# Source code for tornado.simple_httpclient

    from tornado.escape import _unicode
    from tornado import gen, version
    from tornado.httpclient import (
        HTTPResponse,
        HTTPError,
        AsyncHTTPClient,
        main,
        _RequestProxy,
        HTTPRequest,
    )
    from tornado import httputil
    from tornado.http1connection import HTTP1Connection, HTTP1ConnectionParameters
    from tornado.ioloop import IOLoop
    from tornado.iostream import StreamClosedError, IOStream
    from tornado.netutil import (
        Resolver,
        OverrideResolver,
        _client_ssl_defaults,
        is_valid_ip,
    )
    from tornado.log import gen_log
    from tornado.tcpclient import TCPClient

    import base64
    import collections
    import copy
    import functools
    import re
    import socket
    import ssl
    import sys
    import time
    from io import BytesIO
    import urllib.parse

    from typing import Dict, Any, Callable, Optional, Type, Union
    from types import TracebackType
    import typing

    if typing.TYPE_CHECKING:
        from typing import Deque, Tuple, List  # noqa: F401

    class HTTPTimeoutError(HTTPError):
        """Error raised by SimpleAsyncHTTPClient on timeout.

        For historical reasons, this is a subclass of `.HTTPClientError`
        which simulates a response code of 599.

        .. versionadded:: 5.1
        """

        def __init__(self, message: str) -> None:
            super().__init__(599, message=message)

        def __str__(self) -> str:
            return self.message or "Timeout"

    class HTTPStreamClosedError(HTTPError):
        """Error raised by SimpleAsyncHTTPClient when the underlying stream is closed.

        When a more specific exception is available (such as `ConnectionResetError`),
        it may be raised instead of this one.

        For historical reasons, this is a subclass of `.HTTPClientError`
        which simulates a response code of 599.

        .. versionadded:: 5.1
        """

        def __init__(self, message: str) -> None:
            super().__init__(599, message=message)

        def __str__(self) -> str:
            return self.message or "Stream closed"

    class SimpleAsyncHTTPClient(AsyncHTTPClient):
        """Non-blocking HTTP client with no external dependencies.

        This class implements an HTTP 1.1 client on top of Tornado's IOStreams.
        Some features found in the curl-based AsyncHTTPClient are not yet
        supported.  In particular, proxies are not supported, connections
        are not reused, and callers cannot select the network interface to be
        used.

        This implementation supports the following arguments, which can be passed
        to ``configure()`` to control the global singleton, or to the constructor
        when ``force_instance=True``.

        ``max_clients`` is the number of concurrent requests that can be
        in progress; when this limit is reached additional requests will be
        queued. Note that time spent waiting in this queue still counts
        against the ``request_timeout``.

        ``defaults`` is a dict of parameters that will be used as defaults on all
        `.HTTPRequest` objects submitted to this client.

        ``hostname_mapping`` is a dictionary mapping hostnames to IP addresses.
        It can be used to make local DNS changes when modifying system-wide
        settings like ``/etc/hosts`` is not possible or desirable (e.g. in
        unittests). ``resolver`` is similar, but using the `.Resolver` interface
        instead of a simple mapping.

        ``max_buffer_size`` (default 100MB) is the number of bytes
        that can be read into memory at once. ``max_body_size``
        (defaults to ``max_buffer_size``) is the largest response body
        that the client will accept.  Without a
        ``streaming_callback``, the smaller of these two limits
        applies; with a ``streaming_callback`` only ``max_body_size``
        does.

