apiclient/model.py

#!/usr/bin/python2.4
#
# Copyright (C) 2010 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.

"""Model objects for requests and responses.

Each API may support one or more serializations, such
as JSON, Atom, etc. The model classes are responsible
for converting between the wire format and the Python
object representation.
"""

__author__ = 'jcgregorio@google.com (Joe Gregorio)'

import gflags
import logging
import urllib

from anyjson import simplejson
from errors import HttpError

FLAGS = gflags.FLAGS

gflags.DEFINE_boolean('dump_request_response', False,
                      'Dump all http server requests and responses. '
                     )


def _abstract():
  raise NotImplementedError('You need to override this function')


class Model(object):
  """Model base class.

  All Model classes should implement this interface.
  The Model serializes and de-serializes between a wire
  format such as JSON and a Python object representation.
  """

  def request(self, headers, path_params, query_params, body_value):
    """Updates outgoing requests with a serialized body.

    Args:
      headers: dict, request headers
      path_params: dict, parameters that appear in the request path
      query_params: dict, parameters that appear in the query
      body_value: object, the request body as a Python object, which must be
                  serializable.
    Returns:
      A tuple of (headers, path_params, query, body)

      headers: dict, request headers
      path_params: dict, parameters that appear in the request path
      query: string, query part of the request URI
      body: string, the body serialized in the desired wire format.
    """
    _abstract()

  def response(self, resp, content):
    """Convert the response wire format into a Python object.

    Args:
      resp: httplib2.Response, the HTTP response headers and status
      content: string, the body of the HTTP response

    Returns:
      The body de-serialized as a Python object.

    Raises:
      apiclient.errors.HttpError if a non 2xx response is received.
    """
    _abstract()


class BaseModel(Model):
  """Base model class.

  Subclasses should provide implementations for the "serialize" and
  "deserialize" methods, as well as values for the following class attributes.

  Attributes:
    accept: The value to use for the HTTP Accept header.
    content_type: The value to use for the HTTP Content-type header.
    no_content_response: The value to return when deserializing a 204 "No
        Content" response.
    alt_param: The value to supply as the "alt" query parameter for requests.
  """

  accept = None
  content_type = None
  no_content_response = None
  alt_param = None

  def _log_request(self, headers, path_params, query, body):
    """Logs debugging information about the request if requested."""
    if FLAGS.dump_request_response:
      logging.info('--request-start--')
      logging.info('-headers-start-')
      for h, v in headers.iteritems():
        logging.info('%s: %s', h, v)
      logging.info('-headers-end-')
      logging.info('-path-parameters-start-')
      for h, v in path_params.iteritems():
        logging.info('%s: %s', h, v)
      logging.info('-path-parameters-end-')
      logging.info('body: %s', body)
      logging.info('query: %s', query)
      logging.info('--request-end--')

  def request(self, headers, path_params, query_params, body_value):
    """Updates outgoing requests with a serialized body.

    Args:
      headers: dict, request headers
      path_params: dict, parameters that appear in the request path
      query_params: dict, parameters that appear in the query
      body_value: object, the request body as a Python object, which must be
                  serializable by simplejson.
    Returns:
      A tuple of (headers, path_params, query, body)

      headers: dict, request headers
      path_params: dict, parameters that appear in the request path
      query: string, query part of the request URI
      body: string, the body serialized as JSON
    """
    query = self._build_query(query_params)
    headers['accept'] = self.accept
    headers['accept-encoding'] = 'gzip, deflate'
    if 'user-agent' in headers:
      headers['user-agent'] += ' '
    else:
      headers['user-agent'] = ''
    headers['user-agent'] += 'google-api-python-client/1.0'

    if body_value is not None:
      headers['content-type'] = self.content_type
      body_value = self.serialize(body_value)
    self._log_request(headers, path_params, query, body_value)
    return (headers, path_params, query, body_value)

  def _build_query(self, params):
    """Builds a query string.

    Args:
      params: dict, the query parameters

    Returns:
      The query parameters properly encoded into an HTTP URI query string.
    """
    params.update({'alt': self.alt_param})
    astuples = []
    for key, value in params.iteritems():
      if type(value) == type([]):
        for x in value:
          x = x.encode('utf-8')
          astuples.append((key, x))
      else:
        if getattr(value, 'encode', False) and callable(value.encode):
          value = value.encode('utf-8')
        astuples.append((key, value))
    return '?' + urllib.urlencode(astuples)

  def _log_response(self, resp, content):
    """Logs debugging information about the response if requested."""
    if FLAGS.dump_request_response:
      logging.info('--response-start--')
      for h, v in resp.iteritems():
        logging.info('%s: %s', h, v)
      if content:
        logging.info(content)
      logging.info('--response-end--')

  def response(self, resp, content):
    """Convert the response wire format into a Python object.

