HttpResponseNotModified (source code) returns the HTTP 304 status code from a Django web application view. The HTTP 304 status code indicates that the resource has not been modified since the client last requested it.
HttpResponseRedirect and HttpResponsePermanentRedirect are other types of 300-level HTTP status codes that can be sent as a response by your Django application.
wagtail (project website) is a fantastic Django-based CMS with code that is open source under the BSD 3-Clause "New" or "Revised" License.
wagtail / wagtail / utils / sendfile_streaming_backend.py
# Sendfile "streaming" backend
# This is based on sendfiles builtin "simple" backend but uses a StreamingHttpResponse
import os
import re
import stat
from email.utils import mktime_tz, parsedate_tz
from wsgiref.util import FileWrapper
from django.http import HttpResponseNotModified, StreamingHttpResponse
from django.utils.http import http_date
def sendfile(request, filename, **kwargs):
# Respect the If-Modified-Since header.
statobj = os.stat(filename)
if not was_modified_since(request.META.get('HTTP_IF_MODIFIED_SINCE'),
statobj[stat.ST_MTIME], statobj[stat.ST_SIZE]):
return HttpResponseNotModified()
response = StreamingHttpResponse(FileWrapper(open(filename, 'rb')))
response["Last-Modified"] = http_date(statobj[stat.ST_MTIME])
return response
def was_modified_since(header=None, mtime=0, size=0):
"""
Was something modified since the user last downloaded it?
header
This is the value of the If-Modified-Since header. If this is None,
I'll just return True.
mtime
This is the modification time of the item we're talking about.
size
This is the size of the item we're talking about.
"""
try:
if header is None:
raise ValueError
matches = re.match(r"^([^;]+)(; length=([0-9]+))?$", header,
re.IGNORECASE)
header_date = parsedate_tz(matches.group(1))
if header_date is None:
raise ValueError
header_mtime = mktime_tz(header_date)
header_len = matches.group(3)
if header_len and int(header_len) != size:
raise ValueError
if mtime > header_mtime:
raise ValueError
except (AttributeError, ValueError, OverflowError):
return True
return False