Crate prometheus_extensions 

Prometheus extensions for richer metric collection.

This crate provides three utilities that complement the prometheus crate:

Type	Purpose
AggregateCounter	A CounterVec wrapper that automatically emits an extra unlabeled total alongside every per-label counter.
ScientificEncoder	A lightweight Prometheus text-format encoder that renders counter values in scientific notation (1.23E4) with a trailing comma after the last label — matching the format Kafka JMX exporters produce.
Sensor	A lock-free exponential moving average (EMA) gauge for tracking rates or throughput.

Quick start

use prometheus::Opts;
use prometheus::core::Collector;
use prometheus_extensions::{AggregateCounter, ScientificEncoder};

// 1. Create an aggregate counter
let counter = AggregateCounter::new(
    Opts::new("http_requests_total", "Total HTTP requests"),
    &["method"],
).unwrap();

counter.with_label_values(&["GET"]).inc_by(100.0);
counter.with_label_values(&["POST"]).inc_by(42.0);

// Collecting yields 3 metrics: the unlabeled total (142) plus the two labeled ones.
let families = counter.collect();
assert_eq!(families[0].get_metric().len(), 3);

// 2. Encode in Kafka-compatible scientific notation
let encoder = ScientificEncoder::new();
let mut buf = Vec::new();
encoder.encode(&families, &mut buf).unwrap();
let output = String::from_utf8(buf).unwrap();
assert!(output.contains("http_requests_total 1.4200000000E2"));

Sensor (EMA)

use prometheus_extensions::Sensor;

let sensor = Sensor::new(0.05); // alpha = 0.05
sensor.measure(100.0);
sensor.measure(200.0);
// EMA tracks the smoothed value
let value = sensor.get();
assert!(value > 0.0);

Structs

AggregateCounter

A Prometheus CounterVec wrapper that automatically produces an extra unlabeled aggregate metric (the sum of all label combinations) in addition to the per-label counters.

ScientificEncoder

A Prometheus text-format encoder that renders counter values in scientific notation ({:.10E}) and appends a trailing comma after the last label.

Sensor

A lock-free exponential moving average (EMA) gauge.