Optimize server startup speed, client update caching, and HTTP 304 conditional downloads

src/Server.py

@@ -1497,11 +1497,17 @@ def check_client_update(
 
 
 @app.get("/api/client/update/download")
-def download_client_update_package(os: Optional[str] = "windows", os_name: Optional[str] = None):
+def download_client_update_package(
+    request: Request,
+    os: Optional[str] = "windows",
+    os_name: Optional[str] = None
+):
     """
     Streams the latest client binary or installer package for the specified OS.
+    Supports HTTP ETag and conditional 304 Not Modified requests to minimize network bandwidth.
     """
     import os as _os
+    import email.utils
     target_os = os_name or os or "windows"
     mgr: ServerUpdateManager = SERVER_STATE.get("update_manager") or UPDATE_MANAGER
     pkg_tuple = mgr.get_client_package_path(os_type=target_os)
@@ -1512,14 +1518,50 @@ def download_client_update_package(os: Optional[str] = "windows", os_name: Optio
     if not _os.path.exists(file_path):
         raise HTTPException(status_code=404, detail="Client package file missing on server disk.")
 
+    etag = f'"{sha256}"'
+    if request is not None:
+        if_none_match = request.headers.get("if-none-match")
+        if if_none_match and (if_none_match == etag or if_none_match.strip('"') == sha256):
+            return Response(
+                status_code=304,
+                headers={
+                    "ETag": etag,
+                    "Cache-Control": "public, max-age=300, must-revalidate",
+                    "X-Checksum-SHA256": sha256
+                }
+            )
+
+    try:
+        mtime = _os.path.getmtime(file_path)
+        last_modified = email.utils.formatdate(mtime, usegmt=True)
+    except Exception:
+        last_modified = None
+
+    if_modified_since = request.headers.get("if-modified-since")
+    if if_modified_since and last_modified and if_modified_since == last_modified:
+        return Response(
+            status_code=304,
+            headers={
+                "ETag": etag,
+                "Cache-Control": "public, max-age=300, must-revalidate",
+                "X-Checksum-SHA256": sha256
+            }
+        )
+
+    headers = {
+        "ETag": etag,
+        "Cache-Control": "public, max-age=300, must-revalidate",
+        "X-Checksum-SHA256": sha256,
+        "Content-Disposition": f'attachment; filename="{filename}"'
+    }
+    if last_modified:
+        headers["Last-Modified"] = last_modified
+
     return FileResponse(
         path=file_path,
         filename=filename,
         media_type="application/octet-stream",
-        headers={
-            "X-Checksum-SHA256": sha256,
-            "Content-Disposition": f'attachment; filename="{filename}"'
-        }
+        headers=headers
     )
 
 
@@ -2360,7 +2402,6 @@ def main():
     csr_path = os.path.join(cert_dir, "ca.csr")
     if not os.path.exists(csr_path):
         enrollment.generate_ca_csr(cert_dir=cert_dir)
-    export_license_request_lic(config)
 
     srv_cert, srv_key, srv_pem, srv_key_pem = enrollment.generate_server_cert_if_needed(
         ca_cert, ca_key,