diff -r 685639f9430d -r 60fecc5b14a4 mercurial/bundle2.py
--- a/mercurial/bundle2.py	Mon Apr 06 15:40:12 2015 -0700
+++ b/mercurial/bundle2.py	Mon Apr 06 16:04:33 2015 -0700
@@ -521,6 +521,10 @@
         if util.safehasattr(self._fp, 'close'):
             return self._fp.close()
 
+def getunbundler(ui, fp, header=None):
+    """return a valid unbundler object for a given header"""
+    return unbundle20(ui, fp, header)
+
 class unbundle20(unpackermixin):
     """interpret a bundle2 stream