openstack/deb-python-falcon
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deb-python-falcon/falcon/response.py
John Vrbanac 3495344ff4 feat: Request and Response media-type handling (#1050) 
This is a first pass at a non-breaking change that'll allow for a customizable media handling system. This approach combines many of the suggestions brought up by the community in #145.

One the thing that is left out of this PR is handling full content negotiation (i.e. connecting the request's accept header to the response's content-type). Unfortunately, this is a harder problem to solve in a backwards compatible fashion that doesn't affect performance. However, especially as we move towards v2, I think that would be a great opportunity to revisit full negotiation. In the meantime, there are several easy workarounds for people needing this functionality.

Closes #145
2017-06-14 23:38:47 -06:00

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# Copyright 2013 by Rackspace Hosting, Inc.
#
# 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.
"""Response class."""
from six import PY2
from six import string_types as STRING_TYPES
# 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
from falcon import DEFAULT_MEDIA_TYPE
from falcon.media import Handlers
from falcon.response_helpers import (
format_header_value_list,
format_range,
header_property,
is_ascii_encodable,
)
from falcon.util import dt_to_http, TimezoneGMT
from falcon.util.uri import encode as uri_encode
from falcon.util.uri import encode_value as uri_encode_value
SimpleCookie = http_cookies.SimpleCookie
CookieError = http_cookies.CookieError
GMT_TIMEZONE = TimezoneGMT()
class Response(object):
"""Represents an HTTP response to a client request.
Note:
`Response` is not meant to be instantiated directly by responders.
Keyword Arguments:
options (dict): Set of global options passed from the API handler.
Attributes:
status (str): HTTP status line (e.g., '200 OK'). Falcon requires the
full status line, not just the code (e.g., 200). This design
makes the framework more efficient because it does not have to
do any kind of conversion or lookup when composing the WSGI
response.
If not set explicitly, the status defaults to '200 OK'.
Note:
Falcon provides a number of constants for common status
codes. They all start with the ``HTTP_`` prefix, as in:
``falcon.HTTP_204``.
body (str or unicode): String representing response content. If
Unicode, Falcon will encode as UTF-8 in the response. If
data is already a byte string, use the data attribute
instead (it's faster).
data (bytes): Byte string representing response content.
Use this attribute in lieu of `body` when your content is
already a byte string (``str`` or ``bytes`` in Python 2, or
simply ``bytes`` in Python 3). See also the note below.
Note:
Under Python 2.x, if your content is of type ``str``, using
the `data` attribute instead of `body` is the most
efficient approach. However, if
your text is of type ``unicode``, you will need to use the
`body` attribute instead.
Under Python 3.x, on the other hand, the 2.x ``str`` type can
be thought of as
having been replaced by what was once the ``unicode`` type,
and so you will need to always use the `body` attribute for
strings to
ensure Unicode characters are properly encoded in the
HTTP response.
media (object): A serializable object supported by the media handlers
configured via :class:`falcon.RequestOptions`.
See :ref:`media` for more information regarding media handling.
stream: Either a file-like object with a `read()` method that takes
an optional size argument and returns a block of bytes, or an
iterable object, representing response content, and yielding
blocks as byte strings. Falcon will use *wsgi.file_wrapper*, if
provided by the WSGI server, in order to efficiently serve
file-like objects.
stream_len (int): Expected length of `stream`. If `stream` is set,
but `stream_len` is not, Falcon will not supply a
Content-Length header to the WSGI server. Consequently, the
server may choose to use chunked encoding or one of the
other strategies suggested by PEP-3333.
context (dict): Dictionary to hold any data about the response which is
specific to your app. 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.Response``, and then passing that new class to
`falcon.API()` by way of the latter's `response_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 Response instance. Therefore the first argument is
the Response instance itself (self).
options (dict): Set of global options passed from the API handler.
