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


package filedesc

import (
	"sync"

	"google.golang.org/protobuf/encoding/protowire"
	"google.golang.org/protobuf/internal/genid"
	"google.golang.org/protobuf/internal/strs"
	pref "google.golang.org/protobuf/reflect/protoreflect"
)

fileRaw is a data struct used when initializing a file descriptor from a raw FileDescriptorProto.

type fileRaw struct {
	builder       Builder
	allEnums      []Enum
	allMessages   []Message
	allExtensions []Extension
	allServices   []Service
}

func newRawFile(db Builder) *File {
	fd := &File{fileRaw: fileRaw{builder: db}}
	fd.initDecls(db.NumEnums, db.NumMessages, db.NumExtensions, db.NumServices)
	fd.unmarshalSeed(db.RawDescriptor)

Extended message targets are eagerly resolved since registration needs this information at program init time.

	for i := range fd.allExtensions {
		xd := &fd.allExtensions[i]
		xd.L1.Extendee = fd.resolveMessageDependency(xd.L1.Extendee, listExtTargets, int32(i))
	}

	fd.checkDecls()
	return fd
}

initDecls pre-allocates slices for the exact number of enums, messages (including map entries), extensions, and services declared in the proto file. This is done to avoid regrowing the slice, which would change the address for any previously seen declaration. The alloc methods "allocates" slices by pulling from the capacity.

func (fd *File) initDecls(numEnums, numMessages, numExtensions, numServices int32) {
	fd.allEnums = make([]Enum, 0, numEnums)
	fd.allMessages = make([]Message, 0, numMessages)
	fd.allExtensions = make([]Extension, 0, numExtensions)
	fd.allServices = make([]Service, 0, numServices)
}

func (fd *File) allocEnums(n int) []Enum {
	total := len(fd.allEnums)
	es := fd.allEnums[total : total+n]
	fd.allEnums = fd.allEnums[:total+n]
	return es
}
func (fd *File) allocMessages(n int) []Message {
	total := len(fd.allMessages)
	ms := fd.allMessages[total : total+n]
	fd.allMessages = fd.allMessages[:total+n]
	return ms
}
func (fd *File) allocExtensions(n int) []Extension {
	total := len(fd.allExtensions)
	xs := fd.allExtensions[total : total+n]
	fd.allExtensions = fd.allExtensions[:total+n]
	return xs
}
func (fd *File) allocServices(n int) []Service {
	total := len(fd.allServices)
	xs := fd.allServices[total : total+n]
	fd.allServices = fd.allServices[:total+n]
	return xs
}

checkDecls performs a sanity check that the expected number of expected declarations matches the number that were found in the descriptor proto.

func (fd *File) checkDecls() {
	switch {
	case len(fd.allEnums) != cap(fd.allEnums):
	case len(fd.allMessages) != cap(fd.allMessages):
	case len(fd.allExtensions) != cap(fd.allExtensions):
	case len(fd.allServices) != cap(fd.allServices):
	default:
		return
	}
	panic("mismatching cardinality")
}

func (fd *File) unmarshalSeed(b []byte) {
	sb := getBuilder()
	defer putBuilder(sb)

	var prevField pref.FieldNumber
	var numEnums, numMessages, numExtensions, numServices int
	var posEnums, posMessages, posExtensions, posServices int
	b0 := b
	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:]
			switch num {
			case genid.FileDescriptorProto_Syntax_field_number:
				switch string(v) {
				case "proto2":
					fd.L1.Syntax = pref.Proto2
				case "proto3":
					fd.L1.Syntax = pref.Proto3
				default:
					panic("invalid syntax")
				}
			case genid.FileDescriptorProto_Name_field_number:
				fd.L1.Path = sb.MakeString(v)
			case genid.FileDescriptorProto_Package_field_number:
				fd.L1.Package = pref.FullName(sb.MakeString(v))
			case genid.FileDescriptorProto_EnumType_field_number:
				if prevField != genid.FileDescriptorProto_EnumType_field_number {
					if numEnums > 0 {
						panic("non-contiguous repeated field")
					}
					posEnums = len(b0) - len(b) - n - m
				}
				numEnums++
			case genid.FileDescriptorProto_MessageType_field_number:
				if prevField != genid.FileDescriptorProto_MessageType_field_number {
					if numMessages > 0 {
						panic("non-contiguous repeated field")
					}
					posMessages = len(b0) - len(b) - n - m
				}
				numMessages++
			case genid.FileDescriptorProto_Extension_field_number:
				if prevField != genid.FileDescriptorProto_Extension_field_number {
					if numExtensions > 0 {
						panic("non-contiguous repeated field")
					}
					posExtensions = len(b0) - len(b) - n - m
				}
				numExtensions++
			case genid.FileDescriptorProto_Service_field_number:
				if prevField != genid.FileDescriptorProto_Service_field_number {
					if numServices > 0 {
						panic("non-contiguous repeated field")
					}
					posServices = len(b0) - len(b) - n - m
				}
				numServices++
			}
			prevField = num
		default:
			m := protowire.ConsumeFieldValue(num, typ, b)
			b = b[m:]
			prevField = -1 // ignore known field numbers of unknown wire type
		}
	}

