[chrome-devtools-frontend] Migrate to cloudstorage client

gae/cloudstorage/storage_api.py

+# Copyright 2012 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.
+
+"""Python wrappers for the Google Storage RESTful API."""
+
+
+
+
+
+__all__ = ['ReadBuffer',
+           'StreamingBuffer',
+          ]
+
+import collections
+import os
+import urlparse
+
+from . import api_utils
+from . import common
+from . import errors
+from . import rest_api
+
+try:
+  from google.appengine.api import urlfetch
+  from google.appengine.ext import ndb
+except ImportError:
+  from google.appengine.api import urlfetch
+  from google.appengine.ext import ndb
+
+
+
+def _get_storage_api(retry_params, account_id=None):
+  """Returns storage_api instance for API methods.
+
+  Args:
+    retry_params: An instance of api_utils.RetryParams. If none,
+     thread's default will be used.
+    account_id: Internal-use only.
+
+  Returns:
+    A storage_api instance to handle urlfetch work to GCS.
+    On dev appserver, this instance by default will talk to a local stub
+    unless common.ACCESS_TOKEN is set. That token will be used to talk
+    to the real GCS.
+  """
+
+
+  api = _StorageApi(_StorageApi.full_control_scope,
+                    service_account_id=account_id,
+                    retry_params=retry_params)
+  if common.local_run() and not common.get_access_token():
+    api.api_url = common.local_api_url()
+  if common.get_access_token():
+    api.token = common.get_access_token()
+  return api
+
+
+class _StorageApi(rest_api._RestApi):
+  """A simple wrapper for the Google Storage RESTful API.
+
+  WARNING: Do NOT directly use this api. It's an implementation detail
+  and is subject to change at any release.
+
+  All async methods have similar args and returns.
+
+  Args:
+    path: The path to the Google Storage object or bucket, e.g.
+      '/mybucket/myfile' or '/mybucket'.
+    **kwd: Options for urlfetch. e.g.
+      headers={'content-type': 'text/plain'}, payload='blah'.
+
+  Returns:
+    A ndb Future. When fulfilled, future.get_result() should return
+    a tuple of (status, headers, content) that represents a HTTP response
+    of Google Cloud Storage XML API.
+  """
+
+  api_url = 'https://storage.googleapis.com'
+  read_only_scope = 'https://www.googleapis.com/auth/devstorage.read_only'
+  read_write_scope = 'https://www.googleapis.com/auth/devstorage.read_write'
+  full_control_scope = 'https://www.googleapis.com/auth/devstorage.full_control'
+
+  def __getstate__(self):
+    """Store state as part of serialization/pickling.
+
+    Returns:
+      A tuple (of dictionaries) with the state of this object
+    """
+    return (super(_StorageApi, self).__getstate__(), {'api_url': self.api_url})
+
+  def __setstate__(self, state):
+    """Restore state as part of deserialization/unpickling.
+
+    Args:
+      state: the tuple from a __getstate__ call
+    """
+    superstate, localstate = state
+    super(_StorageApi, self).__setstate__(superstate)
+    self.api_url = localstate['api_url']
+
+  @api_utils._eager_tasklet
+  @ndb.tasklet
+  def do_request_async(self, url, method='GET', headers=None, payload=None,
+                       deadline=None, callback=None):
+    """Inherit docs.
+
+    This method translates urlfetch exceptions to more service specific ones.
+    """
+    if headers is None:
+      headers = {}
+    if 'x-goog-api-version' not in headers:
+      headers['x-goog-api-version'] = '2'
+    headers['accept-encoding'] = 'gzip, *'
+    try:
+      resp_tuple = yield super(_StorageApi, self).do_request_async(
+          url, method=method, headers=headers, payload=payload,
+          deadline=deadline, callback=callback)
+    except urlfetch.DownloadError, e:
+      raise errors.TimeoutError(
+          'Request to Google Cloud Storage timed out.', e)
+
+    raise ndb.Return(resp_tuple)
+
+
+  def post_object_async(self, path, **kwds):
+    """POST to an object."""
