import datetime
import os
import re
import time
from pprint import pformat
from urllib import urlencode, quote
from urlparse import urljoin
#try:
#    from StringIO import StringIO
#except ImportError:
from StringIO import StringIO
from copy import deepcopy

try:
    # The mod_python version is more efficient, so try importing it first.
    from mod_python.util import parse_qsl
except ImportError:
    try:
        # Python 2.6 and greater
        from urlparse import parse_qsl
    except ImportError:
        # Python 2.5, 2.4.  Works on Python 2.6 but raises
        # PendingDeprecationWarning
        from cgi import parse_qsl

import Cookie
# httponly support exists in Python 2.6's Cookie library,
# but not in Python 2.4 or 2.5.
_morsel_supports_httponly = Cookie.Morsel._reserved.has_key('httponly')
# Some versions of Python 2.7 and later won't need this encoding bug fix:
_cookie_encodes_correctly = Cookie.SimpleCookie().value_encode(';') == (';', '"\\073"')
# See ticket #13007, http://bugs.python.org/issue2193 and http://trac.edgewall.org/ticket/2256
_tc = Cookie.SimpleCookie()
_tc.load('f:oo')
_cookie_allows_colon_in_names = 'Set-Cookie: f:oo=' in _tc.output()

if False: #_morsel_supports_httponly and _cookie_encodes_correctly and _cookie_allows_colon_in_names:
    SimpleCookie = Cookie.SimpleCookie
else:
    class Morsel(Cookie.Morsel):
        def __getstate__(self):
            d = dict([(k,v) for k,v in dict.items(self)])
            return d
        def __setstate__(self, state):
            for k,v in state.items():
                dict.__setitem__(self, k, v)
        
        if not _morsel_supports_httponly:
            def __setitem__(self, K, V):
                K = K.lower()
                if K == "httponly":
                    if V:
                        # The superclass rejects httponly as a key,
                        # so we jump to the grandparent.
                        super(Cookie.Morsel, self).__setitem__(K, V)
                else:
                    super(Morsel, self).__setitem__(K, V)

            def OutputString(self, attrs=None):
                output = super(Morsel, self).OutputString(attrs)
                if "httponly" in self:
                    output += "; httponly"
                return output

    class SimpleCookie(Cookie.SimpleCookie):
        def __getstate__(self):
            d = dict([(k,v) for k,v in dict.items(self)])
            return d

        def __setstate__(self, state):
            for k,v in state.items():
                dict.__setitem__(self, k, v)

        if not _morsel_supports_httponly:
            def __set(self, key, real_value, coded_value):
                M = self.get(key, Morsel())
                M.set(key, real_value, coded_value)
                dict.__setitem__(self, key, M)

            def __setitem__(self, key, value):
                rval, cval = self.value_encode(value)
                self.__set(key, rval, cval)

        if not _cookie_encodes_correctly:
            def value_encode(self, val):
                # Some browsers do not support quoted-string from RFC 2109,
                # including some versions of Safari and Internet Explorer.
                # These browsers split on ';', and some versions of Safari
                # are known to split on ', '. Therefore, we encode ';' and ','

                # SimpleCookie already does the hard work of encoding and decoding.
                # It uses octal sequences like '\\012' for newline etc.
                # and non-ASCII chars.  We just make use of this mechanism, to
                # avoid introducing two encoding schemes which would be confusing
                # and especially awkward for javascript.

                # NB, contrary to Python docs, value_encode returns a tuple containing
                # (real val, encoded_val)
                val, encoded = super(SimpleCookie, self).value_encode(val)

                encoded = encoded.replace(";", "\\073").replace(",","\\054")
                # If encoded now contains any quoted chars, we need double quotes
                # around the whole string.
                if "\\" in encoded and not encoded.startswith('"'):
                    encoded = '"' + encoded + '"'

                return val, encoded

        if not _cookie_allows_colon_in_names:
            def load(self, rawdata, ignore_parse_errors=False):
                if ignore_parse_errors:
                    self.bad_cookies = set()
                    self._BaseCookie__set = self._loose_set
                super(SimpleCookie, self).load(rawdata)
                if ignore_parse_errors:
                    self._BaseCookie__set = self._strict_set
                    for key in self.bad_cookies:
                        del self[key]

