Class
PhusionPassenger::MessageChannel

In: | lib/phusion_passenger/message_channel.rb
Parent: | Object

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.

Methods

- close
- fileno
- new
- read
- read_scalar
- recv_io
- send_io
- write
- write_scalar

Attributes

[R] | io | The wrapped IO object.

Public Class methods
new(io)

Create a new MessageChannel by wrapping the given IO object.

[ show source ]

        # File lib/phusion_passenger/message_channel.rb, line 77
    77:         def initialize(io)
    78:                 @io = io
    79:         end

Public Instance methods
close()

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

[ show source ]

         # File lib/phusion_passenger/message_channel.rb, line 211
    211:         def close
    212:                 @io.close
    213:         end

fileno()

Return the file descriptor of the underlying IO object.

[ show source ]

         # File lib/phusion_passenger/message_channel.rb, line 205
    205:         def fileno
    206:                 return @io.fileno
    207:         end

read()

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 87
     87:         def read
     88:                 buffer = ''
     89:                 while buffer.size < HEADER_SIZE
     90:                         buffer << @io.readpartial(HEADER_SIZE - buffer.size)
     91:                 end
     92:
     93:                 chunk_size = buffer.unpack('n')[0]
     94:                 buffer = ''
     95:                 while buffer.size < chunk_size
     96:                         buffer << @io.readpartial(chunk_size - buffer.size)
     97:                 end
     98:
     99:                 message = []
    100:                 offset = 0
    101:                 delimiter_pos = buffer.index(DELIMITER, offset)
    102:                 while !delimiter_pos.nil?
    103:                         if delimiter_pos == 0
    104:                                 message << ""
    105:                         else
    106:                                 message << buffer[offset .. delimiter_pos - 1]
    107:                         end
    108:                         offset = delimiter_pos + 1
    109:                         delimiter_pos = buffer.index(DELIMITER, offset)
    110:                 end
    111:                 return message
    112:         rescue Errno::ECONNRESET
    113:                 return nil
    114:         rescue EOFError
    115:                 return nil
    116:         end

read_scalar(max_size = nil)

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 `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 127
    127:         def read_scalar(max_size = nil)
    128:                 buffer = ''
    129:                 temp = ''
    130:                 while buffer.size < 4
    131:                         buffer << @io.readpartial(4 - buffer.size, temp)
    132:                 end
    133:                 size = buffer.unpack('N')[0]
    134:                 if size == 0
    135:                         return ''
    136:                 else
    137:                         if !max_size.nil? && size > max_size
    138:                                 raise SecurityError, "Scalar message size (#{size}) " <<
    139:                                         "exceeds maximum allowed size (#{max_size})."
    140:                         end
    141:                         buffer = ''
    142:                         while buffer.size < size
    143:                                 temp = '' # JRuby doesn't clear the buffer. TODO: remove this when JRuby has been fixed.
    144:                                 buffer << @io.readpartial(size - buffer.size, temp)
    145:                         end
    146:                         return buffer
    147:                 end
    148:         rescue Errno::ECONNRESET
    149:                 return nil
    150:         rescue EOFError
    151:                 return nil
    152:         end

recv_io()

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 190
    190:         def recv_io
    191:                 return @io.recv_io
    192:         end

send_io(io)

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 200
    200:         def send_io(io)
    201:                 @io.send_io(io)
    202:         end

write(name, *args)

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 161
    161:         def write(name, *args)
    162:                 check_argument(name)
    163:                 args.each do |arg|
    164:                         check_argument(arg)
    165:                 end
    166:
    167:                 message = "#{name}#{DELIMITER}"
    168:                 args.each do |arg|
    169:                         message << arg.to_s << DELIMITER
    170:                 end
    171:                 @io.write([message.size].pack('n') << message)
    172:                 @io.flush
    173:         end

write_scalar(data)

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 179
    179:         def write_scalar(data)
    180:                 @io.write([data.size].pack('N') << data)
    181:                 @io.flush
    182:         end