[#586] implement xml_mode() in a new irods.helpers module

Author: d-w-moore

README.md

@@ -736,7 +736,17 @@ QUASI_XML parser for the default one:
 
 ```
     from irods.message import (XML_Parser_Type, ET)
-    ET( XML_Parser_Type.QUASI_XML, session.server_version )
+    ET( XML_Parser_Type.QUASI_XML,
+        server_version = session.server_version
+    )
+```
+
+The server_version parameter can be used independently, if desired, to change the
+current thread's choice of entities during QUASI_XML transactions with the server.
+(This is only a concern when interacting with servers before iRODS 4.2.9.)
+
+```
+    ET(server_version = (4,2,8))
 ```
 
 Two dedicated environment variables may also be used to customize the
@@ -759,8 +769,20 @@ particular server version.
 
 Finally, note that these global defaults, once set, may be overridden on
 a per-thread basis using `ET(parser_type, server_version)`.
-We can also revert the current thread's XML parser back to the global
-default by calling `ET(None)`.
+
+The current thread's XML parser can always be reverted to the global default by the
+explicit use of `ET(None)`.  However, when frequently switching back and forth between
+parsers, it may be more convenient to use the `xml_mode` context manager:
+
+```
+    # ... Interactions with the server now use the default XML parser.
+
+    from irods.helpers import xml_mode
+    with xml_mode('QUASI_XML'):
+        # ... Interactions with the server, in the current thread, temporarily use QUASI_XML
+
+    # ... We have now returned to using the default XML parser.
+```
 
 Rule Execution
 --------------

irods/helpers/__init__.py

@@ -0,0 +1,37 @@
+import contextlib
+import re
+from ..test.helpers import (home_collection,
+                            make_session as make_test_session)
+from irods.message import (ET, XML_Parser_Type)
+
+__all__ = ['make_session', 'home_collection', 'xml_mode']
+
+
+def make_session(test_server_version = False, **kwargs):
+    return make_test_session(test_server_version = test_server_version, **kwargs)
+
+make_session.__doc__ = re.sub(r'(test_server_version\s*)=\s*\w+',r'\1 = False',make_test_session.__doc__)
+
+
+@contextlib.contextmanager
+def xml_mode(s):
+    """In a with-block, this context manager can temporarily change the client's choice of XML parser.
+
+    Example usages:
+        with("QUASI_XML"):
+            # ...
+        with(XML_Parser_Type.QUASI_XML):
+            # ..."""
+
+    try:
+        if isinstance(s,str):
+            ET(getattr(XML_Parser_Type,s))        # e.g. xml_mode("QUASI_XML")
+        elif isinstance(s,XML_Parser_Type):
+            ET(s)                                 # e.g. xml_mode(XML_Parser_Type.QUASI_XML)
+        else:
+            msg = "xml_mode argument must be a string (e.g. 'QUASI_XML') or an XML_Parser_Type enum."
+            raise ValueError(msg)
+        yield
+    finally:
+        ET(None)
+

irods/message/__init__.py

@@ -67,7 +67,9 @@ def __repr__(self):
     XML_Parser_Type.__members__ = {k:v for k,v in XML_Parser_Type.__dict__.items()
                                    if isinstance(v,XML_Parser_Type)}
 
-    PARSER_TYPE_STRINGS = {v:k for k,v in XML_Parser_Type.__members__.items() if v.value != 0}
+# This creates a mapping from the "valid" (nonzero) XML_Parser_Type enums -- those which represent the actual parser
+# choices -- to their corresponding names as strings (e.g. XML_Parser_Type.STANDARD_XML is mapped to 'STANDARD_XML'):
+PARSER_TYPE_STRINGS = {v:k for k,v in XML_Parser_Type.__members__.items() if v.value != 0}
 
 # We maintain values on a per-thread basis of:
 #   - the server version with which we're communicating
@@ -111,6 +113,9 @@ def default_XML_parser(get_module = False):
     d = _default_XML
     return d if not get_module else _XML_parsers[d]
 
+def string_for_XML_parser(parser_enum):
+    return PARSER_TYPE_STRINGS[parser_enum]
+
 _XML_parsers = {
     XML_Parser_Type.STANDARD_XML : ET_xml,
     XML_Parser_Type.QUASI_XML : ET_quasi_xml,

irods/test/data_obj_test.py

@@ -1861,6 +1861,57 @@ def test_access_through_resc_hierarchy__243(self):
         finally:
             s.resources.remove('parent')
 
