python-falcon 1.0.0-2build3 / usr / lib / python2.7 / dist-packages / falcon / request.py

# 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.

from datetime import datetime

try:
    # NOTE(kgrifs): In Python 2.6 and 2.7, socket._fileobject is a
    # standard way of exposing a socket as a file-like object, and
    # is used by wsgiref for wsgi.input.
    import socket
    NativeStream = socket._fileobject
except AttributeError:
    # NOTE(kgriffs): In Python 3.3, wsgiref implements wsgi.input
    # using _io.BufferedReader which is an alias of io.BufferedReader
    import io
    NativeStream = io.BufferedReader

import mimeparse
import six
from wsgiref.validate import InputWrapper

from falcon.errors import *  # NOQA
from falcon import util
from falcon.util.uri import parse_query_string, parse_host, unquote_string
from falcon import request_helpers as helpers

# NOTE(tbug): In some cases, http_cookies is not a module
# but a dict-like structure. This fixes that issue.
# See issue https://github.com/falconry/falcon/issues/556
from six.moves import http_cookies
SimpleCookie = http_cookies.SimpleCookie


DEFAULT_ERROR_LOG_FORMAT = (u'{0:%Y-%m-%d %H:%M:%S} [FALCON] [ERROR]'
                            u' {1} {2}{3} => ')

TRUE_STRINGS = ('true', 'True', 'yes', '1')
FALSE_STRINGS = ('false', 'False', 'no', '0')
WSGI_CONTENT_HEADERS = ('CONTENT_TYPE', 'CONTENT_LENGTH')


_maybe_wrap_wsgi_stream = True


# PERF(kgriffs): Avoid an extra namespace lookup when using these functions
strptime = datetime.strptime
now = datetime.now


class Request(object):
    """Represents a client's HTTP request.

    Note:
        `Request` is not meant to be instantiated directly by responders.

    Args:
        env (dict): A WSGI environment dict passed in from the server. See
            also PEP-3333.
        options (dict): Set of global options passed from the API handler.

    Attributes:
        protocol (str): Either 'http' or 'https'.
        method (str): HTTP method requested (e.g., 'GET', 'POST', etc.)
        host (str): Hostname requested by the client
        subdomain (str): Leftmost (i.e., most specific) subdomain from the
            hostname. If only a single domain name is given, `subdomain`
            will be ``None``.

            Note:
                If the hostname in the request is an IP address, the value
                for `subdomain` is undefined.

        env (dict): Reference to the WSGI environ ``dict`` passed in from the
            server. See also PEP-3333.
        app (str): Name of the WSGI app (if using WSGI's notion of virtual
            hosting).
        access_route(list): IP address of the original client, as well
            as any known addresses of proxies fronting the WSGI server.

            The following request headers are checked, in order of
            preference, to determine the addresses:

                - ``Forwarded``
                - ``X-Forwarded-For``
                - ``X-Real-IP``

            If none of these headers are available, the value of
            :py:attr:`~.remote_addr` is used instead.

            Note:
                Per `RFC 7239`_, the access route may contain "unknown"
                and obfuscated identifiers, in addition to IPv4 and
                IPv6 addresses

                .. _RFC 7239: https://tools.ietf.org/html/rfc7239

            Warning:
                Headers can be forged by any client or proxy. Use this
                property with caution and validate all values before
                using them. Do not rely on the access route to authorize
                requests.

        remote_addr(str): IP address of the closest client or proxy to
            the WSGI server.

            This property is determined by the value of ``REMOTE_ADDR``
            in the WSGI environment dict. Since this address is not
            derived from an HTTP header, clients and proxies can not
            forge it.

            Note:
                If your application is behind one or more reverse
                proxies, you can use :py:attr:`~.access_route`
                to retrieve the real IP address of the client.

        context (dict): Dictionary to hold any data about the request which is
            specific to your app (e.g. session object). Falcon itself will
            not interact with this attribute after it has been initialized.
        context_type (class): Class variable that determines the
            factory or type to use for initializing the
            `context` attribute. By default, the framework will
            instantiate standard
            ``dict`` objects. However, You may override this behavior
            by creating a custom child class of ``falcon.Request``, and
            then passing that new class to `falcon.API()` by way of the
            latter's `request_type` parameter.