+    return self.do_request_async(self.api_url + path, 'POST', **kwds)
+
+  def put_object_async(self, path, **kwds):
+    """PUT an object."""
+    return self.do_request_async(self.api_url + path, 'PUT', **kwds)
+
+  def get_object_async(self, path, **kwds):
+    """GET an object.
+
+    Note: No payload argument is supported.
+    """
+    return self.do_request_async(self.api_url + path, 'GET', **kwds)
+
+  def delete_object_async(self, path, **kwds):
+    """DELETE an object.
+
+    Note: No payload argument is supported.
+    """
+    return self.do_request_async(self.api_url + path, 'DELETE', **kwds)
+
+  def head_object_async(self, path, **kwds):
+    """HEAD an object.
+
+    Depending on request headers, HEAD returns various object properties,
+    e.g. Content-Length, Last-Modified, and ETag.
+
+    Note: No payload argument is supported.
+    """
+    return self.do_request_async(self.api_url + path, 'HEAD', **kwds)
+
+  def get_bucket_async(self, path, **kwds):
+    """GET a bucket."""
+    return self.do_request_async(self.api_url + path, 'GET', **kwds)
+
+  # pylint: disable=too-many-locals
+  def compose_object(self, file_list, destination_file, content_type):
+    """COMPOSE multiple objects together.
+
+    Using the given list of files calls the put object with the compose flag.
+    This call merges all the files into the destination file.
+        
+    Args:
+      file_list: list of dicts with the file name.
+      destination_file: Path to the destination file.
+      content_type: Content type for the destination file.
+    """
+
+    xml_setting_list = ['<ComposeRequest>']
+
+    for meta_data in file_list:
+      xml_setting_list.append('<Component>')
+      for key, val in meta_data.iteritems():
+        xml_setting_list.append('<%s>%s</%s>' % (key, val, key))
+      xml_setting_list.append('</Component>')
+    xml_setting_list.append('</ComposeRequest>')
+    xml = ''.join(xml_setting_list)
+
+    if content_type is not None:
+      headers = {'Content-Type': content_type}
+    else:
+      headers = None
+    # pylint: disable=no-member
+    status, resp_headers, content = self.put_object(
+        api_utils._quote_filename(destination_file) + '?compose',
+        payload=xml,
+        headers=headers)
+    errors.check_status(status, [200], destination_file, resp_headers, body=content)
+
+
+_StorageApi = rest_api.add_sync_methods(_StorageApi)
+
+
+class ReadBuffer(object):
+  """A class for reading Google storage files."""
+
+  DEFAULT_BUFFER_SIZE = 1024 * 1024
+  MAX_REQUEST_SIZE = 30 * DEFAULT_BUFFER_SIZE
+
+  def __init__(self,
+               api,
+               path,
+               offset=0,
+               buffer_size=DEFAULT_BUFFER_SIZE,
+               max_request_size=MAX_REQUEST_SIZE):
+    """Constructor.
+
+    Args:
+      api: A StorageApi instance.
+      path: Quoted/escaped path to the object, e.g. /mybucket/myfile
+      buffer_size: buffer size. The ReadBuffer keeps
+        one buffer. But there may be a pending future that contains
+        a second buffer. This size must be less than max_request_size.
+      max_request_size: Max bytes to request in one urlfetch.
+      offset: Number of bytes to skip at the start of the file. If None, 0 is
+        used.
+    """
+    self._api = api
+    self._path = path
+    self.name = api_utils._unquote_filename(path)
+    self.closed = False
+
+    assert buffer_size <= max_request_size
+    self._buffer_size = buffer_size
+    self._max_request_size = max_request_size
+    self._offset = offset
+    self._buffer = _Buffer()
+    self._etag = None
+
+    get_future = self._get_segment(offset, self._buffer_size, check_response=False)
+
+    status, headers, content = self._api.head_object(path)
+    errors.check_status(status, [200], path, resp_headers=headers, body=content)
+    self._file_size = long(common.get_stored_content_length(headers))
+    self._check_etag(headers.get('etag'))
+
+    self._buffer_future = None
+
+    if self._file_size != 0:
+      content, check_response_closure = get_future.get_result()
+      check_response_closure()
+      self._buffer.reset(content)
+      self._request_next_buffer()
+
+  def __getstate__(self):
+    """Store state as part of serialization/pickling.
