Fit cached FSs better with async backends (#1429)

* Fit cached FSs better with async backends

* Add test

Author: martindurant

fsspec/implementations/cached.py

@@ -393,6 +393,7 @@ def __getattribute__(self, item):
             "open",
             "cat",
             "cat_file",
+            "cat_ranges",
             "get",
             "read_block",
             "tail",
@@ -715,6 +716,17 @@ def save_cache(self):
     def load_cache(self):
         pass
 
+    def cat_ranges(
+        self, paths, starts, ends, max_gap=None, on_error="return", **kwargs
+    ):
+        lpaths = [self._check_file(p) for p in paths]
+        rpaths = [p for l, p in zip(lpaths, paths) if l is False]
+        lpaths = [l for l, p in zip(lpaths, paths) if l is False]
+        self.fs.get(rpaths, lpaths)
+        return super().cat_ranges(
+            paths, starts, ends, max_gap=max_gap, on_error=on_error, **kwargs
+        )
+
     def _open(self, path, mode="rb", **kwargs):
         path = self._strip_protocol(path)
 

fsspec/implementations/reference.py

@@ -624,7 +624,7 @@ def __init__(
                 **(ref_storage_args or target_options or {}), protocol=target_protocol
             )
             ref_fs, fo2 = fsspec.core.url_to_fs(fo, **dic)
-            if ref_fs.isfile(fo):
+            if ref_fs.isfile(fo2):
                 # text JSON
                 with fsspec.open(fo, "rb", **dic) as f:
                     logger.info("Read reference from URL %s", fo)

fsspec/implementations/tests/test_reference.py

@@ -621,3 +621,30 @@ def test_mapping_getitems(m):
     fs = fsspec.filesystem("reference", fo=refs, fs=h)
     mapping = fs.get_mapper("")
     assert mapping.getitems(["b", "a"]) == {"a": b"A", "b": b"B"}
+
+
+def test_cached(m, tmpdir):
+    fn = f"{tmpdir}/ref.json"
+
+    m.pipe({"a": b"A", "b": b"B"})
+    m.pipe("ref.json", b"""{"a": ["a"], "b": ["b"]}""")
+
+    fs = fsspec.filesystem(
+        "reference",
+        fo="simplecache::memory://ref.json",
+        fs=m,
+        target_options={"cache_storage": str(tmpdir), "same_names": True},
+    )
+    assert fs.cat("a") == b"A"
+    assert os.path.exists(fn)
+
+    # truncate original file to show we are loading from the cached version
+    m.pipe("ref.json", b"")
+    fs = fsspec.filesystem(
+        "reference",
+        fo="simplecache::memory://ref.json",
+        fs=m,
+        target_options={"cache_storage": str(tmpdir), "same_names": True},
+        skip_instance_cache=True,
+    )
+    assert fs.cat("a") == b"A"