Etag 笔记

......
If-None-Match: "3c64e7a072b3b57e100c96134e5ed2929e8dc56c"
......

HTTP/1.1 304 Not Modified

Date: Tue, 10 May 2016 06:29:05 GMT

Etag: "3c64e7a072b3b57e100c96134e5ed2929e8dc56c"

Server: TornadoServer/4.3

Tornado Etag 实现

hashlib.sha1

def compute_etag(self):
"""Computes the etag header to be used for this request.

By default uses a hash of the content written so far.

May be overridden to provide custom etag implementations,
or may return None to disable tornado's default etag support.
"""
hasher = hashlib.sha1()
for part in self._write_buffer:
hasher.update(part)
return '"%s"' % hasher.hexdigest()

request

headers

If-None-Match"

def check_etag_header(self):
"""Checks the ``Etag`` header against requests's ``If-None-Match``.

Returns ``True`` if the request's Etag matches and a 304 should be
returned. For example::

self.set_etag_header()
if self.check_etag_header():
self.set_status(304)
return

This method is called automatically when the request is finished,
but may be called earlier for applications that override
`compute_etag` and want to do an early check for ``If-None-Match``
before completing the request.  The ``Etag`` header should be set
(perhaps with `set_etag_header`) before calling this method.
"""
computed_etag = utf8(self._headers.get("Etag", ""))
# Find all weak and strong etag values from If-None-Match header
# because RFC 7232 allows multiple etag values in a single header.
etags = re.findall(
br'\*|(?:W/)?"[^"]*"',
utf8(self.request.headers.get("If-None-Match", ""))
)
if not computed_etag or not etags:
return False
match = False
if etags[0] == b'*':
match = True
else:
# Use a weak comparison when comparing entity-tags.
val = lambda x: x[2:] if x.startswith(b'W/') else x
for etag in etags:
if val(etag) == val(computed_etag):
match = True
break
return match

......
if self.check_etag_header():
self._write_buffer = []
self.set_status(304)
......