# Copyright 2019-2023 by Vytautas Liuolia.
#
# 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.
"""Multipart form media handler."""
import re
from urllib.parse import unquote_to_bytes
from falcon import errors
from falcon.errors import MultipartParseError
from falcon.media.base import BaseHandler
from falcon.stream import BoundedStream
from falcon.util import BufferedReader
from falcon.util import misc
from falcon.util.mediatypes import parse_header
# TODO(vytas):
# * Better support for form-wide charset setting
# * Clean up, simplify, and optimize BufferedReader
# * Better documentation
_ALLOWED_CONTENT_HEADERS = frozenset(
[
b'content-type',
b'content-disposition',
b'content-transfer-encoding',
]
)
_FILENAME_STAR_RFC5987 = re.compile(r"([\w-]+)'[\w]*'(.+)")
_CRLF = b'\r\n'
_CRLF_CRLF = _CRLF + _CRLF
# TODO(vytas): Consider supporting -charset- stuff.
# Does anyone use that (?)
[docs]
class BodyPart:
"""Represents a body part in a multipart form.
Note:
:class:`BodyPart` is meant to be instantiated directly only by the
:class:`MultipartFormHandler` parser.
Attributes:
content_type (str): Value of the Content-Type header, or the multipart
form default ``text/plain`` if the header is missing.
data (bytes): Property that acts as a convenience alias for
:meth:`~.get_data`.
.. tabs::
.. tab:: WSGI
.. code:: python
# Equivalent to: content = part.get_data()
content = part.data
.. tab:: ASGI
The ``await`` keyword must still be added when referencing
the property::
# Equivalent to: content = await part.get_data()
content = await part.data
name(str): The name parameter of the Content-Disposition header.
The value of the "name" parameter is the original field name from
the submitted HTML form.
.. note::
According to `RFC 7578, section 4.2
<https://tools.ietf.org/html/rfc7578#section-4.2>`__, each part
MUST include a Content-Disposition header field of type
"form-data", where the name parameter is mandatory.
However, Falcon will not raise any error if this parameter is
missing; the property value will be ``None`` in that case.
filename (str): File name if the body part is an attached file, and
``None`` otherwise.
secure_filename (str): The sanitized version of `filename` using only
the most common ASCII characters for maximum portability and safety
wrt using this name as a filename on a regular file system.
If `filename` is empty or unset when referencing this property, an
instance of :class:`.MultipartParseError` will be raised.
See also: :func:`~.secure_filename`
stream: File-like input object for reading the body part of the
multipart form request, if any. This object provides direct access
to the server's data stream and is non-seekable. The stream is
automatically delimited according to the multipart stream boundary.
With the exception of being buffered to keep track of the boundary,
the wrapped body part stream interface and behavior mimic
:attr:`Request.bounded_stream <falcon.Request.bounded_stream>`
(WSGI) and :attr:`Request.stream <falcon.asgi.Request.stream>`
(ASGI), respectively:
.. tabs::
.. tab:: WSGI
Reading the whole part content:
.. code:: python
data = part.stream.read()
This is also safe:
.. code:: python
doc = yaml.safe_load(part.stream)
.. tab:: ASGI
Similarly to
:attr:`BoundedStream <falcon.asgi.BoundedStream>`, the most
efficient way to read the body part content is asynchronous
iteration over part data chunks:
.. code:: python
async for data_chunk in part.stream:
pass
media (object): Property that acts as a convenience alias for
:meth:`~.get_media`.
.. tabs::
.. tab:: WSGI
.. code:: python
# Equivalent to: deserialized_media = part.get_media()
deserialized_media = req.media
.. tab:: ASGI
The ``await`` keyword must still be added when referencing
the property::
# Equivalent to: deserialized_media = await part.get_media()
deserialized_media = await part.media
text (str): Property that acts as a convenience alias for
:meth:`~.get_text`.
.. tabs::
.. tab:: WSGI
.. code:: python
# Equivalent to: decoded_text = part.get_text()
decoded_text = part.text
.. tab:: ASGI
The ``await`` keyword must still be added when referencing
the property::
# Equivalent to: decoded_text = await part.get_text()
decoded_text = await part.text
"""
_content_disposition = None
_data = None
_filename = None
_media = None
_name = None
def __init__(self, stream, headers, parse_options):
self.stream = stream
self._headers = headers
self._parse_options = parse_options
[docs]
def get_data(self):
"""Return the body part content bytes.
The maximum number of bytes that may be read is configurable via
:class:`MultipartParseOptions`, and a :class:`.MultipartParseError` is
raised if the body part is larger that this size.
