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Filename : request_handler.rb
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#  Phusion Passenger - https://www.phusionpassenger.com/
#  Copyright (c) 2010-2018 Phusion Holding B.V.
#
#  "Passenger", "Phusion Passenger" and "Union Station" are registered
#  trademarks of Phusion Holding B.V.
#
#  Permission is hereby granted, free of charge, to any person obtaining a copy
#  of this software and associated documentation files (the "Software"), to deal
#  in the Software without restriction, including without limitation the rights
#  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
#  copies of the Software, and to permit persons to whom the Software is
#  furnished to do so, subject to the following conditions:
#
#  The above copyright notice and this permission notice shall be included in
#  all copies or substantial portions of the Software.
#
#  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
#  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
#  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
#  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
#  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
#  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
#  THE SOFTWARE.

require 'socket'
require 'fcntl'
PhusionPassenger.require_passenger_lib 'constants'
PhusionPassenger.require_passenger_lib 'public_api'
PhusionPassenger.require_passenger_lib 'message_client'
PhusionPassenger.require_passenger_lib 'debug_logging'
PhusionPassenger.require_passenger_lib 'native_support'
PhusionPassenger.require_passenger_lib 'utils'
PhusionPassenger.require_passenger_lib 'ruby_core_enhancements'
PhusionPassenger.require_passenger_lib 'ruby_core_io_enhancements'
PhusionPassenger.require_passenger_lib 'request_handler/thread_handler'

module PhusionPassenger

  class RequestHandler
    include DebugLogging
    include Utils

    # Signal which will cause the application to exit immediately.
    HARD_TERMINATION_SIGNAL = "SIGTERM"
    BACKLOG_SIZE    = 500

    # String constants which exist to relieve Ruby's garbage collector.
    IGNORE              = 'IGNORE'              # :nodoc:
    DEFAULT             = 'DEFAULT'             # :nodoc:

    # A hash containing all server sockets that this request handler listens on.
    # The hash is in the form of:
    #
    #   {
    #      name1 => [socket_address1, socket_type1, socket1],
    #      name2 => [socket_address2, socket_type2, socket2],
    #      ...
    #   }
    #
    # +name+ is a Symbol. +socket_addressx+ is the address of the socket,
    # +socket_typex+ is the socket's type (either 'unix' or 'tcp') and
    # +socketx+ is the actual socket IO objec.
    # There's guaranteed to be at least one server socket, namely one with the
    # name +:main+.
    attr_reader :server_sockets

    attr_reader :concurrency

    # A password with which clients must authenticate. Default is unauthenticated.
    attr_accessor :connect_password

    # Create a new RequestHandler with the given owner pipe.
    # +owner_pipe+ must be the readable part of a pipe IO object.
    #
    # Additionally, the following options may be given:
    # - connect_password
    def initialize(owner_pipe, options = {})
      require_option(options, "app_group_name")
      install_options_as_ivars(self, options,
        "app",
        "app_group_name",
        "connect_password"
      )

      @keepalive = options.fetch("keepalive", true).to_s == "true"
      @force_http_session = ENV["_PASSENGER_FORCE_HTTP_SESSION"] == "true"
      if @force_http_session
        @connect_password = nil
      end
      @thread_handler = options["thread_handler"] || ThreadHandler
      @concurrency = 1

      #############
      #############

      @server_sockets = {}

      if should_use_unix_sockets?
        @main_socket_address, @main_socket = create_unix_socket_on_filesystem(options)
      else
        @main_socket_address, @main_socket = create_tcp_socket(options)
      end
      @server_sockets[:main] = {
        :address     => @main_socket_address,
        :socket      => @main_socket,
        :protocol    => @force_http_session ? :http : :session,
        :concurrency => @concurrency,
        :accept_http_requests => true
      }

      @http_socket_address, @http_socket = create_tcp_socket(options)
      @server_sockets[:http] = {
        :address     => @http_socket_address,
        :socket      => @http_socket,
        :protocol    => :http,
        :concurrency => 1
      }

