Class PhusionPassenger::AbstractRequestHandler |
In: | lib/phusion_passenger/abstract_request_handler.rb
Parent: | Object

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

- cleanup
- main_loop
- main_loop_running?
- new
- start_main_loop_thread

Included Modules

- Utils

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.

[ 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

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.

[ 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

main_loop()

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

main_loop_running?()

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

start_main_loop_thread()

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

[ 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