            _strict_set = Cookie.BaseCookie._BaseCookie__set

            def _loose_set(self, key, real_value, coded_value):
                try:
                    self._strict_set(key, real_value, coded_value)
                except Cookie.CookieError:
                    self.bad_cookies.add(key)
                    dict.__setitem__(self, key, Cookie.Morsel())


class CompatCookie(SimpleCookie):
    def __init__(self, *args, **kwargs):
        super(CompatCookie, self).__init__(*args, **kwargs)
        import warnings
        warnings.warn("CompatCookie is deprecated, use django.http.SimpleCookie instead.",
                      PendingDeprecationWarning)

from django.utils.datastructures import MultiValueDict, ImmutableList
from django.utils.encoding import smart_str, iri_to_uri, force_unicode
from django.utils.http import cookie_date
from django.http.multipartparser import MultiPartParser
from django.conf import settings
from django.core.files import uploadhandler
from utils import *

RESERVED_CHARS="!*'();:@&=+$,/?%#[]"

absolute_http_url_re = re.compile(r"^https?://", re.I)

class Http404(Exception):
    pass

class HttpRequestDummy(object):
    """
    A stripped down HTTP request object that's pickle-able
    TODO FILES
    """
    def __init__(self,request):
        self.GET = request.GET
        self.POST = request.POST
        self.COOKIES = request.COOKIES
        self.META = dict([(k,v) for k,v in request.META.items() if not k.startswith('wsgi')])
        self.FILES = request.FILES
        self.path = request.path
        self.session = request.session
        self.path_info = request.path_info
        self.user = request.user
        self.method = request.method
        if hasattr(request, '_messages'):
            self._messages = request._messages

    def __repr__(self):
        return "G: %s \nP: %s \nC: %s\nM: %s\np: %s\nm: %s" % (self.GET, 
                                                               self.POST, 
                                                               self.COOKIES,
                                                               self.META,
                                                               self.path,
                                                               self.method)

    def _get_request(self):
        from django.utils import datastructures
        if not hasattr(self, '_request'):
            self._request = datastructures.MergeDict(self.POST, self.GET)
        return self._request

    def get_host(self):
        """Returns the HTTP host using the environment or request headers."""
        # We try three options, in order of decreasing preference.
        if settings.USE_X_FORWARDED_HOST and (
            'HTTP_X_FORWARDED_HOST' in self.META):
            host = self.META['HTTP_X_FORWARDED_HOST']
        elif 'HTTP_HOST' in self.META:
            host = self.META['HTTP_HOST']
        else:
            # Reconstruct the host using the algorithm from PEP 333.
            host = self.META['SERVER_NAME']
            server_port = str(self.META['SERVER_PORT'])
            if server_port != (self.is_secure() and '443' or '80'):
                host = '%s:%s' % (host, server_port)
        return host

    def get_full_path(self):
        # RFC 3986 requires query string arguments to be in the ASCII range.
        # Rather than crash if this doesn't happen, we encode defensively.
        return '%s%s' % (self.path, self.META.get('QUERY_STRING', '') and ('?' + iri_to_uri(self.META.get('QUERY_STRING', ''))) or '')

    def build_absolute_uri(self, location=None):
        """
        Builds an absolute URI from the location and the variables available in
        this request. If no location is specified, the absolute URI is built on
        ``request.get_full_path()``.
        """
        if not location:
            location = self.get_full_path()
        if not absolute_http_url_re.match(location):
            current_uri = '%s://%s%s' % (self.is_secure() and 'https' or 'http',
                                         self.get_host(), self.path)
            location = urljoin(current_uri, location)
        return iri_to_uri(location)

    def is_secure(self):
        return os.environ.get("HTTPS") == "on"

    def is_ajax(self):
        return self.META.get('HTTP_X_REQUESTED_WITH') == 'XMLHttpRequest'
    REQUEST = property(_get_request)      
  
typeset = [int, float, str, unicode, bool]

class HttpRequest(object):
    """A basic HTTP request."""

