slogutil

Package slogutil provides enhanced logging capabilities for the standard library log/slog package, focusing on context integration and testability.

Features

• Context-Aware Logging: Enriches log records with contextual information from context.Context:

  • The slogctx sub-package provides a handler (slogctx.Handler) and an Extractor API to extract values from the context.
  • Supports adding attributes to the root of the log context or appending them within the current log group.

• Testability: Enables easy testing of log output:

  • Provides an in-memory handler (slogmem) to capture log records during tests, allowing for assertions and verification.

• Attribute Consistency: Provides consistent handling of log attributes:

  • Deduplicates attributes with the same respecting groups. For example: duplicate, duplicate#01, duplcate#02.

Quick Start

package main

import (
	"context"
	"log/slog"

	"github.com/nickbryan/slogutil"
	"github.com/nickbryan/slogutil/slogctx"
)

func main() {
	ctx := slogctx.WithAttrs(context.Background(), slog.String("my_appended_attribute", "my_appended_value"))
	ctx = slogctx.WithRootAttrs(ctx, slog.String("my_root_attribute", "my_root_value"))

	logger := slogutil.NewJSONLogger().WithGroup("my_group")
	logger.InfoContext(ctx, "Info log message", slog.String("my_attribute", "my_value"))

	// Output:
	// {"time":"2024-11-29T10:27:41.460372Z","level":"INFO","source":{"function":"main.main","file":main.go","line":16},"msg":"Info log message","my_root_attribute":"my_root_value","my_group":{"my_attribute":"my_value","my_appended_attribute":"my_appended_value"}}
}

Testing

slogutil provides an in-memory handler (slogmem) to capture log records, enabling you to test log output effectively:

func TestThing(t *testing.T) {
	ctx := slogctx.WithPrependAttrs(context.Background(), slog.String("prepend_attribute", "prepend_value"))
	ctx = slogctx.WithAppendAttrs(ctx, slog.String("append_attribute", "append_value"))

	logger, logs := slogutil.NewInMemoryLogger(slog.LevelDebug)
	logger = logger.With(slog.Int("my_root_attribute", 123))
	logger = logger.WithGroup("my_group")

	logger.InfoContext(ctx, "Info log message", slog.String("my_grouped_attribute", "my_value"))

	if ok, diff := logs.Contains(slogmem.RecordQuery{
		Level:   slog.LevelInfo,
		Message: "Info log message",
		Attrs: map[string]slog.Value{
			"prepend_attribute":             slog.StringValue("prepend_value"),
			"my_root_attribute":             slog.IntValue(123),
			"my_group.my_grouped_attribute": slog.StringValue("my_value"),
			"my_group.append_attribute":     slog.StringValue("append_value"),
		},
	}); !ok {
		t.Errorf("expected log not written, got: %s", diff)
	}
}