Source code for tornado.http1connection

# Copyright 2014 Facebook
# 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
# 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.

"""Client and server implementations of HTTP/1.x.

.. versionadded:: 4.0

import asyncio
import logging
import re
import types

from tornado.concurrent import (
from tornado.escape import native_str, utf8
from tornado import gen
from tornado import httputil
from tornado import iostream
from tornado.log import gen_log, app_log
from tornado.util import GzipDecompressor

from typing import cast, Optional, Type, Awaitable, Callable, Union, Tuple

CR_OR_LF_RE = re.compile(b"\r|\n")

class _QuietException(Exception):
    def __init__(self) -> None:

class _ExceptionLoggingContext(object):
    """Used with the ``with`` statement when calling delegate methods to
    log any exceptions with the given logger.  Any exceptions caught are
    converted to _QuietException

    def __init__(self, logger: logging.Logger) -> None:
        self.logger = logger

    def __enter__(self) -> None:

    def __exit__(
        typ: "Optional[Type[BaseException]]",
        value: Optional[BaseException],
        tb: types.TracebackType,
    ) -> None:
        if value is not None:
            assert typ is not None
            self.logger.error("Uncaught exception", exc_info=(typ, value, tb))
            raise _QuietException

[docs] class HTTP1ConnectionParameters(object): """Parameters for `.HTTP1Connection` and `.HTTP1ServerConnection`.""" def __init__( self, no_keep_alive: bool = False, chunk_size: Optional[int] = None, max_header_size: Optional[int] = None, header_timeout: Optional[float] = None, max_body_size: Optional[int] = None, body_timeout: Optional[float] = None, decompress: bool = False, ) -> None: """ :arg bool no_keep_alive: If true, always close the connection after one request. :arg int chunk_size: how much data to read into memory at once :arg int max_header_size: maximum amount of data for HTTP headers :arg float header_timeout: how long to wait for all headers (seconds) :arg int max_body_size: maximum amount of data for body :arg float body_timeout: how long to wait while reading body (seconds) :arg bool decompress: if true, decode incoming ``Content-Encoding: gzip`` """ self.no_keep_alive = no_keep_alive self.chunk_size = chunk_size or 65536 self.max_header_size = max_header_size or 65536 self.header_timeout = header_timeout self.max_body_size = max_body_size self.body_timeout = body_timeout self.decompress = decompress
[docs] class HTTP1Connection(httputil.HTTPConnection): """Implements the HTTP/1.x protocol. This class can be on its own for clients, or via `HTTP1ServerConnection` for servers. """ def __init__( self, stream: iostream.IOStream, is_client: bool, params: Optional[HTTP1ConnectionParameters] = None, context: Optional[object] = None, ) -> None: """ :arg stream: an `.IOStream` :arg bool is_client: client or server :arg params: a `.HTTP1ConnectionParameters` instance or ``None`` :arg context: an opaque application-defined object that can be accessed as ``connection.context``. """ self.is_client = is_client = stream if params is None: params = HTTP1ConnectionParameters() self.params = params self.context = context self.no_keep_alive = params.no_keep_alive # The body limits can be altered by the delegate, so save them # here instead of just referencing self.params later. self._max_body_size = ( self.params.max_body_size if self.params.max_body_size is not None else ) self._body_timeout = self.params.body_timeout # _write_finished is set to True when finish() has been called, # i.e. there will be no more data sent. Data may still be in the # stream's write buffer. self._write_finished = False # True when we have read the entire incoming body. self._read_finished = False # _finish_future resolves when all data has been written and flushed # to the IOStream. self._finish_future = Future() # type: Future[None] # If true, the connection should be closed after this request # (after the response has been written in the server side, # and after it has been read in the client) self._disconnect_on_finish = False self._clear_callbacks() # Save the start lines after we read or write them; they # affect later processing (e.g. 304 responses and HEAD methods # have content-length but no bodies) self._request_start_line = None # type: Optional[httputil.RequestStartLine] self._response_start_line = None # type: Optional[httputil.ResponseStartLine] self._request_headers = None # type: Optional[httputil.HTTPHeaders] # True if we are writing output with chunked encoding. self._chunking_output = False # While reading a body with a content-length, this is the # amount left to read. self._expected_content_remaining = None # type: Optional[int] # A Future for our outgoing writes, returned by IOStream.write. self._pending_write = None # type: Optional[Future[None]]
