Local downloader w cache (#30)

README.md

@@ -391,6 +391,16 @@ outputs = optimize(
 )
 ```
 
+## Network Drive On-Prem Support
+
+On-prem compute nodes can mount and use network drive. In order to reduce their network overload, the `StreamingDataset` supports `caching` the chunks.
+
+```python
+from lightning.data import StreamingDataset
+
+dataset = StreamingDataset(input_dir="local:/data/shared-drive/some-data")
+```
+
 # ⚡ Contributors
 
 We welcome any contributions, pull requests, or issues. If you use the Streaming Dataset for your own project, please reach out to us on Slack or Discord.

litdata/streaming/downloader.py

@@ -95,7 +95,13 @@ def download_file(self, remote_filepath: str, local_filepath: str) -> None:
             shutil.copy(remote_filepath, local_filepath)
 
 
-_DOWNLOADERS = {"s3://": S3Downloader, "": LocalDownloader}
+class LocalDownloaderWithCache(LocalDownloader):
+    def download_file(self, remote_filepath: str, local_filepath: str) -> None:
+        remote_filepath = remote_filepath.replace("local:", "")
+        super().download_file(remote_filepath, local_filepath)
+
+
+_DOWNLOADERS = {"s3://": S3Downloader, "local:": LocalDownloaderWithCache, "": LocalDownloader}
 
 
 def get_downloader_cls(remote_dir: str, cache_dir: str, chunks: List[Dict[str, Any]]) -> Downloader:

litdata/streaming/resolver.py

@@ -56,6 +56,9 @@ def _resolve_dir(dir_path: Optional[Union[str, Dir]]) -> Dir:
     if dir_path.startswith("s3://"):
         return Dir(path=None, url=dir_path)
 
+    if dir_path.startswith("local:"):
+        return Dir(path=None, url=dir_path)
+
     dir_path = _resolve_time_template(dir_path)
 
     dir_path_absolute = str(Path(dir_path).absolute().resolve())

tests/streaming/test_downloader.py

@@ -1,7 +1,7 @@
 import os
 from unittest.mock import MagicMock
 
-from litdata.streaming.downloader import S3Downloader, subprocess
+from litdata.streaming.downloader import LocalDownloaderWithCache, S3Downloader, shutil, subprocess
 
 
 def test_s3_downloader_fast(tmpdir, monkeypatch):
@@ -11,3 +11,18 @@ def test_s3_downloader_fast(tmpdir, monkeypatch):
     downloader = S3Downloader(tmpdir, tmpdir, [])
     downloader.download_file("s3://random_bucket/a.txt", os.path.join(tmpdir, "a.txt"))
     popen_mock.wait.assert_called()
+
+
+def test_download_with_cache(tmpdir, monkeypatch):
+    # Create a file to download/cache
+    with open("a.txt", "w") as f:
+        f.write("hello")
+
+    try:
+        local_downloader = LocalDownloaderWithCache(tmpdir, tmpdir, [])
+        shutil_mock = MagicMock()
+        monkeypatch.setattr(shutil, "copy", shutil_mock)
+        local_downloader.download_file("local:a.txt", os.path.join(tmpdir, "a.txt"))
+        shutil_mock.assert_called()
+    finally:
+        os.remove("a.txt")