            Note:
                When overriding `context_type` with a factory function (as
                opposed to a class), the function is called like a method of
                the current Request instance. Therefore the first argument is
                the Request instance itself (self).

        uri (str): The fully-qualified URI for the request.
        url (str): alias for `uri`.
        relative_uri (str): The path + query string portion of the full URI.
        path (str): Path portion of the request URL (not including query
            string).
        query_string (str): Query string portion of the request URL, without
            the preceding '?' character.
        user_agent (str): Value of the User-Agent header, or ``None`` if the
            header is missing.
        accept (str): Value of the Accept header, or '*/*' if the header is
            missing.
        auth (str): Value of the Authorization header, or ``None`` if the
            header is missing.
        client_accepts_json (bool): ``True`` if the Accept header indicates
            that the client is willing to receive JSON, otherwise ``False``.
        client_accepts_msgpack (bool): ``True`` if the Accept header indicates
            that the client is willing to receive MessagePack, otherwise
            ``False``.
        client_accepts_xml (bool): ``True`` if the Accept header indicates that
            the client is willing to receive XML, otherwise ``False``.
        content_type (str): Value of the Content-Type header, or ``None`` if
            the header is missing.
        content_length (int): Value of the Content-Length header converted
            to an ``int``, or ``None`` if the header is missing.
        stream: File-like object for reading the body of the request, if any.

            Note:
                If an HTML form is POSTed to the API using the
                *application/x-www-form-urlencoded* media type, and
                the :py:attr:`~.RequestOptions.auto_parse_form_urlencoded`
                option is set, the framework
                will consume `stream` in order to parse the parameters
                and merge them into the query string parameters. In this
                case, the stream will be left at EOF.

        date (datetime): Value of the Date header, converted to a
            ``datetime`` instance. The header value is assumed to
            conform to RFC 1123.
        expect (str): Value of the Expect header, or ``None`` if the
            header is missing.
        range (tuple of int): A 2-member ``tuple`` parsed from the value of the
            Range header.

            The two members correspond to the first and last byte
            positions of the requested resource, inclusive. Negative
            indices indicate offset from the end of the resource,
            where -1 is the last byte, -2 is the second-to-last byte,
            and so forth.

            Only continuous ranges are supported (e.g., "bytes=0-0,-1" would
            result in an HTTPBadRequest exception when the attribute is
            accessed.)
        range_unit (str): Unit of the range parsed from the value of the
            Range header, or ``None`` if the header is missing
        if_match (str): Value of the If-Match header, or ``None`` if the
            header is missing.
        if_none_match (str): Value of the If-None-Match header, or ``None``
            if the header is missing.
        if_modified_since (datetime): Value of the If-Modified-Since header,
            or ``None`` if the header is missing.
        if_unmodified_since (datetime): Value of the If-Unmodified-Since
            header, or ``None`` if the header is missing.
        if_range (str): Value of the If-Range header, or ``None`` if the
            header is missing.

        headers (dict): Raw HTTP headers from the request with
            canonical dash-separated names. Parsing all the headers
            to create this dict is done the first time this attribute
            is accessed. This parsing can be costly, so unless you
            need all the headers in this format, you should use the
            `get_header` method or one of the convenience attributes
            instead, to get a value for a specific header.

        params (dict): The mapping of request query parameter names to their
            values.  Where the parameter appears multiple times in the query
            string, the value mapped to that parameter key will be a list of
            all the values in the order seen.

        options (dict): Set of global options passed from the API handler.

        cookies (dict):
            A dict of name/value cookie pairs.
            See also: :ref:`Getting Cookies <getting-cookies>`

    """

    __slots__ = (
        '_cached_headers',
        '_cached_uri',
        '_cached_relative_uri',
        'content_type',
        'env',
        'method',
        '_params',
        'path',
        'query_string',
        'stream',
        'context',
        '_wsgierrors',
        'options',
        '_cookies',
        '_cached_access_route',
    )

    # Allow child classes to override this
    context_type = None

    def __init__(self, env, options=None):
        global _maybe_wrap_wsgi_stream

        self.env = env
        self.options = options if options else RequestOptions()

        self._wsgierrors = env['wsgi.errors']
        self.stream = env['wsgi.input']
        self.method = env['REQUEST_METHOD']

        # Normalize path
        path = env['PATH_INFO']
        if path:
            if six.PY3:
                # PEP 3333 specifies that PATH_INFO variable are always
                # "bytes tunneled as latin-1" and must be encoded back
                path = path.encode('latin1').decode('utf-8', 'replace')

            if len(path) != 1 and path.endswith('/'):
                self.path = path[:-1]
            else:
                self.path = path
        else:
            self.path = '/'

