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metrics: parse Prometheus text exposition with best practices #1611

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68 changes: 68 additions & 0 deletions Cargo.lock
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1 change: 1 addition & 0 deletions packages/metrics/Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,7 @@ version.workspace = true
[dependencies]
chrono = { version = "0", default-features = false, features = ["clock"] }
derive_more = { version = "2", features = ["constructor"] }
openmetrics-parser = "0.4.4"
serde = { version = "1", features = ["derive"] }
serde_json = "1.0.140"
thiserror = "2"
Expand Down
152 changes: 151 additions & 1 deletion packages/metrics/src/metric_collection/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -229,8 +229,138 @@ impl MetricCollection {

Ok(())
}

/// Parse a Prometheus exposition text (0.0.4 or OpenMetrics-compatible) into a MetricCollection.
/// This currently supports Counter and Gauge families. Other families will return UnsupportedPrometheusMetricType.
pub fn from_prometheus_text(input: &str, now: DurationSinceUnixEpoch) -> Result<Self, Error> {
use openmetrics_parser::prometheus::parse_prometheus;
use openmetrics_parser::{MetricNumber, MetricsExposition, PrometheusType, PrometheusValue};

let exposition: MetricsExposition<PrometheusType, PrometheusValue> =
parse_prometheus(input).map_err(|e| Error::PrometheusTextParse { message: e.to_string() })?;

let mut counters: HashMap<MetricName, Metric<Counter>> = HashMap::new();
let mut gauges: HashMap<MetricName, Metric<Gauge>> = HashMap::new();

for (family_name, family) in exposition.families {
match family.family_type {
PrometheusType::Counter => {
let mut metric = Metric::<Counter>::new(
MetricName::new(&family_name),
None,
if family.help.is_empty() { None } else { Some(MetricDescription::new(&family.help)) },
SampleCollection::default(),
);
for sample in family.into_iter_samples() {
// Build LabelSet from parser's labelset
let parser_label_set = sample
.get_labelset()
.map_err(|e| Error::PrometheusTextParse { message: e.to_string() })?;
let labels: Vec<(String, String)> = parser_label_set
.iter()
.map(|(k, v)| (k.to_string(), v.to_string()))
.collect();
let label_set: LabelSet = labels.into();

// Timestamp (prefer sample's, fallback to now)
let ts = sample.timestamp.and_then(|t| {
if t.is_finite() && t >= 0.0 {
let secs_f = t.trunc();
let frac = t - secs_f;
let secs = secs_f as u64;
let nanos = (frac * 1_000_000_000.0).round() as u32;
let (secs, nanos) = if nanos >= 1_000_000_000 { (secs + 1, nanos - 1_000_000_000) } else { (secs, nanos) };
Some(DurationSinceUnixEpoch::new(secs, nanos))
} else {
None
}
}).unwrap_or(now);

// Value
let value = match sample.value {
PrometheusValue::Counter(cv) => match cv.value {
MetricNumber::Int(i) if i >= 0 => i as u64,
MetricNumber::Float(f) if f.is_finite() && f >= 0.0 => f as u64,
_ => 0,
},
PrometheusValue::Unknown(_) => 0,
_ => {
return Err(Error::UnsupportedPrometheusMetricType {
metric_name: family_name.clone(),
metric_type: "counter(value-mismatch)".to_string(),
})
}
};

metric.absolute(&label_set, value, ts);
}
counters.insert(MetricName::new(&family_name), metric);
}
PrometheusType::Gauge => {
let mut metric = Metric::<Gauge>::new(
MetricName::new(&family_name),
None,
if family.help.is_empty() { None } else { Some(MetricDescription::new(&family.help)) },
SampleCollection::default(),
);
for sample in family.into_iter_samples() {
let parser_label_set = sample
.get_labelset()
.map_err(|e| Error::PrometheusTextParse { message: e.to_string() })?;
let labels: Vec<(String, String)> = parser_label_set
.iter()
.map(|(k, v)| (k.to_string(), v.to_string()))
.collect();
let label_set: LabelSet = labels.into();

// Timestamp (prefer sample's, fallback to now)
let ts = sample.timestamp.and_then(|t| {
if t.is_finite() && t >= 0.0 {
let secs_f = t.trunc();
let frac = t - secs_f;
let secs = secs_f as u64;
let nanos = (frac * 1_000_000_000.0).round() as u32;
let (secs, nanos) = if nanos >= 1_000_000_000 { (secs + 1, nanos - 1_000_000_000) } else { (secs, nanos) };
Some(DurationSinceUnixEpoch::new(secs, nanos))
} else {
None
}
}).unwrap_or(now);

let value = match sample.value {
PrometheusValue::Gauge(mn) => mn.as_f64(),
PrometheusValue::Unknown(_) => 0.0,
_ => {
return Err(Error::UnsupportedPrometheusMetricType {
metric_name: family_name.clone(),
metric_type: "gauge(value-mismatch)".to_string(),
})
}
};

metric.set(&label_set, value, ts);
}
gauges.insert(MetricName::new(&family_name), metric);
}
other => {
return Err(Error::UnsupportedPrometheusMetricType {
metric_name: family_name.clone(),
metric_type: format!("{other:?}"),
});
}
}
}

let counters = MetricKindCollection::new(counters.into_values().collect())
.map_err(|e| Error::PrometheusTextParse { message: e.to_string() })?;
let gauges = MetricKindCollection::new(gauges.into_values().collect())
.map_err(|e| Error::PrometheusTextParse { message: e.to_string() })?;

MetricCollection::new(counters, gauges)
}
}


#[derive(thiserror::Error, Debug, Clone)]
pub enum Error {
#[error("Metric names must be unique across all metrics types.")]
Expand All @@ -247,6 +377,12 @@ pub enum Error {

#[error("Cannot create metric with name '{metric_name}': another metric with this name already exists")]
MetricNameCollisionAdding { metric_name: MetricName },

#[error("Failed to parse Prometheus text: {message}")]
PrometheusTextParse { message: String },

#[error("Unsupported or unknown Prometheus metric type '{metric_type}' for metric '{metric_name}'")]
UnsupportedPrometheusMetricType { metric_name: String, metric_type: String },
}

/// Implements serialization for `MetricCollection`.
Expand Down Expand Up @@ -722,7 +858,21 @@ udp_tracker_server_performance_avg_announce_processing_time_ns{server_binding_ip
}

#[test]
fn it_should_allow_serializing_to_prometheus_format() {
fn it_should_allow_deserializing_from_prometheus_text() {
// Given the fixture's Prometheus exposition
let (expected_metric_collection, _expected_json, prometheus_text) = MetricCollectionFixture::default().deconstruct();
let time = DurationSinceUnixEpoch::from_secs(1_743_552_000);

// Only ensure a trailing newline for the parser
let with_trailing_newline = if prometheus_text.ends_with('\n') { prometheus_text } else { format!("{}\n", prometheus_text) };
let parsed = MetricCollection::from_prometheus_text(&with_trailing_newline, time).unwrap();

// Then it should match the fixture object
assert_eq!(parsed, expected_metric_collection);
}

#[test]
fn it_should_allow_serializing_to_prometheus_format_again() {
let (metric_collection, _expected_json, expected_prometheus) = MetricCollectionFixture::default().deconstruct();

let prometheus_output = metric_collection.to_prometheus();
Expand Down
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