        .. versionchanged:: 4.2
            Added the ``max_body_size`` argument.
        """

        def initialize(  # type: ignore
            self,
            max_clients: int = 10,
            hostname_mapping: Optional[Dict[str, str]] = None,
            max_buffer_size: int = 104857600,
            resolver: Optional[Resolver] = None,
            defaults: Optional[Dict[str, Any]] = None,
            max_header_size: Optional[int] = None,
            max_body_size: Optional[int] = None,
        ) -> None:
            super().initialize(defaults=defaults)
            self.max_clients = max_clients
            self.queue = (
                collections.deque()
            )  # type: Deque[Tuple[object, HTTPRequest, Callable[[HTTPResponse], None]]]
            self.active = (
                {}
            )  # type: Dict[object, Tuple[HTTPRequest, Callable[[HTTPResponse], None]]]
            self.waiting = (
                {}
            )  # type: Dict[object, Tuple[HTTPRequest, Callable[[HTTPResponse], None], object]]
            self.max_buffer_size = max_buffer_size
            self.max_header_size = max_header_size
            self.max_body_size = max_body_size
            # TCPClient could create a Resolver for us, but we have to do it
            # ourselves to support hostname_mapping.
            if resolver:
                self.resolver = resolver
                self.own_resolver = False
            else:
                self.resolver = Resolver()
                self.own_resolver = True
            if hostname_mapping is not None:
                self.resolver = OverrideResolver(
                    resolver=self.resolver, mapping=hostname_mapping
                )
            self.tcp_client = TCPClient(resolver=self.resolver)

        def close(self) -> None:
            super().close()
            if self.own_resolver:
                self.resolver.close()
            self.tcp_client.close()

        def fetch_impl(
            self, request: HTTPRequest, callback: Callable[[HTTPResponse], None]
        ) -> None:
            key = object()
            self.queue.append((key, request, callback))
            assert request.connect_timeout is not None
            assert request.request_timeout is not None
            timeout_handle = None
            if len(self.active) >= self.max_clients:
                timeout = (
                    min(request.connect_timeout, request.request_timeout)
                    or request.connect_timeout
                    or request.request_timeout
                )  # min but skip zero
                if timeout:
                    timeout_handle = self.io_loop.add_timeout(
                        self.io_loop.time() + timeout,
                        functools.partial(self._on_timeout, key, "in request queue"),
                    )
            self.waiting[key] = (request, callback, timeout_handle)
            self._process_queue()
            if self.queue:
                gen_log.debug(
                    "max_clients limit reached, request queued. "
                    "%d active, %d queued requests." % (len(self.active), len(self.queue))
                )

        def _process_queue(self) -> None:
            while self.queue and len(self.active) < self.max_clients:
                key, request, callback = self.queue.popleft()
                if key not in self.waiting:
                    continue
                self._remove_timeout(key)
                self.active[key] = (request, callback)
                release_callback = functools.partial(self._release_fetch, key)
                self._handle_request(request, release_callback, callback)

        def _connection_class(self) -> type:
            return _HTTPConnection

        def _handle_request(
            self,
            request: HTTPRequest,
            release_callback: Callable[[], None],
            final_callback: Callable[[HTTPResponse], None],
        ) -> None:
            self._connection_class()(
                self,
                request,
                release_callback,
                final_callback,
                self.max_buffer_size,
                self.tcp_client,
                self.max_header_size,
                self.max_body_size,
            )

        def _release_fetch(self, key: object) -> None:
            del self.active[key]
            self._process_queue()

        def _remove_timeout(self, key: object) -> None:
            if key in self.waiting:
                request, callback, timeout_handle = self.waiting[key]
                if timeout_handle is not None:
                    self.io_loop.remove_timeout(timeout_handle)
                del self.waiting[key]

        def _on_timeout(self, key: object, info: Optional[str] = None) -> None:
            """Timeout callback of request.

            Construct a timeout HTTPResponse when a timeout occurs.

