path: root/contrib/python/Twisted/py3/twisted/web/client.py

# -*- test-case-name: twisted.web.test.test_webclient,twisted.web.test.test_agent -*-
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.

"""
HTTP client.
"""

from __future__ import annotations

import collections
import os
import warnings
import zlib
from dataclasses import dataclass
from functools import wraps
from http.cookiejar import CookieJar
from typing import TYPE_CHECKING, Iterable, Optional
from urllib.parse import urldefrag, urljoin, urlunparse as _urlunparse

from zope.interface import implementer

from incremental import Version

from twisted.internet import defer, protocol, task
from twisted.internet.abstract import isIPv6Address
from twisted.internet.defer import Deferred
from twisted.internet.endpoints import HostnameEndpoint, wrapClientTLS
from twisted.internet.interfaces import IOpenSSLContextFactory, IProtocol
from twisted.logger import Logger
from twisted.python.compat import nativeString, networkString
from twisted.python.components import proxyForInterface
from twisted.python.deprecate import (
    deprecatedModuleAttribute,
    getDeprecationWarningString,
)
from twisted.python.failure import Failure
from twisted.web import error, http
from twisted.web._newclient import _ensureValidMethod, _ensureValidURI
from twisted.web.http_headers import Headers
from twisted.web.iweb import (
    UNKNOWN_LENGTH,
    IAgent,
    IAgentEndpointFactory,
    IBodyProducer,
    IPolicyForHTTPS,
    IResponse,
)

# For the purpose of type-checking we want our faked-out types to be identical to the types they are replacing.
# For the purpose of the impementation, we want to start
# with a blank slate so that we don't accidentally use
# any of the real implementation.

if TYPE_CHECKING:
    from email.message import EmailMessage as _InfoType
    from http.client import HTTPResponse as _ResponseBase
    from urllib.request import Request as _RequestBase
else:
    _RequestBase = object
    _ResponseBase = object
    _InfoType = object


def urlunparse(parts):
    result = _urlunparse(tuple(p.decode("charmap") for p in parts))
    return result.encode("charmap")


class PartialDownloadError(error.Error):
    """
    Page was only partially downloaded, we got disconnected in middle.

    @ivar response: All of the response body which was downloaded.
    """


class URI:
    """
    A URI object.

    @see: U{https://tools.ietf.org/html/draft-ietf-httpbis-p1-messaging-21}
    """

    def __init__(self, scheme, netloc, host, port, path, params, query, fragment):
        """
        @type scheme: L{bytes}
        @param scheme: URI scheme specifier.

        @type netloc: L{bytes}
        @param netloc: Network location component.

        @type host: L{bytes}
        @param host: Host name. For IPv6 address literals the brackets are
            stripped.

        @type port: L{int}
        @param port: Port number.

        @type path: L{bytes}
        @param path: Hierarchical path.

        @type params: L{bytes}
        @param params: Parameters for last path segment.

        @type query: L{bytes}
        @param query: Query string.

        @type fragment: L{bytes}
        @param fragment: Fragment identifier.
        """
        self.scheme = scheme
        self.netloc = netloc
        self.host = host.strip(b"[]")
        self.port = port
        self.path = path
        self.params = params
        self.query = query
        self.fragment = fragment

    @classmethod
    def fromBytes(cls, uri, defaultPort=None):
        """
        Parse the given URI into a L{URI}.

        @type uri: C{bytes}
        @param uri: URI to parse.

        @type defaultPort: C{int} or L{None}
        @param defaultPort: An alternate value to use as the port if the URI
            does not include one.

        @rtype: L{URI}
        @return: Parsed URI instance.
        """
        uri = uri.strip()
        scheme, netloc, path, params, query, fragment = http.urlparse(uri)

        if defaultPort is None:
            if scheme == b"https":
                defaultPort = 443
            else:
                defaultPort = 80

        if b":" in netloc:
            host, port = netloc.rsplit(b":", 1)
            try:
                port = int(port)
            except ValueError:
                host, port = netloc, defaultPort
        else:
            host, port = netloc, defaultPort
        return cls(scheme, netloc, host, port, path, params, query, fragment)

    def toBytes(self):
        """
        Assemble the individual parts of the I{URI} into a fully formed I{URI}.

        @rtype: C{bytes}
        @return: A fully formed I{URI}.
        """
        return urlunparse(
            (
                self.scheme,
                self.netloc,
                self.path,
                self.params,
                self.query,
                self.fragment,
            )
        )

    @property
    def originForm(self):
        """
        The absolute I{URI} path including I{URI} parameters, query string and
        fragment identifier.

        @see: U{https://tools.ietf.org/html/draft-ietf-httpbis-p1-messaging-21#section-5.3}

        @return: The absolute path in original form.
        @rtype: L{bytes}
        """
        # The HTTP bis draft says the origin form should not include the
        # fragment.
        path = urlunparse((b"", b"", self.path, self.params, self.query, b""))
        if path == b"":
            path = b"/"
        return path


def _urljoin(base, url):
    """
    Construct a full ("absolute") URL by combining a "base URL" with another
    URL. Informally, this uses components of the base URL, in particular the
    addressing scheme, the network location and (part of) the path, to provide
    missing components in the relative URL.

    Additionally, the fragment identifier is preserved according to the HTTP
    1.1 bis draft.

    @type base: C{bytes}
    @param base: Base URL.

    @type url: C{bytes}
    @param url: URL to combine with C{base}.

    @return: An absolute URL resulting from the combination of C{base} and
        C{url}.

    @see: L{urllib.parse.urljoin()}

    @see: U{https://tools.ietf.org/html/draft-ietf-httpbis-p2-semantics-22#section-7.1.2}
    """
    base, baseFrag = urldefrag(base)
    url, urlFrag = urldefrag(urljoin(base, url))
    return urljoin(url, b"#" + (urlFrag or baseFrag))


def _makeGetterFactory(url, factoryFactory, contextFactory=None, *args, **kwargs):
    """
    Create and connect an HTTP page getting factory.

    Any additional positional or keyword arguments are used when calling
    C{factoryFactory}.

