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

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

"""
This is a web server which integrates with the twisted.internet infrastructure.

@var NOT_DONE_YET: A token value which L{twisted.web.resource.IResource.render}
    implementations can return to indicate that the application will later call
    C{.write} and C{.finish} to complete the request, and that the HTTP
    connection should be left open.
@type NOT_DONE_YET: Opaque; do not depend on any particular type for this
    value.
"""


import copy
import os
import re
import zlib
from binascii import hexlify
from html import escape
from typing import List, Optional
from urllib.parse import quote as _quote

from zope.interface import implementer

from incremental import Version

from twisted import copyright
from twisted.internet import address, interfaces
from twisted.internet.error import AlreadyCalled, AlreadyCancelled
from twisted.logger import Logger
from twisted.python import components, failure, reflect
from twisted.python.compat import nativeString, networkString
from twisted.python.deprecate import deprecatedModuleAttribute
from twisted.spread.pb import Copyable, ViewPoint
from twisted.web import http, iweb, resource, util
from twisted.web.error import UnsupportedMethod
from twisted.web.http import unquote

NOT_DONE_YET = 1

__all__ = [
    "supportedMethods",
    "Request",
    "Session",
    "Site",
    "version",
    "NOT_DONE_YET",
    "GzipEncoderFactory",
]


# backwards compatibility
deprecatedModuleAttribute(
    Version("Twisted", 12, 1, 0),
    "Please use twisted.web.http.datetimeToString instead",
    "twisted.web.server",
    "date_time_string",
)
deprecatedModuleAttribute(
    Version("Twisted", 12, 1, 0),
    "Please use twisted.web.http.stringToDatetime instead",
    "twisted.web.server",
    "string_date_time",
)
date_time_string = http.datetimeToString
string_date_time = http.stringToDatetime

# Support for other methods may be implemented on a per-resource basis.
supportedMethods = (b"GET", b"HEAD", b"POST")


def quote(string, *args, **kwargs):
    return _quote(string.decode("charmap"), *args, **kwargs).encode("charmap")


def _addressToTuple(addr):
    if isinstance(addr, address.IPv4Address):
        return ("INET", addr.host, addr.port)
    elif isinstance(addr, address.UNIXAddress):
        return ("UNIX", addr.name)
    else:
        return tuple(addr)


@implementer(iweb.IRequest)
class Request(Copyable, http.Request, components.Componentized):
    """
    An HTTP request.

    @ivar defaultContentType: A L{bytes} giving the default I{Content-Type}
        value to send in responses if no other value is set.  L{None} disables
        the default.

    @ivar _insecureSession: The L{Session} object representing state that will
        be transmitted over plain-text HTTP.

    @ivar _secureSession: The L{Session} object representing the state that
        will be transmitted only over HTTPS.
    """

    defaultContentType: Optional[bytes] = b"text/html"
    site = None
    appRootURL = None
    prepath: Optional[List[bytes]] = None
    postpath: Optional[List[bytes]] = None
    __pychecker__ = "unusednames=issuer"
    _inFakeHead = False
    _encoder = None
    _log = Logger()

    def __init__(self, *args, **kw):
        http.Request.__init__(self, *args, **kw)
        components.Componentized.__init__(self)

    def getStateToCopyFor(self, issuer):
        x = self.__dict__.copy()
        del x["transport"]
        # XXX refactor this attribute out; it's from protocol
        # del x['server']
        del x["channel"]
        del x["content"]
        del x["site"]
        self.content.seek(0, 0)
        x["content_data"] = self.content.read()
        x["remote"] = ViewPoint(issuer, self)

        # Address objects aren't jellyable
        x["host"] = _addressToTuple(x["host"])
        x["client"] = _addressToTuple(x["client"])

        # Header objects also aren't jellyable.
        x["requestHeaders"] = list(x["requestHeaders"].getAllRawHeaders())

        return x

    # HTML generation helpers

    def sibLink(self, name):
        """
        Return the text that links to a sibling of the requested resource.

        @param name: The sibling resource
        @type name: C{bytes}

        @return: A relative URL.
        @rtype: C{bytes}
        """
        if self.postpath:
            return (len(self.postpath) * b"../") + name
        else:
            return name

    def childLink(self, name):
        """
        Return the text that links to a child of the requested resource.

