diff --git a/vendor/google.golang.org/protobuf/internal/encoding/messageset/messageset.go b/vendor/google.golang.org/protobuf/internal/encoding/messageset/messageset.go
new file mode 100644
index 0000000..b1eeea5
--- /dev/null
+++ b/vendor/google.golang.org/protobuf/internal/encoding/messageset/messageset.go
@@ -0,0 +1,258 @@
+// Copyright 2019 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 messageset encodes and decodes the obsolete MessageSet wire format.
+package messageset
+
+import (
+	"math"
+
+	"google.golang.org/protobuf/encoding/protowire"
+	"google.golang.org/protobuf/internal/errors"
+	pref "google.golang.org/protobuf/reflect/protoreflect"
+	preg "google.golang.org/protobuf/reflect/protoregistry"
+)
+
+// The MessageSet wire format is equivalent to a message defiend as follows,
+// where each Item defines an extension field with a field number of 'type_id'
+// and content of 'message'. MessageSet extensions must be non-repeated message
+// fields.
+//
+//	message MessageSet {
+//		repeated group Item = 1 {
+//			required int32 type_id = 2;
+//			required string message = 3;
+//		}
+//	}
+const (
+	FieldItem    = protowire.Number(1)
+	FieldTypeID  = protowire.Number(2)
+	FieldMessage = protowire.Number(3)
+)
+
+// ExtensionName is the field name for extensions of MessageSet.
+//
+// A valid MessageSet extension must be of the form:
+//	message MyMessage {
+//		extend proto2.bridge.MessageSet {
+//			optional MyMessage message_set_extension = 1234;
+//		}
+//		...
+//	}
+const ExtensionName = "message_set_extension"
+
+// IsMessageSet returns whether the message uses the MessageSet wire format.
+func IsMessageSet(md pref.MessageDescriptor) bool {
+	xmd, ok := md.(interface{ IsMessageSet() bool })
+	return ok && xmd.IsMessageSet()
+}
+
+// IsMessageSetExtension reports this field extends a MessageSet.
+func IsMessageSetExtension(fd pref.FieldDescriptor) bool {
+	if fd.Name() != ExtensionName {
+		return false
+	}
+	if fd.FullName().Parent() != fd.Message().FullName() {
+		return false
+	}
+	return IsMessageSet(fd.ContainingMessage())
+}
+
+// FindMessageSetExtension locates a MessageSet extension field by name.
+// In text and JSON formats, the extension name used is the message itself.
+// The extension field name is derived by appending ExtensionName.
+func FindMessageSetExtension(r preg.ExtensionTypeResolver, s pref.FullName) (pref.ExtensionType, error) {
+	name := s.Append(ExtensionName)
+	xt, err := r.FindExtensionByName(name)
+	if err != nil {
+		if err == preg.NotFound {
+			return nil, err
+		}
+		return nil, errors.Wrap(err, "%q", name)
+	}
+	if !IsMessageSetExtension(xt.TypeDescriptor()) {
+		return nil, preg.NotFound
+	}
+	return xt, nil
+}
+
+// SizeField returns the size of a MessageSet item field containing an extension
+// with the given field number, not counting the contents of the message subfield.
+func SizeField(num protowire.Number) int {
+	return 2*protowire.SizeTag(FieldItem) + protowire.SizeTag(FieldTypeID) + protowire.SizeVarint(uint64(num))
+}
+
+// Unmarshal parses a MessageSet.
+//
+// It calls fn with the type ID and value of each item in the MessageSet.
+// Unknown fields are discarded.
+//
+// If wantLen is true, the item values include the varint length prefix.
+// This is ugly, but simplifies the fast-path decoder in internal/impl.
+func Unmarshal(b []byte, wantLen bool, fn func(typeID protowire.Number, value []byte) error) error {
+	for len(b) > 0 {
+		num, wtyp, n := protowire.ConsumeTag(b)
+		if n < 0 {
+			return protowire.ParseError(n)
+		}
+		b = b[n:]
+		if num != FieldItem || wtyp != protowire.StartGroupType {
+			n := protowire.ConsumeFieldValue(num, wtyp, b)
+			if n < 0 {
+				return protowire.ParseError(n)
+			}
+			b = b[n:]
+			continue
+		}
+		typeID, value, n, err := ConsumeFieldValue(b, wantLen)
+		if err != nil {
+			return err
+		}
+		b = b[n:]
+		if typeID == 0 {
+			continue
+		}
+		if err := fn(typeID, value); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// ConsumeFieldValue parses b as a MessageSet item field value until and including
+// the trailing end group marker. It assumes the start group tag has already been parsed.
+// It returns the contents of the type_id and message subfields and the total
+// item length.
+//
+// If wantLen is true, the returned message value includes the length prefix.