    # The encoding used in GET/POST dicts. None means use default setting.
    _encoding = None
    _upload_handlers = []

    def __init__(self):
        self.GET, self.POST, self.COOKIES, self.META, self.FILES = {}, {}, {}, {}, {}
        self.path = ''
        self.path_info = ''
        self.method = None

    def __repr__(self):
        return '<HttpRequest\nGET:%s,\nPOST:%s,\nCOOKIES:%s,\nMETA:%s>' % \
            (pformat(self.GET), pformat(self.POST), pformat(self.COOKIES),
            pformat(self.META))

    def get_host(self):
        """Returns the HTTP host using the environment or request headers."""
        # We try three options, in order of decreasing preference.
        if settings.USE_X_FORWARDED_HOST and (
            'HTTP_X_FORWARDED_HOST' in self.META):
            host = self.META['HTTP_X_FORWARDED_HOST']
        elif 'HTTP_HOST' in self.META:
            host = self.META['HTTP_HOST']
        else:
            # Reconstruct the host using the algorithm from PEP 333.
            host = self.META['SERVER_NAME']
            server_port = str(self.META['SERVER_PORT'])
            if server_port != (self.is_secure() and '443' or '80'):
                host = '%s:%s' % (host, server_port)
        return host

    def get_full_path(self):
        # RFC 3986 requires query string arguments to be in the ASCII range.
        # Rather than crash if this doesn't happen, we encode defensively.
        return '%s%s' % (self.path, self.META.get('QUERY_STRING', '') and ('?' + iri_to_uri(self.META.get('QUERY_STRING', ''))) or '')

    def build_absolute_uri(self, location=None):
        """
        Builds an absolute URI from the location and the variables available in
        this request. If no location is specified, the absolute URI is built on
        ``request.get_full_path()``.
        """
        if not location:
            location = self.get_full_path()
        if not absolute_http_url_re.match(location):
            current_uri = '%s://%s%s' % (self.is_secure() and 'https' or 'http',
                                         self.get_host(), self.path)
            location = urljoin(current_uri, location)
        return iri_to_uri(location)

    def is_secure(self):
        return os.environ.get("HTTPS") == "on"

    def is_ajax(self):
        return self.META.get('HTTP_X_REQUESTED_WITH') == 'XMLHttpRequest'

    def _set_encoding(self, val):
        """
        Sets the encoding used for GET/POST accesses. If the GET or POST
        dictionary has already been created, it is removed and recreated on the
        next access (so that it is decoded correctly).
        """
        self._encoding = val
        if hasattr(self, '_get'):
            del self._get
        if hasattr(self, '_post'):
            del self._post

    def _get_encoding(self):
        return self._encoding

    encoding = property(_get_encoding, _set_encoding)

    def _initialize_handlers(self):
        self._upload_handlers = [uploadhandler.load_handler(handler, self)
                                 for handler in settings.FILE_UPLOAD_HANDLERS]

    def _set_upload_handlers(self, upload_handlers):
        if hasattr(self, '_files'):
            raise AttributeError("You cannot set the upload handlers after the upload has been processed.")
        self._upload_handlers = upload_handlers

    def _get_upload_handlers(self):
        if not self._upload_handlers:
            # If thre are no upload handlers defined, initialize them from settings.
            self._initialize_handlers()
        return self._upload_handlers

    upload_handlers = property(_get_upload_handlers, _set_upload_handlers)

    def parse_file_upload(self, META, post_data):
        """Returns a tuple of (POST QueryDict, FILES MultiValueDict)."""
        self.upload_handlers = ImmutableList(
            self.upload_handlers,
            warning = "You cannot alter upload handlers after the upload has been processed."
        )
        parser = MultiPartParser(META, post_data, self.upload_handlers, self.encoding)
        return parser.parse()

