Django 中的 request

1. Django 中的 request 不需要 import，直接就可以使用，并且经常看到一些调用，在 vscode 中点击它又看不到源码，比如：

def login_view(request):

    if request.method != 'POST':
        form = LoginForm()

上面的代码完全没有 import request 之类的，应该是 Django 内置的，于是下载了 Django 的源码，在 django\http\request.py看到了它的源码，它其实就是一个类 HttpRequest，下面沾有它的代码：
它的成员变量(上面的 method 就是其中一个)：

    def __init__(self):
        # WARNING: The `WSGIRequest` subclass doesn't call `super`.
        # Any variable assignment made here should also happen in
        # `WSGIRequest.__init__()`.

        self.GET = QueryDict(mutable=True)
        self.POST = QueryDict(mutable=True)
        self.COOKIES = {}
        self.META = {}
        self.FILES = MultiValueDict()

        self.path = ""
        self.path_info = ""
        self.method = None
        self.resolver_match = None
        self.content_type = None
        self.content_params = None

所以下面这些调用都是合法的，基本都是 http 的一些属性信息

        request.GET
        request.POST
        request.COOKIES
        request.META
        request.FILES

        request.path
        request.path_info
        request.method
        request.resolver_match
        request.content_type
        request.content_params

2. 完整的源码：

class HttpRequest:
    """A basic HTTP request."""

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

    def __init__(self):
        # WARNING: The `WSGIRequest` subclass doesn't call `super`.
        # Any variable assignment made here should also happen in
        # `WSGIRequest.__init__()`.

        self.GET = QueryDict(mutable=True)
        self.POST = QueryDict(mutable=True)
        self.COOKIES = {}
        self.META = {}
        self.FILES = MultiValueDict()

        self.path = ""
        self.path_info = ""
        self.method = None
        self.resolver_match = None
        self.content_type = None
        self.content_params = None

    def __repr__(self):
        if self.method is None or not self.get_full_path():
            return "<%s>" % self.__class__.__name__
        return "<%s: %s %r>" % (
            self.__class__.__name__,
            self.method,
            self.get_full_path(),
        )

    @cached_property
    def headers(self):
        return HttpHeaders(self.META)

    @cached_property
    def accepted_types(self):
        """Return a list of MediaType instances."""
        return parse_accept_header(self.headers.get("Accept", "*/*"))

    def accepts(self, media_type):
        return any(
            accepted_type.match(media_type) for accepted_type in self.accepted_types
        )

    def _set_content_type_params(self, meta):
        """Set content_type, content_params, and encoding."""
        self.content_type, self.content_params = parse_header_parameters(
            meta.get("CONTENT_TYPE", "")
        )
        if "charset" in self.content_params:
            try:
                codecs.lookup(self.content_params["charset"])
            except LookupError:
                pass
            else:
                self.encoding = self.content_params["charset"]

    def _get_raw_host(self):
        """
        Return the HTTP host using the environment or request headers. Skip
        allowed hosts protection, so may return an insecure host.
        """
        # 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 = self.get_port()
            if server_port != ("443" if self.is_secure() else "80"):
                host = "%s:%s" % (host, server_port)
        return host

    def get_host(self):
        """Return the HTTP host using the environment or request headers."""
        host = self._get_raw_host()

        # Allow variants of localhost if ALLOWED_HOSTS is empty and DEBUG=True.
        allowed_hosts = settings.ALLOWED_HOSTS
        if settings.DEBUG and not allowed_hosts:
            allowed_hosts = [".localhost", "127.0.0.1", "[::1]"]

        domain, port = split_domain_port(host)
        if domain and validate_host(domain, allowed_hosts):
            return host
        else:
            msg = "Invalid HTTP_HOST header: %r." % host
            if domain:
                msg += " You may need to add %r to ALLOWED_HOSTS." % domain
            else:
                msg += (
                    " The domain name provided is not valid according to RFC 1034/1035."
                )
            raise DisallowedHost(msg)

    def get_port(self):
        """Return the port number for the request as a string."""
        if settings.USE_X_FORWARDED_PORT and "HTTP_X_FORWARDED_PORT" in self.META:
            port = self.META["HTTP_X_FORWARDED_PORT"]
        else:
            port = self.META["SERVER_PORT"]
        return str(port)

    def get_full_path(self, force_append_slash=False):
        return self._get_full_path(self.path, force_append_slash)

    def get_full_path_info(self, force_append_slash=False):
        return self._get_full_path(self.path_info, force_append_slash)

    def _get_full_path(self, path, force_append_slash):
        # 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%s" % (
            escape_uri_path(path),
            "/" if force_append_slash and not path.endswith("/") else "",
            ("?" + iri_to_uri(self.META.get("QUERY_STRING", "")))
            if self.META.get("QUERY_STRING", "")
            else "",
        )

    def get_signed_cookie(self, key, default=RAISE_ERROR, salt="", max_age=None):
        """
        Attempt to return a signed cookie. If the signature fails or the
        cookie has expired, raise an exception, unless the `default` argument
        is provided,  in which case return that value.
        """
        try:
            cookie_value = self.COOKIES[key]
        except KeyError:
            if default is not RAISE_ERROR:
                return default
            else:
                raise
        try:
            value = signing.get_cookie_signer(salt=key + salt).unsign(
                cookie_value, max_age=max_age
            )
        except signing.BadSignature:
            if default is not RAISE_ERROR:
                return default
            else:
                raise
        return value

