Upmerge changes from v1.8.x to master

13 files changed, 352 insertions, 476 deletions

diff --git a/src/python/grpcio/grpc/__init__.py b/src/python/grpcio/grpc/__init__.py
index 558ce42129..564772527e 100644
--- a/src/python/grpcio/grpc/__init__.py
+++ b/src/python/grpcio/grpc/__init__.py
@@ -348,26 +348,25 @@ class Call(six.with_metaclass(abc.ABCMeta, RpcContext)):
 class ChannelCredentials(object):
     """An encapsulation of the data required to create a secure Channel.
 
-  This class has no supported interface - it exists to define the type of its
-  instances and its instances exist to be passed to other functions. For
-  example, ssl_channel_credentials returns an instance, and secure_channel
-  consumes an instance of this class.
-  """
+    This class has no supported interface - it exists to define the type of its
+    instances and its instances exist to be passed to other functions. For
+    example, ssl_channel_credentials returns an instance of this class and
+    secure_channel requires an instance of this class.
+    """
 
     def __init__(self, credentials):
         self._credentials = credentials
 
 
 class CallCredentials(object):
-    """An encapsulation of the data required to assert an identity over a
-       channel.
+    """An encapsulation of the data required to assert an identity over a call.
 
-  A CallCredentials may be composed with ChannelCredentials to always assert
-  identity for every call over that Channel.
+    A CallCredentials may be composed with ChannelCredentials to always assert
+    identity for every call over that Channel.
 
-  This class has no supported interface - it exists to define the type of its
-  instances and its instances exist to be passed to other functions.
-  """
+    This class has no supported interface - it exists to define the type of its
+    instances and its instances exist to be passed to other functions.
+    """
 
     def __init__(self, credentials):
         self._credentials = credentials
@@ -376,23 +375,22 @@ class CallCredentials(object):
 class AuthMetadataContext(six.with_metaclass(abc.ABCMeta)):
     """Provides information to call credentials metadata plugins.
 
-  Attributes:
-    service_url: A string URL of the service being called into.
-    method_name: A string of the fully qualified method name being called.
-  """
+    Attributes:
+      service_url: A string URL of the service being called into.
+      method_name: A string of the fully qualified method name being called.
+    """
 
 
 class AuthMetadataPluginCallback(six.with_metaclass(abc.ABCMeta)):
     """Callback object received by a metadata plugin."""
 
     def __call__(self, metadata, error):
-        """Inform the gRPC runtime of the metadata to construct a
-           CallCredentials.
+        """Passes to the gRPC runtime authentication metadata for an RPC.
 
-    Args:
-      metadata: The :term:`metadata` used to construct the CallCredentials.
-      error: An Exception to indicate error or None to indicate success.
-    """
+        Args:
+          metadata: The :term:`metadata` used to construct the CallCredentials.
+          error: An Exception to indicate error or None to indicate success.
+        """
         raise NotImplementedError()
 
 
@@ -402,14 +400,14 @@ class AuthMetadataPlugin(six.with_metaclass(abc.ABCMeta)):
     def __call__(self, context, callback):
         """Implements authentication by passing metadata to a callback.
 
-    Implementations of this method must not block.
+        Implementations of this method must not block.
 
-    Args:
-      context: An AuthMetadataContext providing information on the RPC that the
-        plugin is being called to authenticate.
-      callback: An AuthMetadataPluginCallback to be invoked either synchronously
-        or asynchronously.
-    """
+        Args:
+          context: An AuthMetadataContext providing information on the RPC that
+            the plugin is being called to authenticate.
+          callback: An AuthMetadataPluginCallback to be invoked either
+            synchronously or asynchronously.
+        """
         raise NotImplementedError()
 
 
@@ -1138,99 +1136,86 @@ def ssl_channel_credentials(root_certificates=None,
                             certificate_chain=None):
     """Creates a ChannelCredentials for use with an SSL-enabled Channel.
 
-  Args:
-    root_certificates: The PEM-encoded root certificates as a byte string,
-    or None to retrieve them from a default location chosen by gRPC runtime.
-    private_key: The PEM-encoded private key as a byte string, or None if no
-    private key should be used.
-    certificate_chain: The PEM-encoded certificate chain as a byte string
-    to use or or None if no certificate chain should be used.
+    Args:
+      root_certificates: The PEM-encoded root certificates as a byte string,
+        or None to retrieve them from a default location chosen by gRPC
+        runtime.
+      private_key: The PEM-encoded private key as a byte string, or None if no
+        private key should be used.
+      certificate_chain: The PEM-encoded certificate chain as a byte string
+        to use or or None if no certificate chain should be used.
 
-  Returns:
-    A ChannelCredentials for use with an SSL-enabled Channel.
-  """
-    if private_key is not None or certificate_chain is not None:
-        pair = _cygrpc.SslPemKeyCertPair(private_key, certificate_chain)
-    else:
-        pair = None
+    Returns:
+      A ChannelCredentials for use with an SSL-enabled Channel.
+    """
     return ChannelCredentials(
-        _cygrpc.channel_credentials_ssl(root_certificates, pair))
+        _cygrpc.SSLChannelCredentials(root_certificates, private_key,
+                                      certificate_chain))
 
 
 def metadata_call_credentials(metadata_plugin, name=None):
     """Construct CallCredentials from an AuthMetadataPlugin.
 
-  Args:
-    metadata_plugin: An AuthMetadataPlugin to use for authentication.
-    name: An optional name for the plugin.
+    Args:
+      metadata_plugin: An AuthMetadataPlugin to use for authentication.
+      name: An optional name for the plugin.
 
