Consuming gRPC Server Reflection from C++ Client (that happens to also offer a Server Reflection)

[Alex Stark]

This might seem like an odd pattern, but I'm looking to retrofit an existing client/server framework with gRPC.  That has led me to a question and an issue.

FIrst, the question.  The "Use Server Reflection in a C++ Client" secion of the Server Reflection Tutorial  mentions using the grpc::ProtoReflectionDescriptorDatabase class as the basis of that interaction.  That seems to require me to link in libgrpc++_proto_reflection_desc_db.a which as far as I can tell has no "install" option in the makefile provided.  Is staticlly linking it from the grpc/lib/opts directory the recomended pattern or am I missing something?

To try things out I went ahead and linked it into my client/server framework library directly.  However, from there I'm having issues getting my test server to startup when linking in both my client/server dynamic library (that statically links libgrpc++_proto_reflectin_desc_db.a) and libgrpc++_reflection.so.  The error in question is this:

[libprotobuf ERROR google/protobuf/descriptor_database.cc:58] File already exists in database: src/proto/grpc/reflection/v1alpha/reflection.proto

[libprotobuf FATAL google/protobuf/descriptor.cc:1358] CHECK failed: GeneratedDatabase()->Add(encoded_file_descriptor, size):

terminate called after throwing an instance of 'google::protobuf::FatalException'

  what():  CHECK failed: GeneratedDatabase()->Add(encoded_file_descriptor, size):

I'm planning to continue digging in to see if I can figure out why that's an issue, but the comment foujnd in descriptor.cc around this exception throw isn't initial obvious to me (as a novice) what exactly I might be doing wrong.  Hoping the community might have some insight into whether or not those 2 libraries are inherently incompatable inside the same process.  As far as I can tell I don't even get to the creation of the actual ProtoReflectionDescriptorDatabase construction the error happens while the process is starting up.

Thanks in advance for any advice on those topics.

[Alex Stark]

Upon further debuging it appears the conflict is with /src/proto/grpc/reflection/v1alpha/reflection.pb.cc being included twice.  Which makes sense given the error code.  What I'm not understanding is why that is considered a fatal error.

And of course if there's anyway around it.

[WD J]

I face the same problem, and the scenoria is Binary A use the grpc++_reflection.a and libB.so first not link the grpc++_reflection.a, build the binaryA, and libB.so recompile with linking the grpc++_reflection.a, then binaryA fatal with the same error information.