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

Defined Under Namespace

Classes: Connack, Connect, Disconnect, Pingreq, Pingresp, Puback, Pubcomp, Publish, Pubrec, Pubrel, Suback, Subscribe, Unsuback, Unsubscribe

Constant Summary collapse

ATTR_DEFAULTS =

Default attribute values

{
  :version => '3.1.0',
  :id => 0,
  :body_length => nil
}

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(args = {}) ⇒ Packet

Create a new empty packet



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# File 'lib/mqtt/packet.rb', line 119

def initialize(args = {})
  # We must set flags before the other values
  @flags = [false, false, false, false]
  update_attributes(ATTR_DEFAULTS.merge(args))
end

Instance Attribute Details

#body_length ⇒ Object

The length of the parsed packet body



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# File 'lib/mqtt/packet.rb', line 17

def body_length
  @body_length
end

#flags ⇒ Object

Array of 4 bits in the fixed header



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# File 'lib/mqtt/packet.rb', line 14

def flags
  @flags
end

#id ⇒ Object

Identifier to link related control packets together



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# File 'lib/mqtt/packet.rb', line 11

def id
  @id
end

#version ⇒ Object

The version number of the MQTT protocol to use (default 3.1.0)



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

def version
  @version
end

Class Method Details

.create_from_header(byte) ⇒ Object

Create a new packet object from the first byte of a MQTT packet



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# File 'lib/mqtt/packet.rb', line 103

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

  # Convert the last 4 bits of byte into array of true/false
  flags = (0..3).map { |i| byte & (2**i) != 0 }

  # Create a new packet object
  packet_class.new(:flags => flags)
end

.parse(buffer) ⇒ Object

Parse buffer into new packet object



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# File 'lib/mqtt/packet.rb', line 57

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

.parse_header(buffer) ⇒ Object

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 65

def self.parse_header(buffer)
  # Check that the packet is a long as the minimum packet size
  if buffer.bytesize < 2
    raise ProtocolException, 'Invalid packet: less than 2 bytes long'
  end

  # Create a new packet object
  bytes = buffer.unpack('C5')
  packet = create_from_header(bytes.first)
  packet.validate_flags

  # Parse the packet length
  body_length = 0
  multiplier = 1
  pos = 1

  loop do
    if buffer.bytesize <= pos
      raise ProtocolException, 'The packet length header is incomplete'
    end

    digit = bytes[pos]
    body_length += ((digit & 0x7F) * multiplier)
    multiplier *= 0x80
    pos += 1
    break if (digit & 0x80).zero? || pos > 4
  end

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

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

  packet
end

.read(socket) ⇒ Object

Read in a packet from a socket



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# File 'lib/mqtt/packet.rb', line 27

def self.read(socket)
  # Read in the packet header and create a new packet object
  packet = create_from_header(
    read_byte(socket)
  )
  packet.validate_flags

  # Read in the packet length
  multiplier = 1
  body_length = 0
  pos = 1

  loop do
    digit = read_byte(socket)
    body_length += ((digit & 0x7F) * multiplier)
    multiplier *= 0x80
    pos += 1
    break if (digit & 0x80).zero? || pos > 4
  end

  # 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))

  packet
end

.read_byte(socket) ⇒ Object

Read and unpack a single byte from a socket

Raises:



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# File 'lib/mqtt/packet.rb', line 221

def self.read_byte(socket)
  byte = socket.getbyte
  raise ProtocolException, 'Failed to read byte from socket' if byte.nil?

  byte
end

Instance Method Details

#encode_body ⇒ Object

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



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# File 'lib/mqtt/packet.rb', line 169

def encode_body
  '' # No body by default
end

#inspect ⇒ Object

Returns a human readable string



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# File 'lib/mqtt/packet.rb', line 216

def inspect
  "\#<#{self.class}>"
end

#message_id ⇒ Object

Deprecated.

Please use #id instead



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# File 'lib/mqtt/packet.rb', line 1020

def message_id
  id
end

#message_id=(args) ⇒ Object

Deprecated.

Please use #id= instead



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# File 'lib/mqtt/packet.rb', line 1025

def message_id=(args)
  self.id = args
end

#parse_body(buffer) ⇒ Object

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

Raises:



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# File 'lib/mqtt/packet.rb', line 162

def parse_body(buffer)
  return if buffer.bytesize == body_length

  raise ProtocolException, "Failed to parse packet - input buffer (#{buffer.bytesize}) is not the same as the body length header (#{body_length})"
end

#to_s ⇒ Object

Serialise the packet



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# File 'lib/mqtt/packet.rb', line 174

def to_s
  # Encode the fixed header
  header = [
    ((type_id.to_i & 0x0F) << 4) |
      (flags[3] ? 0x8 : 0x0) |
      (flags[2] ? 0x4 : 0x0) |
      (flags[1] ? 0x2 : 0x0) |
      (flags[0] ? 0x1 : 0x0)
  ]

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

  # Check that that packet isn't too big
  body_length = body.bytesize
  if body_length > 268_435_455
    raise 'Error serialising packet: body is more than 256MB'
  end

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

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

#type_id ⇒ Object

Get the identifer for this packet type



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# File 'lib/mqtt/packet.rb', line 137

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

#type_name ⇒ Object

Get the name of the packet type as a string in capitals (like the MQTT specification uses)

Example: CONNACK



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# File 'lib/mqtt/packet.rb', line 147

def type_name
  self.class.name.split('::').last.upcase
end

#update_attributes(attr = {}) ⇒ Object

Set packet attributes from a hash of attribute names and values



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# File 'lib/mqtt/packet.rb', line 126

def update_attributes(attr = {})
  attr.each_pair do |k, v|
    if v.is_a?(Array) || v.is_a?(Hash)
      send("#{k}=", v.dup)
    else
      send("#{k}=", v)
    end
  end
end

#validate_flags ⇒ Object

Check that fixed header flags are valid for types that don’t use the flags

Raises:



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# File 'lib/mqtt/packet.rb', line 209

def validate_flags
  return if flags == [false, false, false, false]

  raise ProtocolException, "Invalid flags in #{type_name} packet header"
end