client.py

"""HTTP Client for asyncio."""

import asyncio
import base64
import hashlib
import json
import os
import sys
import traceback
import warnings
from collections.abc import Coroutine as CoroutineABC
from typing import Any, Generator, Optional, Tuple

import attr
from multidict import CIMultiDict, MultiDict, MultiDictProxy, istr
from yarl import URL

from . import client_exceptions, client_reqrep
from . import connector as connector_mod
from . import hdrs, http, payload
from .client_exceptions import *  # noqa
from .client_exceptions import (ClientError, ClientOSError, InvalidURL,
                                ServerTimeoutError, TooManyRedirects,
                                WSServerHandshakeError)
from .client_reqrep import *  # noqa
from .client_reqrep import ClientRequest, ClientResponse, _merge_ssl_params
from .client_ws import ClientWebSocketResponse
from .connector import *  # noqa
from .connector import BaseConnector, TCPConnector
from .cookiejar import CookieJar
from .helpers import (DEBUG, PY_36, CeilTimeout, TimeoutHandle,
                      proxies_from_env, sentinel, strip_auth_from_url)
from .http import WS_KEY, WebSocketReader, WebSocketWriter
from .http_websocket import WSHandshakeError, ws_ext_gen, ws_ext_parse
from .streams import FlowControlDataQueue
from .tcp_helpers import tcp_cork, tcp_nodelay
from .tracing import Trace
from .typedefs import StrOrURL


__all__ = (client_exceptions.__all__ +  # noqa
           client_reqrep.__all__ +  # noqa
           connector_mod.__all__ +  # noqa
           ('ClientSession', 'ClientTimeout',
            'ClientWebSocketResponse', 'request'))


@attr.s(frozen=True, slots=True)
class ClientTimeout:
    total = attr.ib(type=float, default=None)
    connect = attr.ib(type=float, default=None)
    sock_read = attr.ib(type=float, default=None)
    sock_connect = attr.ib(type=float, default=None)

    # pool_queue_timeout = attr.ib(type=float, default=None)
    # dns_resolution_timeout = attr.ib(type=float, default=None)
    # socket_connect_timeout = attr.ib(type=float, default=None)
    # connection_acquiring_timeout = attr.ib(type=float, default=None)
    # new_connection_timeout = attr.ib(type=float, default=None)
    # http_header_timeout = attr.ib(type=float, default=None)
    # response_body_timeout = attr.ib(type=float, default=None)

    # to create a timeout specific for a single request, either
    # - create a completely new one to overwrite the default
    # - or use http://www.attrs.org/en/stable/api.html#attr.evolve
    # to overwrite the defaults


# 5 Minute default read timeout
DEFAULT_TIMEOUT = ClientTimeout(total=5*60)


class ClientSession:
    """First-class interface for making HTTP requests."""

    ATTRS = frozenset([
        '_source_traceback', '_connector',
        'requote_redirect_url', '_loop', '_cookie_jar',
        '_connector_owner', '_default_auth',
        '_version', '_json_serialize',
        '_timeout', '_raise_for_status', '_auto_decompress',
        '_trust_env', '_default_headers', '_skip_auto_headers',
        '_request_class', '_response_class',
        '_ws_response_class', '_trace_configs'])

    _source_traceback = None
    _connector = None

    requote_redirect_url = True

    def __init__(self, *, connector=None, loop=None, cookies=None,
                 headers=None, skip_auto_headers=None,
                 auth=None, json_serialize=json.dumps,
                 request_class=ClientRequest, response_class=ClientResponse,
                 ws_response_class=ClientWebSocketResponse,
                 version=http.HttpVersion11,
                 cookie_jar=None, connector_owner=True,
                 raise_for_status=False,
                 read_timeout=sentinel, conn_timeout=None,
                 timeout=sentinel,
                 auto_decompress=True, trust_env=False,
                 trace_configs=None):

        implicit_loop = False
        if loop is None:
            if connector is not None:
                loop = connector._loop
            else:
                implicit_loop = True
                loop = asyncio.get_event_loop()

        if connector is None:
            connector = TCPConnector(loop=loop)