    def build_absolute_uri(self, location=None):
        """
        Build an absolute URI from the location and the variables available in
        this request. If no ``location`` is specified, build the absolute URI
        using request.get_full_path(). If the location is absolute, convert it
        to an RFC 3987 compliant URI and return it. If location is relative or
        is scheme-relative (i.e., ``//example.com/``), urljoin() it to a base
        URL constructed from the request variables.
        """
        if location is None:
            # Make it an absolute url (but schemeless and domainless) for the
            # edge case that the path starts with '//'.
            location = "//%s" % self.get_full_path()
        else:
            # Coerce lazy locations.
            location = str(location)
        bits = urlsplit(location)
        if not (bits.scheme and bits.netloc):
            # Handle the simple, most common case. If the location is absolute
            # and a scheme or host (netloc) isn't provided, skip an expensive
            # urljoin() as long as no path segments are '.' or '..'.
            if (
                bits.path.startswith("/")
                and not bits.scheme
                and not bits.netloc
                and "/./" not in bits.path
                and "/../" not in bits.path
            ):
                # If location starts with '//' but has no netloc, reuse the
                # schema and netloc from the current request. Strip the double
                # slashes and continue as if it wasn't specified.
                location = self._current_scheme_host + location.removeprefix("//")
            else:
                # Join the constructed URL with the provided location, which
                # allows the provided location to apply query strings to the
                # base path.
                location = urljoin(self._current_scheme_host + self.path, location)
        return iri_to_uri(location)

    @cached_property
    def _current_scheme_host(self):
        return "{}://{}".format(self.scheme, self.get_host())

    def _get_scheme(self):
        """
        Hook for subclasses like WSGIRequest to implement. Return 'http' by
        default.
        """
        return "http"

    @property
    def scheme(self):
        if settings.SECURE_PROXY_SSL_HEADER:
            try:
                header, secure_value = settings.SECURE_PROXY_SSL_HEADER
            except ValueError:
                raise ImproperlyConfigured(
                    "The SECURE_PROXY_SSL_HEADER setting must be a tuple containing "
                    "two values."
                )
            header_value = self.META.get(header)
            if header_value is not None:
                header_value, *_ = header_value.split(",", 1)
                return "https" if header_value.strip() == secure_value else "http"
        return self._get_scheme()

    def is_secure(self):
        return self.scheme == "https"

    @property
    def encoding(self):
        return self._encoding

    @encoding.setter
    def encoding(self, val):
        """
        Set the encoding used for GET/POST accesses. If the GET or POST
        dictionary has already been created, remove and recreate it 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 _initialize_handlers(self):
        self._upload_handlers = [
            uploadhandler.load_handler(handler, self)
            for handler in settings.FILE_UPLOAD_HANDLERS
        ]

    @property
    def upload_handlers(self):
        if not self._upload_handlers:
            # If there are no upload handlers defined, initialize them from settings.
            self._initialize_handlers()
        return self._upload_handlers

    @upload_handlers.setter
    def 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 parse_file_upload(self, META, post_data):
        """Return 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()

    @property
    def body(self):
        if not hasattr(self, "_body"):
            if self._read_started:
                raise RawPostDataException(
                    "You cannot access body after reading from request's data stream"
                )

            # Limit the maximum request data size that will be handled in-memory.
            if (
                settings.DATA_UPLOAD_MAX_MEMORY_SIZE is not None
                and int(self.META.get("CONTENT_LENGTH") or 0)
                > settings.DATA_UPLOAD_MAX_MEMORY_SIZE
            ):
                raise RequestDataTooBig(
                    "Request body exceeded settings.DATA_UPLOAD_MAX_MEMORY_SIZE."
                )

            try:
                self._body = self.read()
            except OSError as e:
                raise UnreadablePostError(*e.args) from e
            finally:
                self._stream.close()
            self._stream = BytesIO(self._body)
        return self._body

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

    def _load_post_and_files(self):
        """Populate self._post and self._files if the content-type is a form type"""
        if self.method != "POST":
            self._post, self._files = (
                QueryDict(encoding=self._encoding),
                MultiValueDict(),
            )
            return
        if self._read_started and not hasattr(self, "_body"):
            self._mark_post_parse_error()
            return

        if self.content_type == "multipart/form-data":
            if hasattr(self, "_body"):
                # Use already read data
                data = BytesIO(self._body)
            else:
                data = self
            try:
                self._post, self._files = self.parse_file_upload(self.META, data)
            except (MultiPartParserError, TooManyFilesSent):
                # An error occurred 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.
                self._mark_post_parse_error()
                raise
        elif self.content_type == "application/x-www-form-urlencoded":
            self._post, self._files = (
                QueryDict(self.body, encoding=self._encoding),
                MultiValueDict(),
            )
        else:
            self._post, self._files = (
                QueryDict(encoding=self._encoding),
                MultiValueDict(),
            )

    def close(self):
        if hasattr(self, "_files"):
            for f in chain.from_iterable(list_[1] for list_ in self._files.lists()):
                f.close()

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

    def read(self, *args, **kwargs):
        self._read_started = True
        try:
            return self._stream.read(*args, **kwargs)
        except OSError as e:
            raise UnreadablePostError(*e.args) from e

    def readline(self, *args, **kwargs):
        self._read_started = True
        try:
            return self._stream.readline(*args, **kwargs)
        except OSError as e:
            raise UnreadablePostError(*e.args) from e

    def __iter__(self):
        return iter(self.readline, b"")

    def readlines(self):
        return list(self)