1// Copyright 2019 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5// Package messageset encodes and decodes the obsolete MessageSet wire format.
6package messageset
7
8import (
9 "math"
10
11 "google.golang.org/protobuf/encoding/protowire"
12 "google.golang.org/protobuf/internal/errors"
13 "google.golang.org/protobuf/reflect/protoreflect"
14)
15
16// The MessageSet wire format is equivalent to a message defined as follows,
17// where each Item defines an extension field with a field number of 'type_id'
18// and content of 'message'. MessageSet extensions must be non-repeated message
19// fields.
20//
21// message MessageSet {
22// repeated group Item = 1 {
23// required int32 type_id = 2;
24// required string message = 3;
25// }
26// }
27const (
28 FieldItem = protowire.Number(1)
29 FieldTypeID = protowire.Number(2)
30 FieldMessage = protowire.Number(3)
31)
32
33// ExtensionName is the field name for extensions of MessageSet.
34//
35// A valid MessageSet extension must be of the form:
36//
37// message MyMessage {
38// extend proto2.bridge.MessageSet {
39// optional MyMessage message_set_extension = 1234;
40// }
41// ...
42// }
43const ExtensionName = "message_set_extension"
44
45// IsMessageSet returns whether the message uses the MessageSet wire format.
46func IsMessageSet(md protoreflect.MessageDescriptor) bool {
47 xmd, ok := md.(interface{ IsMessageSet() bool })
48 return ok && xmd.IsMessageSet()
49}
50
51// IsMessageSetExtension reports this field properly extends a MessageSet.
52func IsMessageSetExtension(fd protoreflect.FieldDescriptor) bool {
53 switch {
54 case fd.Name() != ExtensionName:
55 return false
56 case !IsMessageSet(fd.ContainingMessage()):
57 return false
58 case fd.FullName().Parent() != fd.Message().FullName():
59 return false
60 }
61 return true
62}
63
64// SizeField returns the size of a MessageSet item field containing an extension
65// with the given field number, not counting the contents of the message subfield.
66func SizeField(num protowire.Number) int {
67 return 2*protowire.SizeTag(FieldItem) + protowire.SizeTag(FieldTypeID) + protowire.SizeVarint(uint64(num))
68}
69
70// Unmarshal parses a MessageSet.
71//
72// It calls fn with the type ID and value of each item in the MessageSet.
73// Unknown fields are discarded.
74//
75// If wantLen is true, the item values include the varint length prefix.
76// This is ugly, but simplifies the fast-path decoder in internal/impl.
77func Unmarshal(b []byte, wantLen bool, fn func(typeID protowire.Number, value []byte) error) error {
78 for len(b) > 0 {
79 num, wtyp, n := protowire.ConsumeTag(b)
80 if n < 0 {
81 return protowire.ParseError(n)
82 }
83 b = b[n:]
84 if num != FieldItem || wtyp != protowire.StartGroupType {
85 n := protowire.ConsumeFieldValue(num, wtyp, b)
86 if n < 0 {
87 return protowire.ParseError(n)
88 }
89 b = b[n:]
90 continue
91 }
92 typeID, value, n, err := ConsumeFieldValue(b, wantLen)
93 if err != nil {
94 return err
95 }
96 b = b[n:]
97 if typeID == 0 {
98 continue
99 }
100 if err := fn(typeID, value); err != nil {
101 return err
102 }
103 }
104 return nil
105}
106
107// ConsumeFieldValue parses b as a MessageSet item field value until and including
108// the trailing end group marker. It assumes the start group tag has already been parsed.
109// It returns the contents of the type_id and message subfields and the total
110// item length.
111//
112// If wantLen is true, the returned message value includes the length prefix.
113func ConsumeFieldValue(b []byte, wantLen bool) (typeid protowire.Number, message []byte, n int, err error) {
114 ilen := len(b)
115 for {
116 num, wtyp, n := protowire.ConsumeTag(b)
117 if n < 0 {
118 return 0, nil, 0, protowire.ParseError(n)
119 }
120 b = b[n:]
121 switch {
122 case num == FieldItem && wtyp == protowire.EndGroupType:
123 if wantLen && len(message) == 0 {
124 // The message field was missing, which should never happen.
125 // Be prepared for this case anyway.
