grpc ruby error: `block in marshal_proc': undefined method `encode' for String:Class (NoMethodError)

[Bo Tian]

Hi All,

I got an error of : `block in marshal_proc': undefined method `encode' for String:Class (NoMethodError) when sending protobuf message to server.  I wonder if someone can help me on this.

actually there is an encode method in generated service ruby file. here is the snippet

class Service

       include GRPC::GenericService

       self.marshal_class_method = :encode

       self.unmarshal_class_method = :decode

       self.service_name = 'opentelemetry.proto.collector.metrics.v1.MetricsService'

       # For performance reasons, it is recommended to keep this RPC

       # alive for the entire life of the application.

       rpc :Export, ::ExportServiceRequest, ::ExportServiceResponse

      end

      Stub = Service.rpc_stub_class

Here is the call stack:

6: from ./metrics.rb:87:in `main'

5: from /Users/bo/.rvm/gems/ruby-2.6.6/gems/grpc-1.40.0-universal-darwin/src/ruby/lib/grpc/generic/service.rb:171:in `block (3 levels) in rpc_stub_class'

4: from /Users/bo/.rvm/gems/ruby-2.6.6/gems/grpc-1.40.0-universal-darwin/src/ruby/lib/grpc/generic/client_stub.rb:179:in `request_response'

3: from /Users/bo/.rvm/gems/ruby-2.6.6/gems/grpc-1.40.0-universal-darwin/src/ruby/lib/grpc/generic/interceptors.rb:170:in `intercept!'

2: from /Users/bo/.rvm/gems/ruby-2.6.6/gems/grpc-1.40.0-universal-darwin/src/ruby/lib/grpc/generic/client_stub.rb:180:in `block in request_response'

1: from /Users/bo/.rvm/gems/ruby-2.6.6/gems/grpc-1.40.0-universal-darwin/src/ruby/lib/grpc/generic/active_call.rb:352:in `request_response'

/Users/bo.tian/.rvm/gems/ruby-2.6.6/gems/grpc-1.40.0-universal-darwin/src/ruby/lib/grpc/generic/rpc_desc.rb:35:in `block in marshal_proc': undefined method `encode' for String:Class (NoMethodError)

Thanks,

Bo