Ticket #5791: 5791.5.diff

django/views/decorators/http.py

@@ -7 +7 @@
 except ImportError:
     from django.utils.functional import wraps  # Python 2.3, 2.4 fallback.
 
+import re
+from calendar import timegm
+from datetime import timedelta
+from email.Utils import formatdate
 from django.utils.decorators import decorator_from_middleware
 from django.middleware.http import ConditionalGetMiddleware
-from django.http import HttpResponseNotAllowed
+from django.http import HttpResponseNotAllowed, HttpResponseNotModified
 
 conditional_page = decorator_from_middleware(ConditionalGetMiddleware)
 
@@ -36 +40 @@
 require_GET.__doc__ = "Decorator to require that a view only accept the GET method."
 
 require_POST = require_http_methods(["POST"])
-require_POST.__doc__ = "Decorator to require that a view only accept the POST method."
- No newline at end of file
+require_POST.__doc__ = "Decorator to require that a view only accept the POST method."
+
+def _parse_etags(etag_str):
+    """
+    Parses a string with one or several etags passed in If-None-Match and
+    If-Match headers by the rules in RFC 2616. Returns a list of etags
+    without surrounding double quotes (") and unescaped from \<CHAR>.
+    """
+    etags = re.findall(r'(?:W/)?"((?:\\.|[^"])*)"', etag_str)
+    if not etags:
+        # etag_str has wrong format, treat it as an opaque string then
+        return [etag_str]
+    etags = [e.decode('string_escape') for e in etags]
+    return etags
+
+def _quote_etag(etag):
+    '''
+    Wraps a string in double quotes escaping contents as necesary.
+    '''
+    return '"%s"' % etag.replace('\\', '\\\\').replace('"', '\\"')
+
+def condition(etag=None, last_modified=None):
+    """
+    Decorator to support conditional get for a view.  It takes as parameters
+    user-defined functions that calculate etag and/or last modified time.
+
+    Both functions are passed the same parameters as the view itself. "last_modified"
+    should return a standard datetime value and "etag" should return a string.
+
+    Example usage with last_modified::
+
+        @condition(last_modified=lambda r, obj_id: MyObject.objects.get(pk=obj_id).update_time)
+        def my_object_view(request, obj_id):
+            # ...
+
+    You can pass last_modified, etag or both of them (if you really need it).
+    """
+    def decorator(func):
+        def inner(request, *args, **kwargs):
+            if request.method not in ('GET', 'HEAD'):
+                return func(request, *args, **kwargs)
+
+            # Get HTTP request headers
+            if_modified_since = request.META.get('HTTP_IF_MODIFIED_SINCE', None)
+            if_none_match = request.META.get('HTTP_IF_NONE_MATCH', None)
+            if if_none_match:
+                if_none_match = _parse_etags(if_none_match)
+
+            # Get and convert user-defined values
+            if last_modified is not None:
+                dt = last_modified(request, *args, **kwargs)
+                last_modified_value = dt and (formatdate(timegm(dt.utctimetuple()))[:26] + 'GMT')
+            else:
+                last_modified_value = None
+
+            if etag is not None:
+                etag_value = etag(request, *args, **kwargs)
+            else:
+                etag_value = None
+
+            # Calculate "not modified" condition
+            not_modified = (if_modified_since or if_none_match) and \
+                           (not if_modified_since or last_modified_value == if_modified_since) and \
+                           (not if_none_match or etag_value in if_none_match)
+
+            # Create appropriate response
+            if not_modified:
+                response = HttpResponseNotModified()
+            else:
+                response = func(request, *args, **kwargs)
+
+            # Set relevant headers for response
+            if last_modified_value and not response.has_header('Last-Modified'):
+                response['Last-Modified'] = last_modified_value
+            if etag_value and not response.has_header('ETag'):
+                response['ETag'] = _quote_etag(etag_value)
+
+            return response
+        return inner
+    return decorator
+
+# Shortcut decorators for common cases based on ETag or Last-Modified only
+def etag(callable):
+    return condition(etag=callable)
+
+def last_modified(callable):
+    return condition(last_modified=callable)

docs/index.txt

@@ -81 +81 @@
     * :ref:`Admin site <ref-contrib-admin>`
     * :ref:`Authentication <topics-auth>`
     * :ref:`Cache system <topics-cache>`
+    * :ref:`Conditional get <topics-conditional-get>`
     * :ref:`Comments <ref-contrib-comments-index>`
     * :ref:`Content types <ref-contrib-contenttypes>`
     * :ref:`Cross Site Request Forgery protection <ref-contrib-csrf>`