+
+    The contents of the read buffer are not stored, only the current offset for
+    data read by the client. A new read buffer is established at unpickling.
+    The head information for the object (file size and etag) are stored to
+    reduce startup and ensure the file has not changed.
+
+    Returns:
+      A dictionary with the state of this object
+    """
+    return {'api': self._api,
+            'path': self._path,
+            'buffer_size': self._buffer_size,
+            'request_size': self._max_request_size,
+            'etag': self._etag,
+            'size': self._file_size,
+            'offset': self._offset,
+            'closed': self.closed}
+
+  def __setstate__(self, state):
+    """Restore state as part of deserialization/unpickling.
+
+    Args:
+      state: the dictionary from a __getstate__ call
+
+    Along with restoring the state, pre-fetch the next read buffer.
+    """
+    self._api = state['api']
+    self._path = state['path']
+    self.name = api_utils._unquote_filename(self._path)
+    self._buffer_size = state['buffer_size']
+    self._max_request_size = state['request_size']
+    self._etag = state['etag']
+    self._file_size = state['size']
+    self._offset = state['offset']
+    self._buffer = _Buffer()
+    self.closed = state['closed']
+    self._buffer_future = None
+    if self._remaining() and not self.closed:
+      self._request_next_buffer()
+
+  def __iter__(self):
+    """Iterator interface.
+
+    Note the ReadBuffer container itself is the iterator. It's
+    (quote PEP0234)
+    'destructive: they consumes all the values and a second iterator
+    cannot easily be created that iterates independently over the same values.
+    You could open the file for the second time, or seek() to the beginning.'
+
+    Returns:
+      Self.
+    """
+    return self
+
+  def next(self):
+    line = self.readline()
+    if not line:
+      raise StopIteration()
+    return line
+
+  def readline(self, size=-1):
+    """Read one line delimited by '\n' from the file.
+
+    A trailing newline character is kept in the string. It may be absent when a
+    file ends with an incomplete line. If the size argument is non-negative,
+    it specifies the maximum string size (counting the newline) to return.
+    A negative size is the same as unspecified. Empty string is returned
+    only when EOF is encountered immediately.
+
+    Args:
+      size: Maximum number of bytes to read. If not specified, readline stops
+        only on '\n' or EOF.
+
+    Returns:
+      The data read as a string.
+
+    Raises:
+      IOError: When this buffer is closed.
+    """
+    self._check_open()
+    if size == 0 or not self._remaining():
+      return ''
+
+    data_list = []
+    newline_offset = self._buffer.find_newline(size)
+    while newline_offset < 0:
+      data = self._buffer.read(size)
+      size -= len(data)
+      self._offset += len(data)
+      data_list.append(data)
+      if size == 0 or not self._remaining():
+        return ''.join(data_list)
+      self._buffer.reset(self._buffer_future.get_result())
+      self._request_next_buffer()
+      newline_offset = self._buffer.find_newline(size)
+
+    data = self._buffer.read_to_offset(newline_offset + 1)
+    self._offset += len(data)
+    data_list.append(data)
+
+    return ''.join(data_list)
+
+  def read(self, size=-1):
+    """Read data from RAW file.
+
+    Args:
+      size: Number of bytes to read as integer. Actual number of bytes
+        read is always equal to size unless EOF is reached. If size is
+        negative or unspecified, read the entire file.
+
+    Returns:
+      data read as str.
+
+    Raises:
+      IOError: When this buffer is closed.