"""
__slots__ = (
'body',
'data',
'_headers',
'_cookies',
'status',
'stream',
'stream_len',
'context',
'options',
'__dict__',
)
# Child classes may override this
context_type = None
def __init__(self, options=None):
self.status = '200 OK'
self._headers = {}
self.options = ResponseOptions() if options is None else options
# NOTE(tbug): will be set to a SimpleCookie object
# when cookie is set via set_cookie
self._cookies = None
self._media = None
self.body = None
self.data = None
self.stream = None
self.stream_len = None
if self.context_type is None:
# PERF(kgriffs): The literal syntax is more efficient than dict().
self.context = {}
else:
self.context = self.context_type()
@property
def media(self):
return self._media
@media.setter
def media(self, obj):
self._media = obj
if not self.content_type:
self.content_type = self.options.default_media_type
handler = self.options.media_handlers.find_by_media_type(
self.content_type,
self.options.default_media_type
)
self.data = handler.serialize(self._media)
def __repr__(self):
return '<%s: %s>' % (self.__class__.__name__, self.status)
def set_stream(self, stream, stream_len):
"""Convenience method for setting both `stream` and `stream_len`.
Although the `stream` and `stream_len` properties may be set
directly, using this method ensures `stream_len` is not
accidentally neglected when the length of the stream is known in
advance.
Note:
If the stream length is unknown, you can set `stream`
directly, and ignore `stream_len`. In this case, the
WSGI server may choose to use chunked encoding or one
of the other strategies suggested by PEP-3333.
"""
self.stream = stream
self.stream_len = stream_len
def set_cookie(self, name, value, expires=None, max_age=None,
domain=None, path=None, secure=None, http_only=True):
"""Set a response cookie.
Note:
This method can be called multiple times to add one or
more cookies to the response.
See Also:
To learn more about setting cookies, see
:ref:`Setting Cookies <setting-cookies>`. The parameters
listed below correspond to those defined in `RFC 6265`_.
Args:
name (str): Cookie name
value (str): Cookie value
Keyword Args:
expires (datetime): Specifies when the cookie should expire.
By default, cookies expire when the user agent exits.
(See also: RFC 6265, Section 4.1.2.1)
max_age (int): Defines the lifetime of the cookie in
seconds. By default, cookies expire when the user agent
exits. If both `max_age` and `expires` are set, the
latter is ignored by the user agent.
Note:
Coercion to ``int`` is attempted if provided with
``float`` or ``str``.
(See also: RFC 6265, Section 4.1.2.2)
domain (str): Restricts the cookie to a specific domain and
any subdomains of that domain. By default, the user
agent will return the cookie only to the origin server.
When overriding this default behavior, the specified
domain must include the origin server. Otherwise, the
user agent will reject the cookie.
(See also: RFC 6265, Section 4.1.2.3)
path (str): Scopes the cookie to the given path plus any
subdirectories under that path (the "/" character is
interpreted as a directory separator). If the cookie
does not specify a path, the user agent defaults to the
path component of the requested URI.
Warning:
User agent interfaces do not always isolate
cookies by path, and so this should not be
considered an effective security measure.
(See also: RFC 6265, Section 4.1.2.4)
secure (bool): Direct the client to only return the cookie
in subsequent requests if they are made over HTTPS
(default: ``True``). This prevents attackers from
reading sensitive cookie data.
Note:
The default value for this argument is normally
``True``, but can be modified by setting
:py:attr:`~.ResponseOptions.secure_cookies_by_default`
via :any:`API.resp_options`.
Warning:
For the `secure` cookie attribute to be effective,
your application will need to enforce HTTPS.
(See also: RFC 6265, Section 4.1.2.5)
http_only (bool): Direct the client to only transfer the
cookie with unscripted HTTP requests
(default: ``True``). This is intended to mitigate some
forms of cross-site scripting.
(See also: RFC 6265, Section 4.1.2.6)
Raises:
KeyError: `name` is not a valid cookie name.
