Add Puma plugin

README.md

@@ -8,8 +8,34 @@ The installer will create your default Sass input file in `app/assets/stylesheet
 
 If you need to configure the build process – beyond configuring the build files – you can run `bundle exec dartsass` to access the platform-specific executable, and give it your own build options.
 
-When you're developing your application, you want to run Dart Sass in watch mode, so changes are automatically reflected in the generated CSS output. You can do this either by running `rails dartsass:watch` as a separate process, or by running `./bin/dev` which uses [foreman](https://github.com/ddollar/foreman) to start both the Dart Sass watch process and the rails server in development mode.
+## Live rebuild
 
+While you're developing your application, you want to run Dartsass in "watch"
+mode, so changes are automatically reflected in the generated CSS output. You
+can do this in a few different ways:
+
+- use this gem's [Puma](https://puma.io/) plugin to integrate "watch" with `rails server`,
+- or run `rails dartsass:watch` as a separate process,
+- or run `bin/dev` which uses [Foreman](https://github.com/ddollar/foreman)
+
+### Puma plugin
+
+This gem ships with a Puma plugin. To use it, add this line to your `puma.rb` configuration:
+
+```ruby
+plugin :dartsass if ENV.fetch("RAILS_ENV", "development") == "development"
+```
+
+and then running `rails server` will run the Dartsass watch process in the background
+
+### Run `rails dartsass:watch`
+
+Running `./bin/rails dartsass:watch` starts the Dartsass process in watch mode.
+
+### Foreman
+
+Running `bin/dev` invokes Foreman to start both the Dartsass watch process and
+the rails server in development mode based on your `Procfile.dev` file.
 
 ## Installation
 

lib/dartsass/runner.rb

@@ -23,5 +23,9 @@ def dartsass_load_paths
     def dartsass_compile_command
       [ RbConfig.ruby, EXEC_PATH ].concat(dartsass_build_options).concat(dartsass_load_paths).concat(dartsass_build_mapping)
     end
+
+    def dartsass_watch_command
+      dartsass_compile_command << "--watch"
+    end
   end
 end

lib/puma/plugin/dartsass.rb

@@ -0,0 +1,69 @@
+require "dartsass/runner"
+require "puma/plugin"
+
+Puma::Plugin.create do
+  attr_reader :puma_pid, :dartsass_pid, :log_writer
+
+  def start(launcher)
+    @log_writer = launcher.log_writer
+    @puma_pid = $$
+    @dartsass_pid = fork do
+      Thread.new { monitor_puma }
+      # Using IO.popen(command, 'r+') will avoid watch_command read from $stdin.
+      # If we use system(*command) instead, IRB and Debug can't read from $stdin
+      # correctly bacause some keystrokes will be taken by watch_command.
+      IO.popen(Dartsass::Runner.dartsass_watch_command, 'r+') do |io|
+        IO.copy_stream(io, $stdout)
+      end
+    end
+
+    launcher.events.on_stopped { stop_dartsass }
+
+    in_background do
+      monitor_dartsass
+    end
+  end
+
+  private
+    def stop_dartsass
+      Process.waitpid(dartsass_pid, Process::WNOHANG)
+      log "Stopping dartsass..."
+      Process.kill(:INT, dartsass_pid) if dartsass_pid
+      Process.wait(dartsass_pid)
+    rescue Errno::ECHILD, Errno::ESRCH
+    end
+
+    def monitor_puma
+      monitor(:puma_dead?, "Detected Puma has gone away, stopping dartsass...")
+    end
+
+    def monitor_dartsass
+      monitor(:dartsass_dead?, "Detected dartsass has gone away, stopping Puma...")
+    end
+
+    def monitor(process_dead, message)
+      loop do
+        if send(process_dead)
+          log message
+          Process.kill(:INT, $$)
+          break
+        end
+        sleep 2
+      end
+    end
+
+    def dartsass_dead?
+      Process.waitpid(dartsass_pid, Process::WNOHANG)
+      false
+    rescue Errno::ECHILD, Errno::ESRCH
+      true
+    end
+
+    def puma_dead?
+      Process.ppid != puma_pid
+    end
+
+    def log(...)
+      log_writer.log(...)
+    end
+end

lib/tasks/build.rake

@@ -8,7 +8,7 @@ namespace :dartsass do
 
   desc "Watch and build your Dart Sass CSS on file changes"
   task watch: :environment do
-    system(*Dartsass::Runner.dartsass_compile_command, "--watch", exception: true)
+    system(*Dartsass::Runner.dartsass_watch_command, exception: true)
   end
 end