        # PERF(kgriffs): if...in is faster than using env.get(...)
        if 'QUERY_STRING' in env:
            self.query_string = env['QUERY_STRING']

            if self.query_string:
                self._params = parse_query_string(
                    self.query_string,
                    keep_blank_qs_values=self.options.keep_blank_qs_values,
                )

            else:
                self._params = {}

        else:
            self.query_string = ''
            self._params = {}

        self._cookies = None

        self._cached_headers = None
        self._cached_uri = None
        self._cached_relative_uri = None
        self._cached_access_route = None

        try:
            self.content_type = self.env['CONTENT_TYPE']
        except KeyError:
            self.content_type = None

        # NOTE(kgriffs): Wrap wsgi.input if needed to make read() more robust,
        # normalizing semantics between, e.g., gunicorn and wsgiref.
        if _maybe_wrap_wsgi_stream:
            if isinstance(self.stream, (NativeStream, InputWrapper,)):
                self._wrap_stream()
            else:
                # PERF(kgriffs): If self.stream does not need to be wrapped
                # this time, it never needs to be wrapped since the server
                # will continue using the same type for wsgi.input.
                _maybe_wrap_wsgi_stream = False

        # PERF(kgriffs): Technically, we should spend a few more
        # cycles and parse the content type for real, but
        # this heuristic will work virtually all the time.
        if (self.options.auto_parse_form_urlencoded and
                self.content_type is not None and
                'application/x-www-form-urlencoded' in self.content_type):
            self._parse_form_urlencoded()

        if self.context_type is None:
            # Literal syntax is more efficient than using dict()
            self.context = {}
        else:
            self.context = self.context_type()

    # ------------------------------------------------------------------------
    # Properties
    # ------------------------------------------------------------------------

    user_agent = helpers.header_property('HTTP_USER_AGENT')
    auth = helpers.header_property('HTTP_AUTHORIZATION')

    expect = helpers.header_property('HTTP_EXPECT')

    if_match = helpers.header_property('HTTP_IF_MATCH')
    if_none_match = helpers.header_property('HTTP_IF_NONE_MATCH')
    if_range = helpers.header_property('HTTP_IF_RANGE')

    @property
    def client_accepts_json(self):
        return self.client_accepts('application/json')

    @property
    def client_accepts_msgpack(self):
        return (self.client_accepts('application/x-msgpack') or
                self.client_accepts('application/msgpack'))

    @property
    def client_accepts_xml(self):
        return self.client_accepts('application/xml')

    @property
    def accept(self):
        # NOTE(kgriffs): Per RFC, a missing accept header is
        # equivalent to '*/*'
        try:
            return self.env['HTTP_ACCEPT'] or '*/*'
        except KeyError:
            return '*/*'

    @property
    def content_length(self):
        try:
            value = self.env['CONTENT_LENGTH']
        except KeyError:
            return None

        # NOTE(kgriffs): Normalize an empty value to behave as if
        # the header were not included; wsgiref, at least, inserts
        # an empty CONTENT_LENGTH value if the request does not
        # set the header. Gunicorn and uWSGI do not do this, but
        # others might if they are trying to match wsgiref's
        # behavior too closely.
        if not value:
            return None

        try:
            value_as_int = int(value)
        except ValueError:
            msg = 'The value of the header must be a number.'
            raise HTTPInvalidHeader(msg, 'Content-Length')

        if value_as_int < 0:
            msg = 'The value of the header must be a positive number.'
            raise HTTPInvalidHeader(msg, 'Content-Length')

        return value_as_int

    @property
    def date(self):
        return self.get_header_as_datetime('Date')

    @property
    def if_modified_since(self):
        return self.get_header_as_datetime('If-Modified-Since')

    @property
    def if_unmodified_since(self):
        return self.get_header_as_datetime('If-Unmodified-Since')

