# This contains the main Connection class. Everything in h11 revolves around
# this.
from typing import Any, Callable, cast, Dict, List, Optional, Tuple, Type, Union
from ._events import (
ConnectionClosed,
Data,
EndOfMessage,
Event,
InformationalResponse,
Request,
Response,
)
from ._headers import get_comma_header, has_expect_100_continue, set_comma_header
from ._readers import READERS, ReadersType
from ._receivebuffer import ReceiveBuffer
from ._state import (
_SWITCH_CONNECT,
_SWITCH_UPGRADE,
CLIENT,
ConnectionState,
DONE,
ERROR,
MIGHT_SWITCH_PROTOCOL,
SEND_BODY,
SERVER,
SWITCHED_PROTOCOL,
)
from ._util import ( # Import the internal things we need
LocalProtocolError,
RemoteProtocolError,
Sentinel,
)
from ._writers import WRITERS, WritersType
# Everything in __all__ gets re-exported as part of the h11 public API.
__all__ = ["Connection", "NEED_DATA", "PAUSED"]
class NEED_DATA(Sentinel, metaclass=Sentinel):
pass
class PAUSED(Sentinel, metaclass=Sentinel):
pass
# If we ever have this much buffered without it making a complete parseable
# event, we error out. The only time we really buffer is when reading the
# request/response line + headers together, so this is effectively the limit on
# the size of that.
#
# Some precedents for defaults:
# - node.js: 80 * 1024
# - tomcat: 8 * 1024
# - IIS: 16 * 1024
# - Apache: <8 KiB per line>
DEFAULT_MAX_INCOMPLETE_EVENT_SIZE = 16 * 1024
# RFC 7230's rules for connection lifecycles:
# - If either side says they want to close the connection, then the connection
# must close.
# - HTTP/1.1 defaults to keep-alive unless someone says Connection: close
# - HTTP/1.0 defaults to close unless both sides say Connection: keep-alive
# (and even this is a mess -- e.g. if you're implementing a proxy then
# sending Connection: keep-alive is forbidden).
#
# We simplify life by simply not supporting keep-alive with HTTP/1.0 peers. So
# our rule is:
# - If someone says Connection: close, we will close
# - If someone uses HTTP/1.0, we will close.
def _keep_alive(event: Union[Request, Response]) -> bool:
connection = get_comma_header(event.headers, b"connection")
if b"close" in connection:
return False
if getattr(event, "http_version", b"1.1") < b"1.1":
return False
return True
def _body_framing(
request_method: bytes, event: Union[Request, Response]
) -> Tuple[str, Union[Tuple[()], Tuple[int]]]:
# Called when we enter SEND_BODY to figure out framing information for
# this body.
#
# These are the only two events that can trigger a SEND_BODY state:
assert type(event) in (Request, Response)
# Returns one of:
#
# ("content-length", count)
# ("chunked", ())
# ("http/1.0", ())
#
# which are (lookup key, *args) for constructing body reader/writer
# objects.
#
# Reference: https://tools.ietf.org/html/rfc7230#section-3.3.3
#
# Step 1: some responses always have an empty body, regardless of what the
# headers say.
if type(event) is Response:
if (
event.status_code in (204, 304)
or request_method == b"HEAD"
or (request_method == b"CONNECT" and 200 <= event.status_code < 300)
):
return ("content-length", (0,))
# Section 3.3.3 also lists another case -- responses with status_code
# < 200. For us these are InformationalResponses, not Responses, so
# they can't get into this function in the first place.
assert event.status_code >= 200
# Step 2: check for Transfer-Encoding (T-E beats C-L):
transfer_encodings = get_comma_header(event.headers, b"transfer-encoding")
if transfer_encodings:
assert transfer_encodings == [b"chunked"]
return ("chunked", ())
# Step 3: check for Content-Length
content_lengths = get_comma_header(event.headers, b"content-length")
if content_lengths:
return ("content-length", (int(content_lengths[0]),))
# Step 4: no applicable headers; fallback/default depends on type
if type(event) is Request:
return ("content-length", (0,))
else:
return ("http/1.0", ())
################################################################
#
# The main Connection class
#
################################################################
class Connection:
"""An object encapsulating the state of an HTTP connection.