ValueError: `value` is not a valid cookie value.
.. _RFC 6265:
http://tools.ietf.org/html/rfc6265
"""
if not is_ascii_encodable(name):
raise KeyError('"name" is not ascii encodable')
if not is_ascii_encodable(value):
raise ValueError('"value" is not ascii encodable')
if PY2:
name = str(name)
value = str(value)
if self._cookies is None:
self._cookies = SimpleCookie()
try:
self._cookies[name] = value
except CookieError as e: # pragma: no cover
# NOTE(tbug): we raise a KeyError here, to avoid leaking
# the CookieError to the user. SimpleCookie (well, BaseCookie)
# only throws CookieError on issues with the cookie key
raise KeyError(str(e))
if expires:
# set Expires on cookie. Format is Wdy, DD Mon YYYY HH:MM:SS GMT
# NOTE(tbug): we never actually need to
# know that GMT is named GMT when formatting cookies.
# It is a function call less to just write "GMT" in the fmt string:
fmt = '%a, %d %b %Y %H:%M:%S GMT'
if expires.tzinfo is None:
# naive
self._cookies[name]['expires'] = expires.strftime(fmt)
else:
# aware
gmt_expires = expires.astimezone(GMT_TIMEZONE)
self._cookies[name]['expires'] = gmt_expires.strftime(fmt)
if max_age:
# RFC 6265 section 5.2.2 says about the max-age value:
# "If the remainder of attribute-value contains a non-DIGIT
# character, ignore the cookie-av."
# That is, RFC-compliant response parsers will ignore the max-age
# attribute if the value contains a dot, as in floating point
# numbers. Therefore, attempt to convert the value to an integer.
self._cookies[name]['max-age'] = int(max_age)
if domain:
self._cookies[name]['domain'] = domain
if path:
self._cookies[name]['path'] = path
if secure is None:
is_secure = self.options.secure_cookies_by_default
else:
is_secure = secure
if is_secure:
self._cookies[name]['secure'] = True
if http_only:
self._cookies[name]['httponly'] = http_only
def unset_cookie(self, name):
"""Unset a cookie in the response
Clears the contents of the cookie, and instructs the user
agent to immediately expire its own copy of the cookie.
Warning:
In order to successfully remove a cookie, both the
path and the domain must match the values that were
used when the cookie was created.
"""
if self._cookies is None:
self._cookies = SimpleCookie()
self._cookies[name] = ''
# NOTE(Freezerburn): SimpleCookie apparently special cases the
# expires attribute to automatically use strftime and set the
# time as a delta from the current time. We use -1 here to
# basically tell the browser to immediately expire the cookie,
# thus removing it from future request objects.
self._cookies[name]['expires'] = -1
def get_header(self, name):
"""Retrieve the raw string value for the given header.
Args:
name (str): Header name, case-insensitive. Must be of type ``str``
or ``StringType``, and only character values 0x00 through 0xFF
may be used on platforms that use wide characters.
Returns:
str: The header's value if set, otherwise ``None``.
"""
return self._headers.get(name.lower(), None)
def set_header(self, name, value):
"""Set a header for this response to a given value.
Warning:
Calling this method overwrites the existing value, if any.
Warning:
For setting cookies, see instead :meth:`~.set_cookie`
Args:
name (str): Header name (case-insensitive). The restrictions
noted below for the header's value also apply here.
value (str): Value for the header. Must be of type ``str`` or
``StringType`` and contain only US-ASCII characters.
Under Python 2.x, the ``unicode`` type is also accepted,
although such strings are also limited to US-ASCII.
"""
if PY2:
# NOTE(kgriffs): uwsgi fails with a TypeError if any header
# is not a str, so do the conversion here. It's actually
# faster to not do an isinstance check. str() will encode
# to US-ASCII.
name = str(name)
value = str(value)
# NOTE(kgriffs): normalize name by lowercasing it
self._headers[name.lower()] = value
def delete_header(self, name):
"""Delete a header for this response.