    @property
    def range(self):
        try:
            value = self.env['HTTP_RANGE']
            if '=' in value:
                unit, sep, req_range = value.partition('=')
            else:
                msg = "The value must be prefixed with a range unit, e.g. 'bytes='"
                raise HTTPInvalidHeader(msg, 'Range')
        except KeyError:
            return None

        if ',' in req_range:
            msg = 'The value must be a continuous range.'
            raise HTTPInvalidHeader(msg, 'Range')

        try:
            first, sep, last = req_range.partition('-')

            if not sep:
                raise ValueError()

            if first:
                return (int(first), int(last or -1))
            elif last:
                return (-int(last), -1)
            else:
                msg = 'The range offsets are missing.'
                raise HTTPInvalidHeader(msg, 'Range')

        except ValueError:
            href = 'http://goo.gl/zZ6Ey'
            href_text = 'HTTP/1.1 Range Requests'
            msg = ('It must be a range formatted according to RFC 7233.')
            raise HTTPInvalidHeader(msg, 'Range', href=href,
                                    href_text=href_text)

    @property
    def range_unit(self):
        try:
            value = self.env['HTTP_RANGE']

            if '=' in value:
                unit, sep, req_range = value.partition('=')
                return unit
            else:
                msg = "The value must be prefixed with a range unit, e.g. 'bytes='"
                raise HTTPInvalidHeader(msg, 'Range')
        except KeyError:
            return None

    @property
    def app(self):
        return self.env.get('SCRIPT_NAME', '')

    @property
    def protocol(self):
        return self.env['wsgi.url_scheme']

    @property
    def uri(self):
        if self._cached_uri is None:
            env = self.env
            protocol = env['wsgi.url_scheme']

            # NOTE(kgriffs): According to PEP-3333 we should first
            # try to use the Host header if present.
            #
            # PERF(kgriffs): try..except is faster than .get
            try:
                host = env['HTTP_HOST']
            except KeyError:
                host = env['SERVER_NAME']
                port = env['SERVER_PORT']

                if protocol == 'https':
                    if port != '443':
                        host += ':' + port
                else:
                    if port != '80':
                        host += ':' + port

            # PERF: For small numbers of items, '+' is faster
            # than ''.join(...). Concatenation is also generally
            # faster than formatting.
            value = (protocol + '://' +
                     host +
                     self.app +
                     self.path)

            if self.query_string:
                value = value + '?' + self.query_string

            self._cached_uri = value

        return self._cached_uri

    url = uri

    @property
    def host(self):
        try:
            # NOTE(kgriffs): Prefer the host header; the web server
            # isn't supposed to mess with it, so it should be what
            # the client actually sent.
            host_header = self.env['HTTP_HOST']
            host, port = parse_host(host_header)
        except KeyError:
            # PERF(kgriffs): According to PEP-3333, this header
            # will always be present.
            host = self.env['SERVER_NAME']

        return host

    @property
    def subdomain(self):
        # PERF(kgriffs): .partition is slightly faster than .split
        subdomain, sep, remainder = self.host.partition('.')
        return subdomain if sep else None

    @property
    def relative_uri(self):
        if self._cached_relative_uri is None:
            if self.query_string:
                self._cached_relative_uri = (self.app + self.path + '?' +
                                             self.query_string)
            else:
                self._cached_relative_uri = self.app + self.path

        return self._cached_relative_uri

    @property
    def headers(self):
        # NOTE(kgriffs: First time here will cache the dict so all we
        # have to do is clone it in the future.
        if self._cached_headers is None:
            headers = self._cached_headers = {}

            env = self.env
            for name, value in env.items():
                if name.startswith('HTTP_'):
                    # NOTE(kgriffs): Don't take the time to fix the case
                    # since headers are supposed to be case-insensitive
                    # anyway.
                    headers[name[5:].replace('_', '-')] = value

                elif name in WSGI_CONTENT_HEADERS:
                    headers[name.replace('_', '-')] = value

        return self._cached_headers.copy()

    @property
    def params(self):
        return self._params

    @property
    def cookies(self):
        if self._cookies is None:
            # NOTE(tbug): We might want to look into parsing
            # cookies ourselves. The SimpleCookie is doing a
            # lot if stuff only required to SEND cookies.
            parser = SimpleCookie(self.get_header('Cookie'))
            cookies = {}
            for morsel in parser.values():
                cookies[morsel.key] = morsel.value

            self._cookies = cookies

        return self._cookies.copy()

    @property
    def access_route(self):
        if self._cached_access_route is None:
            # NOTE(kgriffs): Try different headers in order of
            # preference; if none are found, fall back to REMOTE_ADDR.
            #
            # If one of these headers is present, but its value is
            # malformed such that we end up with an empty list, or
            # a non-empty list containing malformed values, go ahead
            # and return the results as-is. The alternative would be
            # to fall back to another header or to REMOTE_ADDR, but
            # that only masks the problem; the operator needs to be
            # aware that an upstream proxy is malfunctioning.

