`pkg/logger`¶

A structured logging handler built on top of log/slog. It fans each record out to CLI, rotating files (via lumberjack), and syslog simultaneously, while enforcing context contracts such as type, application, and operation.

Quick Start¶

import (
    "context"
    "log/slog"
    mangolog "github.com/bitstep-ie/mango-go/pkg/logger"
)

func newLogger() *slog.Logger {
    cfg := &mangolog.LogConfig{
        MangoConfig: &mangolog.MangoConfig{
            Strict: true,
            CorrelationId: &mangolog.CorrelationIdConfig{
                Strict:       true,
                AutoGenerate: true,
            },
        },
        Out: &mangolog.OutConfig{
            Enabled: true,
            Cli: &mangolog.CliConfig{
                Enabled:  true,
                Friendly: true,
                Verbose:  false,
            },
            File: &mangolog.FileOutputConfig{
                Enabled:  true,
                Debug:    false,
                Path:     "/var/log/service.log",
                MaxSize:  50,
                Compress: true,
            },
        },
    }
    return slog.New(mangolog.NewMangoLogger(cfg))
}

func logExample(logger *slog.Logger) {
    ctx := context.Background()
    ctx = context.WithValue(ctx, mangolog.APPLICATION, "checkout-api")
    ctx = context.WithValue(ctx, mangolog.OPERATION, "cart-create")
    ctx = context.WithValue(ctx, mangolog.TYPE, mangolog.BusinessType)

    logger.InfoContext(ctx, "cart created",
        slog.Int("items", 3),
        slog.String("country", "IE"),
    )
}

Configuration¶

LogConfig is split into:

MangoConfig: strict mode + correlation-id behaviour.
Out: toggles for File, Cli, and Syslog.

mango:
  strict: true
  correlation-id:
    strict: true
    auto-generate: true
out:
  enabled: true
  cli:
    enabled: true
    friendly: true
    friendly-format: '"[\(.level)] \(.operation) - \(.message)"'
    verbose: true
    verbose-format: "."
  file:
    enabled: true
    debug: false
    path: /var/log/mango.log
    max-size: 100
    max-backups: 5
    max-age: 7
    compress: true
  syslog:
    facility: local0

Friendly/verbose formats consume jq strings (gojq) and default to built-in templates when left empty.

Context Requirements¶

Strict mode enforces presence (and validity) of:

mangolog.TYPE – must be one of Business, Security, Performance.
mangolog.APPLICATION
mangolog.OPERATION
mangolog.CORRELATION_ID (when correlation-id.strict is true; auto-generated if auto-generate is true).

On missing or invalid fields, Handle logs an error and returns it to the slog caller.

Outputs¶

CLI¶

When friendly is true, Mango Logger runs the log through the jq template (e.g., "[INFO] create - success").
Otherwise, it prints raw JSON to stdout/stderr.
verbose gates debug logs on stdout and includes correlation IDs for INFO-level messages.

File¶

Writes newline-delimited JSON (StructuredLog) using lumberjack rotation.
debug controls whether LevelDebug entries reach the file.

Syslog¶

Enabled by setting out.syslog.facility or the corresponding constant (e.g., mangolog.SyslogFacilityLocal0).
Severity is derived from the slog level.
Not available on Windows (build tags guard the implementation).

Structured Output¶

{
  "ts": "2025-01-15T09:53:34.717-0500",
  "type": "Business",
  "application": "checkout-api",
  "operation": "cart-create",
  "correlationid": "a52b0129-9d49-4f29-acbb-3575aa4442f4",
  "logId": "67e36893-0a7e-476c-b799-4a2772e9bd17",
  "level": "INFO",
  "message": "cart created",
  "attributes": {
    "items": 3,
    "country": "IE"
  }
}

Tips¶

Use middleware to stamp context keys (TYPE, APPLICATION, OPERATION, CORRELATION_ID) once per request.
Toggle Cli.Verbose via CLI flags (--verbose) to expose debug logs during troubleshooting.
When Strict is enabled, avoid mutating the global REQUIRED_FIELDS; create fresh contexts per request to prevent leaking values across goroutines.

pkg/logger¶