slogctx

slogctx

slogctx is a simple context logger implementation for the slog logger introduced in go 1.21

To use this module in your project run:

go get github.com/BrandonBentley/slogctx

There are a few ways to use this module.

The recommended way is to set the slog default logger to use the JSONContextHandler. This way all logs will use the context handler, which if no values are in the context, behaves as a slog.JSONHandler. See the code below for example usage:

package main

import (
	"context"
	"log/slog"
	"os"

	"github.com/BrandonBentley/slogctx"
)

func main() {
	slog.SetDefault(slog.New(slogctx.NewJSONContextHandler(os.Stdout, nil)))

	ctx := context.Background()

	ctx = slogctx.WithAttrs(
		ctx,
		slog.String("someKey", "someVal"),
	)

	slog.InfoContext(
		ctx,
		"I have some info for you",
	)
}

Output

{
  "time": "2025-04-11T01:22:31.706502-06:00",
  "level": "INFO",
  "msg": "I have some info for you",
  "someKey": "someVal"
}

sloginit

You can also use the sloginit package provided to initialize the default slog logger with the slogctx.JSONContextHandler and not require any code for initializing

package main

import (
	"context"
	"log/slog"

	"github.com/BrandonBentley/slogctx"
	_ "github.com/BrandonBentley/slogctx/sloginit"
)

func main() {
	ctx := context.Background()

	ctx = slogctx.WithAttrs(
		ctx,
		slog.String("Key1", "Val1"),
	)

	slog.InfoContext(
		ctx,
		"I have some info for you",
	)
}

Output

{
  "time": "2025-04-11T01:43:33.14336-06:00",
  "level": "INFO",
  "msg": "I have some info for you",
  "Key1": "Val1"
}

No More Duplicates!

A significant update: slogctx.ContextHandler will now remove duplicate keys, keeping the last provided value, and maintains the order in which keys where added

package main

import (
	"context"
	"log/slog"

	"github.com/BrandonBentley/slogctx"
	_ "github.com/BrandonBentley/slogctx/sloginit"
)

func main() {
	firstContext := slogctx.WithAttrs(
		context.Background(),
		slog.String("Key1", "Val1"),
	)

	ctx := firstContext
	slog.ErrorContext(
		ctx,
		"Original Value",
	)

	ctx = slogctx.WithAttrs(
		ctx,
		slog.String("key2", "val2"),
		slog.String("Key1", "IChangedIt"),
	)

	slog.InfoContext(
		ctx,
		"I Changed the first one",
	)

	ctx = slogctx.With(
		ctx,
		"key2", 7,
	)

	slog.InfoContext(
		ctx,
		"You can see the second one is now a number",
	)

	slog.WarnContext(
		firstContext,
		"the first context is unchanged",
	)
}

Output

{
    "time": "2025-04-11T01:53:29.677325-06:00",
    "level": "ERROR",
    "msg": "Original Value",
    "Key1": "Val1"
}
{
    "time": "2025-04-11T01:53:29.677446-06:00",
    "level": "INFO",
    "msg": "I Changed the first one",
    "Key1": "IChangedIt",
    "key2": "val2"
}
{
    "time": "2025-04-11T01:53:29.677449-06:00",
    "level": "INFO",
    "msg": "You can see the second one is now a number",
    "Key1": "IChangedIt",
    "key2": 7
}
{
    "time": "2025-04-11T01:53:29.677472-06:00",
    "level": "WARN",
    "msg": "the first context is unchanged",
    "Key1": "Val1"
}