            :arg object key: A simple object to mark the request.
            :info string key: More detailed timeout information.
            """
            request, callback, timeout_handle = self.waiting[key]
            self.queue.remove((key, request, callback))

            error_message = "Timeout {0}".format(info) if info else "Timeout"
            timeout_response = HTTPResponse(
                request,
                599,
                error=HTTPTimeoutError(error_message),
                request_time=self.io_loop.time() - request.start_time,
            )
            self.io_loop.add_callback(callback, timeout_response)
            del self.waiting[key]

    class _HTTPConnection(httputil.HTTPMessageDelegate):
        _SUPPORTED_METHODS = set(
            ["GET", "HEAD", "POST", "PUT", "DELETE", "PATCH", "OPTIONS"]
        )

        def __init__(
            self,
            client: Optional[SimpleAsyncHTTPClient],
            request: HTTPRequest,
            release_callback: Callable[[], None],
            final_callback: Callable[[HTTPResponse], None],
            max_buffer_size: int,
            tcp_client: TCPClient,
            max_header_size: int,
            max_body_size: int,
        ) -> None:
            self.io_loop = IOLoop.current()
            self.start_time = self.io_loop.time()
            self.start_wall_time = time.time()
            self.client = client
            self.request = request
            self.release_callback = release_callback
            self.final_callback = final_callback
            self.max_buffer_size = max_buffer_size
            self.tcp_client = tcp_client
            self.max_header_size = max_header_size
            self.max_body_size = max_body_size
            self.code = None  # type: Optional[int]
            self.headers = None  # type: Optional[httputil.HTTPHeaders]
            self.chunks = []  # type: List[bytes]
            self._decompressor = None
            # Timeout handle returned by IOLoop.add_timeout
            self._timeout = None  # type: object
            self._sockaddr = None
            IOLoop.current().add_future(
                gen.convert_yielded(self.run()), lambda f: f.result()
            )

        async def run(self) -> None:
            try:
                self.parsed = urllib.parse.urlsplit(_unicode(self.request.url))
                if self.parsed.scheme not in ("http", "https"):
                    raise ValueError("Unsupported url scheme: %s" % self.request.url)
                # urlsplit results have hostname and port results, but they
                # didn't support ipv6 literals until python 2.7.
                netloc = self.parsed.netloc
                if "@" in netloc:
                    userpass, _, netloc = netloc.rpartition("@")
                host, port = httputil.split_host_and_port(netloc)
                if port is None:
                    port = 443 if self.parsed.scheme == "https" else 80
                if re.match(r"^\[.*\]$", host):
                    # raw ipv6 addresses in urls are enclosed in brackets
                    host = host[1:-1]
                self.parsed_hostname = host  # save final host for _on_connect

                if self.request.allow_ipv6 is False:
                    af = socket.AF_INET
                else:
                    af = socket.AF_UNSPEC

                ssl_options = self._get_ssl_options(self.parsed.scheme)

                source_ip = None
                if self.request.network_interface:
                    if is_valid_ip(self.request.network_interface):
                        source_ip = self.request.network_interface
                    else:
                        raise ValueError(
                            "Unrecognized IPv4 or IPv6 address for network_interface, got %r"
                            % (self.request.network_interface,)
                        )

                if self.request.connect_timeout and self.request.request_timeout:
                    timeout = min(
                        self.request.connect_timeout, self.request.request_timeout
                    )
                elif self.request.connect_timeout:
                    timeout = self.request.connect_timeout
                elif self.request.request_timeout:
                    timeout = self.request.request_timeout
                else:
                    timeout = 0
                if timeout:
                    self._timeout = self.io_loop.add_timeout(
                        self.start_time + timeout,
                        functools.partial(self._on_timeout, "while connecting"),
                    )
                stream = await self.tcp_client.connect(
                    host,
                    port,
                    af=af,
                    ssl_options=ssl_options,
                    max_buffer_size=self.max_buffer_size,
                    source_ip=source_ip,
                )

