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 26

def initialize(line_reader)
  unless line_reader.respond_to? :each_line
    fail 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

False by default.

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

#throw_on_unrecognized_type ⇒ bool

False by default. Typically for development.

Returns:

  • (bool) —

    whether to throw an exception on message types that aren’t supported



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# File 'lib/nmea_plus.rb', line 23

def throw_on_unrecognized_type
  @throw_on_unrecognized_type
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.

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 81

def each_complete_message
  partials = {}  # hash of message type to message-chain-in-progress
  each_message do |msg|
    slot = msg.data_type   # the slot in the hash

    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 49

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