#
# Copyright 2009 Facebook
#
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.

"""A non-blocking, single-threaded HTTP server.

Typical applications have little direct interaction with the `HTTPServer`
class except to start a server at the beginning of the process
(and even that is often done indirectly via `tornado.web.Application.listen`).

.. versionchanged:: 4.0

   The ``HTTPRequest`` class that used to live in this module has been moved
   to `tornado.httputil.HTTPServerRequest`.  The old name remains as an alias.
"""

import socket
import ssl

from tornado.escape import native_str
from tornado.http1connection import HTTP1ServerConnection, HTTP1ConnectionParameters
from tornado import httputil
from tornado import iostream
from tornado import netutil
from tornado.tcpserver import TCPServer
from tornado.util import Configurable

import typing
from typing import Union, Any, Dict, Callable, List, Type, Tuple, Optional, Awaitable

if typing.TYPE_CHECKING:
    from typing import Set  # noqa: F401


class HTTPServer(TCPServer, Configurable, httputil.HTTPServerConnectionDelegate):
    r"""A non-blocking, single-threaded HTTP server.

    A server is defined by a subclass of `.HTTPServerConnectionDelegate`,
    or, for backwards compatibility, a callback that takes an
    `.HTTPServerRequest` as an argument. The delegate is usually a
    `tornado.web.Application`.

    `HTTPServer` supports keep-alive connections by default
    (automatically for HTTP/1.1, or for HTTP/1.0 when the client
    requests ``Connection: keep-alive``).

    If ``xheaders`` is ``True``, we support the
    ``X-Real-Ip``/``X-Forwarded-For`` and
    ``X-Scheme``/``X-Forwarded-Proto`` headers, which override the
    remote IP and URI scheme/protocol for all requests.  These headers
    are useful when running Tornado behind a reverse proxy or load
    balancer.  The ``protocol`` argument can also be set to ``https``
    if Tornado is run behind an SSL-decoding proxy that does not set one of
    the supported ``xheaders``.

    By default, when parsing the ``X-Forwarded-For`` header, Tornado will
    select the last (i.e., the closest) address on the list of hosts as the
    remote host IP address.  To select the next server in the chain, a list of
    trusted downstream hosts may be passed as the ``trusted_downstream``
    argument.  These hosts will be skipped when parsing the ``X-Forwarded-For``
    header.

    To make this server serve SSL traffic, send the ``ssl_options`` keyword
    argument with an `ssl.SSLContext` object. For compatibility with older
    versions of Python ``ssl_options`` may also be a dictionary of keyword
    arguments for the `ssl.wrap_socket` method.::

       ssl_ctx = ssl.create_default_context(ssl.Purpose.CLIENT_AUTH)
       ssl_ctx.load_cert_chain(os.path.join(data_dir, "mydomain.crt"),
                               os.path.join(data_dir, "mydomain.key"))
       HTTPServer(application, ssl_options=ssl_ctx)

    `HTTPServer` initialization follows one of three patterns (the
    initialization methods are defined on `tornado.tcpserver.TCPServer`):

    1. `~tornado.tcpserver.TCPServer.listen`: simple single-process::

            server = HTTPServer(app)
            server.listen(8888)
            IOLoop.current().start()

       In many cases, `tornado.web.Application.listen` can be used to avoid
       the need to explicitly create the `HTTPServer`.

    2. `~tornado.tcpserver.TCPServer.bind`/`~tornado.tcpserver.TCPServer.start`:
       simple multi-process::

            server = HTTPServer(app)
            server.bind(8888)
            server.start(0)  # Forks multiple sub-processes
            IOLoop.current().start()

       When using this interface, an `.IOLoop` must *not* be passed
       to the `HTTPServer` constructor.  `~.TCPServer.start` will always start
       the server on the default singleton `.IOLoop`.

    3. `~tornado.tcpserver.TCPServer.add_sockets`: advanced multi-process::

            sockets = tornado.netutil.bind_sockets(8888)
            tornado.process.fork_processes(0)
            server = HTTPServer(app)
            server.add_sockets(sockets)
            IOLoop.current().start()

       The `~.TCPServer.add_sockets` interface is more complicated,
       but it can be used with `tornado.process.fork_processes` to
       give you more flexibility in when the fork happens.
       `~.TCPServer.add_sockets` can also be used in single-process
       servers if you want to create your listening sockets in some
       way other than `tornado.netutil.bind_sockets`.

    .. versionchanged:: 4.0
       Added ``decompress_request``, ``chunk_size``, ``max_header_size``,
       ``idle_connection_timeout``, ``body_timeout``, ``max_body_size``
       arguments.  Added support for `.HTTPServerConnectionDelegate`
       instances as ``request_callback``.

