Settings: Expand variables in configuration (#25075)

pkg/setting/expanders.go

@@ -0,0 +1,147 @@
+package setting
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"regexp"
+	"sort"
+	"strings"
+
+	"gopkg.in/ini.v1"
+)
+
+type Expander interface {
+	SetupExpander(file *ini.File) error
+	Expand(string) (string, error)
+}
+
+type registeredExpander struct {
+	name     string
+	priority int64
+	expander Expander
+}
+
+var expanders = []registeredExpander{
+	{
+		name:     "env",
+		priority: -10,
+		expander: envExpander{},
+	},
+	{
+		name:     "file",
+		priority: -5,
+		expander: fileExpander{},
+	},
+}
+
+func AddExpander(name string, priority int64, e Expander) {
+	expanders = append(expanders, registeredExpander{
+		name:     name,
+		priority: priority,
+		expander: e,
+	})
+}
+
+var regex = regexp.MustCompile(`\$(|__\w+){([^}]+)}`)
+
+func expandConfig(file *ini.File) error {
+	sort.Slice(expanders, func(i, j int) bool {
+		return expanders[i].priority < expanders[j].priority
+	})
+
+	for _, expander := range expanders {
+		err := expander.expander.SetupExpander(file)
+		if err != nil {
+			return fmt.Errorf("got error during initilazation of expander '%s': %w", expander.name, err)
+		}
+
+		for _, section := range file.Sections() {
+			for _, key := range section.Keys() {
+				updated, err := applyExpander(key.Value(), expander)
+				if err != nil {
+					return fmt.Errorf("got error while expanding %s.%s with expander '%s': %w",
+						section.Name(),
+						key.Name(),
+						expander.name,
+						err)
+				}
+
+				key.SetValue(updated)
+			}
+		}
+	}
+	return nil
+}
+
+func ExpandVar(s string) (string, error) {
+	for _, expander := range expanders {
+		var err error
+		s, err = applyExpander(s, expander)
+		if err != nil {
+			return "", fmt.Errorf("got error while expanding expander %s: %w", expander.name, err)
+		}
+	}
+	return s, nil
+}
+
+func applyExpander(s string, e registeredExpander) (string, error) {
+	matches := regex.FindAllStringSubmatch(s, -1)
+
+	for _, match := range matches {
+		if len(match) < 3 {
+			return "", fmt.Errorf("regex error, got %d results back for match, expected 3", len(match))
+		}
+
+		_, isEnv := e.expander.(envExpander)
+		if match[1] == "__"+e.name || (match[1] == "" && isEnv) {
+			updated, err := e.expander.Expand(match[2])
+			if err != nil {
+				return "", err
+			}
+
+			s = strings.Replace(s, match[0], updated, 1)
+		}
+	}
+
+	return s, nil
+}
+
+type envExpander struct {
+}
+
+func (e envExpander) SetupExpander(file *ini.File) error {
+	return nil
+}
+
+func (e envExpander) Expand(s string) (string, error) {
+	envValue := os.Getenv(s)
+
+	// if env variable is hostname and it is empty use os.Hostname as default
+	if s == "HOSTNAME" && envValue == "" {
+		return os.Hostname()
+	}
+
+	return os.Getenv(s), nil
+}
+
+type fileExpander struct {
+}
+
+func (e fileExpander) SetupExpander(file *ini.File) error {
+	return nil
+}
+
+func (e fileExpander) Expand(s string) (string, error) {
+	_, err := os.Stat(s)
+	if err != nil {
+		return "", err
+	}
+
+	f, err := ioutil.ReadFile(s)
+	if err != nil {
+		return "", err
+	}
+
+	return strings.TrimSpace(string(f)), nil
+}