[docs] def read_response(self, delegate: httputil.HTTPMessageDelegate) -> Awaitable[bool]: """Read a single HTTP response. Typical client-mode usage is to write a request using `write_headers`, `write`, and `finish`, and then call ``read_response``. :arg delegate: a `.HTTPMessageDelegate` Returns a `.Future` that resolves to a bool after the full response has been read. The result is true if the stream is still open. """ if self.params.decompress: delegate = _GzipMessageDelegate(delegate, self.params.chunk_size) return self._read_message(delegate)
async def _read_message(self, delegate: httputil.HTTPMessageDelegate) -> bool: need_delegate_close = False try: header_future = b"\r?\n\r?\n", max_bytes=self.params.max_header_size ) if self.params.header_timeout is None: header_data = await header_future else: try: header_data = await gen.with_timeout( + self.params.header_timeout, header_future, quiet_exceptions=iostream.StreamClosedError, ) except gen.TimeoutError: self.close() return False start_line_str, headers = self._parse_headers(header_data) if self.is_client: resp_start_line = httputil.parse_response_start_line(start_line_str) self._response_start_line = resp_start_line start_line = ( resp_start_line ) # type: Union[httputil.RequestStartLine, httputil.ResponseStartLine] # TODO: this will need to change to support client-side keepalive self._disconnect_on_finish = False else: req_start_line = httputil.parse_request_start_line(start_line_str) self._request_start_line = req_start_line self._request_headers = headers start_line = req_start_line self._disconnect_on_finish = not self._can_keep_alive( req_start_line, headers ) need_delegate_close = True with _ExceptionLoggingContext(app_log): header_recv_future = delegate.headers_received(start_line, headers) if header_recv_future is not None: await header_recv_future if is None: # We've been detached. need_delegate_close = False return False skip_body = False if self.is_client: assert isinstance(start_line, httputil.ResponseStartLine) if ( self._request_start_line is not None and self._request_start_line.method == "HEAD" ): skip_body = True code = start_line.code if code == 304: # 304 responses may include the content-length header # but do not actually have a body. # skip_body = True if 100 <= code < 200: # 1xx responses should never indicate the presence of # a body. if "Content-Length" in headers or "Transfer-Encoding" in headers: raise httputil.HTTPInputError( "Response code %d cannot have body" % code ) # TODO: client delegates will get headers_received twice # in the case of a 100-continue. Document or change? await self._read_message(delegate) else: if headers.get("Expect") == "100-continue" and not self._write_finished:"HTTP/1.1 100 (Continue)\r\n\r\n") if not skip_body: body_future = self._read_body( resp_start_line.code if self.is_client else 0, headers, delegate ) if body_future is not None: if self._body_timeout is None: await body_future else: try: await gen.with_timeout( + self._body_timeout, body_future, quiet_exceptions=iostream.StreamClosedError, ) except gen.TimeoutError:"Timeout reading body from %s", self.context) return False self._read_finished = True if not self._write_finished or self.is_client: need_delegate_close = False with _ExceptionLoggingContext(app_log): delegate.finish() # If we're waiting for the application to produce an asynchronous # response, and we're not detached, register a close callback # on the stream (we didn't need one while we were reading) if ( not self._finish_future.done() and is not None and not ): await self._finish_future if self.is_client and self._disconnect_on_finish: self.close() if is None: return False except httputil.HTTPInputError as e:"Malformed HTTP message from %s: %s", self.context, e) if not self.is_client: await"HTTP/1.1 400 Bad Request\r\n\r\n") self.close() return False finally: if need_delegate_close: with _ExceptionLoggingContext(app_log): delegate.on_connection_close() header_future = None # type: ignore self._clear_callbacks() return True def _clear_callbacks(self) -> None: """Clears the callback attributes. This allows the request handler to be garbage collected more quickly in CPython by breaking up reference cycles. """ self._write_callback = None self._write_future = None # type: Optional[Future[None]] self._close_callback = None # type: Optional[Callable[[], None]] if is not None:
[docs] def set_close_callback(self, callback: Optional[Callable[[], None]]) -> None: """Sets a callback that will be run when the connection is closed. Note that this callback is slightly different from `.HTTPMessageDelegate.on_connection_close`: The `.HTTPMessageDelegate` method is called when the connection is closed while receiving a message. This callback is used when there is not an active delegate (for example, on the server side this callback is used if the client closes the connection after sending its request but before receiving all the response. """ self._close_callback = callback
def _on_connection_close(self) -> None: # Note that this callback is only registered on the IOStream # when we have finished reading the request and are waiting for # the application to produce its response. if self._close_callback is not None: callback = self._close_callback self._close_callback = None callback() if not self._finish_future.done(): future_set_result_unless_cancelled(self._finish_future, None) self._clear_callbacks() def close(self) -> None: if is not None: self._clear_callbacks() if not self._finish_future.done(): future_set_result_unless_cancelled(self._finish_future, None)
[docs] def detach(self) -> iostream.IOStream: """Take control of the underlying stream. Returns the underlying `.IOStream` object and stops all further HTTP processing. May only be called during `.HTTPMessageDelegate.headers_received`. Intended for implementing protocols like websockets that tunnel over an HTTP handshake. """ self._clear_callbacks() stream = = None # type: ignore if not self._finish_future.done(): future_set_result_unless_cancelled(self._finish_future, None) return stream
[docs] def set_body_timeout(self, timeout: float) -> None: """Sets the body timeout for a single request. Overrides the value from `.HTTP1ConnectionParameters`. """ self._body_timeout = timeout
[docs] def set_max_body_size(self, max_body_size: int) -> None: """Sets the body size limit for a single request. Overrides the value from `.HTTP1ConnectionParameters`. """ self._max_body_size = max_body_size
[docs] def write_headers( self, start_line: Union[httputil.RequestStartLine, httputil.ResponseStartLine], headers: httputil.HTTPHeaders, chunk: Optional[bytes] = None, ) -> "Future[None]": """Implements `.HTTPConnection.write_headers`.""" lines = [] if self.is_client: assert isinstance(start_line, httputil.RequestStartLine) self._request_start_line = start_line lines.append(utf8("%s %s HTTP/1.1" % (start_line[0], start_line[1]))) # Client requests with a non-empty body must have either a # Content-Length or a Transfer-Encoding. If Content-Length is not # present we'll add our Transfer-Encoding below. self._chunking_output = ( start_line.method in ("POST", "PUT", "PATCH") and "Content-Length" not in headers ) else: assert isinstance(start_line, httputil.ResponseStartLine) assert self._request_start_line is not None assert self._request_headers is not None self._response_start_line = start_line lines.append(utf8("HTTP/1.1 %d %s" % (start_line[1], start_line[2]))) self._chunking_output = ( # TODO: should this use # self._request_start_line.version or # start_line.version? self._request_start_line.version == "HTTP/1.1" # Omit payload header field for HEAD request. and self._request_start_line.method != "HEAD" # 1xx, 204 and 304 responses have no body (not even a zero-length # body), and so should not have either Content-Length or # Transfer-Encoding headers. and start_line.code not in (204, 304) and (start_line.code < 100 or start_line.code >= 200) # No need to chunk the output if a Content-Length is specified. and "Content-Length" not in headers ) # If connection to a 1.1 client will be closed, inform client if ( self._request_start_line.version == "HTTP/1.1" and self._disconnect_on_finish ): headers["Connection"] = "close" # If a 1.0 client asked for keep-alive, add the header. if ( self._request_start_line.version == "HTTP/1.0" and self._request_headers.get("Connection", "").lower() == "keep-alive" ): headers["Connection"] = "Keep-Alive" if self._chunking_output: headers["Transfer-Encoding"] = "chunked" if not self.is_client and ( self._request_start_line.method == "HEAD" or cast(httputil.ResponseStartLine, start_line).code == 304 ): self._expected_content_remaining = 0 elif "Content-Length" in headers: self._expected_content_remaining = parse_int(headers["Content-Length"]) else: self._expected_content_remaining = None # TODO: headers are supposed to be of type str, but we still have some # cases that let bytes slip through. Remove these native_str calls when those # are fixed. header_lines = ( native_str(n) + ": " + native_str(v) for n, v in headers.get_all() ) lines.extend(line.encode("latin1") for line in header_lines) for line in lines: if raise ValueError("Illegal characters (CR or LF) in header: %r" % line) future = None if future = self._write_future = Future() future.set_exception(iostream.StreamClosedError()) future.exception() else: future = self._write_future = Future() data = b"\r\n".join(lines) + b"\r\n\r\n" if chunk: data += self._format_chunk(chunk) self._pending_write = future_add_done_callback(self._pending_write, self._on_write_complete) return future
def _format_chunk(self, chunk: bytes) -> bytes: if self._expected_content_remaining is not None: self._expected_content_remaining -= len(chunk) if self._expected_content_remaining < 0: # Close the stream now to stop further framing errors. raise httputil.HTTPOutputError( "Tried to write more data than Content-Length" ) if self._chunking_output and chunk: # Don't write out empty chunks because that means END-OF-STREAM # with chunked encoding return utf8("%x" % len(chunk)) + b"\r\n" + chunk + b"\r\n" else: return chunk
[docs] def write(self, chunk: bytes) -> "Future[None]": """Implements `.HTTPConnection.write`. For backwards compatibility it is allowed but deprecated to skip `write_headers` and instead call `write()` with a pre-encoded header block. """ future = None if future = self._write_future = Future() self._write_future.set_exception(iostream.StreamClosedError()) self._write_future.exception() else: future = self._write_future = Future() self._pending_write = future_add_done_callback(self._pending_write, self._on_write_complete) return future
[docs] def finish(self) -> None: """Implements `.HTTPConnection.finish`.""" if ( self._expected_content_remaining is not None and self._expected_content_remaining != 0 and not ): raise httputil.HTTPOutputError( "Tried to write %d bytes less than Content-Length" % self._expected_content_remaining ) if self._chunking_output: if not self._pending_write ="0\r\n\r\n") self._pending_write.add_done_callback(self._on_write_complete) self._write_finished = True # If the app finished the request while we're still reading, # divert any remaining data away from the delegate and # close the connection when we're done sending our response. # Closing the connection is the only way to avoid reading the # whole input body. if not self._read_finished: self._disconnect_on_finish = True # No more data is coming, so instruct TCP to send any remaining # data immediately instead of waiting for a full packet or ack. if self._pending_write is None: self._finish_request(None) else: future_add_done_callback(self._pending_write, self._finish_request)
def _on_write_complete(self, future: "Future[None]") -> None: exc = future.exception() if exc is not None and not isinstance(exc, iostream.StreamClosedError): future.result() if self._write_callback is not None: callback = self._write_callback self._write_callback = None if self._write_future is not None: future = self._write_future self._write_future = None future_set_result_unless_cancelled(future, None) def _can_keep_alive( self, start_line: httputil.RequestStartLine, headers: httputil.HTTPHeaders ) -> bool: if self.params.no_keep_alive: return False connection_header = headers.get("Connection") if connection_header is not None: connection_header = connection_header.lower() if start_line.version == "HTTP/1.1": return connection_header != "close" elif ( "Content-Length" in headers or is_transfer_encoding_chunked(headers) or getattr(start_line, "method", None) in ("HEAD", "GET") ): # start_line may be a request or response start line; only # the former has a method attribute. return connection_header == "keep-alive" return False def _finish_request(self, future: "Optional[Future[None]]") -> None: self._clear_callbacks() if not self.is_client and self._disconnect_on_finish: self.close() return # Turn Nagle's algorithm back on, leaving the stream in its # default state for the next request. if not self._finish_future.done(): future_set_result_unless_cancelled(self._finish_future, None) def _parse_headers(self, data: bytes) -> Tuple[str, httputil.HTTPHeaders]: # The lstrip removes newlines that some implementations sometimes # insert between messages of a reused connection. Per RFC 7230, # we SHOULD ignore at least one empty line before the request. # data_str = native_str(data.decode("latin1")).lstrip("\r\n") # RFC 7230 section allows for both CRLF and bare LF. eol = data_str.find("\n") start_line = data_str[:eol].rstrip("\r") headers = httputil.HTTPHeaders.parse(data_str[eol:]) return start_line, headers def _read_body( self, code: int, headers: httputil.HTTPHeaders, delegate: httputil.HTTPMessageDelegate, ) -> Optional[Awaitable[None]]: if "Content-Length" in headers: if "," in headers["Content-Length"]: # Proxies sometimes cause Content-Length headers to get # duplicated. If all the values are identical then we can # use them but if they differ it's an error. pieces = re.split(r",\s*", headers["Content-Length"]) if any(i != pieces[0] for i in pieces): raise httputil.HTTPInputError( "Multiple unequal Content-Lengths: %r" % headers["Content-Length"] ) headers["Content-Length"] = pieces[0] try: content_length: Optional[int] = parse_int(headers["Content-Length"]) except ValueError: # Handles non-integer Content-Length value. raise httputil.HTTPInputError( "Only integer Content-Length is allowed: %s" % headers["Content-Length"] ) if cast(int, content_length) > self._max_body_size: raise httputil.HTTPInputError("Content-Length too long") else: content_length = None is_chunked = is_transfer_encoding_chunked(headers) if code == 204: # This response code is not allowed to have a non-empty body, # and has an implicit length of zero instead of read-until-close. # if is_chunked or content_length not in (None, 0): raise httputil.HTTPInputError( "Response with code %d should not have body" % code ) content_length = 0 if is_chunked: return self._read_chunked_body(delegate) if content_length is not None: return self._read_fixed_body(content_length, delegate) if self.is_client: return self._read_body_until_close(delegate) return None async def _read_fixed_body( self, content_length: int, delegate: httputil.HTTPMessageDelegate ) -> None: while content_length > 0: body = await min(self.params.chunk_size, content_length), partial=True ) content_length -= len(body) if not self._write_finished or self.is_client: with _ExceptionLoggingContext(app_log): ret = delegate.data_received(body) if ret is not None: await ret async def _read_chunked_body(self, delegate: httputil.HTTPMessageDelegate) -> None: # TODO: "chunk extensions" total_size = 0 while True: chunk_len_str = await"\r\n", max_bytes=64) try: chunk_len = parse_hex_int(native_str(chunk_len_str[:-2])) except ValueError: raise httputil.HTTPInputError("invalid chunk size") if chunk_len == 0: crlf = await if crlf != b"\r\n": raise httputil.HTTPInputError( "improperly terminated chunked request" ) return total_size += chunk_len if total_size > self._max_body_size: raise httputil.HTTPInputError("chunked body too large") bytes_to_read = chunk_len while bytes_to_read: chunk = await min(bytes_to_read, self.params.chunk_size), partial=True ) bytes_to_read -= len(chunk) if not self._write_finished or self.is_client: with _ExceptionLoggingContext(app_log): ret = delegate.data_received(chunk) if ret is not None: await ret # chunk ends with \r\n crlf = await assert crlf == b"\r\n" async def _read_body_until_close( self, delegate: httputil.HTTPMessageDelegate ) -> None: body = await if not self._write_finished or self.is_client: with _ExceptionLoggingContext(app_log): ret = delegate.data_received(body) if ret is not None: await ret
class _GzipMessageDelegate(httputil.HTTPMessageDelegate): """Wraps an `HTTPMessageDelegate` to decode ``Content-Encoding: gzip``.""" def __init__(self, delegate: httputil.HTTPMessageDelegate, chunk_size: int) -> None: self._delegate = delegate self._chunk_size = chunk_size self._decompressor = None # type: Optional[GzipDecompressor] def headers_received( self, start_line: Union[httputil.RequestStartLine, httputil.ResponseStartLine], headers: httputil.HTTPHeaders, ) -> Optional[Awaitable[None]]: if headers.get("Content-Encoding", "").lower() == "gzip": self._decompressor = GzipDecompressor() # Downstream delegates will only see uncompressed data, # so rename the content-encoding header. # (but note that curl_httpclient doesn't do this). headers.add("X-Consumed-Content-Encoding", headers["Content-Encoding"]) del headers["Content-Encoding"] return self._delegate.headers_received(start_line, headers) async def data_received(self, chunk: bytes) -> None: if self._decompressor: compressed_data = chunk while compressed_data: decompressed = self._decompressor.decompress( compressed_data, self._chunk_size ) if decompressed: ret = self._delegate.data_received(decompressed) if ret is not None: await