refactor: move slog package to root, add configuration options and tests

options.go

+package slog
+
+import (
+	"golang.org/x/exp/slog"
+	"io"
+)
+
+type Options struct {
+	Leveler slog.Leveler
+	Writer  io.Writer
+}
+
+type Option func(*Options)
+
+func WithLeveler(leveler slog.Leveler) Option {
+	return func(o *Options) {
+		o.Leveler = leveler
+	}
+}
+
+func WithWriter(writer io.Writer) Option {
+	return func(o *Options) {
+		o.Writer = writer
+	}
+}

src/slog/slog.go → slog.go

@@ -6,36 +6,46 @@ import (
 	"strings"
 )
 
-func InitLogger() *slog.Logger {
-	// Could set logger level via ENV vars in future.
-	programLevel := new(slog.LevelVar)
-	programLevel.Set(slog.LevelDebug)
+func New(opts ...Option) *slog.Logger {
+	options := &Options{
+		Leveler: slog.LevelDebug,
+		Writer:  os.Stdout,
+	}
+	for _, opt := range opts {
+		opt(options)
+	}
 
 	// Attributes modified for datadog schema via HandlerOptions.ReplaceAttr
 	// Per recommendation at https://pkg.go.dev/golang.org/x/exp/slog#JSONHandler
 	// See datadog: https://docs.datadoghq.com/logs/log_configuration/attributes_naming_convention/#reserved-attributes
-	loggerReplace := func(groups []string, a slog.Attr) slog.Attr {
-		if a.Key == "msg" {
-			a.Key = "message"
+	replaceAttr := func(groups []string, attr slog.Attr) slog.Attr {
+		if attr.Key == "msg" {
+			attr.Key = "message"
 		}
-		if a.Key == "time" {
-			a.Key = "date"
+		if attr.Key == "time" {
+			attr.Key = "date"
 		}
-		if a.Key == "level" {
-			a.Key = "status"
-			a.Value = slog.StringValue(strings.ToLower(a.Value.String()))
+		if attr.Key == "level" {
+			attr.Key = "status"
+			attr.Value = slog.StringValue(strings.ToLower(attr.Value.String()))
 		}
-		return a
+		return attr
 	}
-	logger := slog.New(slog.NewJSONHandler(os.Stdout,
-		&slog.HandlerOptions{Level: programLevel, AddSource: true, ReplaceAttr: loggerReplace}))
-	hostname, hostnameErr := os.Hostname()
-	if hostnameErr == nil {
-		logger = logger.With("host", hostname)
+
+	handlerOptions := &slog.HandlerOptions{
+		Level:       options.Leveler,
+		AddSource:   true,
+		ReplaceAttr: replaceAttr,
+	}
+	logHandler := slog.NewJSONHandler(options.Writer, handlerOptions)
+	logger := slog.New(logHandler)
+
+	hostname, err := os.Hostname()
+	if err != nil {
+		logger.Error("Failed to get hostname.", slog.String("error", err.Error()))
 	} else {
-		logger.Error("Failed to get hostname.", slog.String("error", hostnameErr.Error()))
+		logger = logger.With("host", hostname)
 	}
 
-	logger.Info("Initialised.")
 	return logger
 }

slog_test.go

+package slog
+
+import (
+	"bufio"
+	"bytes"
+	"encoding/json"
+	"golang.org/x/exp/slog"
+	"testing"
+)
+
+func TestNew(t *testing.T) {
+	var buf bytes.Buffer
+
+	logger := New(WithWriter(&buf))
+	logger.Info("Foo", slog.String("bar", "baz"))
+	logger.Error("Bar", slog.String("baz", "qux"))
+
+	scanner := bufio.NewScanner(&buf)
+
+	// Scan the first log.
+	scanner.Scan()
+	infoLog := scanner.Bytes()
+	var infoLogMap map[string]any
+	if err := json.Unmarshal(infoLog, &infoLogMap); err != nil {
+		t.Errorf("Failed to unmarshal info log: %s", err.Error())
+	}
+	t.Log(infoLogMap)
+	if infoLogMap["status"] != "info" {
+		t.Errorf("Expected info log level, got %s", infoLogMap["level"])
+	}
+	if infoLogMap["bar"] != "baz" {
+		t.Errorf("Expected bar=baz, got %s", infoLogMap["bar"])
+	}
+}

src/main/main.go

-package main
-
-import (
-	"gitlab.nexdev.uk/pub/go-slog/src/slog"
-)
-
-func main() {
-	logger := slog.InitLogger()
-	logger.Info("Logger test.")
-}