    def _get_raw_post_data(self):
        if not hasattr(self, '_raw_post_data'):
            if self._read_started:
                raise Exception("You cannot access raw_post_data after reading from request's data stream")
            try:
                content_length = int(self.META.get('CONTENT_LENGTH', 0))
            except (ValueError, TypeError):
                # If CONTENT_LENGTH was empty string or not an integer, don't
                # error out. We've also seen None passed in here (against all
                # specs, but see ticket #8259), so we handle TypeError as well.
                content_length = 0
            if content_length:
                self._raw_post_data = self.read(content_length)
            else:
                self._raw_post_data = self.read()
            self._stream = StringIO(self._raw_post_data) # HACHI: used to be self._stream -- uh oh, 0-copy fuckup.
            #self._streamed = _stream.getvalue()
        return self._raw_post_data
    raw_post_data = property(_get_raw_post_data)

    def _mark_post_parse_error(self):
        self._post = QueryDict('')
        self._files = MultiValueDict()
        self._post_parse_error = True

    def _load_post_and_files(self):
        # Populates self._post and self._files
        if self.method != 'POST':
            self._post, self._files = QueryDict('', encoding=self._encoding), MultiValueDict()
            return
        if self._read_started and not hasattr(self, '_raw_post_data'):
            self._mark_post_parse_error()
            return

        if self.META.get('CONTENT_TYPE', '').startswith('multipart'):
            if hasattr(self, '_raw_post_data'):
                # Use already read data
                data = StringIO(self._raw_post_data)
            else:
                data = self
            try:
                self._post, self._files = self.parse_file_upload(self.META, data)
            except:
                # An error occured while parsing POST data.  Since when
                # formatting the error the request handler might access
                # self.POST, set self._post and self._file to prevent
                # attempts to parse POST data again.
                # Mark that an error occured.  This allows self.__repr__ to
                # be explicit about it instead of simply representing an
                # empty POST
                self._mark_post_parse_error()
                raise
        else:
            self._post, self._files = QueryDict(self.raw_post_data, encoding=self._encoding), MultiValueDict()

    ## File-like and iterator interface.
    ##
    ## Expects self._stream to be set to an appropriate source of bytes by
    ## a corresponding request subclass (WSGIRequest or ModPythonRequest).
    ## Also when request data has already been read by request.POST or
    ## request.raw_post_data, self._stream points to a StringIO instance
    ## containing that data.

    def read(self, size=0):
        self._read_started = True
        return self._stream.read(size)

    def readline(self, *args, **kwargs):
        self._read_started = True
        return self._stream.readline(*args, **kwargs)

    def xreadlines(self):
        while True:
            buf = self.readline()
            if not buf:
                break
            yield buf
    __iter__ = xreadlines

    def readlines(self):
        return list(iter(self))

def get_changeset(request):
    """
    Right now, this just makes a dict of all the attributes that we allow to be modified.
    """
    d = {}
    for attr, val in request.__dict__.items():
        if callable(val):
            continue
        if attr in ['PUT', 'GET', 'REQUEST', 'META', 'path', 'path_info', 'script_name',
                    'method', '_request', '_post', '_files']:
            continue
        d[attr] = val
    return d

class RequestDelta(object):
    def __init__(self, wrapped):
        self._wrapped = wrapped
        self.changeset = {}
    def __getattr__(self, name):
        # if an attribute is fetched, we should add it to the changset :(
        if name in self.changeset:
            return self.changeset[name]
        if not hasattr(self._wrapped, name):
            raise AttributeError("Barfing %s on %s" % (name, type(self._wrapped) ))
        val = getattr(self._wrapped, name)
        if name in ['PUT', 'GET', 'REQUEST', 'META']: # these are immutable now, so deal with it punks
            return val
        if callable(val):
            return val
        if type(val) not in typeset:
            self.changeset[name] = val
        return val

    def __setattr__(self, name, val):
        if name == '_wrapped' or name == 'changeset':
            self.__dict__[name] = val
        else:
            self.changeset[name] = val

    def __getstate__(self):
        return self.changeset

    def __setstate__(self, state):
        if '_wrapped' not in self.__dict__:
            self._wrapped = None
        self.changeset = state

class QueryDict(MultiValueDict):
    """
    A specialized MultiValueDict that takes a query string when initialized.
    This is immutable unless you create a copy of it.

