/// Latency histogram buckets for HTTP request duration, in seconds.
103pub const HTTP_LATENCY_BUCKETS: [f64; 11] = [
104    0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1.0, 2.5, 5.0, 10.0,
105];
106
107/// Body-size histogram buckets for HTTP request bodies, in bytes.
108pub const HTTP_BODY_SIZE_BUCKETS: [f64; 12] = [
109    100.0, 200.0, 400.0, 800.0, 1_600.0, 3_200.0, 6_400.0, 12_800.0, 25_600.0, 51_200.0, 102_400.0,
110    204_800.0,
111];
112
113/// Latency histogram buckets for document conversion duration, in seconds.
114///
115/// Shares the same breakpoints as [`HTTP_LATENCY_BUCKETS`].
116pub const CONVERSION_DURATION_BUCKETS: [f64; 11] = HTTP_LATENCY_BUCKETS;
117
118/// Size histogram buckets for conversion output bytes.
119///
120/// Shares the same breakpoints as [`HTTP_BODY_SIZE_BUCKETS`] for symmetry
121/// between request body size and conversion output size in dashboards.
122pub const CONVERSION_OUTPUT_BYTES_BUCKETS: [f64; 12] = HTTP_BODY_SIZE_BUCKETS;
123
124// ─── Recorder builder ──────────────────────────────────────────────────────
125
126fn configure_buckets(builder: PrometheusBuilder) -> Result<PrometheusBuilder, BuildError> {
127    builder
128        .set_buckets_for_metric(
129            Matcher::Full(METRIC_HTTP_REQUEST_DURATION_SECONDS.to_owned()),
130            &HTTP_LATENCY_BUCKETS,
131        )?
132        .set_buckets_for_metric(
133            Matcher::Full(METRIC_HTTP_REQUEST_BODY_BYTES.to_owned()),
134            &HTTP_BODY_SIZE_BUCKETS,
135        )?
136        .set_buckets_for_metric(
137            Matcher::Full(METRIC_CONVERSION_DURATION_SECONDS.to_owned()),
138            &CONVERSION_DURATION_BUCKETS,
139        )?
140        .set_buckets_for_metric(
141            Matcher::Full(METRIC_CONVERSION_OUTPUT_BYTES.to_owned()),
142            &CONVERSION_OUTPUT_BYTES_BUCKETS,
143        )
144}
145
146/// Builds a configured [`PrometheusRecorder`] and its [`PrometheusHandle`]
147/// **without** installing it globally.
148///
149/// Use this in tests together with [`metrics::with_local_recorder`] to keep
150/// test runs isolated from one another and from the global recorder.
151///
152/// # Errors
153///
154/// Returns [`BuildError`] when bucket values are empty or otherwise invalid.
155#[inline]
156pub fn build_recorder() -> Result<(PrometheusRecorder, PrometheusHandle), BuildError> {
157    let recorder = configure_buckets(PrometheusBuilder::new())?.build_recorder();
158    let handle = recorder.handle();
159    Ok((recorder, handle))
160}
161
162/// Installs the Prometheus recorder globally and registers HELP text for every
163/// metric.
164///
165/// Call **once** at server startup before accepting requests. Returns the
166/// [`PrometheusHandle`] needed to scrape the `/metrics` endpoint.
167///
168/// # Errors
169///
170/// Returns [`BuildError`] when bucket configuration or recorder installation
171/// fails (e.g., a global recorder is already installed).
172#[inline]
173pub fn install_global() -> Result<PrometheusHandle, BuildError> {
174    let handle = configure_buckets(PrometheusBuilder::new())?.install_recorder()?;
175
176    describe_counter!(METRIC_HTTP_REQUESTS_TOTAL, "Total HTTP requests received.");
177    describe_histogram!(
178        METRIC_HTTP_REQUEST_DURATION_SECONDS,
179        "HTTP request latency in seconds."
180    );
181    describe_histogram!(
182        METRIC_HTTP_REQUEST_BODY_BYTES,
183        "HTTP request body size in bytes, labeled by input MIME type."
184    );
185    describe_counter!(
186        METRIC_CONVERSIONS_TOTAL,
187        "Total document conversions, labeled by result, error class, and input/output MIME type."
188    );
189    describe_histogram!(
190        METRIC_CONVERSION_DURATION_SECONDS,
191        "Document conversion duration in seconds, labeled by result and input/output MIME type."
192    );
193    describe_histogram!(
194        METRIC_CONVERSION_OUTPUT_BYTES,
195        "Document conversion output size in bytes (recorded only on successful conversions), labeled by input/output MIME type."
196    );
197
198    Ok(handle)
199}
200
201// ─── Metrics endpoint handler ──────────────────────────────────────────────
202
203/// Returns a clone-safe handler closure that renders Prometheus metrics as an
204/// HTTP response with the correct Content-Type.
205///
206/// Mount the returned closure at `/metrics`. The response Content-Type is
207/// `text/plain; version=0.0.4; charset=utf-8` as required by the Prometheus
208/// exposition format specification.
209#[inline]
210pub fn metrics_handler(
211    handle: PrometheusHandle,
212) -> impl Fn() -> core::future::Ready<axum::response::Response> + Clone + Send + 'static {
213    move || {
214        let output = handle.render();
215        core::future::ready(
216            axum::http::Response::builder()
217                .header(CONTENT_TYPE, "text/plain; version=0.0.4; charset=utf-8")
218                .body(axum::body::Body::from(output))
219                .unwrap_or_else(|_| {
220                    let mut response = axum::response::Response::new(axum::body::Body::from(
221                        "failed to render metrics response",
222                    ));
223                    *response.status_mut() = axum::http::StatusCode::INTERNAL_SERVER_ERROR;
224                    response
225                }),
226        )
227    }
228}
229
230#[cfg(test)]
231mod handler_tests {
232    #![allow(
233        clippy::tests_outside_test_module,
234        clippy::unwrap_used,
235        clippy::expect_used
236    )]
237
238    use super::*;
239    use axum::body::to_bytes;
240
241    #[tokio::test]
242    async fn metrics_handler_returns_200() {
243        let (recorder, handle) = build_recorder().expect("test recorder builds");
244        let result = metrics::with_local_recorder(&recorder, || {
245            let handler = metrics_handler(handle);
246            handler()
247        });
248        let response = result.await;
249        assert_eq!(response.status(), axum::http::StatusCode::OK);
250    }
251
252    #[tokio::test]
253    async fn metrics_handler_content_type_is_prometheus_text() {
254        let (recorder, handle) = build_recorder().expect("test recorder builds");
255        let result = metrics::with_local_recorder(&recorder, || {
256            let handler = metrics_handler(handle);
257            handler()
258        });
259        let response = result.await;
260        let content_type = response
261            .headers()
262            .get(axum::http::header::CONTENT_TYPE)
263            .expect("content-type header present")
264            .to_str()
265            .expect("content-type is valid str");
266        assert_eq!(content_type, "text/plain; version=0.0.4; charset=utf-8");
267    }
268
269    #[tokio::test]
270    async fn metrics_handler_body_is_valid_utf8() {
271        let (recorder, handle) = build_recorder().expect("test recorder builds");
272        let result = metrics::with_local_recorder(&recorder, || {
273            let handler = metrics_handler(handle);
274            handler()
275        });
276        let response = result.await;
277        let body_bytes = to_bytes(response.into_body(), usize::MAX)
278            .await
279            .expect("body readable");
280        let _body_str = String::from_utf8(body_bytes.to_vec()).expect("body is valid UTF-8");
281    }
282}
docspec_http/metrics/mod.rs

docspec_http/metrics/
mod.rs