      @owner_pipe = owner_pipe
      @options = options
      @previous_signal_handlers = {}
      @main_loop_generation  = 0
      @main_loop_thread_lock = Mutex.new
      @main_loop_thread_cond = ConditionVariable.new
      @threads = []
      @threads_mutex = Mutex.new
      @main_loop_running  = false

      #############
    end

    # Clean up temporary stuff created by the request handler.
    #
    # If the main loop was started by #main_loop, then this method may only
    # be called after the main loop has exited.
    #
    # If the main loop was started by #start_main_loop_thread, then this method
    # may be called at any time, and it will stop the main loop thread.
    def cleanup
      if @main_loop_thread
        @main_loop_thread_lock.synchronize do
          @graceful_termination_pipe[1].close rescue nil
        end
        @main_loop_thread.join
      end
      @server_sockets.each_value do |info|
        socket = info[:socket]
        type = get_socket_address_type(info[:address])

        begin
          socket.close if !socket.closed?
        rescue Exception => e
          # Ignore "stream closed" error, which occurs in some unit tests.
          # We catch Exception here instead of IOError because of a Ruby 1.8.7 bug.
          if e.to_s !~ /stream closed/ && e.message.to_s !~ /stream closed/
            raise e
          end
        end
        if type == :unix
          filename = info[:address].sub(/^unix:/, '')
          File.unlink(filename) rescue nil
        end
      end
      @owner_pipe.close rescue nil
    end

    # Check whether the main loop's currently running.
    def main_loop_running?
      @main_loop_thread_lock.synchronize do
        return @main_loop_running
      end
    end

    # Enter the request handler's main loop.
    def main_loop
      debug("Entering request handler main loop")
      reset_signal_handlers
      begin
        @graceful_termination_pipe = IO.pipe
        @graceful_termination_pipe[0].close_on_exec!
        @graceful_termination_pipe[1].close_on_exec!

        @main_loop_thread_lock.synchronize do
          @main_loop_generation += 1
          @main_loop_running = true
          @main_loop_thread_cond.broadcast

          @select_timeout = nil

          @selectable_sockets = []
          @server_sockets.each_value do |value|
            socket = value[2]
            @selectable_sockets << socket if socket
          end
          @selectable_sockets << @owner_pipe
          @selectable_sockets << @graceful_termination_pipe[0]
        end

        install_useful_signal_handlers
        start_threads
        wait_until_termination_requested
        wait_until_all_threads_are_idle
        terminate_threads
        debug("Request handler main loop exited normally")

      rescue EOFError
        # Exit main loop.
        trace(2, "Request handler main loop interrupted by EOFError exception")
      rescue Interrupt
        # Exit main loop.
        trace(2, "Request handler main loop interrupted by Interrupt exception")
      rescue SignalException => signal
        trace(2, "Request handler main loop interrupted by SignalException")
        if signal.message != HARD_TERMINATION_SIGNAL
          raise
        end
      rescue Exception => e
        trace(2, "Request handler main loop interrupted by #{e.class} exception")
        raise
      ensure
        debug("Exiting request handler main loop")
        revert_signal_handlers
        @main_loop_thread_lock.synchronize do
          @graceful_termination_pipe[1].close rescue nil
          @graceful_termination_pipe[0].close rescue nil
          @selectable_sockets = []
          @main_loop_generation += 1
          @main_loop_running = false
          @main_loop_thread_cond.broadcast
        end
      end
    end

