Logging Registry (`logging`, `logging/slog`)

Import: github.com/matiasmartin-labs/common-fwk/logging

Purpose

Deterministic named logger registry backed by log/slog. Each logger is scoped by name and applies root/per-logger config precedence deterministically.

Logger Interface

type Logger interface {
    Debugf(format string, args ...any)
    Infof(format string, args ...any)
    Warnf(format string, args ...any)
    Errorf(format string, args ...any)
}

Access via Application

logger, err := application.GetLogger("auth")

Error semantics

Condition	Error
`UseConfig` not called	`logging.ErrLoggingNotReady`
Empty name	`logging.ErrLoggerNameRequired`

Determinism guarantee

Same logger name on the same Application instance always returns the same Logger instance. Logger caches are isolated per Application.

Config Keys

logging:
  enabled: true
  level: info      # debug | info | warn | error
  format: json     # json | text
  loggers:
    auth:
      enabled: true
      level: debug
    billing:
      enabled: false

Env overrides

COMMON_FWK_LOGGING_ENABLED=true
COMMON_FWK_LOGGING_LEVEL=warn
COMMON_FWK_LOGGING_FORMAT=json
COMMON_FWK_LOGGING_LOGGERS_AUTH_ENABLED=true
COMMON_FWK_LOGGING_LOGGERS_AUTH_LEVEL=debug

Precedence Matrix

Setting	Resolution
`enabled`	per-logger override → root
`level`	per-logger override → root
`format`	root only (no per-logger override)

Output Contract

Every accepted log record includes these fields:

Field	Description
`logger`	Logger name
`ts`	Timestamp
`level`	Effective level
`msg`	Message

Both json and text formats include all four fields.

Loki Integration Guidance

Use a collector-first approach:

Ship logs via Promtail or OpenTelemetry Collector → Loki.
Do not couple the app directly to a Loki HTTP sink.
Preserve structured fields (logger, ts, level, msg) through the transport pipeline.
Configure parser rules in Promtail/OTel to match the json format emitted by this registry.

Logging Registry (logging, logging/slog)