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descriptor.go
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descriptor.go
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// Copyright (C) 2017 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package protoutil
import (
"bytes"
"compress/gzip"
"io/ioutil"
"sync"
"github.com/golang/protobuf/proto"
"github.com/golang/protobuf/protoc-gen-go/descriptor"
)
type (
// Described is the interface to something that self describes with a compressed
// FileDescriptorProto.
Described interface {
Descriptor() ([]byte, []int)
}
)
var (
fileCache = map[*byte]*descriptor.FileDescriptorProto{}
cacheLock = sync.Mutex{}
)
func GetFileDescriptor(data []byte) (*descriptor.FileDescriptorProto, error) {
if len(data) == 0 {
return nil, nil
}
cacheLock.Lock()
defer cacheLock.Unlock()
if d, found := fileCache[&data[0]]; found {
return d, nil
}
d, err := decodeFileDescriptor(data)
if err != nil {
return nil, err
}
fileCache[&data[0]] = d
return d, nil
}
func decodeFileDescriptor(data []byte) (*descriptor.FileDescriptorProto, error) {
r, err := gzip.NewReader(bytes.NewReader(data))
if err != nil {
return nil, err
}
defer r.Close()
b, err := ioutil.ReadAll(r)
if err != nil {
return nil, err
}
fd := &descriptor.FileDescriptorProto{}
if err := proto.Unmarshal(b, fd); err != nil {
return nil, err
}
return fd, nil
}
// DescriptorOf returns the descriptor for a given proto message.
func DescriptorOf(msg Described) (*descriptor.DescriptorProto, error) {
data, path := msg.Descriptor()
fileDescriptor, err := GetFileDescriptor(data)
if err != nil {
return nil, err
}
messageDescriptor := fileDescriptor.MessageType[path[0]]
for _, i := range path[1:] {
messageDescriptor = messageDescriptor.NestedType[i]
}
return messageDescriptor, nil
}