feat: initial commit

README.md

+# slog
+
+Go module for structured logging.
+
+Configures a logger with a JSON formatter using a schema suitable for datadog log ingestion.
+
+## Example usage
+
+Initialise and use the logger:
+
+```
+go run src/main/main.go
+```

go.mod

+module gitlab.nexdev.uk/pub/go-slog
+
+go 1.20
+
+require golang.org/x/exp v0.0.0-20230711023510-fffb14384f22

go.sum

+golang.org/x/exp v0.0.0-20230711023510-fffb14384f22 h1:FqrVOBQxQ8r/UwwXibI0KMolVhvFiGobSfdE33deHJM=
+golang.org/x/exp v0.0.0-20230711023510-fffb14384f22/go.mod h1:FXUEEKJgO7OQYeo8N01OfiKP8RXMtf6e8aTskBGqWdc=

src/main/main.go

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

src/slog/slog.go

+package slog
+
+import (
+	"golang.org/x/exp/slog"
+	"os"
+	"strings"
+)
+
+func InitLogger() *slog.Logger {
+	// Could set logger level via ENV vars in future.
+	programLevel := new(slog.LevelVar)
+	programLevel.Set(slog.LevelDebug)
+
+	// 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"
+		}
+		if a.Key == "time" {
+			a.Key = "date"
+		}
+		if a.Key == "level" {
+			a.Key = "status"
+			a.Value = slog.StringValue(strings.ToLower(a.Value.String()))
+		}
+		return a
+	}
+	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)
+	} else {
+		logger.Error("Failed to get hostname.", slog.String("error", hostnameErr.Error()))
+	}
+
+	logger.Info("Initialised.")
+	return logger
+}