Monkey patch gruf interceptor

README.md

@@ -154,9 +154,22 @@ service MyService {
 
 ## Gruf Interceptors
 
-grpc-rest supports [gruf](https://github.com/bigcommerce/gruf) Interceptors. As long as you're not using a custom interceptor
+grpc-rest supports [gruf](https://github.com/bigcommerce/gruf) Interceptors through a custom `GrpcRest::BaseInterceptor` class. As long as you're not using a custom interceptor
 registry, your interceptors will be called normally around the controller.
 
+```ruby
+module Interceptors
+  # Interceptor for catching errors from controllers
+  class ErrorInterceptor < GrpcRest::BaseInterceptor
+
+    def call
+      # Your code here
+    end
+
+  end
+end
+```
+
 ## To Do
 
 * Replace Go implementation with Ruby (+ executable)

lib/base_interceptor.rb

@@ -0,0 +1,46 @@
+# frozen_string_literal: true
+
+require 'gruf'
+
+module GrpcRest
+    # This is a monkey-patch that fixes an issue we were having with using the fail! method in
+    # interceptors where an active call was not instantiated yet.
+    # Basically, we overloaded this function: https://github.com/bigcommerce/gruf/blob/main/lib/gruf/errors/helpers.rb#L34
+  class BaseInterceptor < ::Gruf::Interceptors::ServerInterceptor
+    def fail!(error_code, message = 'unknown error', metadata = {})
+      raise grpc_error(error_code, message.to_s, metadata)
+    end
+
+    private
+
+    # Ported from https://github.com/flipp-oss/grpc-rest/blob/main/lib/grpc_rest.rb#L142
+    def grpc_error(error_code, message, metadata)
+      case error_code
+      when :ok
+        GRPC::Ok.new(message, metadata)
+      when 499
+        GRPC::Cancelled.new(message, metadata)
+      when :bad_request, :invalid_argument
+        GRPC::InvalidArgument.new(message, metadata)
+      when :gateway_timeout
+        GRPC::DeadlineExceeded.new(message, metadata)
+      when :not_found
+        GRPC::NotFound.new(message, metadata)
+      when :conflict
+        GRPC::AlreadyExists.new(message, metadata)
+      when :forbidden
+        GRPC::PermissionDenied.new(message, metadata)
+      when :unauthorized
+        GRPC::Unauthenticated.new(message, metadata)
+      when :too_many_requests
+        GRPC::ResourceExhausted.new(message, metadata)
+      when :not_implemented
+        GRPC::Unimplemented.new(message, metadata)
+      when :service_unavailable
+        GRPC::Unavailable.new(message, metadata)
+      else
+        GRPC::Internal.new(message, metadata)
+      end
+    end
+  end
+end

spec/base_interceptor_spec.rb

@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+
+require_relative './spec_helper'
+require 'src/proto/grpc/testing/test_services_pb'
+
+RSpec.describe GrpcRest::BaseInterceptor, type: :class do
+  let(:rpc_service) { Grpc::Testing::TestService::Service.new }
+  let(:rpc_desc) { Grpc::Testing::TestService::Service.rpc_descs.values.first}
+  let(:message) { Grpc::Testing::SimpleRequest.new }
+
+  describe '#fail!' do
+    let(:error_message) { 'some message' }
+    let(:error_code) { :invalid_argument }
+
+    it 'fails properly' do
+      request = Gruf::Controllers::Request.new(
+        method_key: :UnaryCall,
+        service: rpc_service,
+        rpc_desc: rpc_desc,
+        active_call: nil,
+        message: message)
+      interceptor = GrpcRest::BaseInterceptor.new(request, Gruf::Error.new)
+
+      expect{ interceptor.fail!(error_code, error_message) }.to raise_error(GRPC::InvalidArgument) do |error|
+        expect(error.message).to match(error_message)
+        expect(error.code).to eq(GRPC::Core::StatusCodes::INVALID_ARGUMENT)
+      end
+    end
+  end
+end

spec/spec_helper.rb

@@ -17,6 +17,7 @@ class GrpcApp < Rails::Application
 loader.ignore("#{Rails.root}/spec/test_service_pb.rb")
 loader.setup
 require "#{Rails.root}/spec/test_service_pb.rb"
+require "#{Rails.root}/lib/base_interceptor.rb"
 
 $LOAD_PATH.unshift(File.expand_path('../lib', __dir__))