Parsing of .desc fails for message with custom option

[Marc Schafer]

Parsing fails on a .desc file generated from a message with a custom option as shown below. I understand this is happening because the message defined in descriptor.proto doesn't know about my extension but I am not sure how to fix it. I'm using C++.

Here is my .proto:

syntax = "proto3";

package foo;

// extending MessageOptions prevents parsing of generated .desc

import "google/protobuf/descriptor.proto";

// extensions start at 1000

extend google.protobuf.MessageOptions {

  optional string my_option = 1992;

}

message SearchRequest {

  option (my_option) = "custom";  

  string query = 1;

  int32 page_number = 2;

  int32 result_per_page = 3;

}

-Best

Marc

[Adam Cozzette]

I think the easiest solution would be to include the .proto file that defines the custom option in the serialized descriptor set. I assume you're generating the .desc file by invoking protoc with -o or --descriptor_set_out, so just make sure to add the custom option .proto file as one of the command line arguments to protoc when you do that.

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[Marc Schafer]

I am invoking protoc –descriptor_set_out on the .proto file with contents described below that include the definition of the custom option. I’m not sure what else you are suggesting I include.

 

I attached the .proto file to clarify the reproduction steps.

protoc –descriptor_set_out simple.proto

 

Use this snippet of code to parse the resulting .desc file:

 

    fdiName = “simple.desc";

    std::ifstream fdi(fdiName);

    google::protobuf::FileDescriptorSet fds;

    auto r = fds.ParseFromIstream(&fdi);

    assert(r);

 

The assertion will fail

 

Best,

Marc

[Adam Cozzette]

I don't think this necessarily has anything to do with the custom option. FileDescriptorSet is itself just a protocol buffer message, so parsing it doesn't involve interpreting the meaning of its contents. It's just like parsing any other proto, so if it's failing then either the descriptors were somehow corrupted or are not being read from disk successfully.

Here is what I would suggest trying:

1. Run this and make sure the results look reasonable: protoc --decode_raw < simple.desc

This will print out the raw field numbers and values in the descriptor.

2. Change your code to read in a string and then parse the string (with ParseFromString instead of ParseFromIstream). This way you can verify that the string you read in exactly matches the file on disk (or at least do a quick check to verify that the length is the same).

[Marc Schafer]

Thank you for the pointers Adam. The string did not match the file on disk because I neglected to open the file in binary mode. Commenting out the custom option coincidentally made everything work leading me down the rat hole but the real fix is to open in binary mode and then everything works.