This crate implements a structured logging API similar to the one in Serilog. In systems programming, this style of logging is most often found in Windows' ETW. Web and distributed applications use similar techniques to improve machine-readabililty when dealing with large event volumes.
"Emitted" log events consist of a format and list of named properties, as in the eminfo!() call below.
```rust
extern crate emit;
use std::env; use emit::PipelineBuilder; use emit::collectors::seq;
fn main() { let flush = PipelineBuilder::new() .atlevel(emit::LogLevel::Info) .sendto(seq::SeqCollector::newlocal()) .init();
eminfo!("Hello, {}!", name: env::var("USERNAME").unwrap());
} ```
The named arguments are captured as key/value properties that can be rendered in a structured format such as JSON:
json
{
"@t": "2016-03-17T00:17:01Z",
"@mt": "Hello, {name}!",
"name": "nblumhardt",
"target": "web_we_are"
}
This makes log searches in an appropriate back-end collector much simpler:
Events can be written to io::stdout in a number of formats:
```rust use emit::collectors::stdio::StdioCollector; use formatters::text::PlainTextFormatter;
let flush = PipelineBuilder::new() .writeto(StdioCollector::new(PlainTextFormatter::new())) .init(); ```
Produces:
2016-03-24T05:03:36Z INFO Hello, "nblumhardt"!
What about the log crate?
The log!() macros are the established way to capture diagnostic events in Rust today. However, log destructively renders events into text:
rust
info!("Hello, {}!", env::var("USERNAME").unwrap());
There's no way for a log processing system to later pull the username value from this message, except through handwritten parsers/regular expressions.
The idea of emit is that rendering can happen at any point - but the original values are preserved for easy machine processing as well.
To keep these two worlds in harmony, emit will be able to mirror events to log (#7).