    @param factoryFactory: Factory factory that is called with C{url}, C{args}
        and C{kwargs} to produce the getter

    @param contextFactory: Context factory to use when creating a secure
        connection, defaulting to L{None}

    @return: The factory created by C{factoryFactory}
    """
    uri = URI.fromBytes(_ensureValidURI(url.strip()))
    factory = factoryFactory(url, *args, **kwargs)
    from twisted.internet import reactor

    if uri.scheme == b"https":
        from twisted.internet import ssl

        if contextFactory is None:
            contextFactory = ssl.ClientContextFactory()
        reactor.connectSSL(nativeString(uri.host), uri.port, factory, contextFactory)
    else:
        reactor.connectTCP(nativeString(uri.host), uri.port, factory)
    return factory


# The code which follows is based on the new HTTP client implementation.  It
# should be significantly better than anything above, though it is not yet
# feature equivalent.

from twisted.web._newclient import (
    HTTP11ClientProtocol,
    PotentialDataLoss,
    Request,
    RequestGenerationFailed,
    RequestNotSent,
    RequestTransmissionFailed,
    Response,
    ResponseDone,
    ResponseFailed,
    ResponseNeverReceived,
    _WrapperException,
)
from twisted.web.error import SchemeNotSupported

try:
    from OpenSSL import SSL
except ImportError:
    SSL = None  # type: ignore[assignment]
else:
    from twisted.internet.ssl import (
        CertificateOptions,
        optionsForClientTLS,
        platformTrust,
    )


def _requireSSL(decoratee):
    """
    The decorated method requires pyOpenSSL to be present, or it raises
    L{NotImplementedError}.

    @param decoratee: A function which requires pyOpenSSL.
    @type decoratee: L{callable}

    @return: A function which raises L{NotImplementedError} if pyOpenSSL is not
        installed; otherwise, if it is installed, simply return C{decoratee}.
    @rtype: L{callable}
    """
    if SSL is None:

        @wraps(decoratee)
        def raiseNotImplemented(*a, **kw):
            """
            pyOpenSSL is not available.

            @param a: The positional arguments for C{decoratee}.

            @param kw: The keyword arguments for C{decoratee}.

            @raise NotImplementedError: Always.
            """
            raise NotImplementedError("SSL support unavailable")

        return raiseNotImplemented
    return decoratee


class WebClientContextFactory:
    """
    This class is deprecated.  Please simply use L{Agent} as-is, or if you want
    to customize something, use L{BrowserLikePolicyForHTTPS}.

    A L{WebClientContextFactory} is an HTTPS policy which totally ignores the
    hostname and port.  It performs basic certificate verification, however the
    lack of validation of service identity (e.g.  hostname validation) means it
    is still vulnerable to man-in-the-middle attacks.  Don't use it any more.
    """

    def _getCertificateOptions(self, hostname, port):
        """
        Return a L{CertificateOptions}.

        @param hostname: ignored

        @param port: ignored

        @return: A new CertificateOptions instance.
        @rtype: L{CertificateOptions}
        """
        return CertificateOptions(method=SSL.SSLv23_METHOD, trustRoot=platformTrust())

    @_requireSSL
    def getContext(self, hostname, port):
        """
        Return an L{OpenSSL.SSL.Context}.

        @param hostname: ignored
        @param port: ignored

        @return: A new SSL context.
        @rtype: L{OpenSSL.SSL.Context}
        """
        return self._getCertificateOptions(hostname, port).getContext()


@implementer(IPolicyForHTTPS)
class BrowserLikePolicyForHTTPS:
    """
    SSL connection creator for web clients.
    """

    def __init__(self, trustRoot=None):
        self._trustRoot = trustRoot

    @_requireSSL
    def creatorForNetloc(self, hostname, port):
        """
        Create a L{client connection creator
        <twisted.internet.interfaces.IOpenSSLClientConnectionCreator>} for a
        given network location.

        @param hostname: The hostname part of the URI.
        @type hostname: L{bytes}

        @param port: The port part of the URI.
        @type port: L{int}

        @return: a connection creator with appropriate verification
            restrictions set
        @rtype: L{client connection creator
            <twisted.internet.interfaces.IOpenSSLClientConnectionCreator>}
        """
        return optionsForClientTLS(hostname.decode("ascii"), trustRoot=self._trustRoot)


deprecatedModuleAttribute(
    Version("Twisted", 14, 0, 0),
    getDeprecationWarningString(
        WebClientContextFactory,
        Version("Twisted", 14, 0, 0),
        replacement=BrowserLikePolicyForHTTPS,
    ).split("; ")[1],
    WebClientContextFactory.__module__,
    WebClientContextFactory.__name__,
)


@implementer(IPolicyForHTTPS)
class HostnameCachingHTTPSPolicy:
    """
    IPolicyForHTTPS that wraps a L{IPolicyForHTTPS} and caches the created
    L{IOpenSSLClientConnectionCreator}.

    This policy will cache up to C{cacheSize}
    L{client connection creators <twisted.internet.interfaces.
    IOpenSSLClientConnectionCreator>} for reuse in subsequent requests to
    the same hostname.

    @ivar _policyForHTTPS: See C{policyforHTTPS} parameter of L{__init__}.

    @ivar _cache: A cache associating hostnames to their
        L{client connection creators <twisted.internet.interfaces.
        IOpenSSLClientConnectionCreator>}.
    @type _cache: L{collections.OrderedDict}

    @ivar _cacheSize: See C{cacheSize} parameter of L{__init__}.

    @since: Twisted 19.2.0
    """

    def __init__(self, policyforHTTPS, cacheSize=20):
        """
        @param policyforHTTPS: The IPolicyForHTTPS to wrap.
        @type policyforHTTPS: L{IPolicyForHTTPS}

        @param cacheSize: The maximum size of the hostname cache.
        @type cacheSize: L{int}
        """
        self._policyForHTTPS = policyforHTTPS
        self._cache = collections.OrderedDict()
        self._cacheSize = cacheSize

    def creatorForNetloc(self, hostname, port):
        """
        Create a L{client connection creator
        <twisted.internet.interfaces.IOpenSSLClientConnectionCreator>} for a
        given network location and cache it for future use.

        @param hostname: The hostname part of the URI.
        @type hostname: L{bytes}

        @param port: The port part of the URI.
        @type port: L{int}

        @return: a connection creator with appropriate verification
            restrictions set
        @rtype: L{client connection creator
            <twisted.internet.interfaces.IOpenSSLClientConnectionCreator>}
        """
        host = hostname.decode("ascii")
        try:
            creator = self._cache.pop(host)
        except KeyError:
            creator = self._policyForHTTPS.creatorForNetloc(hostname, port)

        self._cache[host] = creator
        if len(self._cache) > self._cacheSize:
            self._cache.popitem(last=False)

        return creator


@implementer(IOpenSSLContextFactory)
class _ContextFactoryWithContext:
    """
    A L{_ContextFactoryWithContext} is like a
    L{twisted.internet.ssl.ContextFactory} with a pre-created context.

    @ivar _context: A Context.
    @type _context: L{OpenSSL.SSL.Context}
    """

    def __init__(self, context):
        """
        Initialize a L{_ContextFactoryWithContext} with a context.

