Crate rustler_logger 

Simplify logging from Rust to Elixir.

rustler provides fairly seamless integration between Rust and Elixir. However, Rust console output is emitted without much concern for what Elixir might be doing with the console. Notably, panic messages can be difficult to read when using iex. The lack of integration with Elixir’s logging infrastructure also leaves a hole in observability of tools built with rustler.

This crate provides some of this missing integration. You get…

• the log_to_elixir attribute that provides logging functionality in nifs
• the log! macro to actually emit log messages explicitly
• a panic handler that routes panic message to Elixir

Usage

1. Use the log_to_elixir attribute on nifs to enable logging.
2. Initialize logging with rustler_logger::log_init() (optional).
3. Use logging macros!

Example

use rustler::{nif, Env, Term};
use rustler_logger::{log, log_to_elixir};

#[log_to_elixir]
#[nif]
fn hello() {
  log!(
    "Hello, ~p! ~p items on your list labeled ~p",  // erlang-style format string
    "world", 42, "TODO",                            // format arguments
    user="bob", answer=420/10                       // log metadata
  );
}

// This is necessary to load the panic hook.
fn load(_env: Env, _term: Term) -> bool {
    rustler_logger::log_init();
    true
}

rustler::init!("Elixir.Your.Module", load = load);

Formatting

The log! macro accepts a format string and a list of arguments, similar to the format! macro, though the formatting is done by Elixir’s logger using the notation provided by OTP. It handles arguments of different types automatically and allows arbitrary expressions for values.

Metadata

Assignment statements can be used to add metadata for structured logging. The variable before the = will be turned into an atom to conform to Elixir’s convention for log message metadata.

Panic Handling

A panic hook is provided to emit a more detailed panic message to Elixir’s logger. It does not (currently) catch the panic, just resumes panicking.

Macros

alert

send an alert level log entry to the BEAM VM

critical

send a critical level log entry to the BEAM VM

debug

send a debug level log entry to the BEAM VM

emergency

send a emergency level log entry to the BEAM VM

error

send an error level log entry to the BEAM VM

fatal

send a fatal level log entry to the BEAM VM

info

send an info level log entry to the BEAM VM

log

send a log entry to the BEAM VM

notice

send a notice level log entry to the BEAM VM

trace

send a trace level log entry to the BEAM VM

warn

send a warning level log entry to the BEAM VM

warning

send a warning level log entry to the BEAM VM

Structs

Log

A structure to represent log messages.

Enums

LogLevel

An enumeration representing log levels.

Functions

log_init

Initialize Elixir logging.

Attribute Macros

log_to_elixir

wrapper for nif functions needed to set up logging to BEAM