Reload the development server when application code changes

.rerun

@@ -0,0 +1 @@
+--pattern {app.rb,api/**/*.rb,app/**/*.rb,config/**/*.rb}

Gemfile

@@ -8,6 +8,7 @@ gem 'rack-contrib', '~> 1.4.0'
 
 group :development do
   gem 'rake'
+  gem 'rerun', '~> 0.14', require: false
   gem 'rubocop'
 end
 

Gemfile.lock

@@ -62,6 +62,8 @@ GEM
       addressable (>= 2.1.1)
       eventmachine (>= 0.12.9)
     eventmachine (1.2.7)
+    ffi (1.17.4)
+    ffi (1.17.4-arm64-darwin)
     git-version-bump (0.19.1)
     goliath (1.0.7)
       async-rack
@@ -89,6 +91,10 @@ GEM
     json (3.1.0)
     language_server-protocol (3.17.0.6)
     lint_roller (1.1.0)
+    listen (3.10.1)
+      logger
+      rb-fsevent (~> 0.10, >= 0.10.3)
+      rb-inotify (~> 0.9, >= 0.9.10)
     log4r (1.1.10)
     logger (1.7.0)
     minitest (6.0.6)
@@ -118,11 +124,16 @@ GEM
       rack (>= 1.3)
     rainbow (3.1.1)
     rake (13.4.2)
+    rb-fsevent (0.11.2)
+    rb-inotify (0.11.1)
+      ffi (~> 1.0)
     readline (0.0.4)
       reline
     regexp_parser (2.13.1)
     reline (0.7.0)
       io-console (~> 0.5)
+    rerun (0.14.0)
+      listen (~> 3.0)
     rspec (3.13.2)
       rspec-core (~> 3.13.0)
       rspec-expectations (~> 3.13.0)
@@ -163,6 +174,7 @@ GEM
     zeitwerk (2.8.3)
 
 PLATFORMS
+  arm64-darwin-23
   ruby
 
 DEPENDENCIES
@@ -174,6 +186,7 @@ DEPENDENCIES
   rack-contrib (~> 1.4.0)
   rack-test
   rake
+  rerun (~> 0.14)
   rspec
   rubocop
   simplecov

README.md

@@ -28,6 +28,18 @@ $ bundle exec ruby app.rb -sv
 
 `app.rb` enables Goliath's application runner. Loading the environment for Rake or tests loads only the API, avoiding an extra server starting when those processes exit.
 
+### Development Reloading
+
+To pick up code changes automatically, run:
+
+```
+bundle exec rerun -- ruby app.rb -sv -e development
+```
+
+[Rerun](https://github.com/alexch/rerun) watches `app.rb` and Ruby files under `api/`, `app/`, and `config/`, restarting the server when files are added, changed, or removed. For example, edit the response in `api/ping.rb`, save, and request `/api/ping` again after the server restarts. On shared filesystems that do not deliver file notifications, add `--force-polling` before `--`.
+
+The whole process restarts deliberately: Grape compiles routes and retains references to mounted API classes, so reloading individual files with `Rack::Reloader` does not reliably update mounted routes. Requests can be interrupted during a restart; use this command only for development. The plain `bundle exec ruby app.rb -sv` command above does not watch or reload files.
+
 ### Hello World
 
 Navigate to http://localhost:9000/api/ping with a browser or use `curl`.

spec/development_reloading_spec.rb

@@ -0,0 +1,65 @@
+require 'spec_helper'
+require 'fileutils'
+require 'net/http'
+require 'rbconfig'
+require 'socket'
+require 'tmpdir'
+require 'timeout'
+
+describe 'Development reloading' do
+  def wait_for_response(port, path, body)
+    Timeout.timeout(30) do
+      loop do
+        begin
+          response = Net::HTTP.start('127.0.0.1', port, open_timeout: 1, read_timeout: 1) { |http| http.get(path) }
+          return response if response.code == '200' && response.body == body
+        rescue Errno::ECONNREFUSED, Errno::ECONNRESET, EOFError, Net::ReadTimeout
+          # A restart briefly closes the listening socket and existing connections.
+        end
+        sleep 0.1
+      end
+    end
+  end
+
+  it 'replaces mounted routes and responses after an API file changes' do
+    Dir.mktmpdir('grape-on-goliath-reloading') do |directory|
+      root = File.expand_path('..', __dir__)
+      FileUtils.cp_r(%w[api app config app.rb .rerun].map { |path| File.join(root, path) }, directory)
+      socket = TCPServer.new('127.0.0.1', 0)
+      port = socket.addr[1]
+      socket.close
+
+      File.open(File.join(directory, 'server.log'), 'w+') do |log|
+        pid = Process.spawn(
+          RbConfig.ruby, '-e', '$stdout.sync = true; load Gem.bin_path("rerun", "rerun")', '--',
+          '--background', '--no-notify', '--force-polling', '--',
+          RbConfig.ruby, 'app.rb', '-sv', '-e', 'development', '-p', port.to_s,
+          chdir: directory, pgroup: true, out: log, err: %i[child out]
+        )
+        begin
+          expect(wait_for_response(port, '/api/ping', '{"ping":"pong"}').code).to eq('200')
+          Timeout.timeout(30) do
+            sleep 0.1 until File.read(log.path).include?('[rerun] Watching ')
+          end
+
+          path = File.join(directory, 'api/ping.rb')
+          File.write(path, File.read(path).sub("get '/ping'", "get '/updated'").sub("'pong'", "'updated'"))
+
+          expect(wait_for_response(port, '/api/updated', '{"ping":"updated"}').code).to eq('200')
+          expect(Net::HTTP.get_response(URI("http://127.0.0.1:#{port}/api/ping")).code).to eq('404')
+        rescue Timeout::Error
+          log.rewind
+          raise "Development server did not return the expected response:\n#{log.read}"
+        ensure
+          Process.kill('TERM', -pid)
+          begin
+            Timeout.timeout(10) { Process.wait(pid) }
+          rescue Timeout::Error
+            Process.kill('KILL', -pid)
+            Process.wait(pid)
+          end
+        end
+      end
+    end
+  end
+end