Cadence

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An extensible Statsd client for Rust!

Statsd is a network server that listens for metrics (things like counters and timers) sent over UDP and sends aggregates of these metrics to a backend service of some kind (often Graphite).

Cadence is a client written in Rust for interacting with a Statsd server. You might want to emit metrics (using Cadence, sending them to a Statsd server) in your Rust server application.

For example, if you are running a Rust web service you might want to record:

Cadence is a flexible and easy way to do this!

Features

Install

To make use of Cadence in your project, add it as a dependency in your Cargo.toml file.

toml [dependencies] cadence = "x.y.z"

Then, link to it in your library or application.

``` rust,no_run // bin.rs or lib.rs extern crate cadence;

// rest of your library or application ```

Usage

Some examples of how to use Cadence are shown below.

Simple Use

Simple usage of Cadence is shown below. In this example, we just import the client, create an instance that will write to some imaginary metrics server, and send a few metrics.

``` rust,norun // Import the client. use cadence::prelude::*; use cadence::{StatsdClient, UdpMetricSink, DEFAULTPORT};

// Create client that will write to the given host over UDP. // // Note that you'll probably want to actually handle any errors creating // the client when you use it for real in your application. We're just // using .unwrap() here since this is an example! let host = ("metrics.example.com", DEFAULTPORT); let client = StatsdClient::::fromudp_host( "my.metrics", host).unwrap();

// Emit metrics! client.incr("some.counter"); client.time("some.methodCall", 42); client.gauge("some.thing", 7); client.meter("some.value", 5); ```

Counted, Timed, Gauged, Metered, and MetricClient Traits

Each of the methods that the Cadence StatsdClient struct uses to send metrics are implemented as a trait. There is also a trait that combines all of these other traits. If we want, we can just use one of the trait types to refer to the client instance. This might be useful to you if you'd like to swap out the actual Cadence client with a dummy version when you are unit testing your code or want to abstract away all the implementation details of the client being used behind a trait and pointer.

Each of these traits are exported in the prelude module. They are also available in the main module but aren't typically used like that.

``` rust,norun use cadence::prelude::*; use cadence::{StatsdClient, UdpMetricSink, DEFAULTPORT};

pub struct User { id: u64, username: String, email: String }

// Here's a simple DAO (Data Access Object) that doesn't do anything but // uses a metric client to keep track of the number of times the // 'getUserById' method gets called. pub struct MyUserDao { metrics: Box }

impl MyUserDao { // Create a new instance that will use the StatsdClient pub fn new(metrics: T) -> MyUserDao { MyUserDao { metrics: Box::new(metrics) } }

/// Get a new user by their ID
pub fn get_user_by_id(&self, id: u64) -> Option<User> {
    self.metrics.incr("getUserById");
    None
}

}

// Create a new Statsd client that writes to "metrics.example.com" let host = ("metrics.example.com", DEFAULTPORT); let metrics = StatsdClient::::fromudp_host( "counter.example", host).unwrap();

// Create a new instance of the DAO that will use the client let dao = MyUserDao::new(metrics);

// Try to lookup a user by ID! match dao.getuserby_id(123) { Some(u) => println!("Found a user!"), None => println!("No user!") }; ```

Custom Metric Sinks

The Cadence StatsdClient uses implementations of the MetricSink trait to send metrics to a metric server. Most users of the Candence library probably want to use the UdpMetricSink implementation. This is the way people typically interact with a Statsd server, sending packets over UDP.

However, maybe you'd like to do something custom: use a thread pool, send multiple metrics at the same time, or something else. An example of creating a custom sink is below.

``` rust,norun use std::io; use cadence::prelude::*; use cadence::{StatsdClient, MetricSink, DEFAULTPORT};

pub struct MyMetricSink;

impl MetricSink for MyMetricSink { fn emit(&self, metric: &str) -> io::Result { // Your custom metric sink implementation goes here! Ok(0) } }

let sink = MyMetricSink; let client = StatsdClient::from_sink("my.prefix", sink);

client.count("my.counter.thing", 42); client.time("my.method.time", 25); client.incr("some.other.counter"); ```

Custom UDP Socket

Most users of the Cadence StatsdClient will be using it to send metrics over a UDP socket. If you need to customize the socket, for example you want to use the socket in blocking mode but set a write timeout, you can do that as demonstrated below.

``` rust,norun use std::net::UdpSocket; use std::time::Duration; use cadence::prelude::*; use cadence::{StatsdClient, UdpMetricSink, DEFAULTPORT};

let socket = UdpSocket::bind("0.0.0.0:0").unwrap(); socket.setwritetimeout(Some(Duration::from_millis(1))).unwrap();

let host = ("metrics.example.com", DEFAULTPORT); let sink = UdpMetricSink::from(host, socket).unwrap(); let client = StatsdClient::fromsink("my.prefix", sink);

client.count("my.counter.thing", 29); client.time("my.service.call", 214); client.incr("some.event"); ```

Documentation

The documentation is available at https://tshlabs.github.io/cadence/

Source

The source code is available on GitHub at https://github.com/tshlabs/cadence

Changes

Release notes for Cadence can be found in the CHANGES.md file.

Development

Cadence uses Cargo for performing various development tasks.

To build Cadence:

$ cargo build

To run tests:

$ cargo test

or:

$ cargo test -- --ignored

To run benchmarks:

$ cargo bench

To build documentation:

$ cargo doc

License

Licensed under either of * Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0) * MIT license (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 shall be dual licensed as above, without any additional terms or conditions.