Add CacheMapper to map from remote URL to local cached basename (#1296)

* Add CacheMapper to map from remote URL to local cached basename

* Raise exception if 'fn' not in cached metadata

* Fix tests on Windows

fsspec/implementations/cache_mapper.py

@@ -0,0 +1,57 @@
+from __future__ import annotations
+
+import abc
+import hashlib
+import os
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from typing import Any
+
+
+class AbstractCacheMapper(abc.ABC):
+    """Abstract super-class for mappers from remote URLs to local cached
+    basenames.
+    """
+
+    @abc.abstractmethod
+    def __call__(self, path: str) -> str:
+        ...
+
+    def __eq__(self, other: Any) -> bool:
+        # Identity only depends on class. When derived classes have attributes
+        # they will need to be included.
+        return isinstance(other, type(self))
+
+    def __hash__(self) -> int:
+        # Identity only depends on class. When derived classes have attributes
+        # they will need to be included.
+        return hash(type(self))
+
+
+class BasenameCacheMapper(AbstractCacheMapper):
+    """Cache mapper that uses the basename of the remote URL.
+
+    Different paths with the same basename will therefore have the same cached
+    basename.
+    """
+
+    def __call__(self, path: str) -> str:
+        return os.path.basename(path)
+
+
+class HashCacheMapper(AbstractCacheMapper):
+    """Cache mapper that uses a hash of the remote URL."""
+
+    def __call__(self, path: str) -> str:
+        return hashlib.sha256(path.encode()).hexdigest()
+
+
+def create_cache_mapper(same_names: bool) -> AbstractCacheMapper:
+    """Factory method to create cache mapper for backward compatibility with
+    ``CachingFileSystem`` constructor using ``same_names`` kwarg.
+    """
+    if same_names:
+        return BasenameCacheMapper()
+    else:
+        return HashCacheMapper()

fsspec/implementations/cached.py

@@ -1,21 +1,21 @@
 from __future__ import annotations
 
 import contextlib
-import hashlib
 import inspect
 import logging
 import os
 import pickle
 import tempfile
 import time
 from shutil import rmtree
-from typing import ClassVar
+from typing import Any, ClassVar
 
 from fsspec import AbstractFileSystem, filesystem
 from fsspec.callbacks import _DEFAULT_CALLBACK
 from fsspec.compression import compr
 from fsspec.core import BaseCache, MMapCache
 from fsspec.exceptions import BlocksizeMismatchError
+from fsspec.implementations.cache_mapper import create_cache_mapper
 from fsspec.spec import AbstractBufferedFile
 from fsspec.utils import infer_compression
 
@@ -115,9 +115,7 @@ def __init__(
         self.check_files = check_files
         self.expiry = expiry_time
         self.compression = compression
-        # TODO: same_names should allow for variable prefix, not only
-        #  to keep the basename
-        self.same_names = same_names
+        self._mapper = create_cache_mapper(same_names)
         self.target_protocol = (
             target_protocol
             if isinstance(target_protocol, str)
@@ -255,11 +253,12 @@ def clear_expired_cache(self, expiry_time=None):
 
         for path, detail in self.cached_files[-1].copy().items():
             if time.time() - detail["time"] > expiry_time:
-                if self.same_names:
-                    basename = os.path.basename(detail["original"])
-                    fn = os.path.join(self.storage[-1], basename)
-                else:
-                    fn = os.path.join(self.storage[-1], detail["fn"])
+                fn = detail.get("fn", "")
+                if not fn:
+                    raise RuntimeError(
+                        f"Cache metadata does not contain 'fn' for {path}"
+                    )
+                fn = os.path.join(self.storage[-1], fn)
                 if os.path.exists(fn):
                     os.remove(fn)
                     self.cached_files[-1].pop(path)
@@ -339,7 +338,7 @@ def _open(
             # TODO: action where partial file exists in read-only cache
             logger.debug("Opening partially cached copy of %s" % path)
         else:
-            hash = self.hash_name(path, self.same_names)
+            hash = self._mapper(path)
             fn = os.path.join(self.storage[-1], hash)
             blocks = set()
             detail = {
@@ -385,8 +384,10 @@ def _open(
         self.save_cache()
         return f
 
