URLFile: don't cache non-existent file's lengths (#30071)

* urlfile empty

* simplify with mock

* better test name

* PR cleanup

* cleanup the length file

tools/lib/tests/test_caching.py

@@ -1,6 +1,12 @@
 #!/usr/bin/env python3
 import os
 import unittest
+
+from pathlib import Path
+from parameterized import parameterized
+from unittest import mock
+
+from openpilot.system.hardware.hw import Paths
 from openpilot.tools.lib.url_file import URLFile
 
 
@@ -59,6 +65,34 @@ class TestFileDownload(unittest.TestCase):
     self.compare_loads(large_file_url, length - 100, 100)
     self.compare_loads(large_file_url)
 
+  @parameterized.expand([(True, ), (False, )])
+  def test_recover_from_missing_file(self, cache_enabled):
+    os.environ["FILEREADER_CACHE"] = "1" if cache_enabled else "0"
+
+    file_url = "http://localhost:5001/test.png"
+
+    file_exists = False
+
+    def get_length_online_mock(self):
+      if file_exists:
+        return 4
+      return -1
+
+    patch_length = mock.patch.object(URLFile, "get_length_online", get_length_online_mock)
+    patch_length.start()
+    try:
+      length = URLFile(file_url).get_length()
+      self.assertEqual(length, -1)
+
+      file_exists = True
+      length = URLFile(file_url).get_length()
+      self.assertEqual(length, 4)
+    finally:
+      tempfile_length = Path(Paths.download_cache_root()) / "ba2119904385654cb0105a2da174875f8e7648db175f202ecae6d6428b0e838f_length"
+      if tempfile_length.exists():
+        tempfile_length.unlink()
+      patch_length.stop()
+
 
 if __name__ == "__main__":
   unittest.main()

tools/lib/url_file.py

@@ -73,7 +73,7 @@ class URLFile:
           return self._length
 
     self._length = self.get_length_online()
-    if not self._force_download:
+    if not self._force_download and self._length != -1:
       with atomic_write_in_dir(file_length_path, mode="w") as file_length:
         file_length.write(str(self._length))
     return self._length