httpserver.py

#!/usr/bin/env python
#
# 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`).

This module also defines the `HTTPRequest` class which is exposed via
`tornado.web.RequestHandler.request`.
"""

import errno
import logging
import os
import socket
import time
import urlparse

from tornado.escape import utf8, native_str, parse_qs_bytes
from tornado import httputil
from tornado import ioloop
from tornado import iostream
from tornado import stack_context
from tornado.util import b, bytes_type

try:
    import fcntl
except ImportError:
    if os.name == 'nt':
        from tornado import win32_support as fcntl
    else:
        raise

try:
    import ssl # Python 2.6+
except ImportError:
    ssl = None

try:
    import multiprocessing # Python 2.6+
except ImportError:
    multiprocessing = None

def _cpu_count():
    if multiprocessing is not None:
        try:
            return multiprocessing.cpu_count()
        except NotImplementedError:
            pass
    try:
        return os.sysconf("SC_NPROCESSORS_CONF")
    except ValueError:
        pass
    logging.error("Could not detect number of processors; "
                  "running with one process")
    return 1


class HTTPServer(object):
    r"""A non-blocking, single-threaded HTTP server.

    A server is defined by a request callback that takes an HTTPRequest
    instance as an argument and writes a valid HTTP response with
    request.write(). request.finish() finishes the request (but does not
    necessarily close the connection in the case of HTTP/1.1 keep-alive
    requests). A simple example server that echoes back the URI you
    requested::

        import httpserver
        import ioloop

        def handle_request(request):
           message = "You requested %s\n" % request.uri
           request.write("HTTP/1.1 200 OK\r\nContent-Length: %d\r\n\r\n%s" % (
                         len(message), message))
           request.finish()

        http_server = httpserver.HTTPServer(handle_request)
        http_server.listen(8888)
        ioloop.IOLoop.instance().start()

    HTTPServer is a very basic connection handler. Beyond parsing the
    HTTP request body and headers, the only HTTP semantics implemented
    in HTTPServer is HTTP/1.1 keep-alive connections. We do not, however,
    implement chunked encoding, so the request callback must provide a
    Content-Length header or implement chunked encoding for HTTP/1.1
    requests for the server to run correctly for HTTP/1.1 clients. If
    the request handler is unable to do this, you can provide the
    no_keep_alive argument to the HTTPServer constructor, which will
    ensure the connection is closed on every request no matter what HTTP
    version the client is using.

    If xheaders is True, we support the X-Real-Ip and X-Scheme headers,
    which override the remote IP and HTTP scheme for all requests. These
    headers are useful when running Tornado behind a reverse proxy or
    load balancer.

    HTTPServer can serve HTTPS (SSL) traffic with Python 2.6+ and OpenSSL.
    To make this server serve SSL traffic, send the ssl_options dictionary
    argument with the arguments required for the ssl.wrap_socket() method,
    including "certfile" and "keyfile"::

       HTTPServer(applicaton, ssl_options={
           "certfile": os.path.join(data_dir, "mydomain.crt"),
           "keyfile": os.path.join(data_dir, "mydomain.key"),
       })

    By default, listen() runs in a single thread in a single process. You
    can utilize all available CPUs on this machine by calling bind() and
    start() instead of listen()::

        http_server = httpserver.HTTPServer(handle_request)
        http_server.bind(8888)
        http_server.start(0) # Forks multiple sub-processes
        ioloop.IOLoop.instance().start()

    start(0) detects the number of CPUs on this machine and "pre-forks" that
    number of child processes so that we have one Tornado process per CPU,
    all with their own IOLoop. You can also pass in the specific number of
    child processes you want to run with if you want to override this
    auto-detection.
    """
    def __init__(self, request_callback, no_keep_alive=False, io_loop=None,
                 xheaders=False, ssl_options=None):
        """Initializes the server with the given request callback.

        If you use pre-forking/start() instead of the listen() method to
        start your server, you should not pass an IOLoop instance to this
        constructor. Each pre-forked child process will create its own
        IOLoop instance after the forking process.
        """
        self.request_callback = request_callback
        self.no_keep_alive = no_keep_alive
        self.io_loop = io_loop
        self.xheaders = xheaders
        self.ssl_options = ssl_options
        self._sockets = {}  # fd -> socket object
        self._started = False

    def listen(self, port, address=""):
        """Binds to the given port and starts the server in a single process.

        This method is a shortcut for:

            server.bind(port, address)
            server.start(1)

        """
        self.bind(port, address)
        self.start(1)

    def bind(self, port, address=None, family=socket.AF_UNSPEC):
        """Binds this server to the given port on the given address.

        To start the server, call start(). If you want to run this server
        in a single process, you can call listen() as a shortcut to the
        sequence of bind() and start() calls.