    Values retrieved from this class are converted from the given encoding
    (DEFAULT_CHARSET by default) to unicode.
    """
    # These are both reset in __init__, but is specified here at the class
    # level so that unpickling will have valid values
    _mutable = True
    _encoding = None

    def __init__(self, query_string, mutable=False, encoding=None):
        MultiValueDict.__init__(self)
        if not encoding:
            # *Important*: do not import settings any earlier because of note
            # in core.handlers.modpython.
            from django.conf import settings
            encoding = settings.DEFAULT_CHARSET
        self.encoding = encoding
        for key, value in parse_qsl((query_string or ''), True): # keep_blank_values=True
            self.appendlist(force_unicode(key, encoding, errors='replace'),
                            force_unicode(value, encoding, errors='replace'))
        self._mutable = mutable

    def _get_encoding(self):
        if self._encoding is None:
            # *Important*: do not import settings at the module level because
            # of the note in core.handlers.modpython.
            from django.conf import settings
            self._encoding = settings.DEFAULT_CHARSET
        return self._encoding

    def _set_encoding(self, value):
        self._encoding = value

    encoding = property(_get_encoding, _set_encoding)

    def _assert_mutable(self):
        if not self._mutable:
            raise AttributeError("This QueryDict instance is immutable")

    def __setitem__(self, key, value):
        self._assert_mutable()
        key = str_to_unicode(key, self.encoding)
        value = str_to_unicode(value, self.encoding)
        MultiValueDict.__setitem__(self, key, value)

    def __delitem__(self, key):
        self._assert_mutable()
        super(QueryDict, self).__delitem__(key)

    def __copy__(self):
        result = self.__class__('', mutable=True, encoding=self.encoding)
        for key, value in dict.items(self):
            dict.__setitem__(result, key, value)
        return result

    def __deepcopy__(self, memo):
        import django.utils.copycompat as copy
        result = self.__class__('', mutable=True, encoding=self.encoding)
        memo[id(self)] = result
        for key, value in dict.items(self):
            dict.__setitem__(result, copy.deepcopy(key, memo), copy.deepcopy(value, memo))
        return result

    def setlist(self, key, list_):
        self._assert_mutable()
        key = str_to_unicode(key, self.encoding)
        list_ = [str_to_unicode(elt, self.encoding) for elt in list_]
        MultiValueDict.setlist(self, key, list_)

    def setlistdefault(self, key, default_list=()):
        self._assert_mutable()
        if key not in self:
            self.setlist(key, default_list)
        return MultiValueDict.getlist(self, key)

    def appendlist(self, key, value):
        self._assert_mutable()
        key = str_to_unicode(key, self.encoding)
        value = str_to_unicode(value, self.encoding)
        MultiValueDict.appendlist(self, key, value)

    def update(self, other_dict):
        self._assert_mutable()
        f = lambda s: str_to_unicode(s, self.encoding)
        if hasattr(other_dict, 'lists'):
            for key, valuelist in other_dict.lists():
                for value in valuelist:
                    MultiValueDict.update(self, {f(key): f(value)})
        else:
            d = dict([(f(k), f(v)) for k, v in other_dict.items()])
            MultiValueDict.update(self, d)

    def pop(self, key, *args):
        self._assert_mutable()
        return MultiValueDict.pop(self, key, *args)

    def popitem(self):
        self._assert_mutable()
        return MultiValueDict.popitem(self)

    def clear(self):
        self._assert_mutable()
        MultiValueDict.clear(self)

    def setdefault(self, key, default=None):
        self._assert_mutable()
        key = str_to_unicode(key, self.encoding)
        default = str_to_unicode(default, self.encoding)
        return MultiValueDict.setdefault(self, key, default)

    def copy(self):
        """Returns a mutable copy of this object."""
        return self.__deepcopy__({})

    def urlencode(self, safe=None):
        """
        Returns an encoded string of all query string arguments.