126 message = protowire.AppendVarint(message, 0)
127 }
128 return typeid, message, ilen - len(b), nil
129 case num == FieldTypeID && wtyp == protowire.VarintType:
130 v, n := protowire.ConsumeVarint(b)
131 if n < 0 {
132 return 0, nil, 0, protowire.ParseError(n)
133 }
134 b = b[n:]
135 if v < 1 || v > math.MaxInt32 {
136 return 0, nil, 0, errors.New("invalid type_id in message set")
137 }
138 typeid = protowire.Number(v)
139 case num == FieldMessage && wtyp == protowire.BytesType:
140 m, n := protowire.ConsumeBytes(b)
141 if n < 0 {
142 return 0, nil, 0, protowire.ParseError(n)
143 }
144 if message == nil {
145 if wantLen {
146 message = b[:n:n]
147 } else {
148 message = m[:len(m):len(m)]
149 }
150 } else {
151 // This case should never happen in practice, but handle it for
152 // correctness: The MessageSet item contains multiple message
153 // fields, which need to be merged.
154 //
155 // In the case where we're returning the length, this becomes
156 // quite inefficient since we need to strip the length off
157 // the existing data and reconstruct it with the combined length.
158 if wantLen {
159 _, nn := protowire.ConsumeVarint(message)
160 m0 := message[nn:]
161 message = nil
162 message = protowire.AppendVarint(message, uint64(len(m0)+len(m)))
163 message = append(message, m0...)
164 message = append(message, m...)
165 } else {
166 message = append(message, m...)
167 }
168 }
169 b = b[n:]
170 default:
171 // We have no place to put it, so we just ignore unknown fields.
172 n := protowire.ConsumeFieldValue(num, wtyp, b)
173 if n < 0 {
174 return 0, nil, 0, protowire.ParseError(n)
175 }
176 b = b[n:]
177 }
178 }
179}
180
181// AppendFieldStart appends the start of a MessageSet item field containing
182// an extension with the given number. The caller must add the message
183// subfield (including the tag).
184func AppendFieldStart(b []byte, num protowire.Number) []byte {
185 b = protowire.AppendTag(b, FieldItem, protowire.StartGroupType)
186 b = protowire.AppendTag(b, FieldTypeID, protowire.VarintType)
187 b = protowire.AppendVarint(b, uint64(num))
188 return b
189}
190
191// AppendFieldEnd appends the trailing end group marker for a MessageSet item field.
192func AppendFieldEnd(b []byte) []byte {
193 return protowire.AppendTag(b, FieldItem, protowire.EndGroupType)
194}
195
196// SizeUnknown returns the size of an unknown fields section in MessageSet format.
197//
198// See AppendUnknown.
199func SizeUnknown(unknown []byte) (size int) {
200 for len(unknown) > 0 {
201 num, typ, n := protowire.ConsumeTag(unknown)
202 if n < 0 || typ != protowire.BytesType {
203 return 0
204 }
205 unknown = unknown[n:]
206 _, n = protowire.ConsumeBytes(unknown)
207 if n < 0 {
208 return 0
209 }
210 unknown = unknown[n:]
211 size += SizeField(num) + protowire.SizeTag(FieldMessage) + n
212 }
213 return size
214}
215
216// AppendUnknown appends unknown fields to b in MessageSet format.
217//
218// For historic reasons, unresolved items in a MessageSet are stored in a
219// message's unknown fields section in non-MessageSet format. That is, an
220// unknown item with typeID T and value V appears in the unknown fields as
221// a field with number T and value V.
222//
223// This function converts the unknown fields back into MessageSet form.
224func AppendUnknown(b, unknown []byte) ([]byte, error) {
225 for len(unknown) > 0 {
226 num, typ, n := protowire.ConsumeTag(unknown)
227 if n < 0 || typ != protowire.BytesType {
228 return nil, errors.New("invalid data in message set unknown fields")
229 }
230 unknown = unknown[n:]
231 _, n = protowire.ConsumeBytes(unknown)
232 if n < 0 {
233 return nil, errors.New("invalid data in message set unknown fields")
234 }
235 b = AppendFieldStart(b, num)
236 b = protowire.AppendTag(b, FieldMessage, protowire.BytesType)
237 b = append(b, unknown[:n]...)
238 b = AppendFieldEnd(b)
239 unknown = unknown[n:]
240 }
241 return b, nil
242}