2 unstable releases

0.2.0 Jan 15, 2023
0.1.0 Sep 11, 2022

#337 in Debugging

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bunyarrs is a very opinionated, low performance logging library, modelled on node bunyan.

let logger = Bunyarr::with_name("my-module");

let foo = init_foo();
let bar = init_bar();

logger.info(vars! { foo, bar }, "initialisation complete");

Will print, to stdout, on one line (whitespace added for the docs):

  "msg":"initialisation complete",
  "foo": 5,
  "bar": {
    "baz": 5,
    "badger": "mushroom"


The default log level is info, so info or higher will be generated. This can be controlled with the environment variable LOG_LEVEL, for example, LOG_LEVEL=error will hide any debug, info, or warn logs, but still show error and fatal logs.


It's better than eprintln! and easier to get going with than slog.

This "bunyan" format is supported by a number of log ingest tools. Using it saves you from attempting to handle objects, multi-line strings and the like during your log search.

The library is designed to encourage good use of this format, specifically, there is no support for format strings, or dynamic strings at all, on purpose.

Other tools, such as the bunyan rust port and pino-pretty exist to turn these logs back into text, if you want to view them as text. Piping the above output through pino-pretty results in:

[16:19:33.166] INFO (my-module/1337): initialisation complete
    foo: 5
    bar: {
      "baz": 5,
      "badger": "mushroom"
    v: 0

I need support for...

Files, rotation? Nope. Write to stdout, it's well-supported by all orchestration tools.

Threads, performance? Nope. Use the slog ecosystem, and see their justification for the complexities.

Objects, naming? Use the serde ecosystem tools.

The existing rust-log ecosystem? Sorry, they use format strings, which is banned.

Custom formatters? Maybe you want to write your own vars! macro?

How slow is it?

Bunyarr::with_name() tries not to do work, e.g. it pre-loads the hostname.

logger.info() is probably more efficient than you building an object and writing it yourself, but probably less efficient than you writing out an object, and writing it yourself, if you're careful. Bunyarr tries to be very careful, but is not willing to sacrifice the interface for speed.

Should I use this in a rust library I want people to use?



cargo fmt, cargo test, github PRs or issues, please.


MIT OR Apache-2.0


~44K SLoC