Args:
our_role: If you're implementing a client, pass :data:`h11.CLIENT`. If
you're implementing a server, pass :data:`h11.SERVER`.
max_incomplete_event_size (int):
The maximum number of bytes we're willing to buffer of an
incomplete event. In practice this mostly sets a limit on the
maximum size of the request/response line + headers. If this is
exceeded, then :meth:`next_event` will raise
:exc:`RemoteProtocolError`.
"""
def __init__(
self,
our_role: Type[Sentinel],
max_incomplete_event_size: int = DEFAULT_MAX_INCOMPLETE_EVENT_SIZE,
) -> None:
self._max_incomplete_event_size = max_incomplete_event_size
# State and role tracking
if our_role not in (CLIENT, SERVER):
raise ValueError("expected CLIENT or SERVER, not {!r}".format(our_role))
self.our_role = our_role
self.their_role: Type[Sentinel]
if our_role is CLIENT:
self.their_role = SERVER
else:
self.their_role = CLIENT
self._cstate = ConnectionState()
# Callables for converting data->events or vice-versa given the
# current state
self._writer = self._get_io_object(self.our_role, None, WRITERS)
self._reader = self._get_io_object(self.their_role, None, READERS)
# Holds any unprocessed received data
self._receive_buffer = ReceiveBuffer()
# If this is true, then it indicates that the incoming connection was
# closed *after* the end of whatever's in self._receive_buffer:
self._receive_buffer_closed = False
# Extra bits of state that don't fit into the state machine.
#
# These two are only used to interpret framing headers for figuring
# out how to read/write response bodies. their_http_version is also
# made available as a convenient public API.
self.their_http_version: Optional[bytes] = None
self._request_method: Optional[bytes] = None
# This is pure flow-control and doesn't at all affect the set of legal
# transitions, so no need to bother ConnectionState with it:
self.client_is_waiting_for_100_continue = False
@property
def states(self) -> Dict[Type[Sentinel], Type[Sentinel]]:
"""A dictionary like::
{CLIENT: <client state>, SERVER: <server state>}
See :ref:`state-machine` for details.
"""
return dict(self._cstate.states)
@property
def our_state(self) -> Type[Sentinel]:
"""The current state of whichever role we are playing. See
:ref:`state-machine` for details.
"""
return self._cstate.states[self.our_role]
@property
def their_state(self) -> Type[Sentinel]:
"""The current state of whichever role we are NOT playing. See
:ref:`state-machine` for details.
"""
return self._cstate.states[self.their_role]
@property
def they_are_waiting_for_100_continue(self) -> bool:
return self.their_role is CLIENT and self.client_is_waiting_for_100_continue
def start_next_cycle(self) -> None:
"""Attempt to reset our connection state for a new request/response
cycle.
If both client and server are in :data:`DONE` state, then resets them
both to :data:`IDLE` state in preparation for a new request/response
cycle on this same connection. Otherwise, raises a
:exc:`LocalProtocolError`.
See :ref:`keepalive-and-pipelining`.
"""
old_states = dict(self._cstate.states)
self._cstate.start_next_cycle()
self._request_method = None
# self.their_http_version gets left alone, since it presumably lasts
# beyond a single request/response cycle
assert not self.client_is_waiting_for_100_continue
self._respond_to_state_changes(old_states)
def _process_error(self, role: Type[Sentinel]) -> None:
old_states = dict(self._cstate.states)
self._cstate.process_error(role)
self._respond_to_state_changes(old_states)
def _server_switch_event(self, event: Event) -> Optional[Type[Sentinel]]:
if type(event) is InformationalResponse and event.status_code == 101:
return _SWITCH_UPGRADE
if type(event) is Response:
if (
_SWITCH_CONNECT in self._cstate.pending_switch_proposals
and 200 <= event.status_code < 300
):
return _SWITCH_CONNECT
return None
# All events go through here
def _process_event(self, role: Type[Sentinel], event: Event) -> None:
# First, pass the event through the state machine to make sure it
# succeeds.
old_states = dict(self._cstate.states)
if role is CLIENT and type(event) is Request:
if event.method == b"CONNECT":
self._cstate.process_client_switch_proposal(_SWITCH_CONNECT)
if get_comma_header(event.headers, b"upgrade"):
self._cstate.process_client_switch_proposal(_SWITCH_UPGRADE)
server_switch_event = None
if role is SERVER:
server_switch_event = self._server_switch_event(event)
self._cstate.process_event(role, type(event), server_switch_event)
# Then perform the updates triggered by it.
if type(event) is Request:
self._request_method = event.method
if role is self.their_role and type(event) in (
Request,
Response,
InformationalResponse,
):
event = cast(Union[Request, Response, InformationalResponse], event)
self.their_http_version = event.http_version
# Keep alive handling
#
# RFC 7230 doesn't really say what one should do if Connection: close
# shows up on a 1xx InformationalResponse. I think the idea is that
# this is not supposed to happen. In any case, if it does happen, we
# ignore it.
if type(event) in (Request, Response) and not _keep_alive(
cast(Union[Request, Response], event)
):
self._cstate.process_keep_alive_disabled()
# 100-continue
if type(event) is Request and has_expect_100_continue(event):
self.client_is_waiting_for_100_continue = True
if type(event) in (InformationalResponse, Response):
self.client_is_waiting_for_100_continue = False
if role is CLIENT and type(event) in (Data, EndOfMessage):
self.client_is_waiting_for_100_continue = False
self._respond_to_state_changes(old_states, event)
def _get_io_object(
self,
role: Type[Sentinel],
event: Optional[Event],
io_dict: Union[ReadersType, WritersType],
) -> Optional[Callable[..., Any]]:
# event may be None; it's only used when entering SEND_BODY
state = self._cstate.states[role]
if state is SEND_BODY:
# Special case: the io_dict has a dict of reader/writer factories
# that depend on the request/response framing.
framing_type, args = _body_framing(
cast(bytes, self._request_method), cast(Union[Request, Response], event)
)
return io_dict[SEND_BODY][framing_type](*args) # type: ignore[index]
else:
# General case: the io_dict just has the appropriate reader/writer
# for this state
return io_dict.get((role, state)) # type: ignore[return-value]
# This must be called after any action that might have caused
# self._cstate.states to change.
def _respond_to_state_changes(
self,
old_states: Dict[Type[Sentinel], Type[Sentinel]],
event: Optional[Event] = None,
) -> None:
# Update reader/writer
if self.our_state != old_states[self.our_role]:
self._writer = self._get_io_object(self.our_role, event, WRITERS)
if self.their_state != old_states[self.their_role]:
self._reader = self._get_io_object(self.their_role, event, READERS)
@property
def trailing_data(self) -> Tuple[bytes, bool]:
"""Data that has been received, but not yet processed, represented as
a tuple with two elements, where the first is a byte-string containing
the unprocessed data itself, and the second is a bool that is True if
the receive connection was closed.
See :ref:`switching-protocols` for discussion of why you'd want this.
"""
return (bytes(self._receive_buffer), self._receive_buffer_closed)
def receive_data(self, data: bytes) -> None:
"""Add data to our internal receive buffer.
This does not actually do any processing on the data, just stores
it. To trigger processing, you have to call :meth:`next_event`.
Args:
data (:term:`bytes-like object`):
The new data that was just received.
Special case: If *data* is an empty byte-string like ``b""``,
then this indicates that the remote side has closed the
connection (end of file). Normally this is convenient, because
standard Python APIs like :meth:`file.read` or
:meth:`socket.recv` use ``b""`` to indicate end-of-file, while
other failures to read are indicated using other mechanisms
like raising :exc:`TimeoutError`. When using such an API you
can just blindly pass through whatever you get from ``read``
to :meth:`receive_data`, and everything will work.
But, if you have an API where reading an empty string is a
valid non-EOF condition, then you need to be aware of this and
make sure to check for such strings and avoid passing them to
:meth:`receive_data`.
Returns:
Nothing, but after calling this you should call :meth:`next_event`
to parse the newly received data.
Raises:
RuntimeError:
Raised if you pass an empty *data*, indicating EOF, and then
pass a non-empty *data*, indicating more data that somehow
arrived after the EOF.
(Calling ``receive_data(b"")`` multiple times is fine,
and equivalent to calling it once.)
