[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.

Closes: #427

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_daemon_version(self):
+        username, password = get_localhost_auth()
+        yield client.connect(
+            'localhost', self.listen_port, username=username, password=password
+        )
+
+        assert client.daemon_version == get_version()
+
+    @pytest_twisted.inlineCallbacks
+    def test_daemon_version_check_min(self):
+        username, password = get_localhost_auth()
+        yield client.connect(
+            'localhost', self.listen_port, username=username, password=password
+        )
+
+        assert client.daemon_version_check_min(get_version())
+        assert not client.daemon_version_check_min(f'{get_version()}1')
+        assert client.daemon_version_check_min('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_version = 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_version = None
         self.authentication_level = 0
 
         self.connected = False
@@ -389,7 +391,7 @@ def __on_connect(self, result):
         log.debug('__on_connect called')
 
         def on_info(daemon_info):
-            self.daemon_info = daemon_info
+            self.daemon_version = daemon_info
             log.debug('Got info from daemon: %s', daemon_info)
             self.daemon_info_deferred.callback(daemon_info)
 
@@ -741,6 +743,26 @@ def connection_info(self):
 
         return None
 
+    @property
+    def daemon_version(self) -> str:
+        """Get the connected daemon version
+
+        Returns:
+            The daemon version
+        """
+        return self._daemon_proxy.daemon_version if self.connected() else ''
+
+    def daemon_version_check_min(self, min_version=get_version()) -> bool:
+        """Check connected daemon against a minimum version.
+
+        Returns:
+            If connected daemon meets minimum version requirement.
+        """
+        if not (self.daemon_version and min_version):
+            return False
+
+        return VersionSplit(self.daemon_version) >= VersionSplit(min_version)
+
     def register_event_handler(self, event, handler):
         """
         Registers a handler that will be called when an event is received from the daemon.