        @param context: An SSL context.
        @type context: L{OpenSSL.SSL.Context}
        """
        self._context = context

    def getContext(self):
        """
        Return the context created by
        L{_DeprecatedToCurrentPolicyForHTTPS._webContextFactory}.

        @return: A context.
        @rtype: L{OpenSSL.SSL.Context}
        """
        return self._context


@implementer(IPolicyForHTTPS)
class _DeprecatedToCurrentPolicyForHTTPS:
    """
    Adapt a web context factory to a normal context factory.

    @ivar _webContextFactory: An object providing a getContext method with
        C{hostname} and C{port} arguments.
    @type _webContextFactory: L{WebClientContextFactory} (or object with a
        similar C{getContext} method).
    """

    def __init__(self, webContextFactory):
        """
        Wrap a web context factory in an L{IPolicyForHTTPS}.

        @param webContextFactory: An object providing a getContext method with
            C{hostname} and C{port} arguments.
        @type webContextFactory: L{WebClientContextFactory} (or object with a
            similar C{getContext} method).
        """
        self._webContextFactory = webContextFactory

    def creatorForNetloc(self, hostname, port):
        """
        Called the wrapped web context factory's C{getContext} method with a
        hostname and port number and return the resulting context object.

        @param hostname: The hostname part of the URI.
        @type hostname: L{bytes}

        @param port: The port part of the URI.
        @type port: L{int}

        @return: A context factory.
        @rtype: L{IOpenSSLContextFactory}
        """
        context = self._webContextFactory.getContext(hostname, port)
        return _ContextFactoryWithContext(context)


@implementer(IBodyProducer)
class FileBodyProducer:
    """
    L{FileBodyProducer} produces bytes from an input file object incrementally
    and writes them to a consumer.

    Since file-like objects cannot be read from in an event-driven manner,
    L{FileBodyProducer} uses a L{Cooperator} instance to schedule reads from
    the file.  This process is also paused and resumed based on notifications
    from the L{IConsumer} provider being written to.

    The file is closed after it has been read, or if the producer is stopped
    early.

    @ivar _inputFile: Any file-like object, bytes read from which will be
        written to a consumer.

    @ivar _cooperate: A method like L{Cooperator.cooperate} which is used to
        schedule all reads.

    @ivar _readSize: The number of bytes to read from C{_inputFile} at a time.
    """

    def __init__(self, inputFile, cooperator=task, readSize=2**16):
        self._inputFile = inputFile
        self._cooperate = cooperator.cooperate
        self._readSize = readSize
        self.length = self._determineLength(inputFile)

    def _determineLength(self, fObj):
        """
        Determine how many bytes can be read out of C{fObj} (assuming it is not
        modified from this point on).  If the determination cannot be made,
        return C{UNKNOWN_LENGTH}.
        """
        try:
            seek = fObj.seek
            tell = fObj.tell
        except AttributeError:
            return UNKNOWN_LENGTH
        originalPosition = tell()
        seek(0, os.SEEK_END)
        end = tell()
        seek(originalPosition, os.SEEK_SET)
        return end - originalPosition

    def stopProducing(self):
        """
        Permanently stop writing bytes from the file to the consumer by
        stopping the underlying L{CooperativeTask}.
        """
        self._inputFile.close()
        try:
            self._task.stop()
        except task.TaskFinished:
            pass

    def startProducing(self, consumer):
        """
        Start a cooperative task which will read bytes from the input file and
        write them to C{consumer}.  Return a L{Deferred} which fires after all
        bytes have been written.  If this L{Deferred} is cancelled before it is
        fired, stop reading and writing bytes.

        @param consumer: Any L{IConsumer} provider
        """
        self._task = self._cooperate(self._writeloop(consumer))
        d = self._task.whenDone()

        def maybeStopped(reason):
            if reason.check(defer.CancelledError):
                self.stopProducing()
            elif reason.check(task.TaskStopped):
                pass
            else:
                return reason
            # IBodyProducer.startProducing's Deferred isn't supposed to fire if
            # stopProducing is called.
            return defer.Deferred()

        d.addCallbacks(lambda ignored: None, maybeStopped)
        return d

    def _writeloop(self, consumer):
        """
        Return an iterator which reads one chunk of bytes from the input file
        and writes them to the consumer for each time it is iterated.
        """
        while True:
            bytes = self._inputFile.read(self._readSize)
            if not bytes:
                self._inputFile.close()
                break
            consumer.write(bytes)
            yield None

    def pauseProducing(self):
        """
        Temporarily suspend copying bytes from the input file to the consumer
        by pausing the L{CooperativeTask} which drives that activity.
        """
        self._task.pause()

    def resumeProducing(self):
        """
        Undo the effects of a previous C{pauseProducing} and resume copying
        bytes to the consumer by resuming the L{CooperativeTask} which drives
        the write activity.
        """
        self._task.resume()


class _HTTP11ClientFactory(protocol.Factory):
    """
    A factory for L{HTTP11ClientProtocol}, used by L{HTTPConnectionPool}.

    @ivar _quiescentCallback: The quiescent callback to be passed to protocol
        instances, used to return them to the connection pool.

    @ivar _metadata: Metadata about the low-level connection details,
        used to make the repr more useful.

    @since: 11.1
    """

    def __init__(self, quiescentCallback, metadata):
        self._quiescentCallback = quiescentCallback
        self._metadata = metadata

    def __repr__(self) -> str:
        return "_HTTP11ClientFactory({}, {})".format(
            self._quiescentCallback, self._metadata
        )

    def buildProtocol(self, addr):
        return HTTP11ClientProtocol(self._quiescentCallback)


class _RetryingHTTP11ClientProtocol:
    """
    A wrapper for L{HTTP11ClientProtocol} that automatically retries requests.

    @ivar _clientProtocol: The underlying L{HTTP11ClientProtocol}.

    @ivar _newConnection: A callable that creates a new connection for a
        retry.
    """

    def __init__(self, clientProtocol, newConnection):
        self._clientProtocol = clientProtocol
        self._newConnection = newConnection

    def _shouldRetry(self, method, exception, bodyProducer):
        """
        Indicate whether request should be retried.

        Only returns C{True} if method is idempotent, no response was
        received, the reason for the failed request was not due to
        user-requested cancellation, and no body was sent. The latter
        requirement may be relaxed in the future, and PUT added to approved
        method list.