        @param name: The child resource
        @type name: C{bytes}

        @return: A relative URL.
        @rtype: C{bytes}
        """
        lpp = len(self.postpath)
        if lpp > 1:
            return ((lpp - 1) * b"../") + name
        elif lpp == 1:
            return name
        else:  # lpp == 0
            if len(self.prepath) and self.prepath[-1]:
                return self.prepath[-1] + b"/" + name
            else:
                return name

    def gotLength(self, length):
        """
        Called when HTTP channel got length of content in this request.

        This method is not intended for users.

        @param length: The length of the request body, as indicated by the
            request headers.  L{None} if the request headers do not indicate a
            length.
        """
        try:
            getContentFile = self.channel.site.getContentFile
        except AttributeError:
            http.Request.gotLength(self, length)
        else:
            self.content = getContentFile(length)

    def process(self):
        """
        Process a request.

        Find the addressed resource in this request's L{Site},
        and call L{self.render()<Request.render()>} with it.

        @see: L{Site.getResourceFor()}
        """

        # get site from channel
        self.site = self.channel.site

        # set various default headers
        self.setHeader(b"server", version)
        self.setHeader(b"date", http.datetimeToString())

        # Resource Identification
        self.prepath = []
        self.postpath = list(map(unquote, self.path[1:].split(b"/")))

        # Short-circuit for requests whose path is '*'.
        if self.path == b"*":
            self._handleStar()
            return

        try:
            resrc = self.site.getResourceFor(self)
            if resource._IEncodingResource.providedBy(resrc):
                encoder = resrc.getEncoder(self)
                if encoder is not None:
                    self._encoder = encoder
            self.render(resrc)
        except BaseException:
            self.processingFailed(failure.Failure())

    def write(self, data):
        """
        Write data to the transport (if not responding to a HEAD request).

        @param data: A string to write to the response.
        @type data: L{bytes}
        """
        if not self.startedWriting:
            # Before doing the first write, check to see if a default
            # Content-Type header should be supplied. We omit it on
            # NOT_MODIFIED and NO_CONTENT responses. We also omit it if there
            # is a Content-Length header set to 0, as empty bodies don't need
            # a content-type.
            needsCT = self.code not in (http.NOT_MODIFIED, http.NO_CONTENT)
            contentType = self.responseHeaders.getRawHeaders(b"content-type")
            contentLength = self.responseHeaders.getRawHeaders(b"content-length")
            contentLengthZero = contentLength and (contentLength[0] == b"0")

            if (
                needsCT
                and contentType is None
                and self.defaultContentType is not None
                and not contentLengthZero
            ):
                self.responseHeaders.setRawHeaders(
                    b"content-type", [self.defaultContentType]
                )

        # Only let the write happen if we're not generating a HEAD response by
        # faking out the request method.  Note, if we are doing that,
        # startedWriting will never be true, and the above logic may run
        # multiple times.  It will only actually change the responseHeaders
        # once though, so it's still okay.
        if not self._inFakeHead:
            if self._encoder:
                data = self._encoder.encode(data)
            http.Request.write(self, data)

    def finish(self):
        """
        Override C{http.Request.finish} for possible encoding.
        """
        if self._encoder:
            data = self._encoder.finish()
            if data:
                http.Request.write(self, data)
        return http.Request.finish(self)

    def render(self, resrc):
        """
        Ask a resource to render itself.

        If the resource does not support the requested method,
        generate a C{NOT IMPLEMENTED} or C{NOT ALLOWED} response.

        @param resrc: The resource to render.
        @type resrc: L{twisted.web.resource.IResource}

        @see: L{IResource.render()<twisted.web.resource.IResource.render()>}
        """
        try:
            body = resrc.render(self)
        except UnsupportedMethod as e:
            allowedMethods = e.allowedMethods
            if (self.method == b"HEAD") and (b"GET" in allowedMethods):
                # We must support HEAD (RFC 2616, 5.1.1).  If the
                # resource doesn't, fake it by giving the resource
                # a 'GET' request and then return only the headers,
                # not the body.
                self._log.info(
                    "Using GET to fake a HEAD request for {resrc}", resrc=resrc
                )
                self.method = b"GET"
                self._inFakeHead = True
                body = resrc.render(self)

