[fbsync] resolve redirection for HTTP resources (#5151)

Summary:
* resolve redirection for HTTP resources

* appease mypy

* address review

Reviewed By: kazhang

Differential Revision: D33927505

fbshipit-source-id: a6b39b2809fd63419620523f6b84a60e91147818

Author: yiwen-song

torchvision/prototype/datasets/utils/_resource.py

@@ -20,6 +20,8 @@
     extract_archive,
     _decompress,
     download_file_from_google_drive,
+    _get_redirect_url,
+    _get_google_drive_file_id,
 )
 
 
@@ -134,9 +136,41 @@ def __init__(
         super().__init__(file_name=file_name or pathlib.Path(urlparse(url).path).name, **kwargs)
         self.url = url
         self.mirrors = mirrors
+        self._resolved = False
+
+    def resolve(self) -> OnlineResource:
+        if self._resolved:
+            return self
+
+        redirect_url = _get_redirect_url(self.url)
+        if redirect_url == self.url:
+            self._resolved = True
+            return self
+
+        meta = {
+            attr.lstrip("_"): getattr(self, attr)
+            for attr in (
+                "file_name",
+                "sha256",
+                "_preprocess",
+                "_loader",
+            )
+        }
+
+        gdrive_id = _get_google_drive_file_id(redirect_url)
+        if gdrive_id:
+            return GDriveResource(gdrive_id, **meta)
+
+        http_resource = HttpResource(redirect_url, **meta)
+        http_resource._resolved = True
+        return http_resource
 
     def _download(self, root: pathlib.Path) -> None:
+        if not self._resolved:
+            return self.resolve()._download(root)
+
         for url in itertools.chain((self.url,), self.mirrors):
+
             try:
                 download_url(url, str(root), filename=self.file_name, md5=None)
             # TODO: make this more precise