[UI][Common] Add daemon version check

For new UI features to be added, one should make sure the backend daemon
is supported and add fallback in case it doesn't.
Here we add the ability to get the daemon version from the `Client`
class and also check the version against a desired version.

deluge/tests/test_client.py

@@ -8,7 +8,7 @@
 from twisted.internet import defer
 
 from deluge import error
-from deluge.common import AUTH_LEVEL_NORMAL, get_localhost_auth
+from deluge.common import AUTH_LEVEL_NORMAL, get_localhost_auth, get_version
 from deluge.core.authmanager import AUTH_LEVEL_ADMIN
 from deluge.ui.client import Client, DaemonSSLProxy, client
 
@@ -170,3 +170,23 @@ def on_failure(failure):
 
         d.addCallbacks(self.fail, on_failure)
         return d
+
+    @pytest_twisted.inlineCallbacks
+    def test_connection_version(self):
+        username, password = get_localhost_auth()
+        yield client.connect(
+            'localhost', self.listen_port, username=username, password=password
+        )
+
+        assert client.connection_version() == get_version()
+
+    @pytest_twisted.inlineCallbacks
+    def test_daemon_version_above(self):
+        username, password = get_localhost_auth()
+        yield client.connect(
+            'localhost', self.listen_port, username=username, password=password
+        )
+
+        assert client.is_daemon_version_equal_or_greater(get_version())
+        assert not client.is_daemon_version_equal_or_greater(f'{get_version()}1')
+        assert client.is_daemon_version_equal_or_greater('0.1.0')

deluge/ui/client.py

@@ -15,7 +15,7 @@
 from twisted.internet.protocol import ClientFactory
 
 from deluge import error
-from deluge.common import get_localhost_auth, get_version
+from deluge.common import VersionSplit, get_localhost_auth, get_version
 from deluge.decorators import deprecated
 from deluge.transfer import DelugeTransferProtocol
 
@@ -227,6 +227,7 @@ def clientConnectionLost(self, connector, reason):  # NOQA: N802
         self.daemon.host = None
         self.daemon.port = None
         self.daemon.username = None
+        self.daemon.daemon_info = None
         self.daemon.connected = False
 
         if (
@@ -260,6 +261,7 @@ def __init__(self, event_handlers=None):
         self.host = None
         self.port = None
         self.username = None
+        self.daemon_info = None
         self.authentication_level = 0
 
         self.connected = False
@@ -741,6 +743,25 @@ def connection_info(self):
 
         return None
 
+    def connection_version(self):
+        """
+        Get the connected daemon version
+
+        Returns:
+            str: the daemon version
+        """
+        if self.connected():
+            return self._daemon_proxy.daemon_info
+
+        return ''
+
+    def is_daemon_version_equal_or_greater(self, version_check):
+        if VersionSplit(version_check) and self.connected():
+            daemon_version = self.connection_version()
+            return VersionSplit(daemon_version) >= VersionSplit(version_check)
+
+        return False
+
     def register_event_handler(self, event, handler):
         """
         Registers a handler that will be called when an event is received from the daemon.