Review fixes: add pxd declaration, clean up error path, fix typo

- Add unpack_col_encrypted_row declaration to RowParser base class in
  parsing.pxd and NotImplementedError stub in parsing.pyx, for
  consistency with unpack_plain_row and to enable C-level dispatch.
- Split the error-handling path in protocol.py to avoid building
  unnecessary col_descs when column_encryption_policy is not set.
- Fix 'otherwsise' typo in obj_parser.pyx docstring.

Author: mykaul

cassandra/obj_parser.pyx

@@ -63,7 +63,7 @@ cdef class TupleRowParser(RowParser):
 
         (obj1, ..., objN)
     If CE (Column encryption) policy is enabled - use unpack_col_encrypted_row(),
-    otherwsise use unpack_plain_row()
+    otherwise use unpack_plain_row()
     """
 
     @cython.boundscheck(False)

cassandra/parsing.pxd

@@ -29,4 +29,5 @@ cdef class ColumnParser:
 
 cdef class RowParser:
     cpdef unpack_plain_row(self, BytesIOReader reader, ParseDesc desc)
+    cpdef unpack_col_encrypted_row(self, BytesIOReader reader, ParseDesc desc)
 

cassandra/parsing.pyx

@@ -44,3 +44,9 @@ cdef class RowParser:
         Unpack a single row of data in a ResultMessage.
         """
         raise NotImplementedError
+
+    cpdef unpack_col_encrypted_row(self, BytesIOReader reader, ParseDesc desc):
+        """
+        Unpack a single row of data in a ResultMessage, with column encryption support.
+        """
+        raise NotImplementedError

cassandra/protocol.py

@@ -742,19 +742,24 @@ def decode_row(row):
         try:
             self.parsed_rows = [decode_row(row) for row in rows]
         except Exception:
-            if not column_encryption_policy:
-                col_descs = [ColDesc(md[0], md[1], md[2]) for md in column_metadata]
-            for row in rows:
-                for val, col_md, col_desc in zip(row, column_metadata, col_descs):
-                    try:
-                        if column_encryption_policy:
+            if column_encryption_policy:
+                for row in rows:
+                    for val, col_md, col_desc in zip(row, column_metadata, col_descs):
+                        try:
                             decode_val(val, col_md, col_desc)
-                        else:
+                        except Exception as e:
+                            raise DriverException('Failed decoding result column "%s" of type %s: %s' % (col_md[2],
+                                                                                                         col_md[3].cql_parameterized_type(),
+                                                                                                         str(e)))
+            else:
+                for row in rows:
+                    for val, col_md in zip(row, column_metadata):
+                        try:
                             col_md[3].from_binary(val, protocol_version)
-                    except Exception as e:
-                        raise DriverException('Failed decoding result column "%s" of type %s: %s' % (col_md[2],
-                                                                                                     col_md[3].cql_parameterized_type(),
-                                                                                                     str(e)))
+                        except Exception as e:
+                            raise DriverException('Failed decoding result column "%s" of type %s: %s' % (col_md[2],
+                                                                                                         col_md[3].cql_parameterized_type(),
+                                                                                                         str(e)))
 
     def recv_results_prepared(self, f, protocol_version, protocol_features, user_type_map):
         self.query_id = read_binary_string(f)