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 request was text/markdown (current sole supported reader).
82pub const INPUT_MIME_MARKDOWN: &str = "text/markdown";
83
84/// Value for [`LABEL_INPUT_MIME_TYPE`] when the Content-Type header was present but not a supported reader format.
85pub const INPUT_MIME_UNSUPPORTED: &str = "unsupported";
86
87/// Value for [`LABEL_INPUT_MIME_TYPE`] when the Content-Type header was absent.
88pub const INPUT_MIME_NONE: &str = "none";
89
90/// Value for [`LABEL_OUTPUT_MIME_TYPE`] when the conversion produced `BlockNote` JSON.
91pub const OUTPUT_MIME_BLOCKNOTE: &str = "application/vnd.docspec.blocknote+json";
92
93/// Value for [`LABEL_OUTPUT_MIME_TYPE`] when the conversion produced `oxa.dev` JSON.
94pub const OUTPUT_MIME_OXA: &str = "application/vnd.oxa+json";
95
96/// Value for [`LABEL_OUTPUT_MIME_TYPE`] when no output was produced (any error path).
97pub const OUTPUT_MIME_NONE: &str = "none";
98
99// ─── Histogram bucket arrays ───────────────────────────────────────────────
100
101/// Latency histogram buckets for HTTP request duration, in seconds.
102pub const HTTP_LATENCY_BUCKETS: [f64; 11] = [
103    0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1.0, 2.5, 5.0, 10.0,
104];
105
106/// Body-size histogram buckets for HTTP request bodies, in bytes.
107pub const HTTP_BODY_SIZE_BUCKETS: [f64; 12] = [
108    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,
109    204_800.0,
110];
111
112/// Latency histogram buckets for document conversion duration, in seconds.
113///
114/// Shares the same breakpoints as [`HTTP_LATENCY_BUCKETS`].
115pub const CONVERSION_DURATION_BUCKETS: [f64; 11] = HTTP_LATENCY_BUCKETS;
116
117/// Size histogram buckets for conversion output bytes.
118///
119/// Shares the same breakpoints as [`HTTP_BODY_SIZE_BUCKETS`] for symmetry
120/// between request body size and conversion output size in dashboards.
121pub const CONVERSION_OUTPUT_BYTES_BUCKETS: [f64; 12] = HTTP_BODY_SIZE_BUCKETS;
122
123// ─── Recorder builder ──────────────────────────────────────────────────────
124
125fn configure_buckets(builder: PrometheusBuilder) -> Result<PrometheusBuilder, BuildError> {
126    builder
127        .set_buckets_for_metric(
128            Matcher::Full(METRIC_HTTP_REQUEST_DURATION_SECONDS.to_owned()),
129            &HTTP_LATENCY_BUCKETS,
130        )?
131        .set_buckets_for_metric(
132            Matcher::Full(METRIC_HTTP_REQUEST_BODY_BYTES.to_owned()),
133            &HTTP_BODY_SIZE_BUCKETS,
134        )?
135        .set_buckets_for_metric(
136            Matcher::Full(METRIC_CONVERSION_DURATION_SECONDS.to_owned()),
137            &CONVERSION_DURATION_BUCKETS,
138        )?
139        .set_buckets_for_metric(
140            Matcher::Full(METRIC_CONVERSION_OUTPUT_BYTES.to_owned()),
141            &CONVERSION_OUTPUT_BYTES_BUCKETS,
142        )
143}
144
145/// Builds a configured [`PrometheusRecorder`] and its [`PrometheusHandle`]
146/// **without** installing it globally.
147///
148/// Use this in tests together with [`metrics::with_local_recorder`] to keep
149/// test runs isolated from one another and from the global recorder.
150///
151/// # Errors
152///
153/// Returns [`BuildError`] when bucket values are empty or otherwise invalid.
154#[inline]
155pub fn build_recorder() -> Result<(PrometheusRecorder, PrometheusHandle), BuildError> {
156    let recorder = configure_buckets(PrometheusBuilder::new())?.build_recorder();
157    let handle = recorder.handle();
158    Ok((recorder, handle))
159}
160
161/// Installs the Prometheus recorder globally and registers HELP text for every
162/// metric.
163///
164/// Call **once** at server startup before accepting requests. Returns the
165/// [`PrometheusHandle`] needed to scrape the `/metrics` endpoint.