        if connector._loop is not loop:
            raise RuntimeError(
                "Session and connector has to use same event loop")

        self._loop = loop

        if loop.get_debug():
            self._source_traceback = traceback.extract_stack(sys._getframe(1))

        if implicit_loop and not loop.is_running():
            warnings.warn("Creating a client session outside of coroutine is "
                          "a very dangerous idea",
                          stacklevel=2)
            context = {'client_session': self,
                       'message': 'Creating a client session outside '
                       'of coroutine'}
            if self._source_traceback is not None:
                context['source_traceback'] = self._source_traceback
            loop.call_exception_handler(context)

        if cookie_jar is None:
            cookie_jar = CookieJar(loop=loop)
        self._cookie_jar = cookie_jar

        if cookies is not None:
            self._cookie_jar.update_cookies(cookies)

        self._connector = connector  # type: BaseConnector
        self._connector_owner = connector_owner
        self._default_auth = auth
        self._version = version
        self._json_serialize = json_serialize
        if timeout is not sentinel:
            self._timeout = timeout
            if read_timeout is not sentinel:
                raise ValueError("read_timeout and timeout parameters "
                                 "conflict, please setup "
                                 "timeout.read")
            if conn_timeout is not None:
                raise ValueError("conn_timeout and timeout parameters "
                                 "conflict, please setup "
                                 "timeout.connect")
        else:
            self._timeout = DEFAULT_TIMEOUT
            if read_timeout is not sentinel:
                self._timeout = attr.evolve(self._timeout, total=read_timeout)
            if conn_timeout is not None:
                self._timeout = attr.evolve(self._timeout,
                                            connect=conn_timeout)
        self._raise_for_status = raise_for_status
        self._auto_decompress = auto_decompress
        self._trust_env = trust_env

        # Convert to list of tuples
        if headers:
            headers = CIMultiDict(headers)
        else:
            headers = CIMultiDict()
        self._default_headers = headers
        if skip_auto_headers is not None:
            self._skip_auto_headers = frozenset([istr(i)
                                                 for i in skip_auto_headers])
        else:
            self._skip_auto_headers = frozenset()

        self._request_class = request_class
        self._response_class = response_class
        self._ws_response_class = ws_response_class

        self._trace_configs = trace_configs or []
        for trace_config in self._trace_configs:
            trace_config.freeze()

    def __init_subclass__(cls):
        warnings.warn("Inheritance class {} from ClientSession "
                      "is discouraged".format(cls.__name__),
                      DeprecationWarning,
                      stacklevel=2)

    if DEBUG:
        def __setattr__(self, name, val):
            if name not in self.ATTRS:
                warnings.warn("Setting custom ClientSession.{} attribute "
                              "is discouraged".format(name),
                              DeprecationWarning,
                              stacklevel=2)
            super().__setattr__(name, val)

    def __del__(self, _warnings=warnings):
        if not self.closed:
            if PY_36:
                kwargs = {'source': self}
            else:
                kwargs = {}
            _warnings.warn("Unclosed client session {!r}".format(self),
                           ResourceWarning,
                           **kwargs)
            context = {'client_session': self,
                       'message': 'Unclosed client session'}
            if self._source_traceback is not None:
                context['source_traceback'] = self._source_traceback
            self._loop.call_exception_handler(context)

    def request(self,
                method: str,
                url: StrOrURL,
                **kwargs) -> '_RequestContextManager':
        """Perform HTTP request."""
        return _RequestContextManager(self._request(method, url, **kwargs))

    async def _request(self, method, url, *,
                       params=None,
                       data=None,
                       json=None,
                       headers=None,
                       skip_auto_headers=None,
                       auth=None,
                       allow_redirects=True,
                       max_redirects=10,
                       compress=None,
                       chunked=None,
                       expect100=False,
                       raise_for_status=None,
                       read_until_eof=True,
                       proxy=None,
                       proxy_auth=None,
                       timeout=sentinel,
                       verify_ssl=None,
                       fingerprint=None,
                       ssl_context=None,
                       ssl=None,
                       proxy_headers=None,
                       trace_request_ctx=None):

        # NOTE: timeout clamps existing connect and read timeouts.  We cannot
        # set the default to None because we need to detect if the user wants
        # to use the existing timeouts by setting timeout to None.

