path: root/google-appengine/google/appengine/api/apiproxy_stub_map.py

#!/usr/bin/env python
#
# Copyright 2007 Google Inc.
#
# 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.
#

"""Container of APIProxy stubs for more convenient unittesting.

Classes/variables/functions defined here:
  APIProxyStubMap: container of APIProxy stubs.
  apiproxy: global instance of an APIProxyStubMap.
  MakeSyncCall: APIProxy entry point.
  UserRPC: User-visible class wrapping asynchronous RPCs.
"""





import inspect
import sys

from google.appengine.api import apiproxy_rpc


def CreateRPC(service):
  """Creates a RPC instance for the given service.

  The instance is suitable for talking to remote services.
  Each RPC instance can be used only once, and should not be reused.

  Args:
    service: string representing which service to call.

  Returns:
    the rpc object.

  Raises:
    AssertionError or RuntimeError if the stub for service doesn't supply a
    CreateRPC method.
  """
  stub = apiproxy.GetStub(service)
  assert stub, 'No api proxy found for service "%s"' % service
  assert hasattr(stub, 'CreateRPC'), (('The service "%s" doesn\'t have ' +
                                       'a CreateRPC method.') % service)
  return stub.CreateRPC()


def MakeSyncCall(service, call, request, response):
  """The APIProxy entry point for a synchronous API call.

  Args:
    service: string representing which service to call
    call: string representing which function to call
    request: protocol buffer for the request
    response: protocol buffer for the response

  Returns:
    Response protocol buffer or None. Some implementations may return
    a response protocol buffer instead of modifying 'response'.
    Caller must use returned value in such cases. If 'response' is modified
    then returns None.

  Raises:
    apiproxy_errors.Error or a subclass.
  """
  return apiproxy.MakeSyncCall(service, call, request, response)


class ListOfHooks(object):
  """An ordered collection of hooks for a particular API call.

  A hook is a function that has exactly the same signature as
  a service stub. It will be called before or after an api hook is
  executed, depending on whether this list is for precall of postcall hooks.
  Hooks can be used for debugging purposes (check certain
  pre- or postconditions on api calls) or to apply patches to protocol
  buffers before/after a call gets submitted.
  """

  def __init__(self):
    """Constructor."""

    self.__content = []

    self.__unique_keys = set()

  def __len__(self):
    """Returns the amount of elements in the collection."""
    return self.__content.__len__()

  def __Insert(self, index, key, function, service=None):
    """Appends a hook at a certain position in the list.

    Args:
      index: the index of where to insert the function
      key: a unique key (within the module) for this particular function.
        If something from the same module with the same key is already
        registered, nothing will be added.
      function: the hook to be added.
      service: optional argument that restricts the hook to a particular api

    Returns:
      True if the collection was modified.
    """
    unique_key = (key, inspect.getmodule(function))
    if unique_key in self.__unique_keys:
      return False
    num_args = len(inspect.getargspec(function)[0])
    if (inspect.ismethod(function)):
      num_args -= 1
    self.__content.insert(index, (key, function, service, num_args))
    self.__unique_keys.add(unique_key)
    return True

  def Append(self, key, function, service=None):
    """Appends a hook at the end of the list.

    Args:
      key: a unique key (within the module) for this particular function.
        If something from the same module with the same key is already
        registered, nothing will be added.
      function: the hook to be added.
      service: optional argument that restricts the hook to a particular api

    Returns:
      True if the collection was modified.
    """
    return self.__Insert(len(self), key, function, service)

  def Push(self, key, function, service=None):
    """Inserts a hook at the beginning of the list.

    Args:
      key: a unique key (within the module) for this particular function.
        If something from the same module with the same key is already
        registered, nothing will be added.
      function: the hook to be added.
      service: optional argument that restricts the hook to a particular api

    Returns:
      True if the collection was modified.
    """
    return self.__Insert(0, key, function, service)

  def Clear(self):
    """Removes all hooks from the list (useful for unit tests)."""
    self.__content = []
    self.__unique_keys = set()

  def Call(self, service, call, request, response, rpc=None, error=None):
    """Invokes all hooks in this collection.

    NOTE: For backwards compatibility, if error is not None, hooks
    with 4 or 5 arguments are *not* called.  This situation
    (error=None) only occurs when the RPC request raised an exception;
    in the past no hooks would be called at all in that case.

    Args:
      service: string representing which service to call
      call: string representing which function to call
      request: protocol buffer for the request
      response: protocol buffer for the response
      rpc: optional RPC used to make this call
      error: optional Exception instance to be passed as 6th argument
    """
    for key, function, srv, num_args in self.__content:
      if srv is None or srv == service:
        if num_args == 6:
          function(service, call, request, response, rpc, error)
        elif error is not None:
          pass
        elif num_args == 5:
          function(service, call, request, response, rpc)
        else:
          function(service, call, request, response)


class APIProxyStubMap(object):
  """Container of APIProxy stubs for more convenient unittesting.

