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.

Abstract namespace Unix sockets

AbstractRequestHandler listens on a Unix socket for incoming requests. If possible, AbstractRequestHandler 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, AbstractRequestHandler will automatically fallback to using regular Unix socket files.

It is possible to force AbstractRequestHandler 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. 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.

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
PASSENGER_VERSION = determine_passenger_version
PASSENGER_HEADER = determine_passenger_header
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/abstract_request_handler.rb, line 119
119:         def initialize(owner_pipe)
120:                 if abstract_namespace_sockets_allowed?
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:         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/abstract_request_handler.rb, line 134
134:         def cleanup
135:                 @socket.close rescue nil
136:                 @owner_pipe.close rescue nil
137:                 if !using_abstract_namespace?
138:                         File.unlink(@socket_name) rescue nil
139:                 end
140:         end
main_loop()

Enter the request handler‘s main loop.

     # File lib/passenger/abstract_request_handler.rb, line 148
148:         def main_loop
149:                 reset_signal_handlers
150:                 begin
151:                         done = false
152:                         while !done
153:                                 client = accept_connection
154:                                 if client.nil?
155:                                         break
156:                                 end
157:                                 trap SOFT_TERMINATION_SIGNAL do
158:                                         done = true
159:                                 end
160:                                 begin
161:                                         headers, input = parse_request(client)
162:                                         if headers
163:                                                 process_request(headers, input, client)
164:                                         end
165:                                 rescue IOError, SocketError, SystemCallError => e
166:                                         print_exception("Passenger RequestHandler", e)
167:                                 ensure
168:                                         client.close rescue nil
169:                                 end
170:                                 trap SOFT_TERMINATION_SIGNAL, DEFAULT
171:                         end
172:                 rescue EOFError
173:                         # Exit main loop.
174:                 rescue Interrupt
175:                         # Exit main loop.
176:                 rescue SignalException => signal
177:                         if signal.message != HARD_TERMINATION_SIGNAL &&
178:                            signal.message != SOFT_TERMINATION_SIGNAL
179:                                 raise
180:                         end
181:                 ensure
182:                         revert_signal_handlers
183:                 end
184:         end
using_abstract_namespace?()

Returns whether socket_name refers to an abstract namespace Unix socket.

     # File lib/passenger/abstract_request_handler.rb, line 143
143:         def using_abstract_namespace?
144:                 return @using_abstract_namespace
145:         end