[ENG-2157] [Refix] Allow `rx.download` to resolve `rx.get_upload_url` (#4470)

* [ENG-2157] [Refix] Allow `rx.download` to resolve `rx.get_upload_url`

Update the special case in a way that works with the new Var system and its
unstoppable determination to concatenate strings instead of using template
string

This has been broken since 0.6.0, so a regression test was added to avoid
future inadvertant breakage.

Fix #2812 (again)

* use safer indirect eval

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

@@ -208,11 +208,16 @@ export const applyEvent = async (event, socket) => {
   if (event.name == "_download") {
     const a = document.createElement("a");
     a.hidden = true;
+    a.href = event.payload.url;
     // Special case when linking to uploaded files
-    a.href = event.payload.url.replace(
-      "${getBackendURL(env.UPLOAD)}",
-      getBackendURL(env.UPLOAD)
-    );
+    if (a.href.includes("getBackendURL(env.UPLOAD)")) {
+      a.href = eval?.(
+        event.payload.url.replace(
+          "getBackendURL(env.UPLOAD)",
+          `"${getBackendURL(env.UPLOAD)}"`
+        )
+      );
+    }
     a.download = event.payload.filename;
     a.click();
     a.remove();

tests/integration/test_upload.py

@@ -6,12 +6,16 @@ import asyncio
 import time
 from pathlib import Path
 from typing import Generator
+from urllib.parse import urlsplit
 
 import pytest
 from selenium.webdriver.common.by import By
 
+from reflex.constants.event import Endpoint
 from reflex.testing import AppHarness, WebDriver
 
+from .utils import poll_for_navigation
+
 
 def UploadFile():
     """App for testing dynamic routes."""
@@ -23,7 +27,7 @@ def UploadFile():
 
     class UploadState(rx.State):
         _file_data: Dict[str, str] = {}
-        event_order: List[str] = []
+        event_order: rx.Field[List[str]] = rx.field([])
         progress_dicts: List[dict] = []
         disabled: bool = False
         large_data: str = ""
@@ -50,6 +54,15 @@ def UploadFile():
             self.large_data = ""
             self.event_order.append("chain_event")
 
+        async def handle_upload_tertiary(self, files: List[rx.UploadFile]):
+            for file in files:
+                (rx.get_upload_dir() / (file.filename or "INVALID")).write_bytes(
+                    await file.read()
+                )
+
+        def do_download(self):
+            return rx.download(rx.get_upload_url("test.txt"))
+
     def index():
         return rx.vstack(
             rx.input(
@@ -123,6 +136,34 @@ def UploadFile():
                 on_click=rx.cancel_upload("secondary"),
                 id="cancel_button_secondary",
             ),
+            rx.heading("Tertiary Upload/Download"),
+            rx.upload.root(
+                rx.vstack(
+                    rx.button("Select File"),
+                    rx.text("Drag and drop files here or click to select files"),
+                ),
+                id="tertiary",
+            ),
+            rx.button(
+                "Upload",
+                on_click=UploadState.handle_upload_tertiary(  # type: ignore
+                    rx.upload_files(
+                        upload_id="tertiary",
+                    ),
+                ),
+                id="upload_button_tertiary",
+            ),
+            rx.button(
+                "Download - Frontend",
+                on_click=rx.download(rx.get_upload_url("test.txt")),
+                id="download-frontend",
+            ),
+            rx.button(
+                "Download - Backend",
+                on_click=UploadState.do_download,
+                id="download-backend",
+            ),
+            rx.text(UploadState.event_order.to_string(), id="event-order"),
         )
 
     app = rx.App(state=rx.State)
@@ -164,6 +205,24 @@ def driver(upload_file: AppHarness):
         driver.quit()
 
 
+def poll_for_token(driver: WebDriver, upload_file: AppHarness) -> str:
+    """Poll for the token input to be populated.
+
+    Args:
+        driver: WebDriver instance.
+        upload_file: harness for UploadFile app.
+
+    Returns:
+        token value
+    """
+    token_input = driver.find_element(By.ID, "token")
+    assert token_input
+    # wait for the backend connection to send the token
+    token = upload_file.poll_for_value(token_input)
+    assert token is not None
+    return token
+
+
 @pytest.mark.parametrize("secondary", [False, True])
 @pytest.mark.asyncio
 async def test_upload_file(
@@ -178,11 +237,7 @@ async def test_upload_file(
         secondary: whether to use the secondary upload form
     """
     assert upload_file.app_instance is not None
-    token_input = driver.find_element(By.ID, "token")
-    assert token_input
-    # wait for the backend connection to send the token
-    token = upload_file.poll_for_value(token_input)
-    assert token is not None
+    token = poll_for_token(driver, upload_file)
     full_state_name = upload_file.get_full_state_name(["_upload_state"])
     state_name = upload_file.get_state_name("_upload_state")
     substate_token = f"{token}_{full_state_name}"
@@ -204,6 +259,19 @@ async def test_upload_file(
     upload_box.send_keys(str(target_file))
     upload_button.click()
 