docs/topics/conditional-get.txt

@@ +1 @@
+========================
+Per-view conditional get
+========================
+
+`Conditional get`_ is a feature of HTTP that allows you to omit sending a response
+if the client signals in a request that it has a cached copy of reponse. To control
+whether the cached copy is expired the client may use time of its last modification
+or an "entity tag" - a short value that changes whenever the response itself changes
+(typically it's simply a hash over the response).
+
+.. _`Conditional get`: http://www.w3.org/Protocols/rfc2616/rfc2616-sec13.html#sec13.3
+
+Django allows simple usage of this feature with ``ConditionalGetMiddleware`` and
+``CommonMiddleware`` (see `middleware documentation`_ for their usage). But, while
+simple, they both have limitations:
+
+* they are applied gloablly to all views in your project
+* they don't spare you from generating the response itself, which may be expensive
+
+.. _`middleware documentation`: ../middleware/
+
+Decorators
+==========
+
+When you need more fine-grained control you may use per-view conditional get
+decorators.
+
+Decorators ``etag`` and ``last_modified`` accept a user-defined function that
+takes the same parameters as the view itself. ``last_modified`` should return a
+standard datetime value and ``etag`` should return a string (you don't need to
+wrap it in double quotes, Django will escape the string for you).
+
+Example usage of ``last_modified``::
+
+    @last_modified(lambda r, obj_id: MyObject.objects.get(pk=obj_id).update_time)
+    def my_object_view(request, obj_id):
+        # Expensive generation of response with MyObject instance
+
+In this example we're taking advantage of the fact that MyObject instance stores
+the time when it was last updated in a field.
+
+Usage of ``etag`` is similar.
+
+HTTP allows to use both "ETag" and "Last-Modified" headers in your response. Then
+a response is considered not modified only if the client sends both headers back and
+they're both equal to the response headers. This means that you can't just chain
+decorators on your view:
+
+    @etag(etag_func)
+    @last_modified(last_modified_func)
+    def my_view(request):
+        # ...
+
+Because the first decorator doesn't know anything about the second and can answer
+that the response is not modified even if the second decorators would think otherwise.
+In this case you should use a more general decorator - ``condition`` that accepts
+two functions at once:
+
+    @condition(etag_func, last_modified_func)
+    def my_view(request):
+        # ...

