from __future__ import annotations
import asyncio
from datetime import datetime
from datetime import timezone
from functools import partial
import io
import os
from pathlib import Path
import re
from re import Pattern
from typing import Any, ClassVar, IO, TYPE_CHECKING
import falcon
from falcon.typing import ReadableIO
if TYPE_CHECKING:
from falcon import asgi
from falcon import Request
from falcon import Response
def _open_file(file_path: str | Path) -> tuple[io.BufferedReader, os.stat_result]:
"""Open a file for a static file request and read file stat.
Args:
file_path (Union[str, Path]): Path to the file to open.
Returns:
tuple: Tuple of (BufferedReader, stat_result).
"""
fh: io.BufferedReader | None = None
try:
fh = io.open(file_path, 'rb') # noqa: UP020
st = os.fstat(fh.fileno())
except OSError:
if fh is not None:
fh.close()
raise falcon.HTTPNotFound()
return fh, st
def _set_range(
fh: io.BufferedReader, st: os.stat_result, req_range: tuple[int, int] | None
) -> tuple[ReadableIO, int, tuple[int, int, int] | None]:
"""Process file handle for a ranged request.
Args:
fh (io.BufferedReader): file handle of the file.
st (os.stat_result): fs stat result of the file.
req_range (Optional[Tuple[int, int]]): Request.range value.
Returns:
tuple: Three-member tuple of (stream, content-length, content-range).
If req_range is ``None`` or ignored, content-range will be
``None``; otherwise, the stream will be appropriately seeked and
possibly bounded, and the content-range will be a tuple of
(start, end, size).
"""
size = st.st_size
if req_range is None:
return fh, size, None
start, end = req_range
if size == 0:
# NOTE(tipabu): Ignore Range headers for zero-byte files; just serve
# the empty body since Content-Range can't be used to express a
# zero-byte body.
return fh, 0, None
if start < 0 and end == -1:
# NOTE(tipabu): Special case: only want the last N bytes.
start = max(start, -size)
fh.seek(start, os.SEEK_END)
# NOTE(vytas): Wrap in order to prevent sendfile from being used, as
# its implementation was found to be buggy in many popular WSGI
# servers for open files with a non-zero offset.
return _BoundedFile(fh, -start), -start, (size + start, size - 1, size)
if start >= size:
fh.close()
raise falcon.HTTPRangeNotSatisfiable(size)
fh.seek(start)
if end == -1:
# NOTE(vytas): Wrap in order to prevent sendfile from being used, as
# its implementation was found to be buggy in many popular WSGI
# servers for open files with a non-zero offset.
length = size - start
return _BoundedFile(fh, length), length, (start, size - 1, size)
end = min(end, size - 1)
length = end - start + 1
return _BoundedFile(fh, length), length, (start, end, size)
def _is_not_modified(
req: falcon.Request, current_etag: str, last_modified: datetime
) -> bool:
"""Check whether the requested resource can be served with 304 Not Modified."""
# NOTE(Cycloctane): RFC 9110 Section 13.1.3: A recipient MUST ignore
# If-Modified-Since if the request contains an If-None-Match header
# field. See also:
# https://www.rfc-editor.org/rfc/rfc9110#section-13.1.3-5
# https://www.rfc-editor.org/rfc/rfc9110#section-13.2.2
if req.if_none_match is not None:
return (len(req.if_none_match) == 1 and req.if_none_match[0] == '*') or any(
current_etag == etag for etag in req.if_none_match
)
if req.if_modified_since is not None:
return last_modified <= req.if_modified_since
return False
class _BoundedFile:
"""Wrap a file to only allow part of it to be read.
Args:
fh: The file object to wrap. Should be opened in binary mode,
and already seeked to an appropriate position. The object must
expose a ``.close()`` method.
length (int): Number of bytes that may be read.
"""
def __init__(self, fh: IO[bytes], length: int) -> None:
self.fh = fh
self.close = fh.close
self.remaining = length
def read(self, size: int | None = -1) -> bytes:
"""Read the underlying file object, within the specified bounds."""
if size is None or size < 0:
size = self.remaining
else:
size = min(size, self.remaining)
data = self.fh.read(size)
self.remaining -= len(data)
return data
[docs]
class StaticRoute:
"""Represents a static route.
Args:
prefix (str): The path prefix to match for this route. If the
path in the requested URI starts with this string, the remainder
of the path will be appended to the source directory to
determine the file to serve. This is done in a secure manner
to prevent an attacker from requesting a file outside the
specified directory.
Note that static routes are matched in LIFO order, and are only
attempted after checking dynamic routes and sinks.
directory (Union[str, pathlib.Path]): The source directory from which to
serve files. Must be an absolute path.
downloadable (bool): Set to ``True`` to include a
Content-Disposition header in the response. The "filename"
directive is simply set to the name of the requested file.
fallback_filename (str): Fallback filename used when the requested file
is not found. Can be a relative path inside the prefix folder or
any valid absolute path.
Note:
If the fallback file is served instead of the requested file,
the response Content-Type header, as well as the
Content-Disposition header (provided it was requested with the
`downloadable` parameter described above), are derived from the
fallback filename, as opposed to the requested filename.
