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.
| [RW] | io | The wrapped IO object. |
Create a new MessageChannel by wrapping the given IO object.
[ show source ]
# File lib/phusion_passenger/message_channel.rb, line 88
88: def initialize(io = nil)
89: @io = io
90: # Make it binary just in case.
91: @io.binmode if @io
92: end
Close the underlying IO stream. Might raise SystemCallError or IOError when something goes wrong.
[ show source ]
# File lib/phusion_passenger/message_channel.rb, line 360
360: def close
361: @io.close
362: end
Checks whether the underlying IO stream is closed.
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# File lib/phusion_passenger/message_channel.rb, line 365
365: def closed?
366: return @io.closed?
367: end
Return the file descriptor of the underlying IO object.
[ show source ]
# File lib/phusion_passenger/message_channel.rb, line 354
354: def fileno
355: return @io.fileno
356: end
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.
[ show source ]
# File lib/phusion_passenger/message_channel.rb, line 100
100: def read
101: buffer = new_buffer
102: if !@io.read(HEADER_SIZE, buffer)
103: return nil
104: end
105: while buffer.size < HEADER_SIZE
106: tmp = @io.read(HEADER_SIZE - buffer.size)
107: if tmp.empty?
108: return nil
109: else
110: buffer << tmp
111: end
112: end
113:
114: chunk_size = buffer.unpack(UINT16_PACK_FORMAT)[0]
115: if !@io.read(chunk_size, buffer)
116: return nil
117: end
118: while buffer.size < chunk_size
119: tmp = @io.read(chunk_size - buffer.size)
120: if tmp.empty?
121: return nil
122: else
123: buffer << tmp
124: end
125: end
126:
127: message = []
128: offset = 0
129: delimiter_pos = buffer.index(DELIMITER, offset)
130: while !delimiter_pos.nil?
131: if delimiter_pos == 0
132: message << ""
133: else
134: message << buffer[offset .. delimiter_pos - 1]
135: end
136: offset = delimiter_pos + 1
137: delimiter_pos = buffer.index(DELIMITER, offset)
138: end
139: return message
140: rescue Errno::ECONNRESET
141: return nil
142: end
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.
[ show source ]
# File lib/phusion_passenger/message_channel.rb, line 151
151: def read_hash
152: buffer = new_buffer
153: if !@io.read(HEADER_SIZE, buffer)
154: return nil
155: end
156: while buffer.size < HEADER_SIZE
157: tmp = @io.read(HEADER_SIZE - buffer.size)
158: if tmp.empty?
159: return nil
160: else
161: buffer << tmp
162: end
163: end
164:
165: chunk_size = buffer.unpack(UINT16_PACK_FORMAT)[0]
166: if !@io.read(chunk_size, buffer)
167: return nil
168: end
169: while buffer.size < chunk_size
170: tmp = @io.read(chunk_size - buffer.size)
171: if tmp.empty?
172: return nil
173: else
174: buffer << tmp
175: end
176: end
177:
178: result = {}
179: offset = 0
180: delimiter_pos = buffer.index(DELIMITER, offset)
181: while !delimiter_pos.nil?
182: if delimiter_pos == 0
183: name = ""
184: else
185: name = buffer[offset .. delimiter_pos - 1]
186: end
187:
188: offset = delimiter_pos + 1
189: delimiter_pos = buffer.index(DELIMITER, offset)
190: if delimiter_pos.nil?
191: raise InvalidHashError
192: elsif delimiter_pos == 0
193: value = ""
194: else
195: value = buffer[offset .. delimiter_pos - 1]
196: end
197:
198: result[name] = value
199: offset = delimiter_pos + 1
200: delimiter_pos = buffer.index(DELIMITER, offset)
201: end
202: return result
203: rescue Errno::ECONNRESET
204: return nil
205: end
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.
[ show source ]
# File lib/phusion_passenger/message_channel.rb, line 220
220: def read_scalar(buffer = new_buffer, max_size = nil)
221: if !@io.read(4, buffer)
222: return nil
223: end
224: while buffer.size < 4
225: tmp = @io.read(4 - buffer.size)
226: if tmp.empty?
227: return nil
228: else
229: buffer << tmp
230: end
231: end
232:
233: size = buffer.unpack(UINT32_PACK_FORMAT)[0]
234: if size == 0
235: buffer.replace('')
236: return buffer
237: else
238: if !max_size.nil? && size > max_size
239: raise SecurityError, "Scalar message size (#{size}) " <<
240: "exceeds maximum allowed size (#{max_size})."
241: end
242: if !@io.read(size, buffer)
243: return nil
244: end
245: if buffer.size < size
246: tmp = ''
247: while buffer.size < size
248: if !@io.read(size - buffer.size, tmp)
249: return nil
250: else
251: buffer << tmp
252: end
253: end
254: end
255: return buffer
256: end
257: rescue Errno::ECONNRESET
258: return nil
259: end
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.
[ show source ]
# File lib/phusion_passenger/message_channel.rb, line 297
297: def recv_io(klass = IO, negotiate = true)
298: write("pass IO") if negotiate
299: io = @io.recv_io(klass)
300: write("got IO") if negotiate
301: return io
302: end
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.
[ show source ]
# File lib/phusion_passenger/message_channel.rb, line 310
310: def send_io(io)
311: # We read a message before actually calling #send_io
312: # in order to prevent the other side from accidentally
313: # read()ing past the normal data and reading our file
314: # descriptor too.
315: #
316: # For example suppose that side A looks like this:
317: #
318: # read(fd, buf, 1024)
319: # read_io(fd)
320: #
321: # and side B:
322: #
323: # write(fd, buf, 100)
324: # send_io(fd_to_pass)
325: #
326: # If B completes both write() and send_io(), then A's read() call
327: # reads past the 100 bytes that B sent. On some platforms, like
328: # Linux, this will cause read_io() to fail. And it just so happens
329: # that Ruby's IO#read method slurps more than just the given amount
330: # of bytes.
331: result = read
332: if !result
333: raise EOFError, "End of stream"
334: elsif result != ["pass IO"]
335: raise IOError, "IO passing pre-negotiation header expected"
336: else
337: @io.send_io(io)
338: # Once you've sent the IO you expect to be able to close it on the
339: # sender's side, even if the other side hasn't read the IO yet.
340: # Not so: on some operating systems (I'm looking at you OS X) this
341: # can cause the receiving side to receive a bad file descriptor.
342: # The post negotiation protocol ensures that we block until the
343: # other side has really received the IO.
344: result = read
345: if !result
346: raise EOFError, "End of stream"
347: elsif result != ["got IO"]
348: raise IOError, "IO passing post-negotiation header expected"
349: end
350: end
351: end
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.
[ show source ]
# File lib/phusion_passenger/message_channel.rb, line 268
268: def write(name, *args)
269: check_argument(name)
270: args.each do |arg|
271: check_argument(arg)
272: end
273:
274: message = "#{name}#{DELIMITER}"
275: args.each do |arg|
276: message << arg.to_s << DELIMITER
277: end
278: @io.write([message.size].pack('n') << message)
279: @io.flush
280: end
Send a scalar message over the underlying IO object.
Might raise SystemCallError, IOError or SocketError when something goes wrong.
[ show source ]
# File lib/phusion_passenger/message_channel.rb, line 286
286: def write_scalar(data)
287: @io.write([data.size].pack('N') << data)
288: @io.flush
289: end