    .. versionchanged:: 4.1
       `.HTTPServerConnectionDelegate.start_request` is now called with
       two arguments ``(server_conn, request_conn)`` (in accordance with the
       documentation) instead of one ``(request_conn)``.

    .. versionchanged:: 4.2
       `HTTPServer` is now a subclass of `tornado.util.Configurable`.

    .. versionchanged:: 4.5
       Added the ``trusted_downstream`` argument.

    .. versionchanged:: 5.0
       The ``io_loop`` argument has been removed.
    """

    def __init__(self, *args: Any, **kwargs: Any) -> None:
        # Ignore args to __init__; real initialization belongs in
        # initialize since we're Configurable. (there's something
        # weird in initialization order between this class,
        # Configurable, and TCPServer so we can't leave __init__ out
        # completely)
        pass

    def initialize(
        self,
        request_callback: Union[
            httputil.HTTPServerConnectionDelegate,
            Callable[[httputil.HTTPServerRequest], None],
        ],
        no_keep_alive: bool = False,
        xheaders: bool = False,
        ssl_options: Union[Dict[str, Any], ssl.SSLContext] = None,
        protocol: str = None,
        decompress_request: bool = False,
        chunk_size: int = None,
        max_header_size: int = None,
        idle_connection_timeout: float = None,
        body_timeout: float = None,
        max_body_size: int = None,
        max_buffer_size: int = None,
        trusted_downstream: List[str] = None,
    ) -> None:
        # This method's signature is not extracted with autodoc
        # because we want its arguments to appear on the class
        # constructor. When changing this signature, also update the
        # copy in httpserver.rst.
        self.request_callback = request_callback
        self.xheaders = xheaders
        self.protocol = protocol
        self.conn_params = HTTP1ConnectionParameters(
            decompress=decompress_request,
            chunk_size=chunk_size,
            max_header_size=max_header_size,
            header_timeout=idle_connection_timeout or 3600,
            max_body_size=max_body_size,
            body_timeout=body_timeout,
            no_keep_alive=no_keep_alive,
        )
        TCPServer.__init__(
            self,
            ssl_options=ssl_options,
            max_buffer_size=max_buffer_size,
            read_chunk_size=chunk_size,
        )
        self._connections = set()  # type: Set[HTTP1ServerConnection]
        self.trusted_downstream = trusted_downstream

    @classmethod
    def configurable_base(cls) -> Type[Configurable]:
        return HTTPServer

    @classmethod
    def configurable_default(cls) -> Type[Configurable]:
        return HTTPServer

    async def close_all_connections(self) -> None:
        """Close all open connections and asynchronously wait for them to finish.

        This method is used in combination with `~.TCPServer.stop` to
        support clean shutdowns (especially for unittests). Typical
        usage would call ``stop()`` first to stop accepting new
        connections, then ``await close_all_connections()`` to wait for
        existing connections to finish.

        This method does not currently close open websocket connections.

        Note that this method is a coroutine and must be caled with ``await``.

        """
        while self._connections:
            # Peek at an arbitrary element of the set
            conn = next(iter(self._connections))
            await conn.close()

    def handle_stream(self, stream: iostream.IOStream, address: Tuple) -> None:
        context = _HTTPRequestContext(
            stream, address, self.protocol, self.trusted_downstream
        )
        conn = HTTP1ServerConnection(stream, self.conn_params, context)
        self._connections.add(conn)
        conn.start_serving(self)

    def start_request(
        self, server_conn: object, request_conn: httputil.HTTPConnection
    ) -> httputil.HTTPMessageDelegate:
        if isinstance(self.request_callback, httputil.HTTPServerConnectionDelegate):
            delegate = self.request_callback.start_request(server_conn, request_conn)
        else:
            delegate = _CallableAdapter(self.request_callback, request_conn)

        if self.xheaders:
            delegate = _ProxyAdapter(delegate, request_conn)

        return delegate

    def on_close(self, server_conn: object) -> None:
        self._connections.remove(typing.cast(HTTP1ServerConnection, server_conn))


class _CallableAdapter(httputil.HTTPMessageDelegate):
    def __init__(
        self,
        request_callback: Callable[[httputil.HTTPServerRequest], None],
        request_conn: httputil.HTTPConnection,
    ) -> None:
        self.connection = request_conn
        self.request_callback = request_callback
        self.request = None  # type: Optional[httputil.HTTPServerRequest]
        self.delegate = None
        self._chunks = []  # type: List[bytes]

