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.

Design decisions

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

Abstract namespace Unix sockets

RequestHandler listens on a Unix socket for incoming requests. If possible, RequestHandler will try to create a Unix socket on the _abstract namespace_, instead of on the filesystem. If the RoR application crashes (segfault), or if it gets killed by SIGKILL, or if the system loses power, then there will be no stale socket files left on the filesystem. Unfortunately, abstract namespace Unix sockets are only supported by Linux. On systems that do not support abstract namespace Unix sockets, RequestHandler will automatically fallback to using regular Unix socket files.

It is possible to force RequestHandler to use regular Unix socket files by setting the environment variable PASSENGER_NO_ABSTRACT_NAMESPACE_SOCKETS to 1.

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 owned by the web server. RequestHandler 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.

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 = 50
MAX_HEADER_SIZE = 128 * 1024
NINJA_PATCHING_LOCK = Mutex.new
PASSENGER_VERSION = $1
Attributes
[R] socket_name The name of the socket on which the request handler accepts new connections. This is either a Unix socket filename, or the name for an abstract namespace Unix socket.

If socket_name refers to an abstract namespace Unix socket, then the name does not contain a leading null byte.

See also using_abstract_namespace?

Public Class methods
new(owner_pipe)

Create a new RequestHandler with the given owner pipe. owner_pipe must be the readable part of a pipe IO object.

     # File lib/passenger/request_handler.rb, line 119
119:         def initialize(owner_pipe)
120:                 if ENV['PASSENGER_NO_ABSTRACT_NAMESPACE_SOCKETS'].blank?
121:                         @using_abstract_namespace = create_unix_socket_on_abstract_namespace
122:                 else
123:                         @using_abstract_namespace = false
124:                 end
125:                 if !@using_abstract_namespace
126:                         create_unix_socket_on_filesystem
127:                 end
128:                 @owner_pipe = owner_pipe
129:                 @previous_signal_handlers = {}
130:                 
131:                 NINJA_PATCHING_LOCK.synchronize do
132:                         if !@@ninja_patched_action_controller && defined?(::ActionController::Base) \
133:                         && ::ActionController::Base.private_method_defined?(:perform_action)
134:                                 @@ninja_patched_action_controller = true
135:                                 ::ActionController::Base.class_eval do
136:                                         alias passenger_orig_perform_action perform_action
137:                                         
138:                                         def perform_action(*whatever)
139:                                                 headers["X-Powered-By"] = "Phusion Passenger (mod_rails) #{PASSENGER_VERSION}"
140:                                                 passenger_orig_perform_action(*whatever)
141:                                         end
142:                                 end
143:                         end
144:                 end
145:         end
Public Instance methods
cleanup()

Clean up temporary stuff created by the request handler. This method should be called after the main loop has exited.

     # File lib/passenger/request_handler.rb, line 149
149:         def cleanup
150:                 @socket.close rescue nil
151:                 @owner_pipe.close rescue nil
152:                 if !using_abstract_namespace?
153:                         File.unlink(@socket_name) rescue nil
154:                 end
155:         end
main_loop()

Enter the request handler‘s main loop.

     # File lib/passenger/request_handler.rb, line 163
163:         def main_loop
164:                 reset_signal_handlers
165:                 begin
166:                         done = false
167:                         while !done
168:                                 client = accept_connection
169:                                 if client.nil?
170:                                         break
171:                                 end
172:                                 trap SOFT_TERMINATION_SIGNAL do
173:                                         done = true
174:                                 end
175:                                 process_request(client)
176:                                 trap SOFT_TERMINATION_SIGNAL, DEFAULT
177:                         end
178:                 rescue EOFError
179:                         # Exit main loop.
180:                 rescue Interrupt
181:                         # Exit main loop.
182:                 rescue SignalException => signal
183:                         if signal.message != HARD_TERMINATION_SIGNAL &&
184:                            signal.message != SOFT_TERMINATION_SIGNAL
185:                                 raise
186:                         end
187:                 ensure
188:                         revert_signal_handlers
189:                 end
190:         end
perform_action(*whatever)
     # File lib/passenger/request_handler.rb, line 138
138:                                         def perform_action(*whatever)
139:                                                 headers["X-Powered-By"] = "Phusion Passenger (mod_rails) #{PASSENGER_VERSION}"
140:                                                 passenger_orig_perform_action(*whatever)
141:                                         end
using_abstract_namespace?()

Returns whether socket_name refers to an abstract namespace Unix socket.

     # File lib/passenger/request_handler.rb, line 158
158:         def using_abstract_namespace?
159:                 return @using_abstract_namespace
160:         end