Task 1.12: Structured Logging

Summary

Implement structured logging system for buylater.email with different log levels, proper formatting, and configurable output to improve debugging and operational monitoring.

Motivation

Following Let’s Go Chapter 3.2, we need to replace basic log.Println() calls with a structured logging system that provides better visibility into application behavior and makes debugging easier in production.

Acceptance Criteria

Create separate loggers for different types of messages (info, error)
Implement structured log message formatting with timestamps
Add log levels (INFO, ERROR, WARN) with proper filtering
Configure log output destinations (stdout, stderr, files)
Add contextual logging throughout the application
Implement request logging for HTTP requests
Add configuration for log level and output format
Update all existing logging to use structured format
Add operational logging for key application events

Technical Requirements

Logger Structure

type application struct {
    config config
    logger struct {
        info  *log.Logger
        error *log.Logger
    }
    serviceName string
}

Implementation Details

Use Go’s standard log package with custom configuration
Create separate loggers for different message types
Implement consistent log message formatting
Add request ID tracking for better traceability
Include relevant context in all log messages
Configure log prefixes and formatting flags

Dependencies

Task 1.11 completed (configuration management foundation)

Testing Strategy

Unit Tests

Test logger initialization and configuration
Verify log message formatting and output
Test different log levels and filtering

Integration Tests

Log messages appear in correct output streams
Request logging captures all HTTP requests
Error logging works for all error conditions

Manual Testing

Start application and verify startup logging
Make HTTP requests and check request logs
Trigger errors and verify error logging format
Test different log level configurations
Verify log output goes to correct destinations

Definition of Done

All acceptance criteria met
All specified tests pass
Code follows project conventions (go fmt, go vet)
Logging system is consistent throughout application
Log messages are informative and properly formatted
No remaining uses of basic log.Println()
Human verification completed successfully
Git commit created with proper message format

Implementation Notes

Approach

Replace ad-hoc logging with a structured system that provides clear, consistent, and useful log messages for both development and production operations.

Key Files to Modify

cmd/web/main.go - Initialize structured loggers
cmd/web/handlers.go - Update all logging calls
Add request logging middleware (prepare for future middleware)

Log Message Categories

INFO: Application startup, configuration, normal operations
ERROR: Application errors, HTTP errors, template errors
REQUEST: HTTP request details (method, path, response code, duration)

Log Message Format

2025/07/24 10:30:45 INFO  Starting server on http://localhost:4000
2025/07/24 10:30:46 ERROR Template parsing failed: template not found
2025/07/24 10:30:47 INFO  Request: GET / -> 200 OK (15ms)

Potential Risks

Log volume could impact performance
Log formatting changes might break log parsing tools
Missing error context could reduce debugging effectiveness

Success Metrics

Professional logging system that provides clear visibility into buylater.email application behavior with structured, consistent, and useful log messages for operations and debugging.

Blocks: Future monitoring, alerting, and operational tools
Blocked by: Task 3.1 (needs configuration system)
Related: Error handling, monitoring, and debugging

Implementation Log

Implementation details will be recorded here during development.

Final Verification

Human Tester: [Name]
Date Completed: [YYYY-MM-DD]
Verification Result: [Pass/Fail]
Notes: [Any issues found or additional observations]

task_id: “1.12” title: “Structured Logging” status: “pending” priority: “high” estimated_effort: “medium” created: “2025-07-24” assigned_to: “pair” related_rfds: “RFD 004”