            if 'HTTP_FORWARDED' in self.env:
                self._cached_access_route = self._parse_rfc_forwarded()
            elif 'HTTP_X_FORWARDED_FOR' in self.env:
                addresses = self.env['HTTP_X_FORWARDED_FOR'].split(',')
                self._cached_access_route = [ip.strip() for ip in addresses]
            elif 'HTTP_X_REAL_IP' in self.env:
                self._cached_access_route = [self.env['HTTP_X_REAL_IP']]
            elif 'REMOTE_ADDR' in self.env:
                self._cached_access_route = [self.env['REMOTE_ADDR']]
            else:
                self._cached_access_route = []

        return self._cached_access_route

    @property
    def remote_addr(self):
        return self.env.get('REMOTE_ADDR')

    # ------------------------------------------------------------------------
    # Methods
    # ------------------------------------------------------------------------

    def client_accepts(self, media_type):
        """Determines whether or not the client accepts a given media type.

        Args:
            media_type (str): An Internet media type to check.

        Returns:
            bool: ``True`` if the client has indicated in the Accept header
                that it accepts the specified media type. Otherwise, returns
                ``False``.
        """

        accept = self.accept

        # PERF(kgriffs): Usually the following will be true, so
        # try it first.
        if (accept == media_type) or (accept == '*/*'):
            return True

        # Fall back to full-blown parsing
        try:
            return mimeparse.quality(media_type, accept) != 0.0
        except ValueError:
            return False

    def client_prefers(self, media_types):
        """Returns the client's preferred media type, given several choices.

        Args:
            media_types (iterable of str): One or more Internet media types
                from which to choose the client's preferred type. This value
                **must** be an iterable collection of strings.

        Returns:
            str: The client's preferred media type, based on the Accept
                header. Returns ``None`` if the client does not accept any
                of the given types.
        """

        try:
            # NOTE(kgriffs): best_match will return '' if no match is found
            preferred_type = mimeparse.best_match(media_types, self.accept)
        except ValueError:
            # Value for the accept header was not formatted correctly
            preferred_type = ''

        return (preferred_type if preferred_type else None)

    def get_header(self, name, required=False):
        """Retrieve the raw string value for the given header.

        Args:
            name (str): Header name, case-insensitive (e.g., 'Content-Type')
            required (bool, optional): Set to ``True`` to raise
                ``HTTPBadRequest`` instead of returning gracefully when the
                header is not found (default ``False``).

        Returns:
            str: The value of the specified header if it exists, or ``None`` if
                the header is not found and is not required.

        Raises:
            HTTPBadRequest: The header was not found in the request, but
                it was required.

        """

        wsgi_name = name.upper().replace('-', '_')

        # Use try..except to optimize for the header existing in most cases
        try:
            # Don't take the time to cache beforehand, using HTTP naming.
            # This will be faster, assuming that most headers are looked
            # up only once, and not all headers will be requested.
            return self.env['HTTP_' + wsgi_name]

        except KeyError:
            # NOTE(kgriffs): There are a couple headers that do not
            # use the HTTP prefix in the env, so try those. We expect
            # people to usually just use the relevant helper properties
            # to access these instead of .get_header.
            if wsgi_name in WSGI_CONTENT_HEADERS:
                try:
                    return self.env[wsgi_name]
                except KeyError:
                    pass

            if not required:
                return None

            raise HTTPMissingHeader(name)

    def get_header_as_datetime(self, header, required=False, obs_date=False):
        """Return an HTTP header with HTTP-Date values as a datetime.

        Args:
            name (str): Header name, case-insensitive (e.g., 'Date')
            required (bool, optional): Set to ``True`` to raise
                ``HTTPBadRequest`` instead of returning gracefully when the
                header is not found (default ``False``).
            obs_date (bool, optional): Support obs-date formats according to
                RFC 7231, e.g.: "Sunday, 06-Nov-94 08:49:37 GMT"
                (default ``False``).

        Returns:
            datetime: The value of the specified header if it exists,
                or ``None`` if the header is not found and is not required.

        Raises:
            HTTPBadRequest: The header was not found in the request, but
                it was required.
            HttpInvalidHeader: The header contained a malformed/invalid value.
        """

        try:
            http_date = self.get_header(header, required=required)
            return util.http_date_to_dt(http_date, obs_date=obs_date)
        except TypeError:
            # When the header does not exist and isn't required
            return None
        except ValueError:
            msg = ('It must be formatted according to RFC 7231, '
                   'Section 7.1.1.1')
            raise HTTPInvalidHeader(msg, header)

    def get_param(self, name, required=False, store=None, default=None):
        """Return the raw value of a query string parameter as a string.