If the header was not previously set, do nothing.
Args:
name (str): Header name (case-insensitive). Must be of type
``str`` or ``StringType`` and contain only US-ASCII characters.
Under Python 2.x, the ``unicode`` type is also accepted,
although such strings are also limited to US-ASCII.
"""
# NOTE(kgriffs): normalize name by lowercasing it
self._headers.pop(name.lower(), None)
def append_header(self, name, value):
"""Set or append a header for this response.
Warning:
If the header already exists, the new value will be appended
to it, delimited by a comma. Most header specifications support
this format, Set-Cookie being the notable exceptions.
Warning:
For setting cookies, see :py:meth:`~.set_cookie`
Args:
name (str): Header name (case-insensitive). The restrictions
noted below for the header's value also apply here.
value (str): Value for the header. Must be of type ``str`` or
``StringType`` and contain only US-ASCII characters.
Under Python 2.x, the ``unicode`` type is also accepted,
although such strings are also limited to US-ASCII.
"""
if PY2:
# NOTE(kgriffs): uwsgi fails with a TypeError if any header
# is not a str, so do the conversion here. It's actually
# faster to not do an isinstance check. str() will encode
# to US-ASCII.
name = str(name)
value = str(value)
name = name.lower()
if name in self._headers:
value = self._headers[name] + ',' + value
self._headers[name] = value
def set_headers(self, headers):
"""Set several headers at once.
Warning:
Calling this method overwrites existing values, if any.
Args:
headers (dict or list): A dictionary of header names and values
to set, or a ``list`` of (*name*, *value*) tuples. Both *name*
and *value* must be of type ``str`` or ``StringType`` and
contain only US-ASCII characters. Under Python 2.x, the
``unicode`` type is also accepted, although such strings are
also limited to US-ASCII.
Note:
Falcon can process a list of tuples slightly faster
than a dict.
Raises:
ValueError: `headers` was not a ``dict`` or ``list`` of ``tuple``.
"""
if isinstance(headers, dict):
headers = headers.items()
# NOTE(kgriffs): We can't use dict.update because we have to
# normalize the header names.
_headers = self._headers
if PY2:
for name, value in headers:
# NOTE(kgriffs): uwsgi fails with a TypeError if any header
# is not a str, so do the conversion here. It's actually
# faster to not do an isinstance check. str() will encode
# to US-ASCII.
name = str(name)
value = str(value)
_headers[name.lower()] = value
else:
for name, value in headers:
_headers[name.lower()] = value
def add_link(self, target, rel, title=None, title_star=None,
anchor=None, hreflang=None, type_hint=None):
"""Add a link header to the response.
See also: https://tools.ietf.org/html/rfc5988
Note:
Calling this method repeatedly will cause each link to be
appended to the Link header value, separated by commas.
Note:
So-called "link-extension" elements, as defined by RFC 5988,
are not yet supported. See also Issue #288.
Args:
target (str): Target IRI for the resource identified by the
link. Will be converted to a URI, if necessary, per
RFC 3987, Section 3.1.
rel (str): Relation type of the link, such as "next" or
"bookmark". See also http://goo.gl/618GHr for a list
of registered link relation types.
Keyword Args:
title (str): Human-readable label for the destination of
the link (default ``None``). If the title includes non-ASCII
characters, you will need to use `title_star` instead, or
provide both a US-ASCII version using `title` and a
Unicode version using `title_star`.
title_star (tuple of str): Localized title describing the
destination of the link (default ``None``). The value must be a
two-member tuple in the form of (*language-tag*, *text*),
where *language-tag* is a standard language identifier as
defined in RFC 5646, Section 2.1, and *text* is a Unicode
string.
Note:
*language-tag* may be an empty string, in which case the
client will assume the language from the general context
of the current request.
