ctxkey

Provides generic context keys with getter and setter methods. Also provides a function to automatically log the context key.

Example

package main

import (
    "context"
    "os"

    "log/slog"

    "github.com/sollniss/ctxkey"
)

var someContextKey ctxkey.Key[string]
var someOtherContextKey ctxkey.Key[int]

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

    // add someContextKey with the value "hello world" to the context
    ctx = someContextKey.WithValue(ctx, "hello world")

    // logger options
    opts := slog.HandlerOptions{
        AddSource: false,
        Level:     slog.LevelDebug,
    }

    // the default handler
    var logHandler slog.Handler = slog.NewJSONHandler(os.Stderr, &opts)

    // add both context keys to the log
    logHandler = someContextKey.AttachToLog("my_context_key", logHandler)
    logHandler = someOtherContextKey.AttachToLog("some_id", logHandler)

    // set the logger as default
    slog.SetDefault(slog.New(logHandler))

    // log 1
    slog.InfoContext(ctx, "test")

    // add another value to the context, this time an int
    ctx = someOtherContextKey.WithValue(ctx, 123)

    // create a new logger with a group
    logger := slog.Default()
    logger = logger.WithGroup("test-group")

    // log 2
    logger.InfoContext(ctx, "test2")

    // explicitly get value from context
    noCtxLogger := slog.New(slog.NewJSONHandler(os.Stderr, &opts))
    some, err := someContextKey.Value(ctx)
    if err != nil {
        // key not found
        noCtxLogger.InfoContext(ctx, "explicit key", slog.String("key_not_found", err.Error()))
    } else {
        noCtxLogger.InfoContext(ctx, "explicit key", slog.String("some_key", some))
    }
}

prints

{"time":"2023-10-04T11:37:00.6478478+09:00","level":"INFO","msg":"test","my_context_key":"hello world"}
{"time":"2023-10-04T11:37:00.6737874+09:00","level":"INFO","msg":"test2","test-group":{"some_id":123,"my_context_key":"hello world"}}
{"time":"2023-10-04T11:37:00.6737874+09:00","level":"INFO","msg":"explicit key","some_key":"hello world"}

Note that the context keys will be attached to the log last. So they are inside the group we defined.