-  Returns:
-    A CallCredentials.
-  """
+    Returns:
+      A CallCredentials.
+    """
     from grpc import _plugin_wrapping  # pylint: disable=cyclic-import
-    if name is None:
-        try:
-            effective_name = metadata_plugin.__name__
-        except AttributeError:
-            effective_name = metadata_plugin.__class__.__name__
-    else:
-        effective_name = name
-    return CallCredentials(
-        _plugin_wrapping.call_credentials_metadata_plugin(metadata_plugin,
-                                                          effective_name))
+    return _plugin_wrapping.metadata_plugin_call_credentials(metadata_plugin,
+                                                             name)
 
 
 def access_token_call_credentials(access_token):
     """Construct CallCredentials from an access token.
 
-  Args:
-    access_token: A string to place directly in the http request
-      authorization header, for example
-      "authorization: Bearer <access_token>".
+    Args:
+      access_token: A string to place directly in the http request
+        authorization header, for example
+        "authorization: Bearer <access_token>".
 
-  Returns:
-    A CallCredentials.
-  """
+    Returns:
+      A CallCredentials.
+    """
     from grpc import _auth  # pylint: disable=cyclic-import
-    return metadata_call_credentials(
-        _auth.AccessTokenCallCredentials(access_token))
+    from grpc import _plugin_wrapping  # pylint: disable=cyclic-import
+    return _plugin_wrapping.metadata_plugin_call_credentials(
+        _auth.AccessTokenAuthMetadataPlugin(access_token), None)
 
 
 def composite_call_credentials(*call_credentials):
     """Compose multiple CallCredentials to make a new CallCredentials.
 
-  Args:
-    *call_credentials: At least two CallCredentials objects.
+    Args:
+      *call_credentials: At least two CallCredentials objects.
 
-  Returns:
-    A CallCredentials object composed of the given CallCredentials objects.
-  """
-    from grpc import _credential_composition  # pylint: disable=cyclic-import
-    cygrpc_call_credentials = tuple(
-        single_call_credentials._credentials
-        for single_call_credentials in call_credentials)
+    Returns:
+      A CallCredentials object composed of the given CallCredentials objects.
+    """
     return CallCredentials(
-        _credential_composition.call(cygrpc_call_credentials))
+        _cygrpc.CompositeCallCredentials(
+            tuple(single_call_credentials._credentials
+                  for single_call_credentials in call_credentials)))
 
 
 def composite_channel_credentials(channel_credentials, *call_credentials):
     """Compose a ChannelCredentials and one or more CallCredentials objects.
 
-  Args:
-    channel_credentials: A ChannelCredentials object.
-    *call_credentials: One or more CallCredentials objects.
+    Args:
+      channel_credentials: A ChannelCredentials object.
+      *call_credentials: One or more CallCredentials objects.
 
-  Returns:
-    A ChannelCredentials composed of the given ChannelCredentials and
-    CallCredentials objects.
-  """
-    from grpc import _credential_composition  # pylint: disable=cyclic-import
-    cygrpc_call_credentials = tuple(
-        single_call_credentials._credentials
-        for single_call_credentials in call_credentials)
+    Returns:
+      A ChannelCredentials composed of the given ChannelCredentials and
+        CallCredentials objects.
+    """
     return ChannelCredentials(
-        _credential_composition.channel(channel_credentials._credentials,
-                                        cygrpc_call_credentials))
+        _cygrpc.CompositeChannelCredentials(
+            tuple(single_call_credentials._credentials
+                  for single_call_credentials in call_credentials),
+            channel_credentials._credentials))
 
 
 def ssl_server_credentials(private_key_certificate_chain_pairs,
diff --git a/src/python/grpcio/grpc/_auth.py b/src/python/grpcio/grpc/_auth.py
index c6542d0135..9a339b5900 100644
--- a/src/python/grpcio/grpc/_auth.py
+++ b/src/python/grpcio/grpc/_auth.py
@@ -63,7 +63,7 @@ class GoogleCallCredentials(grpc.AuthMetadataPlugin):
         self._pool.shutdown(wait=False)
 
 
-class AccessTokenCallCredentials(grpc.AuthMetadataPlugin):
+class AccessTokenAuthMetadataPlugin(grpc.AuthMetadataPlugin):
     """Metadata wrapper for raw access token credentials."""
 
     def __init__(self, access_token):
diff --git a/src/python/grpcio/grpc/_credential_composition.py b/src/python/grpcio/grpc/_credential_composition.py
deleted file mode 100644
index f652cc3ae7..0000000000
--- a/src/python/grpcio/grpc/_credential_composition.py
+++ /dev/null
@@ -1,33 +0,0 @@
-# Copyright 2016 gRPC authors.
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-from grpc._cython import cygrpc
-
-
-def _call(call_credentialses):
-    call_credentials_iterator = iter(call_credentialses)
-    composition = next(call_credentials_iterator)
-    for additional_call_credentials in call_credentials_iterator:
-        composition = cygrpc.call_credentials_composite(
-            composition, additional_call_credentials)
-    return composition
-
-
-def call(call_credentialses):
-    return _call(call_credentialses)
-
-
-def channel(channel_credentials, call_credentialses):
-    return cygrpc.channel_credentials_composite(channel_credentials,
-                                                _call(call_credentialses))
diff --git a/src/python/grpcio/grpc/_cython/_cygrpc/call.pyx.pxi b/src/python/grpcio/grpc/_cython/_cygrpc/call.pyx.pxi
index 752fb330d0..6b3a276097 100644
--- a/src/python/grpcio/grpc/_cython/_cygrpc/call.pyx.pxi
+++ b/src/python/grpcio/grpc/_cython/_cygrpc/call.pyx.pxi
@@ -72,13 +72,12 @@ cdef class Call:
         result = grpc_call_cancel(self.c_call, NULL)
       return result
 
