python · serhiy-storchaka · Apr 2, 2017 · Feb 25, 2017 · Feb 26, 2017 · Feb 26, 2017
diff --git a/Doc/whatsnew/3.7.rst b/Doc/whatsnew/3.7.rst
@@ -110,6 +110,12 @@ urllib.parse
 adding `~` to the set of characters that is never quoted by default.
 (Contributed by Christian Theune and Ratnadeep Debnath in :issue:`16285`.)
 
+http.server
+-----------
+:class:`SimpleHTTPRequestHandler` supports the HTTP If-Modified-Since header.
+The server returns the 304 response status if the target file was not
+modified after the datetime specified in the header.
+(Contributed by Pierre Quentel in :issue:`29654`.)
 
 Optimizations
 =============

diff --git a/Lib/http/server.py b/Lib/http/server.py
@@ -100,6 +100,7 @@
 import socketserver
 import sys
 import time
+import datetime
 import urllib.parse
 import copy
 import argparse
@@ -686,10 +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
+                    and "If-None-Match" not in self.headers):
+                # compare If-Modified-Since and time of last file modification
+                ims = email.utils.parsedate_to_datetime(
+                    self.headers["If-Modified-Since"])
+                if (ims is not None and
+                        ims.tzinfo is datetime.timezone.utc):
+                    # compare to UTC datetime of last modification, 
+                    # rounded to the second
+                    mtime = int(fs.st_mtime)
+                    last_modif = datetime.datetime.fromtimestamp(mtime, 
+                        ims.tzinfo)
+                    if last_modif <= ims:
+                        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()
@@ -1212,3 +1233,4 @@ def test(HandlerClass=BaseHTTPRequestHandler,
     else:
         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
@@ -444,6 +444,45 @@ def test_head(self):
         self.assertEqual(response.getheader('content-type'),
                          'application/octet-stream')
 
+    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)
+        last_modif = response.headers['Last-modified']
+
+        # send new request to the same url with request header 
+        # 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_to_datetime(last_modif)
+        # build datetime object : 365 days before last modification
+        old_dt = dt - datetime.timedelta(days=365)
+        headers = Message()
+        headers['If-Modified-Since'] = email.utils.format_datetime(old_dt,
+            usegmt=True)
+        response = self.request(self.base_url + '/test', headers=headers)
+        self.check_status_and_reason(response, HTTPStatus.OK)
+
+        # one hour after last modification : must return 304
+        new_dt = dt + datetime.timedelta(hours=1)
+        headers = Message()
+        headers['If-Modified-Since'] = email.utils.format_datetime(new_dt,
+            usegmt=True)
+        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)

diff --git a/Misc/NEWS b/Misc/NEWS
@@ -666,6 +666,9 @@ Library
 - Issue #24142: Reading a corrupt config file left configparser in an
   invalid state.  Original patch by Florian Höch.
 
+- bpo-29654 : Support If-Modified-Since HTTP header (browser cache). Patch
+  by Pierre Quentel.
+
 Windows
 -------