simplify OnlineResource.load (#5990)

* simplify OnlineResource.load

* [PoC] merge mock data preparation and loading

* Revert "cache mock data based on config"

This reverts commit 5ed6eedef74865e0baa746a375d5ec1f0ab1bde7.

* Revert "[PoC] merge mock data preparation and loading"

This reverts commit d62747962f9ed6a7b0b80849e7c971efabb5d3da.

* remove preprocess returning a new path in favor of querying twice

* address test comments

* clarify comment

* mypy

* use builtin decompress utility

test/test_prototype_datasets_utils.py

+import gzip
+import pathlib
 import sys
 
 import numpy as np
 import pytest
 import torch
-from datasets_utils import make_fake_flo_file
+from datasets_utils import make_fake_flo_file, make_tar
+from torchdata.datapipes.iter import FileOpener, TarArchiveLoader
 from torchvision.datasets._optical_flow import _read_flo as read_flo_ref
-from torchvision.prototype.datasets.utils import HttpResource, GDriveResource, Dataset
+from torchvision.datasets.utils import _decompress
+from torchvision.prototype.datasets.utils import HttpResource, GDriveResource, Dataset, OnlineResource
 from torchvision.prototype.datasets.utils._internal import read_flo, fromfile
 
 
@@ -48,6 +52,183 @@ def test_read_flo(tmpdir):
     torch.testing.assert_close(actual, expected)
 