If syntax is missing, it is assumed to be proto2.

	if fd.L1.Syntax == 0 {
		fd.L1.Syntax = pref.Proto2
	}

Must allocate all declarations before parsing each descriptor type to ensure we handled all descriptors in "flattened ordering".

	if numEnums > 0 {
		fd.L1.Enums.List = fd.allocEnums(numEnums)
	}
	if numMessages > 0 {
		fd.L1.Messages.List = fd.allocMessages(numMessages)
	}
	if numExtensions > 0 {
		fd.L1.Extensions.List = fd.allocExtensions(numExtensions)
	}
	if numServices > 0 {
		fd.L1.Services.List = fd.allocServices(numServices)
	}

	if numEnums > 0 {
		b := b0[posEnums:]
		for i := range fd.L1.Enums.List {
			_, n := protowire.ConsumeVarint(b)
			v, m := protowire.ConsumeBytes(b[n:])
			fd.L1.Enums.List[i].unmarshalSeed(v, sb, fd, fd, i)
			b = b[n+m:]
		}
	}
	if numMessages > 0 {
		b := b0[posMessages:]
		for i := range fd.L1.Messages.List {
			_, n := protowire.ConsumeVarint(b)
			v, m := protowire.ConsumeBytes(b[n:])
			fd.L1.Messages.List[i].unmarshalSeed(v, sb, fd, fd, i)
			b = b[n+m:]
		}
	}
	if numExtensions > 0 {
		b := b0[posExtensions:]
		for i := range fd.L1.Extensions.List {
			_, n := protowire.ConsumeVarint(b)
			v, m := protowire.ConsumeBytes(b[n:])
			fd.L1.Extensions.List[i].unmarshalSeed(v, sb, fd, fd, i)
			b = b[n+m:]
		}
	}
	if numServices > 0 {
		b := b0[posServices:]
		for i := range fd.L1.Services.List {
			_, n := protowire.ConsumeVarint(b)
			v, m := protowire.ConsumeBytes(b[n:])
			fd.L1.Services.List[i].unmarshalSeed(v, sb, fd, fd, i)
			b = b[n+m:]
		}
	}
}

func (ed *Enum) unmarshalSeed(b []byte, sb *strs.Builder, pf *File, pd pref.Descriptor, i int) {
	ed.L0.ParentFile = pf
	ed.L0.Parent = pd
	ed.L0.Index = i

	var numValues int
	for b := b; 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:]
			switch num {
			case genid.EnumDescriptorProto_Name_field_number:
				ed.L0.FullName = appendFullName(sb, pd.FullName(), v)
			case genid.EnumDescriptorProto_Value_field_number:
				numValues++
			}
		default:
			m := protowire.ConsumeFieldValue(num, typ, b)
			b = b[m:]
		}
	}

Only construct enum value descriptors for top-level enums since they are needed for registration.

	if pd != pf {
		return
	}
	ed.L1.eagerValues = true
	ed.L2 = new(EnumL2)
	ed.L2.Values.List = make([]EnumValue, numValues)
	for i := 0; 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:]
			switch num {
			case genid.EnumDescriptorProto_Value_field_number:
				ed.L2.Values.List[i].unmarshalFull(v, sb, pf, ed, i)
				i++
			}
		default:
			m := protowire.ConsumeFieldValue(num, typ, b)
			b = b[m:]
		}
	}
}

func (md *Message) unmarshalSeed(b []byte, sb *strs.Builder, pf *File, pd pref.Descriptor, i int) {
	md.L0.ParentFile = pf
	md.L0.Parent = pd
	md.L0.Index = i

	var prevField pref.FieldNumber
	var numEnums, numMessages, numExtensions int
	var posEnums, posMessages, posExtensions int
	b0 := b
	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:]
			switch num {
			case genid.DescriptorProto_Name_field_number:
				md.L0.FullName = appendFullName(sb, pd.FullName(), v)
			case genid.DescriptorProto_EnumType_field_number:
				if prevField != genid.DescriptorProto_EnumType_field_number {
					if numEnums > 0 {
						panic("non-contiguous repeated field")
					}
					posEnums = len(b0) - len(b) - n - m
				}
				numEnums++
			case genid.DescriptorProto_NestedType_field_number:
				if prevField != genid.DescriptorProto_NestedType_field_number {
					if numMessages > 0 {
						panic("non-contiguous repeated field")
					}
					posMessages = len(b0) - len(b) - n - m
				}
				numMessages++
			case genid.DescriptorProto_Extension_field_number:
				if prevField != genid.DescriptorProto_Extension_field_number {
					if numExtensions > 0 {
						panic("non-contiguous repeated field")
					}
					posExtensions = len(b0) - len(b) - n - m
				}
				numExtensions++
			case genid.DescriptorProto_Options_field_number:
				md.unmarshalSeedOptions(v)
			}
			prevField = num
		default:
			m := protowire.ConsumeFieldValue(num, typ, b)
			b = b[m:]
			prevField = -1 // ignore known field numbers of unknown wire type
		}
	}