        Note:
            If an HTML form is POSTed to the API using the
            *application/x-www-form-urlencoded* media type, the
            parameters from the request body will be merged into
            the query string parameters.

            If a key appears more than once in the form data, one of the
            values will be returned as a string, but it is undefined which
            one. Use `req.get_param_as_list()` to retrieve all the values.

        Note:
            Similar to the way multiple keys in form data is handled,
            if a query parameter is assigned a comma-separated list of
            values (e.g., 'foo=a,b,c'), only one of those values will be
            returned, and it is undefined which one. Use
            `req.get_param_as_list()` to retrieve all the values.

        Args:
            name (str): Parameter name, case-sensitive (e.g., 'sort').
            required (bool, optional): Set to ``True`` to raise
                ``HTTPBadRequest`` instead of returning ``None`` when the
                parameter is not found (default ``False``).
            store (dict, optional): A ``dict``-like object in which to place
                the value of the param, but only if the param is present.
            default (any, optional): If the param is not found returns the
                given value instead of None

        Returns:
            str: The value of the param as a string, or ``None`` if param is
                not found and is not required.

        Raises:
            HTTPBadRequest: A required param is missing from the request.

        """

        params = self._params

        # PERF: Use if..in since it is a good all-around performer; we don't
        #       know how likely params are to be specified by clients.
        if name in params:
            # NOTE(warsaw): If the key appeared multiple times, it will be
            # stored internally as a list.  We do not define which one
            # actually gets returned, but let's pick the last one for grins.
            param = params[name]
            if isinstance(param, list):
                param = param[-1]

            if store is not None:
                store[name] = param

            return param

        if not required:
            return default

        raise HTTPMissingParam(name)

    def get_param_as_int(self, name,
                         required=False, min=None, max=None, store=None):
        """Return the value of a query string parameter as an int.

        Args:
            name (str): Parameter name, case-sensitive (e.g., 'limit').
            required (bool, optional): Set to ``True`` to raise
                ``HTTPBadRequest`` instead of returning ``None`` when the
                parameter is not found or is not an integer (default
                ``False``).
            min (int, optional): Set to the minimum value allowed for this
                param. If the param is found and it is less than min, an
                ``HTTPError`` is raised.
            max (int, optional): Set to the maximum value allowed for this
                param. If the param is found and its value is greater than
                max, an ``HTTPError`` is raised.
            store (dict, optional): A ``dict``-like object in which to place
                the value of the param, but only if the param is found
                (default ``None``).

        Returns:
            int: The value of the param if it is found and can be converted to
                an integer. If the param is not found, returns ``None``, unless
                `required` is ``True``.

        Raises
            HTTPBadRequest: The param was not found in the request, even though
                it was required to be there. Also raised if the param's value
                falls outside the given interval, i.e., the value must be in
                the interval: min <= value <= max to avoid triggering an error.

        """

        params = self._params

        # PERF: Use if..in since it is a good all-around performer; we don't
        #       know how likely params are to be specified by clients.
        if name in params:
            val = params[name]
            if isinstance(val, list):
                val = val[-1]

            try:
                val = int(val)
            except ValueError:
                msg = 'The value must be an integer.'
                raise HTTPInvalidParam(msg, name)

            if min is not None and val < min:
                msg = 'The value must be at least ' + str(min)
                raise HTTPInvalidParam(msg, name)

            if max is not None and max < val:
                msg = 'The value may not exceed ' + str(max)
                raise HTTPInvalidParam(msg, name)

            if store is not None:
                store[name] = val

            return val

        if not required:
            return None

        raise HTTPMissingParam(name)

    def get_param_as_bool(self, name, required=False, store=None,
                          blank_as_true=False):
        """Return the value of a query string parameter as a boolean

        The following boolean strings are supported::

            TRUE_STRINGS = ('true', 'True', 'yes', '1')
            FALSE_STRINGS = ('false', 'False', 'no', '0')

        Args:
            name (str): Parameter name, case-sensitive (e.g., 'detailed').
            required (bool, optional): Set to ``True`` to raise
                ``HTTPBadRequest`` instead of returning ``None`` when the
                parameter is not found or is not a recognized boolean
                string (default ``False``).
            store (dict, optional): A ``dict``-like object in which to place
                the value of the param, but only if the param is found (default
                ``None``).
            blank_as_true (bool): If ``True``, an empty string value will be
                treated as ``True``. Normally empty strings are ignored; if
                you would like to recognize such parameters, you must set the
                `keep_blank_qs_values` request option to ``True``. Request
                options are set globally for each instance of ``falcon.API``
                through the `req_options` attribute.

