fix: close file handle in get_file_taste using a with statement

`get_file_taste` opened a file handle with `sample_path.open("rb").read(8)`,
discarding the file object without explicitly closing it. CPython reference-
counting closes it promptly in practice, but other implementations (PyPy,
Jython) and CPython under GC pressure may defer closure. Use a `with` statement
to guarantee the handle is released immediately after reading.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CHANGELOG.md

@@ -11,6 +11,7 @@
 -
 
 ### Bug Fixes
+- fix: close file handle in get_file_taste using a with statement @williballenthin
 - fix: correct off-by-one in dynamic analysis call_count debug log (enumerate -> explicit counter) @williballenthin
 - fix: correct capa/subscope-rule key in RuleMetadata so is_subscope_rule is no longer always False @williballenthin
 - fix: remove unreachable backports.functools_lru_cache fallback and dead dependency @williballenthin

capa/helpers.py

@@ -88,8 +88,8 @@ def hex(n: int) -> str:
 def get_file_taste(sample_path: Path) -> bytes:
     if not sample_path.exists():
         raise IOError(f"sample path {sample_path} does not exist or cannot be accessed")
-    taste = sample_path.open("rb").read(8)
-    return taste
+    with sample_path.open("rb") as f:
+        return f.read(8)
 
 
 def is_runtime_ida():

tests/test_helpers.py

@@ -14,10 +14,13 @@
 
 
 import codecs
+import tempfile
 from pathlib import Path
 
+import pytest
+
 import capa.helpers
-from capa.helpers import get_format_from_extension
+from capa.helpers import get_file_taste, get_format_from_extension
 from capa.features.common import (
     FORMAT_ELF,
     FORMAT_SC32,
@@ -101,3 +104,20 @@ def test_get_format_from_extension():
     assert get_format_from_extension(Path("sample.BinExport2")) == FORMAT_BINEXPORT2
     assert get_format_from_extension(Path("sample.bndb")) == FORMAT_BINJA_DB
     assert get_format_from_extension(Path("sample.exe")) == FORMAT_UNKNOWN
+
+
+def test_get_file_taste_reads_first_bytes():
+    with tempfile.NamedTemporaryFile(delete=False) as tmp:
+        tmp.write(b"\x4d\x5a\x90\x00\x01\x02\x03\x04\xff\xfe")
+        tmp_path = Path(tmp.name)
+    try:
+        taste = get_file_taste(tmp_path)
+        assert taste == b"\x4d\x5a\x90\x00\x01\x02\x03\x04"
+        assert len(taste) == 8
+    finally:
+        tmp_path.unlink()
+
+
+def test_get_file_taste_missing_file_raises():
+    with pytest.raises(IOError):
+        get_file_taste(Path("/nonexistent/path/sample.exe"))