How to use custom options in official docs

[shiy...@redhat.com]

the example in https://developers.google.com/protocol-buffers/docs/proto#customoptions below

message FooOptions {
  optional int32 opt1 = 1;
  optional string opt2 = 2;
}

extend google.protobuf.FieldOptions {
  optional FooOptions foo_options = 1234;
}

// usage:
message Bar {
  optional int32 a = 1 [(foo_options).opt1 = 123, (foo_options).opt2 = "baz"];
  // alternative aggregate syntax (uses TextFormat):
  optional int32 b = 2 [(foo_options) = { opt1: 456 opt2: "xaa" }];
}

assume I have a message Bar here:

var msg Bar
_, md := ForMessage(&msg)
md.Field[0].GetOptions().String()  only a string, How do i parse that ??

How to I get the exact value of Bar.b.opt1 which is 123 (default value)

What I want is like this

md.Field[0].GetOptions().GetOpt1()   // 123
md.Field[0].GetOptions().GetOpt2()    // baz
md.Field[1].GetOptions().GetOpt1()   // 456
md.Field[1].GetOptions().GetOpt2()   // xaa

Can we achieve that ?

[Feng Xiao]

The exact API to access custom options is language specific, It generally uses the same syntax as accessing extensions. For go, you can post the question to https://github.com/golang/protobuf

 

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[Josh Humphries]

The proto package has methods for accessing extensions. And the generated .pb.go file contains exported symbols that describe those extensions. Put them together, and you can get the custom options out -- something like so:

opts := md.Field[0].GetOptions()

foo, err := proto.GetExtension(opts, E_FooOptions)

if err != nil {

  fmt.Println(foo.GetOpt1()) // 123

  fmt.Println(foo.GetOpt2()) // baz

}

opts = md.Field[1].GetOptions()

foo, err = proto.GetExtension(opts, E_FooOptions)

if err != nil {

  fmt.Println(foo.GetOpt1()) // 456

  fmt.Println(foo.GetOpt2()) // xaa

}

----
Josh Humphries
jh...@bluegosling.com

--

[shiy...@redhat.com]

hi Josh,

Thank you for the reply, I tried your approach, but still doesn't works. it throws error when I using those code to test

func TestABCMessage(t *testing.T) {

   var msg Bar
   
   _, md := ForMessage(&msg)

   opts := md.Field[0].GetOptions()

   foo, err := proto.GetExtension(opts, E_FooOptions)
   if err != nil {

      spew.Dump(err)
      spew.Dump(foo) // 123
   }
}

protoc --version

libprotoc 3.4.0

go version go1.8.3 linux/amd64

command I use protoc  --go_out=.  ./test.proto

proto file

syntax = "proto2";
package cmd;

import "google/protobuf/descriptor.proto";

message FooOptions {
  optional int32 opt1 = 1;
  optional string opt2 = 2;
}

extend google.protobuf.FieldOptions {
  optional FooOptions foo_options = 1234;
}

// usage:
message Bar {
  optional int32 a = 1 [(foo_options).opt1 = 123, (foo_options).opt2 = "baz"];
  // alternative aggregate syntax (uses TextFormat):
  optional int32 b = 2 [(foo_options) = { opt1: 456 opt2: "xaa" }];
}

generated file

// Code generated by protoc-gen-go.
// source: version.proto
// DO NOT EDIT!

/*
Package cmd is a generated protocol buffer package.

It is generated from these files:
   version.proto

It has these top-level messages:
   FooOptions
   Bar
*/
package cmd

import proto "github.com/golang/protobuf/proto"
import fmt "fmt"
import math "math"
import google_protobuf "github.com/golang/protobuf/protoc-gen-go/descriptor"

// Reference imports to suppress errors if they are not otherwise used.
var _ = proto.Marshal
var _ = fmt.Errorf
var _ = math.Inf

// This is a compile-time assertion to ensure that this generated file
// is compatible with the proto package it is being compiled against.
// A compilation error at this line likely means your copy of the
// proto package needs to be updated.
const _ = proto.ProtoPackageIsVersion2 // please upgrade the proto package

type FooOptions struct {
   Opt1             *int32  `protobuf:"varint,1,opt,name=opt1" json:"opt1,omitempty"`
   Opt2             *string `protobuf:"bytes,2,opt,name=opt2" json:"opt2,omitempty"`
   XXX_unrecognized []byte  `json:"-"`
}

func (m *FooOptions) Reset()                    { *m = FooOptions{} }
func (m *FooOptions) String() string            { return proto.CompactTextString(m) }
func (*FooOptions) ProtoMessage()               {}
func (*FooOptions) Descriptor() ([]byte, []int) { return fileDescriptor0, []int{0} }

func (m *FooOptions) GetOpt1() int32 {
   if m != nil && m.Opt1 != nil {
      return *m.Opt1
   }
   return 0
}

func (m *FooOptions) GetOpt2() string {
   if m != nil && m.Opt2 != nil {
      return *m.Opt2
   }
   return ""
}

// usage:
type Bar struct {
   A *int32 `protobuf:"varint,1,opt,name=a" json:"a,omitempty"`

   // alternative aggregate syntax (uses TextFormat):