        if self.closed:
            raise RuntimeError('Session is closed')

        ssl = _merge_ssl_params(ssl, verify_ssl, ssl_context, fingerprint)

        if data is not None and json is not None:
            raise ValueError(
                'data and json parameters can not be used at the same time')
        elif json is not None:
            data = payload.JsonPayload(json, dumps=self._json_serialize)

        if not isinstance(chunked, bool) and chunked is not None:
            warnings.warn(
                'Chunk size is deprecated #1615', DeprecationWarning)

        redirects = 0
        history = []
        version = self._version

        # Merge with default headers and transform to CIMultiDict
        headers = self._prepare_headers(headers)
        proxy_headers = self._prepare_headers(proxy_headers)

        try:
            url = URL(url)
        except ValueError:
            raise InvalidURL(url)

        skip_headers = set(self._skip_auto_headers)
        if skip_auto_headers is not None:
            for i in skip_auto_headers:
                skip_headers.add(istr(i))

        if proxy is not None:
            try:
                proxy = URL(proxy)
            except ValueError:
                raise InvalidURL(proxy)

        if timeout is sentinel:
            timeout = self._timeout
        else:
            if not isinstance(timeout, ClientTimeout):
                timeout = ClientTimeout(total=timeout)
        # timeout is cumulative for all request operations
        # (request, redirects, responses, data consuming)
        tm = TimeoutHandle(self._loop, timeout.total)
        handle = tm.start()

        traces = [
            Trace(
                self,
                trace_config,
                trace_config.trace_config_ctx(
                    trace_request_ctx=trace_request_ctx)
            )
            for trace_config in self._trace_configs
        ]

        for trace in traces:
            await trace.send_request_start(
                method,
                url,
                headers
            )

        timer = tm.timer()
        try:
            with timer:
                while True:
                    url, auth_from_url = strip_auth_from_url(url)
                    if auth and auth_from_url:
                        raise ValueError("Cannot combine AUTH argument with "
                                         "credentials encoded in URL")

                    if auth is None:
                        auth = auth_from_url
                    if auth is None:
                        auth = self._default_auth
                    # It would be confusing if we support explicit
                    # Authorization header with auth argument
                    if (headers is not None and
                            auth is not None and
                            hdrs.AUTHORIZATION in headers):
                        raise ValueError("Cannot combine AUTHORIZATION header "
                                         "with AUTH argument or credentials "
                                         "encoded in URL")

                    cookies = self._cookie_jar.filter_cookies(url)

                    if proxy is not None:
                        proxy = URL(proxy)
                    elif self._trust_env:
                        for scheme, proxy_info in proxies_from_env().items():
                            if scheme == url.scheme:
                                proxy = proxy_info.proxy
                                proxy_auth = proxy_info.proxy_auth
                                break

                    req = self._request_class(
                        method, url, params=params, headers=headers,
                        skip_auto_headers=skip_headers, data=data,
                        cookies=cookies, auth=auth, version=version,
                        compress=compress, chunked=chunked,
                        expect100=expect100, loop=self._loop,
                        response_class=self._response_class,
                        proxy=proxy, proxy_auth=proxy_auth, timer=timer,
                        session=self,
                        ssl=ssl, proxy_headers=proxy_headers, traces=traces)

                    # connection timeout
                    try:
                        with CeilTimeout(self._timeout.connect,
                                         loop=self._loop):
                            conn = await self._connector.connect(
                                req,
                                traces=traces,
                                timeout=timeout
                            )
                    except asyncio.TimeoutError as exc:
                        raise ServerTimeoutError(
                            'Connection timeout '
                            'to host {0}'.format(url)) from exc

                    tcp_nodelay(conn.transport, True)
                    tcp_cork(conn.transport, False)

                    conn.protocol.set_response_params(
                        timer=timer,
                        skip_payload=method.upper() == 'HEAD',
                        read_until_eof=read_until_eof,
                        auto_decompress=self._auto_decompress,
                        read_timeout=timeout.sock_read)

                    try:
                        try:
                            resp = await req.send(conn)
                            try:
                                await resp.start(conn)
                            except BaseException:
                                resp.close()
                                raise
                        except BaseException:
                            conn.close()
                            raise
                    except ClientError:
                        raise
                    except OSError as exc:
                        raise ClientOSError(*exc.args) from exc

                    self._cookie_jar.update_cookies(resp.cookies, resp.url)