The size limit guards against reading unexpectedly large amount of data
into memory by referencing :attr:`data` and :attr:`text` properties
that build upon this method.
For large bodies, such as attached files, use the input :attr:`stream`
directly.
Note:
Calling this method the first time will consume the part's input
stream. The result is cached for subsequent access, and follow-up
calls will just retrieve the cached content.
Returns:
bytes: The body part content.
"""
if self._data is None:
max_size = self._parse_options.max_body_part_buffer_size + 1
self._data = self.stream.read(max_size)
if len(self._data) >= max_size:
raise MultipartParseError(description='body part is too large')
return self._data
[docs]
def get_text(self):
"""Return the body part content decoded as a text string.
Text is decoded from the part content (as returned by
:meth:`~.get_data`) using the charset specified in the `Content-Type`
header, or, if omitted, the
:data:`default charset <MultipartParseOptions.default_charset>`.
The charset must be supported by Python's ``bytes.decode()``
function. The list of standard encodings (charsets) supported by the
Python 3 standard library can be found `here
<https://docs.python.org/3/library/codecs.html#standard-encodings>`__.
If decoding fails due to invalid `data` bytes (for the specified
encoding), or the specified encoding itself is unsupported, a
:class:`.MultipartParseError` will be raised when referencing this
property.
Note:
As this method builds upon :meth:`~.get_data`, it will consume the
part's input stream in the same way.
Returns:
str: The part decoded as a text string provided the part is
encoded as ``text/plain``, ``None`` otherwise.
"""
content_type, options = parse_header(self.content_type)
if content_type != 'text/plain':
return None
charset = options.get('charset', self._parse_options.default_charset)
try:
return self.data.decode(charset)
except (ValueError, LookupError) as err:
raise MultipartParseError(
description='invalid text or charset: {}'.format(charset)
) from err
@property
def content_type(self):
# NOTE(vytas): RFC 7578, section 4.4.
# Each part MAY have an (optional) "Content-Type" header field, which
# defaults to "text/plain".
value = self._headers.get(b'content-type', b'text/plain')
return value.decode('ascii')
@property
def filename(self):
if self._filename is None:
if self._content_disposition is None:
value = self._headers.get(b'content-disposition', b'')
self._content_disposition = parse_header(value.decode())
_, params = self._content_disposition
# NOTE(vytas): Supporting filename* as per RFC 5987, as that has
# been spotted in the wild, even though RFC 7578 forbids it.
match = _FILENAME_STAR_RFC5987.match(params.get('filename*', ''))
if match:
charset, value = match.groups()
try:
self._filename = unquote_to_bytes(value).decode(charset)
except (ValueError, LookupError) as err:
raise MultipartParseError(
description='invalid text or charset: {}'.format(charset)
) from err
else:
value = params.get('filename')
if value is None:
return None
self._filename = value
return self._filename
@property
def secure_filename(self):
try:
return misc.secure_filename(self.filename)
except ValueError as ex:
raise MultipartParseError(description=str(ex)) from ex
@property
def name(self):
if self._name is None:
if self._content_disposition is None:
value = self._headers.get(b'content-disposition', b'')
self._content_disposition = parse_header(value.decode())
_, params = self._content_disposition
self._name = params.get('name')
return self._name
[docs]
def get_media(self):
"""Return a deserialized form of the multipart body part.
When called, this method will attempt to deserialize the body part
stream using the Content-Type header as well as the media-type handlers
configured via :class:`MultipartParseOptions`.
.. tabs::
.. tab:: WSGI
The result will be cached and returned in subsequent calls::
deserialized_media = part.get_media()
.. tab:: ASGI
The result will be cached and returned in subsequent calls::
deserialized_media = await part.get_media()
Returns:
object: The deserialized media representation.
"""
if self._media is None:
handler, _, _ = self._parse_options.media_handlers._resolve(
self.content_type, 'text/plain'
)
try:
self._media = handler.deserialize(self.stream, self.content_type, None)
finally:
if handler.exhaust_stream:
self.stream.exhaust()
return self._media
data = property(get_data)
media = property(get_media)
text = property(get_text)
class MultipartForm:
def __init__(self, stream, boundary, content_length, parse_options):