   B                *int32 `protobuf:"varint,2,opt,name=b" json:"b,omitempty"`
   XXX_unrecognized []byte `json:"-"`
}

func (m *Bar) Reset()                    { *m = Bar{} }
func (m *Bar) String() string            { return proto.CompactTextString(m) }
func (*Bar) ProtoMessage()               {}
func (*Bar) Descriptor() ([]byte, []int) { return fileDescriptor0, []int{1} }

func (m *Bar) GetA() int32 {
   if m != nil && m.A != nil {
      return *m.A
   }
   return 0
}

func (m *Bar) GetB() int32 {
   if m != nil && m.B != nil {
      return *m.B
   }
   return 0
}

var E_FooOptions = &proto.ExtensionDesc{
   ExtendedType:  (*google_protobuf.FieldOptions)(nil),
   ExtensionType: (*FooOptions)(nil),
   Field:         1234,
   Name:          "cmd.foo_options",
   Tag:           "bytes,1234,opt,name=foo_options,json=fooOptions",
}

func init() {
   proto.RegisterType((*FooOptions)(nil), "cmd.FooOptions")
   proto.RegisterType((*Bar)(nil), "cmd.Bar")
   proto.RegisterExtension(E_FooOptions)
}

func init() { proto.RegisterFile("version.proto", fileDescriptor0) }

var fileDescriptor0 = []byte{
   // 218 bytes of a gzipped FileDescriptorProto
   0x1f, 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0xff, 0xe2, 0xe2, 0x2d, 0x4b, 0x2d, 0x2a,
   0xce, 0xcc, 0xcf, 0xd3, 0x2b, 0x28, 0xca, 0x2f, 0xc9, 0x17, 0x62, 0x4e, 0xce, 0x4d, 0x91, 0x52,
   0x48, 0xcf, 0xcf, 0x4f, 0xcf, 0x49, 0xd5, 0x07, 0x0b, 0x25, 0x95, 0xa6, 0xe9, 0xa7, 0xa4, 0x16,
   0x27, 0x17, 0x65, 0x16, 0x94, 0xe4, 0x17, 0x41, 0x94, 0x29, 0x99, 0x70, 0x71, 0xb9, 0xe5, 0xe7,
   0xfb, 0x17, 0x94, 0x64, 0xe6, 0xe7, 0x15, 0x0b, 0x09, 0x71, 0xb1, 0xe4, 0x17, 0x94, 0x18, 0x4a,
   0x30, 0x2a, 0x30, 0x6a, 0xb0, 0x06, 0x81, 0xd9, 0x50, 0x31, 0x23, 0x09, 0x26, 0x05, 0x46, 0x0d,
   0x4e, 0xb0, 0x98, 0x91, 0x92, 0x2d, 0x17, 0xb3, 0x53, 0x62, 0x91, 0x90, 0x34, 0x17, 0x63, 0x22,
   0x44, 0xad, 0x13, 0xef, 0x24, 0x5f, 0x26, 0x8e, 0xea, 0x49, 0xbe, 0xac, 0x42, 0xcc, 0x49, 0x89,
   0x55, 0x41, 0x8c, 0x89, 0x42, 0x92, 0x5c, 0x8c, 0x49, 0x60, 0x4d, 0xac, 0x4e, 0xdc, 0x93, 0x7c,
   0x39, 0x38, 0x4e, 0x30, 0x0b, 0x31, 0x57, 0x24, 0x26, 0x06, 0x31, 0x26, 0x59, 0x05, 0x70, 0x71,
   0xa7, 0xe5, 0xe7, 0xc7, 0xe7, 0x43, 0x6d, 0x95, 0xd5, 0x83, 0x38, 0x53, 0x0f, 0xe6, 0x4c, 0x3d,
   0xb7, 0xcc, 0xd4, 0x9c, 0x14, 0xa8, 0xa3, 0x24, 0x2e, 0x71, 0x2a, 0x30, 0x6a, 0x70, 0x1b, 0xf1,
   0xeb, 0x25, 0xe7, 0xa6, 0xe8, 0x21, 0x1c, 0x1b, 0xc4, 0x95, 0x06, 0x67, 0x03, 0x02, 0x00, 0x00,
   0xff, 0xff, 0xc1, 0xd1, 0xc2, 0x4e, 0xfd, 0x00, 0x00, 0x00,
}

/tmp/TestABCMessage_in_version_abc_test_gogo -test.v -test.run ^TestABCMessage$

(*errors.errorString)(0xc4201731c0)(proto: not an extendable proto)

(interface {}) <nil>

Process finished with exit code 0

proto: not an extendable proto

----
Josh Humphries
jh...@bluegosling.com

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[shiy...@redhat.com]

/tmp/TestABCMessage_in_version_abc_test_gogo -test.v -test.run ^TestABCMessage$

(*errors.errorString)(0xc420214af0)(proto: not an extendable proto)

(interface {}) <nil>

[shiy...@redhat.com]

Hey, I think I already found the problems, vendor of our code base need to update, when I create an independent project it works, thanks !!!

[Josh Humphries]

It works fine when I run it.

> go test -v .

=== RUN   TestABCMessage

opt1:123 opt2:"baz" 

--- PASS: TestABCMessage (0.00s)

PASS

ok  test 0.007s

However, your test file was incomplete. Maybe you have imported the wrong stuff? Double-check that you are linking against the latest version of the github.com/golang/protobuf packages.

I had to add imports, and I also changed the handling of the output since I don't know what "spew" is:

package cmd

import (

  "fmt"

  "testing"

  "github.com/golang/protobuf/descriptor"

  "github.com/golang/protobuf/proto"

)

func TestABCMessage(t *testing.T) {

   var msg Bar

   

   _, md := descriptor.ForMessage(&msg)

   opts := md.Field[0].GetOptions()

   foo, err := proto.GetExtension(opts, E_FooOptions)

   if err != nil {

      t.Errorf("failed: %v", err)

  } else {

      fmt.Println(foo)

   }

}

----
Josh Humphries
jh...@bluegosling.com

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[Shiyang Wang]

Thank you, problem solved !!

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