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:
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.
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.
Create a new MessageChannel by wrapping the given IO object.
# File lib/phusion_passenger/message_channel.rb, line 87 def initialize(io = nil) @io = io # Make it binary just in case. @io.binmode if @io end
Close the underlying IO stream. Might raise SystemCallError or IOError when something goes wrong.
# File lib/phusion_passenger/message_channel.rb, line 359 def close @io.close end
Checks whether the underlying IO stream is closed.
# File lib/phusion_passenger/message_channel.rb, line 364 def closed? return @io.closed? end
Return the file descriptor of the underlying IO object.
# File lib/phusion_passenger/message_channel.rb, line 353 def fileno return @io.fileno 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.
# File lib/phusion_passenger/message_channel.rb, line 99 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 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.
# File lib/phusion_passenger/message_channel.rb, line 150 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 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.
# File lib/phusion_passenger/message_channel.rb, line 219 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
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.
# File lib/phusion_passenger/message_channel.rb, line 296 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 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.
# File lib/phusion_passenger/message_channel.rb, line 309 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
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.
# File lib/phusion_passenger/message_channel.rb, line 267 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
Send a scalar message over the underlying IO object.
Might raise SystemCallError, IOError or SocketError when something goes wrong.
# File lib/phusion_passenger/message_channel.rb, line 285 def write_scalar(data) @io.write([data.size].pack('N') << data) @io.flush end
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