"""
if data:
if self._receive_buffer_closed:
raise RuntimeError("received close, then received more data?")
self._receive_buffer += data
else:
self._receive_buffer_closed = True
def _extract_next_receive_event(
self,
) -> Union[Event, Type[NEED_DATA], Type[PAUSED]]:
state = self.their_state
# We don't pause immediately when they enter DONE, because even in
# DONE state we can still process a ConnectionClosed() event. But
# if we have data in our buffer, then we definitely aren't getting
# a ConnectionClosed() immediately and we need to pause.
if state is DONE and self._receive_buffer:
return PAUSED
if state is MIGHT_SWITCH_PROTOCOL or state is SWITCHED_PROTOCOL:
return PAUSED
assert self._reader is not None
event = self._reader(self._receive_buffer)
if event is None:
if not self._receive_buffer and self._receive_buffer_closed:
# In some unusual cases (basically just HTTP/1.0 bodies), EOF
# triggers an actual protocol event; in that case, we want to
# return that event, and then the state will change and we'll
# get called again to generate the actual ConnectionClosed().
if hasattr(self._reader, "read_eof"):
event = self._reader.read_eof() # type: ignore[attr-defined]
else:
event = ConnectionClosed()
if event is None:
event = NEED_DATA
return event # type: ignore[no-any-return]
def next_event(self) -> Union[Event, Type[NEED_DATA], Type[PAUSED]]:
"""Parse the next event out of our receive buffer, update our internal
state, and return it.
This is a mutating operation -- think of it like calling :func:`next`
on an iterator.
Returns:
: One of three things:
1) An event object -- see :ref:`events`.
2) The special constant :data:`NEED_DATA`, which indicates that
you need to read more data from your socket and pass it to
:meth:`receive_data` before this method will be able to return
any more events.
3) The special constant :data:`PAUSED`, which indicates that we
are not in a state where we can process incoming data (usually
because the peer has finished their part of the current
request/response cycle, and you have not yet called
:meth:`start_next_cycle`). See :ref:`flow-control` for details.
Raises:
RemoteProtocolError:
The peer has misbehaved. You should close the connection
(possibly after sending some kind of 4xx response).
Once this method returns :class:`ConnectionClosed` once, then all
subsequent calls will also return :class:`ConnectionClosed`.
If this method raises any exception besides :exc:`RemoteProtocolError`
then that's a bug -- if it happens please file a bug report!
If this method raises any exception then it also sets
:attr:`Connection.their_state` to :data:`ERROR` -- see
:ref:`error-handling` for discussion.
"""
if self.their_state is ERROR:
raise RemoteProtocolError("Can't receive data when peer state is ERROR")
try:
event = self._extract_next_receive_event()
if event not in [NEED_DATA, PAUSED]:
self._process_event(self.their_role, cast(Event, event))
if event is NEED_DATA:
if len(self._receive_buffer) > self._max_incomplete_event_size:
# 431 is "Request header fields too large" which is pretty
# much the only situation where we can get here
raise RemoteProtocolError(
"Receive buffer too long", error_status_hint=431
)
if self._receive_buffer_closed:
# We're still trying to complete some event, but that's
# never going to happen because no more data is coming
raise RemoteProtocolError("peer unexpectedly closed connection")
return event
except BaseException as exc:
self._process_error(self.their_role)
if isinstance(exc, LocalProtocolError):
exc._reraise_as_remote_protocol_error()
else:
raise
def send(self, event: Event) -> Optional[bytes]:
"""Convert a high-level event into bytes that can be sent to the peer,
while updating our internal state machine.
Args:
event: The :ref:`event <events>` to send.
Returns:
If ``type(event) is ConnectionClosed``, then returns
``None``. Otherwise, returns a :term:`bytes-like object`.
Raises:
LocalProtocolError:
Sending this event at this time would violate our
understanding of the HTTP/1.1 protocol.
If this method raises any exception then it also sets
:attr:`Connection.our_state` to :data:`ERROR` -- see
:ref:`error-handling` for discussion.
"""
data_list = self.send_with_data_passthrough(event)
if data_list is None:
return None
else:
return b"".join(data_list)
def send_with_data_passthrough(self, event: Event) -> Optional[List[bytes]]:
"""Identical to :meth:`send`, except that in situations where
:meth:`send` returns a single :term:`bytes-like object`, this instead
returns a list of them -- and when sending a :class:`Data` event, this
list is guaranteed to contain the exact object you passed in as
:attr:`Data.data`. See :ref:`sendfile` for discussion.