        :arg safe: Used to specify characters which do not require quoting, for
            example::

                >>> q = QueryDict('', mutable=True)
                >>> q['next'] = '/a&b/'
                >>> q.urlencode()
                'next=%2Fa%26b%2F'
                >>> q.urlencode(safe='/')
                'next=/a%26b/'

        """
        output = []
        if safe:
            encode = lambda k, v: '%s=%s' % ((quote(k, safe), quote(v, safe)))
        else:
            encode = lambda k, v: urlencode({k: v})
        for k, list_ in self.lists():
            k = smart_str(k, self.encoding)
            output.extend([encode(k, smart_str(v, self.encoding))
                           for v in list_])
        return '&'.join(output)

def parse_cookie(cookie):
    if cookie == '':
        return {}
    if not isinstance(cookie, Cookie.BaseCookie):
        try:
            c = SimpleCookie()
            c.load(cookie, ignore_parse_errors=True)
        except Cookie.CookieError:
            # Invalid cookie
            return {}
    else:
        c = cookie
    cookiedict = {}
    for key in c.keys():
        cookiedict[key] = c.get(key).value
    return cookiedict

class BadHeaderError(ValueError):
    pass

class HttpResponse(object):
    """A basic HTTP response, with content and dictionary-accessed headers."""

    status_code = 200

    def __init__(self, content='', mimetype=None, status=None,
            content_type=None):
        # _headers is a mapping of the lower-case name to the original case of
        # the header (required for working with legacy systems) and the header
        # value.  Both the name of the header and its value are ASCII strings.
        self._headers = {}
        self._charset = settings.DEFAULT_CHARSET
        if mimetype:
            content_type = mimetype     # For backwards compatibility
        if not content_type:
            content_type = "%s; charset=%s" % (settings.DEFAULT_CONTENT_TYPE,
                    self._charset)
        if not isinstance(content, basestring) and hasattr(content, '__iter__'):
            self._container = content
            self._is_string = False
        else:
            self._container = [content]
            self._is_string = True
        self.cookies = SimpleCookie()
        if status:
            self.status_code = status

        self['Content-Type'] = content_type

    def __str__(self):
        """Full HTTP message, including headers."""
        return '\n'.join(['%s: %s' % (key, value)
            for key, value in self._headers.values()]) \
            + '\n\n' + self.content

    def _convert_to_ascii(self, *values):
        """Converts all values to ascii strings."""
        for value in values:
            if isinstance(value, unicode):
                try:
                    value = value.encode('us-ascii')
                except UnicodeError, e:
                    e.reason += ', HTTP response headers must be in US-ASCII format'
                    raise
            else:
                value = str(value)
            if '\n' in value or '\r' in value:
                raise BadHeaderError("Header values can't contain newlines (got %r)" % (value))
            yield value

    def __setitem__(self, header, value):
        header, value = self._convert_to_ascii(header, value)
        self._headers[header.lower()] = (header, value)

    def __delitem__(self, header):
        try:
            del self._headers[header.lower()]
        except KeyError:
            pass

    def __getitem__(self, header):
        return self._headers[header.lower()][1]

    def has_header(self, header):
        """Case-insensitive check for a header."""
        return self._headers.has_key(header.lower())

    __contains__ = has_header

    def items(self):
        return self._headers.values()

    def get(self, header, alternate):
        return self._headers.get(header.lower(), (None, alternate))[1]

    def set_cookie(self, key, value='', max_age=None, expires=None, path='/',
                   domain=None, secure=False, httponly=False):
        """
        Sets a cookie.

