获取golang的协议缓冲区选项信息

Protocol Buffer definition as following, the TestMessage has two options msg_option_a and msg_option_b:

syntax = "proto3";
package grpctest;

option go_package = "pb";

import "google/protobuf/descriptor.proto";

extend google.protobuf.MessageOptions {
  int32 msg_option_a = 50011;
  int32 msg_option_b = 50012;
}

message TestMessage {
  option (msg_option_a) = 22;
  option (msg_option_b) = 33;
  string name = 1;
}

I'd like to read the definition value of the two options:

var msg *pb.TestMessage
_, md := descriptor.ForMessage(msg)
options := md.GetOptions()

fmt.Println(options.String()) // --> [grpcapi.msg_option_a]:22 [grpcapi.msg_option_b]:33
fmt.Println(len(options.GetUninterpretedOption())) // --> 0

It can get all options info when print the whole MessageOptions, GetUninterpretedOption() return a array of option definition, but it has a zero length.

The following is the comment of type UninterpretedOption , but I cant get what it means, and haven't found any info about DescriptorPool:

// A message representing a option the parser does not recognize. This only
// appears in options protos created by the compiler::Parser class.
// DescriptorPool resolves these when building Descriptor objects. Therefore,
// options protos in descriptor objects (e.g. returned by Descriptor::options(),
// or produced by Descriptor::CopyTo()) will never have UninterpretedOptions
// in them.

I want to get a specific option value， but no ideas now.

Please help! Thanks!

use proto.GetExtension get option value:

var msg *pb.TestMessage
_, md := descriptor.ForMessage(msg)
options := md.GetOptions()

fmt.Println(options.String()) // --> [grpcapi.msg_option_a]:22 [grpcapi.msg_option_b]:33
fmt.Println(len(options.GetUninterpretedOption())) // --> 0

a, _ := proto.GetExtension(options, pb.E_MsgOptionA)
fmt.Println(*a.(*int32)) // --> 22

b, _ := proto.GetExtension(options, pb.E_MsgOptionB)
fmt.Println(*b.(*int32)) // --> 33