feat(model): ValidationScheme implements pflag.Value and json.Marshaler/Unmarshaler interfaces

Signed-off-by: Julius Hinze <julius.hinze@grafana.com>

Author: juliusmh

model/metric.go

@@ -14,6 +14,7 @@
 package model
 
 import (
+	"encoding/json"
 	"errors"
 	"fmt"
 	"regexp"
@@ -77,10 +78,12 @@ const (
 	UTF8Validation
 )
 
-var (
-	_ yaml.Marshaler = UnsetValidation
-	_ fmt.Stringer   = UnsetValidation
-)
+var _ interface {
+	yaml.Marshaler
+	yaml.Unmarshaler
+	json.Marshaler
+	json.Unmarshaler
+} = new(ValidationScheme)
 
 // String returns the string representation of s.
 func (s ValidationScheme) String() string {
@@ -114,19 +117,50 @@ func (s *ValidationScheme) UnmarshalYAML(unmarshal func(any) error) error {
 	if err := unmarshal(&scheme); err != nil {
 		return err
 	}
-	switch scheme {
+	return s.Set(scheme)
+}
+
+// MarshalJSON implements the json.Marshaler interface.
+func (s ValidationScheme) MarshalJSON() ([]byte, error) {
+	switch s {
+	case UnsetValidation:
+		return json.Marshal("")
+	case UTF8Validation, LegacyValidation:
+		return json.Marshal(s.String())
+	default:
+		return nil, fmt.Errorf("unhandled ValidationScheme: %d", s)
+	}
+}
+
+// UnmarshalJSON implements the json.Unmarshaler interface.
+func (s *ValidationScheme) UnmarshalJSON(bytes []byte) error {
+	var repr string
+	if err := json.Unmarshal(bytes, &repr); err != nil {
+		return err
+	}
+	return s.Set(repr)
+}
+
+// Set implements the pflag.Value interface.
+func (s *ValidationScheme) Set(text string) error {
+	switch text {
 	case "":
 		// Don't change the value.
-	case "legacy":
+	case LegacyValidation.String():
 		*s = LegacyValidation
-	case "utf8":
+	case UTF8Validation.String():
 		*s = UTF8Validation
 	default:
-		return fmt.Errorf("unrecognized ValidationScheme: %q", scheme)
+		return fmt.Errorf("unrecognized ValidationScheme: %q", text)
 	}
 	return nil
 }
 
+// Type implements the pflag.Value interface.
+func (s ValidationScheme) Type() string {
+	return "validationScheme"
+}
+
 type EscapingScheme int
 
 const (

model/metric_test.go

@@ -14,6 +14,7 @@
 package model
 
 import (
+	"encoding/json"
 	"errors"
 	"strings"
 	"testing"
@@ -202,6 +203,94 @@ func TestValidationScheme_UnmarshalYAML(t *testing.T) {
 	}
 }
 
+func TestValidationScheme_UnmarshalJSON(t *testing.T) {
+	testCases := []struct {
+		name    string
+		input   string
+		want    ValidationScheme
+		wantErr bool
+	}{
+		{
+			name:    "invalid",
+			input:   `invalid`,
+			wantErr: true,
+		},
+		{
+			name:  "empty",
+			input: `""`,
+			want:  UnsetValidation,
+		},
+		{
+			name:  "legacy validation",
+			input: `"legacy"`,
+			want:  LegacyValidation,
+		},
+		{
+			name:  "utf8 validation",
+			input: `"utf8"`,
+			want:  UTF8Validation,
+		},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			var got ValidationScheme
+			err := json.Unmarshal([]byte(tc.input), &got)
+			if tc.wantErr {
+				require.Error(t, err)
+				return
+			}
+			require.NoError(t, err)
+			require.Equal(t, tc.want, ValidationScheme(got))
+
+			output, err := json.Marshal(got)
+			require.NoError(t, err)
+			require.Equal(t, tc.input, string(output))
+		})
+	}
+}
+
+func TestValidationScheme_Set(t *testing.T) {
+	testCases := []struct {
+		name    string
+		input   string
+		want    ValidationScheme
+		wantErr bool
+	}{
+		{
+			name:    "invalid",
+			input:   `invalid`,
+			wantErr: true,
+		},
+		{
+			name:  "empty",
+			input: ``,
+			want:  UnsetValidation,
+		},
+		{
+			name:  "legacy validation",
+			input: `legacy`,
+			want:  LegacyValidation,
+		},
+		{
+			name:  "utf8 validation",
+			input: `utf8`,
+			want:  UTF8Validation,
+		},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			var got ValidationScheme
+			err := got.Set(tc.input)
+			if tc.wantErr {
+				require.Error(t, err)
+				return
+			}
+			require.NoError(t, err)
+			require.Equal(t, tc.want, ValidationScheme(got))
+		})
+	}
+}
+
 func TestMetricNameIsLegacyValid(t *testing.T) {
 	scenarios := []struct {
 		mn          LabelValue