        @param method: The method of the request.
        @type method: L{bytes}
        """
        if method not in (b"GET", b"HEAD", b"OPTIONS", b"DELETE", b"TRACE"):
            return False
        if not isinstance(
            exception,
            (RequestNotSent, RequestTransmissionFailed, ResponseNeverReceived),
        ):
            return False
        if isinstance(exception, _WrapperException):
            for aFailure in exception.reasons:
                if aFailure.check(defer.CancelledError):
                    return False
        if bodyProducer is not None:
            return False
        return True

    def request(self, request):
        """
        Do a request, and retry once (with a new connection) if it fails in
        a retryable manner.

        @param request: A L{Request} instance that will be requested using the
            wrapped protocol.
        """
        d = self._clientProtocol.request(request)

        def failed(reason):
            if self._shouldRetry(request.method, reason.value, request.bodyProducer):
                return self._newConnection().addCallback(
                    lambda connection: connection.request(request)
                )
            else:
                return reason

        d.addErrback(failed)
        return d


class HTTPConnectionPool:
    """
    A pool of persistent HTTP connections.

    Features:
     - Cached connections will eventually time out.
     - Limits on maximum number of persistent connections.

    Connections are stored using keys, which should be chosen such that any
    connections stored under a given key can be used interchangeably.

    Failed requests done using previously cached connections will be retried
    once if they use an idempotent method (e.g. GET), in case the HTTP server
    timed them out.

    @ivar persistent: Boolean indicating whether connections should be
        persistent. Connections are persistent by default.

    @ivar maxPersistentPerHost: The maximum number of cached persistent
        connections for a C{host:port} destination.
    @type maxPersistentPerHost: C{int}

    @ivar cachedConnectionTimeout: Number of seconds a cached persistent
        connection will stay open before disconnecting.

    @ivar retryAutomatically: C{boolean} indicating whether idempotent
        requests should be retried once if no response was received.

    @ivar _factory: The factory used to connect to the proxy.

    @ivar _connections: Map (scheme, host, port) to lists of
        L{HTTP11ClientProtocol} instances.

    @ivar _timeouts: Map L{HTTP11ClientProtocol} instances to a
        C{IDelayedCall} instance of their timeout.

    @since: 12.1
    """

    _factory = _HTTP11ClientFactory
    maxPersistentPerHost = 2
    cachedConnectionTimeout = 240
    retryAutomatically = True
    _log = Logger()

    def __init__(self, reactor, persistent=True):
        self._reactor = reactor
        self.persistent = persistent
        self._connections = {}
        self._timeouts = {}

    def getConnection(self, key, endpoint):
        """
        Supply a connection, newly created or retrieved from the pool, to be
        used for one HTTP request.

        The connection will remain out of the pool (not available to be
        returned from future calls to this method) until one HTTP request has
        been completed over it.

        Afterwards, if the connection is still open, it will automatically be
        added to the pool.

        @param key: A unique key identifying connections that can be used
            interchangeably.

        @param endpoint: An endpoint that can be used to open a new connection
            if no cached connection is available.

        @return: A C{Deferred} that will fire with a L{HTTP11ClientProtocol}
           (or a wrapper) that can be used to send a single HTTP request.
        """
        # Try to get cached version:
        connections = self._connections.get(key)
        while connections:
            connection = connections.pop(0)
            # Cancel timeout:
            self._timeouts[connection].cancel()
            del self._timeouts[connection]
            if connection.state == "QUIESCENT":
                if self.retryAutomatically:
                    newConnection = lambda: self._newConnection(key, endpoint)
                    connection = _RetryingHTTP11ClientProtocol(
                        connection, newConnection
                    )
                return defer.succeed(connection)

        return self._newConnection(key, endpoint)

    def _newConnection(self, key, endpoint):
        """
        Create a new connection.

        This implements the new connection code path for L{getConnection}.
        """

        def quiescentCallback(protocol):
            self._putConnection(key, protocol)

        factory = self._factory(quiescentCallback, repr(endpoint))
        return endpoint.connect(factory)

    def _removeConnection(self, key, connection):
        """
        Remove a connection from the cache and disconnect it.
        """
        connection.transport.loseConnection()
        self._connections[key].remove(connection)
        del self._timeouts[connection]

    def _putConnection(self, key, connection):
        """
        Return a persistent connection to the pool. This will be called by
        L{HTTP11ClientProtocol} when the connection becomes quiescent.
        """
        if connection.state != "QUIESCENT":
            # Log with traceback for debugging purposes:
            try:
                raise RuntimeError(
                    "BUG: Non-quiescent protocol added to connection pool."
                )
            except BaseException:
                self._log.failure(
                    "BUG: Non-quiescent protocol added to connection pool."
                )
            return
        connections = self._connections.setdefault(key, [])
        if len(connections) == self.maxPersistentPerHost:
            dropped = connections.pop(0)
            dropped.transport.loseConnection()
            self._timeouts[dropped].cancel()
            del self._timeouts[dropped]
        connections.append(connection)
        cid = self._reactor.callLater(
            self.cachedConnectionTimeout, self._removeConnection, key, connection
        )
        self._timeouts[connection] = cid

    def closeCachedConnections(self):
        """
        Close all persistent connections and remove them from the pool.

        @return: L{defer.Deferred} that fires when all connections have been
            closed.
        """
        results = []
        for protocols in self._connections.values():
            for p in protocols:
                results.append(p.abort())
        self._connections = {}
        for dc in self._timeouts.values():
            dc.cancel()
        self._timeouts = {}
        return defer.gatherResults(results).addCallback(lambda ign: None)


class _AgentBase:
    """
    Base class offering common facilities for L{Agent}-type classes.

    @ivar _reactor: The C{IReactorTime} implementation which will be used by
        the pool, and perhaps by subclasses as well.

    @ivar _pool: The L{HTTPConnectionPool} used to manage HTTP connections.
    """

    def __init__(self, reactor, pool):
        if pool is None:
            pool = HTTPConnectionPool(reactor, False)
        self._reactor = reactor
        self._pool = pool

    def _computeHostValue(self, scheme, host, port):
        """
        Compute the string to use for the value of the I{Host} header, based on
        the given scheme, host name, and port number.
        """
        if isIPv6Address(nativeString(host)):
            host = b"[" + host + b"]"
        if (scheme, port) in ((b"http", 80), (b"https", 443)):
            return host
        return b"%b:%d" % (host, port)

    def _requestWithEndpoint(
        self, key, endpoint, method, parsedURI, headers, bodyProducer, requestPath
    ):
        """
        Issue a new request, given the endpoint and the path sent as part of
        the request.
        """
        if not isinstance(method, bytes):
            raise TypeError(f"method={method!r} is {type(method)}, but must be bytes")

        method = _ensureValidMethod(method)

        # Create minimal headers, if necessary:
        if headers is None:
            headers = Headers()
        if not headers.hasHeader(b"host"):
            headers = headers.copy()
            headers.addRawHeader(
                b"host",
                self._computeHostValue(
                    parsedURI.scheme, parsedURI.host, parsedURI.port
                ),
            )

        d = self._pool.getConnection(key, endpoint)

        def cbConnected(proto):
            return proto.request(
                Request._construct(
                    method,
                    requestPath,
                    headers,
                    bodyProducer,
                    persistent=self._pool.persistent,
                    parsedURI=parsedURI,
                )
            )

        d.addCallback(cbConnected)
        return d


@implementer(IAgentEndpointFactory)
class _StandardEndpointFactory:
    """
    Standard HTTP endpoint destinations - TCP for HTTP, TCP+TLS for HTTPS.