# NOTE(vytas): More lenient check whether the provided stream is not
# already an instance of BufferedReader.
# This approach makes testing both the Cythonized and pure-Python
# streams easier within the same test/benchmark suite.
if not hasattr(stream, 'read_until'):
if isinstance(stream, BoundedStream):
stream = BufferedReader(stream.stream.read, content_length)
else:
stream = BufferedReader(stream.read, content_length)
self._stream = stream
self._boundary = boundary
# NOTE(vytas): Here self._dash_boundary is not prepended with CRLF
# (yet) for parsing the prologue. The CRLF will be prepended later to
# construct the inter-part delimiter as per RFC 7578, section 4.1
# (see the note below).
self._dash_boundary = b'--' + boundary
self._parse_options = parse_options
def __iter__(self):
prologue = True
delimiter = self._dash_boundary
stream = self._stream
max_headers_size = self._parse_options.max_body_part_headers_size
remaining_parts = self._parse_options.max_body_part_count
while True:
# NOTE(vytas): Either exhaust the unused stream part, or skip
# the prologue.
try:
stream.pipe_until(delimiter, consume_delimiter=True)
if prologue:
# NOTE(vytas): RFC 7578, section 4.1.
# As with other multipart types, the parts are delimited
# with a boundary delimiter, constructed using CRLF,
# "--", and the value of the "boundary" parameter.
delimiter = _CRLF + delimiter
prologue = False
separator = stream.read_until(_CRLF, 2, consume_delimiter=True)
if separator == b'--':
# NOTE(vytas): boundary delimiter + '--\r\n' signals the
# end of a multipart form.
break
elif separator:
raise MultipartParseError(description='unexpected form structure')
except errors.DelimiterError as err:
raise MultipartParseError(
description='unexpected form structure'
) from err
headers = {}
try:
headers_block = stream.read_until(
_CRLF_CRLF, max_headers_size, consume_delimiter=True
)
except errors.DelimiterError as err:
raise MultipartParseError(
description='incomplete body part headers'
) from err
for line in headers_block.split(_CRLF):
name, sep, value = line.partition(b': ')
if sep:
name = name.lower()
# NOTE(vytas): RFC 7578, section 4.5.
# This use is deprecated for use in contexts that support
# binary data such as HTTP. Senders SHOULD NOT generate
# any parts with a Content-Transfer-Encoding header
# field.
#
# Currently, no deployed implementations that send such
# bodies have been discovered.
if name == b'content-transfer-encoding' and value != b'binary':
raise MultipartParseError(
description=(
'the deprecated Content-Transfer-Encoding '
'header field is unsupported'
)
)
# NOTE(vytas): RFC 7578, section 4.8.
# Other header fields MUST NOT be included and MUST be
# ignored.
elif name in _ALLOWED_CONTENT_HEADERS:
headers[name] = value
remaining_parts -= 1
if remaining_parts < 0 < self._parse_options.max_body_part_count:
raise MultipartParseError(
description='maximum number of form body parts exceeded'
)
yield BodyPart(stream.delimit(delimiter), headers, self._parse_options)
# PERF(vytas): To avoid typos and improve storage space and speed over a dict.
# Inspired by RequestOptions.
[docs]
class MultipartParseOptions:
"""Defines a set of configurable multipart form parser options.
An instance of this class is exposed via the
:attr:`MultipartFormHandler.parse_options
<falcon.media.MultipartFormHandler.parse_options>` attribute.
The handler's options are also passed down to every :class:`BodyPart`
it instantiates.
See also: :ref:`multipart_parser_conf`.
Attributes:
default_charset (str): The default character encoding for
:meth:`text fields <BodyPart.get_text>` (default: ``utf-8``).
max_body_part_count (int): The maximum number of body parts in the form
(default: 64). If the form contains more parts than this number,
an instance of :class:`.MultipartParseError` will be raised. If this
option is set to 0, no limit will be imposed by the parser.
max_body_part_buffer_size (int): The maximum number of bytes to buffer
and return when the :meth:`BodyPart.get_data` method is called
(default: 1 MiB). If the body part size exceeds this value, an
instance of :class:`.MultipartParseError` will be raised.
max_body_part_headers_size (int): The maximum size (in bytes) of the
body part headers structure (default: 8192). If the body part
headers size exceeds this value, an instance of
:class:`.MultipartParseError` will be raised.
media_handlers (Handlers): A dict-like object for configuring the
media-types to handle. By default, handlers are provided for the
``application/json`` and ``application/x-www-form-urlencoded``
media types.
"""
_DEFAULT_HANDLERS = None
__slots__ = (
'default_charset',
'max_body_part_buffer_size',
'max_body_part_count',
'max_body_part_headers_size',
'media_handlers',
)
def __init__(self):
self.default_charset = 'utf-8'
self.max_body_part_buffer_size = 1024 * 1024
self.max_body_part_count = 64
self.max_body_part_headers_size = 8192
self.media_handlers = self._DEFAULT_HANDLERS