                if body is NOT_DONE_YET:
                    self._log.info(
                        "Tried to fake a HEAD request for {resrc}, but "
                        "it got away from me.",
                        resrc=resrc,
                    )
                    # Oh well, I guess we won't include the content length.
                else:
                    self.setHeader(b"content-length", b"%d" % (len(body),))

                self._inFakeHead = False
                self.method = b"HEAD"
                self.write(b"")
                self.finish()
                return

            if self.method in (supportedMethods):
                # We MUST include an Allow header
                # (RFC 2616, 10.4.6 and 14.7)
                self.setHeader(b"Allow", b", ".join(allowedMethods))
                s = (
                    """Your browser approached me (at %(URI)s) with"""
                    """ the method "%(method)s".  I only allow"""
                    """ the method%(plural)s %(allowed)s here."""
                    % {
                        "URI": escape(nativeString(self.uri)),
                        "method": nativeString(self.method),
                        "plural": ((len(allowedMethods) > 1) and "s") or "",
                        "allowed": ", ".join([nativeString(x) for x in allowedMethods]),
                    }
                )
                epage = resource._UnsafeErrorPage(
                    http.NOT_ALLOWED, "Method Not Allowed", s
                )
                body = epage.render(self)
            else:
                epage = resource._UnsafeErrorPage(
                    http.NOT_IMPLEMENTED,
                    "Huh?",
                    "I don't know how to treat a %s request."
                    % (escape(self.method.decode("charmap")),),
                )
                body = epage.render(self)
        # end except UnsupportedMethod

        if body is NOT_DONE_YET:
            return
        if not isinstance(body, bytes):
            body = resource._UnsafeErrorPage(
                http.INTERNAL_SERVER_ERROR,
                "Request did not return bytes",
                "Request: "
                # GHSA-vg46-2rrj-3647 note: _PRE does HTML-escape the input.
                + util._PRE(reflect.safe_repr(self))
                + "<br />"
                + "Resource: "
                + util._PRE(reflect.safe_repr(resrc))
                + "<br />"
                + "Value: "
                + util._PRE(reflect.safe_repr(body)),
            ).render(self)

        if self.method == b"HEAD":
            if len(body) > 0:
                # This is a Bad Thing (RFC 2616, 9.4)
                self._log.info(
                    "Warning: HEAD request {slf} for resource {resrc} is"
                    " returning a message body. I think I'll eat it.",
                    slf=self,
                    resrc=resrc,
                )
                self.setHeader(b"content-length", b"%d" % (len(body),))
            self.write(b"")
        else:
            self.setHeader(b"content-length", b"%d" % (len(body),))
            self.write(body)
        self.finish()

    def processingFailed(self, reason):
        """
        Finish this request with an indication that processing failed and
        possibly display a traceback.

        @param reason: Reason this request has failed.
        @type reason: L{twisted.python.failure.Failure}

        @return: The reason passed to this method.
        @rtype: L{twisted.python.failure.Failure}
        """
        self._log.failure("", failure=reason)
        if self.site.displayTracebacks:
            body = (
                b"<html><head><title>web.Server Traceback"
                b" (most recent call last)</title></head>"
                b"<body><b>web.Server Traceback"
                b" (most recent call last):</b>\n\n"
                + util.formatFailure(reason)
                + b"\n\n</body></html>\n"
            )
        else:
            body = (
                b"<html><head><title>Processing Failed"
                b"</title></head><body>"
                b"<b>Processing Failed</b></body></html>"
            )

        self.setResponseCode(http.INTERNAL_SERVER_ERROR)
        self.setHeader(b"content-type", b"text/html")
        self.setHeader(b"content-length", b"%d" % (len(body),))
        self.write(body)
        self.finish()
        return reason

    def view_write(self, issuer, data):
        """Remote version of write; same interface."""
        self.write(data)

    def view_finish(self, issuer):
        """Remote version of finish; same interface."""
        self.finish()

    def view_addCookie(self, issuer, k, v, **kwargs):
        """Remote version of addCookie; same interface."""
        self.addCookie(k, v, **kwargs)

    def view_setHeader(self, issuer, k, v):
        """Remote version of setHeader; same interface."""
        self.setHeader(k, v)

    def view_setLastModified(self, issuer, when):
        """Remote version of setLastModified; same interface."""
        self.setLastModified(when)

    def view_setETag(self, issuer, tag):
        """Remote version of setETag; same interface."""
        self.setETag(tag)

    def view_setResponseCode(self, issuer, code, message=None):
        """
        Remote version of setResponseCode; same interface.
        """
        self.setResponseCode(code, message)

    def view_registerProducer(self, issuer, producer, streaming):
        """Remote version of registerProducer; same interface.
        (requires a remote producer.)
        """
        self.registerProducer(_RemoteProducerWrapper(producer), streaming)

    def view_unregisterProducer(self, issuer):
        self.unregisterProducer()