    @ivar _policyForHTTPS: A web context factory which will be used to create
        SSL context objects for any SSL connections the agent needs to make.

    @ivar _connectTimeout: If not L{None}, the timeout passed to
        L{HostnameEndpoint} for specifying the connection timeout.

    @ivar _bindAddress: If not L{None}, the address passed to
        L{HostnameEndpoint} for specifying the local address to bind to.
    """

    def __init__(self, reactor, contextFactory, connectTimeout, bindAddress):
        """
        @param reactor: A provider to use to create endpoints.
        @type reactor: see L{HostnameEndpoint.__init__} for acceptable reactor
            types.

        @param contextFactory: A factory for TLS contexts, to control the
            verification parameters of OpenSSL.
        @type contextFactory: L{IPolicyForHTTPS}.

        @param connectTimeout: The amount of time that this L{Agent} will wait
            for the peer to accept a connection.
        @type connectTimeout: L{float} or L{None}

        @param bindAddress: The local address for client sockets to bind to.
        @type bindAddress: L{bytes} or L{None}
        """
        self._reactor = reactor
        self._policyForHTTPS = contextFactory
        self._connectTimeout = connectTimeout
        self._bindAddress = bindAddress

    def endpointForURI(self, uri):
        """
        Connect directly over TCP for C{b'http'} scheme, and TLS for
        C{b'https'}.

        @param uri: L{URI} to connect to.

        @return: Endpoint to connect to.
        @rtype: L{IStreamClientEndpoint}
        """
        kwargs = {}
        if self._connectTimeout is not None:
            kwargs["timeout"] = self._connectTimeout
        kwargs["bindAddress"] = self._bindAddress

        try:
            host = nativeString(uri.host)
        except UnicodeDecodeError:
            raise ValueError(
                (
                    "The host of the provided URI ({uri.host!r}) "
                    "contains non-ASCII octets, it should be ASCII "
                    "decodable."
                ).format(uri=uri)
            )

        endpoint = HostnameEndpoint(self._reactor, host, uri.port, **kwargs)
        if uri.scheme == b"http":
            return endpoint
        elif uri.scheme == b"https":
            connectionCreator = self._policyForHTTPS.creatorForNetloc(
                uri.host, uri.port
            )
            return wrapClientTLS(connectionCreator, endpoint)
        else:
            raise SchemeNotSupported(f"Unsupported scheme: {uri.scheme!r}")


@implementer(IAgent)
class Agent(_AgentBase):
    """
    L{Agent} is a very basic HTTP client.  It supports I{HTTP} and I{HTTPS}
    scheme URIs.

    @ivar _pool: An L{HTTPConnectionPool} instance.

    @ivar _endpointFactory: The L{IAgentEndpointFactory} which will
        be used to create endpoints for outgoing connections.

    @since: 9.0
    """

    def __init__(
        self,
        reactor,
        contextFactory=BrowserLikePolicyForHTTPS(),
        connectTimeout=None,
        bindAddress=None,
        pool=None,
    ):
        """
        Create an L{Agent}.

        @param reactor: A reactor for this L{Agent} to place outgoing
            connections.
        @type reactor: see L{HostnameEndpoint.__init__} for acceptable reactor
            types.

        @param contextFactory: A factory for TLS contexts, to control the
            verification parameters of OpenSSL.  The default is to use a
            L{BrowserLikePolicyForHTTPS}, so unless you have special
            requirements you can leave this as-is.
        @type contextFactory: L{IPolicyForHTTPS}.

        @param connectTimeout: The amount of time that this L{Agent} will wait
            for the peer to accept a connection.
        @type connectTimeout: L{float}

        @param bindAddress: The local address for client sockets to bind to.
        @type bindAddress: L{bytes}

        @param pool: An L{HTTPConnectionPool} instance, or L{None}, in which
            case a non-persistent L{HTTPConnectionPool} instance will be
            created.
        @type pool: L{HTTPConnectionPool}
        """
        if not IPolicyForHTTPS.providedBy(contextFactory):
            warnings.warn(
                repr(contextFactory)
                + " was passed as the HTTPS policy for an Agent, but it does "
                "not provide IPolicyForHTTPS.  Since Twisted 14.0, you must "
                "pass a provider of IPolicyForHTTPS.",
                stacklevel=2,
                category=DeprecationWarning,
            )
            contextFactory = _DeprecatedToCurrentPolicyForHTTPS(contextFactory)
        endpointFactory = _StandardEndpointFactory(
            reactor, contextFactory, connectTimeout, bindAddress
        )
        self._init(reactor, endpointFactory, pool)

    @classmethod
    def usingEndpointFactory(cls, reactor, endpointFactory, pool=None):
        """
        Create a new L{Agent} that will use the endpoint factory to figure
        out how to connect to the server.

        @param reactor: A reactor for this L{Agent} to place outgoing
            connections.
        @type reactor: see L{HostnameEndpoint.__init__} for acceptable reactor
            types.

        @param endpointFactory: Used to construct endpoints which the
            HTTP client will connect with.
        @type endpointFactory: an L{IAgentEndpointFactory} provider.

        @param pool: An L{HTTPConnectionPool} instance, or L{None}, in which
            case a non-persistent L{HTTPConnectionPool} instance will be
            created.
        @type pool: L{HTTPConnectionPool}

        @return: A new L{Agent}.
        """
        agent = cls.__new__(cls)
        agent._init(reactor, endpointFactory, pool)
        return agent

    def _init(self, reactor, endpointFactory, pool):
        """
        Initialize a new L{Agent}.

        @param reactor: A reactor for this L{Agent} to place outgoing
            connections.
        @type reactor: see L{HostnameEndpoint.__init__} for acceptable reactor
            types.

        @param endpointFactory: Used to construct endpoints which the
            HTTP client will connect with.
        @type endpointFactory: an L{IAgentEndpointFactory} provider.

