Class: MQTT::Packet

Inherits:
Object
  • Object
show all
Defined in:
lib/mqtt/packet.rb

Overview

Class representing a MQTT Packet Performs binary encoding and decoding of headers

Constant Summary

DEFAULTS = 
{
  :duplicate => false,
  :qos => 0,
  :retain => false,
  :body_length => nil
}

Instance Attribute Summary (collapse)

Class Method Summary (collapse)

Instance Method Summary (collapse)

Constructor Details

- (Packet) initialize(args = {})

Create a new empty packet



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# File 'lib/mqtt/packet.rb', line 100

def initialize(args={})
  update_attributes(DEFAULTS.merge(args))
end

Instance Attribute Details

- (Object) body_length

Duplicate delivery flag Retain flag Quality of Service level The length of the parsed packet body



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# File 'lib/mqtt/packet.rb', line 9

def body_length
  @body_length
end

- (Object) duplicate

Returns the value of attribute duplicate



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# File 'lib/mqtt/packet.rb', line 6

def duplicate
  @duplicate
end

- (Object) qos

Returns the value of attribute qos



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# File 'lib/mqtt/packet.rb', line 8

def qos
  @qos
end

- (Object) retain

Returns the value of attribute retain



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# File 'lib/mqtt/packet.rb', line 7

def retain
  @retain
end

Class Method Details

+ (Object) parse(buffer)

Parse buffer into new packet object



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# File 'lib/mqtt/packet.rb', line 52

def self.parse(buffer)
  packet = parse_header(buffer)
  packet.parse_body(buffer)
  return packet
end

+ (Object) parse_header(buffer)

Parse the header and create a new packet object of the correct type The header is removed from the buffer passed into this function



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# File 'lib/mqtt/packet.rb', line 60

def self.parse_header(buffer)
  # Work out the class
  type_id = ((buffer.unpack("C*")[0] & 0xF0) >> 4)
  packet_class = MQTT::PACKET_TYPES[type_id]
  if packet_class.nil?
    raise ProtocolException.new("Invalid packet type identifier: #{type_id}")
  end

  # Create a new packet object
  packet = packet_class.new(
    :duplicate => ((buffer.unpack("C*")[0] & 0x08) >> 3) == 0x01,
    :qos => ((buffer.unpack("C*")[0] & 0x06) >> 1),
    :retain => ((buffer.unpack("C*")[0] & 0x01) >> 0) == 0x01
  )

  # Parse the packet length
  body_length = 0
  multiplier = 1
  pos = 1
  begin
    if buffer.length <= pos
      raise ProtocolException.new("The packet length header is incomplete")
    end
    digit = buffer.unpack("C*")[pos]
    body_length += ((digit & 0x7F) * multiplier)
    multiplier *= 0x80
    pos += 1
  end while ((digit & 0x80) != 0x00) and pos <= 4

  # Store the expected body length in the packet
  packet.instance_variable_set('@body_length', body_length)

  # Delete the variable length header from the raw packet passed in
  buffer.slice!(0...pos)

  return packet
end

+ (Object) read(socket)

Read in a packet from a socket



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# File 'lib/mqtt/packet.rb', line 19

def self.read(socket)
  # Read in the packet header and work out the class
  header = read_byte(socket)
  type_id = ((header & 0xF0) >> 4)
  packet_class = MQTT::PACKET_TYPES[type_id]

  # Create a new packet object
  packet = packet_class.new(
    :duplicate => ((header & 0x08) >> 3),
    :qos => ((header & 0x06) >> 1),
    :retain => ((header & 0x01) >> 0)
  )

  # Read in the packet length
  multiplier = 1
  body_length = 0
  begin
    digit = read_byte(socket)
    body_length += ((digit & 0x7F) * multiplier)
    multiplier *= 0x80
  end while ((digit & 0x80) != 0x00)
  # FIXME: only allow 4 bytes?

  # Store the expected body length in the packet
  packet.instance_variable_set('@body_length', body_length)

  # Read in the packet body
  packet.parse_body( socket.read(body_length) )

  return packet
end

Instance Method Details

- (Object) encode_body

Get serialisation of packet's body (variable header and payload)



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# File 'lib/mqtt/packet.rb', line 157

def encode_body
  '' # No body by default
end

- (Object) parse_body(buffer)

Parse the body (variable header and payload) of a packet



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# File 'lib/mqtt/packet.rb', line 148

def parse_body(buffer)
  if buffer.length != body_length
    raise ProtocolException.new(
      "Failed to parse packet - input buffer (#{buffer.length}) is not the same as the body length buffer (#{body_length})"
    )
  end
end

- (Object) to_s

Serialise the packet



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# File 'lib/mqtt/packet.rb', line 163

def to_s
  # Encode the fixed header
  header = [
    ((type_id.to_i & 0x0F) << 4) |
    ((duplicate ? 0x1 : 0x0) << 3) |
    ((qos.to_i & 0x03) << 1) |
    (retain ? 0x1 : 0x0)
  ]

  # Get the packet's variable header and payload
  body = self.encode_body

  # Build up the body length field bytes
  body_length = body.length
  begin
    digit = (body_length % 128)
    body_length = (body_length / 128)
    # if there are more digits to encode, set the top bit of this digit
    digit |= 0x80 if (body_length > 0)
    header.push(digit)
  end while (body_length > 0)

  # Convert header to binary and add on body
  header.pack('C*') + body
end

- (Object) type_id

Get the identifer for this packet type



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# File 'lib/mqtt/packet.rb', line 111

def type_id
  index = MQTT::PACKET_TYPES.index(self.class)
  if index.nil?
    raise "Invalid packet type: #{self.class}"
  end
  return index
end

- (Object) update_attributes(attr = {}) 



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# File 'lib/mqtt/packet.rb', line 104

def update_attributes(attr={})
  attr.each_pair do |k,v|
    send("#{k}=", v)
  end
end