fix: [CN-69] respect struct json tags in JSON encoder with UseJSONTagName enabled

docs/index.md

@@ -180,7 +180,7 @@ Table below shows the names of the configuration options:
 |----------------------|------------------------|---------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------|
 | OutputFormat         | output-format          | text          | The output format that will be used for the formatted values (text or json).                                                                                 |
 | PrintConfigOnInit    | print-config-on-init   | false         | If true, the configuration will be printed when any of available constructors is used.                                                                       |
-| UseJSONTagName       | use-json-tag-name      | false         | If true, the JSON tag name will be used instead of the Go struct field name.                                                                                 |
+| UseJSONTagName       | use-json-tag-name      | false         | If true, struct fields encoded as JSON reuse their `json` tag name. Fields tagged with `json:"-"` stay hidden, and tags without a name fall back to the Go identifier. |
 | MaskValue            | mask-value             | [CENSORED]    | The value that will be used to mask the sensitive information.                                                                                               |
 | DisplayStructName    | display-struct-name    | false         | If true, the struct name will be displayed in the output.                                                                                                    |
 | DisplayMapType       | display-map-type       | false         | If true, the map type will be displayed in the output.                                                                                                       |
@@ -189,6 +189,8 @@ Table below shows the names of the configuration options:
 | ExcludePatterns      | exclude-patterns       | []            | A list of regular expressions that will be compared against all the string values. <br/>If a value matches any of the patterns, that section will be masked. Up to 50 patterns are allowed. |
 
 
+Enabling `UseJSONTagName` mirrors Go's `encoding/json`: only the portion before the first comma is used for the field name, `json:"-"` keeps the field hidden, and tags without an explicit name fall back to the original identifier.
+
 ### Using the `censor.Config` struct
 
 It's possible to define a configuration using `censor.Config` struct:

internal/encoder/json_encoder.go

@@ -6,6 +6,7 @@ import (
 	"encoding/json"
 	"reflect"
 	"strconv"
+	"strings"
 	"unicode/utf8"
 
 	"github.com/shopspring/decimal"
@@ -20,6 +21,7 @@ func NewJSONEncoder(c Config) *JSONEncoder {
 			CensorFieldTag:      defaultCensorFieldTag,
 			ExcludePatterns:     c.ExcludePatterns,
 			MaskValue:           c.MaskValue,
+			UseJSONTagName:      c.UseJSONTagName,
 			structFieldsCache:   cache.NewTypeCache[[]Field](cache.DefaultMaxCacheSize),
 			escapedStringsCache: cache.New[string](cache.DefaultMaxCacheSize),
 			regexpCache:         cache.New[string](cache.DefaultMaxCacheSize),
@@ -133,6 +135,7 @@ func (e *JSONEncoder) Struct(b *bytes.Buffer, v reflect.Value) {
 	b.WriteByte('}')
 }
 
+//nolint:gocognit
 func (e *JSONEncoder) getStructFields(v reflect.Value) []Field {
 	numFields := v.NumField()
 	fields := make([]Field, numFields)
@@ -143,8 +146,27 @@ func (e *JSONEncoder) getStructFields(v reflect.Value) []Field {
 			continue
 		}
 
+		name := field.Name
+
+		if e.UseJSONTagName {
+			tagValue := field.Tag.Get("json")
+			if tagValue != "" {
+				if commaIdx := strings.Index(tagValue, ","); commaIdx != -1 {
+					tagValue = tagValue[:commaIdx]
+				}
+
+				if tagValue == "-" {
+					continue
+				}
+
+				if tagValue != "" {
+					name = tagValue
+				}
+			}
+		}
+
 		fields[i] = Field{
-			Name:     field.Name,
+			Name:     name,
 			IsMasked: field.Tag.Get(e.CensorFieldTag) != display,
 		}
 	}

internal/encoder/json_encoder_test.go

@@ -724,3 +724,39 @@ func TestJSONEncoder_StringEscaped(t *testing.T) {
 		require.Equal(t, `"say \"email: [CENSORED]\""`, b.String())
 	})
 }
+
+func TestJSONEncoder_Struct_UseJSONTagName(t *testing.T) {
+	type payload struct {
+		Tagged  string `json:"alias,omitempty" censor:"display"`
+		Skipped string `json:"-" censor:"display"`
+		Empty   string `json:",omitempty" censor:"display"`
+		Default string `censor:"display"`
+	}
+
+	value := payload{
+		Tagged:  "tagged",
+		Skipped: "skipped",
+		Empty:   "empty",
+		Default: "default",
+	}
+
+	t.Run("disabled uses Go field names", func(t *testing.T) {
+		e := NewJSONEncoder(Config{})
+		var b bytes.Buffer
+		defer b.Reset()
+
+		e.Struct(&b, reflect.ValueOf(value))
+
+		require.Equal(t, `{"Tagged": "tagged","Skipped": "skipped","Empty": "empty","Default": "default"}`, b.String())
+	})
+
+	t.Run("enabled uses json tags and skips dash tag", func(t *testing.T) {
+		e := NewJSONEncoder(Config{UseJSONTagName: true})
+		var b bytes.Buffer
+		defer b.Reset()
+
+		e.Struct(&b, reflect.ValueOf(value))
+
+		require.Equal(t, `{"alias": "tagged","Empty": "empty","Default": "default"}`, b.String())
+	})
+}