+func ConsumeFieldValue(b []byte, wantLen bool) (typeid protowire.Number, message []byte, n int, err error) {
+	ilen := len(b)
+	for {
+		num, wtyp, n := protowire.ConsumeTag(b)
+		if n < 0 {
+			return 0, nil, 0, protowire.ParseError(n)
+		}
+		b = b[n:]
+		switch {
+		case num == FieldItem && wtyp == protowire.EndGroupType:
+			if wantLen && len(message) == 0 {
+				// The message field was missing, which should never happen.
+				// Be prepared for this case anyway.
+				message = protowire.AppendVarint(message, 0)
+			}
+			return typeid, message, ilen - len(b), nil
+		case num == FieldTypeID && wtyp == protowire.VarintType:
+			v, n := protowire.ConsumeVarint(b)
+			if n < 0 {
+				return 0, nil, 0, protowire.ParseError(n)
+			}
+			b = b[n:]
+			if v < 1 || v > math.MaxInt32 {
+				return 0, nil, 0, errors.New("invalid type_id in message set")
+			}
+			typeid = protowire.Number(v)
+		case num == FieldMessage && wtyp == protowire.BytesType:
+			m, n := protowire.ConsumeBytes(b)
+			if n < 0 {
+				return 0, nil, 0, protowire.ParseError(n)
+			}
+			if message == nil {
+				if wantLen {
+					message = b[:n:n]
+				} else {
+					message = m[:len(m):len(m)]
+				}
+			} else {
+				// This case should never happen in practice, but handle it for
+				// correctness: The MessageSet item contains multiple message
+				// fields, which need to be merged.
+				//
+				// In the case where we're returning the length, this becomes
+				// quite inefficient since we need to strip the length off
+				// the existing data and reconstruct it with the combined length.
+				if wantLen {
+					_, nn := protowire.ConsumeVarint(message)
+					m0 := message[nn:]
+					message = nil
+					message = protowire.AppendVarint(message, uint64(len(m0)+len(m)))
+					message = append(message, m0...)
+					message = append(message, m...)
+				} else {
+					message = append(message, m...)
+				}
+			}
+			b = b[n:]
+		default:
+			// We have no place to put it, so we just ignore unknown fields.
+			n := protowire.ConsumeFieldValue(num, wtyp, b)
+			if n < 0 {
+				return 0, nil, 0, protowire.ParseError(n)
+			}
+			b = b[n:]
+		}
+	}
+}
+
+// AppendFieldStart appends the start of a MessageSet item field containing
+// an extension with the given number. The caller must add the message
+// subfield (including the tag).
+func AppendFieldStart(b []byte, num protowire.Number) []byte {
+	b = protowire.AppendTag(b, FieldItem, protowire.StartGroupType)
+	b = protowire.AppendTag(b, FieldTypeID, protowire.VarintType)
+	b = protowire.AppendVarint(b, uint64(num))
+	return b
+}
+
+// AppendFieldEnd appends the trailing end group marker for a MessageSet item field.
+func AppendFieldEnd(b []byte) []byte {
+	return protowire.AppendTag(b, FieldItem, protowire.EndGroupType)
+}
+
+// SizeUnknown returns the size of an unknown fields section in MessageSet format.
+//
+// See AppendUnknown.
+func SizeUnknown(unknown []byte) (size int) {
+	for len(unknown) > 0 {
+		num, typ, n := protowire.ConsumeTag(unknown)
+		if n < 0 || typ != protowire.BytesType {
+			return 0
+		}
+		unknown = unknown[n:]
+		_, n = protowire.ConsumeBytes(unknown)
+		if n < 0 {
+			return 0
+		}
+		unknown = unknown[n:]
+		size += SizeField(num) + protowire.SizeTag(FieldMessage) + n
+	}
+	return size
+}
+
+// AppendUnknown appends unknown fields to b in MessageSet format.
+//
+// For historic reasons, unresolved items in a MessageSet are stored in a
+// message's unknown fields section in non-MessageSet format. That is, an
+// unknown item with typeID T and value V appears in the unknown fields as
+// a field with number T and value V.
+//
+// This function converts the unknown fields back into MessageSet form.
+func AppendUnknown(b, unknown []byte) ([]byte, error) {
+	for len(unknown) > 0 {
+		num, typ, n := protowire.ConsumeTag(unknown)
+		if n < 0 || typ != protowire.BytesType {
+			return nil, errors.New("invalid data in message set unknown fields")
+		}
+		unknown = unknown[n:]
+		_, n = protowire.ConsumeBytes(unknown)
+		if n < 0 {
+			return nil, errors.New("invalid data in message set unknown fields")
+		}
+		b = AppendFieldStart(b, num)
+		b = protowire.AppendTag(b, FieldMessage, protowire.BytesType)
+		b = append(b, unknown[:n]...)
+		b = AppendFieldEnd(b)
+		unknown = unknown[n:]
+	}
+	return b, nil
+}