-  def set_credentials(
-      self, CallCredentials call_credentials not None):
-    cdef grpc_call_error result
-    with nogil:
-      result = grpc_call_set_credentials(
-          self.c_call, call_credentials.c_credentials)
-    return result
+  def set_credentials(self, CallCredentials call_credentials not None):
+    cdef grpc_call_credentials *c_call_credentials = call_credentials.c()
+    cdef grpc_call_error call_error = grpc_call_set_credentials(
+        self.c_call, c_call_credentials)
+    grpc_call_credentials_release(c_call_credentials)
+    return call_error
 
   def peer(self):
     cdef char *peer = NULL
diff --git a/src/python/grpcio/grpc/_cython/_cygrpc/channel.pyx.pxi b/src/python/grpcio/grpc/_cython/_cygrpc/channel.pyx.pxi
index aeabdba021..4c397f8f64 100644
--- a/src/python/grpcio/grpc/_cython/_cygrpc/channel.pyx.pxi
+++ b/src/python/grpcio/grpc/_cython/_cygrpc/channel.pyx.pxi
@@ -33,10 +33,10 @@ cdef class Channel:
         self.c_channel = grpc_insecure_channel_create(c_target, c_arguments,
                                                       NULL)
     else:
-      with nogil:
-        self.c_channel = grpc_secure_channel_create(
-            channel_credentials.c_credentials, c_target, c_arguments, NULL)
-      self.references.append(channel_credentials)
+      c_channel_credentials = channel_credentials.c()
+      self.c_channel = grpc_secure_channel_create(
+          c_channel_credentials, c_target, c_arguments, NULL)
+      grpc_channel_credentials_release(c_channel_credentials)
     self.references.append(target)
     self.references.append(arguments)
 
diff --git a/src/python/grpcio/grpc/_cython/_cygrpc/credentials.pxd.pxi b/src/python/grpcio/grpc/_cython/_cygrpc/credentials.pxd.pxi
index bc0f185c77..7e9ea33ca0 100644
--- a/src/python/grpcio/grpc/_cython/_cygrpc/credentials.pxd.pxi
+++ b/src/python/grpcio/grpc/_cython/_cygrpc/credentials.pxd.pxi
@@ -12,20 +12,66 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-cimport cpython
+
+cdef class CallCredentials:
+
+  cdef grpc_call_credentials *c(self)
+
+  # TODO(https://github.com/grpc/grpc/issues/12531): remove.
+  cdef grpc_call_credentials *c_credentials
+
+
+cdef int _get_metadata(
+    void *state, grpc_auth_metadata_context context,
+    grpc_credentials_plugin_metadata_cb cb, void *user_data,
+    grpc_metadata creds_md[GRPC_METADATA_CREDENTIALS_PLUGIN_SYNC_MAX],
+    size_t *num_creds_md, grpc_status_code *status,
+    const char **error_details) with gil
+
+cdef void _destroy(void *state) with gil
+
+
+cdef class MetadataPluginCallCredentials(CallCredentials):
+
+  cdef readonly object _metadata_plugin
+  cdef readonly bytes _name
+
+  cdef grpc_call_credentials *c(self)
+
+
+cdef grpc_call_credentials *_composition(call_credentialses)
+
+
+cdef class CompositeCallCredentials(CallCredentials):
+
+  cdef readonly tuple _call_credentialses
+
+  cdef grpc_call_credentials *c(self)
 
 
 cdef class ChannelCredentials:
 
+  cdef grpc_channel_credentials *c(self)
+
+  # TODO(https://github.com/grpc/grpc/issues/12531): remove.
   cdef grpc_channel_credentials *c_credentials
-  cdef grpc_ssl_pem_key_cert_pair c_ssl_pem_key_cert_pair
-  cdef list references
 
 
-cdef class CallCredentials:
+cdef class SSLChannelCredentials(ChannelCredentials):
 
-  cdef grpc_call_credentials *c_credentials
-  cdef list references
+  cdef readonly object _pem_root_certificates
+  cdef readonly object _private_key
+  cdef readonly object _certificate_chain
+
+  cdef grpc_channel_credentials *c(self)
+
+
+cdef class CompositeChannelCredentials(ChannelCredentials):
+
+  cdef readonly tuple _call_credentialses
+  cdef readonly ChannelCredentials _channel_credentials
+
+  cdef grpc_channel_credentials *c(self)
 
 
 cdef class ServerCertificateConfig:
@@ -49,27 +95,3 @@ cdef class ServerCredentials:
   cdef object cert_config_fetcher
   # whether C-core has asked for the initial_cert_config
   cdef bint initial_cert_config_fetched
-
-
-cdef class CredentialsMetadataPlugin:
-
-  cdef object plugin_callback
-  cdef bytes plugin_name
-
-
-cdef grpc_metadata_credentials_plugin _c_plugin(CredentialsMetadataPlugin plugin)
-
-
-cdef class AuthMetadataContext:
-
-  cdef grpc_auth_metadata_context context
-
-
-cdef int plugin_get_metadata(
-    void *state, grpc_auth_metadata_context context,
-    grpc_credentials_plugin_metadata_cb cb, void *user_data,
-    grpc_metadata creds_md[GRPC_METADATA_CREDENTIALS_PLUGIN_SYNC_MAX],
-    size_t *num_creds_md, grpc_status_code *status,
-    const char **error_details) with gil
-
-cdef void plugin_destroy_c_plugin_state(void *state) with gil
diff --git a/src/python/grpcio/grpc/_cython/_cygrpc/credentials.pyx.pxi b/src/python/grpcio/grpc/_cython/_cygrpc/credentials.pyx.pxi
index ee1328d2e9..246a271893 100644
--- a/src/python/grpcio/grpc/_cython/_cygrpc/credentials.pyx.pxi
+++ b/src/python/grpcio/grpc/_cython/_cygrpc/credentials.pyx.pxi
@@ -16,47 +16,123 @@ cimport cpython
 
 import grpc
 import threading
-import traceback
 
 
-cdef class ChannelCredentials:
+cdef class CallCredentials:
 
