Keep negative-size range reads within the selected range

b2sdk/_internal/stream/range.py

@@ -63,7 +63,7 @@ def read(self, size=None):
         :rtype: bytes
         """
         remaining = max(0, self.length - self.relative_pos)
-        if size is None:
+        if size is None or size < 0:
             to_read = remaining
         else:
             to_read = min(size, remaining)

changelog.d/+range-negative-read.fixed.md

@@ -0,0 +1 @@
+Keep negative-size reads of `RangeOfInputStream` within the selected range, including empty and exhausted ranges.

test/unit/stream/test_range.py

@@ -0,0 +1,42 @@
+######################################################################
+#
+# File: test/unit/stream/test_range.py
+#
+# Copyright 2026 Backblaze Inc. All Rights Reserved.
+#
+# License https://www.backblaze.com/using_b2_code.html
+#
+######################################################################
+import io
+
+import pytest
+
+from b2sdk.v3 import RangeOfInputStream
+
+
+@pytest.mark.parametrize('size', [-1, -2, None, 99])
+@pytest.mark.parametrize('already_read', [0, 1, 3])
+def test_read_all_stays_within_range(size, already_read):
+    with RangeOfInputStream(io.BytesIO(b'0123456789'), offset=2, length=3) as stream:
+        assert stream.read(already_read) == b'234'[:already_read]
+        assert stream.read(size) == b'234'[already_read:]
+        assert stream.tell() == 3
+        assert stream.read(size) == b''
+        assert stream.tell() == 3
+
+
+def test_negative_read_of_empty_range_does_not_consume_source():
+    with RangeOfInputStream(io.BytesIO(b'0123456789'), offset=2, length=0) as stream:
+        assert stream.read(-1) == b''
+        assert stream.tell() == 0
+        assert stream.stream.tell() == 2
+
+
+def test_zero_and_bounded_reads_preserve_position():
+    with RangeOfInputStream(io.BytesIO(b'0123456789'), offset=2, length=3) as stream:
+        assert stream.read(0) == b''
+        assert stream.tell() == 0
+        assert stream.read(2) == b'23'
+        assert stream.tell() == 2
+        assert stream.read(2) == b'4'
+        assert stream.tell() == 3