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