1 files changed, 123 insertions, 0 deletions
diff --git a/src/python/grpcio/grpc/_plugin_wrapping.py b/src/python/grpcio/grpc/_plugin_wrapping.py
new file mode 100644
index 0000000000..7cb5218c22
--- /dev/null
+++ b/src/python/grpcio/grpc/_plugin_wrapping.py
@@ -0,0 +1,123 @@
+# Copyright 2015, Google Inc.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#     * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+import collections
+import threading
+
+import grpc
+from grpc import _common
+from grpc._cython import cygrpc
+
+
+class AuthMetadataContext(
+    collections.namedtuple(
+        'AuthMetadataContext', ('service_url', 'method_name',)),
+    grpc.AuthMetadataContext):
+  pass
+
+
+class AuthMetadataPluginCallback(grpc.AuthMetadataContext):
+
+  def __init__(self, callback):
+    self._callback = callback
+
+  def __call__(self, metadata, error):
+    self._callback(metadata, error)
+
+
+class _WrappedCygrpcCallback(object):
+
+  def __init__(self, cygrpc_callback):
+    self.is_called = False
+    self.error = None
+    self.is_called_lock = threading.Lock()
+    self.cygrpc_callback = cygrpc_callback
+
+  def _invoke_failure(self, error):
+    # TODO(atash) translate different Exception superclasses into different
+    # status codes.
+    self.cygrpc_callback(
+        _common.EMPTY_METADATA, cygrpc.StatusCode.internal,
+        _common.encode(str(error)))
+
+  def _invoke_success(self, metadata):
+    try:
+      cygrpc_metadata = _common.cygrpc_metadata(metadata)
+    except Exception as error:
+      self._invoke_failure(error)
+      return
+    self.cygrpc_callback(cygrpc_metadata, cygrpc.StatusCode.ok, b'')
+
+  def __call__(self, metadata, error):
+    with self.is_called_lock:
+      if self.is_called:
+        raise RuntimeError('callback should only ever be invoked once')
+      if self.error:
+        self._invoke_failure(self.error)
+        return
+      self.is_called = True
+    if error is None:
+      self._invoke_success(metadata)
+    else:
+      self._invoke_failure(error)
+
+  def notify_failure(self, error):
+    with self.is_called_lock:
+      if not self.is_called:
+        self.error = error
+
+
+class _WrappedPlugin(object):
+
+  def __init__(self, plugin):
+    self.plugin = plugin
+
+  def __call__(self, context, cygrpc_callback):
+    wrapped_cygrpc_callback = _WrappedCygrpcCallback(cygrpc_callback)
+    wrapped_context = AuthMetadataContext(
+        _common.decode(context.service_url), _common.decode(context.method_name))
+    try:
+      self.plugin(
+          wrapped_context, AuthMetadataPluginCallback(wrapped_cygrpc_callback))
+    except Exception as error:
+      wrapped_cygrpc_callback.notify_failure(error)
+      raise
+
+
+def call_credentials_metadata_plugin(plugin, name):
+  """
+  Args:
+    plugin: A callable accepting a grpc.AuthMetadataContext
+      object and a callback (itself accepting a list of metadata key/value
+      2-tuples and a None-able exception value). The callback must be eventually
+      called, but need not be called in plugin's invocation.
+      plugin's invocation must be non-blocking.
+  """
+  return cygrpc.call_credentials_metadata_plugin(
+      cygrpc.CredentialsMetadataPlugin(_WrappedPlugin(plugin), _common.encode(name)))