def patch_cache_control(headers: MutableHeaders, **kwargs: typing.Any) -> None:
"""
Patch headers with an extended version of the initial Cache-Control header by adding
all keyword arguments to it.
"""
cache_control: typing.Dict[str, typing.Any] = {}
for field in parse_http_list(headers.get("Cache-Control", "")):
try:
key, value = field.split("=")
except ValueError:
cache_control[field] = True
else:
cache_control[key] = value
if "max-age" in cache_control and "max_age" in kwargs:
kwargs["max_age"] = min(int(cache_control["max-age"]),
kwargs["max_age"])
if "public" in kwargs:
raise NotImplementedError(
"The 'public' cache control directive isn't supported yet.")
if "private" in kwargs:
raise NotImplementedError(
"The 'private' cache control directive isn't supported yet.")
for key, value in kwargs.items():
key = key.replace("_", "-")
cache_control[key] = value
directives: typing.List[str] = []
for key, value in cache_control.items():
if value is False:
continue
if value is True:
directives.append(key)
else:
directives.append(f"{key}={value}")
patched_cache_control = ", ".join(directives)
if patched_cache_control:
headers["Cache-Control"] = patched_cache_control
else:
del headers["Cache-Control"]
async def __call__(self, scope: Scope, receive: Receive,
send: Send) -> None:
headers = MutableHeaders(scope=scope)
self.should_decode_from_msgpack_to_json = ("application/x-msgpack"
in headers.get(
"content-type", ""))
# Take an initial guess, although we eventually may not
# be able to do the conversion.
self.should_encode_from_json_to_msgpack = (
"application/x-msgpack" in headers.getlist("accept"))
self.receive = receive
self.send = send
if self.should_decode_from_msgpack_to_json:
# We're going to present JSON content to the application,
# so rewrite `Content-Type` for consistency and compliance
# with possible downstream security checks in some frameworks.
# See: https://github.com/florimondmanca/msgpack-asgi/issues/23
headers["content-type"] = "application/json"
await self.app(scope, self.receive_with_msgpack,
self.send_with_msgpack)
async def send_compressed(self, message: Message) -> None:
message_type = message["type"]
if message_type == "http.response.start":
# Don't send the initial message until we've determined how to
# modify the outgoing headers correctly.
self.initial_message = message
headers = MutableHeaders(raw=self.initial_message["headers"])
media_type = headers.get("Content-Type")
for encoding in self.compression_registry.encodings(media_type):
if encoding in self.accepted:
file_factory = self.compression_registry.dispatch(
media_type=media_type, encoding=encoding)
self.compressed_buffer = io.BytesIO()
self.compressed_file = file_factory(self.compressed_buffer)
self.encoding = encoding
break
else:
self.encoding = None
elif message_type == "http.response.body" and not self.started:
headers = MutableHeaders(raw=self.initial_message["headers"])
self.started = True
body = message.get("body", b"")
more_body = message.get("more_body", False)
if len(body) < self.minimum_size and not more_body:
# Don't apply compression to small outgoing responses.
await self.send(self.initial_message)
await self.send(message)
elif not more_body:
if self.encoding is not None:
# Standard (non-streaming) response.
t0 = time.perf_counter()
self.compressed_file.write(body)
self.compressed_file.close()
compression_time = time.perf_counter() - t0
compressed_body = self.compressed_buffer.getvalue()
# Check to see if the compression ratio is significant.
# If it isn't just send the original; the savings isn't worth the decompression time.
compression_ratio = len(body) / len(
compressed_body) # higher is better
THRESHOLD = 1 / 0.9
if compression_ratio > THRESHOLD:
headers["Content-Encoding"] = self.encoding
headers["Content-Length"] = str(len(compressed_body))
headers.add_vary_header("Accept-Encoding")
message["body"] = compressed_body
# The Server-Timing middleware, which runs after this
# CompressionMiddleware, formats these metrics alongside
# others in the Server-Timing header.
self.scope["state"]["metrics"]["compress"] = {
"dur": compression_time, # Units: seconds
"ratio": compression_ratio,
}
await self.send(self.initial_message)
await self.send(message)
else:
# Initial body in streaming response.
if self.encoding is not None:
headers = MutableHeaders(
raw=self.initial_message["headers"])
headers["Content-Encoding"] = self.encoding
headers.add_vary_header("Accept-Encoding")
del headers["Content-Length"]
self.compressed_file.write(body)
message["body"] = self.compressed_buffer.getvalue()
self.compressed_buffer.seek(0)
self.compressed_buffer.truncate()
await self.send(self.initial_message)
await self.send(message)
elif message_type == "http.response.body":
# Remaining body in streaming response.
if self.encoding is not None:
body = message.get("body", b"")
more_body = message.get("more_body", False)
self.compressed_file.write(body)
if not more_body:
self.compressed_file.close()
message["body"] = self.compressed_buffer.getvalue()
self.compressed_buffer.seek(0)
self.compressed_buffer.truncate()
await self.send(message)