        @param pool: An L{HTTPConnectionPool} instance, or L{None}, in which
            case a non-persistent L{HTTPConnectionPool} instance will be
            created.
        @type pool: L{HTTPConnectionPool}

        @return: A new L{Agent}.
        """
        _AgentBase.__init__(self, reactor, pool)
        self._endpointFactory = endpointFactory

    def _getEndpoint(self, uri):
        """
        Get an endpoint for the given URI, using C{self._endpointFactory}.

        @param uri: The URI of the request.
        @type uri: L{URI}

        @return: An endpoint which can be used to connect to given address.
        """
        return self._endpointFactory.endpointForURI(uri)

    def request(self, method, uri, headers=None, bodyProducer=None):
        """
        Issue a request to the server indicated by the given C{uri}.

        An existing connection from the connection pool may be used or a new
        one may be created.

        I{HTTP} and I{HTTPS} schemes are supported in C{uri}.

        @see: L{twisted.web.iweb.IAgent.request}
        """
        uri = _ensureValidURI(uri.strip())
        parsedURI = URI.fromBytes(uri)
        try:
            endpoint = self._getEndpoint(parsedURI)
        except SchemeNotSupported:
            return defer.fail(Failure())
        key = (parsedURI.scheme, parsedURI.host, parsedURI.port)
        return self._requestWithEndpoint(
            key,
            endpoint,
            method,
            parsedURI,
            headers,
            bodyProducer,
            parsedURI.originForm,
        )


@implementer(IAgent)
class ProxyAgent(_AgentBase):
    """
    An HTTP agent able to cross HTTP proxies.

    @ivar _proxyEndpoint: The endpoint used to connect to the proxy.

    @since: 11.1
    """

    def __init__(self, endpoint, reactor=None, pool=None):
        if reactor is None:
            from twisted.internet import reactor
        _AgentBase.__init__(self, reactor, pool)
        self._proxyEndpoint = endpoint

    def request(self, method, uri, headers=None, bodyProducer=None):
        """
        Issue a new request via the configured proxy.
        """
        uri = _ensureValidURI(uri.strip())

        # Cache *all* connections under the same key, since we are only
        # connecting to a single destination, the proxy:
        key = ("http-proxy", self._proxyEndpoint)

        # To support proxying HTTPS via CONNECT, we will use key
        # ("http-proxy-CONNECT", scheme, host, port), and an endpoint that
        # wraps _proxyEndpoint with an additional callback to do the CONNECT.
        return self._requestWithEndpoint(
            key,
            self._proxyEndpoint,
            method,
            URI.fromBytes(uri),
            headers,
            bodyProducer,
            uri,
        )


class _FakeStdlibRequest(_RequestBase):
    """
    A fake L{urllib.request.Request} object for L{cookiejar} to work with.

    @see: U{urllib.request.Request
        <https://docs.python.org/3/library/urllib.request.html#urllib.request.Request>}

    @ivar uri: Request URI.

    @ivar headers: Request headers.

    @ivar type: The scheme of the URI.

    @ivar host: The host[:port] of the URI.

    @since: 11.1
    """

    uri: str
    type: str
    host: str
    # The received headers managed using Twisted API.
    _twistedHeaders: Headers

    def __init__(self, uri: bytes) -> None:
        """
        Create a fake  request.

        @param uri: Request URI.
        """
        self.uri = nativeString(uri)
        self._twistedHeaders = Headers()

        _uri = URI.fromBytes(uri)
        self.type = nativeString(_uri.scheme)
        self.host = nativeString(_uri.host)

        if (_uri.scheme, _uri.port) not in ((b"http", 80), (b"https", 443)):
            # If it's not a schema on the regular port, add the port.
            self.host += ":" + str(_uri.port)

        self.origin_req_host = nativeString(_uri.host)
        self.unverifiable = False

    def has_header(self, header):
        return self._twistedHeaders.hasHeader(networkString(header))

    def add_unredirected_header(self, name, value):
        self._twistedHeaders.addRawHeader(networkString(name), networkString(value))

    def get_full_url(self):
        return self.uri

    def get_header(self, name, default=None):
        headers = self._twistedHeaders.getRawHeaders(networkString(name), default)
        if headers is not None:
            headers = [nativeString(x) for x in headers]
            return headers[0]
        return None

    def get_host(self):
        return self.host

    def get_type(self):
        return self.type

    def is_unverifiable(self):
        # In theory this shouldn't be hardcoded.
        return False


@dataclass
class _FakeUrllibResponseInfo(_InfoType):
    response: IResponse

    def get_all(self, name: str, default: bytes) -> list[str]:  # type:ignore[override]
        headers = self.response.headers.getRawHeaders(networkString(name), default)
        h = [nativeString(x) for x in headers]
        return h


class _FakeStdlibResponse(_ResponseBase):
    """
    A fake L{urllib.response.Response} object for L{http.cookiejar} to work
    with.

    @ivar response: Underlying Twisted Web response.

    @since: 11.1
    """

    response: IResponse

    def __init__(self, response: IResponse) -> None:
        self.response = response

    def info(self) -> _InfoType:
        result = _FakeUrllibResponseInfo(self.response)
        return result


@implementer(IAgent)
class CookieAgent:
    """
    L{CookieAgent} extends the basic L{Agent} to add RFC-compliant handling of
    HTTP cookies.  Cookies are written to and extracted from a L{CookieJar}
    instance.

    The same cookie jar instance will be used for any requests through this
    agent, mutating it whenever a I{Set-Cookie} header appears in a response.

    @ivar _agent: Underlying Twisted Web agent to issue requests through.

    @ivar cookieJar: Initialized cookie jar to read cookies from and store
        cookies to.

    @since: 11.1
    """

    _agent: IAgent
    cookieJar: CookieJar

    def __init__(self, agent: IAgent, cookieJar: CookieJar) -> None:
        self._agent = agent
        self.cookieJar = cookieJar

    def request(
        self,
        method: bytes,
        uri: bytes,
        headers: Optional[Headers] = None,
        bodyProducer: Optional[IBodyProducer] = None,
    ) -> Deferred[IResponse]:
        """
        Issue a new request to the wrapped L{Agent}.

        Send a I{Cookie} header if a cookie for C{uri} is stored in
        L{CookieAgent.cookieJar}. Cookies are automatically extracted and
        stored from requests.

        If a C{'cookie'} header appears in C{headers} it will override the
        automatic cookie header obtained from the cookie jar.

