Look for handlers in both the fully-qualified namespace, or root namespace.

.standard.yml

@@ -2,3 +2,6 @@ ruby_version: 2.7
 plugins:
   - standard-performance
   - standard-rails
+ignore:
+  - '**/*_pb.rb'
+  - '**/*_twirp.rb' 

README.md

@@ -86,7 +86,26 @@ end
 
 Each handler method should return the appropriate Protobuf, or a `Twirp::Error`.
 
-TODO: Give more examples of both
+#### Packages and Namespacing
+
+Handlers can live in directories that reflect the service's package. For example, `haberdasher.proto` defines:
+
+```protobuf
+package twirp.example.haberdasher;
+```
+
+You can use the full path, or because many projects have only one namespace, we also let you skip the namespace for simplicity:
+
+We look for the handler in either location:
+
+`app/handlers/twirp/example/haberdasher/haberdasher_service_handler.rb` defines `Twirp::Example::Haberdasher::HaberdasherServiceHandler`
+
+or
+
+`app/handlers/haberdasher_service_handler.rb` defines `HaberdasherServiceHandler`
+
+
+TODO: Give more examples of handlers
 
 ### Familiar Callbacks
 

lib/twirp/rails/dispatcher.rb

@@ -4,7 +4,13 @@ module Twirp
   module Rails
     class Dispatcher
       def initialize(service_class)
-        @service_handler = "#{service_class.service_name}Handler".constantize
+        # Check for a handler in the service's namespace, or in the root namespace
+        # e.g. Twirp::Example::Cobbler::CobblerHandler or ::CobblerHandler
+        @service_handler = if Object.const_defined?("#{service_class.module_parent}::#{service_class.service_name}Handler")
+          "#{service_class.module_parent}::#{service_class.service_name}Handler".constantize
+        else
+          "#{service_class.service_name}Handler".constantize
+        end
       end
 
       def respond_to_missing?(method, *)

spec/rails_app/app/handlers/twirp/example/cobbler/cobbler_handler.rb

@@ -0,0 +1,21 @@
+module Twirp
+  module Example
+    module Cobbler
+      class CobblerHandler < Twirp::Rails::Handler
+        def make_shoe
+          # We can return a Twirp::Error when appropriate
+          if request.inches < 12
+            return Twirp::Error.invalid_argument("is too small", argument: "inches")
+          end
+
+          # Build the reponse
+          Twirp::Example::Cobbler::Shoe.new(
+            inches: request.inches,
+            name: "Pork Pie",
+            color: "Tan"
+          )
+        end
+      end
+    end
+  end
+end

spec/rails_app/lib/haberdasher_twirp.rb

@@ -1,4 +1,8 @@
-# Code generated by protoc-gen-twirp_ruby 1.10.0, DO NOT EDIT.
+# frozen_string_literal: true
+
+# Generated by the protoc-gen-twirp_ruby gem v1.1.1. DO NOT EDIT!
+# source: haberdasher.proto
+
 require "twirp"
 require_relative "haberdasher_pb"
 

spec/rails_app/lib/twirp/example/cobbler/cobbler_twirp.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+# Generated by the protoc-gen-twirp_ruby gem v1.1.1. DO NOT EDIT!
+# source: twirp/example/cobbler/cobbler.proto
+
+require "twirp"
+require_relative "cobbler_pb"
+
+module Twirp
+  module Example
+    module Cobbler
+      class CobblerService < ::Twirp::Service
+        package "twirp.example.cobbler"
+        service "Cobbler"
+        rpc :MakeShoe, Size, Shoe, ruby_method: :make_shoe
+      end
+
+      class CobblerClient < ::Twirp::Client
+        client_for CobblerService
+      end
+    end
+  end
+end

spec/rails_app/proto/twirp/example/cobbler/cobbler.proto

@@ -0,0 +1,23 @@
+// A close copy of haberdasher.proto
+// We're putting this in /proto/twirp/example/cobbler/ so that we can test namespace handling
+syntax = "proto3";
+
+package twirp.example.cobbler;
+
+// Cobbler service makes shoes for clients.
+service Cobbler {
+  // MakeShoe produces a shoe of mysterious, randomly-selected color!
+  rpc MakeShoe(Size) returns (Shoe);
+}
+
+// Size of a Shoe, in inches.
+message Size {
+  int32 inches = 1; // must be > 0
+}
+
+// A Shoe is a piece of footwear made by a Cobbler.
+message Shoe {
+  int32 inches = 1;
+  string color = 2; // anything but "invisible"
+  string name = 3; // i.e. "oxford"
+}