  Stubs may be either trivial implementations of APIProxy services (e.g.
  DatastoreFileStub, UserServiceStub) or "real" implementations.

  For unittests, we may want to mix and match real and trivial implementations
  of services in order to better focus testing on individual service
  implementations. To achieve this, we allow the client to attach stubs to
  service names, as well as define a default stub to be used if no specific
  matching stub is identified.
  """


  def __init__(self, default_stub=None):
    """Constructor.

    Args:
      default_stub: optional stub

    'default_stub' will be used whenever no specific matching stub is found.
    """
    self.__stub_map = {}
    self.__default_stub = default_stub
    self.__precall_hooks = ListOfHooks()
    self.__postcall_hooks = ListOfHooks()

  def GetPreCallHooks(self):
    """Gets a collection for all precall hooks."""
    return self.__precall_hooks

  def GetPostCallHooks(self):
    """Gets a collection for all precall hooks."""
    return self.__postcall_hooks

  def RegisterStub(self, service, stub):
    """Register the provided stub for the specified service.

    Args:
      service: string
      stub: stub
    """
    assert not self.__stub_map.has_key(service), repr(service)
    self.__stub_map[service] = stub

    if service == 'datastore':
      self.RegisterStub('datastore_v3', stub)

  def GetStub(self, service):
    """Retrieve the stub registered for the specified service.

    Args:
      service: string

    Returns:
      stub

    Returns the stub registered for 'service', and returns the default stub
    if no such stub is found.
    """
    return self.__stub_map.get(service, self.__default_stub)

  def MakeSyncCall(self, service, call, request, response):
    """The APIProxy entry point.

    Args:
      service: string representing which service to call
      call: string representing which function to call
      request: protocol buffer for the request
      response: protocol buffer for the response

    Returns:
      Response protocol buffer or None. Some implementations may return
      a response protocol buffer instead of modifying 'response'.
      Caller must use returned value in such cases. If 'response' is modified
      then returns None.

    Raises:
      apiproxy_errors.Error or a subclass.
    """
    stub = self.GetStub(service)
    assert stub, 'No api proxy found for service "%s"' % service
    if hasattr(stub, 'CreateRPC'):
      rpc = stub.CreateRPC()
      self.__precall_hooks.Call(service, call, request, response, rpc)
      try:
        rpc.MakeCall(service, call, request, response)
        rpc.Wait()
        rpc.CheckSuccess()
      except Exception, err:
        self.__postcall_hooks.Call(service, call, request, response, rpc, err)
        raise
      else:
        self.__postcall_hooks.Call(service, call, request, response, rpc)
    else:
      self.__precall_hooks.Call(service, call, request, response)
      try:
        returned_response = stub.MakeSyncCall(service, call, request, response)
      except Exception, err:
        self.__postcall_hooks.Call(service, call, request, response, None, err)
        raise
      else:
        self.__postcall_hooks.Call(service, call, request,
                                   returned_response or response)
        return returned_response


class UserRPC(object):
  """Wrapper class for asynchronous RPC.

  Simplest low-level usage pattern:

    rpc = UserRPC('service', [deadline], [callback])
    rpc.make_call('method', request, response)
    .
    .
    .
    rpc.wait()
    rpc.check_success()

  However, a service module normally provides a wrapper so that the
  typical usage pattern becomes more like this:

    from google.appengine.api import service
    rpc = service.create_rpc([deadline], [callback])
    service.make_method_call(rpc, [service-specific-args])
    .
    .
    .
    rpc.wait()
    result = rpc.get_result()

  The service.make_method_call() function sets a service- and method-
  specific hook function that is called by rpc.get_result() with the
  rpc object as its first argument, and service-specific value as its
  second argument.  The hook function should call rpc.check_success()
  and then extract the user-level result from the rpc.result
  protobuffer.  Additional arguments may be passed from
  make_method_call() to the get_result hook via the second argument.
  """

  __method = None
  __get_result_hook = None
  __user_data = None
  __postcall_hooks_called = False

  def __init__(self, service, deadline=None, callback=None):
    """Constructor.

    Args:
      service: The service name.
      deadline: Optional deadline.  Default depends on the implementation.
      callback: Optional argument-less callback function.
    """
    self.__service = service
    self.__rpc = CreateRPC(service)
    self.__rpc.deadline = deadline
    self.__rpc.callback = callback

  @property
  def service(self):
    """Return the service name."""
    return self.__service

  @property
  def method(self):
    """Return the method name."""
    return self.__method

  @property
  def deadline(self):
    """Return the deadline, if set explicitly (otherwise None)."""
    return self.__rpc.deadline

  def __get_callback(self):
    """Return the callback attribute, a function without arguments.

