This crate adds support for **external logs**, and for statistics tracking through those logs, to the [`slog`](https://github.com/slog-rs/slog/) ecosystem.

This crate was written by Metaswitch Networks (@Metaswitch) and made freely available under the [Apache License](LICENSE.md).
[Contributions](CONTRIBUTING.md) are welcome.

# Overview

**External logs** are logs that form an external API that end users can rely on, and that do not change without explicit agreement. Using them allows
you to treat logs as objects, rather than strings with metadata, allowing compile-time checking of logs.

This repository provides the following.
 - An API for easily defining external logs.
 - An API for defining statistic values to track, and to modify them based on the external logs
 - A `StatisticsLogger` type that wraps an `slog::Logger`, which handles logging and updating tracked stats.
 - An `xlog!` macro for making the logs through the `StatisticsLogger`.
 - An API for retrieving the current values of all stats from the `StatisticsLogger`.

# Use of this crate

In theory, an external log can be defined simply by making any type implement `ExtLoggable`.  In practice, external logs will be generated by auto-deriving the `ExtLoggable` trait using the `slog-extlog-derive` crate from this repository.

Logs can then be generated by using the `xlog!` macro to make the logs using a `StatisticsLogger` - a wrapper around `slog::Logger` which can also track stats.

For more details, see:
 - the Rust [documentation](https://docs.rs/slog-extlog)
 - the [basic tests](slog-extlog-derive/tests/loggable.rs) for logging examples
 - the [stats tests](tests/stats_extlog.rs) for examples with metrics and statistics tracking.