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.

     6 package messageset

     7 

     8 import (

     9 	"math"

    10 

    11 	"google.golang.org/protobuf/encoding/protowire"

    12 	"google.golang.org/protobuf/internal/errors"

    13 	pref "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 //	}

    27 const (

    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 //	message MyMessage {

    37 //		extend proto2.bridge.MessageSet {

    38 //			optional MyMessage message_set_extension = 1234;

    39 //		}

    40 //		...

    41 //	}

    42 const ExtensionName = "message_set_extension"

    43 

    44 // IsMessageSet returns whether the message uses the MessageSet wire format.

    45 func IsMessageSet(md pref.MessageDescriptor) bool {

    46 	xmd, ok := md.(interface{ IsMessageSet() bool })

    47 	return ok && xmd.IsMessageSet()

    48 }

    49 

    50 // IsMessageSetExtension reports this field properly extends a MessageSet.

    51 func IsMessageSetExtension(fd pref.FieldDescriptor) bool {

    52 	switch {

    53 	case fd.Name() != ExtensionName:

    54 		return false

    55 	case !IsMessageSet(fd.ContainingMessage()):

    56 		return false

    57 	case fd.FullName().Parent() != fd.Message().FullName():

    58 		return false

    59 	}

    60 	return true

    61 }

    62 

    63 // SizeField returns the size of a MessageSet item field containing an extension

    64 // with the given field number, not counting the contents of the message subfield.

    65 func SizeField(num protowire.Number) int {

    66 	return 2*protowire.SizeTag(FieldItem) + protowire.SizeTag(FieldTypeID) + protowire.SizeVarint(uint64(num))

    67 }

    68 

    69 // Unmarshal parses a MessageSet.

    70 //

    71 // It calls fn with the type ID and value of each item in the MessageSet.

    72 // Unknown fields are discarded.

    73 //

    74 // If wantLen is true, the item values include the varint length prefix.

    75 // This is ugly, but simplifies the fast-path decoder in internal/impl.

    76 func Unmarshal(b []byte, wantLen bool, fn func(typeID protowire.Number, value []byte) error) error {

    77 	for len(b) > 0 {

    78 		num, wtyp, n := protowire.ConsumeTag(b)

    79 		if n < 0 {

    80 			return protowire.ParseError(n)

    81 		}

    82 		b = b[n:]

    83 		if num != FieldItem || wtyp != protowire.StartGroupType {

    84 			n := protowire.ConsumeFieldValue(num, wtyp, b)

    85 			if n < 0 {

    86 				return protowire.ParseError(n)

    87 			}

    88 			b = b[n:]

    89 			continue

    90 		}

    91 		typeID, value, n, err := ConsumeFieldValue(b, wantLen)

    92 		if err != nil {

    93 			return err

    94 		}

    95 		b = b[n:]

    96 		if typeID == 0 {

    97 			continue

    98 		}

    99 		if err := fn(typeID, value); err != nil {

   100 			return err

   101 		}

   102 	}

   103 	return nil

   104 }

   105 

   106 // ConsumeFieldValue parses b as a MessageSet item field value until and including

   107 // the trailing end group marker. It assumes the start group tag has already been parsed.

   108 // It returns the contents of the type_id and message subfields and the total

   109 // item length.

   110 //

   111 // If wantLen is true, the returned message value includes the length prefix.

   112 func ConsumeFieldValue(b []byte, wantLen bool) (typeid protowire.Number, message []byte, n int, err error) {

   113 	ilen := len(b)

   114 	for {

   115 		num, wtyp, n := protowire.ConsumeTag(b)

   116 		if n < 0 {

   117 			return 0, nil, 0, protowire.ParseError(n)

   118 		}

   119 		b = b[n:]

   120 		switch {

   121 		case num == FieldItem && wtyp == protowire.EndGroupType:

   122 			if wantLen && len(message) == 0 {

   123 				// The message field was missing, which should never happen.

   124 				// Be prepared for this case anyway.