tests/regressiontests/conditional_get/__init__.py

@@ +1 @@
+# -*- coding:utf-8 -*-

tests/regressiontests/conditional_get/models.py

@@ +1 @@
+# -*- coding:utf-8 -*-
+from datetime import datetime, timedelta
+from calendar import timegm
+from django.test import TestCase
+
+from django.views.decorators.http import _parse_etags, _quote_etag
+
+FULL_RESPONSE = 'Test conditional get response'
+LAST_MODIFIED = datetime(2007, 10, 21, 23, 21, 47)
+LAST_MODIFIED_STR = 'Sun, 21 Oct 2007 23:21:47 GMT'
+EXPIRED_LAST_MODIFIED_STR = 'Sat, 20 Oct 2007 23:21:47 GMT'
+ETAG = 'b4246ffc4f62314ca13147c9d4f76974'
+EXPIRED_ETAG = '7fae4cd4b0f81e7d2914700043aa8ed6'
+
+class ConditionalGet(TestCase):
+    def assertFullResponse(self, response, check_last_modified=True, check_etag=True):
+        self.assertEquals(response.status_code, 200)
+        self.assertEquals(response.content, FULL_RESPONSE)
+        if check_last_modified:
+            self.assertEquals(response['Last-Modified'], LAST_MODIFIED_STR)
+        if check_etag:
+            self.assertEquals(response['ETag'], '"%s"' % ETAG)
+
+    def assertNotModified(self, response):
+        self.assertEquals(response.status_code, 304)
+        self.assertEquals(response.content, '')
+
+    def testWithoutConditions(self):
+        response = self.client.get('/condition/')
+        self.assertFullResponse(response)
+
+    def testIfModifiedSince(self):
+        self.client.defaults['HTTP_IF_MODIFIED_SINCE'] = LAST_MODIFIED_STR
+        response = self.client.get('/condition/')
+        self.assertNotModified(response)
+        self.client.defaults['HTTP_IF_MODIFIED_SINCE'] = EXPIRED_LAST_MODIFIED_STR
+        response = self.client.get('/condition/')
+        self.assertFullResponse(response)
+
+    def testIfNoneMatch(self):
+        self.client.defaults['HTTP_IF_NONE_MATCH'] = '"%s"' % ETAG
+        response = self.client.get('/condition/')
+        self.assertNotModified(response)
+        self.client.defaults['HTTP_IF_NONE_MATCH'] = '"%s"' % EXPIRED_ETAG
+        response = self.client.get('/condition/')
+        self.assertFullResponse(response)
+
+        # Several etags in If-None-Match is a bit exotic but why not?
+        self.client.defaults['HTTP_IF_NONE_MATCH'] = '"%s", "%s"' % (ETAG, EXPIRED_ETAG)
+        response = self.client.get('/condition/')
+        self.assertNotModified(response)
+
+    def testBothHeaders(self):
+        self.client.defaults['HTTP_IF_MODIFIED_SINCE'] = LAST_MODIFIED_STR
+        self.client.defaults['HTTP_IF_NONE_MATCH'] = '"%s"' % ETAG
+        response = self.client.get('/condition/')
+        self.assertNotModified(response)
+        self.client.defaults['HTTP_IF_MODIFIED_SINCE'] = EXPIRED_LAST_MODIFIED_STR
+        self.client.defaults['HTTP_IF_NONE_MATCH'] = '"%s"' % ETAG
+        response = self.client.get('/condition/')
+        self.assertFullResponse(response)
+        self.client.defaults['HTTP_IF_MODIFIED_SINCE'] = LAST_MODIFIED_STR
+        self.client.defaults['HTTP_IF_NONE_MATCH'] = '"%s"' % EXPIRED_ETAG
+        response = self.client.get('/condition/')
+        self.assertFullResponse(response)
+
+    def testSingleConditions(self):
+        self.client.defaults['HTTP_IF_MODIFIED_SINCE'] = LAST_MODIFIED_STR
+        response = self.client.get('/condition/last_modified/')
+        self.assertNotModified(response)
+        response = self.client.get('/condition/etag/')
+        self.assertFullResponse(response, check_last_modified=False)
+
+        del self.client.defaults['HTTP_IF_MODIFIED_SINCE']
+        self.client.defaults['HTTP_IF_NONE_MATCH'] = '"%s"' % ETAG
+        response = self.client.get('/condition/etag/')
+        self.assertNotModified(response)
+        response = self.client.get('/condition/last_modified/')
+        self.assertFullResponse(response, check_etag=False)
+
+        self.client.defaults['HTTP_IF_MODIFIED_SINCE'] = EXPIRED_LAST_MODIFIED_STR
+        self.client.defaults['HTTP_IF_NONE_MATCH'] = '"%s"' % EXPIRED_ETAG
+        response = self.client.get('/condition/last_modified/')
+        self.assertFullResponse(response, check_etag=False)
+        response = self.client.get('/condition/etag/')
+        self.assertFullResponse(response, check_last_modified=False)
+
+
+class ETagProcesing(TestCase):
+    def testParsing(self):
+        etags = _parse_etags(r'"", "etag", "e\"t\"ag", "e\\tag", W/"weak"')
+        self.assertEquals(etags, ['', 'etag', 'e"t"ag', r'e\tag', 'weak'])
+
+    def testQuoting(self):
+        quoted_etag = _quote_etag(r'e\t"ag')
+        self.assertEquals(quoted_etag, r'"e\\t\"ag"')

tests/regressiontests/conditional_get/urls.py

@@ +1 @@
+from django.conf.urls.defaults import *
+import views
+
+urlpatterns = patterns('',
+    ('^$', views.index),
+    ('^last_modified/$', views.last_modified),
+    ('^etag/$', views.etag),
+)

tests/regressiontests/conditional_get/views.py

@@ +1 @@
+# -*- coding:utf-8 -*-
+from django.views.decorators.http import condition
+from django.http import HttpResponse
+
+from models import FULL_RESPONSE, LAST_MODIFIED, ETAG
+
+@condition(lambda r: ETAG, lambda r: LAST_MODIFIED)
+def index(request):
+    return HttpResponse(FULL_RESPONSE)
+
+@condition(last_modified=lambda r: LAST_MODIFIED)
+def last_modified(request):
+    return HttpResponse(FULL_RESPONSE)
+
+@condition(etag=lambda r: ETAG)
+def etag(request):
+    return HttpResponse(FULL_RESPONSE)
+ No newline at end of file

tests/urls.py

@@ -29 +29 @@
 
     # test urlconf for syndication tests
     (r'^syndication/', include('regressiontests.syndication.urls')),
+
+    # conditional get views
+    (r'condition/', include('regressiontests.conditional_get.urls')),
 )