1// Go support for Protocol Buffers - Google's data interchange format
2//
3// Copyright 2016 The Go Authors.  All rights reserved.
4// https://github.com/golang/protobuf
5//
6// Redistribution and use in source and binary forms, with or without
7// modification, are permitted provided that the following conditions are
8// met:
9//
10//     * Redistributions of source code must retain the above copyright
11// notice, this list of conditions and the following disclaimer.
12//     * Redistributions in binary form must reproduce the above
13// copyright notice, this list of conditions and the following disclaimer
14// in the documentation and/or other materials provided with the
15// distribution.
16//     * Neither the name of Google Inc. nor the names of its
17// contributors may be used to endorse or promote products derived from
18// this software without specific prior written permission.
19//
20// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
21// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
22// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
23// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
24// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
25// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
26// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
27// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
28// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
29// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
30// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
31
32// Package descriptor provides functions for obtaining protocol buffer
33// descriptors for generated Go types.
34//
35// These functions cannot go in package proto because they depend on the
36// generated protobuf descriptor messages, which themselves depend on proto.
37package descriptor
38
39import (
40	"bytes"
41	"compress/gzip"
42	"fmt"
43	"io/ioutil"
44
45	"github.com/golang/protobuf/proto"
46	protobuf "github.com/golang/protobuf/protoc-gen-go/descriptor"
47)
48
49// extractFile extracts a FileDescriptorProto from a gzip'd buffer.
50func extractFile(gz []byte) (*protobuf.FileDescriptorProto, error) {
51	r, err := gzip.NewReader(bytes.NewReader(gz))
52	if err != nil {
53		return nil, fmt.Errorf("failed to open gzip reader: %v", err)
54	}
55	defer r.Close()
56
57	b, err := ioutil.ReadAll(r)
58	if err != nil {
59		return nil, fmt.Errorf("failed to uncompress descriptor: %v", err)
60	}
61
62	fd := new(protobuf.FileDescriptorProto)
63	if err := proto.Unmarshal(b, fd); err != nil {
64		return nil, fmt.Errorf("malformed FileDescriptorProto: %v", err)
65	}
66
67	return fd, nil
68}
69
70// Message is a proto.Message with a method to return its descriptor.
71//
72// Message types generated by the protocol compiler always satisfy
73// the Message interface.
74type Message interface {
75	proto.Message
76	Descriptor() ([]byte, []int)
77}
78
79// ForMessage returns a FileDescriptorProto and a DescriptorProto from within it
80// describing the given message.
81func ForMessage(msg Message) (fd *protobuf.FileDescriptorProto, md *protobuf.DescriptorProto) {
82	gz, path := msg.Descriptor()
83	fd, err := extractFile(gz)
84	if err != nil {
85		panic(fmt.Sprintf("invalid FileDescriptorProto for %T: %v", msg, err))
86	}
87
88	md = fd.MessageType[path[0]]
89	for _, i := range path[1:] {
90		md = md.NestedType[i]
91	}
92	return fd, md
93}
94