    # Start the main loop in a new thread. This thread will be stopped by #cleanup.
    def start_main_loop_thread
      current_generation = @main_loop_generation
      @main_loop_thread = create_thread_and_abort_on_exception do
        main_loop
      end
      @main_loop_thread_lock.synchronize do
        while @main_loop_generation == current_generation
          @main_loop_thread_cond.wait(@main_loop_thread_lock)
        end
      end
    end

  private
    def should_use_unix_sockets?
      # Historical note:
      # There seems to be a bug in MacOS X Leopard w.r.t. Unix server
      # sockets file descriptors that are passed to another process.
      # Usually Unix server sockets work fine, but when they're passed
      # to another process, then clients that connect to the socket
      # can incorrectly determine that the client socket is closed,
      # even though that's not actually the case. More specifically:
      # recv()/read() calls on these client sockets can return 0 even
      # when we know EOF is not reached.
      #
      # The ApplicationPool infrastructure used to connect to a backend
      # process's Unix socket in the Passenger core process, and then
      # pass the connection file descriptor to the web server, which
      # triggers this kernel bug. We used to work around this by using
      # TCP sockets instead of Unix sockets; TCP sockets can still fail
      # with this fake-EOF bug once in a while, but not nearly as often
      # as with Unix sockets.
      #
      # This problem no longer applies today. The web server now passes
      # all I/O through the Passenger core, and the bug is no longer
      # triggered. Nevertheless, we keep this function intact so that
      # if something like this ever happens again, we know why, and we
      # can easily reactivate the workaround. Or maybe if we just need
      # TCP sockets for some other reason.

      #return RUBY_PLATFORM !~ /darwin/

      ruby_engine = defined?(RUBY_ENGINE) ? RUBY_ENGINE : "ruby"
      # Unix domain socket implementation on JRuby
      # is still bugged as of version 1.7.0. They can
      # cause unexplicable freezes when used in combination
      # with threading.
      # It's also bugged in Windows Subsystem for Linux
      # as of Windows 10, version 1803 (Fall Creators Update)
      # You will get "Address In Use" errors even if the port is unused.
      return !@force_http_session && ruby_engine != "jruby" && !PlatformInfo.windows_subsystem?
    end

    def create_unix_socket_on_filesystem(options)
      if defined?(NativeSupport)
        unix_path_max = NativeSupport::UNIX_PATH_MAX
      else
        unix_path_max = options.fetch('UNIX_PATH_MAX', 100).to_i
      end
      if options['socket_dir']
        socket_dir = options['socket_dir']
        socket_prefix = "ruby"
      else
        socket_dir = Dir.tmpdir
        socket_prefix = "PsgRubyApp"
      end

      retry_at_most(128, Errno::EADDRINUSE) do
        socket_address = "#{socket_dir}/#{socket_prefix}.#{generate_random_id(:base64)}"
        socket_address = socket_address.slice(0, unix_path_max - 10)
        socket = UNIXServer.new(socket_address)
        socket.listen(BACKLOG_SIZE)
        socket.binmode
        socket.sync = true
        socket.close_on_exec!
        File.chmod(0600, socket_address)
        ["unix:#{socket_address}", socket]
      end
    end

    def create_tcp_socket(options)
      # We default to "127.0.0.1" as address in order to force
      # TCPv4 instead of TCPv6.
      bind_address = options.fetch('bind_address', '127.0.0.1')
      socket = TCPServer.new(bind_address, 0)
      socket.listen(BACKLOG_SIZE)
      socket.setsockopt(Socket::IPPROTO_TCP, Socket::TCP_NODELAY, 1)
      socket.binmode
      socket.sync = true
      socket.close_on_exec!
      socket_address = "tcp://#{bind_address}:#{socket.addr[1]}"
      return [socket_address, socket]
    end

    # Reset signal handlers to their default handler, and install some
    # special handlers for a few signals. The previous signal handlers
    # will be put back by calling revert_signal_handlers.
    def reset_signal_handlers
      Signal.list_trappable.each_key do |signal|
        begin
          prev_handler = trap(signal, DEFAULT)
          if prev_handler != DEFAULT
            @previous_signal_handlers[signal] = prev_handler
          end
        rescue ArgumentError
          # Signal cannot be trapped; ignore it.
        end
      end
      trap('HUP', IGNORE)
      PhusionPassenger.call_event(:after_installing_signal_handlers)
    end

