--- a/mercurial/bundle2.py	Mon Mar 28 17:16:00 2016 -0500
+++ b/mercurial/bundle2.py	Mon Mar 28 14:41:29 2016 -0700
@@ -474,6 +474,19 @@
         chunks.append(ca)
     return '\n'.join(chunks)
 
+bundletypes = {
+    "": ("", None),       # only when using unbundle on ssh and old http servers
+                          # since the unification ssh accepts a header but there
+                          # is no capability signaling it.
+    "HG20": (), # special-cased below
+    "HG10UN": ("HG10UN", None),
+    "HG10BZ": ("HG10", 'BZ'),
+    "HG10GZ": ("HG10GZ", 'GZ'),
+}
+
+# hgweb uses this list to communicate its preferred type
+bundlepriority = ['HG10GZ', 'HG10BZ', 'HG10UN']
+
 class bundle20(object):
     """represent an outgoing bundle2 container
 
@@ -1265,6 +1278,48 @@
     obscaps = caps.get('obsmarkers', ())
     return [int(c[1:]) for c in obscaps if c.startswith('V')]
 
+def writebundle(ui, cg, filename, bundletype, vfs=None, compression=None):
+    """Write a bundle file and return its filename.
+
+    Existing files will not be overwritten.
+    If no filename is specified, a temporary file is created.
+    bz2 compression can be turned off.
+    The bundle file will be deleted in case of errors.
+    """
+
+    if bundletype == "HG20":
+        bundle = bundle20(ui)
+        bundle.setcompression(compression)
+        part = bundle.newpart('changegroup', data=cg.getchunks())
+        part.addparam('version', cg.version)
+        chunkiter = bundle.getchunks()
+    else:
+        # compression argument is only for the bundle2 case
+        assert compression is None
+        if cg.version != '01':
+            raise error.Abort(_('old bundle types only supports v1 '
+                                'changegroups'))
+        header, comp = bundletypes[bundletype]
+        if comp not in util.compressors:
+            raise error.Abort(_('unknown stream compression type: %s')
+                              % comp)
+        z = util.compressors[comp]()
+        subchunkiter = cg.getchunks()
+        def chunkiter():
+            yield header
+            for chunk in subchunkiter:
+                yield z.compress(chunk)
+            yield z.flush()
+        chunkiter = chunkiter()
+
+    # parse the changegroup data, otherwise we will block
+    # in case of sshrepo because we don't know the end of the stream
+
+    # an empty chunkgroup is the end of the changegroup
+    # a changegroup has at least 2 chunkgroups (changelog and manifest).
+    # after that, an empty chunkgroup is the end of the changegroup
+    return changegroup.writechunks(ui, chunkiter, filename, vfs=vfs)
+
 @parthandler('changegroup', ('version', 'nbchanges', 'treemanifest'))
 def handlechangegroup(op, inpart):
     """apply a changegroup part on the repo