+    # check that the selected files are displayed
+    selected_files = driver.find_element(By.ID, f"selected_files{suffix}")
+    assert Path(selected_files.text).name == Path(exp_name).name
+
+    if secondary:
+        event_order_displayed = driver.find_element(By.ID, "event-order")
+        AppHarness._poll_for(lambda: "chain_event" in event_order_displayed.text)
+
+        state = await upload_file.get_state(substate_token)
+        # only the secondary form tracks progress and chain events
+        assert state.substates[state_name].event_order.count("upload_progress") == 1
+        assert state.substates[state_name].event_order.count("chain_event") == 1
+
     # look up the backend state and assert on uploaded contents
     async def get_file_data():
         return (
@@ -217,16 +285,6 @@ async def test_upload_file(
     normalized_file_data = {Path(k).name: v for k, v in file_data.items()}
     assert normalized_file_data[Path(exp_name).name] == exp_contents
 
-    # check that the selected files are displayed
-    selected_files = driver.find_element(By.ID, f"selected_files{suffix}")
-    assert Path(selected_files.text).name == Path(exp_name).name
-
-    state = await upload_file.get_state(substate_token)
-    if secondary:
-        # only the secondary form tracks progress and chain events
-        assert state.substates[state_name].event_order.count("upload_progress") == 1
-        assert state.substates[state_name].event_order.count("chain_event") == 1
-
 
 @pytest.mark.asyncio
 async def test_upload_file_multiple(tmp_path, upload_file: AppHarness, driver):
@@ -238,11 +296,7 @@ async def test_upload_file_multiple(tmp_path, upload_file: AppHarness, driver):
         driver: WebDriver instance.
     """
     assert upload_file.app_instance is not None
-    token_input = driver.find_element(By.ID, "token")
-    assert token_input
-    # wait for the backend connection to send the token
-    token = upload_file.poll_for_value(token_input)
-    assert token is not None
+    token = poll_for_token(driver, upload_file)
     full_state_name = upload_file.get_full_state_name(["_upload_state"])
     state_name = upload_file.get_state_name("_upload_state")
     substate_token = f"{token}_{full_state_name}"
@@ -301,11 +355,7 @@ def test_clear_files(
         secondary: whether to use the secondary upload form.
     """
     assert upload_file.app_instance is not None
-    token_input = driver.find_element(By.ID, "token")
-    assert token_input
-    # wait for the backend connection to send the token
-    token = upload_file.poll_for_value(token_input)
-    assert token is not None
+    poll_for_token(driver, upload_file)
 
     suffix = "_secondary" if secondary else ""
 
@@ -357,11 +407,7 @@ async def test_cancel_upload(tmp_path, upload_file: AppHarness, driver: WebDrive
         driver: WebDriver instance.
     """
     assert upload_file.app_instance is not None
-    token_input = driver.find_element(By.ID, "token")
-    assert token_input
-    # wait for the backend connection to send the token
-    token = upload_file.poll_for_value(token_input)
-    assert token is not None
+    token = poll_for_token(driver, upload_file)
     state_name = upload_file.get_state_name("_upload_state")
     state_full_name = upload_file.get_full_state_name(["_upload_state"])
     substate_token = f"{token}_{state_full_name}"
@@ -403,3 +449,55 @@ async def test_cancel_upload(tmp_path, upload_file: AppHarness, driver: WebDrive
     assert Path(exp_name).name not in normalized_file_data
 
     target_file.unlink()
+
+
+@pytest.mark.asyncio
+async def test_upload_download_file(
+    tmp_path,
+    upload_file: AppHarness,
+    driver: WebDriver,
+):
+    """Submit a file upload and then fetch it with rx.download.
+
+    This checks the special case `getBackendURL` logic in the _download event
+    handler in state.js.
+
+    Args:
+        tmp_path: pytest tmp_path fixture
+        upload_file: harness for UploadFile app.
+        driver: WebDriver instance.
+    """
+    assert upload_file.app_instance is not None
+    poll_for_token(driver, upload_file)
+
+    upload_box = driver.find_elements(By.XPATH, "//input[@type='file']")[2]
+    assert upload_box
+    upload_button = driver.find_element(By.ID, "upload_button_tertiary")
+    assert upload_button
+
+    exp_name = "test.txt"
+    exp_contents = "test file contents!"
+    target_file = tmp_path / exp_name
+    target_file.write_text(exp_contents)
+
+    upload_box.send_keys(str(target_file))
+    upload_button.click()
+
+    # Download via event embedded in frontend code.
+    download_frontend = driver.find_element(By.ID, "download-frontend")
+    with poll_for_navigation(driver):
+        download_frontend.click()
+    assert urlsplit(driver.current_url).path == f"/{Endpoint.UPLOAD.value}/test.txt"
+    assert driver.find_element(by=By.TAG_NAME, value="body").text == exp_contents
+
+    # Go back and wait for the app to reload.
+    with poll_for_navigation(driver):
+        driver.back()
+    poll_for_token(driver, upload_file)
+
+    # Download via backend event handler.
+    download_backend = driver.find_element(By.ID, "download-backend")
+    with poll_for_navigation(driver):
+        download_backend.click()
+    assert urlsplit(driver.current_url).path == f"/{Endpoint.UPLOAD.value}/test.txt"
+    assert driver.find_element(by=By.TAG_NAME, value="body").text == exp_contents