Revert unrelated changes.

Author: serhiy-storchaka

Lib/tarfile.py

@@ -490,27 +490,25 @@ def _init_read_gz(self):
         # taken from gzip.GzipFile with some alterations
         if self.__read(2) != b"\037\213":
             raise ReadError("not a gzip file")
-        method, flag = struct.unpack("<BB6x", self.__read(8))
-        if method != 8:
+        if self.__read(1) != b"\010":
             raise CompressionError("unsupported compression method")
 
-        # process FEXTRA
+        flag = ord(self.__read(1))
+        self.__read(6)
+
         if flag & 4:
-            extra_len, = struct.unpack("<H", self.__read(2))
-            self.__read(extra_len)
-        # process FNAME
+            xlen = ord(self.__read(1)) + 256 * ord(self.__read(1))
+            self.__read(xlen)
         if flag & 8:
             while True:
                 s = self.__read(1)
-                if not s or s == b'\000':
+                if not s or s == NUL:
                     break
-        # process FCOMMENT
         if flag & 16:
             while True:
                 s = self.__read(1)
-                if not s or s == b'\000':
+                if not s or s == NUL:
                     break
-        # process FHCRC
         if flag & 2:
             self.__read(2)