        Returns:
            bool: The value of the param if it is found and can be converted
                to a ``bool``. If the param is not found, returns ``None``
                unless required is ``True``.

        Raises:
            HTTPBadRequest: A required param is missing from the request.

        """

        params = self._params

        # PERF: Use if..in since it is a good all-around performer; we don't
        #       know how likely params are to be specified by clients.
        if name in params:
            val = params[name]
            if isinstance(val, list):
                val = val[-1]

            if val in TRUE_STRINGS:
                val = True
            elif val in FALSE_STRINGS:
                val = False
            elif blank_as_true and not val:
                val = True
            else:
                msg = 'The value of the parameter must be "true" or "false".'
                raise HTTPInvalidParam(msg, name)

            if store is not None:
                store[name] = val

            return val

        if not required:
            return None

        raise HTTPMissingParam(name)

    def get_param_as_list(self, name,
                          transform=None, required=False, store=None):
        """Return the value of a query string parameter as a list.

        List items must be comma-separated or must be provided
        as multiple instances of the same param in the query string
        ala *application/x-www-form-urlencoded*.

        Args:
            name (str): Parameter name, case-sensitive (e.g., 'ids').
            transform (callable, optional): An optional transform function
                that takes as input each element in the list as a ``str`` and
                outputs a transformed element for inclusion in the list that
                will be returned. For example, passing ``int`` will
                transform list items into numbers.
            required (bool, optional): Set to ``True`` to raise
                ``HTTPBadRequest`` instead of returning ``None`` when the
                parameter is not found (default ``False``).
            store (dict, optional): A ``dict``-like object in which to place
                the value of the param, but only if the param is found (default
                ``None``).

        Returns:
            list: The value of the param if it is found. Otherwise, returns
                ``None`` unless required is True. Empty list elements will be
                discarded. For example, the following query strings would
                both result in `['1', '3']`::

                    things=1,,3
                    things=1&things=&things=3

        Raises:
            HTTPBadRequest: A required param is missing from the request.
            HTTPInvalidParam: A transform function raised an instance of
                ``ValueError``.

        """

        params = self._params

        # PERF: Use if..in since it is a good all-around performer; we don't
        #       know how likely params are to be specified by clients.
        if name in params:
            items = params[name]

            # NOTE(warsaw): When a key appears multiple times in the request
            # query, it will already be represented internally as a list.
            # NOTE(kgriffs): Likewise for comma-delimited values.
            if not isinstance(items, list):
                items = [items]

            # PERF(kgriffs): Use if-else rather than a DRY approach
            # that sets transform to a passthrough function; avoids
            # function calling overhead.
            if transform is not None:
                try:
                    items = [transform(i) for i in items]

                except ValueError:
                    msg = 'The value is not formatted correctly.'
                    raise HTTPInvalidParam(msg, name)

            if store is not None:
                store[name] = items

            return items

        if not required:
            return None

        raise HTTPMissingParam(name)

    def get_param_as_date(self, name, format_string='%Y-%m-%d',
                          required=False, store=None):
        """Return the value of a query string parameter as a date.

        Args:
            name (str): Parameter name, case-sensitive (e.g., 'ids').
            format_string (str): String used to parse the param value into a
                date.
                Any format recognized by strptime() is supported.
                (default ``"%Y-%m-%d"``)
            required (bool, optional): Set to ``True`` to raise
                ``HTTPBadRequest`` instead of returning ``None`` when the
                parameter is not found (default ``False``).
            store (dict, optional): A ``dict``-like object in which to place
                the value of the param, but only if the param is found (default
                ``None``).
        Returns:
            datetime.date: The value of the param if it is found and can be
                converted to a ``date`` according to the supplied format
                string. If the param is not found, returns ``None`` unless
                required is ``True``.