 
+class TestOnlineResource:
+    class DummyResource(OnlineResource):
+        def __init__(self, download_fn=None, **kwargs):
+            super().__init__(**kwargs)
+            self._download_fn = download_fn
+
+        def _download(self, root):
+            if self._download_fn is None:
+                raise pytest.UsageError(
+                    "`_download()` was called, but `DummyResource(...)` was constructed without `download_fn`."
+                )
+
+            return self._download_fn(self, root)
+
+    def _make_file(self, root, *, content, name="file.txt"):
+        file = root / name
+        with open(file, "w") as fh:
+            fh.write(content)
+
+        return file
+
+    def _make_folder(self, root, *, name="folder"):
+        folder = root / name
+        subfolder = folder / "subfolder"
+        subfolder.mkdir(parents=True)
+
+        files = {}
+        for idx, root in enumerate([folder, folder, subfolder]):
+            content = f"sentinel{idx}"
+            file = self._make_file(root, name=f"file{idx}.txt", content=content)
+            files[str(file)] = content
+
+        return folder, files
+
+    def _make_tar(self, root, *, name="archive.tar", remove=True):
+        folder, files = self._make_folder(root, name=name.split(".")[0])
+        archive = make_tar(root, name, folder, remove=remove)
+        files = {str(archive / pathlib.Path(file).relative_to(root)): content for file, content in files.items()}
+        return archive, files
+
+    def test_load_file(self, tmp_path):
+        content = "sentinel"
+        file = self._make_file(tmp_path, content=content)
+
+        resource = self.DummyResource(file_name=file.name)
+
+        dp = resource.load(tmp_path)
+        assert isinstance(dp, FileOpener)
+
+        data = list(dp)
+        assert len(data) == 1
+
+        path, buffer = data[0]
+        assert path == str(file)
+        assert buffer.read().decode() == content
+
+    def test_load_folder(self, tmp_path):
+        folder, files = self._make_folder(tmp_path)
+
+        resource = self.DummyResource(file_name=folder.name)
+
+        dp = resource.load(tmp_path)
+        assert isinstance(dp, FileOpener)
+        assert {path: buffer.read().decode() for path, buffer in dp} == files
+
+    def test_load_archive(self, tmp_path):
+        archive, files = self._make_tar(tmp_path)
+
+        resource = self.DummyResource(file_name=archive.name)
+
+        dp = resource.load(tmp_path)
+        assert isinstance(dp, TarArchiveLoader)
+        assert {path: buffer.read().decode() for path, buffer in dp} == files
+
+    def test_priority_decompressed_gt_raw(self, tmp_path):
+        # We don't need to actually compress here. Adding the suffix is sufficient
+        self._make_file(tmp_path, content="raw_sentinel", name="file.txt.gz")
+        file = self._make_file(tmp_path, content="decompressed_sentinel", name="file.txt")
+
+        resource = self.DummyResource(file_name=file.name)
+
+        dp = resource.load(tmp_path)
+        path, buffer = next(iter(dp))
+
+        assert path == str(file)
+        assert buffer.read().decode() == "decompressed_sentinel"
+
+    def test_priority_extracted_gt_decompressed(self, tmp_path):
+        archive, _ = self._make_tar(tmp_path, remove=False)
+
+        resource = self.DummyResource(file_name=archive.name)
+
+        dp = resource.load(tmp_path)
+        # If the archive had been selected, this would be a `TarArchiveReader`
+        assert isinstance(dp, FileOpener)
+
+    def test_download(self, tmp_path):
+        download_fn_was_called = False
+
+        def download_fn(resource, root):
+            nonlocal download_fn_was_called
+            download_fn_was_called = True
+
+            return self._make_file(root, content="_", name=resource.file_name)
+
+        resource = self.DummyResource(
+            file_name="file.txt",
+            download_fn=download_fn,
+        )
+
+        resource.load(tmp_path)
+
+        assert download_fn_was_called, "`download_fn()` was never called"
+
+    # This tests the `"decompress"` literal as well as a custom callable
+    @pytest.mark.parametrize(
+        "preprocess",
+        [
+            "decompress",
+            lambda path: _decompress(str(path), remove_finished=True),
+        ],
+    )
+    def test_preprocess_decompress(self, tmp_path, preprocess):
+        file_name = "file.txt.gz"
+        content = "sentinel"
+
+        def download_fn(resource, root):
+            file = root / resource.file_name
+            with gzip.open(file, "wb") as fh:
+                fh.write(content.encode())
+            return file
+
+        resource = self.DummyResource(file_name=file_name, preprocess=preprocess, download_fn=download_fn)
+
+        dp = resource.load(tmp_path)
+        data = list(dp)
+        assert len(data) == 1
+
+        path, buffer = data[0]
+        assert path == str(tmp_path / file_name).replace(".gz", "")
+        assert buffer.read().decode() == content
+
+    def test_preprocess_extract(self, tmp_path):
+        files = None
+
+        def download_fn(resource, root):
+            nonlocal files
+            archive, files = self._make_tar(root, name=resource.file_name)
+            return archive
+
+        resource = self.DummyResource(file_name="folder.tar", preprocess="extract", download_fn=download_fn)
+
+        dp = resource.load(tmp_path)
+        assert files is not None, "`download_fn()` was never called"
+        assert isinstance(dp, FileOpener)
+
+        actual = {path: buffer.read().decode() for path, buffer in dp}
+        expected = {
+            path.replace(resource.file_name, resource.file_name.split(".")[0]): content
+            for path, content in files.items()
+        }
+        assert actual == expected
+
+    def test_preprocess_only_after_download(self, tmp_path):
+        file = self._make_file(tmp_path, content="_")
+
+        def preprocess(path):
+            raise AssertionError("`preprocess` was called although the file was already present.")
+
+        resource = self.DummyResource(
+            file_name=file.name,
+            preprocess=preprocess,
+        )
+
+        resource.load(tmp_path)
+
+
 class TestHttpResource:
     def test_resolve_to_http(self, mocker):
         file_name = "data.tar"

torchvision/prototype/datasets/utils/_resource.py

@@ -2,7 +2,7 @@ import abc
 import hashlib
 import itertools
 import pathlib
-from typing import Optional, Sequence, Tuple, Callable, IO, Any, Union, NoReturn
+from typing import Optional, Sequence, Tuple, Callable, IO, Any, Union, NoReturn, Set
 from urllib.parse import urlparse
 
 from torchdata.datapipes.iter import (
@@ -32,7 +32,7 @@ class OnlineResource(abc.ABC):
         *,
         file_name: str,
         sha256: Optional[str] = None,
-        preprocess: Optional[Union[Literal["decompress", "extract"], Callable[[pathlib.Path], pathlib.Path]]] = None,
+        preprocess: Optional[Union[Literal["decompress", "extract"], Callable[[pathlib.Path], None]]] = None,
     ) -> None:
         self.file_name = file_name
         self.sha256 = sha256
@@ -50,14 +50,12 @@ class OnlineResource(abc.ABC):
         self._preprocess = preprocess
 
