Implemented (probably quite shaky) static content cache headers.

matemat/webserver/httpd.py

@@ -10,6 +10,7 @@ from http.server import HTTPServer, BaseHTTPRequestHandler
 from http.cookies import SimpleCookie
 from uuid import uuid4
 from datetime import datetime, timedelta
+from time import localtime
 
 import jinja2
 
@@ -323,7 +324,7 @@ class HttpHandler(BaseHTTPRequestHandler):
             # Send the HTTP status code
             self.send_response(hsc)
             # Format the session cookie timeout string and send the session cookie header
-            expires = timeout.strftime("%a, %d %b %Y %H:%M:%S GMT")
+            expires = timeout.strftime('%a, %d %b %Y %H:%M:%S GMT')
             self.send_header('Set-Cookie',
                              f'matemat_session_id={session_id}; expires={expires}')
             # Compute the body length and add the appropriate header
@@ -345,6 +346,21 @@ class HttpHandler(BaseHTTPRequestHandler):
             filepath: str = os.path.abspath(os.path.join(self.server.webroot, path[1:]))
             # Make sure the file is actually inside the webroot directory and that it exists
             if os.path.commonpath([filepath, self.server.webroot]) == self.server.webroot and os.path.exists(filepath):
+                # Parse the If-Modified-Since header to check whether the browser can reuse cached content
+                datestr: str = self.headers.get('If-Modified-Since', 'Thu, 01 Jan 1970 00:00:00 GMT')
+                maxage: datetime = datetime.strptime(datestr, '%a, %d %b %Y %H:%M:%S %Z')
+                # File modification time in LOCAL time
+                filestat: int = int(os.path.getmtime(filepath))
+                # Create timezone-unaware datetime object and subtract UTC offset
+                fileage: datetime = datetime.fromtimestamp(filestat) - timedelta(seconds=localtime().tm_gmtoff)
+
+                # If the file has not been replaced by a newer version than requested by the client, send a 304 response
+                if fileage <= maxage:
+                    self.send_response(304, 'Not Modified')
+                    self.send_header('Content-Length', '0')
+                    self.end_headers()
+                    return
+
                 # Open and read the file
                 with open(filepath, 'rb') as f:
                     data = f.read()
@@ -358,6 +374,8 @@ class HttpHandler(BaseHTTPRequestHandler):
                 # Send content type and length header
                 self.send_header('Content-Type', mimetype)
                 self.send_header('Content-Length', str(len(data)))
+                self.send_header('Last-Modified', fileage.strftime('%a, %d %b %Y %H:%M:%S GMT'))
+                self.send_header('Cache-Control', 'max-age=1')
                 self.end_headers()
                 # Send the requested resource as response body
                 self.wfile.write(data)