Wrapped Gleam logger (which is a wrapper for the Erlang logger)

README.md

Original posting: lpil/logging#7 (comment)

Put

• main.gleam to src/, or use it in your own entrypoint.
• wrapped_logging_ffi.erl to src/

Then things should work. Run as

$ gleam run

It will produce the following output (the "INFO" will be colored; if you want uncolored, update the flag in the wrapper)

2025-08-15T11:29:03Z INFO Hello, Joe!

main.gleam

import gleam/erlang/process
import logging.{Info}

pub fn main() {
  logger_configure()

  logging.log(Info, "Hello, Joe!")
  process.sleep(100)
}

@external(erlang, "wrapped_logging_ffi", "configure")
pub fn logger_configure() -> Nil

wrapped_logging_ffi.erl

-module(wrapped_logging_ffi).
-export([configure/0, format/2]).


format(LogEvent, Config) ->
    Timestamp = calendar:system_time_to_rfc3339(erlang:system_time(second), [{unit, second}, {offset, "Z"}]),
    LogEventWithMeta = LogEvent#{meta => #{}},
    ExistingOutput = logging_ffi:format(LogEventWithMeta, Config),
    
    ActualString = case ExistingOutput of
        {string, Str} -> Str;
        Other -> Other
    end,
    
    iolist_to_binary([Timestamp, " ", ActualString]).

configure() ->
    logging_ffi:configure(),
    logger:update_handler_config(default, #{
        formatter => {wrapped_logging_ffi, #{colored => true}}
    }),
    nil.