MAVExplorer: Add logmessage download/help commands

Download LogMessage XML to .mavproxy/LogMessages folder
Use DFMetaData class to print logmessage help

MAVProxy/tools/MAVExplorer.py

@@ -128,6 +128,7 @@ def __init__(self):
             "dump"      : ['(MESSAGETYPE)'],
             "map"       : ['(VARIABLE) (VARIABLE) (VARIABLE) (VARIABLE) (VARIABLE)'],
             "param"     : ['download', 'check', 'help (PARAMETER)'],
+            "logmessage": ['download', 'help (MESSAGETYPE)'],
             }
         self.aliases = {}
         self.graphs = []
@@ -332,16 +333,23 @@ def load_graphs():
     mestate.graphs = []
     gfiles = ['mavgraphs.xml']
     for dirname, dirnames, filenames in os.walk(mp_util.dot_mavproxy()):
+        # Skip XML files in the LogMessages subfolder
+        if os.path.basename(dirname) == "LogMessages":
+            continue
         for filename in filenames:
             if filename.lower().endswith('.xml'):
                 gfiles.append(os.path.join(dirname, filename))
 
+    # list of parameter files to be skipped when loading graph XML
+    paramfiles = ["ArduSub.xml", "ArduPlane.xml", "APMrover2.xml", "ArduCopter.xml", "AntennaTracker.xml", "Blimp.xml", "Rover.xml"]
+    # loop though files
     for file in gfiles:
         if not os.path.exists(file):
             continue
         # skip parameter files.  They specify an encoding, and under
         # Python3 this leads to a warning from etree
-        if os.path.basename(file) in ["ArduSub.xml", "ArduPlane.xml", "APMrover2.xml", "ArduCopter.xml", "AntennaTracker.xml", "Blimp.xml", "Rover.xml"]:
+        basename = os.path.basename(file)
+        if (basename in paramfiles):
             continue
         graphs = load_graph_xml(open(file).read(), file)
         if graphs:
@@ -1176,6 +1184,38 @@ def cmd_paramchange(args):
         vmap[pname] = pvalue
     mestate.mlog.rewind()
 
+def cmd_logmessage(args):
+    '''show log message information'''
+    mlog = mestate.mlog
+    usage = "Usage: logmessage <help|download>"
+    if len(args) > 0:
+        if args[0] == 'help':
+            if len(args) < 2:
+                print(usage)
+                return
+            if hasattr(mlog,'metadata'):
+                mlog.metadata.print_help(args[1])
+            return
+        if args[0] == 'download':
+            # download XML files for log messages
+            folder = mp_util.dot_mavproxy("LogMessages")
+            mp_util.mkdir_p(folder)
+            files = []
+            for vehicle in ['Rover', 'Copter', 'Plane', 'Tracker', 'Blimp', 'Sub']:
+                url = 'http://autotest.ardupilot.org/LogMessages/%s/LogMessages.xml.gz' % vehicle
+                path = os.path.join(folder,"%s.xml" % vehicle)
+                files.append((url, path))
+            try:
+                child = multiproc.Process(target=mp_util.download_files, args=(files,))
+                child.start()
+            except Exception as e:
+                print(e)
+            if hasattr(mlog,'metadata'):
+                mlog.metadata.reset()
+            return
+    # Print usage if we've dropped through the ifs
+    print(usage)
+
 def cmd_mission(args):
     '''show mission'''
     if (len(args) == 1):
@@ -1463,6 +1503,7 @@ def main_loop():
     'dump'       : (cmd_dump,      'dump messages from log'),
     'file'       : (cmd_file,      'show files'),
     'mission'    : (cmd_mission,   'show mission'),
+    'logmessage' : (cmd_logmessage, 'show log message information'),
     }
 
 def progress_bar(pct):