Corrupt USB-packets will now be recognized

Relocated "checking-for-corrupt-packets" to Command class
and enhanced it to all detectable error cases in replies.

source/Command.m

@@ -12,7 +12,8 @@
 % addSystemCommand          Adds a system command to the command object
 % addDirectCommand          Adds a direct command to the command object
 %
-% checkForError @MMI        Checks error byte in received package.            
+% checkForError @MMI        Checks error byte in received package
+% isCorrupt     @MMI        Checks whether reply packet is corrupt
 %
 % clear                     Clears the command msg
 % display                   Displays the command msg (decimal)
@@ -286,12 +287,45 @@ classdef Command < handle
         function cmd = Command(varargin)
             % Command.cmd Create an empty command
             %
-            % c = Command(OPTIONS) is an object that represents an EV3 command
+            % c = Command() is an object that represents an EV3 command
+            % c = Command([...]) is an object that represents an EV3 reply
             %
             % Example::
             %           c = Command();
             
-            cmd.msg = uint8([]);
+            if nargin > 0  % Packet is a reply
+                try
+                    cmd.msg = uint8(varargin{1});
+                catch ME
+                    id = [ID(), ':', 'InvalidParameter'];
+                    msg = 'Failed to create reply-packet with Command-class.';
+                    baseException = MException(id, msg);
+                    baseException = addCause(baseException, ME);
+                    throw(baseException);
+                end
+                
+                % If corrupt, throw error
+                corrupt = cmd.isValidReply();
+                if corrupt < 1
+                    msg = 'Invalid reply packet';
+                    id = [ID(), ':', 'CorruptPacket'];
+                    ME = MException(id, msg);
+                    switch corrupt
+                        case 0
+                            causeMsg = 'Reply packet too short';
+                        case -1
+                            causeMsg = ['Specified packet length (bytes 1&2) does not equal ',...
+                                        'actual packet length'];
+                        case -2
+                            causeMsg = 'Error type (byte 5) is not valid';
+                    end
+                    cause = MException(id, causeMsg);
+                    ME = addCause(ME, cause);
+                    throw(ME);
+                end
+            else  % Packet is a command
+                cmd.msg = uint8([]);
+            end
         end
             
         function delete(cmd)
@@ -322,6 +356,43 @@ classdef Command < handle
             end
         end
         
+        function state = isValidReply(cmd)
+            % Command.isValidReply Check if reply-packet is valid
+            %
+            % state = cmd.isValidReply checks cmd against reply-packet-format and returns
+            %                          whether if cmd is valid (that is, does not fit the 
+            %                          format).
+            % Notes:
+            %  - state = 1, if reply is not corrupted (at least not in a way that can be
+            %               tested)
+            %  - state = 0, if reply is too short (minimum length = 5 bytes)
+            %  - state = -1, if reply is corrupted due to invalid length/length indicator
+            %  - state = -2, if reply is corrupted due to invalid error type byte
+            %  - IMPORTANT: Of course, the packet can still contain invalid information which
+            %               cannot be tested properly without context. This corruption-test
+            %               only checks the contextless information.
+            %               
+            state = 1;
+            
+            % Minimum length of a reply packet is 5, for a packet without response buffer
+            minLength = 5;
+            if length(cmd.msg) < minLength
+                state = 0; 
+                return
+            end
+            
+            % Note: The two things that can be checked without context are the length and the 
+            %       command type, the remainder varies from packet to packet. 
+            pLength = double(typecast(cmd.msg(1:2),'uint16')) + 2;
+            pCmdType = cmd.msg(5);
+            
+            if pLength ~= length(cmd.msg)
+                state = -1;
+            elseif pCmdType ~= 2 && pCmdType ~=4
+                state = -2;
+            end
+        end
+        
         function addHeaderSystem(cmd,counter)
             % Command.addHeaderSystem Add a system header with no reply
             %