bundle2: move unpackheader closure into the class

With the same argument as the other one, we move this closure into the
`unbundlepart` class.

mercurial/bundle2.py

@@ -559,27 +559,29 b' class unbundlepart(unpackermixin):'
         self._headeroffset += size
         return data
 
-    def _readdata(self):
-        """read the header and setup the object"""
-        # some utility to help reading from the header block
-        def unpackheader(format):
+    def _unpackheader(self, format):
             """read given format from header
 
             This automatically compute the size of the format to read."""
             data = self._fromheader(struct.calcsize(format))
             return _unpack(format, data)
 
-        typesize = unpackheader(_fparttypesize)[0]
+    def _readdata(self):
+        """read the header and setup the object"""
+        # some utility to help reading from the header block
+
+        typesize = self._unpackheader(_fparttypesize)[0]
         self.type = self._fromheader(typesize)
         self.ui.debug('part type: "%s"\n' % self.type)
-        self.id = unpackheader(_fpartid)[0]
+        self.id = self._unpackheader(_fpartid)[0]
         self.ui.debug('part id: "%s"\n' % self.id)
         ## reading parameters
         # param count
-        mancount, advcount = unpackheader(_fpartparamcount)
+        mancount, advcount = self._unpackheader(_fpartparamcount)
         self.ui.debug('part parameters: %i\n' % (mancount + advcount))
         # param size
-        paramsizes = unpackheader(_makefpartparamsizes(mancount + advcount))
+        fparamsizes = _makefpartparamsizes(mancount + advcount)
+        paramsizes = self._unpackheader(fparamsizes)
         # make it a list of couple again
         paramsizes = zip(paramsizes[::2], paramsizes[1::2])
         # split mandatory from advisory