        ``expires`` can be a string in the correct format or a
        ``datetime.datetime`` object in UTC. If ``expires`` is a datetime
        object then ``max_age`` will be calculated.
        """
        self.cookies[key] = value
        if expires is not None:
            if isinstance(expires, datetime.datetime):
                delta = expires - expires.utcnow()
                # Add one second so the date matches exactly (a fraction of
                # time gets lost between converting to a timedelta and
                # then the date string).
                delta = delta + datetime.timedelta(seconds=1)
                # Just set max_age - the max_age logic will set expires.
                expires = None
                max_age = max(0, delta.days * 86400 + delta.seconds)
            else:
                self.cookies[key]['expires'] = expires
        if max_age is not None:
            self.cookies[key]['max-age'] = max_age
            # IE requires expires, so set it if hasn't been already.
            if not expires:
                self.cookies[key]['expires'] = cookie_date(time.time() +
                                                           max_age)
        if path is not None:
            self.cookies[key]['path'] = path
        if domain is not None:
            self.cookies[key]['domain'] = domain
        if secure:
            self.cookies[key]['secure'] = True
        if httponly:
            self.cookies[key]['httponly'] = True

    def delete_cookie(self, key, path='/', domain=None):
        self.set_cookie(key, max_age=0, path=path, domain=domain,
                        expires='Thu, 01-Jan-1970 00:00:00 GMT')

    def _get_content(self):
        if self.has_header('Content-Encoding'):
            return ''.join(self._container)
        return smart_str(''.join(self._container), self._charset)

    def _set_content(self, value):
        self._container = [value]
        self._is_string = True

    content = property(_get_content, _set_content)

    def __iter__(self):
        self._iterator = iter(self._container)
        return self

    def next(self):
        chunk = self._iterator.next()
        if isinstance(chunk, unicode):
            chunk = chunk.encode(self._charset)
        return str(chunk)

    def close(self):
        if hasattr(self._container, 'close'):
            self._container.close()

    # The remaining methods partially implement the file-like object interface.
    # See http://docs.python.org/lib/bltin-file-objects.html
    def write(self, content):
        if not self._is_string:
            raise Exception("This %s instance is not writable" % self.__class__)
        self._container.append(content)

    def flush(self):
        pass

    def tell(self):
        if not self._is_string:
            raise Exception("This %s instance cannot tell its position" % self.__class__)
        return sum([len(chunk) for chunk in self._container])

class HttpResponseRedirect(HttpResponse):
    status_code = 302

    def __init__(self, redirect_to):
        super(HttpResponseRedirect, self).__init__()
        self['Location'] = iri_to_uri(redirect_to)

class HttpResponsePermanentRedirect(HttpResponse):
    status_code = 301

    def __init__(self, redirect_to):
        super(HttpResponsePermanentRedirect, self).__init__()
        self['Location'] = iri_to_uri(redirect_to)

class HttpResponseNotModified(HttpResponse):
    status_code = 304

class HttpResponseBadRequest(HttpResponse):
    status_code = 400

class HttpResponseNotFound(HttpResponse):
    status_code = 404

class HttpResponseForbidden(HttpResponse):
    status_code = 403

class HttpResponseNotAllowed(HttpResponse):
    status_code = 405

    def __init__(self, permitted_methods):
        super(HttpResponseNotAllowed, self).__init__()
        self['Allow'] = ', '.join(permitted_methods)

class HttpResponseGone(HttpResponse):
    status_code = 410

class HttpResponseServerError(HttpResponse):
    status_code = 500

# A backwards compatible alias for HttpRequest.get_host.
def get_host(request):
    return request.get_host()

# It's neither necessary nor appropriate to use
# django.utils.encoding.smart_unicode for parsing URLs and form inputs. Thus,
# this slightly more restricted function.
def str_to_unicode(s, encoding):
    """
    Converts basestring objects to unicode, using the given encoding. Illegally
    encoded input characters are replaced with Unicode "unknown" codepoint
    (\ufffd).

    Returns any non-basestring objects without change.
    """
    if isinstance(s, str):
        return unicode(s, encoding, 'replace')
    else:
        return s

