Use if Py2/Py3 function instead of custom GzipFile class method

scrapy/utils/gz.py

@@ -7,24 +7,35 @@ except ImportError:
 from io import UnsupportedOperation
 from gzip import GzipFile
 
-class ReadOneGzipFile(GzipFile):
-    def readone(self, size=-1):
-        try:
-            return self.read1(size)
-        except UnsupportedOperation:
-            return self.read(size)
+import six
+
+
+# - Python>=3.5 GzipFile's read() has issues returning leftover
+#   uncompressed data when input is corrupted
+#   (regression or bug-fix compared to Python 3.4)
+# - read1(), which fetches data before raising EOFError on next call
+#   works here but is only available from Python>=3.3
+# - scrapy does not support Python 3.2
+# - Python 2.7 GzipFile works fine with standard read() + extrabuf
+if six.PY3:
+    def read1(gzf, size=-1):
+        return gzf.read1(size)
+else:
+    def read1(gzf, size=-1):
+        return gzf.read(size)
+
 
 def gunzip(data):
     """Gunzip the given data and return as much data as possible.
 
     This is resilient to CRC checksum errors.
     """
-    f = ReadOneGzipFile(fileobj=BytesIO(data))
+    f = GzipFile(fileobj=BytesIO(data))
     output = b''
     chunk = b'.'
     while chunk:
         try:
-            chunk = f.readone(8196)
+            chunk = read1(f, 8196)
             output += chunk
         except (IOError, EOFError, struct.error):
             # complete only if there is some data, otherwise re-raise