bitbake: knotty, xmlrpc: add observer-only mode

I add an observer only mode for the knotty UI and
the XMLRPC server that will allow the UI to register
a callback with a server in order to receive events.

The observer-UI is able to send read-only commands to the
server, and also is able to register as an event handler.

Read-only commands are the commands that do not change
the state of the server and have been marked as such in
the command module.

The observer can switch to a full client if it calls addClient
at any time, and the server has no other client running.

(Bitbake rev: 4de9ee21f1fa4d04937cc7430fb1fc8b7a8f61e2)

Signed-off-by: Alexandru DAMIAN <alexandru.damian@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/bin/bitbake

@@ -197,6 +197,9 @@ class BitBakeConfigParameters(cookerdata.ConfigParameters):
         parser.add_option("", "--remote-server", help = "Connect to the specified server",
                    action = "store", dest = "remote_server", default = False)
 
+        parser.add_option("", "--observe-only", help = "Connect to a server as an observing-only client",
+                   action = "store_true", dest = "observe_only", default = False)
+
         options, targets = parser.parse_args(sys.argv)
         return options, targets[1:]
 
@@ -269,6 +272,9 @@ def main():
     if configParams.remote_server and configParams.servertype != "xmlrpc":
         sys.exit("FATAL: If '--remote-server' is defined, we must set the servertype as 'xmlrpc'.\n")
 
+    if configParams.observe_only and (not configParams.remote_server or configParams.bind):
+        sys.exit("FATAL: '--observe-only' can only be used by UI clients connecting to a server.\n")
+
     if "BBDEBUG" in os.environ:
         level = int(os.environ["BBDEBUG"])
         if level > configuration.debug:
@@ -295,7 +301,7 @@ def main():
         server = start_server(servermodule, configParams, configuration)
     else:
         # we start a stub server that is actually a XMLRPClient to
-        server = servermodule.BitBakeXMLRPCClient()
+        server = servermodule.BitBakeXMLRPCClient(configParams.observe_only)
         server.saveConnectionDetails(configParams.remote_server)
 
     logger.removeHandler(handler)