Added support for the infrastructure for on demand access/create the

server connection.

The BaseDriver and BaseConnection are two abstract classes, which allows
us to replace the existing driver with the currently used. The current
implementation supports to connect the PostgreSQL and Postgres Plus
Advanced Server using the psycopg2 driver.

web/pgadmin/utils/ajax.py

@@ -12,7 +12,9 @@
 from flask import Response
 import json
 
-def make_json_response(success=1, errormsg='', info='', result=None, data=None, status=200):
+
+def make_json_response(success=1, errormsg='', info='', result=None,
+                       data=None, status=200):
     """Create a HTML response document describing the results of a request and
     containing the data."""
     doc = dict()
@@ -22,12 +24,71 @@ def make_json_response(success=1, errormsg='', info='', result=None, data=None,
     doc['result'] = result
     doc['data'] = data
 
-    return Response(response=json.dumps(doc),
-                        status=status,
-                        mimetype="text/json")
+    return Response(
+        response=json.dumps(doc),
+        status=status,
+        mimetype="text/json"
+    )
+
 
 def make_response(response=None, status=200):
     """Create a JSON response handled by the backbone models."""
-    return Response(response=json.dumps(response),
-                        status=status,
-                        mimetype="text/json")
+    return Response(
+        response=json.dumps(response),
+        status=status,
+        mimetype="text/json"
+    )
+
+
+def internal_server_error(errormsg=''):
+    """Create a response with HTTP status code 500 - Internal Server Error."""
+    return make_json_response(
+                status=500,
+                success=0,
+                errormsg=errormsg
+    )
+
+
+def forbidden(errmsg=''):
+    """Create a response with HTTP status code 403 - Forbidden."""
+    return make_json_response(
+            status=403,
+            success=0,
+            errormsg=errmsg
+            )
+
+
+def unauthorized(errormsg=''):
+    """Create a response with HTTP status code 401 - Unauthorized."""
+    return make_json_response(
+                status=401,
+                success=0,
+                errormsg=errormsg
+    )
+
+
+def bad_request(errormsg=''):
+    """Create a response with HTTP status code 400 - Bad Request."""
+    return make_json_response(
+                status=400,
+                success=0,
+                errormsg=errormsg
+    )
+
+
+def precondition_required(errormsg=''):
+    """Create a response with HTTP status code 428 - Precondition Required."""
+    return make_json_response(
+                status=428,
+                success=0,
+                errormsg=errormsg
+    )
+
+
+def success_return(message=''):
+    """Create a response with HTTP status code 200 - OK."""
+    return make_json_response(
+                status=200,
+                success=1,
+                info=message
+    )