Class: NMEAPlus::SourceDecoder

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

Overview

The SourceDecoder is meant as the primary entry point into the NMEAPlus module. It wraps a Decoder object and an IO object, converting IO’s #each_line functionality to #each_message and/or #each_complete_message, which yield Message objects representing the parsed data.

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(line_reader) ⇒ SourceDecoder

Returns a new instance of SourceDecoder.

Parameters:

  • line_reader (IO) —

    The source stream for messages



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# File 'lib/nmea_plus.rb', line 22

def initialize(line_reader)
  unless line_reader.respond_to? :each_line
    raise ArgumentError, "line_reader must inherit from type IO (or implement each_line)"
  end
  @throw_on_parse_fail = false
  @source = line_reader
  @decoder = NMEAPlus::Decoder.new
end

Instance Attribute Details

#throw_on_parse_fail ⇒ bool

Whether to raise an exception when lines don’t parse. False by default – ignore such errors.

Returns:

  • (bool) —

    whether to throw an exception on lines that don’t properly parse



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# File 'lib/nmea_plus.rb', line 19

def throw_on_parse_fail
  @throw_on_parse_fail
end

Instance Method Details

#each_complete_message {|NMEAPlus::Message| ... } ⇒ void

This method returns an undefined value.

Attempts to group multipart NMEA messages into chains, and executes the block once for every complete chain. To limit memory use (and be realistic about our ability to match up messages), only 1 message of chain of each NMEA message type can be in progress at any one time.

Examples:

input1 = "!AIVDM,2,1,0,A,58wt8Ui`g??r21`7S=:22058<v05Htp000000015>8OA;0sk,0*7B"
input2 = "!AIVDM,2,2,0,A,eQ8823mDm3kP00000000000,2*5D"
io_source = StringIO.new("#{input1}\n#{input2}")  # source decoder works on any IO object
source_decoder = NMEAPlus::SourceDecoder.new(io_source)
source_decoder.each_complete_message do |message|
  if message.ais && message.ais.message_type == 5
    ais = message.ais  # ais payload shortcut
    puts "Ship with MMSI #{ais.source_mmsi} (#{ais.name.strip}) is going to #{ais.destination.strip}"
    # prints "Ship with MMSI 603916439 (ARCO AVON) is going to HOUSTON"
  end
end

Yields:



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# File 'lib/nmea_plus.rb', line 79

def each_complete_message
  partials = {}  # hash of message type to message-chain-in-progress
  each_message do |msg|
    # don't clutter things up if the message arrives already complete
    if msg.all_messages_received?
      yield msg
      next
    end

    # put message into partials slot (merge if necessary) based on its data type
    slot = msg.data_type
    if partials[slot].nil?                                           # no message in there
      partials[slot] = msg
    elsif 1 != (msg.message_number - partials[slot].message_number)  # broken sequence
      # error! just overwrite what was there
      partials[slot] = msg
    else                                                             # chain on to what's there
      partials[slot].add_message_part(msg)
    end

    # take action if we've completed the chain
    maybe_full = partials[slot]
    if maybe_full.all_messages_received?
      partials[slot] = nil
      yield maybe_full
    end
  end
end

#each_message {|NMEAPlus::Message| ... } ⇒ void

This method returns an undefined value.

Executes the block for every valid NMEA message in the source stream. In practice, you should use #each_complete_message unless you have a very compelling reason not to.

Examples:

input = "$GPGGA,123519,4807.038,N,01131.000,W,1,08,0.9,545.4,M,46.9,M,2.2,123*4b"
io_source = StringIO.new(input)  # source decoder works on any IO object
source_decoder = NMEAPlus::SourceDecoder.new(io_source)
source_decoder.each_message do |message|
  if "GGA" == message.interpreted_data_type
    puts "Latitude: #{message.latitude} / Longitude: #{message.longtitude}"
    # prints "Latitude: 48.1173 / Longitude: -11.516666666666666666"
  end
end

Yields:



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# File 'lib/nmea_plus.rb', line 45

def each_message
  @source.each_line do |line|
    if @throw_on_parse_fail
      yield @decoder.parse(line)
    else
      got_error = false
      begin
        y = @decoder.parse(line)
      rescue
        got_error = true
      end
      yield y unless got_error
    end
  end
end