     @staticmethod
-    def _extract(file: pathlib.Path) -> pathlib.Path:
-        return pathlib.Path(
+    def _extract(file: pathlib.Path) -> None:
         extract_archive(str(file), to_path=str(file).replace("".join(file.suffixes), ""), remove_finished=False)
-        )
 
     @staticmethod
-    def _decompress(file: pathlib.Path) -> pathlib.Path:
-        return pathlib.Path(_decompress(str(file), remove_finished=True))
+    def _decompress(file: pathlib.Path) -> None:
+        _decompress(str(file), remove_finished=True)
 
     def _loader(self, path: pathlib.Path) -> IterDataPipe[Tuple[str, IO]]:
         if path.is_dir():
@@ -91,32 +89,38 @@ class OnlineResource(abc.ABC):
     ) -> IterDataPipe[Tuple[str, IO]]:
         root = pathlib.Path(root)
         path = root / self.file_name
+
         # Instead of the raw file, there might also be files with fewer suffixes after decompression or directories
-        # with no suffixes at all.
+        # with no suffixes at all. `pathlib.Path().stem` will only give us the name with the last suffix removed, which
+        # is not sufficient for files with multiple suffixes, e.g. foo.tar.gz.
         stem = path.name.replace("".join(path.suffixes), "")
 
-        # In a first step, we check for a folder with the same stem as the raw file. If it exists, we use it since
-        # extracted files give the best I/O performance. Note that OnlineResource._extract() makes sure that an archive
-        # is always extracted in a folder with the corresponding file name.
+        def find_candidates() -> Set[pathlib.Path]:
+            # Although it looks like we could glob for f"{stem}*" to find the file candidates as well as the folder
+            # candidate simultaneously, that would also pick up other files that share the same prefix. For example, the
+            # test split of the stanford-cars dataset uses the files
+            # - cars_test.tgz
+            # - cars_test_annos_withlabels.mat
+            # Globbing for `"cars_test*"` picks up both.
+            candidates = {file for file in path.parent.glob(f"{stem}.*")}
             folder_candidate = path.parent / stem
-        if folder_candidate.exists() and folder_candidate.is_dir():
-            return self._loader(folder_candidate)
-
-        # If there is no folder, we look for all files that share the same stem as the raw file, but might have a
-        # different suffix.
-        file_candidates = {file for file in path.parent.glob(stem + ".*")}
-        # If we don't find anything, we download the raw file.
-        if not file_candidates:
-            file_candidates = {self.download(root, skip_integrity_check=skip_integrity_check)}
-        # If the only thing we find is the raw file, we use it and optionally perform some preprocessing steps.
-        if file_candidates == {path}:
+            if folder_candidate.exists():
+                candidates.add(folder_candidate)
+
+            return candidates
+
+        candidates = find_candidates()
+
+        if not candidates:
+            self.download(root, skip_integrity_check=skip_integrity_check)
             if self._preprocess is not None:
-                path = self._preprocess(path)
-        # Otherwise, we use the path with the fewest suffixes. This gives us the decompressed > raw priority that we
-        # want for the best I/O performance.
-        else:
-            path = min(file_candidates, key=lambda path: len(path.suffixes))
-        return self._loader(path)
+                self._preprocess(path)
+            candidates = find_candidates()
+
+        # We use the path with the fewest suffixes. This gives us the
+        # extracted > decompressed > raw
+        # priority that we want for the best I/O performance.
+        return self._loader(min(candidates, key=lambda candidate: len(candidate.suffixes)))
 
     @abc.abstractmethod
     def _download(self, root: pathlib.Path) -> None: