Allow controllers to decorate Twirp::Error

lib/rails_twirp/exception_handling.rb

@@ -20,7 +20,10 @@ def process_action(*)
       # 1. When we 'show exceptions' we make the exception bubble up—this is useful for testing
       #    If the exception gets raised here error reporting will happen in the middleware of the APM package
       #    higher in the call stack.
-      raise e unless http_request.show_exceptions?
+      #
+      # Note that between Rails 7.0 and 7.1 the show_exceptions? helper method on Request
+      # got removed, so we must make do with the config access instead.
+      raise e unless [true, :all].include?(http_request.get_header("action_dispatch.show_exceptions"))
 
       # 2. We report the error to the error tracking service, this needs to be configured.
       RailsTwirp.unhandled_exception_handler&.call(e)
@@ -33,11 +36,14 @@ def process_action(*)
       # 3. When we want to show detailed exceptions we include the exception message in the error
       if http_request.get_header("action_dispatch.show_detailed_exceptions")
         self.response_body = Twirp::Error.internal_with(e)
-        return
+      else
+        # 4. Otherwise we just return a vague internal error message
+        self.response_body = Twirp::Error.internal("Internal error")
       end
 
-      # 4. Otherwise we just return a vague internal error message
-      self.response_body = Twirp::Error.internal("Internal error")
+      decorate_twirp_error_response! if respond_to?(:decorate_twirp_error_response!)
+
+      self.response_body
     end
   end
 end

test/ping_controller_test.rb

@@ -100,6 +100,25 @@ class PingControllerTest < RailsTwirp::IntegrationTest
     Rails.application.env_config["action_dispatch.show_exceptions"] = false
   end
 
+  test "decorates Twirp errors resulting from unhandled exceptions if the controller provides for it" do
+    Rails.application.env_config["action_dispatch.show_exceptions"] = true
+    Rails.application.env_config["action_dispatch.show_detailed_exceptions"] = false
+
+    PingsController.define_method(:decorate_twirp_error_response!)do
+      self.response_body.meta[:encrypted] = "abc"
+    end
+
+    req = RPC::DummyAPI::PingRequest.new
+    rpc RPC::DummyAPI::DummyService, "UncaughtError", req
+    assert_instance_of Twirp::Error, response
+    assert_equal :internal, response.code
+    assert_equal "Internal error", response.msg
+    assert_equal "abc", response.meta["encrypted"]
+  ensure
+    Rails.application.env_config["action_dispatch.show_detailed_exceptions"] = true
+    Rails.application.env_config["action_dispatch.show_exceptions"] = false
+  end
+
   test "before error" do
     req = RPC::DummyAPI::PingRequest.new
     rpc RPC::DummyAPI::DummyService, "BeforeError", req