        Raises:
            HTTPBadRequest: A required param is missing from the request.
            HTTPInvalidParam: A transform function raised an instance of
                ``ValueError``.
        """

        param_value = self.get_param(name, required=required)

        if param_value is None:
            return None

        try:
            date = strptime(param_value, format_string).date()
        except ValueError:
            msg = 'The date value does not match the required format'
            raise HTTPInvalidParam(msg, name)

        if store is not None:
            store[name] = date

        return date

    def log_error(self, message):
        """Write an error message to the server's log.

        Prepends timestamp and request info to message, and writes the
        result out to the WSGI server's error stream (`wsgi.error`).

        Args:
            message (str or unicode): Description of the problem. On Python 2,
                instances of ``unicode`` will be converted to UTF-8.

        """

        if self.query_string:
            query_string_formatted = '?' + self.query_string
        else:
            query_string_formatted = ''

        log_line = (
            DEFAULT_ERROR_LOG_FORMAT.
            format(now(), self.method, self.path, query_string_formatted)
        )

        if six.PY3:
            self._wsgierrors.write(log_line + message + '\n')
        else:
            if isinstance(message, unicode):
                message = message.encode('utf-8')

            self._wsgierrors.write(log_line.encode('utf-8'))
            self._wsgierrors.write(message + '\n')

    # ------------------------------------------------------------------------
    # Helpers
    # ------------------------------------------------------------------------

    def _wrap_stream(self):
        try:
            content_length = self.content_length or 0

        # NOTE(kgriffs): This branch is indeed covered in test_wsgi.py
        # even though coverage isn't able to detect it.
        except HTTPInvalidHeader:  # pragma: no cover
            # NOTE(kgriffs): The content-length header was specified,
            # but it had an invalid value. Assume no content.
            content_length = 0

        self.stream = helpers.Body(self.stream, content_length)

    def _parse_form_urlencoded(self):
        # NOTE(kgriffs): This assumes self.stream has been patched
        # above in the case of wsgiref, so that self.content_length
        # is not needed. Normally we just avoid accessing
        # self.content_length, because it is a little expensive
        # to call. We could cache self.content_length, but the
        # overhead to do that won't usually be helpful, since
        # content length will only ever be read once per
        # request in most cases.
        body = self.stream.read()

        # NOTE(kgriffs): According to http://goo.gl/6rlcux the
        # body should be US-ASCII. Enforcing this also helps
        # catch malicious input.
        try:
            body = body.decode('ascii')
        except UnicodeDecodeError:
            body = None
            self.log_error('Non-ASCII characters found in form body '
                           'with Content-Type of '
                           'application/x-www-form-urlencoded. Body '
                           'will be ignored.')

        if body:
            extra_params = parse_query_string(
                body,
                keep_blank_qs_values=self.options.keep_blank_qs_values,
            )

            self._params.update(extra_params)

    def _parse_rfc_forwarded(self):
        """Parse RFC 7239 "Forwarded" header.

        Returns:
            list: addresses derived from "for" parameters.
        """

        addr = []

        for forwarded in self.env['HTTP_FORWARDED'].split(','):
            for param in forwarded.split(';'):
                # PERF(kgriffs): Partition() is faster than split().
                key, _, val = param.strip().partition('=')
                if not val:
                    # NOTE(kgriffs): The '=' separator was not found or
                    # it was, but the value was missing.
                    continue

                if key.lower() != 'for':
                    # We only want "for" params
                    continue

                host, _ = parse_host(unquote_string(val))
                addr.append(host)

        return addr


# PERF: To avoid typos and improve storage space and speed over a dict.
class RequestOptions(object):
    """This class is a container for ``Request`` options.

    Attributes:
        keep_blank_qs_values (bool): Set to ``True`` in order to retain
            blank values in query string parameters (default ``False``).
        auto_parse_form_urlencoded: Set to ``True`` in order to
            automatically consume the request stream and merge the
            results into the request's query string params when the
            request's content type is
            *application/x-www-form-urlencoded* (default ``False``). In
            this case, the request's content stream will be left at EOF.

            Note:
                The character encoding for fields, before
                percent-encoding non-ASCII bytes, is assumed to be
                UTF-8. The special `_charset_` field is ignored if present.

                Falcon expects form-encoded request bodies to be
                encoded according to the standard W3C algorithm (see
                also http://goo.gl/6rlcux).

    """
    __slots__ = (
        'keep_blank_qs_values',
        'auto_parse_form_urlencoded',
    )

    def __init__(self):
        self.keep_blank_qs_values = False
        self.auto_parse_form_urlencoded = False