                    # redirects
                    if resp.status in (
                            301, 302, 303, 307, 308) and allow_redirects:

                        for trace in traces:
                            await trace.send_request_redirect(
                                method,
                                url,
                                headers,
                                resp
                            )

                        redirects += 1
                        history.append(resp)
                        if max_redirects and redirects >= max_redirects:
                            resp.close()
                            raise TooManyRedirects(
                                history[0].request_info, tuple(history))

                        # For 301 and 302, mimic IE, now changed in RFC
                        # https://github.com/kennethreitz/requests/pull/269
                        if (resp.status == 303 and
                                resp.method != hdrs.METH_HEAD) \
                                or (resp.status in (301, 302) and
                                    resp.method == hdrs.METH_POST):
                            method = hdrs.METH_GET
                            data = None
                            if headers.get(hdrs.CONTENT_LENGTH):
                                headers.pop(hdrs.CONTENT_LENGTH)

                        r_url = (resp.headers.get(hdrs.LOCATION) or
                                 resp.headers.get(hdrs.URI))
                        if r_url is None:
                            # see github.com/aio-libs/aiohttp/issues/2022
                            break
                        else:
                            # reading from correct redirection
                            # response is forbidden
                            resp.release()

                        try:
                            r_url = URL(
                                r_url, encoded=not self.requote_redirect_url)

                        except ValueError:
                            raise InvalidURL(r_url)

                        scheme = r_url.scheme
                        if scheme not in ('http', 'https', ''):
                            resp.close()
                            raise ValueError(
                                'Can redirect only to http or https')
                        elif not scheme:
                            r_url = url.join(r_url)

                        if url.origin() != r_url.origin():
                            auth = None
                            headers.pop(hdrs.AUTHORIZATION, None)

                        url = r_url
                        params = None
                        resp.release()
                        continue

                    break

            # check response status
            if raise_for_status is None:
                raise_for_status = self._raise_for_status
            if raise_for_status:
                resp.raise_for_status()

            # register connection
            if handle is not None:
                if resp.connection is not None:
                    resp.connection.add_callback(handle.cancel)
                else:
                    handle.cancel()

            resp._history = tuple(history)

            for trace in traces:
                await trace.send_request_end(
                    method,
                    url,
                    headers,
                    resp
                )
            return resp

        except BaseException as e:
            # cleanup timer
            tm.close()
            if handle:
                handle.cancel()
                handle = None

            for trace in traces:
                await trace.send_request_exception(
                    method,
                    url,
                    headers,
                    e
                )
            raise

    def ws_connect(self, url: StrOrURL, *,
                   protocols=(),
                   timeout=10.0,
                   receive_timeout=None,
                   autoclose=True,
                   autoping=True,
                   heartbeat=None,
                   auth=None,
                   origin=None,
                   headers=None,
                   proxy=None,
                   proxy_auth=None,
                   ssl=None,
                   verify_ssl=None,
                   fingerprint=None,
                   ssl_context=None,
                   proxy_headers=None,
                   compress=0,
                   max_msg_size=4*1024*1024):
        """Initiate websocket connection."""
        return _WSRequestContextManager(
            self._ws_connect(url,
                             protocols=protocols,
                             timeout=timeout,
                             receive_timeout=receive_timeout,
                             autoclose=autoclose,
                             autoping=autoping,
                             heartbeat=heartbeat,
                             auth=auth,
                             origin=origin,
                             headers=headers,
                             proxy=proxy,
                             proxy_auth=proxy_auth,
                             ssl=ssl,
                             verify_ssl=verify_ssl,
                             fingerprint=fingerprint,
                             ssl_context=ssl_context,
                             proxy_headers=proxy_headers,
                             compress=compress,
                             max_msg_size=max_msg_size))