+    @unittest.skipIf(set(os.environ.keys()) & {'PYTHON_IRODSCLIENT_CONFIG__CONNECTIONS__XML_PARSER_DEFAULT',
+                                               'PYTHON_IRODSCLIENT_CONFIGURATION_PATH', 'PYTHON_IRODSCLIENT_DEFAULT_XML'},
+                     "skipping due to possible overwriting of test-apropos settings by a configuration file or environment setting")
+    def test_temporary_xml_mode_change_with_operation_as_proof__issue_586(self):
+        from irods.helpers import (xml_mode, home_collection)
+        sess = irods.test.helpers.make_session()
+        hc = home_collection(sess)
+        odd_name = '{hc}/\1'.format(**locals())
+
+        # Currently 'STANDARD_XML' is the default, and 'QUASI_XML' is a convenient alternative to use when
+        # object names are used which contain special characters (e.g. '\1') hostile to standard XML parsers.
+        default_xml_parser = 'STANDARD_XML'
+
+        from irods.message import (current_XML_parser, string_for_XML_parser)
+        active_xml_parser_for_thread = lambda : string_for_XML_parser(current_XML_parser())
+
+        self.assertEqual(active_xml_parser_for_thread(), default_xml_parser)
+
+        with xml_mode('QUASI_XML'):
+            sess.data_objects.create(odd_name)
+
+        # Test that the xml parser setting isn't permanently changed
+        self.assertEqual(active_xml_parser_for_thread(), default_xml_parser)
+
+        try:
+            if default_xml_parser == 'STANDARD_XML':
+                with self.assertRaises(xml.etree.ElementTree.ParseError):
+                    sess.collections.get(hc).data_objects
+        finally:
+            with xml_mode('QUASI_XML'):
+                sess.data_objects.unlink(odd_name, force = True)
+
+    def test_temporary_xml_mode_changes_have_desired_thread_limited_effect__issue_586(self):
+        from irods.message import (current_XML_parser, string_for_XML_parser)
+        active_xml_parser_for_thread = lambda : string_for_XML_parser(current_XML_parser())
+        from concurrent.futures import ThreadPoolExecutor
+        from irods.helpers import xml_mode
+        original_xml_parser = active_xml_parser_for_thread()
+        other_xml_parser = list({'STANDARD_XML', 'QUASI_XML', 'SECURE_XML'} - {original_xml_parser})[0]
+
+        self.assertNotEqual(other_xml_parser, original_xml_parser)
+
+        with xml_mode(other_xml_parser):
+            # Test that this thread is the only one affected, and that in it we get 'QUASI_XML' when we call
+            # current_XML_parser(), i.e. the function used internally by ET() to retrieve the current parser module.
+            self.assertEqual(other_xml_parser, active_xml_parser_for_thread())
+            self.assertEqual(original_xml_parser, ThreadPoolExecutor(max_workers = 1).submit(active_xml_parser_for_thread).result())
+
+        self.assertEqual(active_xml_parser_for_thread(), original_xml_parser)
+
+
     def test_register_with_xml_special_chars(self):
         test_dir = helpers.irods_shared_tmp_dir()
         loc_server = self.sess.host in ('localhost', socket.gethostname())

irods/test/helpers.py

@@ -152,6 +152,20 @@ def recast(k):
 # Create a connection for test, based on ~/.irods environment by default.
 
 def make_session(test_server_version = True, **kwargs):
+    """Connect to an iRODS server as determined by any client environment
+    file present at a standard location, and by any keyword arguments given.
+
+    Arguments:
+
+    test_server_version: Of type bool; in the `irods.test.helpers` version of this
+                         function, defaults to True.  A True value causes
+                         *iRODS_Server_Too_Recent* to be raised if the server
+                         connected to is more recent than the current Python iRODS
+                         client's advertised level of compatibility.
+
+    **kwargs:            Keyword arguments.  Fed directly to the iRODSSession
+                         constructor.  """
+
     try:
         env_file = kwargs.pop('irods_env_file')
     except KeyError:
@@ -160,7 +174,6 @@ def make_session(test_server_version = True, **kwargs):
         except KeyError:
             env_file = os.path.expanduser('~/.irods/irods_environment.json')
     session = iRODSSession( irods_env_file = env_file, **kwargs )
-
     if test_server_version:
         connected_version = session.server_version[:3]
         advertised_version = IRODS_VERSION[:3]
@@ -173,6 +186,7 @@ def make_session(test_server_version = True, **kwargs):
 
 
 def home_collection(session):
+    """Return a string value for the given session's home collection."""
     return "/{0.zone}/home/{0.username}".format(session)