Patch: Add after_worker_ready configuration option V2

[Jeremy Evans <code@jeremyevans.net>]

Here's V2 of the after_worker_ready patch.  This adds some more
documentation, and tries to give a better description of the
advantages in the commit message.

From cbc6fe845ade8946b7db2ecd2b86a0bd8e18bbb8 Mon Sep 17 00:00:00 2001
From: Jeremy Evans <code@jeremyevans.net>
Date: Tue, 21 Feb 2017 16:33:09 -0800
Subject: [PATCH] Add after_worker_ready configuration option

This adds a hook that is called after the application has
been loaded by the worker process, directly before it starts
accepting requests.  This hook is necessary if your application
needs to gain access to resources during initialization,
and then drop privileges before serving requests.

This is especially useful in conjunction with chroot support
so the app can load all the normal ruby libraries it needs
to function, and then chroot before accepting requests.

If you are preloading the app, it's possible to drop privileges
or chroot in after_fork, but if you are not preloading the app,
the only way to currently do this is to override the private
HttpServer#init_worker_process method, and overriding private
methods is a recipe for future breakage if the internals are
modified.  This hook allows for such functionality to be
supported and not break in future versions of Unicorn.
---
 lib/unicorn/configurator.rb | 22 ++++++++++++++++++++++
 lib/unicorn/http_server.rb  |  4 ++--
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/lib/unicorn/configurator.rb b/lib/unicorn/configurator.rb
index 1e2b6e4..7ed5ffa 100644
--- a/lib/unicorn/configurator.rb
+++ b/lib/unicorn/configurator.rb
@@ -49,6 +49,9 @@ class Unicorn::Configurator
           server.logger.error(m)
         end
       },
+    :after_worker_ready => lambda { |server, worker|
+        server.logger.info("worker=#{worker.nr} ready")
+      },
     :pid => nil,
     :preload_app => false,
     :check_client_connection => false,
@@ -172,6 +175,21 @@ def after_worker_exit(*args, &block)
     set_hook(:after_worker_exit, block_given? ? block : args[0], 3)
   end
 
+  # sets after_worker_ready hook to a given block.  This block will be called
+  # by a worker process after it has been fully loaded, directly before it
+  # starts responding to requests:
+  #
+  #  after_worker_ready do |server,worker|
+  #    server.logger.info("worker #{worker.nr} ready, dropping privileges")
+  #    worker.user('username', 'groupname')
+  #  end
+  #
+  # Do not use Configurator#user if you rely on changing users in the
+  # after_worker_ready hook.
+  def after_worker_ready(*args, &block)
+    set_hook(:after_worker_ready, block_given? ? block : args[0])
+  end
+
   # sets before_fork got be a given Proc object.  This Proc
   # object will be called by the master process before forking
   # each worker.
@@ -569,6 +587,10 @@ def working_directory(path)
   # This switch will occur after calling the after_fork hook, and only
   # if the Worker#user method is not called in the after_fork hook
   # +group+ is optional and will not change if unspecified.
+  #
+  # Do not use Configurator#user if you rely on changing users in the
+  # after_worker_ready hook.  Instead, you need to call Worker#user
+  # directly in after_worker_ready.
   def user(user, group = nil)
     # raises ArgumentError on invalid user/group
     Etc.getpwnam(user)
diff --git a/lib/unicorn/http_server.rb b/lib/unicorn/http_server.rb
index c2086cb..ef897ad 100644
--- a/lib/unicorn/http_server.rb
+++ b/lib/unicorn/http_server.rb
@@ -15,7 +15,7 @@ class Unicorn::HttpServer
                 :before_fork, :after_fork, :before_exec,
                 :listener_opts, :preload_app,
                 :orig_app, :config, :ready_pipe, :user
-  attr_writer   :after_worker_exit
+  attr_writer   :after_worker_exit, :after_worker_ready
 
   attr_reader :pid, :logger
   include Unicorn::SocketHelper
@@ -644,7 +644,7 @@ def worker_loop(worker)
     trap(:USR1) { nr = -65536 }
 
     ready = readers.dup
-    @logger.info "worker=#{worker.nr} ready"
+    @after_worker_ready.call(self, worker)
 
     begin
       nr < 0 and reopen_worker_logs(worker.nr)
-- 
2.11.0