Add puma plugin

CHANGELOG.md

@@ -1,3 +1,8 @@
+## next / unreleased
+
+* Introduce a Puma plugin to manage the Tailwind "watch" process from `rails server`. (#300) @npezza93
+
+
 ## v2.1.0 / 2023-12-19
 
 * Update to [Tailwind CSS v3.4.0](https://github.com/tailwindlabs/tailwindcss/releases/tag/v3.4.0) from v3.3.6 by @flavorjones

README.md

@@ -60,10 +60,26 @@ The `tailwindcss:build` task is automatically attached to the `test:prepare` Rak
 
 ### Update assets automatically
 
-While you're developing your application, you want to run Tailwind in "watch" mode, so changes are automatically reflected in the generated CSS output. You can do this by:
+While you're developing your application, you want to run Tailwind in "watch" mode, so changes are automatically reflected in the generated CSS output. You can do this in a few different ways:
 
-- running `rails tailwindcss:watch` as a separate process,
-- or by running `./bin/dev` which uses [foreman](https://github.com/ddollar/foreman) to start both the Tailwind watch process and the rails server in development mode.
+- use the [Puma](https://puma.io/) plugin to integrate "watch" with `rails server`, or
+- run `rails tailwindcss:watch` as a separate process, or
+- run `bin/dev` which uses [Foreman](https://github.com/ddollar/foreman)
+
+#### Puma plugin
+
+The Puma plugin requires you to add this line to your `puma.rb` configuration:
+
+```ruby
+plugin :tailwindcss if ENV.fetch("RAILS_ENV", "development") == "development"
+```
+
+and then running `rails server` will run the Tailwind watch process in the background
+
+
+#### Run `rails tailwindcss:watch`
+
+This is a flexible command, which can be run with a few different options.
 
 If you are running `rails tailwindcss:watch` on a system that doesn't fully support file system events, pass a `poll` argument to the task to instruct tailwindcss to instead use polling: `rails tailwindcss:watch[poll]`. If you use `bin/dev` then you should modify your `Procfile.dev`.
 
@@ -72,6 +88,11 @@ If you are running `rails tailwindcss:watch` as a process in a Docker container,
 If you are running `rails tailwindcss:watch` in a docker container without a tty, pass the `always` argument to the task to instruct tailwindcss to keep the watcher alive even when `stdin` is closed: `rails tailwindcss:watch[always]`. If you use `bin/dev` then you should modify your `Procfile.dev`.
 
 
+#### Foreman
+
+Running `bin/dev` invokes Foreman to start both the Tailwind watch process and the rails server in development mode based on your `Procfile.dev` file.
+
+
 ### Debugging with unminified assets
 
 If you want unminified assets, you can pass a `debug` argument to the rake task, i.e. `rails tailwindcss:build[debug]` or `rails tailwindcss:watch[debug]`.

lib/puma/plugin/tailwindcss.rb

@@ -0,0 +1,63 @@
+require "puma/plugin"
+
+Puma::Plugin.create do
+  attr_reader :puma_pid, :tailwind_pid, :log_writer
+
+  def start(launcher)
+    @log_writer = launcher.log_writer
+    @puma_pid = $$
+    @tailwind_pid = fork do
+      Thread.new { monitor_puma }
+      system(*Tailwindcss::Commands.watch_command)
+    end
+
+    launcher.events.on_stopped { stop_tailwind }
+
+    in_background do
+      monitor_tailwind
+    end
+  end
+
+  private
+    def stop_tailwind
+      Process.waitpid(tailwind_pid, Process::WNOHANG)
+      log "Stopping tailwind..."
+      Process.kill(:INT, tailwind_pid) if tailwind_pid
+      Process.wait(tailwind_pid)
+    rescue Errno::ECHILD, Errno::ESRCH
+    end
+
+    def monitor_puma
+      monitor(:puma_dead?, "Detected Puma has gone away, stopping tailwind...")
+    end
+
+    def monitor_tailwind
+      monitor(:tailwind_dead?, "Detected tailwind has gone away, stopping Puma...")
+    end
+
+    def monitor(process_dead, message)
+      loop do
+        if send(process_dead)
+          log message
+          Process.kill(:INT, $$)
+          break
+        end
+        sleep 2
+      end
+    end
+
+    def tailwind_dead?
+      Process.waitpid(tailwind_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