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 (current sole supported writer).
91pub const OUTPUT_MIME_BLOCKNOTE: &str = "application/vnd.docspec.blocknote+json";
92
93/// Value for [`LABEL_OUTPUT_MIME_TYPE`] when no output was produced (any error path).
94pub const OUTPUT_MIME_NONE: &str = "none";
95
96// ─── Histogram bucket arrays ───────────────────────────────────────────────
97
98/// Latency histogram buckets for HTTP request duration, in seconds.
99pub const HTTP_LATENCY_BUCKETS: [f64; 11] = [
100    0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1.0, 2.5, 5.0, 10.0,
101];
102
103/// Body-size histogram buckets for HTTP request bodies, in bytes.
104pub const HTTP_BODY_SIZE_BUCKETS: [f64; 12] = [
105    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,
106    204_800.0,
107];
108
109/// Latency histogram buckets for document conversion duration, in seconds.
110///
111/// Shares the same breakpoints as [`HTTP_LATENCY_BUCKETS`].
112pub const CONVERSION_DURATION_BUCKETS: [f64; 11] = HTTP_LATENCY_BUCKETS;
113
114/// Size histogram buckets for conversion output bytes.
115///
116/// Shares the same breakpoints as [`HTTP_BODY_SIZE_BUCKETS`] for symmetry
117/// between request body size and conversion output size in dashboards.
118pub const CONVERSION_OUTPUT_BYTES_BUCKETS: [f64; 12] = HTTP_BODY_SIZE_BUCKETS;
119
120// ─── Recorder builder ──────────────────────────────────────────────────────
121
122fn configure_buckets(builder: PrometheusBuilder) -> Result<PrometheusBuilder, BuildError> {
123    builder
124        .set_buckets_for_metric(
125            Matcher::Full(METRIC_HTTP_REQUEST_DURATION_SECONDS.to_owned()),
126            &HTTP_LATENCY_BUCKETS,
127        )?
128        .set_buckets_for_metric(
129            Matcher::Full(METRIC_HTTP_REQUEST_BODY_BYTES.to_owned()),
130            &HTTP_BODY_SIZE_BUCKETS,
131        )?
132        .set_buckets_for_metric(
133            Matcher::Full(METRIC_CONVERSION_DURATION_SECONDS.to_owned()),
134            &CONVERSION_DURATION_BUCKETS,
135        )?
136        .set_buckets_for_metric(
137            Matcher::Full(METRIC_CONVERSION_OUTPUT_BYTES.to_owned()),
138            &CONVERSION_OUTPUT_BYTES_BUCKETS,
139        )
140}
141
142/// Builds a configured [`PrometheusRecorder`] and its [`PrometheusHandle`]
143/// **without** installing it globally.
144///
145/// Use this in tests together with [`metrics::with_local_recorder`] to keep
146/// test runs isolated from one another and from the global recorder.
147///
148/// # Errors
149///
150/// Returns [`BuildError`] when bucket values are empty or otherwise invalid.
151#[inline]
152pub fn build_recorder() -> Result<(PrometheusRecorder, PrometheusHandle), BuildError> {
153    let recorder = configure_buckets(PrometheusBuilder::new())?.build_recorder();
154    let handle = recorder.handle();
155    Ok((recorder, handle))
156}
157
158/// Installs the Prometheus recorder globally and registers HELP text for every
159/// metric.
160///
161/// Call **once** at server startup before accepting requests. Returns the
162/// [`PrometheusHandle`] needed to scrape the `/metrics` endpoint.
163///
164/// # Errors
165///
166/// Returns [`BuildError`] when bucket configuration or recorder installation
167/// fails (e.g., a global recorder is already installed).
168#[inline]
169pub fn install_global() -> Result<PrometheusHandle, BuildError> {
170    let handle = configure_buckets(PrometheusBuilder::new())?.install_recorder()?;
171
172    describe_counter!(METRIC_HTTP_REQUESTS_TOTAL, "Total HTTP requests received.");
173    describe_histogram!(
174        METRIC_HTTP_REQUEST_DURATION_SECONDS,
175        "HTTP request latency in seconds."