   125 				message = protowire.AppendVarint(message, 0)

   126 			}

   127 			return typeid, message, ilen - len(b), nil

   128 		case num == FieldTypeID && wtyp == protowire.VarintType:

   129 			v, n := protowire.ConsumeVarint(b)

   130 			if n < 0 {

   131 				return 0, nil, 0, protowire.ParseError(n)

   132 			}

   133 			b = b[n:]

   134 			if v < 1 || v > math.MaxInt32 {

   135 				return 0, nil, 0, errors.New("invalid type_id in message set")

   136 			}

   137 			typeid = protowire.Number(v)

   138 		case num == FieldMessage && wtyp == protowire.BytesType:

   139 			m, n := protowire.ConsumeBytes(b)

   140 			if n < 0 {

   141 				return 0, nil, 0, protowire.ParseError(n)

   142 			}

   143 			if message == nil {

   144 				if wantLen {

   145 					message = b[:n:n]

   146 				} else {

   147 					message = m[:len(m):len(m)]

   148 				}

   149 			} else {

   150 				// This case should never happen in practice, but handle it for

   151 				// correctness: The MessageSet item contains multiple message

   152 				// fields, which need to be merged.

   153 				//

   154 				// In the case where we're returning the length, this becomes

   155 				// quite inefficient since we need to strip the length off

   156 				// the existing data and reconstruct it with the combined length.

   157 				if wantLen {

   158 					_, nn := protowire.ConsumeVarint(message)

   159 					m0 := message[nn:]

   160 					message = nil

   161 					message = protowire.AppendVarint(message, uint64(len(m0)+len(m)))

   162 					message = append(message, m0...)

   163 					message = append(message, m...)

   164 				} else {

   165 					message = append(message, m...)

   166 				}

   167 			}

   168 			b = b[n:]

   169 		default:

   170 			// We have no place to put it, so we just ignore unknown fields.

   171 			n := protowire.ConsumeFieldValue(num, wtyp, b)

   172 			if n < 0 {

   173 				return 0, nil, 0, protowire.ParseError(n)

   174 			}

   175 			b = b[n:]

   176 		}

   177 	}

   178 }

   179 

   180 // AppendFieldStart appends the start of a MessageSet item field containing

   181 // an extension with the given number. The caller must add the message

   182 // subfield (including the tag).

   183 func AppendFieldStart(b []byte, num protowire.Number) []byte {

   184 	b = protowire.AppendTag(b, FieldItem, protowire.StartGroupType)

   185 	b = protowire.AppendTag(b, FieldTypeID, protowire.VarintType)

   186 	b = protowire.AppendVarint(b, uint64(num))

   187 	return b

   188 }

   189 

   190 // AppendFieldEnd appends the trailing end group marker for a MessageSet item field.

   191 func AppendFieldEnd(b []byte) []byte {

   192 	return protowire.AppendTag(b, FieldItem, protowire.EndGroupType)

   193 }

   194 

   195 // SizeUnknown returns the size of an unknown fields section in MessageSet format.

   196 //

   197 // See AppendUnknown.

   198 func SizeUnknown(unknown []byte) (size int) {

   199 	for len(unknown) > 0 {

   200 		num, typ, n := protowire.ConsumeTag(unknown)

   201 		if n < 0 || typ != protowire.BytesType {

   202 			return 0

   203 		}

   204 		unknown = unknown[n:]

   205 		_, n = protowire.ConsumeBytes(unknown)

   206 		if n < 0 {

   207 			return 0

   208 		}

   209 		unknown = unknown[n:]

   210 		size += SizeField(num) + protowire.SizeTag(FieldMessage) + n

   211 	}

   212 	return size

   213 }

   214 

   215 // AppendUnknown appends unknown fields to b in MessageSet format.

   216 //

   217 // For historic reasons, unresolved items in a MessageSet are stored in a

   218 // message's unknown fields section in non-MessageSet format. That is, an

   219 // unknown item with typeID T and value V appears in the unknown fields as

   220 // a field with number T and value V.

   221 //

   222 // This function converts the unknown fields back into MessageSet form.

   223 func AppendUnknown(b, unknown []byte) ([]byte, error) {

   224 	for len(unknown) > 0 {

   225 		num, typ, n := protowire.ConsumeTag(unknown)

   226 		if n < 0 || typ != protowire.BytesType {

   227 			return nil, errors.New("invalid data in message set unknown fields")

   228 		}

   229 		unknown = unknown[n:]

   230 		_, n = protowire.ConsumeBytes(unknown)

   231 		if n < 0 {

   232 			return nil, errors.New("invalid data in message set unknown fields")

   233 		}

   234 		b = AppendFieldStart(b, num)

   235 		b = protowire.AppendTag(b, FieldMessage, protowire.BytesType)

   236 		b = append(b, unknown[:n]...)

   237 		b = AppendFieldEnd(b)

   238 		unknown = unknown[n:]

   239 	}

   240 	return b, nil

   241 }