    async def _ws_connect(self, url, *,
                          protocols=(),
                          timeout=10.0,
                          receive_timeout=None,
                          autoclose=True,
                          autoping=True,
                          heartbeat=None,
                          auth=None,
                          origin=None,
                          headers=None,
                          proxy=None,
                          proxy_auth=None,
                          ssl=None,
                          verify_ssl=None,
                          fingerprint=None,
                          ssl_context=None,
                          proxy_headers=None,
                          compress=0,
                          max_msg_size=4*1024*1024):

        if headers is None:
            headers = CIMultiDict()

        default_headers = {
            hdrs.UPGRADE: hdrs.WEBSOCKET,
            hdrs.CONNECTION: hdrs.UPGRADE,
            hdrs.SEC_WEBSOCKET_VERSION: '13',
        }

        for key, value in default_headers.items():
            if key not in headers:
                headers[key] = value

        sec_key = base64.b64encode(os.urandom(16))
        headers[hdrs.SEC_WEBSOCKET_KEY] = sec_key.decode()

        if protocols:
            headers[hdrs.SEC_WEBSOCKET_PROTOCOL] = ','.join(protocols)
        if origin is not None:
            headers[hdrs.ORIGIN] = origin
        if compress:
            extstr = ws_ext_gen(compress=compress)
            headers[hdrs.SEC_WEBSOCKET_EXTENSIONS] = extstr

        ssl = _merge_ssl_params(ssl, verify_ssl, ssl_context, fingerprint)

        # send request
        resp = await self.get(url, headers=headers,
                              read_until_eof=False,
                              auth=auth,
                              proxy=proxy,
                              proxy_auth=proxy_auth,
                              ssl=ssl,
                              proxy_headers=proxy_headers)

        try:
            # check handshake
            if resp.status != 101:
                raise WSServerHandshakeError(
                    resp.request_info,
                    resp.history,
                    message='Invalid response status',
                    status=resp.status,
                    headers=resp.headers)

            if resp.headers.get(hdrs.UPGRADE, '').lower() != 'websocket':
                raise WSServerHandshakeError(
                    resp.request_info,
                    resp.history,
                    message='Invalid upgrade header',
                    status=resp.status,
                    headers=resp.headers)

            if resp.headers.get(hdrs.CONNECTION, '').lower() != 'upgrade':
                raise WSServerHandshakeError(
                    resp.request_info,
                    resp.history,
                    message='Invalid connection header',
                    status=resp.status,
                    headers=resp.headers)

            # key calculation
            key = resp.headers.get(hdrs.SEC_WEBSOCKET_ACCEPT, '')
            match = base64.b64encode(
                hashlib.sha1(sec_key + WS_KEY).digest()).decode()
            if key != match:
                raise WSServerHandshakeError(
                    resp.request_info,
                    resp.history,
                    message='Invalid challenge response',
                    status=resp.status,
                    headers=resp.headers)

            # websocket protocol
            protocol = None
            if protocols and hdrs.SEC_WEBSOCKET_PROTOCOL in resp.headers:
                resp_protocols = [
                    proto.strip() for proto in
                    resp.headers[hdrs.SEC_WEBSOCKET_PROTOCOL].split(',')]

                for proto in resp_protocols:
                    if proto in protocols:
                        protocol = proto
                        break

            # websocket compress
            notakeover = False
            if compress:
                compress_hdrs = resp.headers.get(hdrs.SEC_WEBSOCKET_EXTENSIONS)
                if compress_hdrs:
                    try:
                        compress, notakeover = ws_ext_parse(compress_hdrs)
                    except WSHandshakeError as exc:
                        raise WSServerHandshakeError(
                            resp.request_info,
                            resp.history,
                            message=exc.args[0],
                            status=resp.status,
                            headers=resp.headers)
                else:
                    compress = 0
                    notakeover = False

            proto = resp.connection.protocol
            transport = resp.connection.transport
            reader = FlowControlDataQueue(
                proto, limit=2 ** 16, loop=self._loop)
            proto.set_parser(WebSocketReader(reader, max_msg_size), reader)
            tcp_nodelay(transport, True)
            writer = WebSocketWriter(
                proto, transport, use_mask=True,
                compress=compress, notakeover=notakeover)
        except BaseException:
            resp.close()
            raise
        else:
            return self._ws_response_class(reader,
                                           writer,
                                           protocol,
                                           resp,
                                           timeout,
                                           autoclose,
                                           autoping,
                                           self._loop,
                                           receive_timeout=receive_timeout,
                                           heartbeat=heartbeat,
                                           compress=compress,
                                           client_notakeover=notakeover)