                if self.final_callback is None:
                    # final_callback is cleared if we've hit our timeout.
                    stream.close()
                    return
                self.stream = stream
                self.stream.set_close_callback(self.on_connection_close)
                self._remove_timeout()
                if self.final_callback is None:
                    return
                if self.request.request_timeout:
                    self._timeout = self.io_loop.add_timeout(
                        self.start_time + self.request.request_timeout,
                        functools.partial(self._on_timeout, "during request"),
                    )
                if (
                    self.request.method not in self._SUPPORTED_METHODS
                    and not self.request.allow_nonstandard_methods
                ):
                    raise KeyError("unknown method %s" % self.request.method)
                for key in (
                    "proxy_host",
                    "proxy_port",
                    "proxy_username",
                    "proxy_password",
                    "proxy_auth_mode",
                ):
                    if getattr(self.request, key, None):
                        raise NotImplementedError("%s not supported" % key)
                if "Connection" not in self.request.headers:
                    self.request.headers["Connection"] = "close"
                if "Host" not in self.request.headers:
                    if "@" in self.parsed.netloc:
                        self.request.headers["Host"] = self.parsed.netloc.rpartition("@")[
                            -1
                        ]
                    else:
                        self.request.headers["Host"] = self.parsed.netloc
                username, password = None, None
                if self.parsed.username is not None:
                    username, password = self.parsed.username, self.parsed.password
                elif self.request.auth_username is not None:
                    username = self.request.auth_username
                    password = self.request.auth_password or ""
                if username is not None:
                    assert password is not None
                    if self.request.auth_mode not in (None, "basic"):
                        raise ValueError("unsupported auth_mode %s", self.request.auth_mode)
                    self.request.headers["Authorization"] = "Basic " + _unicode(
                        base64.b64encode(
                            httputil.encode_username_password(username, password)
                        )
                    )
                if self.request.user_agent:
                    self.request.headers["User-Agent"] = self.request.user_agent
                elif self.request.headers.get("User-Agent") is None:
                    self.request.headers["User-Agent"] = "Tornado/{}".format(version)
                if not self.request.allow_nonstandard_methods:
                    # Some HTTP methods nearly always have bodies while others
                    # almost never do. Fail in this case unless the user has
                    # opted out of sanity checks with allow_nonstandard_methods.
                    body_expected = self.request.method in ("POST", "PATCH", "PUT")
                    body_present = (
                        self.request.body is not None
                        or self.request.body_producer is not None
                    )
                    if (body_expected and not body_present) or (
                        body_present and not body_expected
                    ):
                        raise ValueError(
                            "Body must %sbe None for method %s (unless "
                            "allow_nonstandard_methods is true)"
                            % ("not " if body_expected else "", self.request.method)
                        )
                if self.request.expect_100_continue:
                    self.request.headers["Expect"] = "100-continue"
                if self.request.body is not None:
                    # When body_producer is used the caller is responsible for
                    # setting Content-Length (or else chunked encoding will be used).
                    self.request.headers["Content-Length"] = str(len(self.request.body))
                if (
                    self.request.method == "POST"
                    and "Content-Type" not in self.request.headers
                ):
                    self.request.headers["Content-Type"] = (
                        "application/x-www-form-urlencoded"
                    )
                if self.request.decompress_response:
                    self.request.headers["Accept-Encoding"] = "gzip"
                req_path = (self.parsed.path or "/") + (
                    ("?" + self.parsed.query) if self.parsed.query else ""
                )
                self.connection = self._create_connection(stream)
                start_line = httputil.RequestStartLine(self.request.method, req_path, "")
                self.connection.write_headers(start_line, self.request.headers)
                if self.request.expect_100_continue:
                    await self.connection.read_response(self)
                else:
                    await self._write_body(True)
            except Exception:
                if not self._handle_exception(*sys.exc_info()):
                    raise

