The request handler is the layer which connects Apache with the underlying application‘s request dispatcher (i.e. either Rails‘s Dispatcher class or Rack). The request handler‘s job is to process incoming HTTP requests using the currently loaded Ruby on Rails application. HTTP requests are forwarded to the request handler by the web server. HTTP responses generated by the RoR application are forwarded to the web server, which, in turn, sends the response back to the HTTP client.

AbstractRequestHandler is an abstract base class for easing the implementation of request handlers for Rails and Rack.

Design decisions

Some design decisions are made because we want to decrease system administrator maintenance overhead. These decisions are documented in this section.

Owner pipes

Because only the web server communicates directly with a request handler, we want the request handler to exit if the web server has also exited. This is implemented by using a so-called _owner pipe_. The writable part of the pipe will be passed to the web server* via a Unix socket, and the web server will own that part of the pipe, while AbstractRequestHandler owns the readable part of the pipe. AbstractRequestHandler will continuously check whether the other side of the pipe has been closed. If so, then it knows that the web server has exited, and so the request handler will exit as well. This works even if the web server gets killed by SIGKILL.

  • It might also be passed to the ApplicationPoolServerExecutable, if the web server‘s using ApplicationPoolServer instead of StandardApplicationPool.

Request format

Incoming "HTTP requests" are not true HTTP requests, i.e. their binary representation do not conform to RFC 2616. Instead, the request format is based on CGI, and is similar to that of SCGI.

The format consists of 3 parts:

  • A 32-bit big-endian integer, containing the size of the transformed headers.
  • The transformed HTTP headers.
  • The verbatim (untransformed) HTTP request body.

HTTP headers are transformed to a format that satisfies the following grammar:

 headers ::= header*
 header ::= name NUL value NUL
 name ::= notnull+
 value ::= notnull+
 notnull ::= "\x01" | "\x02" | "\x02" | ... | "\xFF"
 NUL = "\x00"

The web server transforms the HTTP request to the aforementioned format, and sends it to the request handler.

Methods
Included Modules
Constants
HARD_TERMINATION_SIGNAL = "SIGTERM"
  Signal which will cause the Rails application to exit immediately.
SOFT_TERMINATION_SIGNAL = "SIGUSR1"
  Signal which will cause the Rails application to exit as soon as it‘s done processing a request.
BACKLOG_SIZE = 100
MAX_HEADER_SIZE = 128 * 1024
PASSENGER_VERSION = determine_passenger_version
PASSENGER_HEADER = determine_passenger_header
Attributes
[R] iterations The number of times the main loop has iterated so far. Mostly useful for unit test assertions.
[RW] memory_limit Specifies the maximum allowed memory usage, in MB. If after having processed a request AbstractRequestHandler detects that memory usage has risen above this limit, then it will gracefully exit (that is, exit after having processed all pending requests).

A value of 0 (the default) indicates that there‘s no limit.

[R] processed_requests Number of requests processed so far. This includes requests that raised exceptions.
[R] socket_name The name of the socket on which the request handler accepts new connections. At this moment, this value is always the filename of a Unix domain socket.

See also #socket_type.

[R] socket_type The type of socket that #socket_name refers to. At the moment, the value is always ‘unix’, which indicates a Unix domain socket.
Public Class methods
new(owner_pipe, options = {})

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:

  • memory_limit: Used to set the memory_limit attribute.
     # File lib/phusion_passenger/abstract_request_handler.rb, line 132
132:         def initialize(owner_pipe, options = {})
133:                 if should_use_unix_sockets?
134:                         create_unix_socket_on_filesystem
135:                 else
136:                         create_tcp_socket
137:                 end
138:                 @socket.close_on_exec!
139:                 @owner_pipe = owner_pipe
140:                 @previous_signal_handlers = {}
141:                 @main_loop_thread_lock = Mutex.new
142:                 @main_loop_thread_cond = ConditionVariable.new
143:                 @memory_limit = options["memory_limit"] || 0
144:                 @iterations = 0
145:                 @processed_requests = 0
146:         end
Public Instance methods
cleanup()

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.

     # File lib/phusion_passenger/abstract_request_handler.rb, line 155
155:         def cleanup
156:                 if @main_loop_thread
157:                         @main_loop_thread.raise(Interrupt.new("Cleaning up"))
158:                         @main_loop_thread.join
159:                 end
160:                 @socket.close rescue nil
161:                 @owner_pipe.close rescue nil
162:                 File.unlink(@socket_name) rescue nil
163:         end
main_loop()

Enter the request handler‘s main loop.

     # File lib/phusion_passenger/abstract_request_handler.rb, line 171
171:         def main_loop
172:                 reset_signal_handlers
173:                 begin
174:                         @graceful_termination_pipe = IO.pipe
175:                         @graceful_termination_pipe[0].close_on_exec!
176:                         @graceful_termination_pipe[1].close_on_exec!
177:                         
178:                         @main_loop_thread_lock.synchronize do
179:                                 @main_loop_running = true
180:                                 @main_loop_thread_cond.broadcast
181:                         end
182:                         
183:                         install_useful_signal_handlers
184:                         
185:                         while true
186:                                 @iterations += 1
187:                                 client = accept_connection
188:                                 if client.nil?
189:                                         break
190:                                 end
191:                                 begin
192:                                         headers, input = parse_request(client)
193:                                         if headers
194:                                                 if headers[REQUEST_METHOD] == PING
195:                                                         process_ping(headers, input, client)
196:                                                 else
197:                                                         process_request(headers, input, client)
198:                                                 end
199:                                         end
200:                                 rescue IOError, SocketError, SystemCallError => e
201:                                         print_exception("Passenger RequestHandler", e)
202:                                 ensure
203:                                         # 'input' is the same as 'client' so we don't
204:                                         # need to close that.
205:                                         client.close rescue nil
206:                                 end
207:                                 @processed_requests += 1
208:                         end
209:                 rescue EOFError
210:                         # Exit main loop.
211:                 rescue Interrupt
212:                         # Exit main loop.
213:                 rescue SignalException => signal
214:                         if signal.message != HARD_TERMINATION_SIGNAL &&
215:                            signal.message != SOFT_TERMINATION_SIGNAL
216:                                 raise
217:                         end
218:                 ensure
219:                         @graceful_termination_pipe[0].close rescue nil
220:                         @graceful_termination_pipe[1].close rescue nil
221:                         revert_signal_handlers
222:                         @main_loop_thread_lock.synchronize do
223:                                 @main_loop_running = false
224:                                 @main_loop_thread_cond.broadcast
225:                         end
226:                 end
227:         end
main_loop_running?()

Check whether the main loop‘s currently running.

     # File lib/phusion_passenger/abstract_request_handler.rb, line 166
166:         def main_loop_running?
167:                 return @main_loop_running
168:         end
start_main_loop_thread()

Start the main loop in a new thread. This thread will be stopped by #cleanup.

     # File lib/phusion_passenger/abstract_request_handler.rb, line 230
230:         def start_main_loop_thread
231:                 @main_loop_thread = Thread.new do
232:                         main_loop
233:                 end
234:                 @main_loop_thread_lock.synchronize do
235:                         while !@main_loop_running
236:                                 @main_loop_thread_cond.wait(@main_loop_thread_lock)
237:                         end
238:                 end
239:         end