"""
if self.our_state is ERROR:
raise LocalProtocolError("Can't send data when our state is ERROR")
try:
if type(event) is Response:
event = self._clean_up_response_headers_for_sending(event)
# We want to call _process_event before calling the writer,
# because if someone tries to do something invalid then this will
# give a sensible error message, while our writers all just assume
# they will only receive valid events. But, _process_event might
# change self._writer. So we have to do a little dance:
writer = self._writer
self._process_event(self.our_role, event)
if type(event) is ConnectionClosed:
return None
else:
# In any situation where writer is None, process_event should
# have raised ProtocolError
assert writer is not None
data_list: List[bytes] = []
writer(event, data_list.append)
return data_list
except:
self._process_error(self.our_role)
raise
def send_failed(self) -> None:
"""Notify the state machine that we failed to send the data it gave
us.
This causes :attr:`Connection.our_state` to immediately become
:data:`ERROR` -- see :ref:`error-handling` for discussion.
"""
self._process_error(self.our_role)
# When sending a Response, we take responsibility for a few things:
#
# - Sometimes you MUST set Connection: close. We take care of those
# times. (You can also set it yourself if you want, and if you do then
# we'll respect that and close the connection at the right time. But you
# don't have to worry about that unless you want to.)
#
# - The user has to set Content-Length if they want it. Otherwise, for
# responses that have bodies (e.g. not HEAD), then we will automatically
# select the right mechanism for streaming a body of unknown length,
# which depends on depending on the peer's HTTP version.
#
# This function's *only* responsibility is making sure headers are set up
# right -- everything downstream just looks at the headers. There are no
# side channels.
def _clean_up_response_headers_for_sending(self, response: Response) -> Response:
assert type(response) is Response
headers = response.headers
need_close = False
# HEAD requests need some special handling: they always act like they
# have Content-Length: 0, and that's how _body_framing treats
# them. But their headers are supposed to match what we would send if
# the request was a GET. (Technically there is one deviation allowed:
# we're allowed to leave out the framing headers -- see
# https://tools.ietf.org/html/rfc7231#section-4.3.2 . But it's just as
# easy to get them right.)
method_for_choosing_headers = cast(bytes, self._request_method)
if method_for_choosing_headers == b"HEAD":
method_for_choosing_headers = b"GET"
framing_type, _ = _body_framing(method_for_choosing_headers, response)
if framing_type in ("chunked", "http/1.0"):
# This response has a body of unknown length.
# If our peer is HTTP/1.1, we use Transfer-Encoding: chunked
# If our peer is HTTP/1.0, we use no framing headers, and close the
# connection afterwards.
#
# Make sure to clear Content-Length (in principle user could have
# set both and then we ignored Content-Length b/c
# Transfer-Encoding overwrote it -- this would be naughty of them,
# but the HTTP spec says that if our peer does this then we have
# to fix it instead of erroring out, so we'll accord the user the
# same respect).
headers = set_comma_header(headers, b"content-length", [])
if self.their_http_version is None or self.their_http_version < b"1.1":
# Either we never got a valid request and are sending back an
# error (their_http_version is None), so we assume the worst;
# or else we did get a valid HTTP/1.0 request, so we know that
# they don't understand chunked encoding.
headers = set_comma_header(headers, b"transfer-encoding", [])
# This is actually redundant ATM, since currently we
# unconditionally disable keep-alive when talking to HTTP/1.0
# peers. But let's be defensive just in case we add
# Connection: keep-alive support later:
if self._request_method != b"HEAD":
need_close = True
else:
headers = set_comma_header(headers, b"transfer-encoding", [b"chunked"])
if not self._cstate.keep_alive or need_close:
# Make sure Connection: close is set
connection = set(get_comma_header(headers, b"connection"))
connection.discard(b"keep-alive")
connection.add(b"close")
headers = set_comma_header(headers, b"connection", sorted(connection))
return Response(
headers=headers,
status_code=response.status_code,
http_version=response.http_version,
reason=response.reason,
)
