1 files changed, 158 insertions, 0 deletions
diff --git a/internal/filedesc/build.go b/internal/filedesc/build.go
new file mode 100644
index 00000000..b293b694
--- /dev/null
+++ b/internal/filedesc/build.go
@@ -0,0 +1,158 @@
+// 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.
+//
+// The types in this package implement interfaces in the protoreflect package
+// related to protobuf descripriptors.
+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.
+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 {
+		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".
+	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 {
+		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:]
+		}
+	}
+}