[Banner] Added BannerCfg class to hostcfgd to handle Banner messages (#79)

- Why I did it
Added Banner feature related hostcfgd service according to HLD: sonic-net/SONiC#1361

This PR depends on the following PR: sonic-net/sonic-swss-common#826

- How I did it
Added BannerCfg service to hostcfgd. It handles Config DB changes and restart "banner-config" systemd service which will update banners.

- How to verify it
Manual test

Signed-off-by: Yevhen Fastiuk <[email protected]>
Co-authored-by: Yevhen Fastiuk <[email protected]>

Author: SviatoslavBoichuk

scripts/hostcfgd

@@ -1749,6 +1749,84 @@ class SerialConsoleCfg:
         return
 
 
+class BannerCfg(object):
+    """
+    Banner Config Daemon
+    Handles changes in BANNER_MESSAGE table.
+    1) Handle change of feature state
+    2) Handle change of login message
+    3) Handle change of MOTD message
+    4) Handle change of logout message
+    """
+
+    def __init__(self):
+        self.cache = {}
+
+    def load(self, banner_messages_config: dict):
+        """Banner messages configuration
+
+        Force load banner configuration. Login messages should be taken at boot-time by
+        SSH daemon.
+
+        Args:
+            banners_message_config: Configured banner messages.
+        """
+
+        syslog.syslog(syslog.LOG_INFO, 'BannerCfg: load initial')
+
+        if not banner_messages_config:
+            banner_messages_config = {}
+
+        # Force load banner messages.
+        # Login messages show be taken at boot-time by SSH daemon.
+        state_data = banner_messages_config.get("state", {})
+        login_data = banner_messages_config.get("login", {})
+        motd_data = banner_messages_config.get("motd", {})
+        logout_data = banner_messages_config.get("logout", {})
+
+        self.banner_message("state", state_data)
+        self.banner_message("login", login_data)
+        self.banner_message("motd", motd_data)
+        self.banner_message("logout", logout_data)
+
+    def banner_message(self, key, data):
+        """
+        Apply banner message handler.
+
+        Args:
+            cache: Cache to compare/save data.
+            db: DB instance.
+            table: DB table that was changed.
+            key: DB table's key that was triggered change.
+            data: Read table data.
+        """
+        # Handling state, login/logout and MOTD messages. Data should be a dict
+        if type(data) != dict:
+            # Nothing to handle
+            return
+
+        update_required = False
+        # Check with cache
+        for k,v in data.items():
+            if v != self.cache.get(k):
+                update_required = True
+                break
+
+        if update_required == False:
+            return
+
+        try:
+            run_cmd(["systemctl", "restart", "banner-config"], True, True)
+        except Exception:
+            syslog.syslog(syslog.LOG_ERR, 'BannerCfg: Failed to restart '
+                          'banner-config service')
+            return
+
+        # Update cache
+        for k,v in data.items():
+            self.cache[k] = v
+
+
 class HostConfigDaemon:
     def __init__(self):
         self.state_db_conn = DBConnector(STATE_DB, 0)
@@ -1803,6 +1881,9 @@ class HostConfigDaemon:
         # Initialize SerialConsoleCfg
         self.serialconscfg = SerialConsoleCfg()
 
+        # Initialize BannerCfg
+        self.bannermsgcfg = BannerCfg()
+
     def load(self, init_data):
         aaa = init_data['AAA']
         tacacs_global = init_data['TACPLUS']
@@ -1826,6 +1907,7 @@ class HostConfigDaemon:
         ntp_servers = init_data.get(swsscommon.CFG_NTP_SERVER_TABLE_NAME)
         ntp_keys = init_data.get(swsscommon.CFG_NTP_KEY_TABLE_NAME)
         serial_console = init_data.get('SERIAL_CONSOLE', {})
+        banner_messages = init_data.get(swsscommon.CFG_BANNER_MESSAGE_TABLE_NAME)
 
         self.aaacfg.load(aaa, tacacs_global, tacacs_server, radius_global, radius_server, ldap_global, ldap_server)
         self.iptables.load(lpbk_table)
@@ -1839,6 +1921,8 @@ class HostConfigDaemon:
         self.fipscfg.load(fips_cfg)
         self.ntpcfg.load(ntp_global, ntp_servers, ntp_keys)
         self.serialconscfg.load(serial_console)
+        self.bannermsgcfg.load(banner_messages)
+
         self.pamLimitsCfg.update_config_file()
 
         # Update AAA with the hostname
@@ -1992,6 +2076,10 @@ class HostConfigDaemon:
         syslog.syslog(syslog.LOG_INFO, 'SERIAL_CONSOLE table handler...')
         self.serialconscfg.update_serial_console_cfg(key, data)
 
+    def banner_handler(self, key, op, data):
+        syslog.syslog(syslog.LOG_INFO, 'BANNER_MESSAGE table handler...')
+        self.bannermsgcfg.banner_message(key, data)
+
     def wait_till_system_init_done(self):
         # No need to print the output in the log file so using the "--quiet"
         # flag
@@ -2059,6 +2147,10 @@ class HostConfigDaemon:
         self.config_db.subscribe(swsscommon.CFG_NTP_KEY_TABLE_NAME,
                                  make_callback(self.ntp_srv_key_handler))
 
+        # Handle BANNER_MESSAGE changes
+        self.config_db.subscribe(swsscommon.CFG_BANNER_MESSAGE_TABLE_NAME,
+                                 make_callback(self.banner_handler))
+
         syslog.syslog(syslog.LOG_INFO,
                       "Waiting for systemctl to finish initialization")
         self.wait_till_system_init_done()

tests/hostcfgd/hostcfgd_test.py

@@ -354,3 +354,20 @@ def test_load(self):
         data = {}
         dns_cfg.load(data)
         dns_cfg.dns_update.assert_called()
+
+
+class TestBannerCfg:
+    def test_load(self):
+        banner_cfg = hostcfgd.BannerCfg()
+        banner_cfg.banner_message = mock.MagicMock()
+
+        data = {}
+        banner_cfg.load(data)
+        banner_cfg.banner_message.assert_called()
+
+    @mock.patch('hostcfgd.run_cmd')
+    def test_banner_message(self, mock_run_cmd):
+        banner_cfg = hostcfgd.BannerCfg()
+        banner_cfg.banner_message(None, {'test': 'test'})
+
+        mock_run_cmd.assert_has_calls([call(['systemctl', 'restart', 'banner-config'], True, True)])