        @see: L{Agent.request}
        """
        actualHeaders = headers if headers is not None else Headers()
        lastRequest = _FakeStdlibRequest(uri)
        # Setting a cookie header explicitly will disable automatic request
        # cookies.
        if not actualHeaders.hasHeader(b"cookie"):
            self.cookieJar.add_cookie_header(lastRequest)
            cookieHeader = lastRequest.get_header("Cookie", None)
            if cookieHeader is not None:
                actualHeaders = actualHeaders.copy()
                actualHeaders.addRawHeader(b"cookie", networkString(cookieHeader))

        return self._agent.request(
            method, uri, actualHeaders, bodyProducer
        ).addCallback(self._extractCookies, lastRequest)

    def _extractCookies(
        self, response: IResponse, request: _FakeStdlibRequest
    ) -> IResponse:
        """
        Extract response cookies and store them in the cookie jar.

        @param response: the Twisted Web response that we are processing.

        @param request: A L{_FakeStdlibRequest} wrapping our Twisted request,
            for L{CookieJar} to extract cookies from.
        """
        self.cookieJar.extract_cookies(_FakeStdlibResponse(response), request)
        return response


class GzipDecoder(proxyForInterface(IResponse)):  # type: ignore[misc]
    """
    A wrapper for a L{Response} instance which handles gzip'ed body.

    @ivar original: The original L{Response} object.

    @since: 11.1
    """

    def __init__(self, response):
        self.original = response
        self.length = UNKNOWN_LENGTH

    def deliverBody(self, protocol):
        """
        Override C{deliverBody} to wrap the given C{protocol} with
        L{_GzipProtocol}.
        """
        self.original.deliverBody(_GzipProtocol(protocol, self.original))


class _GzipProtocol(proxyForInterface(IProtocol)):  # type: ignore[misc]
    """
    A L{Protocol} implementation which wraps another one, transparently
    decompressing received data.

    @ivar _zlibDecompress: A zlib decompress object used to decompress the data
        stream.

    @ivar _response: A reference to the original response, in case of errors.

    @since: 11.1
    """

    def __init__(self, protocol, response):
        self.original = protocol
        self._response = response
        self._zlibDecompress = zlib.decompressobj(16 + zlib.MAX_WBITS)

    def dataReceived(self, data):
        """
        Decompress C{data} with the zlib decompressor, forwarding the raw data
        to the original protocol.
        """
        try:
            rawData = self._zlibDecompress.decompress(data)
        except zlib.error:
            raise ResponseFailed([Failure()], self._response)
        if rawData:
            self.original.dataReceived(rawData)

    def connectionLost(self, reason):
        """
        Forward the connection lost event, flushing remaining data from the
        decompressor if any.
        """
        try:
            rawData = self._zlibDecompress.flush()
        except zlib.error:
            raise ResponseFailed([reason, Failure()], self._response)
        if rawData:
            self.original.dataReceived(rawData)
        self.original.connectionLost(reason)


@implementer(IAgent)
class ContentDecoderAgent:
    """
    An L{Agent} wrapper to handle encoded content.

    It takes care of declaring the support for content in the
    I{Accept-Encoding} header and automatically decompresses the received data
    if the I{Content-Encoding} header indicates a supported encoding.

    For example::

        agent = ContentDecoderAgent(Agent(reactor),
                                    [(b'gzip', GzipDecoder)])

    @param agent: The agent to wrap
    @type agent: L{IAgent}

    @param decoders: A sequence of (name, decoder) objects. The name
        declares which encoding the decoder supports. The decoder must accept
        an L{IResponse} and return an L{IResponse} when called. The order
        determines how the decoders are advertised to the server. Names must
        be unique.not be duplicated.
    @type decoders: sequence of (L{bytes}, L{callable}) tuples

    @since: 11.1

    @see: L{GzipDecoder}
    """

    def __init__(self, agent, decoders):
        self._agent = agent
        self._decoders = dict(decoders)
        self._supported = b",".join([decoder[0] for decoder in decoders])

    def request(self, method, uri, headers=None, bodyProducer=None):
        """
        Send a client request which declares supporting compressed content.

        @see: L{Agent.request}.
        """
        if headers is None:
            headers = Headers()
        else:
            headers = headers.copy()
        headers.addRawHeader(b"accept-encoding", self._supported)
        deferred = self._agent.request(method, uri, headers, bodyProducer)
        return deferred.addCallback(self._handleResponse)

    def _handleResponse(self, response):
        """
        Check if the response is encoded, and wrap it to handle decompression.
        """
        contentEncodingHeaders = response.headers.getRawHeaders(b"content-encoding", [])
        contentEncodingHeaders = b",".join(contentEncodingHeaders).split(b",")
        while contentEncodingHeaders:
            name = contentEncodingHeaders.pop().strip()
            decoder = self._decoders.get(name)
            if decoder is not None:
                response = decoder(response)
            else:
                # Add it back
                contentEncodingHeaders.append(name)
                break
        if contentEncodingHeaders:
            response.headers.setRawHeaders(
                b"content-encoding", [b",".join(contentEncodingHeaders)]
            )
        else:
            response.headers.removeHeader(b"content-encoding")
        return response


_canonicalHeaderName = Headers()._canonicalNameCaps
_defaultSensitiveHeaders = frozenset(
    [
        b"Authorization",
        b"Cookie",
        b"Cookie2",
        b"Proxy-Authorization",
        b"WWW-Authenticate",
    ]
)


@implementer(IAgent)
class RedirectAgent:
    """
    An L{Agent} wrapper which handles HTTP redirects.

    The implementation is rather strict: 301 and 302 behaves like 307, not
    redirecting automatically on methods different from I{GET} and I{HEAD}.

    See L{BrowserLikeRedirectAgent} for a redirecting Agent that behaves more
    like a web browser.

    @param redirectLimit: The maximum number of times the agent is allowed to
        follow redirects before failing with a L{error.InfiniteRedirection}.

    @param sensitiveHeaderNames: An iterable of C{bytes} enumerating the names
        of headers that must not be transmitted when redirecting to a different
        origins.  These will be consulted in addition to the protocol-specified
        set of headers that contain sensitive information.

    @cvar _redirectResponses: A L{list} of HTTP status codes to be redirected
        for I{GET} and I{HEAD} methods.

    @cvar _seeOtherResponses: A L{list} of HTTP status codes to be redirected
        for any method and the method altered to I{GET}.

    @since: 11.1
    """

    _redirectResponses = [
        http.MOVED_PERMANENTLY,
        http.FOUND,
        http.TEMPORARY_REDIRECT,
        http.PERMANENT_REDIRECT,
    ]
    _seeOtherResponses = [http.SEE_OTHER]

    def __init__(
        self,
        agent: IAgent,
        redirectLimit: int = 20,
        sensitiveHeaderNames: Iterable[bytes] = (),
    ):
        self._agent = agent
        self._redirectLimit = redirectLimit
        sensitive = {_canonicalHeaderName(each) for each in sensitiveHeaderNames}
        sensitive.update(_defaultSensitiveHeaders)
        self._sensitiveHeaderNames = sensitive

    def request(self, method, uri, headers=None, bodyProducer=None):
        """
        Send a client request following HTTP redirects.

