units = nanosecond or billionth of a secondA simple log and trace formatter with a structured json output, it flattens events from nested spans, overriding parent fields.
The tracing crate is difficult to understand initially, this crate is designed to be as easy to use as possible with sensible defaults and configuration options. The only two crates you'll need in your Cargo.toml are:
toml
[dependencies]
tracing = "0.1"
traceon = "0.1"
For pretty printing the output like the examples below, install jq and run commands like:
bash
cargo run | jq -R 'fromjson?'
By default env-filter is used at the info level, to change the level you can set an environment variable e.g. RUST_LOG=warn, all the options are detailed here
The extra fields outputted below are defaults that can be turned off:
rust
fn main() {
traceon::on();
tracing::info!("a simple message");
}
json
{
"message": "a simple message",
"level": 30,
"time": "2022-12-27T10:16:24.570889Z",
"file": "src/main.rs:14"
}
Log levels are converted to numbers by default:
text
trace: 10
debug: 20
info: 30
warn: 40
error: 50
If you're using normal functions or async, you can use the tracing::instrument macro to capture the parameters for each function call:
```rust
async fn add(a: i32, b: i32) { tracing::info!("result: {}", a + b); }
async fn main() { traceon::on(); add(5, 10).await; } ```
json
{
"message": "result: 15",
"level": 30,
"time": "2022-12-27T10:48:56.957671Z",
"span": "add",
"file": "src/main.rs:3",
"a": 5,
"b": 10
}
If you need to add some additional context to an async function, you can create a span and instrument it: ```rust use tracing::Instrument;
async fn add(a: i32, b: i32) { tracing::info!("result: {}", a + b); }
async fn main() { traceon::on(); let span = tracing::infospan!("math functions", packagename = env!("CARGOPKGNAME")); add(5, 10).instrument(span).await; } ```
json
{
"message": "result: 15",
"level": 30,
"time": "2022-12-27T11:11:25.540256Z",
"span": "math functions",
"file": "src/main.rs:4",
"package_name": "testing_traceon"
}
The above package_name comes from the environment variable provided by cargo, which gets it from Cargo.toml:
toml
[package]
name = "testing_traceon"
IMPORTANT! for async functions only ever use the above two methods, which are the #[instrument] macro, and Instrument trait. The guard detailed below should not be used across async boundaries.
To combine the output from the two examples above we can enter a span with the arguments added to the trace: ```rust use tracing::Instrument;
async fn add(a: i32, b: i32) {
// Important! Don't put any .await calls in between entered() and exit()
let span = tracing::info_span!("add", a, b).entered();
tracing::info!("result: {}", a + b);
span.exit();
}
async fn main() { traceon::on(); let span = tracing::infospan!("math functions", packagename = env!("CARGOPKGNAME")); add(5, 10).instrument(span).await; } ```
json
{
"message": "result: 15",
"level": 30,
"time": "2022-12-27T11:18:46.805758Z",
"span": "add",
"file": "src/main.rs:5",
"b": 10,
"package_name": "testing_traceon",
"a": 5
}
You can see above that the nested "span": "add" overrode the parent "span": "math functions"
The add function from above could be rewritten like this:
rust
async fn add(a: i32, b: i32) {
let _span = tracing::info_span!("add", a, b).entered();
tracing::info!("result: {}", a + b);
}
This will cause the span to exit at the end of the function when _span is dropped, just remember to be very careful not to put any .await points when an EnteredSpan like _span above is being held.
This is an example of changing all the defaults fields to their opposites:
```rust use traceon::LevelFormat;
mod helpers { pub fn trace() { tracing::info!("in helpers module"); } }
fn main() { traceon::builder() .module(true) .span(false) .file(false) .time(false) .level(LevelFormat::Off) .on();
tracing::info!("only the module and message");
helpers::trace();
}
json
{
"message": "only the module and message",
"module": "bootstrap"
}
{
"message": "in helpers module",
"module": "bootstrap::helpers"
}
``
This was using a Cargo.toml with the binary renamed tobootstrap` for demonstration purposes:
toml
[[bin]]
name = "bootstrap"
path = "src/main.rs"
If you wanted to write to log files instead of std, it's as simple adding the dependency to Cargo.toml:
toml
[dependencies]
tracing-appender = "0.2.2"
And initializing it via the builder:
rust
fn main() {
let file_appender = tracing_appender::rolling::hourly("./", "test.log");
traceon::builder().writer(file_appender).on();
tracing::info!("wow cool!");
}
You can also use the formatting and storage layer with other tracing layers as you get more comfortable with the tracing ecosystem, e.g. to change the filter:
```rust use traceon::Traceon; use tracing_subscriber::{prelude::*, EnvFilter};
fn main() { tracing_subscriber::registry() .with(Traceon::default()) .with(EnvFilter::new("error")) .init();
tracing::info!("info log message won't write to stdout");
tracing::error!("only error messages will write to stdout");
} ```
This crate uses the idea originated from: LukeMathWalker/tracing-bunyan-formatter of storing fields from visited spans in a HashMap instead of a BTreeMap which is more suited for flattening fields, and results in very similar performance to the json formatter in tracing-subcriber:
logging to a sink
units = nanosecond or billionth of a second
logging to stdout
units = microsecond or millionth of a second