    Args:
      resp: httplib2.Response, the HTTP response headers and status
      content: string, the body of the HTTP response

    Returns:
      The body de-serialized as a Python object.

    Raises:
      apiclient.errors.HttpError if a non 2xx response is received.
    """
    self._log_response(resp, content)
    # Error handling is TBD, for example, do we retry
    # for some operation/error combinations?
    if resp.status < 300:
      if resp.status == 204:
        # A 204: No Content response should be treated differently
        # to all the other success states
        return self.no_content_response
      return self.deserialize(content)
    else:
      logging.debug('Content from bad request was: %s' % content)
      raise HttpError(resp, content)

  def serialize(self, body_value):
    """Perform the actual Python object serialization.

    Args:
      body_value: object, the request body as a Python object.

    Returns:
      string, the body in serialized form.
    """
    _abstract()

  def deserialize(self, content):
    """Perform the actual deserialization from response string to Python object.

    Args:
      content: string, the body of the HTTP response

    Returns:
      The body de-serialized as a Python object.
    """
    _abstract()


class JsonModel(BaseModel):
  """Model class for JSON.

  Serializes and de-serializes between JSON and the Python
  object representation of HTTP request and response bodies.
  """
  accept = 'application/json'
  content_type = 'application/json'
  alt_param = 'json'

  def __init__(self, data_wrapper=False):
    """Construct a JsonModel.

    Args:
      data_wrapper: boolean, wrap requests and responses in a data wrapper
    """
    self._data_wrapper = data_wrapper

  def serialize(self, body_value):
    if (isinstance(body_value, dict) and 'data' not in body_value and
        self._data_wrapper):
      body_value = {'data': body_value}
    return simplejson.dumps(body_value)

  def deserialize(self, content):
    body = simplejson.loads(content)
    if isinstance(body, dict) and 'data' in body:
      body = body['data']
    return body

  @property
  def no_content_response(self):
    return {}


class ProtocolBufferModel(BaseModel):
  """Model class for protocol buffers.

  Serializes and de-serializes the binary protocol buffer sent in the HTTP
  request and response bodies.
  """
  accept = 'application/x-protobuf'
  content_type = 'application/x-protobuf'
  alt_param = 'proto'

  def __init__(self, protocol_buffer):
    """Constructs a ProtocolBufferModel.

    The serialzed protocol buffer returned in an HTTP response will be
    de-serialized using the given protocol buffer class.

    Args:
      protocol_buffer: The protocol buffer class used to de-serialize a response
          from the API.
    """
    self._protocol_buffer = protocol_buffer

  def serialize(self, body_value):
    return body_value.SerializeToString()

  def deserialize(self, content):
    return self._protocol_buffer.FromString(content)

  @property
  def no_content_response(self):
    return self._protocol_buffer()


def makepatch(original, modified):
  """Create a patch object.

  Some methods support PATCH, an efficient way to send updates to a resource.
  This method allows the easy construction of patch bodies by looking at the
  differences between a resource before and after it was modified.

  Args:
    original: object, the original deserialized resource
    modified: object, the modified deserialized resource
  Returns:
    An object that contains only the changes from original to modified, in a
    form suitable to pass to a PATCH method.

  Example usage:
    item = service.activities().get(postid=postid, userid=userid).execute()
    original = copy.deepcopy(item)
    item['object']['content'] = 'This is updated.'
    service.activities.patch(postid=postid, userid=userid,
      body=makepatch(original, item)).execute()
  """
  patch = {}
  for key, original_value in original.iteritems():
    modified_value = modified.get(key, None)
    if modified_value is None:
      # Use None to signal that the element is deleted
      patch[key] = None
    elif original_value != modified_value:
      if type(original_value) == type({}):
        # Recursively descend objects
        patch[key] = makepatch(original_value, modified_value)
      else:
        # In the case of simple types or arrays we just replace
        patch[key] = modified_value
    else:
      # Don't add anything to patch if there's no change
      pass
  for key in modified:
    if key not in original:
      patch[key] = modified[key]

  return patch