feat: Add support to collect extra fields

schema.go

@@ -1,7 +1,10 @@
 package jsonschema
 
 import (
+	"maps"
+	"reflect"
 	"regexp"
+	"strings"
 
 	"github.com/go-json-experiment/json"
 	"github.com/go-json-experiment/json/jsontext"
@@ -108,6 +111,9 @@ type Schema struct {
 	ReadOnly    *bool   `json:"readOnly,omitempty"`    // Indicates that the property is read-only.
 	WriteOnly   *bool   `json:"writeOnly,omitempty"`   // Indicates that the property is write-only.
 	Examples    []any   `json:"examples,omitempty"`    // Examples of the instance data that validates against this schema.
+
+	// Extra keywords not in specification
+	Extra map[string]any `json:"-"`
 }
 
 // newSchema parses JSON schema data and returns a Schema object.
@@ -528,6 +534,8 @@ func (s *Schema) MarshalJSON() ([]byte, error) {
 		result["const"] = s.Const.Value
 	}
 
+	maps.Copy(result, s.Extra)
+
 	return json.Marshal(result)
 }
 
@@ -557,9 +565,38 @@ func (s *Schema) UnmarshalJSON(data []byte) error {
 		if s.Const == nil {
 			s.Const = &ConstValue{}
 		}
-		return s.Const.UnmarshalJSON(constData)
+		err := s.Const.UnmarshalJSON(constData)
+		if err != nil {
+			return err
+		}
 	}
 
+	return s.collectExtraFields(data)
+}
+
+func (s *Schema) collectExtraFields(raw []byte) error {
+	extra := make(map[string]any)
+	err := json.Unmarshal(raw, &extra)
+	if err != nil {
+		return err
+	}
+
+	t := reflect.TypeOf(Schema{})
+	for i := range t.NumField() {
+		field := t.Field(i)
+		jsonTagValues := strings.Split(field.Tag.Get("json"), ",")
+		if len(jsonTagValues) == 0 {
+			continue
+		}
+		tagName := jsonTagValues[0]
+		if tagName == "" || tagName == "-" {
+			continue
+		}
+		delete(extra, tagName)
+	}
+	if len(extra) != 0 {
+		s.Extra = extra
+	}
 	return nil
 }
 

tests/extras_test.go

@@ -0,0 +1,70 @@
+package tests
+
+import (
+	"testing"
+
+	"github.com/go-json-experiment/json"
+	"github.com/kaptinlin/jsonschema"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestSchemaWithExtraFields(t *testing.T) {
+	testCases := []struct {
+		name           string
+		schemaJSON     string
+		expectedSchema jsonschema.Schema
+	}{
+		{
+			name: "extra fields collected into Extra",
+			schemaJSON: `{
+				"$schema": "https://json-schema.org/draft/2020-12/schema",
+				"x-component": {
+					"component1": 1,
+					"component2": "2",
+					"componentNested": {"nested": "value"},
+					"componentBool": true
+				},
+			"some-extra-component": true
+			}`,
+			expectedSchema: jsonschema.Schema{
+				Schema: "https://json-schema.org/draft/2020-12/schema",
+				Extra: map[string]any{
+					"x-component": map[string]any{
+						"component1": 1,
+						"component2": "2",
+						"componentNested": map[string]any{
+							"nested": "value",
+						},
+						"componentBool": true,
+					},
+					"some-extra-component": true,
+				},
+			},
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			var schema jsonschema.Schema
+			err := json.Unmarshal([]byte(tc.schemaJSON), &schema)
+			require.NoError(t, err, "Unmarshalling failed unexpectedly")
+			assert.Equal(t, tc.expectedSchema.ID, schema.ID)
+			assert.Equal(t, tc.expectedSchema.Schema, schema.Schema)
+			assert.Equal(t, tc.expectedSchema.Type, schema.Type)
+
+			// Now test marshaling back to JSON
+			marshaledJSON, err := json.Marshal(schema)
+			require.NoError(t, err, "Marshalling failed unexpectedly")
+
+			// Unmarshal marshaled JSON to verify it matches the original schema object
+			var reUnmarshaledSchema jsonschema.Schema
+			err = json.Unmarshal(marshaledJSON, &reUnmarshaledSchema)
+			require.NoError(t, err, "Unmarshalling the marshaled JSON failed")
+			assert.Equal(t, schema, reUnmarshaledSchema, "Re-unmarshaled schema does not match the original")
+
+			// Check if the marshaled JSON matches the original JSON input
+			assert.JSONEq(t, tc.schemaJSON, string(marshaledJSON), "The marshaled JSON should match the original input JSON")
+		})
+	}
+}