    def install_useful_signal_handlers
      trappable_signals = Signal.list_trappable

      trap('ABRT') do
        print_status_report
        abort
      end if trappable_signals.has_key?('ABRT')
      trap('QUIT') do
        print_status_report
      end if trappable_signals.has_key?('QUIT')
    end

    def revert_signal_handlers
      @previous_signal_handlers.each_pair do |signal, handler|
        trap(signal, handler)
      end
    end

    def print_status_report
      warn(Utils.global_backtrace_report)
      warn("Threads: #{@threads.inspect}")
    end

    def start_threads
      common_options = {
        :app              => @app,
        :app_group_name   => @app_group_name,
        :connect_password => @connect_password,
        :keepalive_enabled  => @keepalive
      }
      main_socket_options = common_options.merge(
        :server_socket => @main_socket,
        :socket_name => "main socket",
        :protocol => @server_sockets[:main][:protocol] == :session ?
          :session :
          :http
      )
      http_socket_options = common_options.merge(
        :server_socket => @http_socket,
        :socket_name => "HTTP socket",
        :protocol => :http
      )

      # Used for marking threads that have finished initializing,
      # or failed during initialization. Threads that are not yet done
      # are not in `initialization_state`. Threads that have succeeded
      # set their own state to true. Threads that have failed set their
      # own state to false.
      initialization_state_mutex = Mutex.new
      initialization_state_cond = ConditionVariable.new
      initialization_state = {}
      set_initialization_state = lambda do |value|
        initialization_state_mutex.synchronize do
          initialization_state[Thread.current] = value
          initialization_state_cond.signal
        end
      end
      set_initialization_state_to_true = lambda do
        set_initialization_state.call(true)
      end

      # Actually start all the threads.
      thread_handler = @thread_handler
      expected_nthreads = 0

      @threads_mutex.synchronize do
        @concurrency.times do |i|
          thread = create_thread_and_abort_on_exception(i) do |number|
            begin
              Thread.current[:name] = "Worker #{number + 1}"
              handler = thread_handler.new(self, main_socket_options)
              handler.install
              handler.main_loop(set_initialization_state_to_true)
            ensure
              set_initialization_state.call(false)
              unregister_current_thread
            end
          end
          @threads << thread
          expected_nthreads += 1
        end

        thread = create_thread_and_abort_on_exception do
          begin
            Thread.current[:name] = "HTTP helper worker"
            handler = thread_handler.new(self, http_socket_options)
            handler.install
            handler.main_loop(set_initialization_state_to_true)
          ensure
            set_initialization_state.call(false)
            unregister_current_thread
          end
        end
        @threads << thread
        expected_nthreads += 1
      end

      # Wait until all threads have finished starting.
      initialization_state_mutex.synchronize do
        while initialization_state.size != expected_nthreads
          initialization_state_cond.wait(initialization_state_mutex)
        end
      end
    end

    def unregister_current_thread
      @threads_mutex.synchronize do
        @threads.delete(Thread.current)
      end
    end

    def wait_until_termination_requested
      ruby_engine = defined?(RUBY_ENGINE) ? RUBY_ENGINE : "ruby"
      if ruby_engine == "jruby"
        # On JRuby, selecting on an input TTY always returns, so
        # we use threads to do the job.
        owner_pipe_watcher = IO.pipe
        owner_pipe_watcher_thread = create_thread_and_abort_on_exception do
          Thread.current[:name] = "Owner pipe waiter"
          begin
            @owner_pipe.read(1)
          ensure
            owner_pipe_watcher[1].write('x')
          end
        end
        begin
          ios = select([owner_pipe_watcher[0], @graceful_termination_pipe[0]])[0]
          if ios.include?(owner_pipe_watcher[0])
            trace(2, "Owner pipe closed")
          else
            trace(2, "Graceful termination pipe closed")
          end
        ensure
          owner_pipe_watcher_thread.kill
          owner_pipe_watcher_thread.join
          owner_pipe_watcher[0].close if !owner_pipe_watcher[0].closed?
          owner_pipe_watcher[1].close if !owner_pipe_watcher[1].closed?
        end
      else
        ios = select([@owner_pipe, @graceful_termination_pipe[0]])[0]
        if ios.include?(@owner_pipe)
          trace(2, "Owner pipe closed")
        else
          trace(2, "Graceful termination pipe closed")
        end
      end
    end

