feat: send HSTS header

stapler/handlers.py

@@ -29,6 +29,10 @@ class BaseHandler(abc.ABC, http.server.BaseHTTPRequestHandler):
     timeout = 10
     protocol_version = "HTTP/1.1"
     REQUEST_COUNT = 0
+    RESPONSE_HEADERS: typing.ClassVar = {
+        "Connection": "close",
+        "Strict-Transport-Security": "max-age=31536000; includeSubDomains; preload",
+    }
 
     @typing.override
     def __init__(
@@ -151,7 +155,7 @@ class BaseHandler(abc.ABC, http.server.BaseHTTPRequestHandler):
         self.send_response(code, message)
         self.send_header("Content-Type", f"{content_type}; charset=UTF-8")
         self.send_header("Content-Length", str(len(encoded)))
-        self.send_header("Connection", "close")
+        self._send_basic_headers()
         self.end_headers()
         if self.command != http.HTTPMethod.HEAD:
             self.wfile.write(encoded)
@@ -167,7 +171,7 @@ class BaseHandler(abc.ABC, http.server.BaseHTTPRequestHandler):
             headers = {}
         self.send_response(code, message)
         self.send_header("Content-Length", "0")
-        self.send_header("Connection", "close")
+        self._send_basic_headers()
         for header, value in headers.items():
             self.send_header(header, value)
         self.end_headers()
@@ -221,7 +225,7 @@ class BaseHandler(abc.ABC, http.server.BaseHTTPRequestHandler):
             ]:
                 self.send_header(header, value.replace(target_host, self.host))
         self.send_header("Content-Length", str(out_size := len(response.content)))
-        self.send_header("Connection", "close")
+        self._send_basic_headers()
         self.end_headers()
         if out_size > 0 and self.command != http.HTTPMethod.HEAD:
             self.wfile.write(response.content)
@@ -269,6 +273,10 @@ class BaseHandler(abc.ABC, http.server.BaseHTTPRequestHandler):
             self.send_error(http.HTTPStatus.INTERNAL_SERVER_ERROR, str(e))
             self.logger.exception("Internal Server Error")
 
+    def _send_basic_headers(self) -> None:
+        for header, value in self.RESPONSE_HEADERS.items():
+            self.send_header(header, value)
+
 
 class RequestHandler(http.server.SimpleHTTPRequestHandler, BaseHandler):
     protocol_version = "HTTP/1.1"