# Open Metrics Client Library

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[Rust](https://github.com/rust-lang/) client library implementation of the [Open
Metrics specification](https://github.com/OpenObservability/OpenMetrics). Allows
developers to instrument applications and thus enables operators to monitor said
applications with monitoring systems like [Prometheus](https://prometheus.io/).

**Documentation**: https://docs.rs/open-metrics-client/

## Goals

- No `unsafe`. Don't use unsafe Rust within the library itself.

- Type safe. Leverage Rust's type system to catch common instrumentation
  mistakes at compile time.

- Fast. Don't force users to worry about the performance impact of
  instrumentation. Instead encourage users to instrument often and extensively.

## Specification Compliance

Below is a list of properties where this client library implementation lags
behind the Open Metrics specification. Not being compliant with all requirements
(`MUST` and `MUST NOT`) of the specification is considered a bug and likely to
be fixed in the future. Contributions in all forms are most welcome.

- State set metric.

- Enforce "A Histogram MetricPoint MUST contain at least one bucket".

- Enforce "A MetricFamily MUST have a [...] UNIT metadata".

- Enforce "MetricFamily names [...] MUST be unique within a MetricSet."

- Enforce "Names SHOULD be in snake_case".

- Enforce "MetricFamily names beginning with underscores are RESERVED and MUST
  NOT be used unless specified by this standard".

- Enforce "Exposers SHOULD avoid names that could be confused with the suffixes
  that text format sample metric names use".

- Protobuf wire format. (Follow [spec
  issue](https://github.com/OpenObservability/OpenMetrics/issues/183).)

- Gauge histogram metric.

- Allow "A MetricPoint in a Metric with the type [Counter, Histogram] SHOULD have a Timestamp
  value called Created".

- Summary metric.

## Related Libraries

- [rust-prometheus](https://github.com/tikv/rust-prometheus/): See [tikv/rust-prometheus/#392](https://github.com/tikv/rust-prometheus/issues/392) for a high-level comparison.

## License

Licensed under either of

 * Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0)
 * MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)

at your option.

#### Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in the work by you, as defined in the Apache-2.0 license, shall be
dual licensed as above, without any additional terms or conditions.