Fix bug in datetime comparisons. Ignore If-Modified-Since if If-None-…

…Match is present. Add tests.
python · serhiy-storchaka · Apr 2, 2017 · Feb 25, 2017 · Feb 26, 2017 · Feb 26, 2017
commit f1d8a484dfa2812f57decb259f6bbcde72d59c05
diff --git a/Lib/http/server.py b/Lib/http/server.py
@@ -687,25 +687,30 @@ def send_head(self):
         except OSError:
             self.send_error(HTTPStatus.NOT_FOUND, "File not found")
             return None
+
+        fs = os.fstat(f.fileno())
+
         try:
             # Use browser cache if possible
-            if "If-Modified-Since" in self.headers:
+            if "If-Modified-Since" in self.headers \
+                    and not "If-None-Match" in self.headers:
                 # compare If-Modified-Since and date of last file modification
-                fs = os.stat(path)
                 ims = email.utils.parsedate(self.headers["If-Modified-Since"])
                 if ims is not None:
-                    ims_datetime = datetime.datetime(*ims[:7])
-                    ims_dtstring = ims_datetime.strftime("%d %b %Y %H:%M:%S")
-                    last_modif = datetime.datetime.utcfromtimestamp(
-                        fs.st_mtime).strftime("%d %b %Y %H:%M:%S")
-                    if last_modif <= ims_dtstring:
+                    # If-Modified-Since is UTC, rounded to the second
+                    tzinfo = datetime.timezone(datetime.timedelta(hours=0))
+                    ims_datetime = datetime.datetime(*ims[:7], tzinfo=tzinfo)
+                    # compare to UTC datetime of last modification, also 
+                    # rounded to the second
+                    mtime = int(fs.st_mtime)
+                    last_modif = datetime.datetime.fromtimestamp(mtime, tzinfo)
+                    if last_modif <= ims_datetime:
                         self.send_response(HTTPStatus.NOT_MODIFIED)
                         self.end_headers()
                         f.close()
                        return
             self.send_response(HTTPStatus.OK)
             self.send_header("Content-type", ctype)
-            fs = os.fstat(f.fileno())
             self.send_header("Content-Length", str(fs[6]))
             self.send_header("Last-Modified", self.date_time_string(fs.st_mtime))
             self.end_headers()
@@ -1229,4 +1234,3 @@ def test(HandlerClass=BaseHTTPRequestHandler,
         handler_class = SimpleHTTPRequestHandler
     test(HandlerClass=handler_class, port=args.port, bind=args.bind)
 
-
diff --git a/Lib/test/test_httpservers.py b/Lib/test/test_httpservers.py
@@ -448,16 +448,42 @@ def test_browser_cache(self):
         #constructs the path relative to the root directory of the HTTPServer
         response = self.request(self.base_url + '/test')
         self.check_status_and_reason(response, HTTPStatus.OK, data=self.data)
-        # get Last-Modified response heaer
         last_modif = response.headers['Last-modified']
+
         # send new request to the same url with request header 
-        # If-Modified-Since
+        # If-Modified-Since set to Last-Modified : must return 304
         from email.message import Message
         headers = Message()
         headers['If-Modified-Since'] = last_modif
         response = self.request(self.base_url + '/test', headers=headers)
         self.check_status_and_reason(response, HTTPStatus.NOT_MODIFIED)
 
+        # if If-None-Match header is present, ignore If-Modified-Since
+        headers['If-None-Match'] = "*"
+        response = self.request(self.base_url + '/test', headers=headers)
+        self.check_status_and_reason(response, HTTPStatus.OK)        
+
+        # with If-Modified-Since earlier than Last-Modified, must return 200
+        import datetime
+        import email.utils
+        dt = email.utils.parsedate(last_modif)
+        # build datetime object : one year before last modification
+        old_dt = [dt[0] - 1] + list(dt[1:7])
+        old_dt = datetime.datetime(*old_dt)
+        headers = Message()
+        headers['If-Modified-Since'] = email.utils.format_datetime(old_dt)
+        response = self.request(self.base_url + '/test', headers=headers)
+        self.check_status_and_reason(response, HTTPStatus.OK)
+
+        # build datetime object : one hours after last modification
+        new_dt = [dt[0]] + [dt[1] + 1] + list(dt[2:7])
+        new_dt = datetime.datetime(*new_dt)
+        headers = Message()
+        headers['If-Modified-Since'] = email.utils.format_datetime(new_dt)
+        response = self.request(self.base_url + '/test', headers=headers)
+        self.check_status_and_reason(response, HTTPStatus.NOT_MODIFIED)
+
+
     def test_invalid_requests(self):
         response = self.request('/', method='FOO')
         self.check_status_and_reason(response, HTTPStatus.NOT_IMPLEMENTED)