# 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.
"""Helper class for streaming resumable uploads."""
import collections
import os
from gslib.exception import CommandException
from gslib.util import GetJsonResumableChunkSize
class ResumableStreamingJsonUploadWrapper(object):
"""Wraps an input stream in a buffer for resumable uploads.
This class takes a non-seekable input stream, buffers it, and exposes it
as a stream with limited seek capabilities such that it can be used in a
resumable JSON API upload.
max_buffer_size bytes of buffering is supported.
"""
def __init__(self, stream, max_buffer_size, test_small_buffer=False):
"""Initializes the wrapper.
Args:
stream: Input stream.
max_buffer_size: Maximum size of internal buffer; should be >= the chunk
size of the resumable upload API to ensure that at least one full
chunk write can be replayed in the event of a server error.
test_small_buffer: Skip check for buffer size vs. chunk size, for testing.
"""
self._orig_fp = stream
if not test_small_buffer and max_buffer_size < GetJsonResumableChunkSize():
raise CommandException('Resumable streaming upload created with buffer '
'size %s, JSON resumable upload chunk size %s. '
'Buffer size must be >= JSON resumable upload '
'chunk size to ensure that uploads can be '
'resumed.' % (max_buffer_size,
GetJsonResumableChunkSize()))
self._max_buffer_size = max_buffer_size
self._buffer = collections.deque()
self._buffer_start = 0
self._buffer_end = 0
self._position = 0
def read(self, size=-1): # pylint: disable=invalid-name
""""Reads from the wrapped stream.
Args:
size: The amount of bytes to read. If omitted or negative, the entire
contents of the stream will be read and returned.
Returns:
Bytes from the wrapped stream.
"""
read_all_bytes = size is None or size < 0
if read_all_bytes:
bytes_remaining = self._max_buffer_size
else:
bytes_remaining = size
data = b''
buffered_data = []
if self._position < self._buffer_end:
# There was a backwards seek, so read from the buffer first.
# TODO: Performance test to validate if it is worth re-aligning
# the buffers in this case. Also, seeking through the buffer for
# each read on a long catch-up is probably not performant, but we'd
# need a more complex data structure than a deque to get around this.
pos_in_buffer = self._buffer_start
buffer_index = 0
# First, find the start position in the buffer.
while pos_in_buffer + len(self._buffer[buffer_index]) < self._position:
# When this loop exits, buffer_index will refer to a buffer that
# has at least some overlap with self._position, and
# pos_in_buffer will be >= self._position
pos_in_buffer += len(self._buffer[buffer_index])
buffer_index += 1
# Read until we've read enough or we're out of buffer.
while pos_in_buffer < self._buffer_end and bytes_remaining > 0:
buffer_len = len(self._buffer[buffer_index])
# This describes how far into the current buffer self._position is.
offset_from_position = self._position - pos_in_buffer
bytes_available_this_buffer = buffer_len - offset_from_position
read_size = min(bytes_available_this_buffer, bytes_remaining)
buffered_data.append(
self._buffer[buffer_index]
[offset_from_position:offset_from_position + read_size])
bytes_remaining -= read_size
pos_in_buffer += buffer_len
buffer_index += 1
self._position += read_size
# At this point we're guaranteed that if there are any bytes left to read,
# then self._position == self._buffer_end, and we can read from the
# wrapped stream if needed.
if read_all_bytes:
# TODO: The user is requesting reading until the end of an
# arbitrary length stream, which is bad we'll need to return data
# with no size limits; if the stream is sufficiently long, we could run
# out of memory. We could break this down into smaller reads and
# buffer it as we go, but we're still left returning the data all at
# once to the caller. We could raise, but for now trust the caller to
# be sane and have enough memory to hold the remaining stream contents.
new_data = self._orig_fp.read(size)
data_len = len(new_data)
if not buffered_data:
data = new_data
else:
buffered_data.append(new_data)
data = b''.join(buffered_data)
self._position += data_len
elif bytes_remaining:
new_data = self._orig_fp.read(bytes_remaining)
if not buffered_data:
data = new_data
else:
buffered_data.append(new_data)
data = b''.join(buffered_data)
data_len = len(new_data)
if data_len:
self._position += data_len
self._buffer.append(new_data)
self._buffer_end += data_len
oldest_data = None
while self._buffer_end - self._buffer_start > self._max_buffer_size:
oldest_data = self._buffer.popleft()
self._buffer_start += len(oldest_data)
if oldest_data:
refill_amount = self._max_buffer_size - (self._buffer_end -
self._buffer_start)
if refill_amount:
self._buffer.appendleft(oldest_data[-refill_amount:])
self._buffer_start -= refill_amount
else:
data = b''.join(buffered_data) if buffered_data else b''
return data
def tell(self): # pylint: disable=invalid-name
"""Returns the current stream position."""
return self._position
def seekable(self): # pylint: disable=invalid-name
"""Returns true since limited seek support exists."""
return True
def seek(self, offset, whence=os.SEEK_SET): # pylint: disable=invalid-name
"""Seeks on the buffered stream.
Args:
offset: The offset to seek to; must be within the buffer bounds.
whence: Must be os.SEEK_SET.
Raises:
CommandException if an unsupported seek mode or position is used.
"""
if whence == os.SEEK_SET:
if offset < self._buffer_start or offset > self._buffer_end:
raise CommandException('Unable to resume upload because of limited '
'buffering available for streaming uploads. '
'Offset %s was requested, but only data from '
'%s to %s is buffered.' %
(offset, self._buffer_start, self._buffer_end))
# Move to a position within the buffer.
self._position = offset
elif whence == os.SEEK_END:
if offset > self._max_buffer_size:
raise CommandException('Invalid SEEK_END offset %s on streaming '
'upload. Only %s can be buffered.' %
(offset, self._max_buffer_size))
# Read to the end and rely on buffering to handle the offset.
while self.read(self._max_buffer_size):
pass
# Now we're at the end.
self._position -= offset
else:
raise CommandException('Invalid seek mode on streaming upload. '
'(mode %s, offset %s)' % (whence, offset))
def close(self): # pylint: disable=invalid-name
return self._orig_fp.close()