+    """
+    self._check_open()
+    if not self._remaining():
+      return ''
+
+    data_list = []
+    while True:
+      remaining = self._buffer.remaining()
+      if size >= 0 and size < remaining:
+        data_list.append(self._buffer.read(size))
+        self._offset += size
+        break
+      else:
+        size -= remaining
+        self._offset += remaining
+        data_list.append(self._buffer.read())
+
+        if self._buffer_future is None:
+          if size < 0 or size >= self._remaining():
+            needs = self._remaining()
+          else:
+            needs = size
+          data_list.extend(self._get_segments(self._offset, needs))
+          self._offset += needs
+          break
+
+        if self._buffer_future:
+          self._buffer.reset(self._buffer_future.get_result())
+          self._buffer_future = None
+
+    if self._buffer_future is None:
+      self._request_next_buffer()
+    return ''.join(data_list)
+
+  def _remaining(self):
+    return self._file_size - self._offset
+
+  def _request_next_buffer(self):
+    """Request next buffer.
+
+    Requires self._offset and self._buffer are in consistent state.
+    """
+    self._buffer_future = None
+    next_offset = self._offset + self._buffer.remaining()
+    if next_offset != self._file_size:
+      self._buffer_future = self._get_segment(next_offset,
+                                              self._buffer_size)
+
+  def _get_segments(self, start, request_size):
+    """Get segments of the file from Google Storage as a list.
+
+    A large request is broken into segments to avoid hitting urlfetch
+    response size limit. Each segment is returned from a separate urlfetch.
+
+    Args:
+      start: start offset to request. Inclusive. Have to be within the
+        range of the file.
+      request_size: number of bytes to request.
+
+    Returns:
+      A list of file segments in order
+    """
+    if not request_size:
+      return []
+
+    end = start + request_size
+    futures = []
+
+    while request_size > self._max_request_size:
+      futures.append(self._get_segment(start, self._max_request_size))
+      request_size -= self._max_request_size
+      start += self._max_request_size
+    if start < end:
+      futures.append(self._get_segment(start, end - start))
+    return [fut.get_result() for fut in futures]
+
+  @ndb.tasklet
+  def _get_segment(self, start, request_size, check_response=True):
+    """Get a segment of the file from Google Storage.
+
+    Args:
+      start: start offset of the segment. Inclusive. Have to be within the
+        range of the file.
+      request_size: number of bytes to request. Have to be small enough
+        for a single urlfetch request. May go over the logical range of the
+        file.
+      check_response: True to check the validity of GCS response automatically
+        before the future returns. False otherwise. See Yields section.
+
+    Yields:
+      If check_response is True, the segment [start, start + request_size)
+      of the file.
+      Otherwise, a tuple. The first element is the unverified file segment.
+      The second element is a closure that checks response. Caller should
+      first invoke the closure before consuing the file segment.
+
+    Raises:
+      ValueError: if the file has changed while reading.
+    """
+    end = start + request_size - 1
+    content_range = '%d-%d' % (start, end)
+    headers = {'Range': 'bytes=' + content_range}
+    status, resp_headers, content = yield self._api.get_object_async(
+        self._path, headers=headers)
+    def _checker():
+      errors.check_status(status, [200, 206], self._path, headers,
+                          resp_headers, body=content)
+      self._check_etag(resp_headers.get('etag'))
+    if check_response:
+      _checker()
+      raise ndb.Return(content)
+    raise ndb.Return(content, _checker)
+
+  def _check_etag(self, etag):
+    """Check if etag is the same across requests to GCS.
+
+    If self._etag is None, set it. If etag is set, check that the new
+    etag equals the old one.
+
+    In the __init__ method, we fire one HEAD and one GET request using
+    ndb tasklet. One of them would return first and set the first value.
+
+    Args:
+      etag: etag from a GCS HTTP response. None if etag is not part of the
+        response header. It could be None for example in the case of GCS
+        composite file.
+
+    Raises:
+      ValueError: if two etags are not equal.
