simple_logger

Documentation | GitHub

Enhanced logging facade for Eiffel with structured fields and JSON output. Wraps EiffelStudio's logging library with a cleaner API.

Overview

simple_logger provides a SIMPLE_LOGGER class that enhances Eiffel's LOG_LOGGING_FACILITY with:

• Structured logging - Key-value fields in log entries
• JSON output - Machine-parseable format for log aggregation
• Child loggers - Inherit context fields from parent
• Enter/exit tracing - Automatic indentation for call traces
• Duration logging - Built-in timer for operation timing

Installation

1. Clone the repository
2. Set environment variable (one-time setup for all simple_* libraries): SIMPLE_EIFFEL=D:\prod
3. Add to your ECF:

<library name="simple_logger" location="$SIMPLE_EIFFEL/simple_logger/simple_logger.ecf"/>

Dependencies

Library	Purpose	Environment Variable
simple_json	JSON output format	$SIMPLE_JSON

Quick Start

local
    log: SIMPLE_LOGGER
do
    -- Basic logging
    create log.make
    log.info ("Application started")
    log.warn ("Low disk space")
    log.error ("Connection failed")

    -- Change log level
    log.set_level (log.Level_debug)
    log.debug_log ("Verbose output")
end

Structured Logging

local
    log: SIMPLE_LOGGER
    fields: HASH_TABLE [ANY, STRING]
do
    create log.make

    -- With HASH_TABLE
    create fields.make (2)
    fields.put ("user123", "user_id")
    fields.put (42, "order_id")
    log.info_with ("Order processed", fields)
    -- Output: 2025-12-06 14:30:00 INFO Order processed user_id=user123 order_id=42

    -- With tuple array (convenience)
    log.info_fields ("Login successful", << ["user", "alice"], ["ip", "192.168.1.1"] >>)
end

JSON Output

local
    log: SIMPLE_LOGGER
do
    create log.make
    log.set_json_output (True)
    log.info ("Server started")
    -- Output: {"timestamp":"2025-12-06T14:30:00Z","level":"info","message":"Server started"}

    log.info_fields ("Request handled", << ["method", "GET"], ["path", "/api/users"], ["status", 200] >>)
    -- Output: {"timestamp":"2025-12-06T14:30:01Z","level":"info","message":"Request handled","method":"GET","path":"/api/users","status":200}
end

Child Loggers (Context Inheritance)

local
    log, request_log: SIMPLE_LOGGER
do
    create log.make

    -- Create child with request context
    request_log := log.child_with ("request_id", "req-abc-123")

    -- All logs from request_log include request_id
    request_log.info ("Processing request")
    -- Output: 2025-12-06 14:30:00 INFO Processing request request_id=req-abc-123

    request_log.info ("Request complete")
    -- Output: 2025-12-06 14:30:01 INFO Request complete request_id=req-abc-123
end

Enter/Exit Tracing

local
    log: SIMPLE_LOGGER
do
    create log.make_with_level ({SIMPLE_LOGGER}.Level_debug)
    log.enter ("process_order")
        log.info ("Validating order")
        log.enter ("calculate_total")
            log.debug_log ("Applying discount")
        log.exit ("calculate_total")
    log.exit ("process_order")
    -- Output with indentation showing call hierarchy
end

Duration Logging

local
    log: SIMPLE_LOGGER
    timer: SIMPLE_LOG_TIMER
do
    create log.make
    timer := log.start_timer

    -- Do some work
    process_data

    log.log_duration (timer, "Data processing complete")
    -- Output: 2025-12-06 14:30:01 INFO Data processing complete duration_ms=152
end

File Output

local
    log: SIMPLE_LOGGER
do
    -- Direct to file
    create log.make_to_file ("app.log")

    -- Or add file output to existing logger
    create log.make
    log.add_file_output ("app.log")

    log.info ("This goes to console AND file")
end

Log Levels

Level	Constant	Use Case
DEBUG	Level_debug	Verbose debugging information
INFO	Level_info	Normal operational messages
WARN	Level_warn	Warning conditions
ERROR	Level_error	Error conditions
FATAL	Level_fatal	System failure

API Summary

Creation

• make - Console output, INFO level
• make_with_level (level) - Console output, specified level
• make_to_file (path) - File output

Configuration

• set_level (level) - Change minimum log level
• set_json_output (enabled) - Enable/disable JSON format
• add_context (key, value) - Add persistent context field
• add_file_output (path) - Add file output

Logging

• debug_log (message), info (message), warn (message), error (message), fatal (message)
• *_with (message, fields) - With HASH_TABLE fields
• info_fields (message, tuples) - With tuple array

Context

• child (context) - Create child logger with context
• child_with (key, value) - Convenience for single field

Tracing

• enter (feature_name), exit (feature_name) - Call tracing

Timing

• start_timer - Create timer
• log_duration (timer, message) - Log with elapsed time

Integration with Eiffel Logging

simple_logger uses LOG_LOGGING_FACILITY internally, so it's compatible with existing Eiffel logging infrastructure. You get the enhanced API while keeping compatibility with the standard library.

License

MIT License - Copyright (c) 2024-2025, Larry Rix