-  def __cinit__(self):
-    grpc_init()
-    self.c_credentials = NULL
-    self.c_ssl_pem_key_cert_pair.private_key = NULL
-    self.c_ssl_pem_key_cert_pair.certificate_chain = NULL
-    self.references = []
+  cdef grpc_call_credentials *c(self):
+    raise NotImplementedError()
 
-  # The object *can* be invalid in Python if we fail to make the credentials
-  # (and the core thus returns NULL credentials). Used primarily for debugging.
-  @property
-  def is_valid(self):
-    return self.c_credentials != NULL
 
-  def __dealloc__(self):
-    if self.c_credentials != NULL:
-      grpc_channel_credentials_release(self.c_credentials)
-    grpc_shutdown()
+cdef int _get_metadata(
+    void *state, grpc_auth_metadata_context context,
+    grpc_credentials_plugin_metadata_cb cb, void *user_data,
+    grpc_metadata creds_md[GRPC_METADATA_CREDENTIALS_PLUGIN_SYNC_MAX],
+    size_t *num_creds_md, grpc_status_code *status,
+    const char **error_details) with gil:
+  def callback(Metadata metadata, grpc_status_code status, bytes error_details):
+    if status is StatusCode.ok:
+      cb(user_data, metadata.c_metadata, metadata.c_count, status, NULL)
+    else:
+      cb(user_data, NULL, 0, status, error_details)
+  args = context.service_url, context.method_name, callback,
+  threading.Thread(target=<object>state, args=args).start()
+  return 0  # Asynchronous return
 
 
-cdef class CallCredentials:
+cdef void _destroy(void *state) with gil:
+  cpython.Py_DECREF(<object>state)
 
-  def __cinit__(self):
-    grpc_init()
-    self.c_credentials = NULL
-    self.references = []
 
-  # The object *can* be invalid in Python if we fail to make the credentials
-  # (and the core thus returns NULL credentials). Used primarily for debugging.
-  @property
-  def is_valid(self):
-    return self.c_credentials != NULL
+cdef class MetadataPluginCallCredentials(CallCredentials):
 
-  def __dealloc__(self):
-    if self.c_credentials != NULL:
-      grpc_call_credentials_release(self.c_credentials)
-    grpc_shutdown()
+  def __cinit__(self, metadata_plugin, name):
+    self._metadata_plugin = metadata_plugin
+    self._name = name
+
+  cdef grpc_call_credentials *c(self):
+    cdef grpc_metadata_credentials_plugin c_metadata_plugin
+    c_metadata_plugin.get_metadata = _get_metadata
+    c_metadata_plugin.destroy = _destroy
+    c_metadata_plugin.state = <void *>self._metadata_plugin
+    c_metadata_plugin.type = self._name
+    cpython.Py_INCREF(self._metadata_plugin)
+    return grpc_metadata_credentials_create_from_plugin(c_metadata_plugin, NULL)
+
+
+cdef grpc_call_credentials *_composition(call_credentialses):
+  call_credentials_iterator = iter(call_credentialses)
+  cdef CallCredentials composition = next(call_credentials_iterator)
+  cdef grpc_call_credentials *c_composition = composition.c()
+  cdef CallCredentials additional_call_credentials
+  cdef grpc_call_credentials *c_additional_call_credentials
+  cdef grpc_call_credentials *c_next_composition
+  for additional_call_credentials in call_credentials_iterator:
+    c_additional_call_credentials = additional_call_credentials.c()
+    c_next_composition = grpc_composite_call_credentials_create(
+        c_composition, c_additional_call_credentials, NULL)
+    grpc_call_credentials_release(c_composition)
+    grpc_call_credentials_release(c_additional_call_credentials)
+    c_composition = c_next_composition
+  return c_composition
+
+
+cdef class CompositeCallCredentials(CallCredentials):
+
+  def __cinit__(self, call_credentialses):
+    self._call_credentialses = call_credentialses
+
+  cdef grpc_call_credentials *c(self):
+    return _composition(self._call_credentialses)
+
+
+cdef class ChannelCredentials:
+
+  cdef grpc_channel_credentials *c(self):
+    raise NotImplementedError()
+
+
+cdef class SSLChannelCredentials(ChannelCredentials):
+
+  def __cinit__(self, pem_root_certificates, private_key, certificate_chain):
+    self._pem_root_certificates = pem_root_certificates
+    self._private_key = private_key
+    self._certificate_chain = certificate_chain
+
+  cdef grpc_channel_credentials *c(self):
+    cdef const char *c_pem_root_certificates
+    cdef grpc_ssl_pem_key_cert_pair c_pem_key_certificate_pair
+    if self._pem_root_certificates is None:
+      c_pem_root_certificates = NULL
+    else:
+      c_pem_root_certificates = self._pem_root_certificates
+    if self._private_key is None and self._certificate_chain is None:
+      return grpc_ssl_credentials_create(
+          c_pem_root_certificates, NULL, NULL)
+    else:
+      c_pem_key_certificate_pair.private_key = self._private_key
+      c_pem_key_certificate_pair.certificate_chain = self._certificate_chain
+      return grpc_ssl_credentials_create(
+          c_pem_root_certificates, &c_pem_key_certificate_pair, NULL)
+
+
+cdef class CompositeChannelCredentials(ChannelCredentials):
+
+  def __cinit__(self, call_credentialses, channel_credentials):
+    self._call_credentialses = call_credentialses
+    self._channel_credentials = channel_credentials
+
+  cdef grpc_channel_credentials *c(self):
+    cdef grpc_channel_credentials *c_channel_credentials
+    c_channel_credentials = self._channel_credentials.c()
+    cdef grpc_call_credentials *c_call_credentials_composition = _composition(
+        self._call_credentialses)
+    cdef grpc_channel_credentials *composition
+    c_composition = grpc_composite_channel_credentials_create(
+        c_channel_credentials, c_call_credentials_composition, NULL)
+    grpc_channel_credentials_release(c_channel_credentials)
+    grpc_call_credentials_release(c_call_credentials_composition)
+    return c_composition
 
