Implemented automatic caching for the discovery documents.

Author: Takashi Matsuo

googleapiclient/discovery.py

@@ -149,7 +149,9 @@ def build(serviceName,
           developerKey=None,
           model=None,
           requestBuilder=HttpRequest,
-          credentials=None):
+          credentials=None,
+          cache_discovery=True,
+          cache=None):
   """Construct a Resource for interacting with an API.
 
   Construct a Resource object for interacting with an API. The serviceName and
@@ -171,6 +173,9 @@ def build(serviceName,
       request.
     credentials: oauth2client.Credentials, credentials to be used for
       authentication.
+    cache_discovery: Boolean, whether or not to cache the discovery doc.
+    cache: googleapiclient.discovery_cache.base.CacheBase, an optional
+      cache object for the discovery documents.
 
   Returns:
     A Resource object with methods for interacting with the service.
@@ -185,22 +190,60 @@ def build(serviceName,
 
   requested_url = uritemplate.expand(discoveryServiceUrl, params)
 
+  content = _retrieve_discovery_doc(requested_url, http, cache_discovery, cache)
+
+  return build_from_document(content, base=discoveryServiceUrl, http=http,
+      developerKey=developerKey, model=model, requestBuilder=requestBuilder,
+      credentials=credentials)
+
+
+def _retrieve_discovery_doc(url, http, cache_discovery, cache=None):
+  """Retrieves the discovery_doc from cache or the internet.
+
+  Args:
+    url: string, the URL of the discovery document.
+    http: httplib2.Http, An instance of httplib2.Http or something that acts
+      like it that HTTP requests will be made through.
+    cache_discovery: Boolean, whether or not to cache the discovery doc.
+    cache: googleapiclient.discovery_cache.base.CacheBase, an optional
+      cache object for the discovery documents.
+
+  Returns:
+    A unicode string representation of the discovery document.
+  """
+  if http is None:
+    http = httplib2.Http()
+
+  if cache_discovery:
+    from . import discovery_cache
+    from .discovery_cache import base
+    if cache is None:
+      cache = discovery_cache.autodetect()
+    if cache:
+      if isinstance(cache, base.CacheBase):
+        content = cache.get(url)
+        if content:
+          return content
+      else:
+        logging.warning('The given cache object is not an instance of '
+                        'googleapiclient.discovery_cache.base.CacheBase.')
+
+  actual_url = url
   # REMOTE_ADDR is defined by the CGI spec [RFC3875] as the environment
   # variable that contains the network address of the client sending the
   # request. If it exists then add that to the request for the discovery
   # document to avoid exceeding the quota on discovery requests.
   if 'REMOTE_ADDR' in os.environ:
-    requested_url = _add_query_parameter(requested_url, 'userIp',
-                                         os.environ['REMOTE_ADDR'])
-  logger.info('URL being requested: GET %s' % requested_url)
+    actual_url = _add_query_parameter(url, 'userIp', os.environ['REMOTE_ADDR'])
+  logger.info('URL being requested: GET %s' % actual_url)
 
-  resp, content = http.request(requested_url)
+  resp, content = http.request(actual_url)
 
   if resp.status == 404:
     raise UnknownApiNameOrVersion("name: %s  version: %s" % (serviceName,
-                                                            version))
+                                                             version))
   if resp.status >= 400:
-    raise HttpError(resp, content, uri=requested_url)
+    raise HttpError(resp, content, uri=actual_url)
 
   try:
     content = content.decode('utf-8')
@@ -212,10 +255,9 @@ def build(serviceName,
   except ValueError as e:
     logger.error('Failed to parse as JSON: ' + content)
     raise InvalidJsonError()
-
-  return build_from_document(content, base=discoveryServiceUrl, http=http,
-      developerKey=developerKey, model=model, requestBuilder=requestBuilder,
-      credentials=credentials)
+  if cache_discovery and cache and isinstance(cache, base.CacheBase):
+    cache.set(url, content)
+  return content
 
 
 @positional(1)

googleapiclient/discovery_cache/__init__.py

@@ -0,0 +1,42 @@
+# Copyright 2014 Google Inc. All Rights Reserved.
+#
+# 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.
+
+"""Caching utility for the discovery document."""
+
+
+from __future__ import absolute_import
+
+import logging
+import datetime
+
+
+DISCOVERY_DOC_MAX_AGE = 60 * 60 * 24  # 1 day
+
+
+def autodetect():
+  """Detects an appropriate cache module and returns it.
+
+  Returns:
+    An object with the following methods; get(url), set(url, content).
+  """
+  try:
+    from google.appengine.api import memcache
+    from . import appengine_memcache
+    return appengine_memcache.Cache(max_age = DISCOVERY_DOC_MAX_AGE)
+  except:
+    try:
+      from . import file_cache
+      return file_cache.Cache(max_age = DISCOVERY_DOC_MAX_AGE)
+    except Exception as e:
+      logging.warning(e, exc_info=True)