+    """
+    if etag is None:
+      return
+    elif self._etag is None:
+      self._etag = etag
+    elif self._etag != etag:
+      raise ValueError('File on GCS has changed while reading.')
+
+  def close(self):
+    self.closed = True
+    self._buffer = None
+    self._buffer_future = None
+
+  def __enter__(self):
+    return self
+
+  def __exit__(self, atype, value, traceback):
+    self.close()
+    return False
+
+  def seek(self, offset, whence=os.SEEK_SET):
+    """Set the file's current offset.
+
+    Note if the new offset is out of bound, it is adjusted to either 0 or EOF.
+
+    Args:
+      offset: seek offset as number.
+      whence: seek mode. Supported modes are os.SEEK_SET (absolute seek),
+        os.SEEK_CUR (seek relative to the current position), and os.SEEK_END
+        (seek relative to the end, offset should be negative).
+
+    Raises:
+      IOError: When this buffer is closed.
+      ValueError: When whence is invalid.
+    """
+    self._check_open()
+
+    self._buffer.reset()
+    self._buffer_future = None
+
+    if whence == os.SEEK_SET:
+      self._offset = offset
+    elif whence == os.SEEK_CUR:
+      self._offset += offset
+    elif whence == os.SEEK_END:
+      self._offset = self._file_size + offset
+    else:
+      raise ValueError('Whence mode %s is invalid.' % str(whence))
+
+    self._offset = min(self._offset, self._file_size)
+    self._offset = max(self._offset, 0)
+    if self._remaining():
+      self._request_next_buffer()
+
+  def tell(self):
+    """Tell the file's current offset.
+
+    Returns:
+      current offset in reading this file.
+
+    Raises:
+      IOError: When this buffer is closed.
+    """
+    self._check_open()
+    return self._offset
+
+  def _check_open(self):
+    if self.closed:
+      raise IOError('Buffer is closed.')
+
+  def seekable(self):
+    return True
+
+  def readable(self):
+    return True
+
+  def writable(self):
+    return False
+
+
+class _Buffer(object):
+  """In memory buffer."""
+
+  def __init__(self):
+    self.reset()
+
+  def reset(self, content='', offset=0):
+    self._buffer = content
+    self._offset = offset
+
+  def read(self, size=-1):
+    """Returns bytes from self._buffer and update related offsets.
+
+    Args:
+      size: number of bytes to read starting from current offset.
+        Read the entire buffer if negative.
+
+    Returns:
+      Requested bytes from buffer.
+    """
+    if size < 0:
+      offset = len(self._buffer)
+    else:
+      offset = self._offset + size
+    return self.read_to_offset(offset)
+
+  def read_to_offset(self, offset):
+    """Returns bytes from self._buffer and update related offsets.
+
+    Args:
+      offset: read from current offset to this offset, exclusive.
+
+    Returns:
+      Requested bytes from buffer.
+    """
+    assert offset >= self._offset
+    result = self._buffer[self._offset: offset]
+    self._offset += len(result)
+    return result
+
+  def remaining(self):
+    return len(self._buffer) - self._offset
+
+  def find_newline(self, size=-1):
+    """Search for newline char in buffer starting from current offset.
+
+    Args:
+      size: number of bytes to search. -1 means all.
+
+    Returns:
+      offset of newline char in buffer. -1 if doesn't exist.
+    """
+    if size < 0:
+      return self._buffer.find('\n', self._offset)
+    return self._buffer.find('\n', self._offset, self._offset + size)
+
+
+class StreamingBuffer(object):
+  """A class for creating large objects using the 'resumable' API.
+
+  The API is a subset of the Python writable stream API sufficient to
+  support writing zip files using the zipfile module.
+
+  The exact sequence of calls and use of headers is documented at
+  https://developers.google.com/storage/docs/developer-guide#unknownresumables
+  """
+
+  _blocksize = 256 * 1024
+
+  _flushsize = 8 * _blocksize
+
+  _maxrequestsize = 9 * 4 * _blocksize
+
+  def __init__(self,
+               api,
+               path,
+               content_type=None,
+               gcs_headers=None):
+    """Constructor.