        def _get_ssl_options(
            self, scheme: str
        ) -> Union[None, Dict[str, Any], ssl.SSLContext]:
            if scheme == "https":
                if self.request.ssl_options is not None:
                    return self.request.ssl_options
                # If we are using the defaults, don't construct a
                # new SSLContext.
                if (
                    self.request.validate_cert
                    and self.request.ca_certs is None
                    and self.request.client_cert is None
                    and self.request.client_key is None
                ):
                    return _client_ssl_defaults
                ssl_ctx = ssl.create_default_context(
                    ssl.Purpose.SERVER_AUTH, cafile=self.request.ca_certs
                )
                if not self.request.validate_cert:
                    ssl_ctx.check_hostname = False
                    ssl_ctx.verify_mode = ssl.CERT_NONE
                if self.request.client_cert is not None:
                    ssl_ctx.load_cert_chain(
                        self.request.client_cert, self.request.client_key
                    )
                if hasattr(ssl, "OP_NO_COMPRESSION"):
                    # See netutil.ssl_options_to_context
                    ssl_ctx.options |= ssl.OP_NO_COMPRESSION
                return ssl_ctx
            return None

        def _on_timeout(self, info: Optional[str] = None) -> None:
            """Timeout callback of _HTTPConnection instance.

            Raise a `HTTPTimeoutError` when a timeout occurs.

            :info string key: More detailed timeout information.
            """
            self._timeout = None
            error_message = "Timeout {0}".format(info) if info else "Timeout"
            if self.final_callback is not None:
                self._handle_exception(
                    HTTPTimeoutError, HTTPTimeoutError(error_message), None
                )

        def _remove_timeout(self) -> None:
            if self._timeout is not None:
                self.io_loop.remove_timeout(self._timeout)
                self._timeout = None

        def _create_connection(self, stream: IOStream) -> HTTP1Connection:
            stream.set_nodelay(True)
            connection = HTTP1Connection(
                stream,
                True,
                HTTP1ConnectionParameters(
                    no_keep_alive=True,
                    max_header_size=self.max_header_size,
                    max_body_size=self.max_body_size,
                    decompress=bool(self.request.decompress_response),
                ),
                self._sockaddr,
            )
            return connection

        async def _write_body(self, start_read: bool) -> None:
            if self.request.body is not None:
                self.connection.write(self.request.body)
            elif self.request.body_producer is not None:
                fut = self.request.body_producer(self.connection.write)
                if fut is not None:
                    await fut
            self.connection.finish()
            if start_read:
                try:
                    await self.connection.read_response(self)
                except StreamClosedError:
                    if not self._handle_exception(*sys.exc_info()):
                        raise

        def _release(self) -> None:
            if self.release_callback is not None:
                release_callback = self.release_callback
                self.release_callback = None  # type: ignore
                release_callback()

        def _run_callback(self, response: HTTPResponse) -> None:
            self._release()
            if self.final_callback is not None:
                final_callback = self.final_callback
                self.final_callback = None  # type: ignore
                self.io_loop.add_callback(final_callback, response)

        def _handle_exception(
            self,
            typ: "Optional[Type[BaseException]]",
            value: Optional[BaseException],
            tb: Optional[TracebackType],
        ) -> bool:
            if self.final_callback is not None:
                self._remove_timeout()
                if isinstance(value, StreamClosedError):
                    if value.real_error is None:
                        value = HTTPStreamClosedError("Stream closed")
                    else:
                        value = value.real_error
                self._run_callback(
                    HTTPResponse(
                        self.request,
                        599,
                        error=value,
                        request_time=self.io_loop.time() - self.start_time,
                        start_time=self.start_wall_time,
                    )
                )

                if hasattr(self, "stream"):
                    # TODO: this may cause a StreamClosedError to be raised
                    # by the connection's Future.  Should we cancel the
                    # connection more gracefully?
                    self.stream.close()
                return True
            else:
                # If our callback has already been called, we are probably
                # catching an exception that is not caused by us but rather
                # some child of our callback. Rather than drop it on the floor,
                # pass it along, unless it's just the stream being closed.
                return isinstance(value, StreamClosedError)

        def on_connection_close(self) -> None:
            if self.final_callback is not None:
                message = "Connection closed"
                if self.stream.error:
                    raise self.stream.error
                try:
                    raise HTTPStreamClosedError(message)
                except HTTPStreamClosedError:
                    self._handle_exception(*sys.exc_info())