    This attribute can also be assigned to.  For example, the
    following code calls some_other_function(rpc) when the RPC is
    complete:

      rpc = service.create_rpc()
      rpc.callback = lambda: some_other_function(rpc)
      service.make_method_call(rpc)
      rpc.wait()
    """
    return self.__rpc.callback
  def __set_callback(self, callback):
    """Set the callback function."""
    self.__rpc.callback = callback
  callback = property(__get_callback, __set_callback)

  @property
  def request(self):
    """Return the request protocol buffer object."""
    return self.__rpc.request

  @property
  def response(self):
    """Return the response protocol buffer object."""
    return self.__rpc.response

  @property
  def state(self):
    """Return the RPC state.

    Possible values are attributes of apiproxy_rpc.RPC: IDLE, RUNNING,
    FINISHING.
    """
    return self.__rpc.state

  @property
  def get_result_hook(self):
    """Return the get-result hook function."""
    return self.__get_result_hook

  @property
  def user_data(self):
    """Return the user data for the hook function."""
    return self.__user_data

  def make_call(self, method, request, response,
                get_result_hook=None, user_data=None):
    """Initiate a call.

    Args:
      method: The method name.
      request: The request protocol buffer.
      response: The response protocol buffer.
      get_result_hook: Optional get-result hook function.  If not None,
        this must be a function with exactly one argument, the RPC
        object (self).  Its return value is returned from get_result().
      user_data: Optional additional arbitrary data for the get-result
        hook function.  This can be accessed as rpc.user_data.  The
        type of this value is up to the service module.

    This function may only be called once per RPC object.  It sends
    the request to the remote server, but does not wait for a
    response.  This allows concurrent execution of the remote call and
    further local processing (e.g., making additional remote calls).

    Before the call is initiated, the precall hooks are called.
    """
    assert self.__rpc.state == apiproxy_rpc.RPC.IDLE, repr(self.state)
    self.__method = method
    self.__get_result_hook = get_result_hook
    self.__user_data = user_data
    apiproxy.GetPreCallHooks().Call(
        self.__service, method, request, response, self.__rpc)
    self.__rpc.MakeCall(self.__service, method, request, response)

  def wait(self):
    """Wait for the call to complete, and call callbacks.

    This is the only time callback functions may be called.  (However,
    note that check_success() and get_result() call wait().)   Waiting
    for one RPC may cause callbacks for other RPCs to be called.
    Callback functions may call check_success() and get_result().

    Callbacks are called without arguments; if a callback needs access
    to the RPC object a Python nested function (a.k.a. closure) or a
    bound may be used.  To facilitate this, the callback may be
    assigned after the RPC object is created (but before make_call()
    is called).

    Note: don't confuse callbacks with get-result hooks or precall
    and postcall hooks.
    """
    assert self.__rpc.state != apiproxy_rpc.RPC.IDLE, repr(self.state)
    if self.__rpc.state == apiproxy_rpc.RPC.RUNNING:
      self.__rpc.Wait()
    assert self.__rpc.state == apiproxy_rpc.RPC.FINISHING, repr(self.state)

  def check_success(self):
    """Check for success of the RPC, possibly raising an exception.

    This function should be called at least once per RPC.  If wait()
    hasn't been called yet, it is called first.  If the RPC caused
    an exceptional condition, an exception will be raised here.
    The first time check_success() is called, the postcall hooks
    are called.
    """
    self.wait()
    try:
      self.__rpc.CheckSuccess()
    except Exception, err:
      if not self.__postcall_hooks_called:
        self.__postcall_hooks_called = True
        apiproxy.GetPostCallHooks().Call(self.__service, self.__method,
                                         self.request, self.response,
                                         self.__rpc, err)
      raise
    else:
      if not self.__postcall_hooks_called:
        self.__postcall_hooks_called = True
        apiproxy.GetPostCallHooks().Call(self.__service, self.__method,
                                         self.request, self.response, self.__rpc)

  def get_result(self):
    """Get the result of the RPC, or possibly raise an exception.

    This implies a call to check_success().  If a get-result hook was
    passed to make_call(), that hook is responsible for calling
    check_success(), and the return value of the hook is returned.
    Otherwise, check_success() is called directly and None is
    returned.
    """
    if self.__get_result_hook is None:
      self.check_success()
      return None
    else:
      return self.__get_result_hook(self)


def GetDefaultAPIProxy():
  try:
    runtime = __import__('google.appengine.runtime', globals(), locals(),
                         ['apiproxy'])
    return APIProxyStubMap(runtime.apiproxy)
  except (AttributeError, ImportError):
    return APIProxyStubMap()


apiproxy = GetDefaultAPIProxy()