        Address may be either an IP address or hostname.  If it's a hostname,
        the server will listen on all IP addresses associated with the
        name.  Address may be an empty string or None to listen on all
        available interfaces.  Family may be set to either socket.AF_INET
        or socket.AF_INET6 to restrict to ipv4 or ipv6 addresses, otherwise
        both will be used if available.

        This method may be called multiple times prior to start() to listen
        on multiple ports or interfaces.
        """
        if address == "":
            address = None
        for res in socket.getaddrinfo(address, port, family, socket.SOCK_STREAM,
                                      0, socket.AI_PASSIVE | socket.AI_ADDRCONFIG):
            af, socktype, proto, canonname, sockaddr = res
            sock = socket.socket(af, socktype, proto)
            flags = fcntl.fcntl(sock.fileno(), fcntl.F_GETFD)
            flags |= fcntl.FD_CLOEXEC
            fcntl.fcntl(sock.fileno(), fcntl.F_SETFD, flags)
            sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
            if af == socket.AF_INET6:
                # On linux, ipv6 sockets accept ipv4 too by default,
                # but this makes it impossible to bind to both
                # 0.0.0.0 in ipv4 and :: in ipv6.  On other systems,
                # separate sockets *must* be used to listen for both ipv4
                # and ipv6.  For consistency, always disable ipv4 on our
                # ipv6 sockets and use a separate ipv4 socket when needed.
                #
                # Python 2.x on windows doesn't have IPPROTO_IPV6.
                if hasattr(socket, "IPPROTO_IPV6"):
                    sock.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_V6ONLY, 1)
            sock.setblocking(0)
            sock.bind(sockaddr)
            sock.listen(128)
            self._sockets[sock.fileno()] = sock
            if self._started:
                self.io_loop.add_handler(sock.fileno(), self._handle_events,
                                         ioloop.IOLoop.READ)

    def start(self, num_processes=1):
        """Starts this server in the IOLoop.

        By default, we run the server in this process and do not fork any
        additional child process.

        If num_processes is None or <= 0, we detect the number of cores
        available on this machine and fork that number of child
        processes. If num_processes is given and > 1, we fork that
        specific number of sub-processes.

        Since we use processes and not threads, there is no shared memory
        between any server code.

        Note that multiple processes are not compatible with the autoreload
        module (or the debug=True option to tornado.web.Application).
        When using multiple processes, no IOLoops can be created or
        referenced until after the call to HTTPServer.start(n).
        """
        assert not self._started
        self._started = True
        if num_processes is None or num_processes <= 0:
            num_processes = _cpu_count()
        if num_processes > 1 and ioloop.IOLoop.initialized():
            logging.error("Cannot run in multiple processes: IOLoop instance "
                          "has already been initialized. You cannot call "
                          "IOLoop.instance() before calling start()")
            num_processes = 1
        if num_processes > 1:
            logging.info("Pre-forking %d server processes", num_processes)
            for i in range(num_processes):
                if os.fork() == 0:
                    import random
                    from binascii import hexlify
                    try:
                        # If available, use the same method as
                        # random.py
                        seed = long(hexlify(os.urandom(16)), 16)
                    except NotImplementedError:
                        # Include the pid to avoid initializing two
                        # processes to the same value
                        seed(int(time.time() * 1000) ^ os.getpid())
                    random.seed(seed)
                    self.io_loop = ioloop.IOLoop.instance()
                    for fd in self._sockets.keys():
                        self.io_loop.add_handler(fd, self._handle_events,
                                                 ioloop.IOLoop.READ)
                    return
            os.waitpid(-1, 0)
        else:
            if not self.io_loop:
                self.io_loop = ioloop.IOLoop.instance()
            for fd in self._sockets.keys():
                self.io_loop.add_handler(fd, self._handle_events,
                                         ioloop.IOLoop.READ)

    def stop(self):
        """Stops listening for new connections.

        Requests currently in progress may still continue after the
        server is stopped.
        """
        for fd, sock in self._sockets.iteritems():
            self.io_loop.remove_handler(fd)
            sock.close()

    def _handle_events(self, fd, events):
        while True:
            try:
                connection, address = self._sockets[fd].accept()
            except socket.error, e:
                if e.args[0] in (errno.EWOULDBLOCK, errno.EAGAIN):
                    return
                raise
            if self.ssl_options is not None:
                assert ssl, "Python 2.6+ and OpenSSL required for SSL"
                try:
                    connection = ssl.wrap_socket(connection,
                                                 server_side=True,
                                                 do_handshake_on_connect=False,
                                                 **self.ssl_options)
                except ssl.SSLError, err:
                    if err.args[0] == ssl.SSL_ERROR_EOF:
                        return connection.close()
                    else:
                        raise
                except socket.error, err:
                    if err.args[0] == errno.ECONNABORTED:
                        return connection.close()
                    else:
                        raise
            try:
                if self.ssl_options is not None:
                    stream = iostream.SSLIOStream(connection, io_loop=self.io_loop)
                else:
                    stream = iostream.IOStream(connection, io_loop=self.io_loop)
                HTTPConnection(stream, address, self.request_callback,
                               self.no_keep_alive, self.xheaders)
            except:
                logging.error("Error in connection callback", exc_info=True)

class _BadRequestException(Exception):
    """Exception class for malformed HTTP requests."""
    pass

class HTTPConnection(object):
    """Handles a connection to an HTTP client, executing HTTP requests.