    def wakeup_all_threads
      threads = []
      if get_socket_address_type(@server_sockets[:main][:address]) == :unix &&
         !File.exist?(@server_sockets[:main][:address].sub(/^unix:/, ''))
        # It looks like someone deleted the Unix domain socket we listen on.
        # This makes it impossible to wake up the worker threads gracefully,
        # so we hard kill them.
        warn("Unix domain socket gone; force aborting all threads")
        @threads_mutex.synchronize do
          @threads.each do |thread|
            thread.raise(RuntimeError.new("Force abort"))
          end
        end
      else
        @concurrency.times do
          threads << create_thread_and_abort_on_exception(@server_sockets[:main][:address]) do |address|
            begin
              debug("Shutting down worker thread by connecting to #{address}")
              connect_to_server(address).close
            rescue Errno::ECONNREFUSED
              debug("Worker thread listening on #{address} already exited")
            rescue SystemCallError, IOError => e
              debug("Error shutting down worker thread (#{address}): #{e} (#{e.class})")
            end
          end
        end
      end
      threads << create_thread_and_abort_on_exception(@server_sockets[:http][:address]) do |address|
        begin
          debug("Shutting down HTTP thread by connecting to #{address}")
          connect_to_server(address).close
        rescue Errno::ECONNREFUSED
          debug("Worker thread listening on #{address} already exited")
        rescue SystemCallError, IOError => e
          debug("Error shutting down HTTP thread (#{address}): #{e} (#{e.class})")
        end
      end
      return threads
    end

    def terminate_threads
      debug("Stopping all threads")
      threads = @threads_mutex.synchronize do
        @threads.dup
      end
      threads.each do |thr|
        thr.raise(ThreadHandler::Interrupted.new)
      end
      threads.each do |thr|
        thr.join
      end
      debug("All threads stopped")
    end

    def wait_until_all_threads_are_idle
      debug("Waiting until all threads have become idle...")

      # We wait until 100 ms have passed since all handlers have become
      # interruptable and remained in the same iterations.

      done = false

      while !done
        handlers = @threads_mutex.synchronize do
          @threads.map do |thr|
            thr[:passenger_thread_handler]
          end
        end
        debug("There are currently #{handlers.size} threads")
        if handlers.empty?
          # There are no threads, so we're done.
          done = true
          break
        end

        # Record initial state.
        handlers.each { |h| h.stats_mutex.lock }
        iterations = handlers.map { |h| h.iteration }
        handlers.each { |h| h.stats_mutex.unlock }

        start_time = Time.now
        sleep 0.01

        while true
          if handlers.size != @threads_mutex.synchronize { @threads.size }
            debug("The number of threads changed. Restarting waiting algorithm")
            break
          end

          # Record current state.
          handlers.each { |h| h.stats_mutex.lock }
          all_interruptable = handlers.all? { |h| h.interruptable }
          new_iterations    = handlers.map  { |h| h.iteration }

          # Are all threads interruptable and has there been no activity
          # since last time we checked?
          if all_interruptable && new_iterations == iterations
            # Yes. If enough time has passed then we're done.
            handlers.each { |h| h.stats_mutex.unlock }
            if Time.now >= start_time + 0.1
              done = true
              break
            end
          else
            # No. We reset the timer and check again later.
            handlers.each { |h| h.stats_mutex.unlock }
            iterations = new_iterations
            start_time = Time.now
            sleep 0.01
          end
        end
      end

      debug("All threads are now idle")
    end
  end

end # module PhusionPassenger