Must allocate all declarations before parsing each descriptor type to ensure we handled all descriptors in "flattened ordering".

	if numEnums > 0 {
		md.L1.Enums.List = pf.allocEnums(numEnums)
	}
	if numMessages > 0 {
		md.L1.Messages.List = pf.allocMessages(numMessages)
	}
	if numExtensions > 0 {
		md.L1.Extensions.List = pf.allocExtensions(numExtensions)
	}

	if numEnums > 0 {
		b := b0[posEnums:]
		for i := range md.L1.Enums.List {
			_, n := protowire.ConsumeVarint(b)
			v, m := protowire.ConsumeBytes(b[n:])
			md.L1.Enums.List[i].unmarshalSeed(v, sb, pf, md, i)
			b = b[n+m:]
		}
	}
	if numMessages > 0 {
		b := b0[posMessages:]
		for i := range md.L1.Messages.List {
			_, n := protowire.ConsumeVarint(b)
			v, m := protowire.ConsumeBytes(b[n:])
			md.L1.Messages.List[i].unmarshalSeed(v, sb, pf, md, i)
			b = b[n+m:]
		}
	}
	if numExtensions > 0 {
		b := b0[posExtensions:]
		for i := range md.L1.Extensions.List {
			_, n := protowire.ConsumeVarint(b)
			v, m := protowire.ConsumeBytes(b[n:])
			md.L1.Extensions.List[i].unmarshalSeed(v, sb, pf, md, i)
			b = b[n+m:]
		}
	}
}

func (md *Message) unmarshalSeedOptions(b []byte) {
	for len(b) > 0 {
		num, typ, n := protowire.ConsumeTag(b)
		b = b[n:]
		switch typ {
		case protowire.VarintType:
			v, m := protowire.ConsumeVarint(b)
			b = b[m:]
			switch num {
			case genid.MessageOptions_MapEntry_field_number:
				md.L1.IsMapEntry = protowire.DecodeBool(v)
			case genid.MessageOptions_MessageSetWireFormat_field_number:
				md.L1.IsMessageSet = protowire.DecodeBool(v)
			}
		default:
			m := protowire.ConsumeFieldValue(num, typ, b)
			b = b[m:]
		}
	}
}

func (xd *Extension) unmarshalSeed(b []byte, sb *strs.Builder, pf *File, pd pref.Descriptor, i int) {
	xd.L0.ParentFile = pf
	xd.L0.Parent = pd
	xd.L0.Index = i

	for len(b) > 0 {
		num, typ, n := protowire.ConsumeTag(b)
		b = b[n:]
		switch typ {
		case protowire.VarintType:
			v, m := protowire.ConsumeVarint(b)
			b = b[m:]
			switch num {
			case genid.FieldDescriptorProto_Number_field_number:
				xd.L1.Number = pref.FieldNumber(v)
			case genid.FieldDescriptorProto_Label_field_number:
				xd.L1.Cardinality = pref.Cardinality(v)
			case genid.FieldDescriptorProto_Type_field_number:
				xd.L1.Kind = pref.Kind(v)
			}
		case protowire.BytesType:
			v, m := protowire.ConsumeBytes(b)
			b = b[m:]
			switch num {
			case genid.FieldDescriptorProto_Name_field_number:
				xd.L0.FullName = appendFullName(sb, pd.FullName(), v)
			case genid.FieldDescriptorProto_Extendee_field_number:
				xd.L1.Extendee = PlaceholderMessage(makeFullName(sb, v))
			}
		default:
			m := protowire.ConsumeFieldValue(num, typ, b)
			b = b[m:]
		}
	}
}

func (sd *Service) unmarshalSeed(b []byte, sb *strs.Builder, pf *File, pd pref.Descriptor, i int) {
	sd.L0.ParentFile = pf
	sd.L0.Parent = pd
	sd.L0.Index = i

	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:]
			switch num {
			case genid.ServiceDescriptorProto_Name_field_number:
				sd.L0.FullName = appendFullName(sb, pd.FullName(), v)
			}
		default:
			m := protowire.ConsumeFieldValue(num, typ, b)
			b = b[m:]
		}
	}
}

var nameBuilderPool = sync.Pool{
	New: func() interface{} { return new(strs.Builder) },
}

func getBuilder() *strs.Builder {
	return nameBuilderPool.Get().(*strs.Builder)
}
func putBuilder(b *strs.Builder) {
	nameBuilderPool.Put(b)
}

makeFullName converts b to a protoreflect.FullName, where b must start with a leading dot.

func makeFullName(sb *strs.Builder, b []byte) pref.FullName {
	if len(b) == 0 || b[0] != '.' {
		panic("name reference must be fully qualified")
	}
	return pref.FullName(sb.MakeString(b[1:]))
}

func appendFullName(sb *strs.Builder, prefix pref.FullName, suffix []byte) pref.FullName {
	return sb.AppendFullName(prefix, pref.Name(strs.UnsafeString(suffix)))