googleapiclient/discovery_cache/appengine_memcache.py

@@ -0,0 +1,64 @@
+# Copyright 2014 Google Inc. All Rights Reserved.
+#
+# 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.
+
+"""App Engine memcache based cache for the discovery document."""
+
+
+import logging
+
+# This is only an optional dependency because we only import this
+# module when google.appengine.api.memcache is available.
+from google.appengine.api import memcache
+
+from . import base
+
+NAMESPACE = 'google-api-client'
+
+
+class Cache(base.CacheBase):
+  """A cache with app engine memcache API.
+
+  Attributes:
+    max_age: Cache expiration in seconds.
+  """
+  def __init__(self, max_age):
+      """Constructor for appengine_memcache.Cache.
+
+      Args:
+        max_age: Cache expiration in seconds.
+      """
+      self.max_age = max_age
+
+  def get(self, url):
+    """Gets the content from the memcache with a given key.
+
+    Args:
+      url: string, the key for the cache.
+    """
+    try:
+      return memcache.get(url, namespace=NAMESPACE)
+    except Exception as e:
+      logging.warning(e, exc_info=True)
+
+  def set(self, url, content):
+    """Sets the given key and content in the cache.
+
+    Args:
+      url: string, the key for the cache.
+      content: string, the discovery document.
+    """
+    try:
+      memcache.set(url, content, time=int(self.max_age), namespace=NAMESPACE)
+    except Exception as e:
+      logging.warning(e, exc_info=True)

googleapiclient/discovery_cache/base.py

@@ -0,0 +1,42 @@
+# Copyright 2014 Google Inc. All Rights Reserved.
+#
+# 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.
+
+"""An abstract class for caching the discovery document."""
+
+
+import abc
+
+
+class CacheBase(object):
+  """A base abstract cache class."""
+  __metaclass__ = abc.ABCMeta
+
+  @abc.abstractmethod  
+  def get(self, url):
+    """Gets the content from the memcache with a given key.
+
+    Args:
+      url: string, the key for the cache.
+    """
+    return
+
+  @abc.abstractmethod  
+  def set(self, url, content):
+    """Sets the given key and content in the cache.
+
+    Args:
+      url: string, the key for the cache.
+      content: string, the discovery document.
+    """
+    return

googleapiclient/discovery_cache/file_cache.py

@@ -0,0 +1,89 @@
+# Copyright 2014 Google Inc. All Rights Reserved.
+#
+# 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.
+
+"""File based cache for the discovery document."""
+
+
+import datetime
+import json
+import logging
+import os
+import tempfile
+import threading
+
+from . import base
+
+
+FILENAME = 'discovery-doc.cache'
+EPOCH = datetime.datetime.utcfromtimestamp(0)
+
+
+def to_timestamp(d):
+  return (d - EPOCH).total_seconds()
+
+
+class Cache(base.CacheBase):
+  """A file based cache for the discovery documents.
+
+  Attributes:
+    max_age: Cache expiration in seconds.
+    lock: threading.Lock, to make the operations thread safe.
+    cache_file: string, full path to the cache file.
+  """
+  def __init__(self, max_age):
+      """Constructor for appengine_memcache.Cache.
+
+      Args:
+        max_age: Cache expiration in seconds.
+      """
+      self.max_age = max_age
+      self.lock = threading.Lock()
+      self.cache_file = os.path.join(tempfile.gettempdir(), FILENAME)
+      if not os.path.isfile(self.cache_file):
+        with open(self.cache_file, 'w+') as f:
+          json.dump({}, f)
+
+  def get(self, url):
+    """Gets the content from the memcache with a given key.
+
+    Args:
+      url: string, the key for the cache.
+    """
+    try:
+      with self.lock:
+        with open(self.cache_file, 'r') as f:
+          cache = json.load(f)
+        if url in cache:
+          content, t = cache.get(url, (None, 0))
+          if to_timestamp(datetime.datetime.now()) < t + self.max_age:
+            return content
+    except Exception as e:
+      logging.warning(e, exc_info=True)
+
+  def set(self, url, content):
+    """Sets the given key and content in the cache.
+
+    Args:
+      url: string, the key for the cache.
+      content: string, the discovery document.
+    """
+    try:
+      with self.lock:
+        with open(self.cache_file, 'r+') as f:
+          cache = json.load(f)
+          cache[url] = (content, to_timestamp(datetime.datetime.now()))
+          f.seek(0)
+          json.dump(cache, f)
+    except Exception as e:
+      logging.warning(e, exc_info=True)