-    def hash_name(self, path, same_name):
-        return hash_name(path, same_name=same_name)
+    def hash_name(self, path: str, *args: Any) -> str:
+        # Kept for backward compatibility with downstream libraries.
+        # Ignores extra arguments, previously same_name boolean.
+        return self._mapper(path)
 
     def close_and_update(self, f, close):
         """Called when a file is closing, so store the set of blocks"""
@@ -488,7 +489,7 @@ def __eq__(self, other):
             and self.check_files == other.check_files
             and self.expiry == other.expiry
             and self.compression == other.compression
-            and self.same_names == other.same_names
+            and self._mapper == other._mapper
             and self.target_protocol == other.target_protocol
         )
 
@@ -501,7 +502,7 @@ def __hash__(self):
             ^ hash(self.check_files)
             ^ hash(self.expiry)
             ^ hash(self.compression)
-            ^ hash(self.same_names)
+            ^ hash(self._mapper)
             ^ hash(self.target_protocol)
         )
 
@@ -546,7 +547,7 @@ def open_many(self, open_files):
         details = [self._check_file(sp) for sp in paths]
         downpath = [p for p, d in zip(paths, details) if not d]
         downfn0 = [
-            os.path.join(self.storage[-1], self.hash_name(p, self.same_names))
+            os.path.join(self.storage[-1], self._mapper(p))
             for p, d in zip(paths, details)
         ]  # keep these path names for opening later
         downfn = [fn for fn, d in zip(downfn0, details) if not d]
@@ -558,7 +559,7 @@ def open_many(self, open_files):
             newdetail = [
                 {
                     "original": path,
-                    "fn": self.hash_name(path, self.same_names),
+                    "fn": self._mapper(path),
                     "blocks": True,
                     "time": time.time(),
                     "uid": self.fs.ukey(path),
@@ -590,7 +591,7 @@ def commit_many(self, open_files):
                 pass
 
     def _make_local_details(self, path):
-        hash = self.hash_name(path, self.same_names)
+        hash = self._mapper(path)
         fn = os.path.join(self.storage[-1], hash)
         detail = {
             "original": path,
@@ -731,7 +732,7 @@ def __init__(self, **kwargs):
 
     def _check_file(self, path):
         self._check_cache()
-        sha = self.hash_name(path, self.same_names)
+        sha = self._mapper(path)
         for storage in self.storage:
             fn = os.path.join(storage, sha)
             if os.path.exists(fn):
@@ -752,7 +753,7 @@ def _open(self, path, mode="rb", **kwargs):
         if fn:
             return open(fn, mode)
 
-        sha = self.hash_name(path, self.same_names)
+        sha = self._mapper(path)
         fn = os.path.join(self.storage[-1], sha)
         logger.debug("Copying %s to local cache" % path)
         kwargs["mode"] = mode
@@ -838,14 +839,6 @@ def __getattr__(self, item):
         return getattr(self.fh, item)
 
 
-def hash_name(path, same_name):
-    if same_name:
-        hash = os.path.basename(path)
-    else:
-        hash = hashlib.sha256(path.encode()).hexdigest()
-    return hash
-
-
 @contextlib.contextmanager
 def atomic_write(path, mode="wb"):
     """

fsspec/implementations/tests/test_cached.py

@@ -8,7 +8,9 @@
 import fsspec
 from fsspec.compression import compr
 from fsspec.exceptions import BlocksizeMismatchError
+from fsspec.implementations.cache_mapper import create_cache_mapper
 from fsspec.implementations.cached import CachingFileSystem, LocalTempFile
+from fsspec.implementations.local import make_path_posix
 
 from .test_ftp import FTPFileSystem
 
@@ -32,6 +34,61 @@ def local_filecache():
     return data, original_file, cache_location, fs
 
