# -*- coding: utf-8 -*-
"""
h2/frame_buffer
~~~~~~~~~~~~~~~
A data structure that provides a way to iterate over a byte buffer in terms of
frames.
"""
from vinetrimmer.vendor.hyperframe.exceptions import UnknownFrameError, InvalidFrameError
from vinetrimmer.vendor.hyperframe.frame import (
Frame, HeadersFrame, ContinuationFrame, PushPromiseFrame
)
from .exceptions import (
ProtocolError, FrameTooLargeError, FrameDataMissingError
)
# To avoid a DOS attack based on sending loads of continuation frames, we limit
# the maximum number we're perpared to receive. In this case, we'll set the
# limit to 64, which means the largest encoded header block we can receive by
# default is 262144 bytes long, and the largest possible *at all* is 1073741760
# bytes long.
#
# This value seems reasonable for now, but in future we may want to evaluate
# making it configurable.
CONTINUATION_BACKLOG = 64
class FrameBuffer(object):
"""
This is a data structure that expects to act as a buffer for HTTP/2 data
that allows iteraton in terms of H2 frames.
"""
def __init__(self, server=False):
self.data = b''
self.max_frame_size = 0
self._preamble = b'PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n' if server else b''
self._preamble_len = len(self._preamble)
self._headers_buffer = []
def add_data(self, data):
"""
Add more data to the frame buffer.
:param data: A bytestring containing the byte buffer.
"""
if self._preamble_len:
data_len = len(data)
of_which_preamble = min(self._preamble_len, data_len)
if self._preamble[:of_which_preamble] != data[:of_which_preamble]:
raise ProtocolError("Invalid HTTP/2 preamble.")
data = data[of_which_preamble:]
self._preamble_len -= of_which_preamble
self._preamble = self._preamble[of_which_preamble:]
self.data += data
def _parse_frame_header(self, data):
"""
Parses the frame header from the data. Either returns a tuple of
(frame, length), or throws an exception. The returned frame may be None
if the frame is of unknown type.
"""
try:
frame, length = Frame.parse_frame_header(data[:9])
except UnknownFrameError as e: # Platform-specific: Hyperframe < 5.0
# Here we do something a bit odd. We want to consume the frame data
# as consistently as possible, but we also don't ever want to yield
# None. Instead, we make sure that, if there is no frame, we
# recurse into ourselves.
# This can only happen now on older versions of hyperframe.
# TODO: Remove in 3.0
length = e.length
frame = None
except ValueError as e:
# The frame header is invalid. This is a ProtocolError
raise ProtocolError("Invalid frame header received: %s" % str(e))
return frame, length
def _validate_frame_length(self, length):
"""
Confirm that the frame is an appropriate length.
"""
if length > self.max_frame_size:
raise FrameTooLargeError(
"Received overlong frame: length %d, max %d" %
(length, self.max_frame_size)
)
def _update_header_buffer(self, f):
"""
Updates the internal header buffer. Returns a frame that should replace
the current one. May throw exceptions if this frame is invalid.
"""
# Check if we're in the middle of a headers block. If we are, this
# frame *must* be a CONTINUATION frame with the same stream ID as the
# leading HEADERS or PUSH_PROMISE frame. Anything else is a
# ProtocolError. If the frame *is* valid, append it to the header
# buffer.
if self._headers_buffer:
stream_id = self._headers_buffer[0].stream_id
valid_frame = (
f is not None and
isinstance(f, ContinuationFrame) and
f.stream_id == stream_id
)
if not valid_frame:
raise ProtocolError("Invalid frame during header block.")
# Append the frame to the buffer.
self._headers_buffer.append(f)
if len(self._headers_buffer) > CONTINUATION_BACKLOG:
raise ProtocolError("Too many continuation frames received.")
# If this is the end of the header block, then we want to build a
# mutant HEADERS frame that's massive. Use the original one we got,
# then set END_HEADERS and set its data appopriately. If it's not
# the end of the block, lose the current frame: we can't yield it.
if 'END_HEADERS' in f.flags:
f = self._headers_buffer[0]
f.flags.add('END_HEADERS')
f.data = b''.join(x.data for x in self._headers_buffer)
self._headers_buffer = []
else:
f = None
elif (isinstance(f, (HeadersFrame, PushPromiseFrame)) and
'END_HEADERS' not in f.flags):
# This is the start of a headers block! Save the frame off and then
# act like we didn't receive one.
self._headers_buffer.append(f)
f = None
return f
# The methods below support the iterator protocol.
def __iter__(self):
return self
def next(self): # Python 2
# First, check that we have enough data to successfully parse the
# next frame header. If not, bail. Otherwise, parse it.
if len(self.data) < 9:
raise StopIteration()
try:
f, length = self._parse_frame_header(self.data)
except InvalidFrameError: # pragma: no cover
raise ProtocolError("Received frame with invalid frame header.")
# Next, check that we have enough length to parse the frame body. If
# not, bail, leaving the frame header data in the buffer for next time.
if len(self.data) < length + 9:
raise StopIteration()
# Confirm the frame has an appropriate length.
self._validate_frame_length(length)
# Don't try to parse the body if we didn't get a frame we know about:
# there's nothing we can do with it anyway.
if f is not None:
try:
f.parse_body(memoryview(self.data[9:9+length]))
except InvalidFrameError:
raise FrameDataMissingError("Frame data missing or invalid")
# At this point, as we know we'll use or discard the entire frame, we
# can update the data.
self.data = self.data[9+length:]
# Pass the frame through the header buffer.
f = self._update_header_buffer(f)
# If we got a frame we didn't understand or shouldn't yield, rather
# than return None it'd be better if we just tried to get the next
# frame in the sequence instead. Recurse back into ourselves to do
# that. This is safe because the amount of work we have to do here is
# strictly bounded by the length of the buffer.
return f if f is not None else self.next()
def __next__(self): # Python 3
return self.next()