        async def headers_received(
            self,
            first_line: Union[httputil.ResponseStartLine, httputil.RequestStartLine],
            headers: httputil.HTTPHeaders,
        ) -> None:
            assert isinstance(first_line, httputil.ResponseStartLine)
            if self.request.expect_100_continue and first_line.code == 100:
                await self._write_body(False)
                return
            self.code = first_line.code
            self.reason = first_line.reason
            self.headers = headers

            if self._should_follow_redirect():
                return

            if self.request.header_callback is not None:
                # Reassemble the start line.
                self.request.header_callback("%s %s %s\r\n" % first_line)
                for k, v in self.headers.get_all():
                    self.request.header_callback("%s: %s\r\n" % (k, v))
                self.request.header_callback("\r\n")

        def _should_follow_redirect(self) -> bool:
            if self.request.follow_redirects:
                assert self.request.max_redirects is not None
                return (
                    self.code in (301, 302, 303, 307, 308)
                    and self.request.max_redirects > 0
                    and self.headers is not None
                    and self.headers.get("Location") is not None
                )
            return False

        def finish(self) -> None:
            assert self.code is not None
            data = b"".join(self.chunks)
            self._remove_timeout()
            original_request = getattr(self.request, "original_request", self.request)
            if self._should_follow_redirect():
                assert isinstance(self.request, _RequestProxy)
                assert self.headers is not None
                new_request = copy.copy(self.request.request)
                new_request.url = urllib.parse.urljoin(
                    self.request.url, self.headers["Location"]
                )
                assert self.request.max_redirects is not None
                new_request.max_redirects = self.request.max_redirects - 1
                del new_request.headers["Host"]
                # https://tools.ietf.org/html/rfc7231#section-6.4
                #
                # The original HTTP spec said that after a 301 or 302
                # redirect, the request method should be preserved.
                # However, browsers implemented this by changing the
                # method to GET, and the behavior stuck. 303 redirects
                # always specified this POST-to-GET behavior, arguably
                # for *all* methods, but libcurl < 7.70 only does this
                # for POST, while libcurl >= 7.70 does it for other methods.
                if (self.code == 303 and self.request.method != "HEAD") or (
                    self.code in (301, 302) and self.request.method == "POST"
                ):
                    new_request.method = "GET"
                    new_request.body = None  # type: ignore
                    for h in [
                        "Content-Length",
                        "Content-Type",
                        "Content-Encoding",
                        "Transfer-Encoding",
                    ]:
                        try:
                            del self.request.headers[h]
                        except KeyError:
                            pass
                new_request.original_request = original_request  # type: ignore
                final_callback = self.final_callback
                self.final_callback = None  # type: ignore
                self._release()
                assert self.client is not None
                fut = self.client.fetch(new_request, raise_error=False)
                fut.add_done_callback(lambda f: final_callback(f.result()))
                self._on_end_request()
                return
            if self.request.streaming_callback:
                buffer = BytesIO()
            else:
                buffer = BytesIO(data)  # TODO: don't require one big string?
            response = HTTPResponse(
                original_request,
                self.code,
                reason=getattr(self, "reason", None),
                headers=self.headers,
                request_time=self.io_loop.time() - self.start_time,
                start_time=self.start_wall_time,
                buffer=buffer,
                effective_url=self.request.url,
            )
            self._run_callback(response)
            self._on_end_request()

        def _on_end_request(self) -> None:
            self.stream.close()

        def data_received(self, chunk: bytes) -> None:
            if self._should_follow_redirect():
                # We're going to follow a redirect so just discard the body.
                return
            if self.request.streaming_callback is not None:
                self.request.streaming_callback(chunk)
            else:
                self.chunks.append(chunk)

    if __name__ == "__main__":
        AsyncHTTPClient.configure(SimpleAsyncHTTPClient)
        main()