 
+def test_mapper():
+    mapper0 = create_cache_mapper(True)
+    assert mapper0("/somedir/somefile") == "somefile"
+    assert mapper0("/otherdir/somefile") == "somefile"
+
+    mapper1 = create_cache_mapper(False)
+    assert (
+        mapper1("/somedir/somefile")
+        == "67a6956e5a5f95231263f03758c1fd9254fdb1c564d311674cec56b0372d2056"
+    )
+    assert (
+        mapper1("/otherdir/somefile")
+        == "f043dee01ab9b752c7f2ecaeb1a5e1b2d872018e2d0a1a26c43835ebf34e7d3e"
+    )
+
+    assert mapper0 != mapper1
+    assert create_cache_mapper(True) == mapper0
+    assert create_cache_mapper(False) == mapper1
+
+    assert hash(mapper0) != hash(mapper1)
+    assert hash(create_cache_mapper(True)) == hash(mapper0)
+    assert hash(create_cache_mapper(False)) == hash(mapper1)
+
+
+@pytest.mark.parametrize("same_names", [False, True])
+def test_metadata(tmpdir, same_names):
+    source = os.path.join(tmpdir, "source")
+    afile = os.path.join(source, "afile")
+    os.mkdir(source)
+    open(afile, "w").write("test")
+
+    fs = fsspec.filesystem(
+        "filecache",
+        target_protocol="file",
+        cache_storage=os.path.join(tmpdir, "cache"),
+        same_names=same_names,
+    )
+
+    with fs.open(afile, "rb") as f:
+        assert f.read(5) == b"test"
+
+    afile_posix = make_path_posix(afile)
+    detail = fs.cached_files[0][afile_posix]
+    assert sorted(detail.keys()) == ["blocks", "fn", "original", "time", "uid"]
+    assert isinstance(detail["blocks"], bool)
+    assert isinstance(detail["fn"], str)
+    assert isinstance(detail["time"], float)
+    assert isinstance(detail["uid"], str)
+
+    assert detail["original"] == afile_posix
+    assert detail["fn"] == fs._mapper(afile_posix)
+    if same_names:
+        assert detail["fn"] == "afile"
+
+
 def test_idempotent():
     fs = CachingFileSystem("file")
     fs2 = CachingFileSystem("file")
@@ -154,7 +211,7 @@ def test_clear():
 
 
 def test_clear_expired(tmp_path):
-    def __ager(cache_fn, fn):
+    def __ager(cache_fn, fn, del_fn=False):
         """
         Modify the cache file to virtually add time lag to selected files.
 
@@ -164,6 +221,8 @@ def __ager(cache_fn, fn):
             cache path
         fn: str
             file name to be modified
+        del_fn: bool
+            whether or not to delete 'fn' from cache details
         """
         import pathlib
         import time
@@ -174,6 +233,8 @@ def __ager(cache_fn, fn):
                 fn_posix = pathlib.Path(fn).as_posix()
                 cached_files[fn_posix]["time"] = cached_files[fn_posix]["time"] - 691200
             assert os.access(cache_fn, os.W_OK), "Cache is not writable"
+            if del_fn:
+                del cached_files[fn_posix]["fn"]
             with open(cache_fn, "wb") as f:
                 pickle.dump(cached_files, f)
             time.sleep(1)
@@ -255,6 +316,22 @@ def __ager(cache_fn, fn):
     fs.clear_expired_cache()
     assert not fs._check_file(str(f4))
 
+    # check cache metadata lacking 'fn' raises RuntimeError.
+    fs = fsspec.filesystem(
+        "filecache",
+        target_protocol="file",
+        cache_storage=str(cache1),
+        same_names=True,
+        cache_check=1,
+    )
+    assert fs.cat(str(f1)) == data
+
+    cache_fn = os.path.join(fs.storage[-1], "cache")
+    __ager(cache_fn, f1, del_fn=True)
+
+    with pytest.raises(RuntimeError, match="Cache metadata does not contain 'fn' for"):
+        fs.clear_expired_cache()
+
 
 def test_pop():
     import tempfile

fsspec/tests/test_api.py

@@ -308,6 +308,7 @@ def test_chained_equivalent():
     #  since the parameters don't quite match. Also, the url understood by the two
     #  of s are not the same (path gets munged a bit differently)
     assert of.fs == of2.fs
+    assert hash(of.fs) == hash(of2.fs)
     assert of.open().read() == of2.open().read()