From a62abf3a30a54abd85137c0f3c9517f622a0d773 Mon Sep 17 00:00:00 2001
From: Philipp Gesang <philipp.gesang@intra2net.com>
Date: Thu, 6 Apr 2017 15:09:10 +0200
Subject: [PATCH] prefer symbolic constants over literals referring to gzip header

The mixed use of hex and octal is pretty confusing to say the
least, use named constants instead that are defined only in
tarfile.
---
 deltatar/tarfile.py             |    9 ++++++---
 rescue_tar.py                   |    2 +-
 testing/test_concat_compress.py |    6 +++---
 3 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/deltatar/tarfile.py b/deltatar/tarfile.py
index bf1f03a..4143821 100644
--- a/deltatar/tarfile.py
+++ b/deltatar/tarfile.py
@@ -124,6 +124,9 @@ GZ_METHOD_DEFLATE    = 0x08 # 0o10
 GZ_FLAG_ORIG_NAME    = 0x08 # 0o10, default in gzip
 GZ_DEFLATE_FLAGS     = 0x00 # 0o00, never read (deflate.c)
 GZ_OS_CODE           = 0x03 # 0o03, default in gzip (tailor.h)
+GZ_MAGIC_BYTES       = struct.pack ("<BB", GZ_MAGIC [0], GZ_MAGIC [1])
+GZ_MAGIC_DEFLATE     = struct.pack ("<BBB", GZ_MAGIC [0], GZ_MAGIC [1],
+                                    GZ_METHOD_DEFLATE)
 
 #---------------------------------------------------------
 # tarfile constants
@@ -378,7 +381,6 @@ class _LowLevelFile:
         self.offset = pos
 
 
-
 def gz_header (name=None):
     timestamp = int(time.time())
     flags     = 0x0
@@ -404,6 +406,7 @@ def gz_header (name=None):
 
     return hdr + name
 
+
 class _Stream:
     """Class that serves as an adapter between TarFile and
        a stream-like object.  The stream-like object only
@@ -733,7 +736,7 @@ class _Stream:
 
         # taken from gzip.GzipFile with some alterations
         read2 = self.__read(2)
-        if read2 != b"\037\213":
+        if read2 != GZ_MAGIC_BYTES:
             raise ReadError("not a gzip file")
 
         read1 = self.__read(1)
@@ -963,7 +966,7 @@ class _StreamProxy(object):
         return self.buf
 
     def getcomptype(self):
-        if self.buf.startswith(b"\x1f\x8b\x08"):
+        if self.buf.startswith(GZ_MAGIC_DEFLATE):
             return "gz"
         elif self.buf[0:3] == b"BZh" and self.buf[4:10] == b"1AY&SY":
             return "bz2"
diff --git a/rescue_tar.py b/rescue_tar.py
index 7ff1f55..6ddd83a 100644
--- a/rescue_tar.py
+++ b/rescue_tar.py
@@ -76,7 +76,7 @@ def rescue(tar_files, rescue_dir=None):
 
         # split in compressed chunks
         for f in tar_files:
-            filesplit.split_file(b'\x1f\x8b',
+            filesplit.split_file(tarfile.GZ_MAGIC_BYTES,
                 os.path.join(rescue_dir, base_name), f, new_gz)
 
     # includes volumes already extracted with new_volume_handler
diff --git a/testing/test_concat_compress.py b/testing/test_concat_compress.py
index ea425af..56f58e0 100644
--- a/testing/test_concat_compress.py
+++ b/testing/test_concat_compress.py
@@ -17,7 +17,7 @@
 
 import os, unittest, hashlib, string
 
-from deltatar.tarfile import TarFile, GNU_FORMAT
+from deltatar.tarfile import TarFile, GNU_FORMAT, GZ_MAGIC_BYTES
 
 import filesplit
 from . import BaseTest, new_volume_handler
@@ -337,7 +337,7 @@ class ConcatCompressTest(BaseTest):
         os.unlink("small")
         os.unlink("small2")
 
-        filesplit.split_file(b'\x1f\x8b', "sample.tar.gz.", "sample.tar.gz")
+        filesplit.split_file(GZ_MAGIC_BYTES, "sample.tar.gz.", "sample.tar.gz")
 
         assert os.path.exists("sample.tar.gz.0") # beginning of the tar file
         assert os.path.exists("sample.tar.gz.1") # first file
@@ -439,7 +439,7 @@ class ConcatCompressTest(BaseTest):
         os.unlink("small2")
 
         # equivalent to $ python filesplit.py -s $'\x1f\x8b' -p sample.tar.gz. sample.tar.gz
-        filesplit.split_file(b'\x1f\x8b', "sample.tar.gz.", "sample.tar.gz")
+        filesplit.split_file(GZ_MAGIC_BYTES, "sample.tar.gz.", "sample.tar.gz")
 
         assert os.path.exists("sample.tar.gz.0") # beginning of the tar file
         assert os.path.exists("sample.tar.gz.1") # first file
-- 
1.7.1