"""
# NOTE(kgriffs): Don't allow control characters and reserved chars
_DISALLOWED_CHARS_PATTERN: ClassVar[Pattern[str]] = re.compile(
'[\x00-\x1f\x80-\x9f\ufffd~?<>:*|\'"]'
)
# NOTE(vytas): Match the behavior of the underlying os.path.normpath.
_DISALLOWED_NORMALIZED_PREFIXES: ClassVar[tuple[str, ...]] = (
'..' + os.path.sep,
os.path.sep,
)
# NOTE(kgriffs): If somehow an executable code exploit is triggerable, this
# minimizes how much can be included in the payload.
_MAX_NON_PREFIXED_LEN: ClassVar[int] = 512
def __init__(
self,
prefix: str,
directory: str | Path,
downloadable: bool = False,
fallback_filename: str | None = None,
) -> None:
if not prefix.startswith('/'):
raise ValueError("prefix must start with '/'")
self._directory = os.path.normpath(directory)
if not os.path.isabs(self._directory):
raise ValueError('directory must be an absolute path')
if fallback_filename is None:
self._fallback_filename = None
else:
self._fallback_filename = os.path.normpath(
os.path.join(self._directory, fallback_filename)
)
if not os.path.isfile(self._fallback_filename):
raise ValueError('fallback_filename is not a file')
# NOTE(kgriffs): Ensure it ends with a path separator to ensure
# we only match on the complete segment. Don't raise an error
# because most people won't expect to have to append a slash.
if not prefix.endswith('/'):
prefix += '/'
self._prefix = prefix
self._downloadable = downloadable
[docs]
def match(self, path: str) -> bool:
"""Check whether the given path matches this route."""
if self._fallback_filename is None:
return path.startswith(self._prefix)
return path.startswith(self._prefix) or path == self._prefix[:-1]
def __call__(self, req: Request, resp: Response, **kw: Any) -> None:
"""Resource responder for this route."""
assert not kw
if req.method == 'OPTIONS':
# it's likely a CORS request. Set the allow header to the appropriate value.
resp.set_header('Allow', 'GET')
resp.set_header('Content-Length', '0')
return
without_prefix = req.path[len(self._prefix) :]
# NOTE(kgriffs): Check surrounding whitespace and strip trailing
# periods, which are illegal on windows
# NOTE(CaselIT): An empty filename is allowed when fallback_filename is provided
if (
not (without_prefix or self._fallback_filename is not None)
or without_prefix.strip().rstrip('.') != without_prefix
or self._DISALLOWED_CHARS_PATTERN.search(without_prefix)
or '\\' in without_prefix
or '//' in without_prefix
or len(without_prefix) > self._MAX_NON_PREFIXED_LEN
):
raise falcon.HTTPNotFound()
normalized = os.path.normpath(without_prefix)
if normalized.startswith(self._DISALLOWED_NORMALIZED_PREFIXES):
raise falcon.HTTPNotFound()
file_path = os.path.join(self._directory, normalized)
# NOTE(kgriffs): Final sanity-check just to be safe. This check
# should never succeed, but this should guard against us having
# overlooked something.
if '..' in file_path or not file_path.startswith(self._directory):
raise falcon.HTTPNotFound()
if self._fallback_filename is None:
fh, st = _open_file(file_path)
else:
try:
fh, st = _open_file(file_path)
except falcon.HTTPNotFound:
fh, st = _open_file(self._fallback_filename)
file_path = self._fallback_filename
etag = f'{int(st.st_mtime):x}-{st.st_size:x}'
resp.etag = etag
last_modified = datetime.fromtimestamp(st.st_mtime, timezone.utc)
# NOTE(vytas): Strip the microsecond part because that is not reflected
# in HTTP date, and when the client passes a previous value via
# If-Modified-Since, it will look as if our copy is ostensibly newer.
last_modified = last_modified.replace(microsecond=0)
resp.last_modified = last_modified
if _is_not_modified(req, etag, last_modified):
fh.close()
resp.status = falcon.HTTP_304
return
req_range = req.range if req.range_unit == 'bytes' else None
try:
stream, length, content_range = _set_range(fh, st, req_range)
except OSError:
fh.close()
raise falcon.HTTPNotFound()
resp.set_stream(stream, length)
suffix = os.path.splitext(file_path)[1]
resp.content_type = resp.options.static_media_types.get(
suffix, 'application/octet-stream'
)
resp.accept_ranges = 'bytes'
if self._downloadable:
resp.downloadable_as = os.path.basename(file_path)
if content_range:
resp.status = falcon.HTTP_206
resp.content_range = content_range
class StaticRouteAsync(StaticRoute):
"""Subclass of StaticRoute with modifications to support ASGI apps."""
async def __call__( # type: ignore[override]
self,
req: asgi.Request,
resp: asgi.Response,
ws: asgi.WebSocket | None = None,
**kw: Any,
) -> None:
if ws is not None:
raise falcon.HTTPBadRequest()
super().__call__(req, resp, **kw)
if resp.stream is not None: # None when in an option request
# NOTE(kgriffs): Fixup resp.stream so that it is non-blocking
resp.stream = _AsyncFileReader(resp.stream) # type: ignore[assignment,arg-type]
class _AsyncFileReader:
"""Adapts a standard file I/O object so that reads are non-blocking."""
def __init__(self, file: IO[bytes]) -> None:
self._file = file
self._loop = asyncio.get_running_loop()
async def read(self, size: int = -1) -> bytes:
return await self._loop.run_in_executor(None, partial(self._file.read, size))
async def close(self) -> None:
await self._loop.run_in_executor(None, self._file.close)