166///
167/// # Errors
168///
169/// Returns [`BuildError`] when bucket configuration or recorder installation
170/// fails (e.g., a global recorder is already installed).
171#[inline]
172pub fn install_global() -> Result<PrometheusHandle, BuildError> {
173    let handle = configure_buckets(PrometheusBuilder::new())?.install_recorder()?;
174
175    describe_counter!(METRIC_HTTP_REQUESTS_TOTAL, "Total HTTP requests received.");
176    describe_histogram!(
177        METRIC_HTTP_REQUEST_DURATION_SECONDS,
178        "HTTP request latency in seconds."
179    );
180    describe_histogram!(
181        METRIC_HTTP_REQUEST_BODY_BYTES,
182        "HTTP request body size in bytes, labeled by input MIME type."
183    );
184    describe_counter!(
185        METRIC_CONVERSIONS_TOTAL,
186        "Total document conversions, labeled by result, error class, and input/output MIME type."
187    );
188    describe_histogram!(
189        METRIC_CONVERSION_DURATION_SECONDS,
190        "Document conversion duration in seconds, labeled by result and input/output MIME type."
191    );
192    describe_histogram!(
193        METRIC_CONVERSION_OUTPUT_BYTES,
194        "Document conversion output size in bytes (recorded only on successful conversions), labeled by input/output MIME type."
195    );
196
197    Ok(handle)
198}
199
200// ─── Metrics endpoint handler ──────────────────────────────────────────────
201
202/// Returns a clone-safe handler closure that renders Prometheus metrics as an
203/// HTTP response with the correct Content-Type.
204///
205/// Mount the returned closure at `/metrics`. The response Content-Type is
206/// `text/plain; version=0.0.4; charset=utf-8` as required by the Prometheus
207/// exposition format specification.
208#[inline]
209pub fn metrics_handler(
210    handle: PrometheusHandle,
211) -> impl Fn() -> core::future::Ready<axum::response::Response> + Clone + Send + 'static {
212    move || {
213        let output = handle.render();
214        core::future::ready(
215            axum::http::Response::builder()
216                .header(CONTENT_TYPE, "text/plain; version=0.0.4; charset=utf-8")
217                .body(axum::body::Body::from(output))
218                .unwrap_or_else(|_| {
219                    let mut response = axum::response::Response::new(axum::body::Body::from(
220                        "failed to render metrics response",
221                    ));
222                    *response.status_mut() = axum::http::StatusCode::INTERNAL_SERVER_ERROR;
223                    response
224                }),
225        )
226    }
227}
228
229#[cfg(test)]
230mod handler_tests {
231    #![allow(
232        clippy::tests_outside_test_module,
233        clippy::unwrap_used,
234        clippy::expect_used
235    )]
236
237    use super::*;
238    use axum::body::to_bytes;
239
240    #[tokio::test]
241    async fn metrics_handler_returns_200() {
242        let (recorder, handle) = build_recorder().expect("test recorder builds");
243        let result = metrics::with_local_recorder(&recorder, || {
244            let handler = metrics_handler(handle);
245            handler()
246        });
247        let response = result.await;
248        assert_eq!(response.status(), axum::http::StatusCode::OK);
249    }
250
251    #[tokio::test]
252    async fn metrics_handler_content_type_is_prometheus_text() {
253        let (recorder, handle) = build_recorder().expect("test recorder builds");
254        let result = metrics::with_local_recorder(&recorder, || {
255            let handler = metrics_handler(handle);
256            handler()
257        });
258        let response = result.await;
259        let content_type = response
260            .headers()
261            .get(axum::http::header::CONTENT_TYPE)
262            .expect("content-type header present")
263            .to_str()
264            .expect("content-type is valid str");
265        assert_eq!(content_type, "text/plain; version=0.0.4; charset=utf-8");
266    }
267
268    #[tokio::test]
269    async fn metrics_handler_body_is_valid_utf8() {
270        let (recorder, handle) = build_recorder().expect("test recorder builds");
271        let result = metrics::with_local_recorder(&recorder, || {
272            let handler = metrics_handler(handle);
273            handler()
274        });
275        let response = result.await;
276        let body_bytes = to_bytes(response.into_body(), usize::MAX)
277            .await
278            .expect("body readable");
279        let _body_str = String::from_utf8(body_bytes.to_vec()).expect("body is valid UTF-8");
280    }
281}
docspec_http/metrics/mod.rs

docspec_http/metrics/
mod.rs
