Source: build.go in package google.golang.org/protobuf/internal/filedesc

Package filedesc provides functionality for constructing descriptors.

package filedesc

import (
	"google.golang.org/protobuf/encoding/protowire"
	"google.golang.org/protobuf/internal/genid"
	"google.golang.org/protobuf/reflect/protoreflect"
	pref "google.golang.org/protobuf/reflect/protoreflect"
	preg "google.golang.org/protobuf/reflect/protoregistry"
)

Builder construct a protoreflect.FileDescriptor from the raw descriptor.

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.

NumMessages is the total number of messages declared in the file. It includes the implicit message declarations for map entries.

NumExtensions is the total number of extensions declared in the file.

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 {
		preg.ExtensionTypeResolver
	}

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
	listExtTargets
	listExtDeps
	listMethInDeps
	listMethOutDeps
)

Out is the output of the Builder.

type Out struct {
	File pref.FileDescriptor

Enums is all enum descriptors in "flattened ordering".

Messages is all message descriptors in "flattened ordering". It includes the implicit message declarations for map entries.

Extensions is all extension descriptors in "flattened ordering".

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.

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 {
		panic(err)
	}
	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 := protowire.ConsumeTag(b)
		b = b[n:]
		switch typ {
		case protowire.BytesType:
			v, m := protowire.ConsumeBytes(b)
			b = b[m:]
			if isFile {
				switch num {
				case genid.FileDescriptorProto_EnumType_field_number:
					db.NumEnums++
				case genid.FileDescriptorProto_MessageType_field_number:
					db.unmarshalCounts(v, false)
					db.NumMessages++
				case genid.FileDescriptorProto_Extension_field_number:
					db.NumExtensions++
				case genid.FileDescriptorProto_Service_field_number:
					db.NumServices++
				}
			} else {
				switch num {
				case genid.DescriptorProto_EnumType_field_number:
					db.NumEnums++
				case genid.DescriptorProto_NestedType_field_number:
					db.unmarshalCounts(v, false)
					db.NumMessages++
				case genid.DescriptorProto_Extension_field_number:
					db.NumExtensions++
				}
			}
		default:
			m := protowire.ConsumeFieldValue(num, typ, b)
			b = b[m:]
		}
	}