    We parse HTTP headers and bodies, and execute the request callback
    until the HTTP conection is closed.
    """
    def __init__(self, stream, address, request_callback, no_keep_alive=False,
                 xheaders=False):
        self.stream = stream
        self.address = address
        self.request_callback = request_callback
        self.no_keep_alive = no_keep_alive
        self.xheaders = xheaders
        self._request = None
        self._request_finished = False
        # Save stack context here, outside of any request.  This keeps
        # contexts from one request from leaking into the next.
        self._header_callback = stack_context.wrap(self._on_headers)
        self.stream.read_until(b("\r\n\r\n"), self._header_callback)

    def write(self, chunk):
        """Writes a chunk of output to the stream."""
        assert self._request, "Request closed"
        if not self.stream.closed():
            self.stream.write(chunk, self._on_write_complete)

    def finish(self):
        """Finishes the request."""
        assert self._request, "Request closed"
        self._request_finished = True
        if not self.stream.writing():
            self._finish_request()

    def _on_write_complete(self):
        if self._request_finished:
            self._finish_request()

    def _finish_request(self):
        if self.no_keep_alive:
            disconnect = True
        else:
            connection_header = self._request.headers.get("Connection")
            if self._request.supports_http_1_1():
                disconnect = connection_header == "close"
            elif ("Content-Length" in self._request.headers
                    or self._request.method in ("HEAD", "GET")):
                disconnect = connection_header != "Keep-Alive"
            else:
                disconnect = True
        self._request = None
        self._request_finished = False
        if disconnect:
            self.stream.close()
            return
        self.stream.read_until(b("\r\n\r\n"), self._header_callback)

    def _on_headers(self, data):
        try:
            data = native_str(data.decode('latin1'))
            eol = data.find("\r\n")
            start_line = data[:eol]
            try:
                method, uri, version = start_line.split(" ")
            except ValueError:
                raise _BadRequestException("Malformed HTTP request line")
            if not version.startswith("HTTP/"):
                raise _BadRequestException("Malformed HTTP version in HTTP Request-Line")
            headers = httputil.HTTPHeaders.parse(data[eol:])
            self._request = HTTPRequest(
                connection=self, method=method, uri=uri, version=version,
                headers=headers, remote_ip=self.address[0])

            content_length = headers.get("Content-Length")
            if content_length:
                content_length = int(content_length)
                if content_length > self.stream.max_buffer_size:
                    raise _BadRequestException("Content-Length too long")
                if headers.get("Expect") == "100-continue":
                    self.stream.write("HTTP/1.1 100 (Continue)\r\n\r\n")
                self.stream.read_bytes(content_length, self._on_request_body)
                return

            self.request_callback(self._request)
        except _BadRequestException, e:
            logging.info("Malformed HTTP request from %s: %s",
                         self.address[0], e)
            self.stream.close()
            return

    def _on_request_body(self, data):
        self._request.body = data
        content_type = self._request.headers.get("Content-Type", "")
        if self._request.method in ("POST", "PUT"):
            if content_type.startswith("application/x-www-form-urlencoded"):
                arguments = parse_qs_bytes(native_str(self._request.body))
                for name, values in arguments.iteritems():
                    values = [v for v in values if v]
                    if values:
                        self._request.arguments.setdefault(name, []).extend(
                            values)
            elif content_type.startswith("multipart/form-data"):
                fields = content_type.split(";")
                for field in fields:
                    k, sep, v = field.strip().partition("=")
                    if k == "boundary" and v:
                        httputil.parse_multipart_form_data(
                            utf8(v), data,
                            self._request.arguments,
                            self._request.files)
                        break
                else:
                    logging.warning("Invalid multipart/form-data")
        self.request_callback(self._request)


class HTTPRequest(object):
    """A single HTTP request.

    All attributes are type `str` unless otherwise noted.

    .. attribute:: method

       HTTP request method, e.g. "GET" or "POST"

    .. attribute:: uri

       The requested uri.

    .. attribute:: path

       The path portion of `uri`

    .. attribute:: query

       The query portion of `uri`

    .. attribute:: version

       HTTP version specified in request, e.g. "HTTP/1.1"

    .. attribute:: headers

       `HTTPHeader` dictionary-like object for request headers.  Acts like
       a case-insensitive dictionary with additional methods for repeated
       headers.

