259 lines
8 KiB
Go
259 lines
8 KiB
Go
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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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pref "google.golang.org/protobuf/reflect/protoreflect"
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preg "google.golang.org/protobuf/reflect/protoregistry"
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)
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// The MessageSet wire format is equivalent to a message defiend 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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// 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 pref.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 extends a MessageSet.
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func IsMessageSetExtension(fd pref.FieldDescriptor) bool {
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if fd.Name() != ExtensionName {
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return false
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}
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if fd.FullName().Parent() != fd.Message().FullName() {
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return false
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}
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return IsMessageSet(fd.ContainingMessage())
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}
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// FindMessageSetExtension locates a MessageSet extension field by name.
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// In text and JSON formats, the extension name used is the message itself.
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// The extension field name is derived by appending ExtensionName.
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func FindMessageSetExtension(r preg.ExtensionTypeResolver, s pref.FullName) (pref.ExtensionType, error) {
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name := s.Append(ExtensionName)
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xt, err := r.FindExtensionByName(name)
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if err != nil {
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if err == preg.NotFound {
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return nil, err
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}
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return nil, errors.Wrap(err, "%q", name)
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}
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if !IsMessageSetExtension(xt.TypeDescriptor()) {
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return nil, preg.NotFound
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}
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return xt, nil
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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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}
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