Fix gzip header

Author: rhpvorderman

src/isal/igzip.py

@@ -123,15 +123,19 @@ def __repr__(self):
     def flush(self, zlib_mode=isal_zlib.Z_SYNC_FLUSH):
         super().flush(zlib_mode)
 
-    def _write_gzip_header(self, compresslevel):
+    def _write_gzip_header(self, compresslevel = _COMPRESS_LEVEL_TRADEOFF):
         # Determine what xfl flag is written for the compression level.
         # Equate the fast level to gzip level 1. All the other levels are
         # medium.
-        if compresslevel == _COMPRESS_LEVEL_FAST:
-            compresslevel = gzip._COMPRESS_LEVEL_FAST
+        if sys.version_info[0] == 3 and sys.version_info[1] < 7:
+            # Correct header introduced in 3.7
+            super()._write_gzip_header()
         else:
-            compresslevel = gzip._COMPRESS_LEVEL_TRADEOFF
-        super()._write_gzip_header(compresslevel)
+            if compresslevel == _COMPRESS_LEVEL_FAST:
+                compresslevel = gzip._COMPRESS_LEVEL_FAST
+            else:
+                compresslevel = gzip._COMPRESS_LEVEL_TRADEOFF
+            super()._write_gzip_header(compresslevel)
 
     def write(self, data):
         self._check_not_closed()

tests/test_gzip_compliance.py

@@ -365,8 +365,10 @@ def test_metadata(self):
                              struct.pack('<i', mtime))  # little-endian
 
             xflByte = fRead.read(1)
-            self.assertEqual(xflByte, b'\x02')  # maximum compression
-
+            if sys.version_info[0] == 3 and sys.version_info[1] < 7:
+                self.assertEqual(xflByte, b'\x02')  # maximum compression
+            else:
+                self.assertEqual(xflByte, b'\x00')  # medium compression
             osByte = fRead.read(1)
             self.assertEqual(osByte, b'\xff')  # OS "unknown" (OS-independent)
 
@@ -460,7 +462,7 @@ def test_igzip_BadGzipFile_exception(self):
     def test_bad_gzip_file(self):
         major, minor, _, _, _ = sys.version_info
         if major == 3 and minor >= 8 or major > 3:
-            error = igzip.BadGzipFile
+            error = gzip.BadGzipFile
         else:
             error = OSError