add download event (#1797)

reflex/.templates/web/utils/state.js

@@ -153,6 +153,15 @@ export const applyEvent = async (event, socket) => {
     navigator.clipboard.writeText(content);
     return false;
   }
+  if (event.name == "_download") {
+    const a = document.createElement('a');
+    a.hidden = true;
+    a.href = event.payload.url;
+    a.download = event.payload.filename;
+    a.click();
+    a.remove();
+    return false;
+  }
 
   if (event.name == "_alert") {
     alert(event.payload.message);

reflex/__init__.py

@@ -23,6 +23,7 @@ from .event import EventChain as EventChain
 from .event import FileUpload as upload_files
 from .event import clear_local_storage as clear_local_storage
 from .event import console_log as console_log
+from .event import download as download
 from .event import redirect as redirect
 from .event import remove_cookie as remove_cookie
 from .event import remove_local_storage as remove_local_storage

reflex/event.py

@@ -2,7 +2,7 @@
 from __future__ import annotations
 
 import inspect
-from typing import Any, Callable, Dict, List, Tuple
+from typing import Any, Callable, Dict, List, Optional, Tuple
 
 from reflex import constants
 from reflex.base import Base
@@ -330,6 +330,34 @@ def set_clipboard(content: str) -> EventSpec:
     )
 
 
+def download(url: str, filename: Optional[str] = None) -> EventSpec:
+    """Download the file at a given path.
+
+    Args:
+        url : The URL to the file to download.
+        filename : The name that the file should be saved as after download.
+
+    Raises:
+        ValueError: If the URL provided is invalid.
+
+    Returns:
+        EventSpec: An event to download the associated file.
+    """
+    if not url.startswith("/"):
+        raise ValueError("The URL argument should start with a /")
+
+    # if filename is not provided, infer it from url
+    if filename is None:
+        filename = url.rpartition("/")[-1]
+
+    return server_side(
+        "_download",
+        get_fn_signature(download),
+        url=url,
+        filename=filename,
+    )
+
+
 def get_event(state, event):
     """Get the event from the given state.