gh-75955: tarfile: Allow configuring the record size

Doc/library/tarfile.rst

@@ -368,7 +368,7 @@ be finalized; only the internally used file object will be closed. See the
 .. versionadded:: 3.2
    Added support for the context management protocol.
 
-.. class:: TarFile(name=None, mode='r', fileobj=None, format=DEFAULT_FORMAT, tarinfo=TarInfo, dereference=False, ignore_zeros=False, encoding=ENCODING, errors='surrogateescape', pax_headers=None, debug=0, errorlevel=1, stream=False)
+.. class:: TarFile(name=None, mode='r', fileobj=None, format=DEFAULT_FORMAT, tarinfo=TarInfo, dereference=False, ignore_zeros=False, encoding=ENCODING, errors='surrogateescape', pax_headers=None, debug=0, errorlevel=1, stream=False, blocking_factor=None)
 
    All following arguments are optional and can be accessed as instance attributes
    as well.
@@ -422,6 +422,11 @@ be finalized; only the internally used file object will be closed. See the
    If *stream* is set to :const:`True` then while reading the archive info about files
    in the archive are not cached, saving memory.
 
+   If *blocking_factor* is given, the record size will be blocking_factor * 512 bytes.
+   After writing to an archive, the size will be padded with zeros to an integer number
+   of records. The default blocking factor is 20, corresponding to a record size of
+   10240 bytes.
+
    .. versionchanged:: 3.2
       Use ``'surrogateescape'`` as the default for the *errors* argument.
 
@@ -434,6 +439,9 @@ be finalized; only the internally used file object will be closed. See the
    .. versionchanged:: 3.13
       Add the *stream* parameter.
 
+   .. versionchanged:: 3.14
+      Add the *blocking_factor* parameter.
+
 .. classmethod:: TarFile.open(...)
 
    Alternative constructor. The :func:`tarfile.open` function is actually a

Lib/tarfile.py

@@ -1691,10 +1691,13 @@ class TarFile(object):
 
     extraction_filter = None    # The default filter for extraction.
 
+    record_size = RECORDSIZE    # The default record size, matches tar -b20
+
     def __init__(self, name=None, mode="r", fileobj=None, format=None,
             tarinfo=None, dereference=None, ignore_zeros=None, encoding=None,
             errors="surrogateescape", pax_headers=None, debug=None,
-            errorlevel=None, copybufsize=None, stream=False):
+            errorlevel=None, copybufsize=None, stream=False,
+            blocking_factor=None):
         """Open an (uncompressed) tar archive 'name'. 'mode' is either 'r' to
            read from an existing archive, 'a' to append data to an existing
            file or 'w' to create a new file overwriting an existing one. 'mode'
@@ -1750,6 +1753,8 @@ def __init__(self, name=None, mode="r", fileobj=None, format=None,
             self.debug = debug
         if errorlevel is not None:
             self.errorlevel = errorlevel
+        if blocking_factor is not None:
+            self.record_size = BLOCKSIZE * blocking_factor
 
         # Init datastructures.
         self.copybufsize = copybufsize
@@ -2024,9 +2029,9 @@ def close(self):
                 self.offset += (BLOCKSIZE * 2)
                 # fill up the end with zero-blocks
                 # (like option -b20 for tar does)
-                blocks, remainder = divmod(self.offset, RECORDSIZE)
+                blocks, remainder = divmod(self.offset, self.record_size)
                 if remainder > 0:
-                    self.fileobj.write(NUL * (RECORDSIZE - remainder))
+                    self.fileobj.write(NUL * (self.record_size - remainder))
         finally:
             if not self._extfileobj:
                 self.fileobj.close()
@@ -2882,6 +2887,8 @@ def main():
     parser.add_argument('--filter', metavar='<filtername>',
                         choices=_NAMED_FILTERS,
                         help='Filter for extraction')
+    parser.add_argument('--blocking-factor', metavar='<blocking_factor>', type=int,
+                       help='blocking_factor x 512 bytes per record, defaults to 20')
 
     group = parser.add_mutually_exclusive_group(required=True)
     group.add_argument('-l', '--list', metavar='<tarfile>',
@@ -2899,6 +2906,8 @@ def main():
 
     if args.filter and args.extract is None:
         parser.exit(1, '--filter is only valid for extraction\n')
+    if args.blocking_factor and args.create is None:
+        parser.exit(1, '--blocking-factor is only valid for creation\n')
 
     if args.test is not None:
         src = args.test
@@ -2960,7 +2969,8 @@ def main():
         tar_mode = 'w:' + compressions[ext] if ext in compressions else 'w'
         tar_files = args.create
 
-        with TarFile.open(tar_name, tar_mode) as tf:
+        with TarFile.open(tar_name, tar_mode,
+                          blocking_factor=args.blocking_factor) as tf:
             for file_name in tar_files:
                 tf.add(file_name)
 

Lib/test/test_tarfile.py

@@ -1651,6 +1651,22 @@ def test_missing_fileobj(self):
             with self.assertRaises(ValueError):
                 tar.addfile(tarinfo)
 
+    def test_archive_size(self):
+        # Make sure the archive size is a multiple of the configured
+        # record size
+        for blocking_factor, record_size, records in (
+                (None, tarfile.RECORDSIZE, 1), (1, 512, 4), (2, 1024, 2),
+                (20, 10240, 1), (200, 102400, 1)):
+            tar = tarfile.open(tmpname, self.mode, blocking_factor=blocking_factor)
+            self.assertEqual(tar.record_size, record_size)
+            t = tarfile.TarInfo("foo")
+            t.size = tarfile.BLOCKSIZE
+            tar.addfile(t, io.BytesIO(b"a" * t.size))
+            tar.close()
+
+            with self.open(tmpname, "rb") as fobj:
+                self.assertEqual(len(fobj.read()), record_size * records)
+
 
 class GzipWriteTest(GzipTest, WriteTest):
     pass
@@ -2843,6 +2859,29 @@ def test_create_command_compressed(self):
             finally:
                 os_helper.unlink(tar_name)
 
+    def test_create_command_blocking_factor(self):
+        files = [support.findfile('tokenize_tests.txt',
+                                  subdir='tokenizedata'),
+                 support.findfile('tokenize_tests-no-coding-cookie-'
+                                  'and-utf8-bom-sig-only.txt',
+                                  subdir='tokenizedata')]
+        for opt in '-c', '--create':
+            for blocking_factor, archive_size in (
+                    (1, tarfile.BLOCKSIZE*15),
+                    (20, tarfile.BLOCKSIZE*20),
+                    (100, tarfile.BLOCKSIZE*100)):
+                try:
+                    out = self.tarfilecmd("--blocking-factor", str(blocking_factor),
+                                          opt, tmpname, *files)
+                    self.assertEqual(out, b'')
+                    self.assertEqual(out, b'')
+                    with tarfile.open(tmpname) as tar:
+                        tar.getmembers()
+                    with io.FileIO(tmpname, "rb") as fobj:
+                        self.assertEqual(len(fobj.read()), archive_size)
+                finally:
+                    os_helper.unlink(tmpname)
+
     def test_extract_command(self):
         self.make_simple_tarfile(tmpname)
         for opt in '-e', '--extract':

Misc/ACKS

@@ -1271,6 +1271,7 @@ Paul Monson
 The Dragon De Monsyne
 Bastien Montagne
 Skip Montanaro
+Erik Montnémery
 Peter Moody
 HyunKyun Moon
 Alan D. Moore