Merge pull request #44 from BallAerospace/feature/43-ccsds-log-reader

#43 Add ccsds_log_reader

lib/cosmos/packet_logs.rb

@@ -4,3 +4,4 @@
 require 'cosmos/packet_logs/meta_packet_log_writer'
 require 'cosmos/packet_logs/packet_log_writer_pair'
 require 'cosmos/packet_logs/packet_log_reader'
+require 'cosmos/packet_logs/ccsds_log_reader'

lib/cosmos/packet_logs/ccsds_log_reader.rb

@@ -0,0 +1,103 @@
+# encoding: ascii-8bit
+
+# Copyright 2014 Ball Aerospace & Technologies Corp.
+# All Rights Reserved.
+#
+# This program is free software; you can modify and/or redistribute it
+# under the terms of the GNU General Public License
+# as published by the Free Software Foundation; version 3 with
+# attribution addendums as found in the LICENSE.txt
+
+require 'cosmos/packet_logs/packet_log_reader'
+require 'cosmos/ccsds/ccsds_packet'
+
+module Cosmos
+
+  # Reads a CCSDS packet log of either commands or telemetry.
+  class CcsdsLogReader < PacketLogReader
+
+    # Length of the header on a CCSDS source packet
+    CCSDS_HEADER_LENGTH = 6
+
+    # Create a new log file reader
+    def initialize
+      super()
+      @ccsds_header = CcsdsPacket.new(nil, nil, false)
+    end
+
+    # Read a packet from the log file
+    #
+    # @param identify_and_define (see #each)
+    # @return [Packet]
+    def read(identify_and_define = true)
+      # Read the CCSDS packet header
+      header = @file.read(CCSDS_HEADER_LENGTH)
+      return nil unless header and header.length == CCSDS_HEADER_LENGTH
+      @ccsds_header.buffer = header
+
+      # Extract the length field
+      length = @ccsds_header.read('CcsdsLength') + 1
+
+      # Read the remainder of the packet data
+      data = @file.read(length)
+      return nil unless data and data.length == length
+
+      # Combine into the full packet data
+      packet_data = header << data
+
+      # Determine packet time and set it as received time
+      received_time = determine_received_time(packet_data)
+
+      # Build the actual Packet object
+      if identify_and_define
+        packet = identify_and_define_packet_data(nil, nil, received_time, packet_data)
+      else
+        # Build Packet
+        packet = Packet.new(nil, nil, :BIG_ENDIAN, nil, packet_data)
+        packet.set_received_time_fast(received_time)
+      end
+
+      # Return the packet
+      packet
+    rescue => err
+      close()
+      raise err
+    end
+
+    protected
+
+    # TODO : Add code here or in subclass to derive received time from the packet timestamp
+    # CCSDS timestamp formats and even the presence of a timestamp vary
+    def determine_received_time(packet_data)
+      nil
+    end
+
+    def read_file_header
+      # Read the first CCSDS packet header
+      header = @file.read(CCSDS_HEADER_LENGTH)
+
+      if header and header.length == CCSDS_HEADER_LENGTH
+        @ccsds_header.buffer = header
+        packet_type = @ccsds_header.read('CcsdsType')
+        if packet_type == CcsdsPacket::TELEMETRY
+          @log_type = :TLM
+        else
+          @log_type = :CMD
+        end
+        @configuration_name = nil
+        @hostname = nil
+        @file_header_length = 0
+        @file.seek(0, IO::SEEK_SET)
+        System.load_configuration(nil)
+      else
+        raise "Failed to read at least #{CCSDS_HEADER_LENGTH} bytes from packet log"
+      end
+    end
+
+    def seek_to_time(time)
+      # Not supported
+    end
+
+  end # class CcsdsLogReader
+
+end # module Cosmos