+
+    Args:
+      api: A StorageApi instance.
+      path: Quoted/escaped path to the object, e.g. /mybucket/myfile
+      content_type: Optional content-type; Default value is
+        delegate to Google Cloud Storage.
+      gcs_headers: additional gs headers as a str->str dict, e.g
+        {'x-goog-acl': 'private', 'x-goog-meta-foo': 'foo'}.
+    Raises:
+      IOError: When this location can not be found.
+    """
+    assert self._maxrequestsize > self._blocksize
+    assert self._maxrequestsize % self._blocksize == 0
+    assert self._maxrequestsize >= self._flushsize
+
+    self._api = api
+    self._path = path
+
+    self.name = api_utils._unquote_filename(path)
+    self.closed = False
+
+    self._buffer = collections.deque()
+    self._buffered = 0
+    self._written = 0
+    self._offset = 0
+
+    headers = {'x-goog-resumable': 'start'}
+    if content_type:
+      headers['content-type'] = content_type
+    if gcs_headers:
+      headers.update(gcs_headers)
+    status, resp_headers, content = self._api.post_object(path, headers=headers)
+    errors.check_status(status, [201], path, headers, resp_headers,
+                        body=content)
+    loc = resp_headers.get('location')
+    if not loc:
+      raise IOError('No location header found in 201 response')
+    parsed = urlparse.urlparse(loc)
+    self._path_with_token = '%s?%s' % (self._path, parsed.query)
+
+  def __getstate__(self):
+    """Store state as part of serialization/pickling.
+
+    The contents of the write buffer are stored. Writes to the underlying
+    storage are required to be on block boundaries (_blocksize) except for the
+    last write. In the worst case the pickled version of this object may be
+    slightly larger than the blocksize.
+
+    Returns:
+      A dictionary with the state of this object
+
+    """
+    return {'api': self._api,
+            'path': self._path,
+            'path_token': self._path_with_token,
+            'buffer': self._buffer,
+            'buffered': self._buffered,
+            'written': self._written,
+            'offset': self._offset,
+            'closed': self.closed}
+
+  def __setstate__(self, state):
+    """Restore state as part of deserialization/unpickling.
+
+    Args:
+      state: the dictionary from a __getstate__ call
+    """
+    self._api = state['api']
+    self._path_with_token = state['path_token']
+    self._buffer = state['buffer']
+    self._buffered = state['buffered']
+    self._written = state['written']
+    self._offset = state['offset']
+    self.closed = state['closed']
+    self._path = state['path']
+    self.name = api_utils._unquote_filename(self._path)
+
+  def write(self, data):
+    """Write some bytes.
+
+    Args:
+      data: data to write. str.
+
+    Raises:
+      TypeError: if data is not of type str.
+    """
+    self._check_open()
+    if not isinstance(data, str):
+      raise TypeError('Expected str but got %s.' % type(data))
+    if not data:
+      return
+    self._buffer.append(data)
+    self._buffered += len(data)
+    self._offset += len(data)
+    if self._buffered >= self._flushsize:
+      self._flush()
+
+  def flush(self):
+    """Flush as much as possible to GCS.
+
+    GCS *requires* that all writes except for the final one align on
+    256KB boundaries. So the internal buffer may still have < 256KB bytes left
+    after flush.
+    """
+    self._check_open()
+    self._flush(finish=False)
+
+  def tell(self):
+    """Return the total number of bytes passed to write() so far.
+
+    (There is no seek() method.)
+    """
+    return self._offset
+
+  def close(self):
+    """Flush the buffer and finalize the file.
+
+    When this returns the new file is available for reading.
+    """
+    if not self.closed:
+      self.closed = True
+      self._flush(finish=True)
+      self._buffer = None
+
+  def __enter__(self):
+    return self
+
+  def __exit__(self, atype, value, traceback):
+    self.close()
+    return False
+
+  def _flush(self, finish=False):
+    """Internal API to flush.
