diff --git a/go/vendor/github.com/globalsign/mgo/internal/json/extension.go b/go/vendor/github.com/globalsign/mgo/internal/json/extension.go
new file mode 100644
index 0000000..1c8fd45
--- /dev/null
+++ b/go/vendor/github.com/globalsign/mgo/internal/json/extension.go
@@ -0,0 +1,95 @@
+package json
+
+import (
+	"reflect"
+)
+
+// Extension holds a set of additional rules to be used when unmarshaling
+// strict JSON or JSON-like content.
+type Extension struct {
+	funcs  map[string]funcExt
+	consts map[string]interface{}
+	keyed  map[string]func([]byte) (interface{}, error)
+	encode map[reflect.Type]func(v interface{}) ([]byte, error)
+
+	unquotedKeys   bool
+	trailingCommas bool
+}
+
+type funcExt struct {
+	key  string
+	args []string
+}
+
+// Extend changes the decoder behavior to consider the provided extension.
+func (dec *Decoder) Extend(ext *Extension) { dec.d.ext = *ext }
+
+// Extend changes the encoder behavior to consider the provided extension.
+func (enc *Encoder) Extend(ext *Extension) { enc.ext = *ext }
+
+// Extend includes in e the extensions defined in ext.
+func (e *Extension) Extend(ext *Extension) {
+	for name, fext := range ext.funcs {
+		e.DecodeFunc(name, fext.key, fext.args...)
+	}
+	for name, value := range ext.consts {
+		e.DecodeConst(name, value)
+	}
+	for key, decode := range ext.keyed {
+		e.DecodeKeyed(key, decode)
+	}
+	for typ, encode := range ext.encode {
+		if e.encode == nil {
+			e.encode = make(map[reflect.Type]func(v interface{}) ([]byte, error))
+		}
+		e.encode[typ] = encode
+	}
+}
+
+// DecodeFunc defines a function call that may be observed inside JSON content.
+// A function with the provided name will be unmarshaled as the document
+// {key: {args[0]: ..., args[N]: ...}}.
+func (e *Extension) DecodeFunc(name string, key string, args ...string) {
+	if e.funcs == nil {
+		e.funcs = make(map[string]funcExt)
+	}
+	e.funcs[name] = funcExt{key, args}
+}
+
+// DecodeConst defines a constant name that may be observed inside JSON content
+// and will be decoded with the provided value.
+func (e *Extension) DecodeConst(name string, value interface{}) {
+	if e.consts == nil {
+		e.consts = make(map[string]interface{})
+	}
+	e.consts[name] = value
+}
+
+// DecodeKeyed defines a key that when observed as the first element inside a
+// JSON document triggers the decoding of that document via the provided
+// decode function.
+func (e *Extension) DecodeKeyed(key string, decode func(data []byte) (interface{}, error)) {
+	if e.keyed == nil {
+		e.keyed = make(map[string]func([]byte) (interface{}, error))
+	}
+	e.keyed[key] = decode
+}
+
+// DecodeUnquotedKeys defines whether to accept map keys that are unquoted strings.
+func (e *Extension) DecodeUnquotedKeys(accept bool) {
+	e.unquotedKeys = accept
+}
+
+// DecodeTrailingCommas defines whether to accept trailing commas in maps and arrays.
+func (e *Extension) DecodeTrailingCommas(accept bool) {
+	e.trailingCommas = accept
+}
+
+// EncodeType registers a function to encode values with the same type of the
+// provided sample.
+func (e *Extension) EncodeType(sample interface{}, encode func(v interface{}) ([]byte, error)) {
+	if e.encode == nil {
+		e.encode = make(map[reflect.Type]func(v interface{}) ([]byte, error))
+	}
+	e.encode[reflect.TypeOf(sample)] = encode
+}