    def headers_received(
        self,
        start_line: Union[httputil.RequestStartLine, httputil.ResponseStartLine],
        headers: httputil.HTTPHeaders,
    ) -> Optional[Awaitable[None]]:
        self.request = httputil.HTTPServerRequest(
            connection=self.connection,
            start_line=typing.cast(httputil.RequestStartLine, start_line),
            headers=headers,
        )
        return None

    def data_received(self, chunk: bytes) -> Optional[Awaitable[None]]:
        self._chunks.append(chunk)
        return None

    def finish(self) -> None:
        assert self.request is not None
        self.request.body = b"".join(self._chunks)
        self.request._parse_body()
        self.request_callback(self.request)

    def on_connection_close(self) -> None:
        del self._chunks


class _HTTPRequestContext(object):
    def __init__(
        self,
        stream: iostream.IOStream,
        address: Tuple,
        protocol: Optional[str],
        trusted_downstream: List[str] = None,
    ) -> None:
        self.address = address
        # Save the socket's address family now so we know how to
        # interpret self.address even after the stream is closed
        # and its socket attribute replaced with None.
        if stream.socket is not None:
            self.address_family = stream.socket.family
        else:
            self.address_family = None
        # In HTTPServerRequest we want an IP, not a full socket address.
        if (
            self.address_family in (socket.AF_INET, socket.AF_INET6)
            and address is not None
        ):
            self.remote_ip = address[0]
        else:
            # Unix (or other) socket; fake the remote address.
            self.remote_ip = "0.0.0.0"
        if protocol:
            self.protocol = protocol
        elif isinstance(stream, iostream.SSLIOStream):
            self.protocol = "https"
        else:
            self.protocol = "http"
        self._orig_remote_ip = self.remote_ip
        self._orig_protocol = self.protocol
        self.trusted_downstream = set(trusted_downstream or [])

    def __str__(self) -> str:
        if self.address_family in (socket.AF_INET, socket.AF_INET6):
            return self.remote_ip
        elif isinstance(self.address, bytes):
            # Python 3 with the -bb option warns about str(bytes),
            # so convert it explicitly.
            # Unix socket addresses are str on mac but bytes on linux.
            return native_str(self.address)
        else:
            return str(self.address)

    def _apply_xheaders(self, headers: httputil.HTTPHeaders) -> None:
        """Rewrite the ``remote_ip`` and ``protocol`` fields."""
        # Squid uses X-Forwarded-For, others use X-Real-Ip
        ip = headers.get("X-Forwarded-For", self.remote_ip)
        # Skip trusted downstream hosts in X-Forwarded-For list
        for ip in (cand.strip() for cand in reversed(ip.split(","))):
            if ip not in self.trusted_downstream:
                break
        ip = headers.get("X-Real-Ip", ip)
        if netutil.is_valid_ip(ip):
            self.remote_ip = ip
        # AWS uses X-Forwarded-Proto
        proto_header = headers.get(
            "X-Scheme", headers.get("X-Forwarded-Proto", self.protocol)
        )
        if proto_header:
            # use only the last proto entry if there is more than one
            # TODO: support trusting mutiple layers of proxied protocol
            proto_header = proto_header.split(",")[-1].strip()
        if proto_header in ("http", "https"):
            self.protocol = proto_header

    def _unapply_xheaders(self) -> None:
        """Undo changes from `_apply_xheaders`.

        Xheaders are per-request so they should not leak to the next
        request on the same connection.
        """
        self.remote_ip = self._orig_remote_ip
        self.protocol = self._orig_protocol


class _ProxyAdapter(httputil.HTTPMessageDelegate):
    def __init__(
        self,
        delegate: httputil.HTTPMessageDelegate,
        request_conn: httputil.HTTPConnection,
    ) -> None:
        self.connection = request_conn
        self.delegate = delegate

    def headers_received(
        self,
        start_line: Union[httputil.RequestStartLine, httputil.ResponseStartLine],
        headers: httputil.HTTPHeaders,
    ) -> Optional[Awaitable[None]]:
        # TODO: either make context an official part of the
        # HTTPConnection interface or figure out some other way to do this.
        self.connection.context._apply_xheaders(headers)  # type: ignore
        return self.delegate.headers_received(start_line, headers)

    def data_received(self, chunk: bytes) -> Optional[Awaitable[None]]:
        return self.delegate.data_received(chunk)

    def finish(self) -> None:
        self.delegate.finish()
        self._cleanup()

    def on_connection_close(self) -> None:
        self.delegate.on_connection_close()
        self._cleanup()

    def _cleanup(self) -> None:
        self.connection.context._unapply_xheaders()  # type: ignore


HTTPRequest = httputil.HTTPServerRequest
