move lib/go/gremlin to ent/dialect (#1192)

Summary:
Pull Request resolved: https://github.com/facebookexternal/fbc/pull/1192

Pull Request resolved: https://github.com/facebookincubator/ent/pull/11

Reviewed By: alexsn

Differential Revision: D16377224

fbshipit-source-id: 07ca7436eb9b64fbe2299568560b91466b2417ba

dialect/gremlin/encoding/graphson/extension.go

@@ -0,0 +1,84 @@
+package graphson
+
+import (
+	"reflect"
+
+	"github.com/json-iterator/go"
+	"github.com/modern-go/reflect2"
+)
+
+var (
+	typeEncoders = map[string]jsoniter.ValEncoder{}
+	typeDecoders = map[string]jsoniter.ValDecoder{}
+)
+
+// RegisterTypeEncoder register type encoder for typ.
+func RegisterTypeEncoder(typ string, enc jsoniter.ValEncoder) {
+	typeEncoders[typ] = enc
+}
+
+// RegisterTypeDecoder register type decoder for typ.
+func RegisterTypeDecoder(typ string, dec jsoniter.ValDecoder) {
+	typeDecoders[typ] = dec
+}
+
+type registeredEncoder struct{ jsoniter.ValEncoder }
+
+// EncoderOfNative returns a value encoder of a registered type.
+func (encodeExtension) EncoderOfRegistered(typ reflect2.Type) jsoniter.ValEncoder {
+	enc := typeEncoders[typ.String()]
+	if enc != nil {
+		return registeredEncoder{enc}
+	}
+	if typ.Kind() == reflect.Ptr {
+		ptrType := typ.(reflect2.PtrType)
+		enc := typeEncoders[ptrType.Elem().String()]
+		if enc != nil {
+			return registeredEncoder{
+				ValEncoder: &jsoniter.OptionalEncoder{
+					ValueEncoder: enc,
+				},
+			}
+		}
+	}
+	return nil
+}
+
+// DecoratorOfRegistered decorates a value encoder of a registered type.
+func (encodeExtension) DecoratorOfRegistered(enc jsoniter.ValEncoder) jsoniter.ValEncoder {
+	if _, ok := enc.(registeredEncoder); ok {
+		return enc
+	}
+	return nil
+}
+
+type registeredDecoder struct{ jsoniter.ValDecoder }
+
+// DecoratorOfRegistered returns a value decoder of a registered type.
+func (decodeExtension) DecoderOfRegistered(typ reflect2.Type) jsoniter.ValDecoder {
+	dec := typeDecoders[typ.String()]
+	if dec != nil {
+		return registeredDecoder{dec}
+	}
+	if typ.Kind() == reflect.Ptr {
+		ptrType := typ.(reflect2.PtrType)
+		dec := typeDecoders[ptrType.Elem().String()]
+		if dec != nil {
+			return registeredDecoder{
+				ValDecoder: &jsoniter.OptionalDecoder{
+					ValueType:    ptrType.Elem(),
+					ValueDecoder: dec,
+				},
+			}
+		}
+	}
+	return nil
+}
+
+// DecoratorOfNative decorates a value decoder of a registered type.
+func (decodeExtension) DecoratorOfRegistered(dec jsoniter.ValDecoder) jsoniter.ValDecoder {
+	if _, ok := dec.(registeredDecoder); ok {
+		return dec
+	}
+	return nil
+}