ctxslog

ctxslog is a package that provides slog logger that can be used with context.Context for storing attributes. The logger itself can also be stored and retrieved from context.Context.

Behavior

ctxslog uses a slog.Handler middleware that reads attributes from context and adds them to the log record.

Constructors

ctxslog.NewContext creates a new context with logger stored in it. The logger can be retrieved from context using ctxslog.NewContext function. The logger can also be created using ctxslog.New function which directly returns the logger without manipulating context. The logger can also be created using ctxslog.FromContext function which directly returns the logger without a need for context.

Attributes

Attributes can be added to the context using ctxslog.WithAttrs function. After this point when using context aware slog functions like logger.InfoContext or logger.ErrorContext, attributes will be added similar to how they can be added directly as parameters. ctxslog.WithAttrs also supports adding attributes using a function that returns an array of slog.Attr. This is useful when you want to add dynamic attributes based on the context or the slog.Record. It can also be used to reference values that are stored in context using custom context keys.

Example

package main

import (
    "github.com/pedramktb/go-ctxslog"
    "context"
    "log/slog"
    "os"
    "time"

    // other imports...
)

func main() {
    ctx := ctxslog.NewContext(context.Background(), slog.NewTextHandler(os.Stdout, nil))

    // ...

    attrs := []slog.Attr{
        slog.String("db", db.name),
        slog.String("ip", db.ip),
    }

    ctx = ctxslog.WithAttrs(ctx, attrs...)

    ctx = ctxslog.WithAttrs(ctx, func(ctx context.Context, r slog.Record) []slog.Attr {
        if r.Level == slog.LevelDebug {
            return []slog.Attr{
                slog.String("time_took_to_compute_this_log_attr", time.Now().Sub(r.Time).String()),
            }
        } else {
            return []slog.Attr{
                slog.String(ctx.Value("stage").(string)),
            }
        }
    })

    // ...

    logger := ctxslog.FromContext(ctx)

    // this will log something like: db=products ip=127.0.0.1 time_took_to_compute_this_log_attr=14ns
    logger.DebugContext(ctx, "database started")

    // this will log something like: db=products ip=127.0.0.1 stage=dev
    logger.InfoContext(ctx, "database started")

    // ...
}