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.
| 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 |
| [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. |
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.
[ show source ]
# File lib/phusion_passenger/abstract_request_handler.rb, line 137
137: def initialize(owner_pipe, options = {})
138: if should_use_unix_sockets?
139: create_unix_socket_on_filesystem
140: else
141: create_tcp_socket
142: end
143: @socket.close_on_exec!
144: @owner_pipe = owner_pipe
145: @previous_signal_handlers = {}
146: @main_loop_generation = 0
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: @main_loop_running = false
153: 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.
[ show source ]
# File lib/phusion_passenger/abstract_request_handler.rb, line 162
162: def cleanup
163: if @main_loop_thread
164: @main_loop_thread_lock.synchronize do
165: @graceful_termination_pipe[1].close rescue nil
166: end
167: @main_loop_thread.join
168: end
169: @socket.close rescue nil
170: @owner_pipe.close rescue nil
171: File.unlink(@socket_name) rescue nil
172: end
Enter the request handler‘s main loop.
[ show source ]
# File lib/phusion_passenger/abstract_request_handler.rb, line 180
180: def main_loop
181: reset_signal_handlers
182: begin
183: @graceful_termination_pipe = IO.pipe
184: @graceful_termination_pipe[0].close_on_exec!
185: @graceful_termination_pipe[1].close_on_exec!
186:
187: @main_loop_thread_lock.synchronize do
188: @main_loop_generation += 1
189: @main_loop_running = true
190: @main_loop_thread_cond.broadcast
191: end
192:
193: install_useful_signal_handlers
194:
195: while true
196: @iterations += 1
197: client = accept_connection
198: if client.nil?
199: break
200: end
201: begin
202: headers, input = parse_request(client)
203: if headers
204: if headers[REQUEST_METHOD] == PING
205: process_ping(headers, input, client)
206: else
207: process_request(headers, input, client)
208: end
209: end
210: rescue IOError, SocketError, SystemCallError => e
211: print_exception("Passenger RequestHandler", e)
212: ensure
213: # 'input' is the same as 'client' so we don't
214: # need to close that.
215: # The 'close_write' here prevents forked child
216: # processes from unintentionally keeping the
217: # connection open.
218: client.close_write rescue nil
219: client.close rescue nil
220: end
221: @processed_requests += 1
222: end
223: rescue EOFError
224: # Exit main loop.
225: rescue Interrupt
226: # Exit main loop.
227: rescue SignalException => signal
228: if signal.message != HARD_TERMINATION_SIGNAL &&
229: signal.message != SOFT_TERMINATION_SIGNAL
230: raise
231: end
232: ensure
233: revert_signal_handlers
234: @main_loop_thread_lock.synchronize do
235: @graceful_termination_pipe[0].close rescue nil
236: @graceful_termination_pipe[1].close rescue nil
237: @main_loop_generation += 1
238: @main_loop_running = false
239: @main_loop_thread_cond.broadcast
240: end
241: end
242: end
Check whether the main loop‘s currently running.
[ show source ]
# File lib/phusion_passenger/abstract_request_handler.rb, line 175
175: def main_loop_running?
176: return @main_loop_running
177: end
[ show source ]
# File lib/phusion_passenger/abstract_request_handler.rb, line 245
245: def start_main_loop_thread
246: current_generation = @main_loop_generation
247: @main_loop_thread = Thread.new do
248: main_loop
249: end
250: @main_loop_thread_lock.synchronize do
251: while @main_loop_generation == current_generation
252: @main_loop_thread_cond.wait(@main_loop_thread_lock)
253: end
254: end
255: end