bpo-18819: tarfile: only set device fields for device files (GH-18080)
The GNU docs describe the `devmajor` and `devminor` fields of the tar
header struct only in the context of character and block special files,
suggesting that in other cases they are not populated. Typical utilities
behave accordingly; this patch teaches `tarfile` to do the same.
diff --git a/Lib/tarfile.py b/Lib/tarfile.py
index 90a2c95..e2b6053 100755
--- a/Lib/tarfile.py
+++ b/Lib/tarfile.py
@@ -930,6 +930,14 @@
"""Return a header block. info is a dictionary with file
information, format must be one of the *_FORMAT constants.
"""
+ has_device_fields = info.get("type") in (CHRTYPE, BLKTYPE)
+ if has_device_fields:
+ devmajor = itn(info.get("devmajor", 0), 8, format)
+ devminor = itn(info.get("devminor", 0), 8, format)
+ else:
+ devmajor = stn("", 8, encoding, errors)
+ devminor = stn("", 8, encoding, errors)
+
parts = [
stn(info.get("name", ""), 100, encoding, errors),
itn(info.get("mode", 0) & 0o7777, 8, format),
@@ -943,8 +951,8 @@
info.get("magic", POSIX_MAGIC),
stn(info.get("uname", ""), 32, encoding, errors),
stn(info.get("gname", ""), 32, encoding, errors),
- itn(info.get("devmajor", 0), 8, format),
- itn(info.get("devminor", 0), 8, format),
+ devmajor,
+ devminor,
stn(info.get("prefix", ""), 155, encoding, errors)
]
diff --git a/Lib/test/test_tarfile.py b/Lib/test/test_tarfile.py
index 6a90108..cae9680 100644
--- a/Lib/test/test_tarfile.py
+++ b/Lib/test/test_tarfile.py
@@ -1549,6 +1549,52 @@
("longlnk/" * 127) + "longlink_")
+class DeviceHeaderTest(WriteTestBase, unittest.TestCase):
+
+ prefix = "w:"
+
+ def test_headers_written_only_for_device_files(self):
+ # Regression test for bpo-18819.
+ tempdir = os.path.join(TEMPDIR, "device_header_test")
+ os.mkdir(tempdir)
+ try:
+ tar = tarfile.open(tmpname, self.mode)
+ try:
+ input_blk = tarfile.TarInfo(name="my_block_device")
+ input_reg = tarfile.TarInfo(name="my_regular_file")
+ input_blk.type = tarfile.BLKTYPE
+ input_reg.type = tarfile.REGTYPE
+ tar.addfile(input_blk)
+ tar.addfile(input_reg)
+ finally:
+ tar.close()
+
+ # devmajor and devminor should be *interpreted* as 0 in both...
+ tar = tarfile.open(tmpname, "r")
+ try:
+ output_blk = tar.getmember("my_block_device")
+ output_reg = tar.getmember("my_regular_file")
+ finally:
+ tar.close()
+ self.assertEqual(output_blk.devmajor, 0)
+ self.assertEqual(output_blk.devminor, 0)
+ self.assertEqual(output_reg.devmajor, 0)
+ self.assertEqual(output_reg.devminor, 0)
+
+ # ...but the fields should not actually be set on regular files:
+ with open(tmpname, "rb") as infile:
+ buf = infile.read()
+ buf_blk = buf[output_blk.offset:output_blk.offset_data]
+ buf_reg = buf[output_reg.offset:output_reg.offset_data]
+ # See `struct posixheader` in GNU docs for byte offsets:
+ # <https://www.gnu.org/software/tar/manual/html_node/Standard.html>
+ device_headers = slice(329, 329 + 16)
+ self.assertEqual(buf_blk[device_headers], b"0000000\0" * 2)
+ self.assertEqual(buf_reg[device_headers], b"\0" * 16)
+ finally:
+ support.rmtree(tempdir)
+
+
class CreateTest(WriteTestBase, unittest.TestCase):
prefix = "x:"
diff --git a/Misc/ACKS b/Misc/ACKS
index 5a77983..9334020 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -286,6 +286,7 @@
Greg Chapman
Mitch Chapman
Matt Chaput
+William Chargin
Yogesh Chaudhari
David Chaum
Nicolas Chauvat
diff --git a/Misc/NEWS.d/next/Library/2020-01-20-10-06-19.bpo-18819.H4qsoS.rst b/Misc/NEWS.d/next/Library/2020-01-20-10-06-19.bpo-18819.H4qsoS.rst
new file mode 100644
index 0000000..e9f111a
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-01-20-10-06-19.bpo-18819.H4qsoS.rst
@@ -0,0 +1,3 @@
+Omit ``devmajor`` and ``devminor`` fields for non-device files in
+:mod:`tarfile` archives, enabling bit-for-bit compatibility with GNU
+``tar(1)``.