    ### these calls remain local

    _secureSession = None
    _insecureSession = None

    @property
    def session(self):
        """
        If a session has already been created or looked up with
        L{Request.getSession}, this will return that object.  (This will always
        be the session that matches the security of the request; so if
        C{forceNotSecure} is used on a secure request, this will not return
        that session.)

        @return: the session attribute
        @rtype: L{Session} or L{None}
        """
        if self.isSecure():
            return self._secureSession
        else:
            return self._insecureSession

    def getSession(self, sessionInterface=None, forceNotSecure=False):
        """
        Check if there is a session cookie, and if not, create it.

        By default, the cookie with be secure for HTTPS requests and not secure
        for HTTP requests.  If for some reason you need access to the insecure
        cookie from a secure request you can set C{forceNotSecure = True}.

        @param forceNotSecure: Should we retrieve a session that will be
            transmitted over HTTP, even if this L{Request} was delivered over
            HTTPS?
        @type forceNotSecure: L{bool}
        """
        # Make sure we aren't creating a secure session on a non-secure page
        secure = self.isSecure() and not forceNotSecure

        if not secure:
            cookieString = b"TWISTED_SESSION"
            sessionAttribute = "_insecureSession"
        else:
            cookieString = b"TWISTED_SECURE_SESSION"
            sessionAttribute = "_secureSession"

        session = getattr(self, sessionAttribute)

        if session is not None:
            # We have a previously created session.
            try:
                # Refresh the session, to keep it alive.
                session.touch()
            except (AlreadyCalled, AlreadyCancelled):
                # Session has already expired.
                session = None

        if session is None:
            # No session was created yet for this request.
            cookiename = b"_".join([cookieString] + self.sitepath)
            sessionCookie = self.getCookie(cookiename)
            if sessionCookie:
                try:
                    session = self.site.getSession(sessionCookie)
                except KeyError:
                    pass
            # if it still hasn't been set, fix it up.
            if not session:
                session = self.site.makeSession()
                self.addCookie(cookiename, session.uid, path=b"/", secure=secure)

        setattr(self, sessionAttribute, session)

        if sessionInterface:
            return session.getComponent(sessionInterface)

        return session

    def _prePathURL(self, prepath):
        port = self.getHost().port
        if self.isSecure():
            default = 443
        else:
            default = 80
        if port == default:
            hostport = ""
        else:
            hostport = ":%d" % port
        prefix = networkString(
            "http%s://%s%s/"
            % (
                self.isSecure() and "s" or "",
                nativeString(self.getRequestHostname()),
                hostport,
            )
        )
        path = b"/".join([quote(segment, safe=b"") for segment in prepath])
        return prefix + path

    def prePathURL(self):
        return self._prePathURL(self.prepath)

    def URLPath(self):
        from twisted.python import urlpath

        return urlpath.URLPath.fromRequest(self)

    def rememberRootURL(self):
        """
        Remember the currently-processed part of the URL for later
        recalling.
        """
        url = self._prePathURL(self.prepath[:-1])
        self.appRootURL = url

    def getRootURL(self):
        """
        Get a previously-remembered URL.

        @return: An absolute URL.
        @rtype: L{bytes}
        """
        return self.appRootURL

    def _handleStar(self):
        """
        Handle receiving a request whose path is '*'.

