Class: PhusionPassenger::MessageChannel

Inherits:
Object
  • Object
show all
Defined in:
lib/phusion_passenger/message_channel.rb

Overview

This class provides convenience methods for:

  • sending and receiving raw data over an IO channel.

  • sending and receiving messages over an IO channel.

  • file descriptor (IO object) passing over a Unix socket.

All of these methods use exceptions for error reporting.

There are two kinds of messages:

Array messages

These are just a list of strings, and the message itself has a specific length. The contained strings may not contain NUL characters ('\0'). Note that an array message must have at least one element.

Scalar messages

These are byte strings which may contain arbitrary binary data. Scalar messages also have a specific length.

The protocol is designed to be low overhead, easy to implement and easy to parse.

MessageChannel is to be wrapped around an IO object. For example:

a, b = IO.pipe
channel1 = MessageChannel.new(a)
channel2 = MessageChannel.new(b)

# Send an array message.
channel2.write("hello", "world !!")
channel1.read    # => ["hello", "world !!"]

# Send a scalar message.
channel2.write_scalar("some long string which can contain arbitrary binary data")
channel1.read_scalar

The life time of a MessageChannel is independent from that of the wrapped IO object. If a MessageChannel object is destroyed, the underlying IO object is not automatically closed. Call close() if you want to close the underlying IO object.

Note: Be careful with mixing the sending/receiving of array messages, scalar messages and IO objects. If you send a collection of any of these in a specific order, then the receiving side must receive them in the exact some order. So suppose you first send a message, then an IO object, then a scalar, then the receiving side must first receive a message, then an IO object, then a scalar. If the receiving side does things in the wrong order then bad things will happen.

Defined Under Namespace

Classes: InvalidHashError

Constant Summary collapse

HEADER_SIZE =

:nodoc:

2
DELIMITER =

:nodoc:

"\0"
DELIMITER_NAME =

:nodoc:

"null byte"
UINT16_PACK_FORMAT =

:nodoc:

"n"
UINT32_PACK_FORMAT =

:nodoc:

"N"

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(io = nil) ⇒ MessageChannel

Create a new MessageChannel by wrapping the given IO object.



88
89
90
91
92
 
# File 'lib/phusion_passenger/message_channel.rb', line 88

def initialize(io = nil)
	@io = io
	# Make it binary just in case.
	@io.binmode if @io
end

Instance Attribute Details

#io ⇒ Object

The wrapped IO object.



85
86
87
 
# File 'lib/phusion_passenger/message_channel.rb', line 85

def io
  @io
end

Instance Method Details

#close ⇒ Object

Close the underlying IO stream. Might raise SystemCallError or IOError when something goes wrong.



360
361
362
 
# File 'lib/phusion_passenger/message_channel.rb', line 360

def close
	@io.close
end

#closed? ⇒ Boolean

Checks whether the underlying IO stream is closed.

Returns:

  • (Boolean) 


365
366
367
 
# File 'lib/phusion_passenger/message_channel.rb', line 365

def closed?
	return @io.closed?
end

#fileno ⇒ Object

Return the file descriptor of the underlying IO object.



354
355
356
 
# File 'lib/phusion_passenger/message_channel.rb', line 354

def fileno
	return @io.fileno
end

#read ⇒ Object

Read an array message from the underlying file descriptor. Returns the array message as an array, or nil when end-of-stream has been reached.

Might raise SystemCallError, IOError or SocketError when something goes wrong.



100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
 
# File 'lib/phusion_passenger/message_channel.rb', line 100

def read
	buffer = new_buffer
	if !@io.read(HEADER_SIZE, buffer)
		return nil
	end
	while buffer.size < HEADER_SIZE
		tmp = @io.read(HEADER_SIZE - buffer.size)
		if tmp.empty?
			return nil
		else
			buffer << tmp
		end
	end
	
	chunk_size = buffer.unpack(UINT16_PACK_FORMAT)[0]
	if !@io.read(chunk_size, buffer)
		return nil
	end
	while buffer.size < chunk_size
		tmp = @io.read(chunk_size - buffer.size)
		if tmp.empty?
			return nil
		else
			buffer << tmp
		end
	end
	
	message = []
	offset = 0
	delimiter_pos = buffer.index(DELIMITER, offset)
	while !delimiter_pos.nil?
		if delimiter_pos == 0
			message << ""
		else
			message << buffer[offset .. delimiter_pos - 1]
		end
		offset = delimiter_pos + 1
		delimiter_pos = buffer.index(DELIMITER, offset)
	end
	return message
rescue Errno::ECONNRESET
	return nil
end

#read_hash ⇒ Object

Read an array message from the underlying file descriptor and return the result as a hash instead of an array. This assumes that the array message has an even number of elements. Returns nil when end-of-stream has been reached.

Might raise SystemCallError, IOError or SocketError when something goes wrong.