176    );
177    describe_histogram!(
178        METRIC_HTTP_REQUEST_BODY_BYTES,
179        "HTTP request body size in bytes, labeled by input MIME type."
180    );
181    describe_counter!(
182        METRIC_CONVERSIONS_TOTAL,
183        "Total document conversions, labeled by result, error class, and input/output MIME type."
184    );
185    describe_histogram!(
186        METRIC_CONVERSION_DURATION_SECONDS,
187        "Document conversion duration in seconds, labeled by result and input/output MIME type."
188    );
189    describe_histogram!(
190        METRIC_CONVERSION_OUTPUT_BYTES,
191        "Document conversion output size in bytes (recorded only on successful conversions), labeled by input/output MIME type."
192    );
193
194    Ok(handle)
195}
196
197// ─── Metrics endpoint handler ──────────────────────────────────────────────
198
199/// Returns a clone-safe handler closure that renders Prometheus metrics as an
200/// HTTP response with the correct Content-Type.
201///
202/// Mount the returned closure at `/metrics`. The response Content-Type is
203/// `text/plain; version=0.0.4; charset=utf-8` as required by the Prometheus
204/// exposition format specification.
205#[inline]
206pub fn metrics_handler(
207    handle: PrometheusHandle,
208) -> impl Fn() -> core::future::Ready<axum::response::Response> + Clone + Send + 'static {
209    move || {
210        let output = handle.render();
211        core::future::ready(
212            axum::http::Response::builder()
213                .header(CONTENT_TYPE, "text/plain; version=0.0.4; charset=utf-8")
214                .body(axum::body::Body::from(output))
215                .unwrap_or_else(|_| {
216                    let mut response = axum::response::Response::new(axum::body::Body::from(
217                        "failed to render metrics response",
218                    ));
219                    *response.status_mut() = axum::http::StatusCode::INTERNAL_SERVER_ERROR;
220                    response
221                }),
222        )
223    }
224}
225
226#[cfg(test)]
227mod handler_tests {
228    #![allow(
229        clippy::tests_outside_test_module,
230        clippy::unwrap_used,
231        clippy::expect_used
232    )]
233
234    use super::*;
235    use axum::body::to_bytes;
236
237    #[tokio::test]
238    async fn metrics_handler_returns_200() {
239        let (recorder, handle) = build_recorder().expect("test recorder builds");
240        let result = metrics::with_local_recorder(&recorder, || {
241            let handler = metrics_handler(handle);
242            handler()
243        });
244        let response = result.await;
245        assert_eq!(response.status(), axum::http::StatusCode::OK);
246    }
247
248    #[tokio::test]
249    async fn metrics_handler_content_type_is_prometheus_text() {
250        let (recorder, handle) = build_recorder().expect("test recorder builds");
251        let result = metrics::with_local_recorder(&recorder, || {
252            let handler = metrics_handler(handle);
253            handler()
254        });
255        let response = result.await;
256        let content_type = response
257            .headers()
258            .get(axum::http::header::CONTENT_TYPE)
259            .expect("content-type header present")
260            .to_str()
261            .expect("content-type is valid str");
262        assert_eq!(content_type, "text/plain; version=0.0.4; charset=utf-8");
263    }
264
265    #[tokio::test]
266    async fn metrics_handler_body_is_valid_utf8() {
267        let (recorder, handle) = build_recorder().expect("test recorder builds");
268        let result = metrics::with_local_recorder(&recorder, || {
269            let handler = metrics_handler(handle);
270            handler()
271        });
272        let response = result.await;
273        let body_bytes = to_bytes(response.into_body(), usize::MAX)
274            .await
275            .expect("body readable");
276        let _body_str = String::from_utf8(body_bytes.to_vec()).expect("body is valid UTF-8");
277    }
278}
docspec_http/metrics/mod.rs

docspec_http/metrics/
mod.rs