Note:
*text* will always be encoded as UTF-8. If the string
contains non-ASCII characters, it should be passed as
a ``unicode`` type string (requires the 'u' prefix in
Python 2).
anchor (str): Override the context IRI with a different URI
(default None). By default, the context IRI for the link is
simply the IRI of the requested resource. The value
provided may be a relative URI.
hreflang (str or iterable): Either a single *language-tag*, or
a ``list`` or ``tuple`` of such tags to provide a hint to the
client as to the language of the result of following the link.
A list of tags may be given in order to indicate to the
client that the target resource is available in multiple
languages.
type_hint(str): Provides a hint as to the media type of the
result of dereferencing the link (default ``None``). As noted
in RFC 5988, this is only a hint and does not override the
Content-Type header returned when the link is followed.
"""
# PERF(kgriffs): Heuristic to detect possiblity of an extension
# relation type, in which case it will be a URL that may contain
# reserved characters. Otherwise, don't waste time running the
# string through uri.encode
#
# Example values for rel:
#
# "next"
# "http://example.com/ext-type"
# "https://example.com/ext-type"
# "alternate http://example.com/ext-type"
# "http://example.com/ext-type alternate"
#
if '//' in rel:
if ' ' in rel:
rel = ('"' +
' '.join([uri_encode(r) for r in rel.split()]) +
'"')
else:
rel = '"' + uri_encode(rel) + '"'
value = '<' + uri_encode(target) + '>; rel=' + rel
if title is not None:
value += '; title="' + title + '"'
if title_star is not None:
value += ("; title*=UTF-8'" + title_star[0] + "'" +
uri_encode_value(title_star[1]))
if type_hint is not None:
value += '; type="' + type_hint + '"'
if hreflang is not None:
if isinstance(hreflang, STRING_TYPES):
value += '; hreflang=' + hreflang
else:
value += '; '
value += '; '.join(['hreflang=' + lang for lang in hreflang])
if anchor is not None:
value += '; anchor="' + uri_encode(anchor) + '"'
if PY2:
# NOTE(kgriffs): uwsgi fails with a TypeError if any header
# is not a str, so do the conversion here. It's actually
# faster to not do an isinstance check. str() will encode
# to US-ASCII.
value = str(value)
_headers = self._headers
if 'link' in _headers:
_headers['link'] += ', ' + value
else:
_headers['link'] = value
cache_control = header_property(
'Cache-Control',
"""Set the Cache-Control header.
Used to set a list of cache directives to use as the value of the
Cache-Control header. The list will be joined with ", " to produce
the value for the header.
""",
format_header_value_list)
content_location = header_property(
'Content-Location',
"""Set the Content-Location header.
This value will be URI encoded per RFC 3986. If the value that is
being set is already URI encoded it should be decoded first or the
header should be set manually using the set_header method.
""",
uri_encode)
content_range = header_property(
'Content-Range',
"""A tuple to use in constructing a value for the Content-Range header.
The tuple has the form (*start*, *end*, *length*, [*unit*]), where *start* and
*end* designate the range (inclusive), and *length* is the
total length, or '\*' if unknown. You may pass ``int``'s for
these numbers (no need to convert to ``str`` beforehand). The optional value
*unit* describes the range unit and defaults to 'bytes'
Note:
You only need to use the alternate form, 'bytes \*/1234', for
responses that use the status '416 Range Not Satisfiable'. In this
case, raising ``falcon.HTTPRangeNotSatisfiable`` will do the right
thing.
See also: http://goo.gl/Iglhp
""",
format_range)
content_type = header_property(
'Content-Type',
"""Sets the Content-Type header.
Note:
You can use the following predefined content types: ``falcon.MEDIA_JSON``,
``falcon.MEDIA_HTML``, ``falcon.MEDIA_JS``, ``falcon.MEDIA_XML``,
``falcon.MEDIA_TEXT``, ``falcon.MEDIA_JPEG``, ``falcon.MEDIA_PNG``,
``falcon.MEDIA_YAML`` and ``MEDIA_MSGPACK``
""")
etag = header_property(
'ETag',
'Set the ETag header.')
last_modified = header_property(
'Last-Modified',
"""Set the Last-Modified header. Set to a ``datetime`` (UTC) instance.
