changegroup: introduce "raw" versions of some commands

The commands getchangegroup, getlocalchangegroup and getsubset now each
have a version ending in -raw. The raw versions return the chunk generator
from the changegroup packer directly, without wrapping it in a chunkbuffer
and unpacker. This avoids extra chunkbuffers in the bundle2 code path.

Also, the raw versions can be extended to support alternative packers
in the future, to be used from bundle2.

mercurial/changegroup.py

@@ -443,7 +443,7 b' def _changegroupinfo(repo, nodes, source'
         for node in nodes:
             repo.ui.debug("%s\n" % hex(node))
 
-def getsubset(repo, outgoing, bundler, source, fastpath=False):
+def getsubsetraw(repo, outgoing, bundler, source, fastpath=False):
     repo = repo.unfiltered()
     commonrevs = outgoing.common
     csets = outgoing.missing
@@ -457,7 +457,10 b' def getsubset(repo, outgoing, bundler, s'
 
     repo.hook('preoutgoing', throw=True, source=source)
     _changegroupinfo(repo, csets, source)
-    gengroup = bundler.generate(commonrevs, csets, fastpathlinkrev, source)
+    return bundler.generate(commonrevs, csets, fastpathlinkrev, source)
+
+def getsubset(repo, outgoing, bundler, source, fastpath=False):
+    gengroup = getsubsetraw(repo, outgoing, bundler, source, fastpath)
     return cg1unpacker(util.chunkbuffer(gengroup), 'UN')
 
 def changegroupsubset(repo, roots, heads, source):
@@ -485,6 +488,16 b' def changegroupsubset(repo, roots, heads'
     bundler = cg1packer(repo)
     return getsubset(repo, outgoing, bundler, source)
 
+def getlocalchangegroupraw(repo, source, outgoing, bundlecaps=None):
+    """Like getbundle, but taking a discovery.outgoing as an argument.
+
+    This is only implemented for local repos and reuses potentially
+    precomputed sets in outgoing. Returns a raw changegroup generator."""
+    if not outgoing.missing:
+        return None
+    bundler = cg1packer(repo, bundlecaps)
+    return getsubsetraw(repo, outgoing, bundler, source)
+
 def getlocalchangegroup(repo, source, outgoing, bundlecaps=None):
     """Like getbundle, but taking a discovery.outgoing as an argument.
 
@@ -514,6 +527,18 b' def _computeoutgoing(repo, heads, common'
         heads = cl.heads()
     return discovery.outgoing(cl, common, heads)
 
+def getchangegroupraw(repo, source, heads=None, common=None, bundlecaps=None):
+    """Like changegroupsubset, but returns the set difference between the
+    ancestors of heads and the ancestors common.
+
+    If heads is None, use the local heads. If common is None, use [nullid].
+
+    The nodes in common might not all be known locally due to the way the
+    current discovery protocol works. Returns a raw changegroup generator.
+    """
+    outgoing = _computeoutgoing(repo, heads, common)
+    return getlocalchangegroupraw(repo, source, outgoing, bundlecaps=bundlecaps)
+
 def getchangegroup(repo, source, heads=None, common=None, bundlecaps=None):
     """Like changegroupsubset, but returns the set difference between the
     ancestors of heads and the ancestors common.

mercurial/exchange.py

@@ -445,8 +445,9 b' def _pushb2ctx(pushop, bundler):'
                                      pushop.outgoing)
     if not pushop.force:
         bundler.newpart('B2X:CHECK:HEADS', data=iter(pushop.remoteheads))
-    cg = changegroup.getlocalchangegroup(pushop.repo, 'push', pushop.outgoing)
-    cgpart = bundler.newpart('B2X:CHANGEGROUP', data=cg.getchunks())
+    cg = changegroup.getlocalchangegroupraw(pushop.repo, 'push',
+                                            pushop.outgoing)
+    cgpart = bundler.newpart('B2X:CHANGEGROUP', data=cg)
     def handlereply(op):
         """extract addchangegroup returns from server reply"""
         cgreplies = op.records.getreplies(cgpart.id)
@@ -1185,11 +1186,11 b' def _getbundlechangegrouppart(bundler, r'
     cg = None
     if kwargs.get('cg', True):
         # build changegroup bundle here.
-        cg = changegroup.getchangegroup(repo, source, heads=heads,
-                                        common=common, bundlecaps=bundlecaps)
+        cg = changegroup.getchangegroupraw(repo, source, heads=heads,
+                                           common=common, bundlecaps=bundlecaps)
 
     if cg:
-        bundler.newpart('b2x:changegroup', data=cg.getchunks())
+        bundler.newpart('b2x:changegroup', data=cg)
 
 @getbundle2partsgenerator('listkeys')
 def _getbundlelistkeysparts(bundler, repo, source, bundlecaps=None,