ret compressed_data = self._decompressor.unconsumed_tail if compressed_data and not decompressed: raise httputil.HTTPInputError( "encountered unconsumed gzip data without making progress" ) else: ret = self._delegate.data_received(chunk) if ret is not None: await ret def finish(self) -> None: if self._decompressor is not None: tail = self._decompressor.flush() if tail: # The tail should always be empty: decompress returned # all that it can in data_received and the only # purpose of the flush call is to detect errors such # as truncated input. If we did legitimately get a new # chunk at this point we'd need to change the # interface to make finish() a coroutine. raise ValueError( "decompressor.flush returned data; possible truncated input" ) return self._delegate.finish() def on_connection_close(self) -> None: return self._delegate.on_connection_close()
[docs] class HTTP1ServerConnection(object): """An HTTP/1.x server.""" def __init__( self, stream: iostream.IOStream, params: Optional[HTTP1ConnectionParameters] = None, context: Optional[object] = None, ) -> None: """ :arg stream: an `.IOStream` :arg params: a `.HTTP1ConnectionParameters` or None :arg context: an opaque application-defined object that is accessible as ``connection.context`` """ = stream if params is None: params = HTTP1ConnectionParameters() self.params = params self.context = context self._serving_future = None # type: Optional[Future[None]]
[docs] async def close(self) -> None: """Closes the connection. Returns a `.Future` that resolves after the serving loop has exited. """ # Block until the serving loop is done, but ignore any exceptions # (start_serving is already responsible for logging them). assert self._serving_future is not None try: await self._serving_future except Exception: pass
[docs] def start_serving(self, delegate: httputil.HTTPServerConnectionDelegate) -> None: """Starts serving requests on this connection. :arg delegate: a `.HTTPServerConnectionDelegate` """ assert isinstance(delegate, httputil.HTTPServerConnectionDelegate) fut = gen.convert_yielded(self._server_request_loop(delegate)) self._serving_future = fut # Register the future on the IOLoop so its errors get logged., lambda f: f.result())
async def _server_request_loop( self, delegate: httputil.HTTPServerConnectionDelegate ) -> None: try: while True: conn = HTTP1Connection(, False, self.params, self.context) request_delegate = delegate.start_request(self, conn) try: ret = await conn.read_response(request_delegate) except ( iostream.StreamClosedError, iostream.UnsatisfiableReadError, asyncio.CancelledError, ): return except _QuietException: # This exception was already logged. conn.close() return except Exception: gen_log.error("Uncaught exception", exc_info=True) conn.close() return if not ret: return await asyncio.sleep(0) finally: delegate.on_close(self)
DIGITS = re.compile(r"[0-9]+") HEXDIGITS = re.compile(r"[0-9a-fA-F]+")
[docs] def parse_int(s: str) -> int: """Parse a non-negative integer from a string.""" if DIGITS.fullmatch(s) is None: raise ValueError("not an integer: %r" % s) return int(s)
[docs] def parse_hex_int(s: str) -> int: """Parse a non-negative hexadecimal integer from a string.""" if HEXDIGITS.fullmatch(s) is None: raise ValueError("not a hexadecimal integer: %r" % s) return int(s, 16)
[docs] def is_transfer_encoding_chunked(headers: httputil.HTTPHeaders) -> bool: """Returns true if the headers specify Transfer-Encoding: chunked. Raise httputil.HTTPInputError if any other transfer encoding is used. """ # Note that transfer-encoding is an area in which postel's law can lead # us astray. If a proxy and a backend server are liberal in what they accept, # but accept slightly different things, this can lead to mismatched framing # and request smuggling issues. Therefore we are as strict as possible here # (even technically going beyond the requirements of the RFCs: a value of # ",chunked" is legal but doesn't appear in practice for legitimate traffic) if "Transfer-Encoding" not in headers: return False if "Content-Length" in headers: # Message cannot contain both Content-Length and # Transfer-Encoding headers. # raise httputil.HTTPInputError( "Message with both Transfer-Encoding and Content-Length" ) if headers["Transfer-Encoding"].lower() == "chunked": return True # We do not support any transfer-encodings other than chunked, and we do not # expect to add any support because the concept of transfer-encoding has # been removed in HTTP/2. raise httputil.HTTPInputError( "Unsupported Transfer-Encoding %s" % headers["Transfer-Encoding"] )