151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
 
# File 'lib/phusion_passenger/message_channel.rb', line 151

def read_hash
	buffer = new_buffer
	if !@io.read(HEADER_SIZE, buffer)
		return nil
	end
	while buffer.size < HEADER_SIZE
		tmp = @io.read(HEADER_SIZE - buffer.size)
		if tmp.empty?
			return nil
		else
			buffer << tmp
		end
	end
	
	chunk_size = buffer.unpack(UINT16_PACK_FORMAT)[0]
	if !@io.read(chunk_size, buffer)
		return nil
	end
	while buffer.size < chunk_size
		tmp = @io.read(chunk_size - buffer.size)
		if tmp.empty?
			return nil
		else
			buffer << tmp
		end
	end
	
	result = {}
	offset = 0
	delimiter_pos = buffer.index(DELIMITER, offset)
	while !delimiter_pos.nil?
		if delimiter_pos == 0
			name = ""
		else
			name = buffer[offset .. delimiter_pos - 1]
		end
		
		offset = delimiter_pos + 1
		delimiter_pos = buffer.index(DELIMITER, offset)
		if delimiter_pos.nil?
			raise InvalidHashError
		elsif delimiter_pos == 0
			value = ""
		else
			value = buffer[offset .. delimiter_pos - 1]
		end
		
		result[name] = value
		offset = delimiter_pos + 1
		delimiter_pos = buffer.index(DELIMITER, offset)
	end
	return result
rescue Errno::ECONNRESET
	return nil
end

#read_scalar(buffer = new_buffer, max_size = nil) ⇒ Object

Read a scalar message from the underlying IO object. Returns the read message, or nil on end-of-stream.

Might raise SystemCallError, IOError or SocketError when something goes wrong.

The buffer argument specifies a buffer in which #read_scalar stores the read data. It is good practice to reuse existing buffers in order to minimize stress on the garbage collector.

The max_size argument allows one to specify the maximum allowed size for the scalar message. If the received scalar message’s size is larger than max_size, then a SecurityError will be raised.



220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
 
# File 'lib/phusion_passenger/message_channel.rb', line 220

def read_scalar(buffer = new_buffer, max_size = nil)
	if !@io.read(4, buffer)
		return nil
	end
	while buffer.size < 4
		tmp = @io.read(4 - buffer.size)
		if tmp.empty?
			return nil
		else
			buffer << tmp
		end
	end
	
	size = buffer.unpack(UINT32_PACK_FORMAT)[0]
	if size == 0
		buffer.replace('')
		return buffer
	else
		if !max_size.nil? && size > max_size
			raise SecurityError, "Scalar message size (#{size}) " <<
				"exceeds maximum allowed size (#{max_size})."
		end
		if !@io.read(size, buffer)
			return nil
		end
		if buffer.size < size
			tmp = ''
			while buffer.size < size
				if !@io.read(size - buffer.size, tmp)
					return nil
				else
					buffer << tmp
				end
			end
		end
		return buffer
	end
rescue Errno::ECONNRESET
	return nil
end

#recv_io(klass = IO, negotiate = true) ⇒ Object

Receive an IO object (a file descriptor) from the channel. The other side must have sent an IO object by calling send_io(). Note that this only works on Unix sockets.

Might raise SystemCallError, IOError or SocketError when something goes wrong.



297
298
299
300
301
302
 
# File 'lib/phusion_passenger/message_channel.rb', line 297

def recv_io(klass = IO, negotiate = true)
	write("pass IO") if negotiate
	io = @io.recv_io(klass)
	write("got IO") if negotiate
	return io
end

#send_io(io) ⇒ Object

Send an IO object (a file descriptor) over the channel. The other side must receive the IO object by calling recv_io(). Note that this only works on Unix sockets.

Might raise SystemCallError, IOError or SocketError when something goes wrong.



310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
 
# File 'lib/phusion_passenger/message_channel.rb', line 310

def send_io(io)
	# We read a message before actually calling #send_io
	# in order to prevent the other side from accidentally
	# read()ing past the normal data and reading our file
	# descriptor too.
	#
	# For example suppose that side A looks like this:
	#
	#   read(fd, buf, 1024)
	#   read_io(fd)
	#
	# and side B:
	#
	#   write(fd, buf, 100)
	#   send_io(fd_to_pass)
	#
	# If B completes both write() and send_io(), then A's read() call
	# reads past the 100 bytes that B sent. On some platforms, like
	# Linux, this will cause read_io() to fail. And it just so happens
	# that Ruby's IO#read method slurps more than just the given amount
	# of bytes.
	result = read
	if !result
		raise EOFError, "End of stream"
	elsif result != ["pass IO"]
		raise IOError, "IO passing pre-negotiation header expected"
	else
		@io.send_io(io)
		# Once you've sent the IO you expect to be able to close it on the
		# sender's side, even if the other side hasn't read the IO yet.
		# Not so: on some operating systems (I'm looking at you OS X) this
		# can cause the receiving side to receive a bad file descriptor.
		# The post negotiation protocol ensures that we block until the
		# other side has really received the IO.
		result = read
		if !result
			raise EOFError, "End of stream"
		elsif result != ["got IO"]
			raise IOError, "IO passing post-negotiation header expected"
		end
	end
end

#write(name, *args) ⇒ Object

Send an array message, which consists of the given elements, over the underlying file descriptor. name is the first element in the message, and args are the other elements. These arguments will internally be converted to strings by calling to_s().

Might raise SystemCallError, IOError or SocketError when something goes wrong.



268
269
270
271
272
273
274
275
276
277
278
279
280
 
# File 'lib/phusion_passenger/message_channel.rb', line 268

def write(name, *args)
	check_argument(name)
	args.each do |arg|
		check_argument(arg)
	end
	
	message = "#{name}#{DELIMITER}"
	args.each do |arg|
		message << arg.to_s << DELIMITER
	end
	@io.write([message.size].pack('n') << message)
	@io.flush
end

#write_scalar(data) ⇒ Object

Send a scalar message over the underlying IO object.

Might raise SystemCallError, IOError or SocketError when something goes wrong.



286
287
288
289
 
# File 'lib/phusion_passenger/message_channel.rb', line 286

def write_scalar(data)
	@io.write([data.size].pack('N') << data)
	@io.flush
end