 
 cdef class ServerCertificateConfig:
@@ -89,190 +165,6 @@ cdef class ServerCredentials:
       grpc_server_credentials_release(self.c_credentials)
     grpc_shutdown()
 
-
-cdef class CredentialsMetadataPlugin:
-
-  def __cinit__(self, object plugin_callback, bytes name):
-    """
-    Args:
-      plugin_callback (callable): Callback accepting a service URL (str/bytes)
-        and callback object (accepting a MetadataArray,
-        grpc_status_code, and a str/bytes error message). This argument
-        when called should be non-blocking and eventually call the callback
-        object with the appropriate status code/details and metadata (if
-        successful).
-      name (bytes): Plugin name.
-    """
-    grpc_init()
-    if not callable(plugin_callback):
-      raise ValueError('expected callable plugin_callback')
-    self.plugin_callback = plugin_callback
-    self.plugin_name = name
-
-  def __dealloc__(self):
-    grpc_shutdown()
-
-
-cdef grpc_metadata_credentials_plugin _c_plugin(CredentialsMetadataPlugin plugin):
-  cdef grpc_metadata_credentials_plugin c_plugin
-  c_plugin.get_metadata = plugin_get_metadata
-  c_plugin.destroy = plugin_destroy_c_plugin_state
-  c_plugin.state = <void *>plugin
-  c_plugin.type = plugin.plugin_name
-  cpython.Py_INCREF(plugin)
-  return c_plugin
-
-
-cdef class AuthMetadataContext:
-
-  def __cinit__(self):
-    grpc_init()
-    self.context.service_url = NULL
-    self.context.method_name = NULL
-
-  @property
-  def service_url(self):
-    return self.context.service_url
-
-  @property
-  def method_name(self):
-    return self.context.method_name
-
-  def __dealloc__(self):
-    grpc_shutdown()
-
-
-cdef int plugin_get_metadata(
-    void *state, grpc_auth_metadata_context context,
-    grpc_credentials_plugin_metadata_cb cb, void *user_data,
-    grpc_metadata creds_md[GRPC_METADATA_CREDENTIALS_PLUGIN_SYNC_MAX],
-    size_t *num_creds_md, grpc_status_code *status,
-    const char **error_details) with gil:
-  called_flag = [False]
-  def python_callback(
-      Metadata metadata, grpc_status_code status,
-      bytes error_details):
-    cb(user_data, metadata.c_metadata, metadata.c_count, status, error_details)
-    called_flag[0] = True
-  cdef CredentialsMetadataPlugin self = <CredentialsMetadataPlugin>state
-  cdef AuthMetadataContext cy_context = AuthMetadataContext()
-  cy_context.context = context
-  def async_callback():
-    try:
-      self.plugin_callback(cy_context, python_callback)
-    except Exception as error:
-      if not called_flag[0]:
-        cb(user_data, NULL, 0, StatusCode.unknown,
-           traceback.format_exc().encode())
-  threading.Thread(group=None, target=async_callback).start()
-  return 0  # Asynchronous return
-
-cdef void plugin_destroy_c_plugin_state(void *state) with gil:
-  cpython.Py_DECREF(<CredentialsMetadataPlugin>state)
-
-def channel_credentials_google_default():
-  cdef ChannelCredentials credentials = ChannelCredentials();
-  with nogil:
-    credentials.c_credentials = grpc_google_default_credentials_create()
-  return credentials
-
-def channel_credentials_ssl(pem_root_certificates,
-                            SslPemKeyCertPair ssl_pem_key_cert_pair):
-  pem_root_certificates = str_to_bytes(pem_root_certificates)
-  cdef ChannelCredentials credentials = ChannelCredentials()
-  cdef const char *c_pem_root_certificates = NULL
-  if pem_root_certificates is not None:
-    c_pem_root_certificates = pem_root_certificates
-    credentials.references.append(pem_root_certificates)
-  if ssl_pem_key_cert_pair is not None:
-    with nogil:
-      credentials.c_credentials = grpc_ssl_credentials_create(
-          c_pem_root_certificates, &ssl_pem_key_cert_pair.c_pair, NULL)
-    credentials.references.append(ssl_pem_key_cert_pair)
-  else:
-    with nogil:
-      credentials.c_credentials = grpc_ssl_credentials_create(
-        c_pem_root_certificates, NULL, NULL)
-  return credentials
-
-def channel_credentials_composite(
-    ChannelCredentials credentials_1 not None,
-    CallCredentials credentials_2 not None):
-  if not credentials_1.is_valid or not credentials_2.is_valid:
-    raise ValueError("passed credentials must both be valid")
-  cdef ChannelCredentials credentials = ChannelCredentials()
-  with nogil:
-    credentials.c_credentials = grpc_composite_channel_credentials_create(
-        credentials_1.c_credentials, credentials_2.c_credentials, NULL)
-  credentials.references.append(credentials_1)
-  credentials.references.append(credentials_2)
-  return credentials
-
-def call_credentials_composite(
-    CallCredentials credentials_1 not None,
-    CallCredentials credentials_2 not None):
-  if not credentials_1.is_valid or not credentials_2.is_valid:
-    raise ValueError("passed credentials must both be valid")
-  cdef CallCredentials credentials = CallCredentials()
-  with nogil:
-    credentials.c_credentials = grpc_composite_call_credentials_create(
-        credentials_1.c_credentials, credentials_2.c_credentials, NULL)
-  credentials.references.append(credentials_1)
-  credentials.references.append(credentials_2)
-  return credentials
-
-def call_credentials_google_compute_engine():
-  cdef CallCredentials credentials = CallCredentials()
-  with nogil:
-    credentials.c_credentials = (
-        grpc_google_compute_engine_credentials_create(NULL))
-  return credentials
-
-def call_credentials_service_account_jwt_access(
-    json_key, Timespec token_lifetime not None):
-  json_key = str_to_bytes(json_key)
-  cdef CallCredentials credentials = CallCredentials()
-  cdef char *json_key_c_string = json_key
-  with nogil:
-    credentials.c_credentials = (
-        grpc_service_account_jwt_access_credentials_create(
-            json_key_c_string, token_lifetime.c_time, NULL))
-  credentials.references.append(json_key)
-  return credentials
-
-def call_credentials_google_refresh_token(json_refresh_token):
-  json_refresh_token = str_to_bytes(json_refresh_token)
-  cdef CallCredentials credentials = CallCredentials()
-  cdef char *json_refresh_token_c_string = json_refresh_token
-  with nogil:
-    credentials.c_credentials = grpc_google_refresh_token_credentials_create(
-        json_refresh_token_c_string, NULL)
-  credentials.references.append(json_refresh_token)
-  return credentials
-
-def call_credentials_google_iam(authorization_token, authority_selector):
-  authorization_token = str_to_bytes(authorization_token)
-  authority_selector = str_to_bytes(authority_selector)
-  cdef CallCredentials credentials = CallCredentials()
-  cdef char *authorization_token_c_string = authorization_token
-  cdef char *authority_selector_c_string = authority_selector
-  with nogil:
-    credentials.c_credentials = grpc_google_iam_credentials_create(
-        authorization_token_c_string, authority_selector_c_string, NULL)
-  credentials.references.append(authorization_token)
-  credentials.references.append(authority_selector)
-  return credentials
-
-def call_credentials_metadata_plugin(CredentialsMetadataPlugin plugin):
-  cdef CallCredentials credentials = CallCredentials()
-  cdef grpc_metadata_credentials_plugin c_plugin = _c_plugin(plugin)
-  with nogil:
-    credentials.c_credentials = (
-        grpc_metadata_credentials_create_from_plugin(c_plugin, NULL))
-  # TODO(atash): the following held reference is *probably* never necessary
-  credentials.references.append(plugin)
-  return credentials
-
 cdef const char* _get_c_pem_root_certs(pem_root_certs):
   if pem_root_certs is None:
     return NULL
diff --git a/src/python/grpcio/grpc/_plugin_wrapping.py b/src/python/grpcio/grpc/_plugin_wrapping.py
index bea2c0f139..cd17f4a049 100644
--- a/src/python/grpcio/grpc/_plugin_wrapping.py
+++ b/src/python/grpcio/grpc/_plugin_wrapping.py
@@ -13,6 +13,7 @@
 # limitations under the License.
 