+
+    Buffer is flushed to GCS only when the total amount of buffered data is at
+    least self._blocksize, or to flush the final (incomplete) block of
+    the file with finish=True.
+    """
+    while ((finish and self._buffered >= 0) or
+           (not finish and self._buffered >= self._blocksize)):
+      tmp_buffer = []
+      tmp_buffer_len = 0
+
+      excess = 0
+      while self._buffer:
+        buf = self._buffer.popleft()
+        size = len(buf)
+        self._buffered -= size
+        tmp_buffer.append(buf)
+        tmp_buffer_len += size
+        if tmp_buffer_len >= self._maxrequestsize:
+          excess = tmp_buffer_len - self._maxrequestsize
+          break
+        if not finish and (
+            tmp_buffer_len % self._blocksize + self._buffered <
+            self._blocksize):
+          excess = tmp_buffer_len % self._blocksize
+          break
+
+      if excess:
+        over = tmp_buffer.pop()
+        size = len(over)
+        assert size >= excess
+        tmp_buffer_len -= size
+        head, tail = over[:-excess], over[-excess:]
+        self._buffer.appendleft(tail)
+        self._buffered += len(tail)
+        if head:
+          tmp_buffer.append(head)
+          tmp_buffer_len += len(head)
+
+      data = ''.join(tmp_buffer)
+      file_len = '*'
+      if finish and not self._buffered:
+        file_len = self._written + len(data)
+      self._send_data(data, self._written, file_len)
+      self._written += len(data)
+      if file_len != '*':
+        break
+
+  def _send_data(self, data, start_offset, file_len):
+    """Send the block to the storage service.
+
+    This is a utility method that does not modify self.
+
+    Args:
+      data: data to send in str.
+      start_offset: start offset of the data in relation to the file.
+      file_len: an int if this is the last data to append to the file.
+        Otherwise '*'.
+    """
+    headers = {}
+    end_offset = start_offset + len(data) - 1
+
+    if data:
+      headers['content-range'] = ('bytes %d-%d/%s' %
+                                  (start_offset, end_offset, file_len))
+    else:
+      headers['content-range'] = ('bytes */%s' % file_len)
+
+    status, response_headers, content = self._api.put_object(
+        self._path_with_token, payload=data, headers=headers)
+    if file_len == '*':
+      expected = 308
+    else:
+      expected = 200
+    errors.check_status(status, [expected], self._path, headers,
+                        response_headers, content,
+                        {'upload_path': self._path_with_token})
+
+  def _get_offset_from_gcs(self):
+    """Get the last offset that has been written to GCS.
+
+    This is a utility method that does not modify self.
+
+    Returns:
+      an int of the last offset written to GCS by this upload, inclusive.
+      -1 means nothing has been written.
+    """
+    headers = {'content-range': 'bytes */*'}
+    status, response_headers, content = self._api.put_object(
+        self._path_with_token, headers=headers)
+    errors.check_status(status, [308], self._path, headers,
+                        response_headers, content,
+                        {'upload_path': self._path_with_token})
+    val = response_headers.get('range')
+    if val is None:
+      return -1
+    _, offset = val.rsplit('-', 1)
+    return int(offset)
+
+  def _force_close(self, file_length=None):
+    """Close this buffer on file_length.
+
+    Finalize this upload immediately on file_length.
+    Contents that are still in memory will not be uploaded.
+
+    This is a utility method that does not modify self.
+
+    Args:
+      file_length: file length. Must match what has been uploaded. If None,
+        it will be queried from GCS.
+    """
+    if file_length is None:
+      file_length = self._get_offset_from_gcs() + 1
+    self._send_data('', 0, file_length)
+
+  def _check_open(self):
+    if self.closed:
+      raise IOError('Buffer is closed.')
+
+  def seekable(self):
+    return False
+
+  def readable(self):
+    return False
+
+  def writable(self):
+    return True