    .. attribute:: body

       Request body, if present, as a byte string.

    .. attribute:: remote_ip

       Client's IP address as a string.  If `HTTPServer.xheaders` is set,
       will pass along the real IP address provided by a load balancer
       in the ``X-Real-Ip`` header

    .. attribute:: protocol

       The protocol used, either "http" or "https".  If `HTTPServer.xheaders`
       is seet, will pass along the protocol used by a load balancer if
       reported via an ``X-Scheme`` header.

    .. attribute:: host

       The requested hostname, usually taken from the ``Host`` header.

    .. attribute:: arguments

       GET/POST arguments are available in the arguments property, which
       maps arguments names to lists of values (to support multiple values
       for individual names). Names are of type `str`, while arguments
       are byte strings.  Note that this is different from 
       `RequestHandler.get_argument`, which returns argument values as 
       unicode strings.

    .. attribute:: files

       File uploads are available in the files property, which maps file
       names to list of files. Each file is a dictionary of the form
       {"filename":..., "content_type":..., "body":...}. The content_type
       comes from the provided HTTP header and should not be trusted
       outright given that it can be easily forged.

    .. attribute:: connection

       An HTTP request is attached to a single HTTP connection, which can
       be accessed through the "connection" attribute. Since connections
       are typically kept open in HTTP/1.1, multiple requests can be handled
       sequentially on a single connection.
    """
    def __init__(self, method, uri, version="HTTP/1.0", headers=None,
                 body=None, remote_ip=None, protocol=None, host=None,
                 files=None, connection=None):
        self.method = method
        self.uri = uri
        self.version = version
        self.headers = headers or httputil.HTTPHeaders()
        self.body = body or ""
        if connection and connection.xheaders:
            # Squid uses X-Forwarded-For, others use X-Real-Ip
            self.remote_ip = self.headers.get(
                "X-Real-Ip", self.headers.get("X-Forwarded-For", remote_ip))
            # AWS uses X-Forwarded-Proto
            self.protocol = self.headers.get(
                "X-Scheme", self.headers.get("X-Forwarded-Proto", protocol))
            if self.protocol not in ("http", "https"):
                self.protocol = "http"
        else:
            self.remote_ip = remote_ip
            if protocol:
                self.protocol = protocol
            elif connection and isinstance(connection.stream, 
                                           iostream.SSLIOStream):
                self.protocol = "https"
            else:
                self.protocol = "http"
        self.host = host or self.headers.get("Host") or "127.0.0.1"
        self.files = files or {}
        self.connection = connection
        self._start_time = time.time()
        self._finish_time = None

        scheme, netloc, path, query, fragment = urlparse.urlsplit(native_str(uri))
        self.path = path
        self.query = query
        arguments = parse_qs_bytes(query)
        self.arguments = {}
        for name, values in arguments.iteritems():
            values = [v for v in values if v]
            if values: self.arguments[name] = values

    def supports_http_1_1(self):
        """Returns True if this request supports HTTP/1.1 semantics"""
        return self.version == "HTTP/1.1"

    def write(self, chunk):
        """Writes the given chunk to the response stream."""
        assert isinstance(chunk, bytes_type)
        self.connection.write(chunk)

    def finish(self):
        """Finishes this HTTP request on the open connection."""
        self.connection.finish()
        self._finish_time = time.time()

    def full_url(self):
        """Reconstructs the full URL for this request."""
        return self.protocol + "://" + self.host + self.uri

    def request_time(self):
        """Returns the amount of time it took for this request to execute."""
        if self._finish_time is None:
            return time.time() - self._start_time
        else:
            return self._finish_time - self._start_time

    def get_ssl_certificate(self):
        """Returns the client's SSL certificate, if any.

        To use client certificates, the HTTPServer must have been constructed
        with cert_reqs set in ssl_options, e.g.::

            server = HTTPServer(app,
                ssl_options=dict(
                    certfile="foo.crt",
                    keyfile="foo.key",
                    cert_reqs=ssl.CERT_REQUIRED,
                    ca_certs="cacert.crt"))

        The return value is a dictionary, see SSLSocket.getpeercert() in
        the standard library for more details.
        http://docs.python.org/library/ssl.html#sslsocket-objects
        """
        try:
            return self.connection.stream.socket.getpeercert()
        except ssl.SSLError:
            return None

    def __repr__(self):
        attrs = ("protocol", "host", "method", "uri", "version", "remote_ip",
                 "body")
        args = ", ".join(["%s=%r" % (n, getattr(self, n)) for n in attrs])
        return "%s(%s, headers=%s)" % (
            self.__class__.__name__, args, dict(self.headers))