Puma plugins to run yarn or bun

Author: trevorrjohn

README.md

@@ -39,6 +39,19 @@ Or, in Rails 7+, you can preconfigure your new application to use a specific bun
 
 ## FAQ
 
+### Puma plugin
+
+Using [Puma](https://github.com/puma/puma) in development you can now add a plugin to build and compile your javascript. Just add the following to your `puma.rb`.
+
+```
+# config/puma.rb
+plugin :yarn if ENV.fetch("RAILS_ENV", "development") == "development"
+
+# or if you're using Bun
+plugin :bun if ENV.fetch("RAILS_ENV", "development") == "development"
+
+```
+
 ### Is there a work-around for lack of glob syntax on Windows?
 
 The default build script for esbuild relies on the `app/javascript/*.*` glob pattern to compile multiple entrypoints automatically. This glob pattern is not available by default on Windows, so you need to change the build script in `package.json` to manually list the entrypoints you wish to compile.

lib/puma/plugin/bun.rb

@@ -0,0 +1,68 @@
+require "puma/plugin"
+
+Puma::Plugin.create do
+  attr_reader :puma_pid, :bun_pid, :log_writer
+
+  def start(launcher)
+    @log_writer = launcher.log_writer
+    @puma_pid = $$
+    @bun_pid = fork do
+      Thread.new { monitor_puma }
+      # Using IO.popen(command, 'r+') will avoid watch_command read from $stdin.
+      # If we use system(*command) instead, IRB and Debug can't read from $stdin
+      # correctly bacause some keystrokes will be taken by watch_command.
+      IO.popen("bun run build --watch", "r+") do |io|
+        IO.copy_stream(io, $stdout)
+      end
+    end
+
+    launcher.events.on_stopped { stop_bun }
+
+    in_background do
+      monitor_bun
+    end
+  end
+
+  private
+    def stop_bun
+      Process.waitpid(bun_pid, Process::WNOHANG)
+      log "Stopping Bun..."
+      Process.kill(:INT, bun_pid) if bun_pid
+      Process.wait(bun_pid)
+    rescue Errno::ECHILD, Errno::ESRCH
+    end
+
+    def monitor_puma
+      monitor(:puma_dead?, "Detected Puma has gone away, stopping Bun...")
+    end
+
+    def monitor_bun
+      monitor(:bun_dead?, "Detected Bun has gone away, stopping Puma...")
+    end
+
+    def monitor(process_dead, message)
+      loop do
+        if send(process_dead)
+          log message
+          Process.kill(:INT, $$)
+          break
+        end
+        sleep 2
+      end
+    end
+
+    def bun_dead?
+      Process.waitpid(bun_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/puma/plugin/yarn.rb

@@ -0,0 +1,68 @@
+require "puma/plugin"
+
+Puma::Plugin.create do
+  attr_reader :puma_pid, :yarn_pid, :log_writer
+
+  def start(launcher)
+    @log_writer = launcher.log_writer
+    @puma_pid = $$
+    @yarn_pid = fork do
+      Thread.new { monitor_puma }
+      # Using IO.popen(command, 'r+') will avoid watch_command read from $stdin.
+      # If we use system(*command) instead, IRB and Debug can't read from $stdin
+      # correctly bacause some keystrokes will be taken by watch_command.
+      IO.popen("yarn build --watch", "r+") do |io|
+        IO.copy_stream(io, $stdout)
+      end
+    end
+
+    launcher.events.on_stopped { stop_yarn }
+
+    in_background do
+      monitor_yarn
+    end
+  end
+
+  private
+    def stop_yarn
+      Process.waitpid(yarn_pid, Process::WNOHANG)
+      log "Stopping Yarn..."
+      Process.kill(:INT, yarn_pid) if yarn_pid
+      Process.wait(yarn_pid)
+    rescue Errno::ECHILD, Errno::ESRCH
+    end
+
+    def monitor_puma
+      monitor(:puma_dead?, "Detected Puma has gone away, stopping Yarn...")
+    end
+
+    def monitor_yarn
+      monitor(:yarn_dead?, "Detected Yarn has gone away, stopping Puma...")
+    end
+
+    def monitor(process_dead, message)
+      loop do
+        if send(process_dead)
+          log message
+          Process.kill(:INT, $$)
+          break
+        end
+        sleep 2
+      end
+    end
+
+    def yarn_dead?
+      Process.waitpid(yarn_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