 import collections
+import logging
 import threading
 
 import grpc
@@ -20,89 +21,79 @@ from grpc import _common
 from grpc._cython import cygrpc
 
 
-class AuthMetadataContext(
+class _AuthMetadataContext(
         collections.namedtuple('AuthMetadataContext', (
             'service_url', 'method_name',)), grpc.AuthMetadataContext):
     pass
 
 
-class AuthMetadataPluginCallback(grpc.AuthMetadataContext):
+class _CallbackState(object):
 
-    def __init__(self, callback):
-        self._callback = callback
-
-    def __call__(self, metadata, error):
-        self._callback(metadata, error)
+    def __init__(self):
+        self.lock = threading.Lock()
+        self.called = False
+        self.exception = None
 
 
-class _WrappedCygrpcCallback(object):
+class _AuthMetadataPluginCallback(grpc.AuthMetadataPluginCallback):
 
-    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.to_cygrpc_metadata(metadata)
-        except Exception as exception:  # pylint: disable=broad-except
-            self._invoke_failure(exception)
-            return
-        self.cygrpc_callback(cygrpc_metadata, cygrpc.StatusCode.ok, b'')
+    def __init__(self, state, callback):
+        self._state = state
+        self._callback = callback
 
     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
+        with self._state.lock:
+            if self._state.exception is None:
+                if self._state.called:
+                    raise RuntimeError(
+                        'AuthMetadataPluginCallback invoked more than once!')
+                else:
+                    self._state.called = True
+            else:
+                raise RuntimeError(
+                    'AuthMetadataPluginCallback raised exception "{}"!'.format(
+                        self._state.exception))
         if error is None:
-            self._invoke_success(metadata)
+            self._callback(
+                _common.to_cygrpc_metadata(metadata), cygrpc.StatusCode.ok,
+                None)
         else:
-            self._invoke_failure(error)
-
-    def notify_failure(self, error):
-        with self.is_called_lock:
-            if not self.is_called:
-                self.error = error
+            self._callback(None, cygrpc.StatusCode.internal,
+                           _common.encode(str(error)))
 
