Return empty HTTP ranges when the start is omitted

docs/source/changelog.rst

@@ -12,6 +12,8 @@ Enhancements
 
 Fixes
 
+- Return empty results for HTTP reads ending at offset zero without sending an invalid range request.
+
 - Correct the configuration directory variable and explain JSON parsing of environment overrides (#2324)
 
 - Update contributor linting and formatting instructions for Ruff and pre-commit (#2325)

fsspec/implementations/http.py

@@ -348,7 +348,7 @@ async def _cat_file(self, url, start=None, end=None, **kwargs):
         logger.debug(url)
 
         if start is not None or end is not None:
-            if start == end:
+            if start == end or (start is None and end == 0):
                 return b""
             headers = kw.pop("headers", {}).copy()
 

fsspec/implementations/http_sync.py

@@ -365,7 +365,7 @@ def cat_file(self, url, start=None, end=None, **kwargs):
         logger.debug(url)
 
         if start is not None or end is not None:
-            if start == end:
+            if start == end or (start is None and end == 0):
                 return b""
             headers = kw.pop("headers", {}).copy()
 

fsspec/implementations/tests/test_http.py

@@ -650,6 +650,14 @@ def test_cat_file_range(server):
     assert h.cat(urla, end=-10) == data[:-10]
 
 
+@pytest.mark.parametrize("start,end", [(None, 0), (0, 0), (1, 1), (-1, -1)])
+def test_cat_file_empty_range_does_not_make_request(server, reset_faults, start, end):
+    h = fsspec.filesystem("http", skip_instance_cache=True)
+
+    assert h.cat_file(server.realfile, start=start, end=end) == b""
+    assert HTTPTestHandler.get_counts.get("/index/realfile", 0) == 0
+
+
 def test_cat_file_range_numpy(server):
     np = pytest.importorskip("numpy")
     h = fsspec.filesystem("http", headers={"give_length": "true", "head_ok": "true"})

fsspec/implementations/tests/test_http_sync.py

@@ -6,7 +6,15 @@
 import pytest
 
 import fsspec.utils
-from fsspec.tests.conftest import data, requests, reset_files, server, win  # noqa: F401
+from fsspec.tests.conftest import (  # noqa: F401
+    HTTPTestHandler,
+    data,
+    requests,
+    reset_faults,
+    reset_files,
+    server,
+    win,
+)
 
 
 @pytest.fixture()
@@ -417,6 +425,16 @@ def test_cat_file_range(server, sync):
     assert h.cat(urla, end=-10) == data[:-10]
 
 
+@pytest.mark.parametrize("start,end", [(None, 0), (0, 0), (1, 1), (-1, -1)])
+def test_cat_file_empty_range_does_not_make_request(
+    server, sync, reset_faults, start, end
+):
+    h = fsspec.filesystem("http", skip_instance_cache=True)
+
+    assert h.cat_file(server.realfile, start=start, end=end) == b""
+    assert HTTPTestHandler.get_counts.get("/index/realfile", 0) == 0
+
+
 def test_mcat_cache(server, sync):
     urla = server.address + "/index/realfile"
     urlb = server.address + "/index/otherfile"