add ability to print inline config for better readability in grafana

cmd/loki/main.go

@@ -1,10 +1,13 @@
 package main
 
 import (
+	"errors"
 	"flag"
 	"fmt"
+	"io"
 	"os"
 	"reflect"
+	"strings"
 
 	"github.com/go-kit/kit/log/level"
 	"github.com/prometheus/client_golang/prometheus"
@@ -26,9 +29,13 @@ func init() {
 	prometheus.MustRegister(version.NewCollector("loki"))
 }
 
+var lineReplacer = strings.NewReplacer("\n", "\\n  ")
+
 func main() {
 	printVersion := flag.Bool("version", false, "Print this builds version information")
-	printConfig := flag.Bool("print-config-stderr", false, "Dump the entire YAML config Loki will run with to stderr")
+	printConfig := flag.Bool("print-config-stderr", false, "Dump the entire Loki config object to stderr")
+	printConfigInline := flag.Bool("print-config-stderr-inline", false, "Dump the entire Loki config object to stderr broken up by sections with escaped newline characters, "+
+		"this will display much better when captured by Loki and shown in Grafana")
 
 	var config loki.Config
 	if err := cfg.Parse(&config); err != nil {
@@ -61,11 +68,16 @@ func main() {
 	}
 
 	if *printConfig {
-		lc, err := yaml.Marshal(&config)
+		err := dumpConfig(os.Stderr, &config, false)
 		if err != nil {
-			level.Error(util.Logger).Log("msg", "failed to marshal config for pretty printing", "err", err.Error())
-		} else {
-			fmt.Fprintf(os.Stderr, "---\n# Loki Config\n# %s\n%s\n\n", version.Info(), string(lc))
+			level.Error(util.Logger).Log("msg", "failed to print config to stderr", "err", err.Error())
+		}
+	}
+
+	if *printConfigInline {
+		err := dumpConfig(os.Stderr, &config, true)
+		if err != nil {
+			level.Error(util.Logger).Log("msg", "failed to print config to stderr", "err", err.Error())
 		}
 	}
 
@@ -94,3 +106,76 @@ func main() {
 	err = t.Run()
 	util.CheckFatal("running loki", err)
 }
+
+func dumpConfig(w io.Writer, config *loki.Config, escapeNewlines bool) error {
+	if !escapeNewlines {
+		lc, err := yaml.Marshal(&config)
+		if err != nil {
+			return err
+		}
+		fmt.Fprintf(w, "---\n# Loki Config\n# %s\n%s\n\n", version.Info(), string(lc))
+		return nil
+	}
+
+	s := reflect.ValueOf(config).Elem()
+	typeOfT := s.Type()
+
+	for i := 0; i < s.NumField(); i++ {
+		f := s.Field(i)
+		if !f.CanInterface() {
+			continue
+		}
+		// Lookup the yaml tag to print the field name by the yaml tag, skip if it's not present or empty
+		if alias, ok := typeOfT.Field(i).Tag.Lookup("yaml"); ok {
+			if alias == "" {
+				continue
+			} else {
+				// yaml tags can contain other data like `omitempty` so split by comma and only return first result
+				fmt.Fprint(w, strings.Split(alias, ",")[0]+": ")
+			}
+		} else {
+			continue
+		}
+
+		if f.Kind() == reflect.Slice {
+			return errors.New("the config dumping function was not programmed to handle a configuration array as a top level item in the Loki config")
+		}
+
+		kind := f.Kind()
+		val := f.Interface()
+
+		// Dereference any pointers so we can properly determine the kind of the underlying object
+		if f.Kind() == reflect.Ptr {
+			if !f.IsNil() {
+				kind = f.Elem().Kind()
+				val = f.Elem().Interface()
+			}
+		}
+
+		// If the field is a struct, unmarshal it with a yaml unmarshaller and print it
+		if kind == reflect.Struct {
+			err := unmarshall(w, val)
+			if err != nil {
+				return err
+			}
+		} else {
+			// If it's not a struct, just print the value
+			fmt.Fprint(w, val)
+		}
+		fmt.Fprint(w, "\n")
+	}
+
+	os.Exit(0)
+
+	return nil
+}
+
+func unmarshall(w io.Writer, v interface{}) error {
+	fmt.Fprint(w, "\\n")
+	sc, err := yaml.Marshal(v)
+	if err != nil {
+		return err
+	}
+	fmt.Fprint(w, lineReplacer.Replace(string(sc)))
+	return nil
+}