Method: OpenC3::LengthProtocol#initialize

Defined in:
lib/openc3/interfaces/protocols/length_protocol.rb

#initialize(length_bit_offset = 0, length_bit_size = 16, length_value_offset = 0, length_bytes_per_count = 1, length_endianness = 'BIG_ENDIAN', discard_leading_bytes = 0, sync_pattern = nil, max_length = nil, fill_length_and_sync_pattern = false, allow_empty_data = nil) ⇒ LengthProtocol

Returns a new instance of LengthProtocol.

Parameters:

  • length_bit_offset (Integer) (defaults to: 0) —

    The bit offset of the length field

  • length_bit_size (Integer) (defaults to: 16) —

    The size in bits of the length field

  • length_value_offset (Integer) (defaults to: 0) —

    The offset to apply to the length value once it has been read from the packet. The value in the length field itself plus the length value offset MUST equal the total bytes including any discarded bytes. For example: if your length field really means "length - 1" this value should be 1.

  • length_bytes_per_count (Integer) (defaults to: 1) —

    The number of bytes per each length field 'count'. This is used if the units of the length field is something other than bytes, for example words.

  • length_endianness (String) (defaults to: 'BIG_ENDIAN') —

    The endianness of the length field. Must be either BIG_ENDIAN or LITTLE_ENDIAN.

  • max_length (Integer) (defaults to: nil) —

    The maximum allowed value of the length field

  • fill_length_and_sync_pattern (Boolean) (defaults to: false) —

    Fill the length field and sync pattern when writing packets

  • allow_empty_data (true/false/nil) (defaults to: nil) —

    See Protocol#initialize

  • discard_leading_bytes (Integer) (defaults to: 0) —

    The number of bytes to discard from the binary data after reading. Note that this is often used to remove a sync pattern from the final packet data.

  • sync_pattern (String) (defaults to: nil) —

    String representing a hex number ("0x1234") that will be searched for in the raw data. Bytes encountered before this pattern is found are discarded.



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# File 'lib/openc3/interfaces/protocols/length_protocol.rb', line 49

def initialize(
  length_bit_offset = 0,
  length_bit_size = 16,
  length_value_offset = 0,
  length_bytes_per_count = 1,
  length_endianness = 'BIG_ENDIAN',
  discard_leading_bytes = 0,
  sync_pattern = nil,
  max_length = nil,
  fill_length_and_sync_pattern = false,
  allow_empty_data = nil
)
  super(discard_leading_bytes, sync_pattern, fill_length_and_sync_pattern, allow_empty_data)

  # Save length field attributes
  @length_bit_offset = Integer(length_bit_offset)
  @length_bit_size = Integer(length_bit_size)
  @length_value_offset = Integer(length_value_offset)
  @length_bytes_per_count = Integer(length_bytes_per_count)

  # Save endianness
  if length_endianness.to_s.upcase == 'LITTLE_ENDIAN'
    @length_endianness = :LITTLE_ENDIAN
  else
    @length_endianness = :BIG_ENDIAN
  end

  # Derive number of bytes required to contain entire length field
  if @length_endianness == :BIG_ENDIAN or ((@length_bit_offset % 8) == 0)
    length_bits_needed = @length_bit_offset + @length_bit_size
    length_bits_needed += 8 if (length_bits_needed % 8) != 0
    @length_bytes_needed = ((length_bits_needed - 1) / 8) + 1
  else
    @length_bytes_needed = (length_bit_offset / 8) + 1
  end

  # Save max length setting
  @max_length = ConfigParser.handle_nil(max_length)
  @max_length = Integer(@max_length) if @max_length
end