 
-class _WrappedPlugin(object):
+class _Plugin(object):
 
-    def __init__(self, plugin):
-        self.plugin = plugin
+    def __init__(self, metadata_plugin):
+        self._metadata_plugin = metadata_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))
+    def __call__(self, service_url, method_name, callback):
+        context = _AuthMetadataContext(
+            _common.decode(service_url), _common.decode(method_name))
+        callback_state = _CallbackState()
+        try:
+            self._metadata_plugin(
+                context, _AuthMetadataPluginCallback(callback_state, callback))
+        except Exception as exception:  # pylint: disable=broad-except
+            logging.exception(
+                'AuthMetadataPluginCallback "%s" raised exception!',
+                self._metadata_plugin)
+            with callback_state.lock:
+                callback_state.exception = exception
+                if callback_state.called:
+                    return
+            callback(None, cygrpc.StatusCode.internal,
+                     _common.encode(str(exception)))
+
+
+def metadata_plugin_call_credentials(metadata_plugin, name):
+    if name is None:
         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)))
+            effective_name = metadata_plugin.__name__
+        except AttributeError:
+            effective_name = metadata_plugin.__class__.__name__
+    else:
+        effective_name = name
+    return grpc.CallCredentials(
+        cygrpc.MetadataPluginCallCredentials(
+            _Plugin(metadata_plugin), _common.encode(effective_name)))
diff --git a/src/python/grpcio/grpc/_server.py b/src/python/grpcio/grpc/_server.py
index cd59b07c04..5b4812bffe 100644
--- a/src/python/grpcio/grpc/_server.py
+++ b/src/python/grpcio/grpc/_server.py
@@ -374,10 +374,10 @@ def _call_behavior(rpc_event, state, behavior, argument, request_deserializer):
     context = _Context(rpc_event, state, request_deserializer)
     try:
         return behavior(argument, context), True
-    except Exception as e:  # pylint: disable=broad-except
+    except Exception as exception:  # pylint: disable=broad-except
         with state.condition:
-            if e not in state.rpc_errors:
-                details = 'Exception calling application: {}'.format(e)
+            if exception not in state.rpc_errors:
+                details = 'Exception calling application: {}'.format(exception)
                 logging.exception(details)
                 _abort(state, rpc_event.operation_call,
                        cygrpc.StatusCode.unknown, _common.encode(details))
@@ -389,10 +389,10 @@ def _take_response_from_response_iterator(rpc_event, state, response_iterator):
         return next(response_iterator), True
     except StopIteration:
         return None, True
-    except Exception as e:  # pylint: disable=broad-except
+    except Exception as exception:  # pylint: disable=broad-except
         with state.condition:
-            if e not in state.rpc_errors:
-                details = 'Exception iterating responses: {}'.format(e)
+            if exception not in state.rpc_errors:
+                details = 'Exception iterating responses: {}'.format(exception)
                 logging.exception(details)
                 _abort(state, rpc_event.operation_call,
                        cygrpc.StatusCode.unknown, _common.encode(details))
@@ -591,7 +591,13 @@ def _handle_call(rpc_event, generic_handlers, thread_pool,
     if not rpc_event.success:
         return None, None
     if rpc_event.request_call_details.method is not None:
-        method_handler = _find_method_handler(rpc_event, generic_handlers)
+        try:
+            method_handler = _find_method_handler(rpc_event, generic_handlers)
+        except Exception as exception:  # pylint: disable=broad-except
+            details = 'Exception servicing handler: {}'.format(exception)
+            logging.exception(details)
+            return _reject_rpc(rpc_event, cygrpc.StatusCode.unknown,
+                               b'Error in service handler!'), None
         if method_handler is None:
             return _reject_rpc(rpc_event, cygrpc.StatusCode.unimplemented,
                                b'Method not found!'), None
diff --git a/src/python/grpcio_tests/tests/tests.json b/src/python/grpcio_tests/tests/tests.json
index e277a3ea1d..34cbade92c 100644
--- a/src/python/grpcio_tests/tests/tests.json
+++ b/src/python/grpcio_tests/tests/tests.json
@@ -22,7 +22,7 @@
   "unit._api_test.ChannelConnectivityTest",
   "unit._api_test.ChannelTest",
   "unit._auth_context_test.AuthContextTest",
-  "unit._auth_test.AccessTokenCallCredentialsTest",
+  "unit._auth_test.AccessTokenAuthMetadataPluginTest",
   "unit._auth_test.GoogleCallCredentialsTest",
   "unit._channel_args_test.ChannelArgsTest",
   "unit._channel_connectivity_test.ChannelConnectivityTest",
diff --git a/src/python/grpcio_tests/tests/unit/_auth_test.py b/src/python/grpcio_tests/tests/unit/_auth_test.py
index f61951b80a..e2cb938936 100644
--- a/src/python/grpcio_tests/tests/unit/_auth_test.py
+++ b/src/python/grpcio_tests/tests/unit/_auth_test.py
@@ -61,7 +61,7 @@ class GoogleCallCredentialsTest(unittest.TestCase):
         self.assertTrue(callback_event.wait(1.0))
 
 
-class AccessTokenCallCredentialsTest(unittest.TestCase):
+class AccessTokenAuthMetadataPluginTest(unittest.TestCase):
 
     def test_google_call_credentials_success(self):
         callback_event = threading.Event()
@@ -71,8 +71,8 @@ class AccessTokenCallCredentialsTest(unittest.TestCase):
             self.assertIsNone(error)
             callback_event.set()
 
