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/util.go

@@ -0,0 +1,110 @@
+package graphson
+
+import (
+	"io"
+	"unsafe"
+
+	"github.com/json-iterator/go"
+	"github.com/pkg/errors"
+)
+
+// graphson encoding type / value keys
+const (
+	TypeKey  = "@type"
+	ValueKey = "@value"
+)
+
+// typeEncoder adds graphson type information to a value encoder.
+type typeEncoder struct {
+	jsoniter.ValEncoder
+	Type Type
+}
+
+// Encode belongs to jsoniter.ValEncoder interface.
+func (enc typeEncoder) Encode(ptr unsafe.Pointer, stream *jsoniter.Stream) {
+	stream.WriteObjectStart()
+	stream.WriteObjectField(TypeKey)
+	stream.WriteString(enc.Type.String())
+	stream.WriteMore()
+	stream.WriteObjectField(ValueKey)
+	enc.ValEncoder.Encode(ptr, stream)
+	stream.WriteObjectEnd()
+}
+
+type (
+	// typeDecoder decorates a value decoder and adds graphson type verification.
+	typeDecoder struct {
+		jsoniter.ValDecoder
+		typeChecker
+	}
+
+	// typeChecker defines an interface for graphson type verification.
+	typeChecker interface {
+		CheckType(Type) error
+	}
+
+	// typeCheckerFunc allows the use of functions as type checkers.
+	typeCheckerFunc func(Type) error
+
+	// typeValue defines a graphson type / value pair.
+	typeValue struct {
+		Type  Type
+		Value jsoniter.RawMessage
+	}
+)
+
+// Decode belongs to jsoniter.ValDecoder interface.
+func (dec typeDecoder) Decode(ptr unsafe.Pointer, iter *jsoniter.Iterator) {
+	if iter.WhatIsNext() != jsoniter.ObjectValue {
+		dec.ValDecoder.Decode(ptr, iter)
+		return
+	}
+
+	data := iter.SkipAndReturnBytes()
+	if iter.Error != nil && iter.Error != io.EOF {
+		return
+	}
+
+	var tv typeValue
+	if err := jsoniter.Unmarshal(data, &tv); err != nil {
+		iter.ReportError("unmarshal type value", err.Error())
+		return
+	}
+
+	if err := dec.CheckType(tv.Type); err != nil {
+		iter.ReportError("check type", err.Error())
+		return
+	}
+
+	it := config.BorrowIterator(tv.Value)
+	defer config.ReturnIterator(it)
+
+	dec.ValDecoder.Decode(ptr, it)
+	if it.Error != nil && it.Error != io.EOF {
+		iter.ReportError("decode value", it.Error.Error())
+	}
+}
+
+// UnmarshalJSON implements json.Unmarshaler interface.
+func (tv *typeValue) UnmarshalJSON(data []byte) error {
+	var v struct {
+		Type  *Type               `json:"@type"`
+		Value jsoniter.RawMessage `json:"@value"`
+	}
+
+	if err := jsoniter.Unmarshal(data, &v); err != nil {
+		return err
+	}
+	if v.Type == nil || v.Value == nil {
+		return errors.New("missing type or value")
+	}
+
+	tv.Type = *v.Type
+	tv.Value = v.Value
+	return nil
+}
+
+// CheckType implements typeChecker interface.
+func (f typeCheckerFunc) CheckType(typ Type) error {
+	return f(typ)
+}