Add API to access config db (sonic-net#7)

* Add API to access config db

src/swsssdk/__init__.py

@@ -33,6 +33,7 @@ def _load_connector_map():
 
 try:
     from .dbconnector import SonicV1Connector, SonicV2Connector
+    from .configdb import ConfigDBConnector
 except (KeyError, ValueError):
     msg = "Failed to database connector objects -- incorrect database config schema."
     logger.exception(msg)

src/swsssdk/config/database.json

@@ -19,6 +19,9 @@
       },
       "COUNTERS_DB": {
         "db": 2
+      },
+      "CONFIG_DB": {
+        "db": 4
       }
     }
   }

src/swsssdk/configdb.py

@@ -0,0 +1,102 @@
+"""
+SONiC ConfigDB connection module 
+
+Example:
+    config_db = ConfigDBConnector()
+    config_db.connect()
+    config_db.set_table('bgp_neighbor', '10.0.0.1', {
+        'admin_status': state
+        })
+
+TODO:
+    Will add API on keyspace subscription for incremental configuration support
+    in the incoming versions.
+"""
+
+from .dbconnector import SonicV2Connector
+
+class ConfigDBConnector(SonicV2Connector):
+
+    def __init__(self):
+        """Connect to Redis through TCP, which does not requires root.
+        """
+        super(ConfigDBConnector, self).__init__(host='127.0.0.1')
+
+    def connect(self):
+        SonicV2Connector.connect(self, self.CONFIG_DB, False)
+
+    def set_entry(self, table, key, data):
+        """Write a table entry to config db.
+        Args:
+            table: Table name.
+            key: Key of table entry.
+            data: Table row data in a form of dictionary {'column_key': 'value', ...}
+        """
+        client = self.redis_clients[self.CONFIG_DB]
+        _hash = '{}:{}'.format(table.upper(), key)
+        client.hmset(_hash, data)
+
+    def get_entry(self, table, key):
+        """Read a table entry from config db.
+        Args:
+            table: Table name.
+            key: Key of table entry.
+        Returns: 
+            Table row data in a form of dictionary {'column_key': 'value', ...}
+            Empty dictionary if table does not exist or entry does not exist.
+        """
+        client = self.redis_clients[self.CONFIG_DB]
+        _hash = '{}:{}'.format(table.upper(), key)
+        return client.hgetall(_hash)
+
+    def get_table(self, table):
+        """Read an entire table from config db.
+        Args:
+            table: Table name.
+        Returns: 
+            Table data in a dictionary form of 
+            { 'row_key': {'column_key': 'value', ...}, ...}
+            Empty dictionary if table does not exist.
+        """
+        client = self.redis_clients[self.CONFIG_DB]
+        pattern = '{}:*'.format(table.upper())
+        keys = client.keys(pattern)
+        data = {}
+        for key in keys:
+            data[key.split(':')[1]] = client.hgetall(key)
+        return data
+
+    def set_config(self, data):
+        """Write multiple tables into config db. 
+        Args:
+            data: config data in a dictionary form
+            { 
+                'TABLE_NAME': { 'row_key': {'column_key': 'value', ...}, ...},
+                ...
+            }
+        """
+        for table_name in data:
+            table_data = data[table_name]
+            for key in table_data:
+                self.set_entry(table_name, key, table_data[key])
+
+    def get_config(self):
+        """Read all config data. 
+        Returns:
+            Config data in a dictionary form of 
+            { 
+                'TABLE_NAME': { 'row_key': {'column_key': 'value', ...}, ...},
+                ...
+            }
+        """
+        client = self.redis_clients[self.CONFIG_DB]
+        hashes = client.keys('*')
+        data = {}
+        for _hash in hashes:
+            table_name = _hash.split(':', 1)[0]
+            key = _hash.split(':', 1)[1]
+            if not data.has_key(table_name):
+                data[table_name] = {}
+            data[table_name][key] = client.hgetall(_hash)
+        return data
+