-        call_creds = _auth.AccessTokenCallCredentials('token')
-        call_creds(None, mock_callback)
+        metadata_plugin = _auth.AccessTokenAuthMetadataPlugin('token')
+        metadata_plugin(None, mock_callback)
         self.assertTrue(callback_event.wait(1.0))
 
 
diff --git a/src/python/grpcio_tests/tests/unit/_cython/cygrpc_test.py b/src/python/grpcio_tests/tests/unit/_cython/cygrpc_test.py
index 18d4a6df64..da94cf8028 100644
--- a/src/python/grpcio_tests/tests/unit/_cython/cygrpc_test.py
+++ b/src/python/grpcio_tests/tests/unit/_cython/cygrpc_test.py
@@ -28,7 +28,7 @@ _CALL_CREDENTIALS_METADATA_VALUE = 'call-creds-value'
 _EMPTY_FLAGS = 0
 
 
-def _metadata_plugin_callback(context, callback):
+def _metadata_plugin(context, callback):
     callback(
         cygrpc.Metadata([
             cygrpc.Metadatum(_CALL_CREDENTIALS_METADATA_KEY,
@@ -105,17 +105,9 @@ class TypeSmokeTest(unittest.TestCase):
         channel = cygrpc.Channel(b'[::]:0', cygrpc.ChannelArgs([]))
         del channel
 
-    def testCredentialsMetadataPluginUpDown(self):
-        plugin = cygrpc.CredentialsMetadataPlugin(
-            lambda ignored_a, ignored_b: None, b'')
-        del plugin
-
-    def testCallCredentialsFromPluginUpDown(self):
-        plugin = cygrpc.CredentialsMetadataPlugin(_metadata_plugin_callback,
-                                                  b'')
-        call_credentials = cygrpc.call_credentials_metadata_plugin(plugin)
-        del plugin
-        del call_credentials
+    def test_metadata_plugin_call_credentials_up_down(self):
+        cygrpc.MetadataPluginCallCredentials(_metadata_plugin,
+                                             b'test plugin name!')
 
     def testServerStartNoExplicitShutdown(self):
         server = cygrpc.Server(cygrpc.ChannelArgs([]))
@@ -205,7 +197,7 @@ class ServerClientMixin(object):
 
         return test_utilities.SimpleFuture(performer)
 
-    def testEcho(self):
+    def test_echo(self):
         DEADLINE = time.time() + 5
         DEADLINE_TOLERANCE = 0.25
         CLIENT_METADATA_ASCII_KEY = b'key'
@@ -439,8 +431,8 @@ class SecureServerSecureClient(unittest.TestCase, ServerClientMixin):
             cygrpc.SslPemKeyCertPair(resources.private_key(),
                                      resources.certificate_chain())
         ], False)
-        client_credentials = cygrpc.channel_credentials_ssl(
-            resources.test_root_certificates(), None)
+        client_credentials = cygrpc.SSLChannelCredentials(
+            resources.test_root_certificates(), None, None)
         self.setUpMixin(server_credentials, client_credentials,
                         _SSL_HOST_OVERRIDE)
 
diff --git a/src/python/grpcio_tests/tests/unit/_invocation_defects_test.py b/src/python/grpcio_tests/tests/unit/_invocation_defects_test.py
index 0a1e50c94c..2a1a49ce74 100644
--- a/src/python/grpcio_tests/tests/unit/_invocation_defects_test.py
+++ b/src/python/grpcio_tests/tests/unit/_invocation_defects_test.py
@@ -32,6 +32,7 @@ _UNARY_UNARY = '/test/UnaryUnary'
 _UNARY_STREAM = '/test/UnaryStream'
 _STREAM_UNARY = '/test/StreamUnary'
 _STREAM_STREAM = '/test/StreamStream'
+_DEFECTIVE_GENERIC_RPC_HANDLER = '/test/DefectiveGenericRpcHandler'
 
 
 class _Callback(object):
@@ -95,6 +96,9 @@ class _Handler(object):
             yield request
         self._control.control()
 
+    def defective_generic_rpc_handler(self):
+        raise test_control.Defect()
+
 
 class _MethodHandler(grpc.RpcMethodHandler):
 
@@ -132,6 +136,8 @@ class _GenericHandler(grpc.GenericRpcHandler):
         elif handler_call_details.method == _STREAM_STREAM:
             return _MethodHandler(True, True, None, None, None, None, None,
                                   self._handler.handle_stream_stream)
+        elif handler_call_details.method == _DEFECTIVE_GENERIC_RPC_HANDLER:
+            return self._handler.defective_generic_rpc_handler()
         else:
             return None
 
@@ -176,6 +182,10 @@ def _stream_stream_multi_callable(channel):
     return channel.stream_stream(_STREAM_STREAM)
 
 
+def _defective_handler_multi_callable(channel):
+    return channel.unary_unary(_DEFECTIVE_GENERIC_RPC_HANDLER)
+
+
 class InvocationDefectsTest(unittest.TestCase):
 
     def setUp(self):
@@ -235,6 +245,18 @@ class InvocationDefectsTest(unittest.TestCase):
             for _ in range(test_constants.STREAM_LENGTH // 2 + 1):
                 next(response_iterator)
 
+    def testDefectiveGenericRpcHandlerUnaryResponse(self):
+        request = b'\x07\x08'
+        multi_callable = _defective_handler_multi_callable(self._channel)
+
+        with self.assertRaises(grpc.RpcError) as exception_context:
+            response = multi_callable(
+                request,
+                metadata=(('test', 'DefectiveGenericRpcHandlerUnary'),))
+
+        self.assertIs(grpc.StatusCode.UNKNOWN,
+                      exception_context.exception.code())
+
 
 if __name__ == '__main__':
     unittest.main(verbosity=2)