Note:
Falcon will format the ``datetime`` as an HTTP date string.
""",
dt_to_http)
location = header_property(
'Location',
"""Set the Location header.
This value will be URI encoded per RFC 3986. If the value that is
being set is already URI encoded it should be decoded first or the
header should be set manually using the set_header method.
""",
uri_encode)
retry_after = header_property(
'Retry-After',
"""Set the Retry-After header.
The expected value is an integral number of seconds to use as the
value for the header. The HTTP-date syntax is not supported.
""",
str)
vary = header_property(
'Vary',
"""Value to use for the Vary header.
Set this property to an iterable of header names. For a single
asterisk or field value, simply pass a single-element ``list`` or
``tuple``.
"Tells downstream proxies how to match future request headers
to decide whether the cached response can be used rather than
requesting a fresh one from the origin server."
(Wikipedia)
See also: http://goo.gl/NGHdL
""",
format_header_value_list)
accept_ranges = header_property(
'Accept-Ranges',
"""Set the Accept-Ranges header.
The Accept-Ranges header field indicates to the client which
range units are supported (e.g. "bytes") for the target
resource.
If range requests are not supported for the target resource,
the header may be set to "none" to advise the client not to
attempt any such requests.
Note:
"none" is the literal string, not Python's built-in ``None``
type.
""")
def _set_media_type(self, media_type=None):
"""Wrapper around set_header to set a content-type.
Args:
media_type: Media type to use for the Content-Type
header.
"""
# PERF(kgriffs): Using "in" like this is faster than using
# dict.setdefault (tested on py27).
set_content_type = (media_type is not None and
'content-type' not in self._headers)
if set_content_type:
self.set_header('content-type', media_type)
def _wsgi_headers(self, media_type=None, py2=PY2):
"""Convert headers into the format expected by WSGI servers.
Args:
media_type: Default media type to use for the Content-Type
header if the header was not set explicitly (default ``None``).
"""
headers = self._headers
self._set_media_type(media_type)
if py2:
# PERF(kgriffs): Don't create an extra list object if
# it isn't needed.
items = headers.items()
else:
items = list(headers.items())
if self._cookies is not None:
# PERF(tbug):
# The below implementation is ~23% faster than
# the alternative:
#
# self._cookies.output().split("\\r\\n")
#
# Even without the .split("\\r\\n"), the below
# is still ~17% faster, so don't use .output()
items += [('set-cookie', c.OutputString())
for c in self._cookies.values()]
return items
class ResponseOptions(object):
"""Defines a set of configurable response options.
An instance of this class is exposed via :any:`API.resp_options` for
configuring certain :py:class:`~.Response` behaviors.
Attributes:
secure_cookies_by_default (bool): Set to ``False`` in development
environments to make the `secure` attribute for all cookies
default to ``False``. This can make testing easier by
not requiring HTTPS. Note, however, that this setting can
be overridden via `set_cookie()`'s `secure` kwarg.
default_media_type (str): The default media-type to use when
deserializing a response. This value is normally set to the media
type provided when a :class:`falcon.API` is initialized; however,
if created independently, this will default to the
``DEFAULT_MEDIA_TYPE`` specified by Falcon.
media_handlers (Handlers): A dict-like object that allows you to
configure the media-types that you would like to handle.
By default, a handler is provided for the ``application/json``
media type.
"""
__slots__ = (
'secure_cookies_by_default',
'default_media_type',
'media_handlers',
)
def __init__(self):
self.secure_cookies_by_default = True
self.default_media_type = DEFAULT_MEDIA_TYPE
self.media_handlers = Handlers()
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