diff --git a/unum/vendor/golang.org/x/net/icmp/multipart.go b/unum/vendor/golang.org/x/net/icmp/multipart.go
new file mode 100644
index 0000000..f271356
--- /dev/null
+++ b/unum/vendor/golang.org/x/net/icmp/multipart.go
@@ -0,0 +1,109 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package icmp
+
+import "golang.org/x/net/internal/iana"
+
+// multipartMessageBodyDataLen takes b as an original datagram and
+// exts as extensions, and returns a required length for message body
+// and a required length for a padded original datagram in wire
+// format.
+func multipartMessageBodyDataLen(proto int, b []byte, exts []Extension) (bodyLen, dataLen int) {
+	for _, ext := range exts {
+		bodyLen += ext.Len(proto)
+	}
+	if bodyLen > 0 {
+		dataLen = multipartMessageOrigDatagramLen(proto, b)
+		bodyLen += 4 // length of extension header
+	} else {
+		dataLen = len(b)
+	}
+	bodyLen += dataLen
+	return bodyLen, dataLen
+}
+
+// multipartMessageOrigDatagramLen takes b as an original datagram,
+// and returns a required length for a padded orignal datagram in wire
+// format.
+func multipartMessageOrigDatagramLen(proto int, b []byte) int {
+	roundup := func(b []byte, align int) int {
+		// According to RFC 4884, the padded original datagram
+		// field must contain at least 128 octets.
+		if len(b) < 128 {
+			return 128
+		}
+		r := len(b)
+		return (r + align - 1) & ^(align - 1)
+	}
+	switch proto {
+	case iana.ProtocolICMP:
+		return roundup(b, 4)
+	case iana.ProtocolIPv6ICMP:
+		return roundup(b, 8)
+	default:
+		return len(b)
+	}
+}
+
+// marshalMultipartMessageBody takes data as an original datagram and
+// exts as extesnsions, and returns a binary encoding of message body.
+// It can be used for non-multipart message bodies when exts is nil.
+func marshalMultipartMessageBody(proto int, data []byte, exts []Extension) ([]byte, error) {
+	bodyLen, dataLen := multipartMessageBodyDataLen(proto, data, exts)
+	b := make([]byte, 4+bodyLen)
+	copy(b[4:], data)
+	off := dataLen + 4
+	if len(exts) > 0 {
+		b[dataLen+4] = byte(extensionVersion << 4)
+		off += 4 // length of object header
+		for _, ext := range exts {
+			switch ext := ext.(type) {
+			case *MPLSLabelStack:
+				if err := ext.marshal(proto, b[off:]); err != nil {
+					return nil, err
+				}
+				off += ext.Len(proto)
+			case *InterfaceInfo:
+				attrs, l := ext.attrsAndLen(proto)
+				if err := ext.marshal(proto, b[off:], attrs, l); err != nil {
+					return nil, err
+				}
+				off += ext.Len(proto)
+			}
+		}
+		s := checksum(b[dataLen+4:])
+		b[dataLen+4+2] ^= byte(s)
+		b[dataLen+4+3] ^= byte(s >> 8)
+		switch proto {
+		case iana.ProtocolICMP:
+			b[1] = byte(dataLen / 4)
+		case iana.ProtocolIPv6ICMP:
+			b[0] = byte(dataLen / 8)
+		}
+	}
+	return b, nil
+}
+
+// parseMultipartMessageBody parses b as either a non-multipart
+// message body or a multipart message body.
+func parseMultipartMessageBody(proto int, b []byte) ([]byte, []Extension, error) {
+	var l int
+	switch proto {
+	case iana.ProtocolICMP:
+		l = 4 * int(b[1])
+	case iana.ProtocolIPv6ICMP:
+		l = 8 * int(b[0])
+	}
+	if len(b) == 4 {
+		return nil, nil, nil
+	}
+	exts, l, err := parseExtensions(b[4:], l)
+	if err != nil {
+		l = len(b) - 4
+	}
+	data := make([]byte, l)
+	copy(data, b[4:])
+	return data, exts, nil
+}