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// 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 filedesc provides functionality for constructing descriptors.
package filedesc
import (
pref ""
preg ""
// Builder construct a protoreflect.FileDescriptor from the raw descriptor.
type Builder struct {
// GoPackagePath is the Go package path that is invoking this builder.
GoPackagePath string
// RawDescriptor is the wire-encoded bytes of FileDescriptorProto
// and must be populated.
RawDescriptor []byte
// NumEnums is the total number of enums declared in the file.
NumEnums int32
// NumMessages is the total number of messages declared in the file.
// It includes the implicit message declarations for map entries.
NumMessages int32
// NumExtensions is the total number of extensions declared in the file.
NumExtensions int32
// NumServices is the total number of services declared in the file.
NumServices int32
// TypeResolver resolves extension field types for descriptor options.
// If nil, it uses protoregistry.GlobalTypes.
TypeResolver interface {
// FileRegistry is use to lookup file, enum, and message dependencies.
// Once constructed, the file descriptor is registered here.
// If nil, it uses protoregistry.GlobalFiles.
FileRegistry interface {
FindFileByPath(string) (protoreflect.FileDescriptor, error)
FindDescriptorByName(pref.FullName) (pref.Descriptor, error)
RegisterFile(pref.FileDescriptor) error
// resolverByIndex is an interface Builder.FileRegistry may implement.
// If so, it permits looking up an enum or message dependency based on the
// sub-list and element index into filetype.Builder.DependencyIndexes.
type resolverByIndex interface {
FindEnumByIndex(int32, int32, []Enum, []Message) pref.EnumDescriptor
FindMessageByIndex(int32, int32, []Enum, []Message) pref.MessageDescriptor
// Indexes of each sub-list in filetype.Builder.DependencyIndexes.
const (
listFieldDeps int32 = iota
// Out is the output of the Builder.
type Out struct {
File pref.FileDescriptor
// Enums is all enum descriptors in "flattened ordering".
Enums []Enum
// Messages is all message descriptors in "flattened ordering".
// It includes the implicit message declarations for map entries.
Messages []Message
// Extensions is all extension descriptors in "flattened ordering".
Extensions []Extension
// Service is all service descriptors in "flattened ordering".
Services []Service
// Build constructs a FileDescriptor given the parameters set in Builder.
// It assumes that the inputs are well-formed and panics if any inconsistencies
// are encountered.
// If NumEnums+NumMessages+NumExtensions+NumServices is zero,
// then Build automatically derives them from the raw descriptor.
func (db Builder) Build() (out Out) {
// Populate the counts if uninitialized.
if db.NumEnums+db.NumMessages+db.NumExtensions+db.NumServices == 0 {
db.unmarshalCounts(db.RawDescriptor, true)
// Initialize resolvers and registries if unpopulated.
if db.TypeResolver == nil {
db.TypeResolver = preg.GlobalTypes
if db.FileRegistry == nil {
db.FileRegistry = preg.GlobalFiles
fd := newRawFile(db)
out.File = fd
out.Enums = fd.allEnums
out.Messages = fd.allMessages
out.Extensions = fd.allExtensions
out.Services = fd.allServices
if err := db.FileRegistry.RegisterFile(fd); err != nil {
return out
// unmarshalCounts counts the number of enum, message, extension, and service
// declarations in the raw message, which is either a FileDescriptorProto
// or a MessageDescriptorProto depending on whether isFile is set.
func (db *Builder) unmarshalCounts(b []byte, isFile bool) {
for len(b) > 0 {
num, typ, n := wire.ConsumeTag(b)
b = b[n:]
switch typ {
case wire.BytesType:
v, m := wire.ConsumeBytes(b)
b = b[m:]
if isFile {
switch num {
case fieldnum.FileDescriptorProto_EnumType:
case fieldnum.FileDescriptorProto_MessageType:
db.unmarshalCounts(v, false)
case fieldnum.FileDescriptorProto_Extension:
case fieldnum.FileDescriptorProto_Service:
} else {
switch num {
case fieldnum.DescriptorProto_EnumType:
case fieldnum.DescriptorProto_NestedType:
db.unmarshalCounts(v, false)
case fieldnum.DescriptorProto_Extension:
m := wire.ConsumeFieldValue(num, typ, b)
b = b[m:]