        RFC 7231 defines an OPTIONS * request as being something that a client
        can send as a low-effort way to probe server capabilities or readiness.
        Rather than bother the user with this, we simply fast-path it back to
        an empty 200 OK. Any non-OPTIONS verb gets a 405 Method Not Allowed
        telling the client they can only use OPTIONS.
        """
        if self.method == b"OPTIONS":
            self.setResponseCode(http.OK)
        else:
            self.setResponseCode(http.NOT_ALLOWED)
            self.setHeader(b"Allow", b"OPTIONS")

        # RFC 7231 says we MUST set content-length 0 when responding to this
        # with no body.
        self.setHeader(b"Content-Length", b"0")
        self.finish()


@implementer(iweb._IRequestEncoderFactory)
class GzipEncoderFactory:
    """
    @cvar compressLevel: The compression level used by the compressor, default
        to 9 (highest).

    @since: 12.3
    """

    _gzipCheckRegex = re.compile(rb"(:?^|[\s,])gzip(:?$|[\s,])")
    compressLevel = 9

    def encoderForRequest(self, request):
        """
        Check the headers if the client accepts gzip encoding, and encodes the
        request if so.
        """
        acceptHeaders = b",".join(
            request.requestHeaders.getRawHeaders(b"accept-encoding", [])
        )
        if self._gzipCheckRegex.search(acceptHeaders):
            encoding = request.responseHeaders.getRawHeaders(b"content-encoding")
            if encoding:
                encoding = b",".join(encoding + [b"gzip"])
            else:
                encoding = b"gzip"

            request.responseHeaders.setRawHeaders(b"content-encoding", [encoding])
            return _GzipEncoder(self.compressLevel, request)


@implementer(iweb._IRequestEncoder)
class _GzipEncoder:
    """
    An encoder which supports gzip.

    @ivar _zlibCompressor: The zlib compressor instance used to compress the
        stream.

    @ivar _request: A reference to the originating request.

    @since: 12.3
    """

    _zlibCompressor = None

    def __init__(self, compressLevel, request):
        self._zlibCompressor = zlib.compressobj(
            compressLevel, zlib.DEFLATED, 16 + zlib.MAX_WBITS
        )
        self._request = request

    def encode(self, data):
        """
        Write to the request, automatically compressing data on the fly.
        """
        if not self._request.startedWriting:
            # Remove the content-length header, we can't honor it
            # because we compress on the fly.
            self._request.responseHeaders.removeHeader(b"content-length")
        return self._zlibCompressor.compress(data)

    def finish(self):
        """
        Finish handling the request request, flushing any data from the zlib
        buffer.
        """
        remain = self._zlibCompressor.flush()
        self._zlibCompressor = None
        return remain


class _RemoteProducerWrapper:
    def __init__(self, remote):
        self.resumeProducing = remote.remoteMethod("resumeProducing")
        self.pauseProducing = remote.remoteMethod("pauseProducing")
        self.stopProducing = remote.remoteMethod("stopProducing")


class Session(components.Componentized):
    """
    A user's session with a system.

    This utility class contains no functionality, but is used to
    represent a session.

    @ivar site: The L{Site} that generated the session.
    @type site: L{Site}

    @ivar uid: A unique identifier for the session.
    @type uid: L{bytes}

    @ivar _reactor: An object providing L{IReactorTime} to use for scheduling
        expiration.

    @ivar sessionTimeout: Time after last modification the session will expire,
        in seconds.
    @type sessionTimeout: L{float}

    @ivar lastModified: Time the C{touch()} method was last called (or time the
        session was created). A UNIX timestamp as returned by
        L{IReactorTime.seconds()}.
    @type lastModified: L{float}
    """

    sessionTimeout = 900

    _expireCall = None

    def __init__(self, site, uid, reactor=None):
        """
        Initialize a session with a unique ID for that session.

        @param reactor: L{IReactorTime} used to schedule expiration of the
            session. If C{None}, the reactor associated with I{site} is used.
        """
        super().__init__()

        if reactor is None:
            reactor = site.reactor
        self._reactor = reactor

        self.site = site
        self.uid = uid
        self.expireCallbacks = []
        self.touch()
        self.sessionNamespaces = {}

    def startCheckingExpiration(self):
        """
        Start expiration tracking.