    def _prepare_headers(self, headers):
        """ Add default headers and transform it to CIMultiDict
        """
        # Convert headers to MultiDict
        result = CIMultiDict(self._default_headers)
        if headers:
            if not isinstance(headers, (MultiDictProxy, MultiDict)):
                headers = CIMultiDict(headers)
            added_names = set()
            for key, value in headers.items():
                if key in added_names:
                    result.add(key, value)
                else:
                    result[key] = value
                    added_names.add(key)
        return result

    def get(self, url: StrOrURL, *, allow_redirects: bool=True,
            **kwargs) -> '_RequestContextManager':
        """Perform HTTP GET request."""
        return _RequestContextManager(
            self._request(hdrs.METH_GET, url,
                          allow_redirects=allow_redirects,
                          **kwargs))

    def options(self, url: StrOrURL, *, allow_redirects: bool=True,
                **kwargs) -> '_RequestContextManager':
        """Perform HTTP OPTIONS request."""
        return _RequestContextManager(
            self._request(hdrs.METH_OPTIONS, url,
                          allow_redirects=allow_redirects,
                          **kwargs))

    def head(self, url: StrOrURL, *, allow_redirects: bool=False,
             **kwargs) -> '_RequestContextManager':
        """Perform HTTP HEAD request."""
        return _RequestContextManager(
            self._request(hdrs.METH_HEAD, url,
                          allow_redirects=allow_redirects,
                          **kwargs))

    def post(self, url: StrOrURL,
             *, data: Any=None, **kwargs) -> '_RequestContextManager':
        """Perform HTTP POST request."""
        return _RequestContextManager(
            self._request(hdrs.METH_POST, url,
                          data=data,
                          **kwargs))

    def put(self, url: StrOrURL,
            *, data: Any=None, **kwargs) -> '_RequestContextManager':
        """Perform HTTP PUT request."""
        return _RequestContextManager(
            self._request(hdrs.METH_PUT, url,
                          data=data,
                          **kwargs))

    def patch(self, url: StrOrURL,
              *, data: Any=None, **kwargs) -> '_RequestContextManager':
        """Perform HTTP PATCH request."""
        return _RequestContextManager(
            self._request(hdrs.METH_PATCH, url,
                          data=data,
                          **kwargs))

    def delete(self, url: StrOrURL, **kwargs) -> '_RequestContextManager':
        """Perform HTTP DELETE request."""
        return _RequestContextManager(
            self._request(hdrs.METH_DELETE, url,
                          **kwargs))

    async def close(self) -> None:
        """Close underlying connector.

        Release all acquired resources.
        """
        if not self.closed:
            if self._connector is not None and self._connector_owner:
                self._connector.close()
            self._connector = None

    @property
    def closed(self) -> bool:
        """Is client session closed.

        A readonly property.
        """
        return self._connector is None or self._connector.closed

    @property
    def connector(self) -> Optional[BaseConnector]:
        """Connector instance used for the session."""
        return self._connector

    @property
    def cookie_jar(self) -> CookieJar:
        """The session cookies."""
        return self._cookie_jar

    @property
    def version(self) -> Tuple[int, int]:
        """The session HTTP protocol version."""
        return self._version

    @property
    def loop(self) -> asyncio.AbstractEventLoop:
        """Session's loop."""
        return self._loop

    def detach(self) -> None:
        """Detach connector from session without closing the former.