        @see: L{Agent.request}.
        """
        deferred = self._agent.request(method, uri, headers, bodyProducer)
        return deferred.addCallback(self._handleResponse, method, uri, headers, 0)

    def _resolveLocation(self, requestURI, location):
        """
        Resolve the redirect location against the request I{URI}.

        @type requestURI: C{bytes}
        @param requestURI: The request I{URI}.

        @type location: C{bytes}
        @param location: The redirect location.

        @rtype: C{bytes}
        @return: Final resolved I{URI}.
        """
        return _urljoin(requestURI, location)

    def _handleRedirect(self, response, method, uri, headers, redirectCount):
        """
        Handle a redirect response, checking the number of redirects already
        followed, and extracting the location header fields.
        """
        if redirectCount >= self._redirectLimit:
            err = error.InfiniteRedirection(
                response.code, b"Infinite redirection detected", location=uri
            )
            raise ResponseFailed([Failure(err)], response)
        locationHeaders = response.headers.getRawHeaders(b"location", [])
        if not locationHeaders:
            err = error.RedirectWithNoLocation(
                response.code, b"No location header field", uri
            )
            raise ResponseFailed([Failure(err)], response)
        location = self._resolveLocation(uri, locationHeaders[0])
        if headers:
            parsedURI = URI.fromBytes(uri)
            parsedLocation = URI.fromBytes(location)
            sameOrigin = (
                (parsedURI.scheme == parsedLocation.scheme)
                and (parsedURI.host == parsedLocation.host)
                and (parsedURI.port == parsedLocation.port)
            )
            if not sameOrigin:
                headers = Headers(
                    {
                        rawName: rawValue
                        for rawName, rawValue in headers.getAllRawHeaders()
                        if rawName not in self._sensitiveHeaderNames
                    }
                )
        deferred = self._agent.request(method, location, headers)

        def _chainResponse(newResponse):
            newResponse.setPreviousResponse(response)
            return newResponse

        deferred.addCallback(_chainResponse)
        return deferred.addCallback(
            self._handleResponse, method, uri, headers, redirectCount + 1
        )

    def _handleResponse(self, response, method, uri, headers, redirectCount):
        """
        Handle the response, making another request if it indicates a redirect.
        """
        if response.code in self._redirectResponses:
            if method not in (b"GET", b"HEAD"):
                err = error.PageRedirect(response.code, location=uri)
                raise ResponseFailed([Failure(err)], response)
            return self._handleRedirect(response, method, uri, headers, redirectCount)
        elif response.code in self._seeOtherResponses:
            return self._handleRedirect(response, b"GET", uri, headers, redirectCount)
        return response


class BrowserLikeRedirectAgent(RedirectAgent):
    """
    An L{Agent} wrapper which handles HTTP redirects in the same fashion as web
    browsers.

    Unlike L{RedirectAgent}, the implementation is more relaxed: 301 and 302
    behave like 303, redirecting automatically on any method and altering the
    redirect request to a I{GET}.

    @see: L{RedirectAgent}

    @since: 13.1
    """

    _redirectResponses = [http.TEMPORARY_REDIRECT]
    _seeOtherResponses = [
        http.MOVED_PERMANENTLY,
        http.FOUND,
        http.SEE_OTHER,
        http.PERMANENT_REDIRECT,
    ]


class _ReadBodyProtocol(protocol.Protocol):
    """
    Protocol that collects data sent to it.

    This is a helper for L{IResponse.deliverBody}, which collects the body and
    fires a deferred with it.

    @ivar deferred: See L{__init__}.
    @ivar status: See L{__init__}.
    @ivar message: See L{__init__}.

    @ivar dataBuffer: list of byte-strings received
    @type dataBuffer: L{list} of L{bytes}
    """

    def __init__(self, status, message, deferred):
        """
        @param status: Status of L{IResponse}
        @ivar status: L{int}

        @param message: Message of L{IResponse}
        @type message: L{bytes}

        @param deferred: deferred to fire when response is complete
        @type deferred: L{Deferred} firing with L{bytes}
        """
        self.deferred = deferred
        self.status = status
        self.message = message
        self.dataBuffer = []

    def dataReceived(self, data):
        """
        Accumulate some more bytes from the response.
        """
        self.dataBuffer.append(data)

    def connectionLost(self, reason):
        """
        Deliver the accumulated response bytes to the waiting L{Deferred}, if
        the response body has been completely received without error.
        """
        if reason.check(ResponseDone):
            self.deferred.callback(b"".join(self.dataBuffer))
        elif reason.check(PotentialDataLoss):
            self.deferred.errback(
                PartialDownloadError(
                    self.status, self.message, b"".join(self.dataBuffer)
                )
            )
        else:
            self.deferred.errback(reason)


def readBody(response: IResponse) -> defer.Deferred[bytes]:
    """
    Get the body of an L{IResponse} and return it as a byte string.

    This is a helper function for clients that don't want to incrementally
    receive the body of an HTTP response.

    @param response: The HTTP response for which the body will be read.
    @type response: L{IResponse} provider

    @return: A L{Deferred} which will fire with the body of the response.
        Cancelling it will close the connection to the server immediately.
    """

    def cancel(deferred: defer.Deferred[bytes]) -> None:
        """
        Cancel a L{readBody} call, close the connection to the HTTP server
        immediately, if it is still open.

        @param deferred: The cancelled L{defer.Deferred}.
        """
        abort = getAbort()
        if abort is not None:
            abort()

    d: defer.Deferred[bytes] = defer.Deferred(cancel)
    protocol = _ReadBodyProtocol(response.code, response.phrase, d)

    def getAbort():
        return getattr(protocol.transport, "abortConnection", None)

    response.deliverBody(protocol)

    if protocol.transport is not None and getAbort() is None:
        warnings.warn(
            "Using readBody with a transport that does not have an "
            "abortConnection method",
            category=DeprecationWarning,
            stacklevel=2,
        )

    return d


__all__ = [
    "Agent",
    "BrowserLikePolicyForHTTPS",
    "BrowserLikeRedirectAgent",
    "ContentDecoderAgent",
    "CookieAgent",
    "GzipDecoder",
    "HTTPConnectionPool",
    "PartialDownloadError",
    "ProxyAgent",
    "readBody",
    "RedirectAgent",
    "RequestGenerationFailed",
    "RequestTransmissionFailed",
    "Response",
    "ResponseDone",
    "ResponseFailed",
    "ResponseNeverReceived",
    "URI",
]