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_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 138
138:         def initialize(owner_pipe, options = {})
139:                 if should_use_unix_sockets?
140:                         create_unix_socket_on_filesystem
141:                 else
142:                         create_tcp_socket
143:                 end
144:                 @socket.close_on_exec!
145:                 @owner_pipe = owner_pipe
146:                 @previous_signal_handlers = {}
147:                 @main_loop_thread_lock = Mutex.new
148:                 @main_loop_thread_cond = ConditionVariable.new
149:                 @memory_limit = options["memory_limit"] || 0
150:                 @iterations = 0
151:                 @processed_requests = 0
152:         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 161
161:         def cleanup
162:                 if @main_loop_thread
163:                         @main_loop_thread.raise(Interrupt.new("Cleaning up"))
164:                         @main_loop_thread.join
165:                 end
166:                 @socket.close rescue nil
167:                 @owner_pipe.close rescue nil
168:                 File.unlink(@socket_name) rescue nil
169:         end
main_loop()

Enter the request handler‘s main loop.

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

Check whether the main loop‘s currently running.

     # File lib/phusion_passenger/abstract_request_handler.rb, line 172
172:         def main_loop_running?
173:                 return @main_loop_running
174:         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 236
236:         def start_main_loop_thread
237:                 @main_loop_thread = Thread.new do
238:                         main_loop
239:                 end
240:                 @main_loop_thread_lock.synchronize do
241:                         while !@main_loop_running
242:                                 @main_loop_thread_cond.wait(@main_loop_thread_lock)
243:                         end
244:                 end
245:         end