        Session is switched to closed state anyway.
        """
        self._connector = None

    def __enter__(self):
        raise TypeError("Use async with instead")

    def __exit__(self, exc_type, exc_val, exc_tb):
        # __exit__ should exist in pair with __enter__ but never executed
        pass  # pragma: no cover

    async def __aenter__(self) -> 'ClientSession':
        return self

    async def __aexit__(self, exc_type, exc_val, exc_tb):
        await self.close()


class _BaseRequestContextManager(CoroutineABC):

    __slots__ = ('_coro', '_resp')

    def __init__(self, coro):
        self._coro = coro

    def send(self, arg):
        return self._coro.send(arg)

    def throw(self, arg):
        return self._coro.throw(arg)

    def close(self):
        return self._coro.close()

    def __await__(self) -> Generator[Any, None, ClientResponse]:
        ret = self._coro.__await__()
        return ret

    def __iter__(self):
        return self.__await__()

    async def __aenter__(self) -> ClientResponse:
        self._resp = await self._coro
        return self._resp


class _RequestContextManager(_BaseRequestContextManager):
    async def __aexit__(self, exc_type, exc, tb):
        # We're basing behavior on the exception as it can be caused by
        # user code unrelated to the status of the connection.  If you
        # would like to close a connection you must do that
        # explicitly.  Otherwise connection error handling should kick in
        # and close/recycle the connection as required.
        self._resp.release()


class _WSRequestContextManager(_BaseRequestContextManager):
    async def __aexit__(self, exc_type, exc, tb):
        await self._resp.close()


class _SessionRequestContextManager:

    __slots__ = ('_coro', '_resp', '_session')

    def __init__(self, coro, session):
        self._coro = coro
        self._resp = None
        self._session = session

    async def __aenter__(self) -> ClientResponse:
        self._resp = await self._coro
        return self._resp

    async def __aexit__(self, exc_type, exc_val, exc_tb):
        self._resp.close()
        await self._session.close()


def request(method, url, *,
            params=None,
            data=None,
            json=None,
            headers=None,
            skip_auto_headers=None,
            cookies=None,
            auth=None,
            allow_redirects=True,
            max_redirects=10,
            version=http.HttpVersion11,
            compress=None,
            chunked=None,
            expect100=False,
            raise_for_status=False,
            connector=None,
            loop=None,
            read_until_eof=True,
            timeout=sentinel,
            proxy=None,
            proxy_auth=None) -> _SessionRequestContextManager:
    """Constructs and sends a request. Returns response object.
    method - HTTP method
    url - request url
    params - (optional) Dictionary or bytes to be sent in the query
      string of the new request
    data - (optional) Dictionary, bytes, or file-like object to
      send in the body of the request
    json - (optional) Any json compatibile python object
    headers - (optional) Dictionary of HTTP Headers to send with
      the request
    cookies - (optional) Dict object to send with the request
    auth - (optional) BasicAuth named tuple represent HTTP Basic Auth
    auth - aiohttp.helpers.BasicAuth
    allow_redirects - (optional) If set to False, do not follow
      redirects
    version - Request HTTP version.
    compress - Set to True if request has to be compressed
       with deflate encoding.
    chunked - Set to chunk size for chunked transfer encoding.
    expect100 - Expect 100-continue response from server.
    connector - BaseConnector sub-class instance to support
       connection pooling.
    read_until_eof - Read response until eof if response
       does not have Content-Length header.
    loop - Optional event loop.
    timeout - Optional ClientTimeout settings structure, 5min
       total timeout by default.
    Usage::
      >>> import aiohttp
      >>> resp = await aiohttp.request('GET', 'http://python.org/')
      >>> resp
      <ClientResponse(python.org/) [200]>
      >>> data = await resp.read()
    """
    connector_owner = False
    if connector is None:
        connector_owner = True
        connector = TCPConnector(loop=loop, force_close=True)

    session = ClientSession(
        loop=loop, cookies=cookies, version=version, timeout=timeout,
        connector=connector, connector_owner=connector_owner)

    return _SessionRequestContextManager(
        session._request(method, url,
                         params=params,
                         data=data,
                         json=json,
                         headers=headers,
                         skip_auto_headers=skip_auto_headers,
                         auth=auth,
                         allow_redirects=allow_redirects,
                         max_redirects=max_redirects,
                         compress=compress,
                         chunked=chunked,
                         expect100=expect100,
                         raise_for_status=raise_for_status,
                         read_until_eof=read_until_eof,
                         proxy=proxy,
                         proxy_auth=proxy_auth,),
        session)