        @return: L{None}
        """
        self._expireCall = self._reactor.callLater(self.sessionTimeout, self.expire)

    def notifyOnExpire(self, callback):
        """
        Call this callback when the session expires or logs out.
        """
        self.expireCallbacks.append(callback)

    def expire(self):
        """
        Expire/logout of the session.
        """
        del self.site.sessions[self.uid]
        for c in self.expireCallbacks:
            c()
        self.expireCallbacks = []
        if self._expireCall and self._expireCall.active():
            self._expireCall.cancel()
            # Break reference cycle.
            self._expireCall = None

    def touch(self):
        """
        Mark the session as modified, which resets expiration timer.
        """
        self.lastModified = self._reactor.seconds()
        if self._expireCall is not None:
            self._expireCall.reset(self.sessionTimeout)


version = networkString(f"TwistedWeb/{copyright.version}")


@implementer(interfaces.IProtocolNegotiationFactory)
class Site(http.HTTPFactory):
    """
    A web site: manage log, sessions, and resources.

    @ivar requestFactory: A factory which is called with (channel)
        and creates L{Request} instances. Default to L{Request}.

    @ivar displayTracebacks: If set, unhandled exceptions raised during
        rendering are returned to the client as HTML. Default to C{False}.

    @ivar sessionFactory: factory for sessions objects. Default to L{Session}.

    @ivar sessions: Mapping of session IDs to objects returned by
        C{sessionFactory}.
    @type sessions: L{dict} mapping L{bytes} to L{Session} given the default
        C{sessionFactory}

    @ivar counter: The number of sessions that have been generated.
    @type counter: L{int}

    @ivar sessionCheckTime: Deprecated and unused. See
        L{Session.sessionTimeout} instead.
    """

    counter = 0
    requestFactory = Request
    displayTracebacks = False
    sessionFactory = Session
    sessionCheckTime = 1800
    _entropy = os.urandom

    def __init__(self, resource, requestFactory=None, *args, **kwargs):
        """
        @param resource: The root of the resource hierarchy.  All request
            traversal for requests received by this factory will begin at this
            resource.
        @type resource: L{IResource} provider
        @param requestFactory: Overwrite for default requestFactory.
        @type requestFactory: C{callable} or C{class}.

        @see: L{twisted.web.http.HTTPFactory.__init__}
        """
        super().__init__(*args, **kwargs)
        self.sessions = {}
        self.resource = resource
        if requestFactory is not None:
            self.requestFactory = requestFactory

    def _openLogFile(self, path):
        from twisted.python import logfile

        return logfile.LogFile(os.path.basename(path), os.path.dirname(path))

    def __getstate__(self):
        d = self.__dict__.copy()
        d["sessions"] = {}
        return d

    def _mkuid(self):
        """
        (internal) Generate an opaque, unique ID for a user's session.
        """
        self.counter = self.counter + 1
        return hexlify(self._entropy(32))

    def makeSession(self):
        """
        Generate a new Session instance, and store it for future reference.
        """
        uid = self._mkuid()
        session = self.sessions[uid] = self.sessionFactory(self, uid)
        session.startCheckingExpiration()
        return session

    def getSession(self, uid):
        """
        Get a previously generated session.

        @param uid: Unique ID of the session.
        @type uid: L{bytes}.

        @raise KeyError: If the session is not found.
        """
        return self.sessions[uid]

    def buildProtocol(self, addr):
        """
        Generate a channel attached to this site.
        """
        channel = super().buildProtocol(addr)
        channel.requestFactory = self.requestFactory
        channel.site = self
        return channel

    isLeaf = 0

    def render(self, request):
        """
        Redirect because a Site is always a directory.
        """
        request.redirect(request.prePathURL() + b"/")
        request.finish()

    def getChildWithDefault(self, pathEl, request):
        """
        Emulate a resource's getChild method.
        """
        request.site = self
        return self.resource.getChildWithDefault(pathEl, request)

    def getResourceFor(self, request):
        """
        Get a resource for a request.

        This iterates through the resource hierarchy, calling
        getChildWithDefault on each resource it finds for a path element,
        stopping when it hits an element where isLeaf is true.
        """
        request.site = self
        # Sitepath is used to determine cookie names between distributed
        # servers and disconnected sites.
        request.sitepath = copy.copy(request.prepath)
        return resource.getChildForRequest(self.resource, request)

    # IProtocolNegotiationFactory
    def acceptableProtocols(self):
        """
        Protocols this server can speak.
        """
        baseProtocols = [b"http/1.1"]

        if http.H2_ENABLED:
            baseProtocols.insert(0, b"h2")

        return baseProtocols